Effect of glaze coatings and pressure-heat processing on short-term soft denture liners

luu2 ( .pdf )

EFFECT OF GLAZE COATINGS AND PRESSURE-HEAT PROCESSING ON
SHORT-TERM SOFT DENTURE LINERS













BY

ANTON LUU


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


1999
































To my father, Te The Luu, who passed away on August 9,1999, in Jackson, LA,
while I was busy writing this thesis. Although he was by necessity often an absent
father, he was very active in shaping the person I have become today. He will always
be remembered by his sagacity, fortitude, and devotion in ensuring the well being as
well as the intellectual and moral development of his children.















ACKNOWLEDGMENTS


This study started out from the desire to verify if an unsubstantiated idea

promulgated in a professional journal has any merit. It has many adherents in the

prosthodontic specialty as well as non-believers with little more to back up their belief

than their clinical experience. From the outset, it seemed to be a short, easy study to

conduct until questions from my mentor, Dr. Chiayi Shen, could not be answered

satisfactorily. As usual in any research, the answers to one question lead to more

questions until the scope of the study has reached seemingly unending proportions.

Special acknowledgments are made to Dr. Chiayi Shen, and by extension, the

Department of Dental Biomaterials at the University of Florida, College of Dentistry, for

the help and encouragement to take this study to its fruitful completion. Without his

devotion and patience, it is doubtful whether this study would be finished or have the

depth attained.

Special acknowledgment is also made to the American College of Prosthodontists

for supporting this study through the award of the 1998 Procter & Gamble/American

College of Prosthodontists Research Fellowship in Complete Denture Prosthodontics.

I would also like to thank my committee members Dr. Hansen, Dr. Morton,

Dr. Javid, and Dr. Clark for their guidance in completing this thesis.
















TABLE OF CONTENTS


page

A C K N O W L E D G M E N T S ................................................................................................. iii

LIST OF TABLES .............. ............. ............................. ........ vi

LIST OF FIGURES .................. ................................. .. ....... ..... ........ viii

CHAPTERS

1 BA CK GROUN D .............. ....... .... .......... ..... .. ............. 1

Temporary Soft Denture Liners............................. .... ......................... 1
Extending Service Life of Temporary Soft Denture Liners........................................ 6
P ro p o sed S tu d y ............................................................................................................. 9

2 HYPOTHESES .......... ................................. ........... ..... .......... 10

3 M ATERIAL AND M ETHODS........................................................ ......... ..... 13

Material Selection ........... ........................... ............... 13
M e th o d s .......................................................................... ............... 2 1
Instrum ents for D ata Collection ........................................................ ......... ..... 26
Data Collection and Statistical Analysis ........................................................... 32

4 RESULTS ............ ................................ ............... 34

Surface Resilience by Shore A Hardness ......................................... ............. 34
Dynamic M echanical Test of the Specimen............................................................... 38
Release of Plasticizer in the Immersion Solution by UV/VIS
Spectrophotom eter ............................................... ......................... 41
W eight Changes of the Specim en ........................................ ......................... 44
pH of the Solution .......... .. .... ........................................................... ............. 49
Statistical Correlation between Parameters........................ ....................... 51
Macro Photography and Micro Photography ................... .............................. 53

5 D IS C U S S IO N ............. .. ............... ........................................... 57

Effect of Surface Treatment on the Appearance of the Specimen ............. ............. 57
Plasticizer Leaching, Weight Loss, and pH of Storage Medium ............................ 61










Powder-to-liquid Ratio Influence on weight change........................ .............. 67
Leachants in Extruded Acrylic (Lucite-ES) Substrate ........................................ 68
Mechanical Properties as Influenced by the Coating ....................... .............. 69

6 SUMMARY AND CONCLUSIONS ............................................................. 77

APPENDIX

POLYMERIZATION IN A METHACRYLATE PREPARATION WITH
EXCESS MONOMER MONO-POLY ......................................................... 81

R E FE R EN C E S ........ ......... .............. ................... .......................... .. ............ 90

BIOGRAPHICAL SKETCH ............................................................. .............. 94
















LIST OF TABLES



Table page

1. C hem ical com position of soft liners................................................ ... ................. 19

2. Batch numbers ........................................................................ .... ......... .................. 19

3. Pow der to liquid ratio ........... ...... ....... ..... ........ ....... .............. 23

4. Tim es needed prior to m anipulation........................................... ... ................. 24

5. Shore A hardness values 30- sec after indentation.................. ................ 35

6. Shore A values measured 2-min after indentation ............................................ 36

7. Tukey's grouping of the surface treatment on Shore A hardness.......................... 37

8. Elastic modulus of soft liners as result of surface treatment and time.................. 39

9. Rate of recovery .............. ............... ........... ..................................... 40

10. Tukey's grouping of the surface treatment on dynamic tests............................. 41

11. Estimated leachant loss by UV absorbance at higher wavelength.................... 42

12. Estimated leachant loss by UV absorbance at lower wavelength..................... 43

13. Tukey's grouping of the effect of treatment on the leaching by UV.................... 44

14. Weight change of soft-liners in water with time as influenced by treatment........ 45

15. W eight loss in air........ .......... .................. ... ......... .......... 47

16. Tukey's grouping of the effect of surface treatment on the weight change......... 49

17. pH values of storage solutions at the time of replacement............................... 50

18. Tukey's grouping of the effect of surface treatment on the pH of storage
solutions.............. ... ............................. ... ................... 51









19. Coefficient of determination (r2) of linear regression between leaching
by UV at high and low wavelength .............. ................................. ......... 51

20. Coefficient of determination (r2) of linear regression between leaching
at high wavelength and weight loss by balance .................... ....... ........... 52

21. Coefficient of determination of Linear regression between weight change
in water vs. M odulus of Elasticity .................. ................ ........... ... 52

22. Coefficient of determination of linear regression between weight loss
in w ater and rate of recovery ................................................ ......... ..... 52

23. Coefficient of determination of linear regression between modulus of
elasticity and leachant by UV absorbance at high wavelength..................... 52

24. Coefficient of determination of linear regression between rate of
recovery and leachant by UV absorbance at high wavelength.................... 53

25. Coefficient of determination of linear regression between modulus of
elasticity and rate of recovery.................. ........ ... .............. ....... 53















LIST OF FIGURES

Figure page

1. M olds used in specim en form ing ........................................ ........ .............. 25

2. Shore A Durometer ..................................... ........... 28

3. Typical UV absorption curve .................................................................... 30

4. Hardness values 30 seconds post indentation of Flexacryl-Soft........................... 37

5. Hardness values 30 seconds post indentation of Lynal ................................... 38

6. W eight loss with tim e for Lynal.............. .............. ................... ......... ............. 46

7. W eight loss w ith tim e for Tem po................................................ ... ................. 46

8. Weight loss with time for the control specimens .......................................... 48

9. Weight loss with time for the mono-poly coated specimens ............................. 48

10. Specimen coated with mono-poly ............ ...... ... ...... ....................... 54

11. Microscopic view of specimens coated with Jet Seal ....................................... 55

12. Microscopic view of sections of Tempo and Coe-Soft samples. .......................... 56

13. Shore H ardness indentors......................................... ................ .............. 70

14. Shore A Durom eter readings ................ ................. .................... .............. 70















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

EFFECT OF GLAZE COATINGS AND PRESSURE-HEAT PROCESSING ON
SHORT-TERM SOFT DENTURE LINERS

By

Anton Luu

December 1999

Chairman: Carl Hansen
Major Department: Prosthodontics

Purpose: Post-process treatments of temporary soft denture liners, such as heat and

pressure or sealing with a glaze coat, were reputed to extend service-life of these

materials. This investigation was to examine how these surface treatments may affect

relevant properties and correlations among changes of these properties.

Materials and Methods: Four treatment modalities were used, namely as-prepared by the

manufacturer's instructions, with subsequent exposure either to heat and pressure; or

coating with mono-poly, a solution of ten parts autopolymerizing methacrylate monomer

to one part heat-cured methacrylate polymer; or with Jet Seal, a commercial glaze coat.

These treatments were applied to five materials: Lynal, Coe-Comfort, Coe-Soft, Tempo

and Flexacryl-Soft. Six samples were prepared for each treatment/material combination.

Six more samples were prepared for those with a coating for Shore A hardness testing; it

damaged the coating and necessitated resealing. At baseline, 2, 7, 14, 28, 42, 63 and 84

days after immersion in distilled water, weight changes, Shore A hardness, modulus of









elasticity, recovery rate, plasticizer leaching, pH of storage water, and surface texture for

the 180 samples were collected. The water was renewed at each data collection.

Results: Flexacryl-Soft behaved differently from the other four materials. Both surface

treatment and storage time showed statistical significant influence on the six physical

parameters measured. In general, significant changes occurred within first two weeks of

storage. There is no change in surface appearance for as-prepared and pressure/heat

groups, while there were blister formations with mono-poly and cracks and wrinkles with

Jet Seal. Only Lynal and Flexacryl-Soft show reliable Shore A hardness values.

Nonetheless, mono-poly and pressure/heat yielded higher values. All materials lost

weight in water and air, mainly due to loss of volatile alcohol. Mono-poly consistently

reduced weight loss in water while Jet Seal had no effect. Tempo lost the most both in

air and water due to high alcohol content. Lynal lost more in air than in water, indicating

significant water absorbance. UV absorbance data indicated that leaching of plasticizer

was small; some of which might be due to monomers in coatings. The coating yielded

lower pH values of storage water because of monomer leaching. Mono-poly coating

often resulted in higher modulus of elasticity, except for Tempo, and lowest rate of

recovery. Jet Seal coating often is in the next ranking group.

Conclusion: Pressure/heat does not significantly improve the quality of temporary soft

denture liners. Mono-poly coating is semi-permeable to water and generally minimizes

deterioration of some of the physical properties of the material. This effect is not

consistent across all materials tested or all the parameters tested. Both coatings

developed surface defects with time in storage, which puts in question their benefits

versus the cost of applying them.















CHAPTER 1
BACKGROUND


Temporary Soft Denture Liners



History of Development


Resilient dental materials used to interface a hard prosthesis surface and the oral

tissues that it contacts are generally divided into permanent soft lining materials and

temporary soft liners. Permanent soft lining materials are resilient polymers used to

replace the fitting surface of a hard plastic denture while temporary soft liners and

functional impression materials are used for their viscoelastic properties, specifically,

their ability to flow under masticatory and linguistic forces, spreading the load evenly.

Temporary Soft Denture Liners are also referred to as short-term soft liners,

tissue conditioners and functional impression materials.1 Their use in dentistry goes back

a long time and they provide the clinician with expanded scope for short-term resolution

of patient problems.26 They are generally used for tissue conditioning, lining surgical

splints and stents,6 lining implant interim prostheses, and for stabilizing trial denture

bases, determining optimal arch form, or neutral zone.

Temporary soft liners are used for their viscoelastic properties. Viscoelastic

behavior is an intermediate between elastic solid and viscous solid. By virtue of its

elasticity, it will deform when under load and recover when the load is removed.

Because it is viscous, this recovery is not instantaneous. Furthermore, when the load is









applied over time, it will exhibit permanent deformation and will not recover by itself.7

In other terms, viscoelasticy is the ability of a material to flow and adapt under function

to continuous tissue changes, yet provide some degree of cushioning under load. For

some applications it is desirable to have a longer service life while retaining these

properties, which the long-term soft liners do not possess. This is because long-term soft

liners are used for their elasticity, meaning the ability of the material to instantly recover

its original shape. Therefore, an important factor in temporary soft denture liners is the

time factor, more specifically the time interval required for the material to recover its

initial shape. Ideally, the tissue conditioner should mimic the properties of a viscous

fluid confined within an envelope or a pouch fixed to the borders of the prosthesis so as

to constrain its deformation to a very narrow range while interfacing the mucosa and the

hard prosthesis surface.6


General Composition


Temporary soft liners or tissue conditioners generally consist of a polyethyl

methacrylate powder mixed with copolymers, which when mixed with ethanol and

plasticizers, typically dibutyl phthalate, in the liquid 6, would be uniformly dispersed.

The alcohol is reported to vary from 6 to 40 % 8 by volume. Ethanol

(CH3CH20H, pKa 16.0) is reportedly the most common alcohol used in the liquid

component. It has a low boiling point (78 C) and therefore a high propensity to

evaporate. However, one of the materials included in the study does not contain ethanol,

namely Flexacryl-Soft.









Alcohol is used mainly to facilitate the penetration of plasticizers into the

polymer by swelling the polymer beads.6,9'10 The lower the molecular weight of the

polymer and the smaller the particle size, the greater the alcohol penetration, the faster its

rate of adsorption within the polymer." In contrary, within a single polymer chain, the

larger the meric weight (the weight of each repeating unit in the polymer), the speedier

the alcohol penetration. A longer side chain group is one way to obtain larger meric

weight. It should be noted that longer side chain decreases the density of the polymer

chain, therefore lowering molecular weight. Increasing the number of carbon groups

would also increase the meric weight, decreasing the quantity of alcohol needed to

achieve a reasonable plasticization of the polymer beads. For practical purposes, the

methyl methacrylate rate of adsorption of alcohol is too slow and while that of higher

groups than ethyl methacrylate is too fast. Although a benefit of ethanol in the plastic

composition is its antimicrobial properties, the benefit is of short duration because it

diffuses completely from the gel within 24 hours.12 This is why the majority of the soft

denture liners have ethyl methacrylate as the main ingredient in the powder.

Jones et al.,12 in analyzing the plasticizer content of eight dental soft polymers,

found that ester (a reaction product of an alcohol and an acid) contents of the liquid

portion varied from to 52% with the balance being ethyl alcohol. The authors stated that

it is misleading to think that dibutyl phthalate (DBP) is the most common ester

compound because it does not compose the major proportion of the liquids and in fact is

an impurity associated with butyl phthalyl butyl glycolate (BPBG) standards. They

concluded that on the basis of plasticizer found in appreciable proportion in the liquid

component, BPBG is the most common ester constituent. All the esters have a boiling









point higher than 300C and are therefore relatively non volatile. Phthalate esters have a

low water solubility, which increases with lower the molecular weight. They stated that

benzyl salicylate and benzyl benzoate are in this later category and have a cumulative

leached amount after 14 days of 8.3-8.7 mg/g and 5.7 mg/g respectively. However, they

also stated that this higher rate of loss represents less than 2% of the ester originally

present. These authors also found that there is no significant change in the rate of loss

when the specimens were subjected to cyclic loading. Therefore, the need to simulate the

masticatory cycles when conducting in vitro leakage tests is questionable.

Two of the materials included in this study, Coe-Comfort and Coe-Soft,

according to the manufacturer, were covered by US patents #3,476,854 Nov 4,1969 and

#3,558,540 Jan 25, 1971 and are summarized below.

Patent #3,476,854 covers the use of zinc undercylenate, an antimycotic that could

be combined into soft, pliable plastic compositions in sufficient concentration to be

effective without adversely affecting its physical properties. This heavy salt of

monocarboxylic fatty acids needs to be present in a minimum of 1 wt % concentration to

be effective, whereas concentration above 5 wt % do not further retard fungal growth. It

is claimed that this fungal inhibitor is hydrophobic and does not leach out of the plastic

composition under the effect of saliva or other aqueous solutions. As stated earlier,

although alcohol in the plastic composition inhibits microorganism growth, it diffuses

completely within 24 hours. It is interesting to note that the patent states in the different

examples of tissue conditioner formulations that benzyl benzoate, besides being a

non-toxic solvent/plasticizer, also has fungicidal properties.









Patent #3,558,540 details the range of chemicals that could be used to

manufacture tissue conditioners. One starts with a room temperature soluble resin,

meaning a resin that can be effectively gelatinized by a solvent at ambient temperature.

This resin is preferred to be of the low molecular weight methacrylate polymer or

copolymer in small bead or granular form. For ease of manipulation, a small amount of

anti-tack solid or powder such as calcium carbonate, ultra fine silica, or zinc stearate is

added. Additives such as coloring, fillers and modifiers are then added to the solid

component. The liquid solvent is composed of primary plasticizer, such as DBP or

BPBG, from 5 to 30% by volume, to which extenders such as vegetable oils are added to

control setting time and non-tackiness. Added to the liquid are gel former containing

alcohol and other groups, slow evaporating esters, higher molecular weight glycols, and

benzyl radical containing plasticizer. In particular, benzoic acids and salicylic acids have

been found to be efficient solvent gel former. Benzyl alcohol is also added to the liquid

to operate as a coupling agent. Benzyl alcohol has the added advantage of behaving as a

solvent, gel former and flexibilizer while other higher alcohols such as hexadecyl alcohol

behave only as coupling agents. The disadvantage of benzyl alcohol is that it adds

tackiness. Secondary plasticizers, that is extenders for primary plasticizers, of the alkyl

aryl hydrocarbons group may also be added to the liquids. They typically include

paraffin and its derivatives, toluene, which is also an aromatic, and propylene, which is

alkylated with an aliphatic compound.


Existing Problems


Both short-term and medium-term acrylate-based soft liners suffer plasticizer and

alcohol leakage and in time become progressively more rigid. 12-17 In our experience,









relying on the medium-term soft liner for longer service is not always possible because

although it is resilient, it has a high proportional limit and does not maintain a plastic

phase during service, which means that it would not adapt easily to changing tissue

conditions as inflammation subsides. Because of this lack of adaptation to tissue

changes, the short-term resilient liner is favored as a treatment liner (tissue conditioner)

although replacement linings are required more frequently.

Speculation regarding plasticizer leakage has been described by several

authors.14'18'19 However, Braden and Causton,13 and Ellis et al.14 suggested that

phthalate esters could not leach out in water at 370C and weight loss is due to alcohol

diffusion. This suggestion was not supported by chemical analysis and was based

completely on weight changes. Because of the complex two-way exchange of

alcohol/plasticizer loss and water uptake in the plastic composition, using weight change

alone for quantification of plasticizer loss would not provide an accurate picture.

Although Gas Chromatography would be the instrument of choice for identification and

quantification of leachants, within the confines of this study, UV Spectrophotometry was

selected because of availability.

Extending Service Life of Temporary Soft Denture Liners


The expressions short-term soft denture liners and long-term soft denture liners

are misnomers because they are used for their respective specific physical properties.

The limited service life of the former is a limitation of the available chemistry to achieve

those properties. Therefore, many authors have suggested ways to improve on the

service life of short-term soft denture liners.









Reported Methods for Extending Service Life


Corwin and Saunders20 described a curing technique aimed at extending liner

longevity. The procedure requires the denture with soft liner be placed in a pressure pot

with water at 110 to 115 "F and allowed to cure for an additional 20 to 30 minutes under

25 to 30 psi. They did not present any data to substantiate their claim of an extended

service life.

Gardner and Parr21 described the use of a coating to extend the longevity of

temporary soft liners. They used a syrup-like mixture that was coined mono-poly,

consisting of one part heat-cured clear polymethyl methacrylate beads and 10 parts of

autopolymerizing methyl-methacrylate monomer to seal the porous surface of the soft

liner and form a smooth surface. It was believed that a smooth surface could reduce

fungal and bacterial growth that is often cited as the cause of discoloration and eventual

breakdown of liners.

Vacuum mixing of tissue conditioner was reported by Nimmo et al. 22 to reduce

the presence of voids, hence producing a denser material, but did not reduce bacterial

adhesion. This method would not be used by majority clinicians as it is rarely

recommended in the manufacturer's instructions, requires additional equipment and

clean-up time, it was not included in our study.


Effectiveness of Coatings


Aslan and Avci 23 observed in their in vitro experiment that autopolymerizing

acrylic resin samples covered with mono-poly evidenced a significant reduction in E. coli









colonies compared to the uncoated group, supporting the contention that mono-poly

coating provides a smooth surface that reduce fungal and bacterial growth.

Casey and Scheer 24 showed by Scanning Electron Microscope that Coe-Soft

protected with either mono-poly glaze or Minute-Stain glaze in different areas of the

palatal intaglia of an upper complete denture worn by a patient for 30 days retained the

glasslike appearance that it had immediately after coating. The uncoated area under the

same condition had shown severe degradation as evidenced by the exposure of

subsurface air bubbles incorporated during mixing. Home care instructions included

brushing the denture base with a denture brush twice daily and soaking it overnight in

dish washing liquid. The smooth surface that Gardner and Parr 21 had predicted was not

affected by the normal use. However, no information was provided on whether there is a

marked change in the physical properties of the tissue conditioner. This in vivo study

included only one patient and one material with three parameters. No statistical studies

were available.

Dominguez et al.25 found that the mono-poly coating reduced water absorption,

weight and plasticizer loss from Visco-gel, a tissue conditioner, which was immersed in

water over a one-month period. They concluded that the mono-poly coating acted as a

barrier in preventing water absorption and loss of plasticizer. Gronet et al.26

hypothesized that surface sealing of the temporary soft liner may enhance the life of

these liners and extend their period of resilience. They used mono-poly and Palaseal, a

light cured glaze, to seal the surfaces of the soft liners, thermocycled them 500 times and

measured the resilience of the material as influenced by the coating. Their results

showed that soft liners coated with surface sealers exhibited higher resilience than









uncoated samples. They interpreted the increase in resilience is an indication of

prolonged service life.

Because of the scant information published on the effectiveness of mono-poly,

the absence of properly designed clinical studies, and the fact that it is not the result of

polymerization but only a coat of adhering polymers molecules, the advantage of coating

temporary soft denture liners with this material is very much still in question. It is also

not certain if the properties of a surface sealer and glaze coating would be beneficial

across a wide range of temporary soft liners or if it is limited to certain categories of

liners with a particular chemistry system.

Proposed Study


We propose in this study to evaluate several physical attributes such as weight

change, leachants in and pH of surrounding water, surface hardness, elasticity, and

plastic deformation recovery across a range of temporary denture soft lining materials. It

is hoped that consistency among some results may yield a more accurate picture of the

effect of sealer/glaze coatings on tissue conditioners.















CHAPTER 2
HYPOTHESES

Resiliency, as described by the American Society for Testing &Materials, is the

energy returned by an elastomeric polymer when it is suddenly released from a state of

strain deformation. Resilience, as defined in the Glossary for Prosthodontic Terms

(1999) is the adjective for an object that is capable of withstanding shock without

permanent deformation or rupture or tending to recover from or easily adjust to change.

The synonym is elastic. Resilience, according to Anusavice,27 is the amount of energy

absorbed by a structure when it is stressed to its elastic limit, which is equivalent to the

integrated area under the elastic region of the stress strain curve. It is a measure of the

ability of the material to store elastic energy similar to a compressed spring. In the field

of prosthodontics, resiliency, or the ability to recover its original shape when subjected to

stress, is a property desired for functional impression materials and permanent soft liners.

Although Gronet et al. 28 associated resilience with enhanced life of temporary soft liners,

because softness or plastic deformation is desired for this material, another variable that

also allocates for the time factor would be more appropriate. It is the rate of viscoelastic

recovery.

This rate of viscoelastic recovery reflects the ability of the material to rebound

with time. By inference, if a soft liner retains its plasticizer within its matrix, its rate of

recovery should be maintained with time. Otherwise, if there is a variation in rate of

recovery, there is a change in plasticizer content. In other terms, the loss of plasticizer









will lead to less viscoelastic properties (shorter recovery time) in favor of elastic

properties (higher modulus of elasticity).

In addition to the modulus of elasticity and rate of recovery, other properties may

also be associated with the degradation of the material. Such properties include weight

change, Shore A hardness, acidity of the surrounding liquid and leachants concentration

in the same liquid. Since previous studies have investigated only part of the list, there

may not be enough information to conclude the effectiveness of the coating. It is

necessary that all five parameters be measured in order to confirm the effectiveness of

the treatment.

The purpose of this study is to test the hypothesis that coating with surface sealer

and/or curing in pressurized environment can maintain the physical and mechanical

properties of the temporary soft liners at the level recorded when they were processed.

This study has nine qualitative factors divided in two groups, materials and

treatment. The five materials studied were Lynal, Coe-Comfort, Coe-Soft, Tempo, and

Flexacryl-Soft. The four treatments applied were: prepared as per the manufacturer's

instruction (control); same as before followed by heat and pressure processing; followed

by coating with mono-poly, and followed by coating with Jet Seal, a commercial sealer.

The null hypothesis, Ho, is there is no significant difference between the treated

groups and the control group with time using the following response variables:

weight change by balance

leachants in surrounding water by UV spectrophotometry

pH of surrounding water

surface hardness by Shore A







12

elastic modulus

viscoelastic recovery rate

The alternate hypothesis, Ha, is there is a significant difference between the

treated groups and the control group in at least one material with time using the above

response variable















CHAPTER 3
MATERIAL AND METHODS


Material Selection



Types of Coating


There are many coatings available commercially besides the laboratory prepared

mono-poly. One category is air-dried e.g. Jet Seal, a commercial sealer from Lang

Dental Manufacturer (Wheeling, IL) and the other category is light cured e.g. Palaseal by

Kulzer. Even though Gronet et al.26 in their study considered Palaseal as a suitable liner

coating, we have observed in our preliminary tests that it was a stiff and brittle coating.

The additional rigidity of the Palaseal coating would augment the surface hardness of the

soft denture liner. Its brittle property would favor fracture development in the coating

when the underlying liner deforms viscoelastically in order to comply with the healing

mucosa. Therefore it was deemed unsuitable as a resilient liner coating. Verbal

communication with Mr. Stephen Domschke, product manager for Heraus Kulzer,

confirmed these observations and the unsuitability of its use as a glaze coat for soft

denture liners. Jet Seal was chosen because of its explicit suitability as a surface sealant

to be used for soft relines in the manufacturer's instructions. The general properties of

mono-poly and Jet Seal are described below.









Properties of Mono-Poly


Mono-poly is the name coined by Gardner and Parr 21 for a coating prepared by

dissolving one part of heat-activated clear polymethyl methacrylate (PMMA) powder to

10 parts of autopolymerizing orthodontic methyl methacrylate monomers (MMA). It is

suggested in their paper that the longevity of a temporary soft liner could be extended by

using this coating to render a smooth surface, and seal its porous surface. The authors

stated that after applying it with a brush, the mono-poly sealer should be allowed to dry

for 4 to 5 minutes while held approximately 2 inches away from a 50 or 60 watt lamp.

This process should be repeated twice more. Unfortunately, no study was presented to

support any of the conjectures or how the formula was arrived at.

Mono-poly for this study was prepared according to the instructions given by

Gardner and Parr.21 Hygienic Clear heat-polymerizing denture polymer powder

(Hygenic Corp., Akron, OH) was added in a proportion of 1:10 by weight to a 25-mL

conical flask containing Lang's Orthodontic auto-polymerizing monomer liquid (Lang

Dental Manufacturer, Wheeling, IL) preheated in a water bath at 550C using a stirring

hot plate. The mix was homogenized using a magnetic stirrer for 10 minutes.

In an earlier study, submitted for publication, it has been demonstrated that there

is no polymerization in the coating resulting from a solution of 10 parts of either heat

activated or autopolymerizing monomer to 1 part of polymer of either type. The dry film

weight constitutes 1% of the initial liquid preparation weight. In other terms, in the dry

coat, 99% of the initial monomer evaporated from the preparation. In the absence of

polymerization, the coating's properties will depend on the polymer used in the

preparation. The manuscript, as submitted for publication, is included in the Appendix.









Properties of Jet Seal


Jet Seal is a Lang Dental mfg. Co (Wheeling, IL) product advertised as a

self-curing sealant composed of less than 100% inhibited methyl methacrylate monomer.

According to the manufacturer's instructions, Jet Seal is a surface sealant to be

used for soft relines, hard relines, dentures, temporary crowns and bridges, restorations

and denture repairs. It is also stated that Jet Seal fills in surface porosity and increases

color stability. Chemically, Jet Seal is an autopolymerizing resin. It air-dries in

approximately one minute and will provide a hard surface finish with excellent aesthetics

without any polishing.


Temporary Soft Denture Liners


Temporary soft denture liners are supplied in the form of a polymer powder and a

liquid. After mixing the powder and the liquid to a paste consistency, it is applied to the

tissue side of the prosthesis. Once gelation has reached a satisfactory level for the

application involved, the prosthesis is inserted in the mouth. At this stage, the material is

compliant and will flow from areas of pressure, yet have enough body to stay in place.

Once the appropriate shaping and molding procedures are performed and the prescribed

gelation time has evolved, the prosthesis is removed and the material is trimmed.

Five commercial products representing broad categories of indications and

chemistry were selected for this study. They are Lynal Tissue Conditioner (L.D. Caulk),

Coe-Comfort (GC America), Tempo (Lang), Coe-Soft (GC America), and Flexacryl-Soft

(Lang). The composition and applications of these materials are described below.









Lynal

According to the manufacturer's instructions Lynal is indicated for use as a tissue

conditioner, a soft liner and a functional impression material.

Scant information is available in the published literature regarding this material.

The manufacturer, Dentsply/Caulk (Milford, DE), when contacted could not provide

further information about the chemistry of this material. The Material Safety Data Sheet

included with the merchandise did not reveal its chemistry make-up. An updated MSDS

located at http://www.caulk.com/MSDSDFU/LynalMSDS.html provided some

information. Although the information is incomplete, it showed that the liquid contains

ethyl alcohol and an organic phthalate plasticizer while the powder is made up of

polyethyl methacrylate and benzoyl peroxide.

The mixed gel has a translucent color that becomes opaque with time in clinical

usage.

Coe-Comfort

This material is marketed by GC-America Inc. as a tissue conditioner. Its

instruction pamphlet states that after two to four days, the material is no longer

responsive to tissue movement and needs to be replaced. The reason for its early loss of

resiliency may be due to its high concentration of the plasticizer benzyl benzoate (85-

87% of the liquid component) that is also a fungicide. Due to this plasticizer's small

molecular size, it has relatively higher water solubility.12

Braden8 recovered by hydrolysis of butyl alcohol and phthalic acid in the Coe-

Comfort liquid, confirming the presence of n-butyl phthalate, an aromatic ester 8 used as

a plasticizer. The mixed gel has a white opaque color.









Coe-Soft

According to the manufacturer, GC-America Inc, this product is indicated for

temporary lining of acrylic resin dentures, as a soft liner. The main ingredient of its

liquid component is the plasticizer BPBG (81%) which has a higher molecular weight

than benzyl benzoate used in Coe-Comfort, hence lower water solubility. It also has a

higher ethanol content than Coe-Comfort (15% vs. 8%).

The mixed gel has an opaque pink color.

Tempo

According to the MSDS, this material contains 3% benzoyl peroxide, which is a

polymerizing initiator. Interaction between this benzoyl peroxide and the mono-poly

coating, which as mentioned previously has been found not to polymerize, may be

possible.

The relatively high Ethanol content (25%) of this material, which according to

several studies, accounts for the main weight loss, would indicate that it would be the one

to have the most weight loss. The plasticizer used is dialkyl phthalate, an ester resulting

from the combination of butyl alcohol and phthalic acid.

It is mentioned in the instruction pamphlet that the material should be durable for

3 months.

Flexacryl-Soft

Flexacryl-Soft is indicated as a soft formulation self-curing reline acrylic. This

material differs chemically from the other materials included in the study in that it does

not contain any alcohol as a gel forming solvent in the liquid. In fact, the liquid is

composed of n-butyl methacrylate monomer and the plasticizer DBP in equal

proportions. The remainder is comprised of trimethylolpropane trimethacrylate, in the









range of 3% and a minute amount of dimethyl-p-toluidine, which is a quaternary

ammonium used as an activator.10 The powder is composed mostly of polyethyl

methacrylate.

According to the MSDS, like Tempo, this material contains 2% benzoyl peroxide,

which is a polymerizing initiator. Interaction between this benzoyl peroxide and the

mono-poly coating may be possible.

Flexacryl-Soft has a hard formulation equivalent, Flexacryl-Hard, which does not

contain any dibutyl phthalate, the ester plasticizer. According to the MSDS, the hard

material also has a longer chain component. The manufacturer claims that Flexacryl-Soft

is a self curing denture relining plastic that will set to a soft cushion-like consistency and

will remain soft for at least 12 months. Of the five materials tested, Flexacryl-Soft is the

only material that is exothermic after mixing of the powder and liquid components,

indicating polymerization.

The mixed gel has an opaque orange color.

The components of the four temporary soft denture liners that we have data on are

summarized in Table 1. Table 2 shows the batch number of the materials used in this

study.












Table 1. Chemical composition of soft liners

Lynal (DENTSPLY Caulk) from MSDS
Liquid Powder
Organic phthalate plasticizer Polyethyl methacrylate
Ethyl alcohol Benzoyl peroxide

Coe-Comfort (GC)
Liquid Powder
Benzyl benzoate 85% 8 87.3% 12 Polyethyl methacrylate 8,29,30
(antifungal)7
Ethyl alcohol 6% 8 8.2% 12 Polybutyl methacrylate 8
Dibutyl phthalate 30 4.5% 6 Zinc undecylenate (antifungal) 1%12,31
Dicyclohexyl phthalate 8__

Coe-Soft (GC)
Liquid Powder
Di-n-butyl phthalate 30 4.3% 12 Polyethyl methacrylate 29,30
Benzyl salicylate 30 Zinc undecylenate (antifungal) 1% 12,31
Butyl phthalyl butyl glycolate 80.9% 12
Ethyl alcohol 30 14.8% 12

Tempo (Lang) from MSDS
Liquid Powder
Dialkyl phthalate < 75% Polyethyl methacrylate < 99%
Ethyl alcohol 25% 8< 25% Residual monomers < 1%
Benzoyl peroxide < 3.0%
Mineral pigments <0.01%

Flexacryl-Soft (Lang) from MSDS
Liquid Powder
N-butyl methacrylate monomer <50% Polyethyl methacrylate < 99%
Dibutyl phthalate <50% Benzoyl peroxide < 2.0%
Trimethylolpropane Trimethacrylate <3%
Dimethyl-p-toluidine <1%






Table 2. Batch numbers

Material Manufacturer Batch number
Lynal L.D. Caulk 980819
Coe-Comfort GC America Inc. (Alsip, IL 60803) L0361698A
Coe-Soft GC America Inc. (Alsip, IL 60803) L062298A
Tempo Lang Dental mfg. Co (Wheeling, IL 60090) 090398
Flexacryl-Soft Lang Dental mfg. Co (Wheeling, IL 60090) 090898
Jet Seal Lang Dental mfg. Co (Wheeling, IL 60090) 121498 QC2









Substrate for Soft Reline Resins


Because immediately after mixing, the temporary soft denture liners have the

consistency of a viscous liquid, they needed to be confined between the denture hard

resin base and the oral mucosa or in our case a mold during for the initial set. In

addition, the variable waiting periods between different materials for transition from the

plastic phase to the viscoelastic phase or gel like made standardization of the time needed

for the material preparation difficult.

For in vitro sample preparations, a review of the literature mentioned jar caps 32

and cylindrical containers,10,23,26 were used as molds for specimen preparation.

Dominguez et al.,25 and McCarthy and Moser 33 used a cylindrical sleeve sandwiched

between 2 flat surfaces to form the specimens which were then extruded. Because in our

study, the specimens were tested dynamically using an Instron Dynamic Testing System

to compress them, any holder or substrate for the resilient materials having vertical walls

cannot be used. This would impede the compression of the specimen. A heat cure

methacrylate substrate flat sheet of 2 mm, which is the recommended thickness of

denture resin bases, would approximate clinical settings best. Such a substrate would

introduce another parameter to contend with, namely, contaminants such as MMA and

hydroquinone from the substrate itself into the surrounding immersion liquid.34-36

Lucite-ES, a commercial extruded acrylic resin sheet is a close substitute and would

minimize this factor. It is assumed that the heat extrusion industrial process would not

leave any trace chemical in the Lucite sheet to leach out. As detailed later in the number

of sample section, control bare samples of the Lucite sheet immersed in water were

prepared to verify this assertion using pH change of the surrounding water and UV









spectrophotometry detection. Two hundred squares of 25 x 25 mm (1 x 1 inch) of

Lucite-ES were prepared for the study. They were marked with a serial number in series

of 6 using an electric engraver and weighed individually.


Methods


Samples Preparation


To understand the effect of processing conditions on the properties of the soft

liners, four processing techniques or parameters were applied: (1) prepared according to

the manufacturer's recommendation; (2) prepared according to the manufacturer's

recommended procedure followed immediately by placing in a pressure pot at 550C at 30

psi for 15 minutes; (3) coat the specimen with mono-poly after normal processing; and

(4) coat the specimen with Jet Seal after normal processing.


Number of Samples


Soft liner specimens with a dimension of 30(length) x 30(width) x 6(thickness)

mm were prepared according to the manufacturer's recommendation. Twenty-four (6 x

4) samples were made from each material and divided into four groups as described in

experimental conditions. Each group except for the control group would receive an

additional treatment immediately after the normal preparation. This design would give

us 6 replications for each condition. Throughout the entire experiment, each specimen

were stored in a Corning Snap-Seal No. 1730 container with 50 ml of distilled water and

aged individually at room temperature (25 C).









Considering that the type of soft liner forms five (5) qualitative factors, the type

of coating forms four (4) qualitative factors, that six specimen are needed per factor for

replication, a total of 120 (6 x 4 x 5) samples were prepared. The Shore A hardness

involves dimpling the material surface with an indentor to a depth of about 2 mm, which

may damage the surface of the sealer. In consideration of the possibility of damage to

the coating, separate samples were prepared for this test. The penetration point was

resealed with the appropriate coating after each test and subsequent testing was done at a

different spot. Therefore, an additional sixty (60) sample with coatings was prepared,

thirty (30) each for experimental condition 3 and 4. This brought the total number of

samples to 180 ((6 x 4 x 5) + (6 x 2 x 5)). An additional 6 Snap-Seal vials filled with 50

ml of distilled water and blank Lucite squares were also prepared for leachant

verification by UV spectrophotometry and pH test.


Powder to Liquid Ratio


For clinical convenience, tissue conditioner manufacturers generally recommend

volume measures for preparing the conditioner mix. Because volumetric measures are

notoriously inaccurate when measuring powder, the manufacturer's weight ratio

recommendations for preparing the liners were used in preference when available. For

this study, should that recommendation be unavailable, a powder weight to liquid weight

ratio was established by weighing the respective contents of the measuring cups that

were provided with the kit. The powder container was fluffed before filling the

measuring cup for this purpose. The mixing proportions used for preparing the five

materials are shown in Table 3.











Table 3. Powder-to-liquid ratio
Powder Liquid Powder Liquid Ratio
Volumetric measures Weight measures per Powder:liquid
per portion portion ratio
Lynal 10cc 4cc 6g 4g 3:2
Coe-Comfort 9cc 5cc 6g 5g 6:5
Coe-Soft N/A 8cc 11g 8g 11:8
Tempo 10cc 6cc 6g 6g 1:1
Flexacryl-Soft 10cc 6cc 6g 6g 1:1


Based on Table 3, Tempo and Flexacryl-Soft have the smallest powder to liquid

weight ratio, while Lynal has the largest. In between, Coe-Soft has a larger ratio than

Coe-Comfort. Because the chemicals that could be leached out are in the liquid

component of the material, this ratio may have an influence in our findings.


Preparation Time


Immediately after mixing, the mixture is generally too fluid for intra oral

insertion, hence the manufacturer generally includes a certain waiting time from the start

of mix before oral insertion. This varies from 30 seconds to 3 minutes. We have elected

to apply the mix into the mold immediately after mixing (i.e., 30 seconds after from start

of mix). This was done because total setting time is the predominant factor and it is

easier to insert the mix into the mold while in a fluid consistency.

After insertion, the mix needed to remain in contact with the oral cavity or in our

case, the mold, for a certain time for gelation to occur before it can be withdrawn for

manipulation and still retain the shape of the mold surfaces. Times needed prior to

manipulation of the material indicated by manufacturers are presented in Table 4.











Table 4. Times needed prior to manipulation
Material Manufacturer's recommended time
Lynal 7-8 minutes from start of mix
Coe-Comfort 4-5 minutes intra-oral
Coe-Soft 3 minutes intra-oral, remove for trimming, reseat for another 5 minutes
Tempo 3 minutes intra-oral
Flexacryl-Soft Muscle trim + 3 minutes static + 20 minutes bench cure


In their experiment, Dominguez et a.,25 and Gronet et al.26 allowed 20 minutes

setting time for all specimens before specimen removal from the mold. McCarthy and

Moser 33 allowed 15 minutes. Yoeli et al.32 did not specify the setting time.

In order to have a standardized time, we allowed on average a total of 25 minutes

of setting time from the start of mix in our study before testing. The molding time (time

during which the material left to rest in the mold) was 10 minutes before removal. The

specimens prepared as per the manufacturer's instruction had a 15-minute bench rest

after retrieval from the mold. The heat and pressure specimens were placed in a heated

pressure pot for 15 minutes. The coated ones were dip coated and allowed to bench rest

until 25 minutes had elapsed from initial mixing of the powder/liquid.

During mixing, we made the same observation as Yoeli et al.,32 who found that

Flexacryl-Soft was more fluid and Lynal was more viscous immediately after mixing.

Tempo and Flexacryl-Soft had the essentially the same initial fluidity, while Coe-

Comfort and Coe-Soft were more viscous and Lynal had the highest viscosity.


Specimen Forming


Two wooden specimen former were constructed to be used as mold or former for

specimen preparation as shown in Figure 1. These molds have an internal dimension of

150 x 25 x 8 mm. Before receiving the materials, their walls were lubricated with









petroleum jelly. The dimension of these jigs was calculated to accommodate 6 Lucite

squares. When six specimens were made from one mix made at a time, intra material

data variations associated with preparation would be minimized. Before mixing the

resilient material, the mold's bottom was lined with masking tape, 1 inch wide, adhesive

side up and six pre-weighed Lucite squares marked as a series were aligned on the tape.

The resilient material was mixed, poured into the mold, and covered with wax paper. A

glass sheet was placed atop and held down for 10 minutes to obtain a flat surface for

testing. After this period, the resilient material was retrieved and cut into individual

pieces using Bard Parker knives or piano wire strung over a coping saw. An additional

15 minutes bench rest was allowed before testing.
























Figure 1. Molds used in specimen forming. In the foreground are the six Lucite squares
backed by masking tape ready for insertion in the mold. In the background is a
wooden mold with the Lucite squares in place, ready to receive the tissue
conditioner









In clinical situations, the recommended clinical thickness of tissue conditioner as

a liner under a complete denture prosthesis is 1.5 mm to 3 mm. 3,37 It is not possible to

keep within this recommendation because this thickness would not have yielded valid

hardness data since the Shore A specification requires a minimum material thickness of 6

mm. Therefore this is the thickness of the tissue conditioner specimens manufactured

from the mold former after subtracting the 2 mm Lucite substrate thickness from the 8

mm depth.

Instruments for Data Collection


At each prescribed interval, the following measurements were made:

1. Shore A hardness.

2. Release of plasticizer in the immersion solution.

3. Weight changes of the specimen.

4. Dynamic mechanical test of the specimen.

5. pH of the solution.

6. Surface appearance by visual examination and photographic record when

change was detected.

It is expected that there would be a trend between weight loss and the other

variables, facilitating the understanding of the transformations that the material goes

through and allowing cross validation of the measurements obtained.


Weight Loss by Balance


Weight change was monitored by weighing the specimen at each prescribed

interval with a Denver Instrument XL-410 electronic balance with a precision of 0.001g









(Denver, CO, Max 410g, S/N 0075163). The weight changes in conjunction with

plasticizer leaching would allow estimation the true quantity of water absorption. That

data would also be used to establish if there is a correlation between the water absorption

and the changes in mechanical properties.

Each Lucite-ES substrate was weighed before receiving the designated soft-liner;

the final specimen was also weighed to determine the actual weight of the soft-liner. At

each prescribed time of replacing storage medium, the specimens were dab dried with

Kimwipe before weighing.


Shore A Hardness


The hardness of the material was measured using a Shore Durometer type "A-2"

shown in Figure 2. This Durometer was attached to an operating stand with a standard

1 kg mass securely affixed to it and centered on the axis of the indentor. The operating

stand was then placed on an adjustable platform such that the dial gauge was at eye level

to minimize parallax errors and minimize eye strain. The adjustable on which the

specimen was placed was then moved within 2 cm of the foot of the Durometer and

locked in place. The specimen to be tested was then placed on the adjustable with the

indentor facing a spot that has not been previously tested and the Durometer foot was

lowered steadily onto the material's surface. At this moment of contact, a chronometer

was started and the reading made from the analog dial gauge at the appropriate time.

Because the readings tended to level after 2 minutes of penetration by the Shore A

indentor, it was decided to record the 30 seconds and 2 minutes readings. If the

specimen tested was coated, the penetration point was marked with a permanent marker

and covered with a new dab of the coating material.


































Figure 2. Shore A Durometer


Dynamic Mechanical Test


An Instron Model 8511 Frame F Plus Dynamic Testing System, mounted with a

Sensotec Model 45/8130-05 1KN(2001bs) S/N 654651 load cell (Canton, MA) was used

to test the samples while measuring their compressive strength under load.

Instead of subjecting specimens to a pre-determined amount of stress and

observing the stress relaxation behavior of the lining materials, we elected to load the

specimen using a cyclic mode up to 15 cycles and recorded the peak load at each cycle.

The protocol was comprised of three steps: (1) compress the specimen by 0.15 mm to

assure contact between the actuator head and the specimen; (2) continue the compressing

movement of the actuator head to 0.65 mm at a rate of 0.05 mm per sec; (3) when the









actuator head reaches 0.65 mm, the actuator head switches to cyclic motion, which uses

0.65 mm as the midpoint and cycles with an amplitude of 0.5 mm at the rate of V2 cycle

per second for 15 cycles. At the end of 15th cycle, the actuator head moved back to its

original non-stress position. The entire process took 39 seconds to complete. This mode

of dynamic test yields two sets of data. The first set records the load exerted on the

specimens as the actuator head compresses the specimen to the predetermined position,

approximately 0.65 mm. This set of data was used to estimate the modulus of elasticity

of the specimen. The second set records peak loads as the actuator head compresses and

cycles between 0.15 mm and 1.15 mm depth of the specimens. The data was used to

estimate the recovery of the specimen between cycles.

A viscoelastic material will respond to loading with an instant elastic deformation

and a time-dependent viscous deformation. As the load is being removed, the elastic

strain will recover instantly but the time-dependent deformation will require certain time

to recover. In the present testing protocol, the rate of cycling does not allow the time-

dependent deformation to recover completely when the actuator head reverses from

unloading back to loading. The immediate result is that the peak load of subsequent

loading will always be less than the previous loading cycle. The decay of the peak load

can be expressed as follows:


= Lo exp(- ) (1)


Where, L, is the peak load at respective cycle n, Lo is the estimated maximum

peak load at n = 0, and 77 is a constant unique to a specific testing condition and material.

The variable 77, which we call rate of recovery, reflects the ability of the material to










rebound elastically; a higher value means more elastic, while a lower value means more

viscous flow.


UV Spectrophotometer


A Shimadzu UV 160U UV/Visible Recording Spectrophotometer, S/N 28D6370

(Columbia, MD) was used to quantify plasticizer leakage. In our preliminary study,

leachants from set soft liner specimens into the surrounding water solution were found to

share similar UV absorbency profiles as those of the corresponding liquid component of

the soft liner. This absorbency spectrum appears between 200-400 nm. Figure 3 shows

the typical absorbance profile of leachants, in this case, from Coe-Soft along with the

peaks used for measuring leachant quantity. When we attempted to prepare standard

solutions from the liquid component as reference for estimating the quantity of release,

we found that the liquids were not miscible with water and the quantity that dissolved in

water was negligible. We did find that these liquid components were soluble in 25%

ethanol/water solution, as implied by Jones et al. 12 We then prepared a series of

reference solutions with known concentration of the liquid in ppm. The UV

spectrophotometer does not detect the presence of ethanol because ethyl alcohol is

transparent to UV from the visible into the ultraviolet range near 205 nm.


25
20 Coe- Soft
15
0 236nm
051 303 nm

200 250 300 350 400
Wavelength, nm

Figure 3. Typical UV absorption curve









When the absorbance of the released content exceeded the detection limit of the

instrument, series of dilution were carried out to bring the concentration to within the

limit.


pH of the Solution


Distilled water can register pH in the neighborhood of 5.5, which can change in

the presence of the soft liner and with time. It was not known a priori if that would have

a significance influence on the other values collected. The pH values were recorded

weekly for each specimen with an Orion Research Expandable Ion Analyzer model

EA920 S/N 1192. The pH probe was rinsed with distilled water between each

measurement. Six vials of distilled water without any specimens as controls were also

prepared. The pH values were used to complement the other data collected.


Macro Photography and Micro Photography


Systematic microscopic observation of the tissue conditioner's surface did not

yield any information and was therefore abandoned. Instead, macroscopic observation

via macro photography was substituted.

When macroscopic surface changes were apparent, selected specimen with

representative and noticeable features were selected for macro photography using a

Minolta 350si RZ camera equipped with a Minolta AF100 mm f 1:2.8 (32) macro lens.

Lighting was supplemented by a Minolta 3500 XI slave flash on remote mode placed at a

narrow angle to the specimen. Because of the translucency of the coatings, not all the

visible changes were observable on macro photographs, hence the selection of the most

evident ones. The use of polarizing filters did not help in enhancing the details.









Microscopic examination of the samples showing surface changes did not yield any

evident difference between different areas nor remarkable features.

At the end of the data collection period, a thin section from a specimen of each

coated series was prepared for microscopic examination and photographed using a

Bausch & Lomb Stereo-Zoom 7 microscope attached to a Nikon AFX-II camera system.

The placement of a stage microscale 100 x 0.01 = 1 mm by Graticules, Tonbridge, Kent,

England, under each section allowed measurement of the thickness of the coating.

Special attention was given to areas where gradient changes in color from the surface

inwards, detachment of the coating and voids were observed.

Data Collection and Statistical Analysis


Data were collected at the time of preparation (0 week), 48 hours, 1st, 2nd, 4th,

6th, 8th and 12th week. Each sample was examined for surface change, blotted dry,

weighted, if they are non coated, tested for hardness with the Shore A Durometer and for

viscoelasticity using with the Dynamic Instron machine. The 50ml of distilled water in

the SnapSeal container were replaced every time data collection was made. Twenty (20)

ml of the immersion liquid was saved in a Dilu-Vial (Fisher Scientific) container for later

pH and UV spectrophotometry measurements. Ideally, it should have been replaced as

frequently as possible, but for practical purposes, it was not possible to do it more

frequently than at data collection time. According to the literature, the rate at which

plasticizers would leach out of the material would be most intense during the first two

weeks. Therefore after the first two weeks, longer data collection periods before

leachants saturation in the surrounding liquid was attained would be satisfactory.









Monitoring of the initial data did not reveal any need to intensify the data collection

periods.

The effect of treatment and storage time on the individual variable was first

analyzed by two-way analysis of variance to show their influence on the values of the

measurements. When statistically significant influence was observed, the Tukey's

studentized range tests were performed to group surface treatments or storage times with

mean values that are not significant different on the values at a=0.05. In order to

identify if there are correlations between the values of variables, we conducted a series of

linear regression between any two of the following variables: weight loss in water,

leachant by UV at high and low wavelength, modulus of elasticity, and rate of recovery.















CHAPTER 4
RESULTS


Surface Resilience by Shore A Hardness


Although literature reviewed had reported Shore A hardness values of some of

the material we used, it was found in this study that none of the materials used gave a

stable value. In fact, the dial hand would jump to an initial value and started to decrease

immediately, defeating any attempt at an early accurate reading. The hand then either

dropped to zero (a total penetration of the indentor) or stabilized at a number after a few

minutes. This phenomenon is mostly caused by viscoelastic behavior. There was an

instant elastic resistance to the loading that yielded a maximum deflection of the dial

hand. This was followed by a creep phase represented by the continuing reduction in

hardness value with time. Since we were unable to read the value accurately before it

began to decrease, it was decided to take readings at 30 s and 2 min after the indentor

was lowered on the specimen.

Tables 5 and 6 show the Shore A hardness results recorded at 30 s and 2 min after

placing the load, respectively. Several materials show zero values. We also attempted to

record the duration it would take to reach zero value. Although there is a general trend

for longer time to zero with specimen storage time, the results are not conclusive and are

not shown. It is interesting to note that the Shore A hardness values increased

immediately after the mono-poly coating has dried, which is about 15 minutes after










application. Specimens from as prepared, the heat and pressure, and with the Jet Seal

coating exhibited similar behaviors. Two-way Analysis of Variance of treatment and

storage time shows that both variables have statistically significant influence on the


Table 5. Shore A hardness values 30 sec after indentation

Material Time, day Control Pressure/Heat Mono-poly Jet Seal
Coe-Comfort 0 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Comfort 2 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Comfort 7 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Comfort 14 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Comfort 28 0 (-) 0 (-) 2 (3) 0 (-)
Coe-Comfort 42 0 (-) 0 (-) 1 (1) 0 (-)
Coe-Comfort 63 1 (-) 0 (-) 7 (4) 0 (-)
Coe-Comfort 84 1 (-) 1 (-) 5 (4) 0 (-)
Coe-Soft 0 0 (-) 0 (-) 4 (1) 0 (-)
Coe-Soft 2 0 (-) 0 (-) 1 (1) 0 (-)
Coe-Soft 7 0 (-) 3 (1) 1 (2) 0 (-)
Coe-Soft 14 3 (1) 4 (-) 4 (1) 1 (1)
Coe-Soft 28 3 (-) 4 (1) 7 (1) 4 (1)
Coe-Soft 42 2 (2) 5 (1) 8 (1) 4 (1)
Coe-Soft 63 7 (2) 5 (1) 11 (3) 6 (1)
Coe-Soft 84 5 (2) 7 (1) 10 (2) 7 (2)
Flexacryl-Soft 0 29 (1) 31 (-) 56 (8) 22 (2)
Flexacryl-Soft 2 29 (1) 32 (-) 55 (9) 24 (3)
Flexacryl-Soft 7 30 (1) 32 (1) 51 (9) 25 (2)
Flexacryl-Soft 14 31 (1) 32 (-) 53 (11) 26 (1)
Flexacryl-Soft 28 31 (1) 30 (1) 49 (13) 27 (1)
Flexacryl-Soft 42 30 (1) 30 (1) 52 (12) 27 (1)
Flexacryl-Soft 63 30 (1) 31 (1) 55 (11) 29 (2)
Flexacryl-Soft 84 31 (1) 31 (1) 47 (8) 30 (1)
Lynal 0 0 (-) 14 (1) 20 (4) 2 (3)
Lynal 2 13 (1) 15 (1) 17 (3) 8 (3)
Lynal 7 14 (1) 18 (1) 16 (4) 10 (1)
Lynal 14 15 (2) 17 (1) 18 (1) 11 (2)
Lynal 28 14 (-) 17 (1) 19 (1) 9 (1)
Lynal 42 14 (1) 17 (1) 20 (2) 14 (2)
Lynal 63 14 (1) 14 (2) 20 (4) 15 (2)
Lynal 84 15 (1) 15 (1) 20 (2) 16 (2)
Tempo 0 0 (-) 0 (-) 6 (5) 0 (-)
Tempo 2 0 (-) 0 (-) 0 (-) 4 (2)
Tempo 7 0 (-) 0 (-) 3 (2) 0 (-)
Tempo 14 0 (-) 0 (-) 5 (1) 0 (-)
Tempo 28 0 (-) 0 (-) 10 (5) 0 (-)
Tempo 42 0 (-) 0 (-) 5 (5) 0 (-)
Tempo 63 1 (1) 0 (-) 11 (2) 1 (-)
Tempo 84 0 (-) 1 (-) 9 (6) 1 (1)
Note: The values in parenthesis are standard deviation.










hardness values atP values less than 0.01. Further analysis by Tukey's grouping test

confirmed that mono-poly had a significant influence on the Shore A hardness values

while the other three treatments in general behave similarly. Table 7 shows the summary


Table 6. Shore A values measured 2 min after indentation

Material Time, day Control Pressure/Heat Mono-poly Jet Seal
Coe-Comfort 0 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Comfort 2 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Comfort 7 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Comfort 14 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Comfort 28 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Comfort 42 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Comfort 63 1 (-) 0 (-) 1 (3) 0 (-)
Coe-Comfort 84 1 (-) 1 (-) 0 (-) 0 (-)
Coe-Soft 0 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Soft 2 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Soft 7 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Soft 14 0 (-) 0 (-) 0 (-) 0 (-)
Coe-Soft 28 0 (-) (-) 2 (1) 0 (-)
Coe-Soft 42 0 (-) 1 (1) 2 (2) 1 (1)
Coe-Soft 63 2 (1) 1 (-) 5 (2) 1 (1)
Coe-Soft 84 1 (1) 2 (1) 4 (2) 2 (2)
Flexacryl-Soft 0 24 (-) 23 (2) 52 (8) 17 (2)
Flexacryl-Soft 2 25 (1) 27 (1) 53 (14) 18 (2)
Flexacryl-Soft 7 25 (1) 28 (1) 48 (12) 20 (2)
Flexacryl-Soft 14 27 (1) 28 (1) 47 (11) 21 (1)
Flexacryl-Soft 28 27 (1) 26 (1) 43 (10) 24 (1)
Flexacryl-Soft 42 25 (1) 28 (1) 47 (12) 24 (1)
Flexacryl-Soft 63 27 (1) 27 (1) 47 (9) 24 (3)
Flexacryl-Soft 84 27 (1) 27 (1) 41 (6) 25 (2)
Lynal 0 0 (-) 10 (1) 25 (17) 0 (-)
Lynal 2 9 (1) 11 (1) 11 (2) 4 (2)
Lynal 7 10 (1) 12 (1) 11 (3) 6 (1)
Lynal 14 10 (1) 12 (1) 12 (1) 7 (2)
Lynal 28 10 (-) 13 (2) 14 (1) 6 (1)
Lynal 42 11 (1) 13 (2) 15 (2) 9 (1)
Lynal 63 10 (-) 10 (2) 14 (4) 11 (1)
Lynal 84 10 (-) 11 (1) 14 (3) 12 (1)
Tempo 0 0 (-) 0 (-) 0 (-) 0 (-)
Tempo 2 0 (-) 0 (-) 0 (-) 1 (1)
Tempo 7 0 (-) 0 (-) 0 (-) 0 (-)
Tempo 14 0 (-) 0 (-) 0 (-) 0 (-)
Tempo 28 0 (-) 0 (-) 4 (4) 0 (-)
Tempo 42 0 (-) 0 (-) 1 (1) 0 (-)
Tempo 63 0 (-) 0 (-) 4 (1) 0 (-)
Tempo 84 0 (-) 1 (-) 3 (3) 0 (-)
Note: The values in parenthesis are standard deviation.












Tukey's grouping of the surface treatment on Shore A hardness


Material 30 second 2 minutes

Coe-Comfort M C J P M C P J
Coe-Soft M P J C M J P C
Flexacryl-Soft M P C J M P C J
Lynal MPCJ MPCJ
Tempo M J C P M J C P

Note: C=Control; J=Jet Seal; M=Mono-poly; P=Pressure/heat. The groups are arranged in
descending order from left to right.
The underlined group treatments that are not statistically different at a=0.05.


Flexacryl


-0 Control
o Jet-Seal


-o Mono-poly
-* Pressure/Heat


30 seconds post indentation










-------. --- _- ---.-- ---------
__--0- -------.--.
_,e-- a.- .
S


0 10 20 30 40 50 60 70 80 90 100

Time, day

Figure 4. Hardness values 30 seconds post indentation of Flexacryl-Soft


Table 7.











80
-- Control ----o Mono-poly

7 Lynal -----o Jet-Seal --* Pressure/Heat
70
30 seconds post indentation

60


50


40-

o
t-"
30-


20 --
12 0 0 _--- --- -





0-
0 10 20 30 40 50 60 70 80 90 100

lime, day

Figure 5. Hardness values 30 seconds post indentation of Lynal


of Tukey's grouping for the effect of treatments. This can be illustrated by Figures 8 and

9, which show the hardness values 30 seconds post indentation of Flexacryl-Soft and

Lynal as influenced by treatment and time, respectively.


Dynamic Mechanical Test of the Specimen


Table 8 shows the calculated values of elastic modulus of the specimens as

influenced by the treatment and time of immersion; each value has the unit of MPa.

Higher values mean the material is more rigid. Table 9 shows the rate of recovery of the

specimen as influence by the treatment and the duration of water immersion; the value

has a unit of cycle-1. Higher values mean that the peak load decay is less, which

indicates the material is more elastic. In other words it recovers more rapidly. On the










other hand, a lower value means the material is softer and will not recover as much when

the load is removed.


Table 8. Elastic modulus of soft liners as result of surface treatment and time

Materials Time, day Control Pressure/Heat Mono-poly Jet Seal

Coe-Comfort 0 0.44 (0.04) 0.50 (0.09) 0.36 (0.08) 0.45 (0.07)
Coe-Comfort 2 0.65 (0.07) 0.55 (0.09) 0.69 (0.25) 0.62 (0.05)
Coe-Comfort 7 0.74 (0.08) 0.94 (0.18) 0.80 (0.21) 0.54 (0.31)
Coe-Comfort 14 0.87 (0.11) 0.91 (0.18) 0.80 (0.16) 0.75 (0.15)
Coe-Comfort 28 0.96 (0.10) 0.73 (0.12) 0.85 (0.21) 0.75 (0.18)
Coe-Comfort 42 0.98 (0.10) 0.89 (0.09) 0.89 (0.22) 0.89 (0.13)
Coe-Comfort 63 0.93 (0.11) 0.87 (0.09) 0.96 (0.25) 0.86 (0.13)
Coe-Comfort 84 1.03 (0.11) 0.85 (0.12) 0.77 (0.33) 0.83 (0.13)
Coe-Soft 0 0.42 (0.12) 0.34 (0.11) 0.53 (0.12) 0.53 (0.02)
Coe-Soft 2 0.44 (0.14) 0.66 (0.22) 0.97 (0.24) 0.69 (0.04)
Coe-Soft 7 0.61 (0.12) 1.00 (0.14) 1.09 (0.12) 0.83 (0.08)
Coe-Soft 14 0.80 (0.13) 0.91 (0.09) 1.06 (0.26) 0.80 (0.17)
Coe-Soft 28 0.96 (0.10) 1.30 (0.24) 1.12 (0.18) 1.04 (0.18)
Coe-Soft 42 0.97 (0.11) 1.30 (0.24) 1.30 (0.17) 0.95 (0.26)
Coe-Soft 63 1.06 (0.19) 1.36 (0.27) 1.15 (0.28) 1.00 (0.22)
Coe-Soft 84 1.20 (0.12) 1.51 (0.39) 1.04 (0.32) 1.15 (0.26)
Flexacryl-Soft 0 3.26 (0.40) 4.27 (0.30) 6.36 (0.35) 3.53 (0.52)
Flexacryl-Soft 2 3.37 (0.72) 3.84 (0.32) 7.97 (0.93) 4.53 (0.62)
Flexacryl-Soft 7 3.86 (0.71) 4.84 (0.54) 6.98 (1.17) 4.02 (0.69)
Flexacryl-Soft 14 4.06 (0.46) 4.92 (0.42) 6.71 (0.86) 4.98 (0.71)
Flexacryl-Soft 28 3.95 (0.38) 4.83 (0.64) 7.37 (1.08) 4.96 (0.68)
Flexacryl-Soft 42 4.23 (0.53) 4.89 (0.20) 7.13 (0.78) 5.24 (0.81)
Flexacryl-Soft 63 3.78 (0.38) 5.00 (0.31) 8.49 (0.99) 5.21 (1.06)
Flexacryl-Soft 84 4.62 (0.70) 5.20 (0.47) 7.12 (0.80) 5.22 (1.13)
Lynal 0 0.16 (0.05) 0.28 (0.13) 1.18 (0.23) 1.08 (0.17)
Lynal 2 0.60 (0.40) 0.29 (0.11) 1.67 (0.25) 1.08 (0.32)
Lynal 7 0.90 (0.45) 1.38 (0.49) 1.53 (0.21) 1.12 (0.39)
Lynal 14 1.34 (0.38) 1.29 (0.35) 1.66 (0.17) 1.07 (0.31)
Lynal 28 1.19 (0.28) 0.75 (0.34) 1.50 (0.11) 1.36 (0.49)
Lynal 42 1.29 (0.33) 0.47 (0.12) 1.49 (0.19) 1.46 (0.32)
Lynal 63 1.38 (0.44) 0.53 (0.16) 1.34 (0.19) 1.34 (0.29)
Lynal 84 1.33 (0.37) 0.45 (0.08) 1.30 (0.10) 1.22 (0.35)
Tempo 0 0.31 (0.06) 0.36 (0.05) 0.50 (0.08) 0.31 (0.02)
Tempo 2 0.54 (0.14) 0.46 (0.12) 0.65 (0.07) 0.59 (0.05)
Tempo 7 0.78 (0.19) 1.17 (0.14) 1.02 (0.19) 0.62 (0.23)
Tempo 14 0.87 (0.20) 1.12 (0.13) 0.68 (0.37) 0.93 (0.13)
Tempo 28 1.07 (0.20) 0.81 (0.25) 0.60 (0.28) 0.97 (0.21)
Tempo 42 1.05 (0.24) 1.11 (0.17) 0.92 (0.36) 1.08 (0.24)
Tempo 63 1.14 (0.21) 1.10 (0.20) 0.75 (0.47) 1.07 (0.23)
Tempo 84 1.04 (0.25) 1.04 (0.16) 0.68 (0.33) 1.03 (0.25)
Note: The values are in MPa; the values in parenthesis are standard deviation.










The results of Two-way Analysis of Variance indicate that the effects of

treatment and storage time on the elastic modulus values and rate of recovery are

statistically significant. Further analysis with Tukey's grouping test shows that


Table 9. Rate of recovery


Material Time, day Control Pressure/Heat Mono-poly Jet Seal
Coe-Comfort 0 55.1 (2.1) 64.0 (2.8) 44.4 (4.9) 43.1 (5.7)
Coe-Comfort 2 80.0 (6.5) 72.0 (3.2) 56.6 (8.5) 61.4 (6.8)
Coe-Comfort 7 84.3 (12.7) 84.3 (12.7) 69.7 (6.8) 70.6 (7.2)
Coe-Comfort 14 75.8 (10.0) 86.0 (8.7) 68.6 (6.6) 72.7 (6.9)
Coe-Comfort 28 86.5 (21.5) 95.4 (12.5) 75.9 (5.7) 95.1 (16.5)
Coe-Comfort 42 86.4 (4.2) 88.0 (3.6) 74.0 (5.4) 87.3 (10.0)
Coe-Comfort 63 96.5 (21.1) 80.9 (3.1) 88.5 (6.3) 98.7 (15.0)
Coe-Comfort 84 97.0 (16.7) 86.1 (1.3) 85.1 (4.8) 97.2 (13.4)
Coe-Soft 0 65.6 (4.2) 54.6 (5.2) 67.1 (4.2) 51.1 (2.1)
Coe-Soft 2 80.2 (2.7) 77.3 (5.8) 68.9 (5.0) 64.0 (2.0)
Coe-Soft 7 87.7 (7.4) 80.1 (5.6) 63.7 (1.8) 77.7 (3.9)
Coe-Soft 14 96.2 (4.8) 97.0 (9.0) 63.7 (1.8) 89.2 (4.3)
Coe-Soft 28 124.4 (19.0) 103.4 (7.9) 82.6 (5.4) 94.7 (8.4)
Coe-Soft 42 104.4 (18.2) 98.1 (2.7) 83.4 (3.5) 92.5 (1.9)
Coe-Soft 63 145.3 (31.1) 110.0 (19.7) 98.5 (10.4) 105.6 (5.0)
Coe-Soft 84 102.7 (6.4) 97.5 (5.1) 95.9 (7.3) 89.9 (3.9)
Flexacryl-Soft 0 112.0 (19.7) 110.9 (6.4) 55.0 (3.5) 112.0 (19.6)
Flexacryl-Soft 2 115.6 (7.7) 105.6 (12.3) 72.5 (8.6) 107.8 (6.0)
Flexacryl-Soft 7 109.3 (17.7) 72.3 (5.7) 81.4 (6.9) 118.7 (7.6)
Flexacryl-Soft 14 128.4 (11.3) 115.2 (6.0) 95.5 (9.0) 127.8 (10.5)
Flexacryl-Soft 28 125.0 (14.0) 82.9 (4.9) 83.7 (7.9) 160.7 (16.9)
Flexacryl-Soft 42 136.4 (8.0) 128.5 (9.4) 89.5 (12.8) 126.8 (14.0)
Flexacryl-Soft 63 115.3 (3.6) 110.1 (7.2) 68.5 (6.4) 121.3 (9.5)
Flexacryl-Soft 84 113.6 (10.9) 98.7 (8.7) 72.9 (6.5) 165.2 (28.5)
Lynal 0 33.7 (3.8) 164.0 (19.2) 137.9 (16.3) 96.9 (1.4)
Lynal 2 136.7 (47.5) 177.9 (17.0) 128.7 (16.8) 110.2 (6.2)
Lynal 7 165.2 (20.4) 137.1 (3.8) 143.6 (11.8) 120.5 (6.2)
Lynal 14 131.9 (7.2) 165.8 (4.5) 120.6 (7.6) 128.9 (10.9)
Lynal 28 161.6 (32.7) 156.2 (11.7) 124.7 (6.2) 142.6 (31.0)
Lynal 42 160.5 (13.4) 159.0 (19.8) 125.1 (8.1) 132.6 (5.4)
Lynal 63 176.1 (15.9) 163.7 (14.9) 121.9 (5.9) 137.9 (7.3)
Lynal 84 162.1 (8.6) 152.3 (12.6) 124.1 (9.9) 146.7 (9.7)
Tempo 0 42.5 (4.5) 55.4 (3.3) 44.1 (1.3) 37.2 (2.0)
Tempo 2 79.2 (6.3) 67.1 (2.7) 52.2 (1.6) 53.2 (1.4)
Tempo 7 86.7 (17.7) 72.8 (10.2) 54.0 (3.3) 71.2 (3.6)
Tempo 14 94.0 (4.0) 87.2 (4.2) 61.9 (7.0) 75.9 (1.8)
Tempo 28 127.3 (18.0) 99.4 (8.3) 78.6 (9.9) 80.9 (1.9)
Tempo 42 101.7 (2.1) 99.3 (3.3) 67.7 (5.7) 77.5 (2.3)
Tempo 63 90.5 (5.8) 91.6 (1.8) 85.1 (11.9) 81.1 (4.2)
Tempo 84 104.8 (1.2) 100.3 (3.8) 78.2 (5.1) 83.1 (2.7)
Note: The values are in cycle- ; the values in parenthesis are standard deviation.










significant changes often occur during the first two weeks. After that initial period, the

values began to fluctuate. Table 10 shows the summary of Tukey's grouping for the

effect of treatment on the elastic modulus and rate of recovery.


Table 10. Tukey's grouping of the surface treatment on dynamic tests
Material Modulus of Elasticity Rate of recovery
Coe-Comfort C P M J PCJ M
Coe-Soft M P J C C P J M
Flexacryl-Soft M J P C J C P M
Lynal M J P C P M J C
Tempo P C J M C P J M

Note: C=Control; J=Jet Seal; M=Mono-poly; P=Pressure/heat.
The groups are arranged in descending order from left to right.
The underlines group treatments that are not statistically different at a=0.05.


Release of Plasticizer in the Immersion Solution by UV/VIS Spectrophotometer


Tables 11 and 12 show the mean plasticizer release based on the high and low

wavelength, respectively. Ideally, the calculated amount of release from the liners

should be the same using either wavelength. That, however, is not the case when we

compare the two tables. The possible explanation is that each wavelength represents

materials (i.e., plasticizer) of different chemical nature. In addition, these materials do

not exhibit the same molar extinction coefficient. Therefore, the use of UV absorption as

a mean of estimating the absolute quantity of plasticizer leaching should be limited to

illustrate the effect of various processing methods on the release of plasticizer. For

example, the quantity of release at lower wavelength are higher with Mono-poly and Jet

Seal; this is not surprising since that range of wavelength, 221 to 232 nm, is associated

with MMA and both coatings consist of significant amount of MMA. The information

collected here will not be used to quantify the actual amount of leachants but used to










compare with those collected from the actual weight loss of the specimen. The results of

Two-way Analysis of Variance show that both treatment and storage time have

statistically


Table 11. Estimated leachant loss by UV absorbance at higher wavelength


Material Time, day Control Pressure/Heat Mono-poly Jet Seal
Coe-Comfort 0 0.0 0.0 0.1 (0.0) 0.0 0.0 0.0 0.0
Coe-Comfort 2 5.0 (0.4) 6.3 (0.2) 5.3 (0.7) 4.0 (0.4)
Coe-Comfort 7 10.3 (0.5) 11.9 (0.3) 9.3 (1.2) 4.2 (0.4)
Coe-Comfort 14 15.5 (0.9) 15.3 (0.7) 13.8 (1.6) 10.4 (0.6)
Coe-Comfort 28 22.8 (1.9) 20.9 (0.9) 21.0 (2.6) 15.4 (0.7)
Coe-Comfort 42 29.7 (3.1) 29.9 (1.1) 27.6 (3.6) 24.1 (1.3)
Coe-Comfort 63 38.8 (4.8) 40.6 (2.1) 36.7 (4.7) 33.3 (1.5)
Coe-Comfort 84 50.2 (5.4) 54.2 (3.0) 44.5 (5.9) 41.0 (1.6)
Coe-Soft 0 0.0 0.0 0.2 (0.0) 0.0 0.0 0.0 0.0
Coe-Soft 2 0.3 (0.0) 0.5 (0.0) 0.2 (0.0) 0.2 (0.0)
Coe-Soft 7 0.5 (0.0) 0.7 (0.0) 0.4 (0.0) 0.4 (0.0)
Coe-Soft 14 0.8 (0.0) 0.9 (0.0) 0.6 (0.0) 0.7 (0.0)
Coe-Soft 28 1.1 (0.1) 1.2 (0.0) 1.0 (0.1) 1.0 (0.0)
Coe-Soft 42 1.4 (0.1) 1.6 (0.1) 1.3 (0.2) 1.5 (0.1)
Coe-Soft 63 2.1 (0.5) 2.0 (0.1) 1.9 (0.2) 2.0 (0.1)
Coe-Soft 84 3.1 (0.8) 2.5 (0.2) 2.4 (0.2) 2.5 (0.1)
Flexacryl-Soft 0 0.0 0.0 1.5 (0.1) 0.0 0.0 0.0 0.0
Flexacryl-Soft 2 4.7 (0.3) 4.3 (0.2) 0.8 (0.2) 1.4 (0.1)
Flexacryl-Soft 7 5.8 (0.4) 6.9 (0.4) 1.2 (0.3) 2.8 (0.2)
Flexacryl-Soft 14 8.0 (0.5) 8.0 (0.5) 1.7 (0.6) 4.4 (0.2)
Flexacryl-Soft 28 10.4 (0.7) 9.9 (0.7) 2.2 (0.6) 6.4 (0.3)
Flexacryl-Soft 42 12.0 (0.8) 11.6 (0.7) 2.8 (0.7) 8.2 (0.4)
Flexacryl-Soft 63 13.9 (0.9) 13.1 (0.8) 3.6 (0.8) 10.4 (0.5)
Flexacryl-Soft 84 15.2 (1.0) 14.4 (0.9) 4.3 (0.9) 12.4 (0.6)
Lynal 0 0.0 0.0 0.1 (0.0) 0.0 0.0 0.0 0.0
Lynal 2 0.2 (0.0) 0.2 (0.0) 0.2 (0.0) 0.1 (0.1)
Lynal 7 0.3 (0.0) 0.3 (0.0) 0.3 (0.0) 0.3 (0.1)
Lynal 14 0.4 (0.0) 0.4 (0.0) 0.4 (0.0) 0.4 (0.1)
Lynal 28 0.5 (0.0) 0.6 (0.0) 0.6 (0.0) 0.5 (0.1)
Lynal 42 0.7 (0.0) 0.8 (0.1) 0.7 (0.0) 0.7 (0.1)
Lynal 63 1.0 (0.0) 1.0 (0.1) 0.9 (0.0) 0.8 (0.1)
Lynal 84 1.3 (0.1) 1.4 (0.2) 1.1 (0.0) 1.0 (0.1)
Tempo 0 0.0 0.0 0.1 (0.0) 0.0 0.0 0.0 0.0
Tempo 2 0.2 (0.0) 0.4 (0.0) 2.2 (0.1) 8.3 (1.4)
Tempo 7 0.4 (0.0) 0.6 (0.0) 3.5 (0.1) 13.2 (1.8)
Tempo 14 0.6 (0.0) 0.7 (0.0) 4.8 (0.3) 15.9 (3.1)
Tempo 28 0.8 (0.1) 0.9 (0.0) 6.9 (0.5) 17.8 (3.5)
Tempo 42 1.1 (0.1) 1.2 (0.1) 8.5 (0.6) 19.4 (3.7)
Tempo 63 1.5 (0.1) 1.6 (0.1) 10.4 (0.6) 20.6 (3.7)
Tempo 84 1.8 (0.1) 1.8 (0.1) 12.2 (0.7) 21.5 (3.8)
Note: The values are in mg/g; the values in parenthesis are standard deviation.












Table 12. Estimated leachant loss by UV absorbance at lower wavelength

Material Time, day Control Pressure/Heat Mono-poly Jet Seal
Coe-Comfort 0 0.0 (0.0) 0.1 (0.0) 0.0 (0.0) 0.0 (0.0)
Coe-Comfort 2 0.2 (0.0) 0.3 (0.0) 0.9 (0.1) 0.8 (0.1)
Coe-Comfort 7 0.3 (0.0) 0.5 (0.0) 1.3 (0.2) 1.1 (0.1)
Coe-Comfort 14 0.5 (0.0) 0.6 (0.0) 1.8 (0.3) 1.7 (0.1)
Coe-Comfort 28 0.7 (0.0) 0.7 (0.0) 2.5 (0.4) 2.1 (0.2)
Coe-Comfort 42 0.9 (0.1) 0.9 (0.0) 3.1 (0.4) 2.7 (0.2)
Coe-Comfort 63 1.3 (0.2) 1.3 (0.0) 3.9 (0.4) 3.2 (0.3)
Coe-Comfort 84 1.6 (0.3) 1.8 (0.1) 3.9 (0.4) 3.8 (0.3)
Coe-Soft 0 0.0 (0.0) 0.1 (0.0) 0.0 (0.0) 0.0 (0.0)
Coe-Soft 2 0.2 (0.0) 0.4 (0.0) 0.6 (0.1) 0.7 (0.0)
Coe-Soft 7 0.4 (0.0) 0.5 (0.0) 0.8 (0.1) 1.3 (0.1)
Coe-Soft 14 0.6 (0.0) 0.7 (0.0) 1.1 (0.1) 1.7 (0.1)
Coe-Soft 28 0.8 (0.0) 0.9 (0.0) 1.7 (0.1) 2.2 (0.1)
Coe-Soft 42 1.0 (0.0) 1.1 (0.0) 2.1 (0.2) 2.7 (0.1)
Coe-Soft 63 1.4 (0.3) 1.4 (0.1) 2.7 (0.2) 3.2 (0.0)
Coe-Soft 84 2.0 (0.4) 1.8 (0.1) 3.3 (0.2) 3.6 (0.1)
Flexacryl-Soft 0 0.0 (0.0) 1.1 (0.0) 0.0 (0.0) 0.0 (0.0)
Flexacryl-Soft 2 3.1 (0.2) 3.0 (0.1) 1.9 (0.3) 10.8 (1.7)
Flexacryl-Soft 7 3.9 (0.3) 4.8 (0.3) 2.6 (0.3) 16.6 (2.0)
Flexacryl-Soft 14 5.5 (0.3) 5.6 (0.4) 3.2 (0.4) 21.6 (2.2)
Flexacryl-Soft 28 7.2 (0.5) 6.7 (0.5) 3.9 (0.5) 25.5 (2.1)
Flexacryl-Soft 42 8.2 (0.6) 7.8 (0.6) 4.6 (0.6) 28.9 (2.4)
Flexacryl-Soft 63 9.4 (0.6) 8.7 (0.7) 5.4 (0.6) 32.3 (2.7)
Flexacryl-Soft 84 10.2 (0.7) 9.4 (0.7) 5.5 (0.6) 35.2 (2.9)
Lynal 0 0.0 (0.0) 0.1 (0.0) 0.0 (0.0) 0.0 (0.0)
Lynal 2 0.1 (0.0) 0.1 (0.0) 2.7 (0.5) 2.4 (0.3)
Lynal 7 0.2 (0.0) 0.2 (0.0) 3.8 (0.6) 6.2 (1.1)
Lynal 14 0.2 (0.0) 0.2 (0.0) 4.6 (0.7) 7.8 (1.1)
Lynal 28 0.3 (0.0) 0.3 (0.0) 5.6 (0.9) 9.2 (1.2)
Lynal 42 0.5 (0.0) 0.5 (0.1) 6.4 (0.9) 10.5 (1.2)
Lynal 63 0.7 (0.0) 1.3 (0.3) 7.2 (0.9) 11.6 (1.3)
Lynal 84 1.0 (0.1) 1.6 (0.4) 7.2 (0.9) 12.5 (1.4)
Tempo 0 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) 0.0 (0.0)
Tempo 2 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) 5.8 (0.6)
Tempo 7 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) 9.7 (1.0)
Tempo 14 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) 11.8 (2.2)
Tempo 28 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) 13.3 (2.4)
Tempo 42 0.0 (0.0) 0.0 (0.0) 0.7 (0.1) 14.7 (2.6)
Tempo 63 0.3 (0.0) 0.3 (0.1) 1.4 (0.1) 15.7 (2.7)
Tempo 84 0.5 (0.0) 0.5 (0.1) 2.1 (0.1) 16.3 (2.7)
Note: The values are in mg/g; the values in parenthesis are standard deviation.










significant influence on the quantity of leaching. Table 13 shows the summary of

Tukey's grouping of the effect of treatment on the leaching; it confirms the observation

that specimens with coatings leach more.



Table 13. Tukey's grouping of the effect of treatment on the leaching by UV
Material Higher wavelength Lower wavelength

Coe-Comfort P C M J M JPC
Coe-Soft P C J M J MPC
Flexacryl-Soft C P J M J C P M
Lynal P C M J J MP C
Tempo J MP C JM C P

Note: C=Control; J=Jet Seal; M=Mono-poly; P=Pressure/heat. The groups are arranged in
descending order from left to right.
The underlines group treatments that are not statistically different at o=0.05.

There was no detectable leachants by UV spectrophotometry in the containers

with the bare Lucite substrates.


Weight Changes of the Specimen


Table 14 shows the mean weight loss in distilled water along with respective

standard deviation for each treatment at each weighing. Figures 6 and 7 show the weight

loss with time for Lynal and Tempo, respectively. They represent two extremes of

weight loss. Each data point represents the mean of six replications. The effect of the

coating on the loss does appear consistent through out all five materials. It is also noted

that there is more loss when Jet Seal is used, and less weight loss with mono-poly.












Table 14. Weight change of soft-liners in water with time as influenced by treatment


Materials Time, day Control Pressure/Heat Mono-poly Jet Seal

Coe-Comfort 2 -11.88 (0.60) -12.58 (0.65) -9.86 (2.16) -9.56 (2.13)
Coe-Comfort 7 -16.33 (0.62) -16.93 (1.09) -15.71 (2.64) -21.09 (3.09)
Coe-Comfort 14 -19.54 (0.69) -19.65 (1.05) -18.27 (3.79) -28.33 (3.38)
Coe-Comfort 28 -23.35 (0.72) -23.69 (0.59) -23.43 (4.94) -31.53 (3.55)
Coe-Comfort 42 -23.92 (0.69) -23.24 (1.21) -24.25 (5.63) -38.12 (3.13)
Coe-Comfort 63 -23.50 (0.67) -24.63 (0.65) -29.27 (5.72) -38.19 (3.19)
Coe-Comfort 84 -22.82 (0.79) -21.05 (1.66) -29.99 (5.64) -38.03 (4.00)
Coe-Soft 2 -18.73 (0.98) -18.30 (0.51) -3.71 (0.51) -5.94 (2.26)
Coe-Soft 7 -26.49 (1.00) -27.61 (0.56) -10.49 (2.77) -28.50 (3.09)
Coe-Soft 14 -33.96 (0.90) -30.68 (0.82) -7.94 (4.27) -40.07 (2.15)
Coe-Soft 28 -41.11 (1.13) -38.65 (0.68) -16.97 (1.34) -38.85 (3.04)
Coe-Soft 42 -43.35 (1.15) -40.26 (1.26) -17.69 (0.94) -50.44 (1.62)
Coe-Soft 63 -44.13 (1.05) -43.17 (1.38) -19.03 (0.94) -50.91 (1.67)
Coe-Soft 84 -43.92 (1.65) -41.81 (1.19) -19.31 (0.92) -50.26 (1.82)
Flexacryl-Soft 2 -1.50 (0.89) -3.12 (0.79) 2.18 (0.87) -6.70 (1.36)
Flexacryl-Soft 7 -2.03 (0.61) -2.37 (0.66) 2.82 (1.12) -10.65 (1.36)
Flexacryl-Soft 14 -1.50 (0.79) -2.29 (0.83) 5.19 (1.51) -12.76 (1.31)
Flexacryl-Soft 28 -2.17 (0.93) -2.02 (1.27) 4.55 (1.47) -12.53 (0.81)
Flexacryl-Soft 42 -2.32 (0.95) -2.53 (0.56) 7.58 (1.51) -17.94 (1.37)
Flexacryl-Soft 63 -2.79 (0.96) -3.91 (0.89) 6.06 (1.56) -19.04 (1.45)
Flexacryl-Soft 84 -3.27 (1.38) -4.35 (1.66) 7.00 (1.70) -19.87 (1.72)
Lynal 2 -0.33 (1.75) -1.58 (0.71) -2.01 (1.21) -0.69 (0.73)
Lynal 7 -5.17 (0.76) -3.46 (0.40) -4.12 (1.40) -5.67 (0.49)
Lynal 14 -5.39 (2.67) -4.88 (0.49) -1.68 (1.61) -9.07 (0.55)
Lynal 28 -8.72 (1.01) -7.72 (0.55) -3.08 (2.07) -8.53 (0.84)
Lynal 42 -9.87 (0.93) -8.26 (0.80) -1.24 (2.41) -14.69 (0.62)
Lynal 63 -9.62 (1.20) -10.53 (0.67) -3.30 (2.34) -14.68 (0.81)
Lynal 84 -9.80 (1.18) -9.03 (1.12) -2.63 (2.66) -15.04 (0.98)
Tempo 2 -42.86 (0.77) -42.40 (0.76) -10.93 (1.67) -35.37 (0.82)
Tempo 7 -56.22 (1.23) -64.08 (1.41) -25.35 (3.94) -66.77 (1.10)
Tempo 14 -66.74 (1.32) -69.02 (1.22) -29.68 (5.34) -80.98 (1.50)
Tempo 28 -72.46 (1.84) -77.12 (0.89) -40.97 (5.12) -82.87 (1.45)
Tempo 42 -72.72 (1.97) -77.75 (1.23) -41.84 (5.56) -89.21 (1.64)
Tempo 63 -71.98 (1.54) -78.65 (1.21) -47.86 (5.64) -88.60 (1.36)
Tempo 84 -73.73 (1.85) -78.02 (1.66) -48.51 (5.16) -88.46 (1.69)

Note: The values are in mg/g; the values in parentheses are standard deviation.













40-
-- Control ----o Mono-poly

Lynal -----o Jet-Seal --- Pressure/Heat
20-




0 ----- -- - --

E -------------0 ---------0
-20-

C,

5 -40-


-60-



-80-



-100 -
0 10 20 30 40 50 60 70 80 90 100

Time, day

Figure 6. Weight loss with time for Lynal




40-
-- Control ----o Mono-poly

Tempo --o Jet-Seal --* Pressure/Heat
20-



0-



.c -20-





S ---.-------o0






---.-------------0 --------------- E)





Time, day

Figure 7. Weight loss with time for Tempo
Figure 7. Weight loss with time for Tempo










Although weight loss in air has no clinical significance to the performance of the

material, the results represent the loss of alcohol from the mixture and can be used for

comparison purposes. Table 15 shows the mean weight loss of control and mono-poly

coated specimens up to 30 days in air. Figures 8 and 9 illustrate the weight loss with

time for the control and mono-poly coated specimens, respectively. It is clear that the

weight loss in air has reached a plateau while the mono-poly coated ones continued to

lose weight but at a very slow pace.


Table 15. Weight loss in air

Material Time, day Control Mono-poly

Coe-Comfort 0 0.00 (0.00) 0.00 (0.0)
Coe-Comfort 1 -11.07 (1.36) -17.47 (2.36)
Coe-Comfort 7 -28.27 (1.93) -39.97 (3.35)
Coe-Comfort 12 -30.93 (2.28) -45.40 (3.95)
Coe-Comfort 16 -32.03 (2.28) -49.20 (3.95)
Coe-Comfort 30 -31.63 (2.73) -56.47 (4.72)
Coe-Soft 0 0.00 (0.0) 0.00 (0.0)
Coe-Soft 1 -17.93 (2.02) -13.60 (3.50)
Coe-Soft 7 -47.83 (1.83) -32.50 (3.18)
Coe-Soft 12 -52.23 (1.30) -36.97 (2.25)
Coe-Soft 16 -54.40 (1.34) -41.03 (2.32)
Coe-Soft 30 -55.90 (1.39) -49.70 (2.40)
Flexacryl-Soft 0 0.00 (0.0) 0.00 (0.0)
Flexacryl-Soft 1 -8.07 (0.43) -2.93 (0.74)
Flexacryl-Soft 7 -11.60 (0.57) -4.73 (0.99)
Flexacryl-Soft 12 -11.97 (0.46) -5.40 (0.79)
Flexacryl-Soft 16 -12.57 (0.50) -5.80 (0.87)
Flexacryl-Soft 30 -8.77 (0.62) -5.43 (1.07)
Lynal 0 0.00 (0.0) 0.00 (0.0)
Lynal 1 -6.00 (1.46) -18.63 (2.53)
Lynal 7 -15.40 (2.14) -30.60 (3.70)
Lynal 12 -17.63 (2.34) -33.67 (4.06)
Lynal 16 -19.10 (2.43) -35.73 (4.21)
Lynal 30 -21.50 (2.58) -39.97 (4.47)
Tempo 0 0.00 (0.0) 0.00 (0.0)
Tempo 1 -33.87 (0.47) -14.23 (0.81)
Tempo 7 -82.10 (1.92) -62.67 (3.32)
Tempo 12 -89.67 (1.81) -71.60 (3.13)
Tempo 16 -91.83 (1.66) -77.03 (2.87)
Tempo 30 -92.37 (1.15) -83.50 (2.00)


Note: The values are in mg/g; the values in parenthesis are standard deviation.



































10 15 20 25 30 35 40
Time, day


Figure 8. Weight loss with time for the control specimens


0 5 10 15 20 25 30 35 40
Time, day

Weight loss with time for the mono-poly coated specimens


Figure 9.










The results of Two-way Analysis of Variance show that both treatment and

storage time have a statistically significant influence on the weight loss in water and in

air. Table 16 shows the summary of Tukey's grouping of the treatment.



Table 16. Tukey's grouping of the effect of surface treatment on the weight change
Material In water In air
Coe-Comfort J MP C MC
Coe-Soft J C P M CM
Flexacryl-Soft J P C M C M
Lynal J C P M MC
Tempo JPCM CM
Note: C=Control; J=Jet Seal; M=Mono-poly; P=Pressure/heat. The groups are arranged from
highest loss to highest gain
The underline groups treatments that are not statistically different at a=0.05.


pH of the Solution


Each time the storage solution was replaced, part of the solution was tested for

the pH. The pH values of the distilled control water, which did not contain any

specimen, were consistently at 5.50.1 through out the entire experiment. Table 17

shows the mean pH values along with respective standard deviation at each water change

for each treatment. The pH values for pressure and heat treated specimens were taken

from the solution used for processing. The results of Two-way Analysis of Variance

show that both storage time and treatment have exerted statistical significant influence on

the pH values. The pH values decreased with time from as high as 6.5 and reached a

plateau in the neighborhood of 4.0.












Table 17. pH values of storage solutions at the time of replacement


Materials Time, day Control Pressure/heat Mono-poly Jet Seal


Coe-Comfort 0 5.85 (0.08)
Coe-Comfort 2 5.58 (0.22) 5.24 (0.19) 5.56 (0.38) 5.27 (0.05)
Coe-Comfort 7 5.18 (0.06) 5.48 (0.19) 5.09 (0.07) 4.14 (0.02)
Coe-Comfort 14 5.70 (0.48) 5.74 (0.14) 4.80 (0.07) 4.30 (0.04)
Coe-Comfort 28 4.98 (0.24) 5.47 (0.12) 4.19 (0.06) 4.12 (0.04)
Coe-Comfort 42 4.72 (0.31) 4.68 (0.10) 4.16 (0.05) 4.12 (0.05)
Coe-Comfort 63 4.21 (0.13) 4.21 (0.05) 3.92 (0.03) 4.10 (0.04)
Coe-Comfort 84 4.03 (0.06) 4.13 (0.09) 4.07 (0.09) 4.05 (0.16)
Coe-Soft 0 6.18 (0.08)
Coe-Soft 2 6.16 (0.07) 5.89 (0.04) 5.32 (0.09) 5.37 (0.09)
Coe-Soft 7 5.93 (0.12) 5.80 (0.06) 5.54 (0.24) 4.93 (0.05)
Coe-Soft 14 5.87 (0.11) 5.71 (0.06) 5.22 (0.10) 4.41 (0.02)
Coe-Soft 28 5.24 (0.15) 5.29 (0.14) 4.21 (0.14) 4.14 (0.02)
Coe-Soft 42 4.96 (0.19) 4.82 (0.03) 4.19 (0.06) 4.01 (0.03)
Coe-Soft 63 4.24 (0.29) 4.32 (0.07) 3.93 (0.02) 3.96 (0.03)
Coe-Soft 84 4.00 (0.18) 4.27 (0.11) 4.01 (0.04) 4.11 (0.02)
Flexacryl-Soft 0 4.11 (0.02)
Flexacryl-Soft 2 3.80 (0.02) 3.88 (0.01) 5.27 (0.79) 4.05 (0.02)
Flexacryl-Soft 7 3.95 (0.01) 3.95 (0.05) 5.06 (0.14) 4.04 (0.02)
Flexacryl-Soft 14 3.98 (0.03) 4.41 (0.59) 4.70 (0.31) 4.00 (0.03)
Flexacryl-Soft 28 3.94 (0.04) 4.07 (0.11) 4.58 (0.08) 3.90 (0.03)
Flexacryl-Soft 42 4.13 (0.06) 4.09 (0.05) 4.41 (0.06) 3.92 (0.02)
Flexacryl-Soft 63 4.03 (0.04) 4.17 (0.08) 4.25 (0.04) 3.90 (0.02)
Flexacryl-Soft 84 4.16 (0.07) 4.19 (0.10) 4.24 (0.05) 3.94 (0.02)
Lynal 0 6.45 (0.11)
Lynal 2 6.34 (0.08) 6.00 (0.20) 5.28 (0.18) 4.40 (0.02)
Lynal 7 5.60 (0.11) 5.31 (0.09) 4.84 (0.14) 4.66 (0.19)
Lynal 14 5.36 (0.15) 5.66 (0.29) 4.47 (0.06) 4.11 (0.03)
Lynal 28 4.86 (0.05) 4.90 (0.05) 4.19 (0.04) 4.05 (0.01)
Lynal 42 4.75 (0.08) 4.84 (0.22) 4.20 (0.04) 4.03 (0.04)
Lynal 63 4.55 (0.09) 4.43 (0.09) 4.05 (0.04) 3.98 (0.03)
Lynal 84 4.40 (0.11) 4.45 (0.08) 4.10 (0.03) 3.96 (0.04)
Tempo 0 5.30 (0.10)
Tempo 2 5.26 (0.25) 4.94 (0.11) 4.24 (0.12) 4.69 (0.11)
Tempo 7 5.20 (0.15) 5.26 (0.45) 4.20 (0.05) 4.61 (0.04)
Tempo 14 5.04 (0.13) 5.67 (0.25) 4.20 (0.29) 4.32 (0.02)
Tempo 28 4.75 (0.14) 5.07 (0.21) 3.93 (0.04) 4.22 (0.07)
Tempo 42 4.50 (0.08) 4.63 (0.12) 3.96 (0.06) 4.13 (0.05)
Tempo 63 4.40 (0.04) 4.45 (0.11) 3.84 (0.03) 4.18 (0.06)
Tempo 84 4.55 (0.07) 4.67 (0.15) 3.91 (0.03) 4.18 (0.06)

Note: The values are means of six specimens; numbers in the parenthesis are the standard
deviation. pH values of pressure/heat specimens at time=0 day were taken from the
water in processing chamber.











Table 18. Tukey's grouping of the effect of surface treatment on the pH of storage
solutions.

Material Tukey's Grouping
Coe-Comfort P C M J
Coe-Soft P CM J
Flexacryl-Soft MP C J
Lynal P C M J
Tempo PA J M
Note: C=Control; J=Jet Seal; M=Mono-poly; P=Pressure/heat. The groups are
arranged in descending order from left to right.
The underlines group treatments that are not statistically different at a=0.05.

Two-way Analysis of Variance analysis of the pH of the water in the six Snap-

Seal containers with the Lucite-ES squares and the control water indicated that there is

no difference between them at aX=0.05.


Statistical Correlation between Parameters


To identify if there is any significant correlations between any two parameters

measured in this study, we ran a series of linear regression between several pairs of

parameter. Only the coefficients of determinations, r2, will be shown. Table 19 shows

the r2 values between the leachants measured by UV at low and high wavelength. It

shows relative high correlations. Table 20 shows the results between weight loss by

balance and leachant by UV at high wavelength.


Table 19. Coefficient of determination (r2)
UV at high and low wavelength


of linear regression between leaching by


Material Control Jet Seal Mono-poly Pressure/heat
Coe-Comfort 0.9796 0.9095 0.9281 0.9928
Coe-Soft 0.9960 0.9417 0.9780 0.9983
Flexacryl-Soft 0.9987 0.8912 0.8926 0.9970
Lynal 0.9814 0.9231 0.7826 0.8754
Tempo 0.6683 0.9945 0.7303 0.6429










Table 20. Coefficient of determination (r2) of linear regression between leaching at
high wavelength and weight loss by balance

Control Jet Seal Mono-poly Pressure/heat
Coe-Comfort 0.5759 0.6690 0.8054 0.4825
Coe-Soft 0.5351 0.7186 0.7198 0.7026
Flexacryl-Soft 0.5749 0.8479 0.4846 0.4225
Lynal 0.6634 0.8303 0.0364 0.7592
Tempo 0.5541 0.8439 0.8589 0.5929


Tables 21 and 22 show the linear regression of weight loss by balance against

modulus of elasticity and rate of recovery, respectively.


Table 21. Coefficient of determination of Linear regression between weight change
in water vs. Modulus of Elasticity
Control Jet Seal Mono-poly Pressure/heat
Coe-Comfort 0.8091 0.4814 0.1519 0.3661
Coe-Soft 0.6911 0.4617 0.2755 0.72930
Flexacryl-Soft 0.2341 0.3751 0.0171 0.0220
Lynal 0.4622 0.0787 0.0143 0.0000
Tempo 0.6377 0.6700 0.0119 0.5755


Table 22. Coefficient of determination of linear regression between weight loss in
water and rate of recovery
Control Jet Seal Mono-poly Pressure/heat
Coe-Comfort 0.3544 0.6178 0.5378 0.4833
Coe-Soft 0.4916 0.8489 0.5045 0.7240
Flexacryl-Soft 0.0108 0.1738 0.1505 0.0000
Lynal 0.4540 0.4606 0.0347 0.0000
Tempo 0.7444 0.9625 0.6663 0.9295


Tables 23 and 24 show the linear regression results of the leachant by UV at high

wavelength against modulus of elasticity and rate of recovery, respectively.


Table 23. Coefficient of determination of linear regression between modulus of
elasticity and leachant by UV absorbance at high wavelength
Control Jet Seal Mono-poly Pressure/heat
Coe-Comfort 0.5645 0.3566 0.1007 0.1771
Coe-Soft 0.7330 0.4253 0.0859 0.5931
Flexacryl-Soft 0.2698 0.3025 0.0177 0.3169
Lynal 0.3746 0.0526 0.0000 0.0000
Tempo 0.4836 0.6612 0.0000 0.3060










Table 24. Coefficient of determination of linear regression between rate of recovery
and leachant by UV absorbance at high wavelength
Control Jet Seal Mono-poly Pressure/heat
Coe-Comfort 0.3466 0.5993 0.5957 0.1699
Coe-Soft 0.2956 0.6415 0.7870 0.4665
Flexacryl-Soft 0.0047 0.2904 0.0000 0.0000
Lynal 0.3309 0.4656 0.1189 0.0000
Tempo 0.3739 0.8535 0.6965 0.6779


Table 25 shows the linear regression results between modulus of elasticity and

rate of recovery.


Table 25. Coefficient of determination of linear regression between modulus of
elasticity and rate of recovery
Control Jet Seal Mono-poly Pressure/heat
Coe-Comfort 0.2499 0.2669 0.4984 0.1421
Coe-Soft 0.3549 0.4183 0.0000 0.5171
Flexacryl-Soft 0.0502 0.1067 0.0224 0.0000
Lynal 0.4066 0.2639 0.0000 0.0778
Tempo 0.4395 0.6289 0.0000 0.2851



Macro Photography and Micro Photography


Both visual and optical microscope observations show that there are no detectable

surface changes during storage for the control and pressure and heat treated specimens.

In contrast, there were detectable surface changes for the mono-poly and Jet Seal coated

specimens. At the end of the 2nd week, bubbling on the surface was observed on some of

the mono-poly coated specimens, the most notable ones were with Lynal and followed

by Coe-Soft and Tempo (Figure 10a and 10b). They were not obvious with Flexacryl-

Soft and Coe-Comfort. Some specimens with Jet Seal coatings wrinkled as soon as 24

hours after water immersion; eventually all Jet Seal coated specimens exhibit various

degree of wrinkling on the surface. Multiple superficial crack lines were evident on all

Jet Seal coated specimens when observed under a light microscope. The frequency of









cracks varies from material to material. Figures 11 shows crack appearance of Lynal,

Coe-Comfort, Coe-Soft, Tempo, and Flexacryl, respectively.

Figure 12 shows cross sections of selected coated specimens. The examination of

the coating/soft liner interfaces in monopoly coated specimen showed that the blisters

occurred at the interface between the coating and the bulk of the soft liner material. It is

likely the result of water osmosis through the coating.

The thickness of either coating was measured using a stage microscale to be

around 100 microns. Figure 12c shows the microscopic section of Coe-Soft with a crack

visible in the Jet Seal coating but not extending into the tissue conditioner material.

Contrary to our visual impression that the thickness of Jet Seal would be consistently

thinner, it is within the same range as mono-poly. The observed homogenous thickness

of the coating would support the use of dip coating when an even thickness is desired.

Because of their similar thickness and even coating, these two factors could be

eliminated as a cause for the different surface characteristics between the two coating

materials. There is no apparent difference in the specimen appearance, such as

population of voids.













a) Lynal specimen coated with mono-poly b) Tempo specimen coated with mono-poly
Figure 10. Specimen coated with mono-poly
























a) Lynal coated with Jet Seal at 6.6X


b) Coe-Comfort coated with Jet Seal at 3.3X


d) Tempo coated with Jet Seal at 3.3X


c) Coe-S coated with Jet Seal at 3.3X


e) Flexacryl-Soft coated with Jet Seal at 3.3X


Figure 11. Microscopic view of specimens coated with Jet Seal























b) Mono-poly coating on Tempo


c) Jet Seal coating on Coe-Soft d) Mono-poly coating on Coe-Soft


Figure 12. Microscopic view of sections of Tempo and Coe-Soft samples


a) Jet Seal coating on Tempo















CHAPTER 5
DISCUSSION


The hypothesis of this study is that coating with a surface sealer or curing in a

heat and pressurized environment can maintain the physical and mechanical properties of

the temporary soft liners at the same level when they are processed. Several papers20-24'28

expect these additional steps to extend service life of these temporary soft reline

materials in the clinical setting. The rationale is that surface treatment can prevent or

retard leaching of plasticizer, which is incorporated in the material to render softness, and

thus maintain resilience of the respective soft liners over a longer period of time. To test

the hypothesis, we investigated three major categories of physical parameters: surface

appearance, leaching by UV and weight loss, and dynamic mechanical properties.


Effect of Surface Treatment on the Appearance of the Specimen

During the course of the study, we have not observed any detectable changes for

the control and pressure/heat specimens, in spite of significant changes in the

measurements of other parameters. It is believed that water will not normally alter

surface texture of these temporary soft liners in static conditions. Specimens with

coatings have exhibited several unique features; namely, ripple and crack on Jet Seal

coated specimens and blistering on mono-poly coated specimens.










Jet Seal Coating


As noted in the results, ripples on the surface of Jet Seal coated samples were

observed as early as 24 hours after immersion, while surface cracks were not noticed

until the examination was done with an optical microscope. Presence of rippling

indicated some sort of swelling has occurred on the surface, possibly due to water

absorption. The opaque whitish color exhibited by the coating instead of the initial

transparency observed after drying also mitigated towards moisture absorption. We have

observed in a separate study where Jet Seal was painted on glass slide covers that cracks

developed as the coating dried in a few hours. The coating was fragile during our

attempt to remove the film; a sign of brittle coating. Therefore, it is conceivable that the

cracks could have occurred during the drying period of the Jet Seal coating. Mono-poly,

on the other hand, did not crack and even exhibited slight ductility. Dynamic testing of

the specimen could also have contributed to the crack formation. This is evidenced by

the fact that specimens subjected to dynamic testing exhibited more cracks than

specimens reserved exclusively for Shore A hardness tests. This kind of surface defect

associated with Jet Seal could not be found in the specimens with the three other

treatments. Further study needs to be conducted to shed light on the exact mechanism

for water absorption and crack development in the Jet Seal coating.


Mono-poly Coating


Mono-poly coated specimens were observed to blister after 2 weeks of water

immersion. In contrast, none of the specimen coated with Jet Seal developed blisters.

This is because the superficial cracks would allow free fluid exchange between the









internal and external compartments. In other words, the blisters, although unexpected,

are an indication of the integrity of the coating. It was also observed through

microscopic observation of a section though one of the blisters indicating that the blister

formed at the interface between the coating and the material and not within the depth of

the temporary soft denture liner. Systematic examination of each blister was not done

because it is not within the aim of this study.

At the conclusion of the experiment, we were able to extract some liquid from

inside of the blister with an 18-gauge syringe. The liquid is hydrophilic with consistency

like water and has strong smell of methyl methacrylate. Dominguez et al. 25 concluded

from their study that mono-poly coating allowed evaporation of alcohol but acted as a

barrier to water and plasticizer. Should that be the case, because there is no water in

temporary soft liners composition and the surrounding water could not penetrate through

the coating, the liquid extracted from the blister should be hydrophobic since it could

only contain plasticizer. Apparently, mono-poly in this study did not prevent water

diffusion but allowed water osmosis through the coating; the blister is the result of water

build-up. Presence of methyl methacrylate is from the mono-poly coating itself.

Although of interest, it is beyond the scope and means of this project to determine the

exact nature of the liquid accumulating in the blister. Further analysis of this liquid by

High Performance Gas Chromatography should confirm these findings.


Accelerated Drying Using Heat


To minimize patient exposure to free monomer and chair time, accelerated drying

of the mono-poly coating using a 50-60W incandescent light two inches from the coating

for 4 to 5 minutes was recommended by Gardner and Parr 21. Gronet et al.26 reported no









nefarious side effect when this technique is used. We have observed that exposing the

coated specimen as described has disfigured the specimens, especially to Coe-Comfort,

Coe-Soft and Tempo. The specimens appeared to have swelled and the sharp edges

rounded. Later, the specimen collapsed in the middle. It is hypothesized that the heat

not only accelerates the evaporation of the monomer in the coating but also acts on the

alcohol content of the specimen. Although the thickness of the coating may have

retarded the initial escape of the alcohol but vaporization of the alcohol within the

material may result in swelling, followed by collapse of the coating after the alcohol has

time to escape. In addition, the high temperature may bring the tissue conditioner close

to or beyond its glass phase transition temperature. That can result in softening of the

tissue conditioner, as evidenced by the rounding of the edges. Both phenomena defeat

the purpose of using tissue conditioner treatment to adapt a poorly fitting prosthesis to

the mucosa surface. This drying method was not used in this study and should be

avoided when the alcohol content of the temporary reline material is high and the glass

transition temperature is low.


Heat and Pressure Processing


Corwin and Saunders 20 recommended this technique for extending the useful life

of temporary soft liners based on their observation of diminished surface porosity and

internal voiding when processed with heat and pressure. The results of this study

indicated that there is no improvement in surface quality after putting in the extra time

for this procedure. Other parameters measured also indicate that there are limited

changes between control and pressure/heat specimens. For example, the weight loss

during immersion was almost identical for both control and pressure/heat specimens.









Processing temporary soft denture liners with pressure/heat needs further studies for

validation.

Plasticizer Leaching, Weight Loss, and pH of Storage Medium


Temporary soft liners possess softness by the presence of alcohol and plasticizer.

Both are reported to leach or evaporate with time. We selected two relative simple

techniques to quantify the loss of these components to the surrounding environment. We

used UV spectrophotometer to determine the leaching of plasticizer and weight loss of

individual specimens in water and in air.


UV Spectrophotometry


The first samples tested in this experiment were pressure-treated, and aliquots of

the liquid in which they were pressure treated were taken for UV spectrophotometry

analysis at time zero. Peaks to be used for relative comparison of concentration were

chosen from survey scans of samples from all the systems (Flexacryl-Soft, Coe-Soft,

Coe-Comfort, Lynal, and Tempo). The peaks chosen for measurement were 272 nm and

221 nm for Flexacryl-Soft, 303 nm and 236 nm for Coe-Soft, 305 nm and 232 nm for

Coe-Comfort, 280 nm and 225 nm for Lynal, and 223 nm for Tempo. The same

wavelengths were used for all samples respectively, although another peak at 206 nm

was detected and measured on some samples at a later date.

In an effort to construct calibration curves, the liquid components of the soft liner

materials were diluted to 100 ppm in water. None of the liquid components of the soft

liner materials were completely soluble in pure water; most simply formed beads of

liquid within the water. Therefore, it was not possible to use pure water as a medium to









obtain reference curves to quantify the release of material from the cured specimens. It

was proposed that the powder may act as a surfactant in combination with the liquid

component, therefore liquid and powder components were mixed together in water to try

to obtain absorbance calibration curves. The liquid did not dissolve completely even in

the presence of powder, so calibration could not be performed in this manner either.

Some plasticizers used in Coe-Soft and Coe-Comfort such as benzyl benzoate,

benzyl salicylate, and dibutyl phthalate were found by Jones et al. 12 to be soluble in ethyl

alcohol. Ethyl alcohol has a useful transparent range from the visible into the ultraviolet

range near 205 nm. The first liquid component tested, Coe-Soft, showed proportionality

between the absorbance at 306 nm and the concentration of the liquid component in ethyl

alcohol for concentrations from 100-300 ppm. The absorbance curves for the other

liquid components also showed proportionality between the absorbance and the

concentration of the liquid at the wavelengths chosen for measurements. A comparison

of curves taken from liquid components dissolved in pure ethanol to curves taken from

liquid components dissolved in mixtures of water and ethanol indicated that there is very

little loss in absorbance peak value with the addition of water up to 50% v/v. The

addition of water does reduce the absorbance of the ethyl alcohol itself, however, and

serves to lessen the tendency of the ethyl alcohol to mask the lower wavelength

absorbance of the liquid components.

Calibration curves were constructed from various concentrations of liquid

components in 50% v/v water/ethanol. The mass of 50 pl of liquid was measured by

using a micropipette and a digital scale, and averages of at least five readings were taken

using the same tip. Then, with the same tip used for measuring the mass, dilution was









made in a 100 ml volumetric flask by first adding 50 ml (by macropipette, 25 ml twice)

of ethyl alcohol, then adding 50 [l of the liquid component, and finally completing to the

100 ml mark with distilled water. This created a sample on the order of 1000 ppm

depending upon the measured mass of the liquid. This 1000 ppm sample was then

diluted to obtain other points on a calibration curve. All calibration points for each

specimen are derived from the same parent dilution, so the relative accuracy is high but

absolute accuracy is dependent upon the accuracy of the micropipette.

There was an odor evident in the water from those samples coated with Jet Seal,

and survey spectrum scans of these samples showed an additional peak at 206 nm. Since

Jet Seal contains a solution of polymethyl methacrylate (PMMA) in methyl methacrylate

monomer (MMA), a survey spectrum scan of MMA in water was made which showed a

comparable peak at 206 nm. Since the polymerization of MMA in Jet Seal is kept in

check with an inhibitor, we also examined the spectrum of a common inhibitor,

hydroquinone (HQ), in water. However, the spectrum of the Jet Seal coated samples

matched that of MMA monomer and not that of HQ. It was concluded that the large

peak at 206 nm that was superimposed upon the other soft liner spectra was from MMA

and a calibration curve for MMA was constructed in water. Because this conclusion was

reached a several weeks into the experiment, not all of the earlier Jet Seal coated samples

were measured at 206 nm. To further test the hypothesis of MMA leaching from Jet Seal

film coatings, release curves of plain Jet Seal and mono-poly films in water were

obtained. These were tested for 74 days and showed continuing release of MMA.

Having determined the relationship between the absorbance value and the

concentration of liquid components (ppm), the mass of released liquid components from









all samples was calculated. The assumption that only liquid components are able to

leave the soft liner material is used here. The sample volume was consistently 50 ml, so

this was also used in the calculation to determine the mass of material released with time.


Effect of Coating on the Plasticizer Leaching


According to Table 19, there is a high correlation between the plasticizer leaching

measured at low and high wavelength. It confirms the belief that the two peaks should

change proportionally. There is a difference in the effect of coating on the leaching at

high and low wavelength. Using data from high wavelength, we found that both coatings

reduced the leaching, except for Tempo. On the other hand, data from lower wavelength

show that both coating has enhanced leaching significantly, except for Flexacryl-Soft

with mono-poly. We know that MMA monomer has an UV peak around 206 nm, high

extinct coefficient and the bandwidth can extend to 250 nm and higher with 20 ppm of

MMA in solution. Therefore, the absorbance reading at wavelengths less than 250 nm

can be confounded by MMA. This explains why there is leaching enhancement at lower

wavelength. The abnormal behavior of Tempo at high wavelength, which was 223 nm,

happened for the same reason. Consequently the leaching data gathered at high

wavelength are more reliable. UV is not a suitable technique for Tempo. It is important

to point out that Flexacryl-Soft by design does not contain plasticizers comparable to

those in other materials tested; its results will be excluded from the discussion.


Effect of Coating on the Weight Loss by Balance


Table 16 shows that in contrast with the tendency of less weight loss in water for

mono-poly coated specimens, Jet-Seal coated specimens suffered greater weight loss







65

than the uncoated specimens. Although this finding was totally unexpected, the observed

wrinkles and cracks developed by the coating in Jet Seal coated specimens may have

been the cause of the greater weight loss in time compared to uncoated specimens. These

wrinkles and cracks could have resulted from the dimensional change of two sheets of

material bonded together, e.g. imbibition of water by the Jet Seal coating and solvent

evaporation from the tissue conditioner. This unbalanced area would induce tension in

the superficial layer of the underlying substrate. It is known that substances under

tension tend to release more leachants similar to hand wringing clothes after washing to

remove as much water as possible. A less likely explanation would be that the cracks

would have propagated into the substrate, therefore increasing the area available for

molecular exchange. Cross sectional microscopic observation (Figure 12c) has

eliminated this hypothesis. As greater weight loss of coated specimens vs. uncoated

specimens has never been mentioned in the published literature, the reason for increased

weight loss and therefore, accelerated leachants release by tissue conditioners when

covered by a specific coating could only be the subject of speculation.

Table 16 also shows that mono-poly consistently reduce the weight loss in water.

We concluded earlier that mono-poly coating slowed down the plasticizer leaching. It is

likely that it also slowed down the weight loss in water. By the same token, we should

expect the same situation for the weight loss in air. This, however, is not true with Coe-

Comfort and Lynal. When we compare Figures 8 and 9, we also find that coated

specimens continue to show weight loss after 30 days, while the control specimens have

reached plateau after 16 days. A possible explanation is that some monomer from the

coatings dissolved in the underlying temporary soft liner material instead of evaporating









into ambient air during the drying of the coating. It is also assumed that the temporary

soft liner material has a higher monomer solubility than water. The continued weight

loss would then be explained by the disappearance of monomer in the water, either by

evaporation or after each water renewal, allowing monomer dissolved in the temporary

soft liner to transfer to the surrounding water. In addition, the loss of monomer from

coatings constituted part of initial weight loss, while the dry coating delayed the loss of

alcohol from the bulk of the material. Both Coe-Comfort and Lynal contain lower

alcohol content than Tempo and Coe-soft (Table 1); both materials also have lower

weight loss in air (Table 15). Therefore, the increase in weight loss in Coe-Comfort and

Lynal is due to the drying of the coating. It is likely that when eventually the alcohol in

Tempo and Coe-Soft diffuses through the coating and evaporates, the coated specimen

will show a greater weight loss.

Table 20 shows the correlation between weight loss in water and plasticizer

leaching. The coefficient values are not as high as in Table 19 but show good correlation

except a few incidents. Ideally, the weight loss measured by balance should equal the

sum of weight loss in air and plasticizer leaching. That is not the case by Tables 11, 14

and 15. In fact, the weight loss in air alone is already greater than its respective weight

loss in water. That is an indication that all specimens have absorbed significant amount

of water in the process. Coe-Comfort has shown excessive plasticizer release compared

to other materials tested; the amount even exceeds those of weight loss in water and

approaching those in air. By the profile of leaching with time, one can conclude that the

peak selected is relatively weak in the reference curve and may represent only noise

background.









pH of the Storage Solution


Although the pH of distilled water stored in normal environment can reach as low

as 5.5, the consistent decrease of pH is surprising. For each material investigated, except

Flexacryl-Soft, there are two distinct behaviors of pH changes with time. One group

includes the control and pressure/heat; the other one includes both coated. Coated

specimens generally exhibit lower pH values initially and continue to be lower with time.

Flexacryl-Soft is the only exception that had a low pH without coating. It is necessary to

point out that Flexacryl-Soft is the only material that contains methacrylate monomers,

which is also the common component of the two coating materials. It seems that the

presence of methacrylate monomer is the precursor to the low pH. It has been reported

that acidic environment favor growth of C. albicans;38 the effect of this reduction in pH

induced by the presence of coating leachants requires further investigation


Powder-to-liquid Ratio Influence on weight change


It is reasonable to assume that the more liquid contributing to the composition of

a gel, the greater the potential quantity of available volatile components and leachants.

The powder to liquid ratio (Table 3) of the materials used in this study is in descending

order are Lynal (1.5), Coe-Soft (1.375), Coe-Comfort (1.2), Tempo and Flexacryl-Soft

(1). The ranking of wet weight loss by balance in all treatment groups after 84 days

(Table 14) are in ascending order of Flexacryl-Soft, Lynal, Coe-Comfort, Coe-Soft, and

Tempo.

Flexacryl-Soft is the only material that undergoes polymerization when the liquid

and powder components are mixed and would have less volatile ingredient to lose with









time. There is a correlation between the weight loss and powder:liquid ratio among the

materials tested, except Flexacryl-Soft. For example, Lynal having the highest powder to

liquid ratio also has the least of weight loss, while Tempo with the smallest powder to

liquid ratio shows the largest weight loss. The pattern, however, does not exist between

Coe-Comfort and Coe-Soft. Examination of Table 1 shows that there is more alcohol

content in Coe-Soft, 14.8% vs. 6-8.2%. It should be noted that Tempo has the highest

alcohol content, 25%, while Lynal is unknown. Since alcohol will eventually evaporate

completely,12 one can conclude that the weight loss should closely be related to the

alcohol content of the mixture and powder liquid ratio.

No correlation could be found between leaching by UV spectrophotometry and

powder to liquid ratio.

Leachants in Extruded Acrylic (Lucite-ES) Substrate


The data gathered by UV spectrophotometry indicated that there was no residual

monomer leaching out from the Lucite-ES substrate. This is further supported by the

absence of variation in pH values between the water used to store the substrate squares

and the control water.

It is well known that the industrial extrusion process involves heating granules of

the polymer from which the final material is made until it is homogeneously melted prior

to the extrusion itself. Since this process does not use any chemical additive and the heat

would vaporize any volatile component. If there had been any leachant, it would be safe

to assume that it came from a process applied after the extrusion, leaving residues on the

surface of the material itself. This was not the case.









Therefore, the use of Lucite as a substitute for heat cured methyl methacrylate in

studies requiring the use of a chemically pure methacrylate denture base material to

simulate clinical conditions is desirable. Plexiglas is another commercial name for this

acrylic sheet.


Mechanical Properties as Influenced by the Coating


Tissue conditioners, unlike permanent soft liners, should undergo viscous flow

under load, in order to adapt to the changing contour of the supporting tissue and

maintain a good adaptation of the denture base to the tissue. In describing how to extend

service life of tissue conditioners, the published literature have used increased resilience

value and Shore A hardness as the evidence. Either variable does not truly reflect the

very quality needed for tissue conditioners; it is the ability to change contour under load.

In this study, we examined not only Shore A hardness and modulus of elasticity which is

related to resilience but also the viscoelastic behavior described by the rate of recovery.


Hardness Evaluation by Shore A Durometer


The Shore A durometer is the oldest and best known instrument for testing the

indentation hardness of rubber and elastomeric materials. Its equipment consists of two

elements, a simple spring-loaded indentor or needle that is pressed into the elastomer and

a dial indicator to measure the depth of penetration. This depth is calibrated to an

arbitrary "A"or "D" number depending on the configuration of the indentor. The "A"

tester uses a truncated needle point with a 822-gram mainspring; the "D" tester uses a

needle with a relatively sharp point and a 10-lb mainspring (Figure 13).














Indentors: type A (left) and D

Figure 13. Shore Hardness indentors


All durometer indentors protrude with an extension of 2.50 + 0.04 mm (0.098

0.002 in). Durometer hardness numbers, although arbitrary from 0 to 100 from soft to

hard, have an inverse relationship to indentation by the indentor in thousandths of an

inch. For example, a reading of 36 on Durometer A scale indicates an indentor

indentation of 0.064 in. Similarly, a reading of 90 on a Neoprene faucet washer indicates

an indentor indentation of 0.010 in. Figure 14 shows the relation of hardness number to

the depth of indentation.


Relative Indentor Position and Displayed Value






Zero Value 'in Progress 100 Value


Figure 14. Shore A Durometer readings

The ASTM D2240, "Indentation Hardness of Rubber & Plastic by means of a

Durometer" embodies an authoritative summary of recommended test procedures. The

document specifies that the test specimens should have a minimum thickness of at least

6 mm (0.25 in.) unless it is known that identical results are obtained on thinner

specimens. This requirement was not often followed or attended to in publications where

this instrument was used. If the recommended thickness of tissue conditioner for lining a









hard denture base, which ranges from 1.5 to 3 mm,3'37 is used, it is important that the

thickness of the specimen should be reported along with the hardness values. In

addition, because this thickness range does not fulfill the requirement of a minimum of

6 mm for hardness testing using the Shore A durometer according to ASTM standards,

the values recorded are useable only when several layers of the same thickness of

material stacked on to attain the 6 mm required would yield a similar value. Irregular or

coarsely grained surface can interfere with the indentor penetration and give erroneous

results. The temperature at which the test is made may have a significant effect on the

readings; it is critical that readings should be recorded along with the test temperature if

it is different from room temperature.

The Durometer reading should be taken within one second after firm contact

between its flat bottom and the test specimen has been established. If the dial hand

continues to recede on specimens exhibiting cold flow or creep characteristics, additional

reading may be recorded after a specified time interval, say, 10 or 15 seconds. In our

data collection procedures, we have noted that maximum Durometer readings varied

according to the travel speed of the presser foot of the instrument as it was dropped on

the material. The ASTM recommendation had anticipated this dependency and

recommended a firm smooth downward action that will avoid shock. It further suggests

using an operating stand that can control the rate of descent of the durometer to the test

specimen. Such an instrument along with maximum reading capability will be ideal for

testing temporary soft liner materials where there is a viscoelastic creep behavior. It is

noted in section 5.1.1.8 of the ASTM that analog maximum indicating pointers have a

nominal affect on the values attained. This effect is greater on Durometers of lesser total









mainspring loads, e.g., the effect of a maximum indicating pointer on Type D Durometer

determinations would be less than those determinations achieved using a Type A

Durometer. Therefore, a Digital Maximum Reading Durometer would be the instrument

of choice for measuring tissue conditioner hardness.

The same document also cautions that readings less than 20 and above 90 are

unreliable and should not be recorded. The majority of our readings are below 20, except

those of Flexacryl-Soft and Lynal at 30 second. A review of the literature (Kawano et

al. 17, Yoeli et al.32, Andreopoulos et al.39, and Starcke et al.40) show that many studies

having used this instrument for tissue conditioner hardness did not raise this issue.

Regardless of the statistical significant increase in Shore A hardness values with

storage and surface treatment in Table 7, the low values recorded, well below the ASTM

recommended range of 20-90 for reliable readings, have rendered those values

meaningless. Nonetheless, it is important to point out that specimens with mono-poly

coating consistently exhibit the highest mean hardness values among all treatment, and

those with pressure/heat treatment often rank second.

Surface examination of Shore A hardness specimen show that control and

pressure/heat specimens usually exhibit distinct dents, which eventually recover with

time while the dimples in the coated specimens will only recover partially. It is apparent

that the Shore A indentor has penetrated through the surface coating. We can conclude

that mono-poly alone contributes to the resistance near the superficial region but not in

the bulk of the material. Jet Seal coating, although is relatively more brittle than mono-

poly, does not provide the same degree of resistance and thus provides a lesser degree of

hardness increase.









As observed in Table 7, the mean hardness values of pressure/heat treated

specimens often rank behind that of mono-poly. If the limitations of Shore A hardness

test were disregarded, it can be asserted that additional surface treatment can effectively

increase the resilience of the materials as measured by the Shore A hardness.


Modulus of Elasticity


During the dynamic mechanical tests, the resistance of the material to the

crosshead traveling toward the material to the mid-point of the dynamic test was

recorded as load changes with distance of material displacement. The linear portion of

the curve was taken to determine the modulus of the materials. In general, the elastic

modulus was lower initially and increased with time up to two weeks. After this time,

the values started to fluctuate around a median value, indicating that the changes have

leveled off. The degree of change seemed to coincide with the weight loss measured by

balance, which reached a plateau around two to four weeks after immersion. The one

exception was the pressure/heat treated Lynal, which decreased to the initial level. The

reason for this phenomenon is not known.

The effect of treatment on the elastic modulus is different from one material to

another. The Jet Seal coated specimen often exhibited the highest weight loss elasticity

mainly due to the loss of monomers from the coating. If we exclude the Jet Seal coated

specimen, we would find that the ranking of the treatment for the weight loss and the

elastic modulus are identical for Coe-Comfort, Coe-Soft and Lynal, and partial for

Flexacryl-Soft. Tempo was the only one that shows opposite trend. One should expect

to observe higher elastic modulus when more weight loss has occurred, presumably due

to the loss of plasticizer. This information can only be obtained from Tables 21 and 23.









Table 21 shows that the correlation between weight changes in water and modulus of

elasticity are comparable to that between plasticizer leaching and modulus of elasticity

(Table 23). Mono-poly group and Lynal group show the worst correlation, indicating

any improvement of modulus of elasticity is not due to any leaching or weight loss.

Even though our leaching data by UV absorbance indicated that the leaching of

plasticizer from these temporary soft reline material were relatively low, which was only

a few percent of the weight loss in water and in air, its role in the modulus of elasticity is

the same as that of water loss. It is impossible to separate the two at this point.

Dominguez et al. 25 have arrived at the same conclusion that there is no appreciable

release of plasticizer in water. The significant changes with Flexacryl-Soft and those

with coatings are mainly caused by the leaching of methacrylate monomers, which has

the same boiling point as water. The weight loss of specimens stored in ambient air

appeared to be greater than those stored in water. It signified that the majority of weight

change is due to alcohol loss. The smaller weight change for specimens stored in water

implied absorption of water by the specimens. In other words, total weight change

resulted from the loss of alcohol and gain of water by absorption. Lesser weight loss of

mono-poly coated specimens do not necessary mean more water absorption. It could be

possible that those specimens contained less alcohol since each coated specimen have to

be set aside for a while to allow drying of the coating in addition to the gelling period

before coating, allowing more alcohol evaporation. This would have resulted in less

alcohol at the initial base line. However, the standard total preparation time of 25

minutes before testing would have minimized this possibility. There is no doubt that the

mono-poly coating retarded the ingress of water and thus provides higher elastic modulus









for the samples. Jet Seal coated specimen did not exhibit a similar behavior since there

are cracks on those coatings.

Rate of Recovery

The rate of recovery shows the degree of material recovery during cycling. If the

material behaves elastically, the values as defined should be extremely high. On the

other hand, if the material responds sluggishly to the cyclic loading, the value will be

low. As in the result of elastic modulus, the rate of recovery generally is lower initially

and increases with time up to two weeks. As the time progresses, the change becomes

less significant or the values start to fluctuate. The degree of changes also coincides with

the weight loss by balance, which reaches the plateau around two to four weeks after

immersion. The most dramatic change belongs to the control of Lynal within the two

days of immersion in water. The dependence on time corresponds to the exchanges of

alcohol and water.

The mono-poly coated specimens registered the lowest rate of recovery for all

materials except Lynal. However, if we eliminate the results of the first seven days, we

would find the mono-poly coated groups with the lowest rate of recovery. The effect of

Jet Seal on the rate of recovery is not as consistent. We concluded earlier that mono-poly

yields higher elastic modulus because of less water absorption. The values of rate of

recovery indicates that mono-poly coated specimen retained more viscous component,

the sluggish behavior, than the other groups. Although we concluded that the leaching of

plasticizer is insignificant in quantity, we also found that plasticizer leaching, determined

by the high wavelength and in absolute quantity, from mono-poly coated specimens was









statistically significantly less than the other treatments. That small difference could

contribute to the lower rate of recovery.

Tables 22 and 24 show that there is no correlation between modulus of elasticity

and weight loss or plasticizer leaching for Flexacryl-Soft; this is consistent with the

material properties. Lynal also exhibited the similar situation after pressure/heat

treatment; it is not clear why. Both tables show that weight loss may have exhibited

better correlation to rate of recovery than the plasticizer leaching, it is, however, not

possible at this point to clarify that issue. It is likely that water absorption by the

material has confounded our attempt to distinguish the effect of weight loss and

plasticizer leaching. We may have to subject the specimens to dehydration process to

reduce water content and measure the dynamic properties of the specimen in relation to

the water remained in the specimen. Table 25 shows the correlation between and rate of

recovery and modulus of elasticity. We learned from Table 10 that treatments have

opposite effect to the rate of recovery and modulus of elasticity. It means that an

increase in modulus of elasticity may be accompanied by a lower rate of recovery, such

as in the case of Coe-Soft, Flexacryl-Soft and Lynal. However, when we compare the

correlation between the modulus of elasticity and the rate of recovery, we find they all

have positive slopes (not shown in the table) except those with zero coefficients of

determinant. It suggests that one particular treatment may have opposite effects on the

change of modulus of elasticity and rate of recovery, nonetheless, the relationship

between the two physical parameters still maintains a positive relationship.















CHAPTER 6
SUMMARY AND CONCLUSIONS

The objective of either coating or pressure/heat treatment is to render a surface

different from the one generally formed on the temporary soft reline material if the

manufacturer's instructions alone were followed. This improved surface is expected to

help in maintaining or improving the properties of the bulk reline material; it is inferred

that the service life of the underlying liner can be extended. We examined the effect of

four treatment regimens on the surface appearance and six well-defined physical

parameters of temporary soft reline materials. The results show that majority of changes

occurred during the first two weeks, and different surface treatments can have different

degree of effect on the physical and mechanical properties of each material. Flexacryl-

Soft, which is normally used as a tissue conditioner, is in a class by itself; the effect of

treatment on this material is often different relative to the other four materials.

We found that, in terms of surface appearance, there was no clear overall

advantage of additional surface treatment with time. Coating did provide glossy

appearance but it can deteriorate due to swelling of mono-poly or cracking of Jet Seal.

There is no apparent advantage to heat and pressure processing compared to preparation

according to the manufacturer's instructions alone.

Although Shore A hardness value has been used to infer resilience of soft reline

materials, their use to describe resilience of temporary soft reline material needs further

qualification. Definite reading from the dial at prescribed time is difficult due to the









viscoelastic behavior of these materials. Readings less than 20 are not considered

reliable by the industry standard, therefore only Flexacryl-Soft and some Lynal groups

readings would be considered reliable. Our selection of 30 seconds for the first reading

is unduly long but that was the only way to record values with reasonable reliability

using the instrumentation available to us. In order to make this parameter meaningful,

Shore A hardness values reported in dental literature should include the configuration of

the specimen, such as thickness and substrate, and exact time duration of recording. If

possible, a Digital Maximum Reading Durometer should be used.

Weight changes using a precise balance is simple and direct but cannot

differentiate sources of changes, which can be from alcohol evaporation, plasticizer

leaching and water absorption. UV spectrophotometer can determine quantity organic

compounds leaching if precise reference curves are available, but it would not identify

the exact compound by chemical makeup. The deficiency of this instrument is that a

compound, which is not in the original references and part of its bandwidth covers the

peak used for detection, the leaching can be overestimated. To identify potential

contaminates, one will have to use high performance liquid chromatography. Despite

that deficiency, we managed to obtain reasonable plasticizer leaching data. To examine

the effect of water absorption on the mechanical properties will require a separate study.

Our study has confirmed that mono-poly could serve as a barrier to plasticizer

leaching and weight loss, as shown by Tables 12 and 14, respectively. However, it did

not totally inhibit the process, it just slowed down the process. Figures 8 and 9 clearly

depict that phenomenon in air. Its influence on the mechanical properties, however, is

not as clear-cut. One should keep in mind that retention of plasticizer or absorption of







79

water should render the bulk material more viscoelastic, which means lower modulus of

elasticity and lower rate of recovery. This is not true for all occasions. The logical

explanation is that the rigidity the mono-poly coating itself might have contributed to the

increase of modulus of elasticity. As mentioned earlier, each discipline defined

resilience differently. According to material science textbooks, it is one half the product

of the modulus of elasticity and proportional limit, which was used in the literature that

showed improvement of resilience due to coating. Very often the increase in value is due

to increase in modulus of elasticity, which means the material has become more rigid.

From prosthodontist's point of view, resilience implies softness and easy to adjust. By

that definition, increase in modulus of elasticity will reduce resilience of the materials.

Our experiment indicated that the rate of recovery for coated specimen is actually lower

than control over time, which means more viscoelastic behavior has been retained by the

coating.

Jet Seal has a significant effect in increasing the weight loss of all the above

materials compared to the control. Jet Seal did not retard weight loss as in mono-poly

due to cracks in the coating. The increase in weight loss can be attributed to the loss of

monomer and the stress induced by the coating. More research is needed as to the

effectiveness of Jet Seal in slowing down aging of tissue conditioners.

Coatings based on methyl methacrylate monomer lowered the pH of the storage

medium with time. Flexacryl, which uses the same monomers, also induced lower pH to

its storage medium. We concluded that methyl methacrylate monomer is the cause of

lower pH, which still needs to be validated by a separate research.












Based on the result of this research, we can draw the following conclusions:

1. Pressure/heat process does not impart favorable appearance on the surface

or retain the viscoelastic properties longer than the control groups.

2. Mono-poly coating renders a glossy appearance to the surface but also

forms blister in time; the degree of severity of which differs among

materials. It slows down the weight loss and plasticizer leaching which

help the bulk of temporary soft reline loose its viscoelastic properties at a

slower pace.

3. Jet Seal also yields an initial glossy appearance; the coating, however,

cracks and is not capable of protecting as well as mono-poly can.


















APPENDIX


POLYMERIZATION IN A METHACRYLATE PREPARATION WITH EXCESS
MONOMER MONO-POLY


Abstract


Purpose. Coating by a solution made of one part methyl methacrylate polymer in 10 parts of monomer
was reported to have prolonged the service-life of soft liners. The purpose of this study is to examine if the
coating has resulted from polymerization of accompanying monomers since these reports did not address
that issue.
Materials and Methods. From one heat-activated and one autopolymerizing resin kits, we prepared four
solutions by matching each powder with either of the monomers. Two mL of solution was spread per glass
slide and allowed to sit in ambient air. Six slides were prepared per experiment. One extra set of heat-
activated polymer in autopolymerizing monomer was exposed to 75W incandescent light for the first 20
minutes. The weight change was measured every minute for the first 20 minutes, and at the 24th and 48t
hour.
Results. The results showed that greater than 99% of the original monomer had evaporated and the
remainder constituted approximately 7.9 to 10.0 wt% of the final coating. Additional sets of slides of the
same preparation were immersed in heated water (70 and 1000C) and pressurized to 30 psi for 15 minutes.
The resultant coatings were placed in 25mL of acetone individually; complete dissolution of the coatings
indicated no cross-linked resin, therefore no polymerization occurred. Only those immersed in 1000C
water showed signs of polymerization. The remaining samples did not polymerize, indicating that they
were residues of PMMA polymer after monomer evaporation.
Conclusion. Clinically, in the absence of polymerization, the effectiveness of the mono-poly coating will
depend on the polymer used to make the solution. The substantial amount of monomer released could pose
a health hazard for some patients.


Index words. methacrylate chemistry, sealer











Introduction
Gardner and Parr21 first suggested that the longevity of temporary soft liner could be extended by
using a coating to render a smooth surface, and seal its porous surface. The coating material, mono-poly,
was prepared by dissolving one part of heat-activated clear polymethyl methacrylate (PMMA) powder to
10 parts of autopolymerizing orthodontic methyl methacrylate monomers (MMA). The authors stated that
after applying it with a brush, the mono-poly sealer should be allowed to dry for 4 to 5 minutes while held
approximately 2 inches away from a 50- or 60-watt lamp. This process should be repeated two more times.
Casey and Scheer 24 showed by SEM micrographs that a temporary soft liner glazed with a mono-
poly coat retained the original glass-like appearance, even after it had been worn by a patient for 30 days.
The uncoated specimen given the same conditions had severely degraded, evidenced by the exposure of
subsurface air bubbles incorporated during mixing. Casey & Sheer validated the smooth surface that
Gardner and Parr 21 had predicted but did not indicate if the coating improved the longevity of the soft
liners. Dominguez et al.25 reported that mono-poly coating reduced water absorption and plasticizer loss
from temporary soft liners immersed in water over a one-month period. They deducted that mono-poly
coating acted as a barrier in preventing water absorption and loss of plasticizer. Gronet et a.24,26 concluded
that sealing the surface of temporary soft liners might have enhanced the life of these liners and extended
their period of resilience. Aslan and Avci23 found that autopolymerizing acrylic resin samples coated with
mono-poly harbored fewer E. coli than uncoated samples after vigorous washing. Although it is known
that a smooth surface can reduce fungal and bacterial growth that is often responsible for discoloration and
eventual breakdown of the surface, they also speculated that the presence of MMA monomers might have
inhibited the growth of E. coli.
The liquid component of an autopolymerizing acrylic resin consists of MMA monomer, a cross
linking agent (such as ethylene glycol dimethacrylate), an inhibitor (such as hydroquinone), and activator
(such as dimethyl-p-toluidine). The powder component has PMMA beads and benzoyl peroxide
(initiator).41'43 When an appropriate ratio of powder and liquid is mixed, polymerization occurs. The
polymerization of monomers containing copolymers such as ethylene glycol dimethacrylate should yield
an insoluble network, an evidence of crosslinking.44'45 Although several authors21'25'26 described mono-
poly as semi-set mixture, they did not clarify if the ratio of ten parts liquid to one part powder used in
mono-poly would result in polymerization. Very often prostheses made of autopolymerizing resins are
immediately placed in a heated and pressurized vessel to increase the degree of polymerization and reduce
porosity.46 This is intended to improve the mechanical properties of the autopolymerizing resin although it
is unsubstantiated in the literature.4 Therefore, it is unknown whether heat and pressure would have any
effect on mono-poly.
Dental acrylic resins are packaged as heat-activated and autopolymerizing depending on the
designated activators. There are four possible ways to combine the powder and liquid found in one heat-
activated and one autopolymerizing package. The reason for the selection of heat-activated polymer beads
mixed with autopolymerizing monomer has not been fully explained. The purpose of this study is to test
the hypothesis that polymerization will occur in any of the four combinations of mono-poly in ambient air
or under an incandescent light. Also tested is the hypothesis that heating in a pressurized chamber will
enhance the degree of polymerization.

Material and methods
Preparation of mono-poly
Lang Orthodontic autopolymerizing resin (Lang Dental Manufacturer, Wheeling, IL) and
Hygienic Clear heat-activated denture resin (Hygenic Corp., Akron, OH) were used to prepare the
following four mono-poly combinations: (1) heat-activated PMMA powder and autopolymerizing MMA
liquid; (2) both heat-activated PMMA powder and MMA liquid, (3) both autopolymerizing PMMA powder
and MMA liquid, and (4) autopolymerizing PMMA powder and heat-activated MMA liquid. We weighed
approximately 15 grams of liquid in an empty 25-mL conical flask and 1.5 grams of corresponding powder
separately on a weighing paper. A magnetic stirrer was placed inside the flask, which was then capped
with a rubber stopper to prevent evaporation. The monomer flask was placed in a preheated water bath at
55C by a stirring hot plate with the stirrer turned on. After two minutes, the powder was added while the











monomer was stirred. It took 5 to 10 minutes for the initial cloudy mixture to become clear. The flask was
left on the stirring hot plate for a total of 15 minutes to assure complete dissolution.
Preparation ofsolidified coating
Two mL of the prepared mono-poly from each batch was spread widely on a pre-weighed 75 x 50
x 1 mm glass slide. A computer controlled balance with precision of 0.001g (Model XL-410, Denver
Instruments Co., Arvada, CO) was used to record the weight changes in ambient air at room temperature
(2210C) for 20 minutes in real-time. The same slide was again weighed after 24 and 48 hours. The
process was repeated six times for all four solutions prepared. Weight decrease for six additional slides
coated with heat-activated polymer/autopolymerizing monomer placed at approximately 2 inch under a
75W lamp were recorded in the same time frame. The initial weight of the fresh mono-poly, W,, was
divided by 11 to obtain the original polymer weight, Wp. The difference between Wf and W, is the
contribution of monomer to the final weight, regardless of whether the monomer has polymerized or not.

Wf-Wp
wt% of monomer contribution = x 100% (1)
WI
The solid film on the glass slide was removed with a razor scraper for the polymerization test.
To test the effect of temperature on the final coating obtained after 48 hours in ambient air, the
entire test described in the last paragraph was repeated without recording the weight changes with time.
The films obtained were placed in 1000C water and pressurized to 30 psi for 15 minutes. The films were
recovered, dried and stored for the polymerization tests.
To test the effect of temperature and pressure on the coating, 2 mL of mono-poly was layered
between a Mylar sheet and a glass slide to keep the liquid content from prematurely dispersing in the
subsequent process. Four such preparations were prepared from each mono-poly solution and immediately
placed in a pressure pot preheated to 700C. The lid was closed with the temperature control unchanged and
pressure maintained at 30 psi for 15 minutes. The same experiment was repeated again at 1000C. The
resulting film was removed, dried and stored for the polymerization test. Calculation of the wt% of
monomer contribution to the final weight was not performed since complete recovery of resulting film was
not possible.
Polymerization test
Since both monomer liquids used in this study contain a crosslinking agent, films that occurred as
a result of polymerization that incorporated the cross linking agent are insoluble in acetone. Each film was
placed in a 25-mL cylindrical flask filled with 25 mL of acetone. The film was completely immersed in
the solvent and observed for sign of dissolution for one week. Shavings of set heat-activated and
autopolymerizing acrylic resins, obtained from denture processing and provisional fabrication, were also
included as controls.

Results
The weight values recorded at the 24t hour and 48t hour were virtually the same; the readings
from the 24th hour were used in the analysis. The degree of weight loss indicates that greater than 99wt%
of monomer has evaporated in the process. Table A-1 shows the mean and standard deviation of weight
percent of monomer retained in the final coating. One way analysis of variance of the data showed that
mono-poly made of autopolymerizing polymer in autopolymerizing monomer showed the least amount of
monomer retained, while the other three formulations retained higher percent of monomer and were not
statistically different among themselves at a=0.05. Figure A-1 shows the typical weight change profiles in
ambient air and under 75W lamp. It is clear that mono-poly lost weight faster under a 75W lamp and
reached a plateau in 15 minutes. In ambient air, the weight loss was slower but the final weight 24 and 48
hours later were approximately the same. i.II i.i .ii- there was no difference between the two processes
in the wt% of monomer retained in the final coating (Table A-1). Table A-2 shows the results of solubility
tests. Films that dissolved always exhibited dissolution within 15 minutes of immersion. Only films
obtained from processing mono-poly liquids at 1000C and 30 psi pressure have shown signs of











crosslinking. Figure A-2A shows the films collected from the experiment conducted in ambient air; Figure
A-2B shows the same films after immersion in acetone for 15 minutes. Figure A-3A shows the films
collected from the experiment conducted in 1000C water bath and 30 psi; Figure A-3B shows the same
films after immersion in acetone after 1 week. From the scaffold left behind after dissolution, heat-
activated monomers produce a much higher degree of crosslinking than autopolymerizing monomers.
Both controls, which are shavings left over from denture processing and provisional fabrication, exhibited
solvent resistance in a similar fashion.

Discussion
The results of the solubility test clearly indicate that there is no polymerization in any of the
combinations at room temperature. Apparently, the coating obtained at room temperature was the result of
monomer evaporation. Even mono-poly prepared from autopolymerizing polymer and autopolymerizing
monomer would not polymerize. For polymerization to begin, free radicals must be present. Heat, light or
chemicals are three means of converting initiators to free radicals.43,48 However, to prevent free radicals in
the air from causing accidental polymerization of the monomer during storage, a small amount of inhibitor
is added to all commercial MMA liquids included in heat-activated or autopolymerizing acrylic resin kits.
The presence of inhibitor requires the addition of enough initiator to consume all of the former with some
excess for polymerization when the correct powder to liquid ratio is used. Generally, it is two parts powder
to one part liquid by weight. This inhibitor to initiator ratio should also allow for a generous error margin.
In mono-poly preparation this ratio is exceeded by 20 fold, which is beyond any reasonable margin. This
quantity of inhibitor will undoubtedly consume all available initiator in the mixture as soon as it is
activated. Even when subjected to a 1000C water bath, the air-dried coatings, which still consists of 8-
10wt% of monomer did not show signs of polymerization. This is expected since after MMA evaporation,
the inhibitor concentration becomes even greater, restricting the polymerization of any residual monomer
that trapped between the PMMA molecules.
These results seems to indicate that polymerization does not occur in mono-poly in a clinically
applicable time. However, our study also show that polymerization occurs when liquid mono-poly is
subjected to 1000C water bath and 30 psi pressure. The natural assumption would be that heat, which is an
activator and has been linked to accelerated polymerization, might have caused thermal initiation of the
monomer. Although MMA exhibits thermal self-initiation at high temperature, its rate of initiation is about
0.14% per hour at 127C.49 At this initiation rate spontaneous polymerization of the MMA at 1000C is
unlikelyso. We had observed in our pilot tests that mono-poly contained in a sealed vial and heated to
1000C for 15 minutes remained liquid as long as the integrity of the vial was maintained. This observation
reaffirms that spontaneous polymerization by heat without initiator is not attainable in a short period of
time.
On the same set of tests, we also observed that mono-poly which had leaked from vials during
heating and come into contact with water, polymerized. These results prompted us to conduct the tests in
70 and 1000C water bath and 30 psi. Apparently, the presence of 100C water has provided needed
radicals for polymerization. According to the Merck Index, hydroquinone is soluble in water at a ratio 1 to
14. It is possible that majority of inhibitor may have diffused to water as soon as mono-poly comes in
contact with water, so that there is enough initiator to complete the polymerization. This is not the case
since the same results were not observe in those tests carried out at 700C water, considering that benzoyl
peroxide decomposes around 60C. Pressure (30psi) has no effect since the same solvent resistance was
observed in films prepared without pressure. It was also observed that mono-poly mixed with ten times its
volume of water did not show signs of polymerization at room temperature over a month. The results
obtained at room temperature and 70C water bath indicated that reduction of inhibitor in mono-poly alone
would not be enough to facilitate polymerization. This suggests that there must be a substantial output of
radicals in the presence of 100C water, enough to neutralize inhibitors and allow polymerization to
complete. To identify the exact source of these radicals is beyond the scope of this study and will not be
discussed further.
The presence of the crosslinking agent in the monomer component renders the final polymerized
product non-soluble in acetone. Although only a small amount is needed, a slightly higher quantity can
yield a more crosslinked, less soluble network. Judging by Table A-i, which shows that when











polymerized, mono-poly made of heat-activated monomer yield a less soluble film that those made of
autopolymerizing monomer. Our results imply that heat-activated monomer contains more crosslinking
agent than autopolymerizing monomers, agreeing with findings by Arima et al.44 and the product's
material safety data sheet disclosure of copolymer content.
During the preparation of mono-poly solutions, we observed that heat-activated polymer beads
takes more than ten minutes to dissolve in monomer, while autopolymerizing polymer beads will take less
than ten minutes. The consistency also appears thicker with solution made of heat-activated polymer
beads. This suggests that heat-activated polymer beads are made of higher molecular weight PMMA than
the autopolymerizing one.44,45,51
In the absence of polymerization under clinical conditions, monomer serves only as a solvent and
52-58
could be replaced by another convenient organic diluent that may be less hazardous to the patient. The
weight change recorded for air-dried samples agrees with the findings of Dominguez et al.25 that there is a
continuous weight loss of the coating up to 24 hours after application. Exposing the coating to an
incandescent lamp can reduce the drying process to 15 minutes. If this lamp exposure has no adverse
effect on the underlying material then is should be used routinely. Should a smooth, glossy surface be the
only objective for mono-poly, then lack of polymerization is inconsequential. We have found in our
preliminary tests that there was a wide distribution of data in the calculation of residual monomer when the
solutions were prepared by volumetric measures. The age of solutions, from freshly made to a few weeks
old, also affected the results. It is likely due to the high volatility of the monomer. For clinical purpose,
maintaining the exact ratio may not be critical. There may be room for clinicians to adjust the proportion
according to their needs. A study on the gloss of film coated tablets showed that increasing polymer
concentration in the coating material resulted in significant decrease in gloss.48 This implies that the ratio
of polymer powder to monomer may be modified by the individual clinician to obtain the level of gloss
they prefer. Since there is no polymerization of the coating material, abrasion resistance of the coating
may possibly be dependent on the molecular weight of polymer beads used and the amount of residual
monomer in the final coating. The ability of this coating to restrict plasticizer elements in tissue
conditioner or soft liner from leaching requires further investigation.

Conclusion
The results do not support that MMA in mono-poly will polymerize in a normal clinical situation.
Even though water at 1000C induces polymerization in all four mono-poly solutions, the dispersion of
liquid mono-poly coats at this temperature precludes its clinical use. Within the confines of the brands we
have used, the final coating is a film of linear polymer with 8-10wt% of residual MMA monomer. There is
no need to store the mono-poly solution in a refrigerator as long as the container is sealed tight to avoid
evaporation of monomers. Should the mixture thicken up during storage, mixing additional liquid
monomer will restore the original consistency. Placing a fresh coat of mono-poly under a light bulb would
hasten MMA evaporation, therefore minimizing patient exposure. Mono-poly should be used it in a well
ventilated area. The absence of polymerization of mono-poly raises questions related to the mechanism of
how the coating extends the longevity of tissue conditioners.

References
References for this appendix are incorporated in the main list of references.











Table A-1 Weight percent of monomer contribution in the final coating after 24 hours.

Types of mono-poly formulation Wt(SD) Tukey's
Types of mono-poly formulation Wt% (SD)


groJup11 -


Heat-activated polymer and autopolymerizing monomer (ambient air) 10.0 (0.8) A

Heat-activated polymer and heat-activated monomer (ambient air) 9.9 (1.1) A

Autopolymerizing polymer and heat-activated monomer (ambient air) 9.4 (1.3) A

Heat-activated polymer and autopolymerizing monomer (75W lamp) 9.4 (0.7) A

Autopolymerizing polymer and autopolymerizing monomer (ambient air) 7.9 (0.4) B

Grouping with the same letter means they are statistically the same at a=0.05.


Table A-2 Solubility test of final coating obtained in various conditions

formula Ambient air Ambient air 700C and 1000C and
Types of mono-poly formulation .
with or without then heat & pressurized pressurized
75W lamp pressure

Heat-activated polymer/ Dissolved Dissolved Dissolved Partially
autopolymerizing monomer soluble

Heat-activated polymer/ Dissolved Dissolved Dissolved Insoluble
heat-activated monomer

Autopolymerizing polymer/ Dissolved Dissolved Dissolved Insoluble
heat-activated monomer

Autopolymerizing polymer/ Dissolved Dissolved Dissolved Partially
autopolymerizing monomer soluble


m







87


2.0

1.8

1.6 ---Ambient Air
14 75W Lamp
1.4



1.0

0.8

S 0.6

0.4

0.2 -

0.0 -
0 5 10 15 20 1440

Time in minutes


Figure A-1 Typical weight change profile for mono-poly solutions placed in ambient air and
under a 75W lamp














HP HP


AP AP


HL AL HL AL
Figure A-2A Films harvested from mono-poly processed in ambient air.











HP HP AP AP
HL AL HL AL


Figure A-2B The same film in A-2A after 15 minutes of immersion in acetone.












SII M M
HP HP AP AP
HL AL HL AL
Figure A-3A Films harvested from mono-poly processing in 1000C water
and 30 psi.









HP HP AP AP
HL AL HL AL
Figure A-3B Appearance of the same film in A-3A after one week of
immersion in acetone.















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