Title: Three-dimensional characterization of maxillary molar displacement subsequent to headgear treatment with respect to time and force of application
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Title: Three-dimensional characterization of maxillary molar displacement subsequent to headgear treatment with respect to time and force of application development and pilot test of a novel study method
Physical Description: ix, 76 leaves : ill. (some col.) ; 29 cm.
Language: English
Creator: Bar-Zion, Yossi
Publication Date: 2000
Copyright Date: 2000
 Subjects
Subject: Extraoral Traction Appliances   ( mesh )
Orthodontics   ( mesh )
Odontometry   ( mesh )
Tooth -- physiology   ( mesh )
Dentistry thesis, M.S   ( lcsh )
Dissertations, Academic -- Dentistry -- UF   ( lcsh )
Genre: bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )
 Notes
Abstract: ABSTRACT: Orthodontic headgear for the correction of class II malocclusions has been used in orthodontics since the 1800s. Although the headgear is quite popular in the orthodontic community, the literature is rather contradictory and ambiguous with respect to the amount of time and force necessary for optimal treatment results. A potential source of error leading to the large inconsistencies involving the orthodontic headgear research may be due to the complexity and difficulty of measuring the outcome results objectively, as well as accurately monitoring the time and force of applications. Discrepancies involving inaccurate data collection as well as outcome analysis could potentially lead to misinterpreted findings and contradictory conclusions.
Abstract: The purpose of this study was to develop and pilot test a research methodology to objectively study, measure, and analyze orthodontic treatment outcome subsequent to headgear therapy with respect to time and force of application. To effectively evaluate the therapeutic effect of the headgear, a novel orthodontic time/force recording (OTFR) headgear was developed, capable of monitoring and recording compliance as well as force levels in realtime. The second component of this study involved the development of a digital three-dimensional measurement system for the quantitative and qualitative analysis of the treatment effects.
Abstract: Data collected on a pilot sample of patients treated with our newly developed OTFR headgear were analyzed in order to establish the validity of this device in clinical research, and was compared with the currently used compliance monitoring method --the self reported diary. Study models taken on this group of patients at monthly intervals were digitally analyzed using the three-dimensional measurement system for the characterization of molar displacement and the pilot testing of the technique. The testing of the three-dimensional analysis system has been shown to provide qualitative as well as quantitative results with respect to the molar's spatial displacement subsequent to headgear use. The OTFR headgear appeared to be valid for the monitoring of compliance. The use of patients' self-reported logbook did not correlate with the true compliance as measured using two separate digital timing devices.
Abstract: The future use of such logbooks for the monitoring of compliance does not appear to be warranted. Future implementation of this novel research design in clinical studies would provide invaluable insight into the treatment effects of orthodontic headgear therapy by facilitating intensive real-time data collection and objective three-dimensional tooth movement analysis.
Summary: KEYWORDS: timing headgear, orthodontic headgear, force monitoring, compliance monitoring, orthodontic, tooth movement, compliance, spatial displacement, three dimensional analysis
Thesis: Thesis (M.S.)--University of Florida, 2000.
Bibliography: Includes bibliographical references (leaves 71-75).
Additional Physical Form: Also available on the World Wide Web; PDF reader required.
Statement of Responsibility: by Yossi Bar-Zion.
General Note: Printout.
General Note: Vita.
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Bibliographic ID: UF00100716
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 84061070
alephbibnum - 002566143
notis - AMT2424

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THREE-DIMENSIONAL CHARACTERIZATION OF MAXILLARY MOLAR
DISPLACEMENT SUBSEQUENT TO HEADGEAR TREATMENT WITH RESPECT
TO TIME AND FORCE OF APPLICATION DEVELOPMENT AND PILOT TEST
OF A NOVEL STUDY METHOD











By

YOSSI BAR-ZION


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


2000















ACKNOWLEDGMENTS


To my family my Mother and Father, Yael, Dani, and Hila I am grateful for all

your help and support. I know that none of my accomplishments would have been

possible without your patience and the sacrifices you have made over the years.

To Mandy, thanks for all the moral and emotional support through the years we

shared together. I look forward to a lifetime of happiness together.

I would like to thank the members of my committee Drs. Wheeler, Dolce, Gibbs,

and McGorray. I would particularly like to thank Dr. Wheeler for his mentorship

throughout this project and for all his help and guidance through my clinical training. I

would also like to acknowledge Marie Taylor, research coordinator, and Debbie Walls,

clinical assistant, for their help with the clinical aspect of the project.
















TABLE OF CONTENTS


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

L IST O F T A B L E S .................................................................................................... v

L IST O F F IG U R E S ....................................................................................................... vi

A B S T R A C T ................................................................................................................ v iii

CHAPTERS

1 IN T R O D U C T IO N ................................................................................................... 1

P u rp o se o f Stu dy ................................................................................................ 3
O objectives ......................................................................................... 3

2 REV IEW OF TH E LITERA TURE ......................................................... .............. 5

H historical O verview ................................................................................... . .... 5
M monitoring of Tim e ..................................................................................... ... 5
M monitoring of Force ........................................................................................ 6
M easurement of Tooth Displacement................................................ .............. 8
Sum m ary ..................................................................................................... 14

3 M ATERIALS AND M ETHODS .............................................................. ............. 15

Orthodontic Time/Force Recording (OTFR) Headgear ........................... ............. 15
Development of Tooth Displacement Measurement............................... ............. 18
Stable R reference Point ..................................................................... ............. 19
Three-D im ensional D igitizing ......................................................... .............. 21
Three-D im ensional A analysis ........................................................... .............. 24
C clinical D ata C collection ...................................................................................... 28
Subject Selection ..................................................................................... ... 28
Inclusion criteria ....................................................................................... 29
E exclusion criteria ...................................................................................... 29
S tu d y D e sig n .................................................................................................... 2 9
D ata A n aly sis ........................................................................ ... ......... ...... .............. 3 2
Testing of the Three-Dimensional Molar Measurement System (objective 1).. 32
Analysis of Timing Data (objectives 2 and 3) ....................... ...................... 33


iii









Analysis of Force Data (objective 4) ................................................ 34
Analysis of Tooth Displacement (objective 5).............................. .............. 35

4 RESULTS AN D D ISCU SSION ......................................................... .............. 36

Tooth Displacement Characterization of a Selected Study Model........................ 36
Tim ing D ata............................ ................... .................. 43
Correlation of the OTFR Headgear with Third-Person Log Book.................. 45
Correlation of Timing Headgear with Commercial Timing Device................ 46
Correlation of Timing Headgear with Commercial Timing Device and
P patient D iary ............................................................................ . . ........ 48
F o rc e D ata ................. ........................................................................................ .. 5 0
V ariations betw een H eadgears ..................................................... .............. 55
Variations within Headgears over Tim e........................................ .............. 58
T ooth M ovem ent D ata ............................................................... ................... 59

5 SUM M ARY AND CONCLUSIONS ................................................. .............. 68

R E F E R E N C E S ............................................................................................................ 7 1

BIOGRAPHICAL SKETCH ............................. ............76















LIST OF TABLES


Table page

3-1. Sam ple of data captured spreadsheet ............................................ .............. 24

4-1. Pretreatm ent averaged digitized values ........................................ .............. 37

4-2. Post-treatment averaged digitized values ...................................... .............. 37

4-3. Tim ing data spreadsheet sum m ary ............................................ .............. 44

4-4. OTFR and third party logbook correlation ................................................. 45

4-5. Affirm and third party logbook correlation. ................................................ 46

4-6. A ffirm and O TFR correlation ....................................................... .............. 47

4-7. Patient's diary, Affirm, and OTFR headgear data. ...................................... 48

4-8. Subject 1 Modeling voltage as a function of force (weight). ........................ 55

4-9. Subject 2 Modeling voltage as a function of force (weight). ........................ 56

4-10. Subject 3 Modeling voltage as a function of force (weight). ....................... 56

4-11. Subject 4 Modeling voltage as a function of force (weight). ....................... 57

4-12. Subject 5 Modeling voltage as a function of force (weight). ....................... 57

4-13. Serial study models centroid distance data................................................. 60

4-14. Summary of total and annualized centroid change ..................................... 61

4-15. Descriptive statistics of molar displacement. ............................................. 61

4-16. Linear trends of centroid graphs .................................................. .............. 63
















LIST OF FIGURES


Figure page

3-1. Orthodontic Time / Force Recording Headgear. ........................................... 15

3-2. Schematics of electronic circuitry of the OFTR headgear. ............................ 17

3-3. Three-day data capture of sample patient...................................................... 18

3-4. Custom N ance appliance. ................ ....................................................... 20

3-5. Study model of Nance cemented in place ..................................................... 21

3-6. Tem plates placed on study m odel ................................................... .............. 22

3-7. Centroid displacement and spatial analysis .................................................. 22

3-8. M icroScribe 3D X ......................................................................................... 23

3-9. Finite elem ent analysis ..................................................................... .............. 25

3-10. Centroid displacement and spatial analysis .................................................. 26

3-11. Finite elem ent analysis ..................................................................... .............. 26

3-12. Sam ple object rendering (sim ulation). .............................................. .............. 27

3-13. Sample of serial superimposition object rendering (simulation). ........................... 27

3-14. Computer generated emulation of three-dimensional displacement. ................. 28

3-15. Study design flow chart .................................... .......................... .............. 30

4-1. P retreatm ent m odels ............................................................... ................... 37

4-2. Post-treatm ent m odels. ............................................. ............. .............. 37

4-3. Digital conversion of pre-treatment structures into three-dimensional graphics... 38











4-4. Digital conversion of post-treatment structures into three-dimensional graphics. 38

4-5. Digital superimposition of digitized structures on palatal rugae ....................... 39

4-6. Occlusal view, calculations and graphical emulation .................................... 40

4-7. Posterior view, calculations and graphical emulation.................................... 41

4-8. Buccal view, calculations and graphical emulation....................................... 41

4-9. Patient RS Force calibration recording. ................................. .................... 51

4-10. Patient R S Force / V oltage plots .................................................. .............. 52

4-11. Scatter plot of force/voltage data of entire calibration set.............................. 53

4-12. Subject 1 C entroid graph ................................... ....................... .............. 62

4-13. Subject 2 C entroid graph ................................... ....................... .............. 62

4-14. Subject 3 C entroid graph ................................... ....................... .............. 63

4-15. Subject 4 C entroid graph ................................... ....................... .............. 63

4-16. Subject 5 C entroid graph ................................... ....................... .............. 63

4-17. Mechanism of potential en-mass distalization............................................... 66















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

THREE-DIMENSIONAL CHARACTERIZATION OF MAXILLARY MOLAR
DISPLACEMENT SUBSEQUENT TO HEADGEAR TREATMENT WITH RESPECT
TO TIME AND FORCE OF APPLICATION DEVELOPMENT AND PILOT TEST
OF A NOVEL STUDY METHOD

By

Yossi Bar-Zion

May 2000

Chair: T. T. Wheeler
Major Department: Dentistry

Orthodontic headgear for the correction of class II malocclusions has been used in

orthodontics since the 1800s. Although the headgear is quite popular in the orthodontic

community, the literature is rather contradictory and ambiguous with respect to the

amount of time and force necessary for optimal treatment results.

A potential source of error leading to the large inconsistencies involving the

orthodontic headgear research may be due to the complexity and difficulty of measuring

the outcome results objectively, as well as accurately monitoring the time and force of

applications. Discrepancies involving inaccurate data collection as well as outcome

analysis could potentially lead to misinterpreted findings and contradictory conclusions.

The purpose of this study was to develop and pilot test a research methodology to

objectively study, measure, and analyze orthodontic treatment outcome subsequent to

headgear therapy with respect to time and force of application.









To effectively evaluate the therapeutic effect of the headgear, a novel orthodontic

time/force recording (OTFR) headgear was developed, capable of monitoring and

recording compliance as well as force levels in realtime. The second component of this

study involved the development of a digital three-dimensional measurement system for

the quantitative and qualitative analysis of the treatment effects.

Data collected on a pilot sample of patients treated with our newly developed

OTFR headgear were analyzed in order to establish the validity of this device in clinical

research, and was compared with the currently used compliance monitoring method the

self reported diary. Study models taken on this group of patients at monthly intervals

were digitally analyzed using the three-dimensional measurement system for the

characterization of molar displacement and the pilot testing of the technique.

The testing of the three-dimensional analysis system has been shown to provide

qualitative as well as quantitative results with respect to the molar's spatial displacement

subsequent to headgear use. The OTFR headgear appeared to be valid for the monitoring

of compliance. The use of patients' self-reported logbook did not correlate with the true

compliance as measured using two separate digital timing devices. The future use of such

logbooks for the monitoring of compliance does not appear to be warranted.

Future implementation of this novel research design in clinical studies would

provide invaluable insight into the treatment effects of orthodontic headgear therapy by

facilitating intensive real-time data collection and objective three-dimensional tooth

movement analysis.















CHAPTER 1
INTRODUCTION


Extra-oral force applications to distalize molars for the correction of class II

malocclusions have been used in orthodontics since the 1800s. Historically, extra-oral

maxillary traction appliances were used to improve the dental relationship between the

maxilla and the mandible, as well as the skeletal relationship between the two jaws

(Firouz et al., 1992). Perhaps the most popular of all orthodontic extra-oral maxillary

traction appliances is the orthodontic headgear (Proffit, 1986). The appliance, simplistic

in its concept and design, consists of three basic components: a facebow, strap, and force

module. The facebow is made up of two parts, the inner bow that is designed to engage

the maxillary molars via special attachments placed on orthodontic bands, and the outer

bow to which an extra oral vector of force is applied. The strap, commonly made of

flexible material to conform to the back of the patient's neck or head, is used to

reciprocate the tension produced by the force module. The force module, the link

between the strap and the facebow, may be composed of various materials ranging from

elastic to nickel titanium, and is capable of transferring a range of forces to maxillary

molars via the facebow. There are several types of headgears available for the

orthodontist's use, and the choice is often dictated by the skeletal and dental diagnosis as

well as clinician's preference (Ucem & Yuiksel, 1998; Chaconas, 1976).









Although the use of headgear is quite popular by the orthodontic community, the

literature is ambiguous with respect to the amount of force necessary for effective and

predictable outcome, namely molar distalization. The forces reported vary from 300gm

(Weislander, 1974) to as much as 1000gm (Watson, 1972) per side. There is also

ambiguity on the amount of time the appliance is to be worn to achieve molar

distalization. Armstrong (1971) and Badell (1976) suggest continuous headgear wear (24

hours a day) to achieve optimal orthodontic results, while others advocate intermittent

wear. Furthermore, there is a broad inconsistency in the treatment duration which varies

from several months (Firouz et al., 1992; Watson, 1972) to several years (Weislander,

1974). Ironically, the amount of reported distalization has been rather similar, about 2-

3mm, regardless of the force level and time of wear (Weislander, 1974; Baumrind et al.,

1981; Watson, 1972; Firouz et al., 1992). Generally, most studies report about a 2.5mm

distalization in about 6 months, using an average force of 500gm per side (Ucem &

Yuiksel, 1998; Firouz et al., 1992; Badell, 1976).

This widely reported variability on both force and duration of wear required for

optimal maxillary molar movement, creates confusion and forces the orthodontist to

ultimately rely on anecdotal experiences. Knowledge of the ideal force and time of wear

required for optimal orthodontic outcome would minimize treatment time, patient

discomfort and costs as well as maximize treatment results and outcome. Furthermore,

the efficacy of headgear treatment could be objectively compared to alternative treatment

approaches, such as intra-oral appliances, with respect to cost effectiveness and outcome

results.













Purpose of Study

The purposes of this study were to develop and test a study model, design and

methodology to objectively study, measure, and document not only orthodontic treatment

outcome subsequent to headgear therapy, but also the mode of the obtained correction.

Only by accurately measuring the time appliance wear and force of application, as well as

the subsequent outcomes, can the mechanism of the observed treatment results be

interpreted. Insight into the mechanism and mode of the treatment outcome, could

potentially lead to a more efficient use of present orthodontic appliances, as well as help

in the development of future orthodontic therapy. Furthermore, results of such a study, as

well as future use of the study design and methodology, may provide invaluable data for

the understanding of optimal orthodontic forces and physiologic tooth movement, a

subject under great deal of controversy and uncertainty (Lee, 1996; Nicolai, 1975).



Objectives

The objectives of this study include:

1. To develop a system for precise and accurate measurement tooth movement in three

dimensions of space capable of characterizing the precise tooth movement in terms

of finite elements such as mesial-distal movement, buccal-lingual movement,

intrusion-extrusion, torque, tip, and rotation.

2. To pilot test the reliability and validity of a newly developed force/time recording

headgear with respect to time measurements.






4


3. To test the validity of patients' self-reported compliance logbook.

4. To pilot test the reliability and validity of a newly developed force/time recording

headgear with respect to force measurements.

5. To characterize, using descriptive statistics maxillary molar displacement, subsequent

to headgear wear with respect to force level and wear duration in a pilot sample of

patients.
















CHAPTER 2
REVIEW OF THE LITERATURE


As previously discussed, there is much controversy and conflicting reports on the

optimal use and expected results with orthodontic headgear. Such conflicting reports exist

with respect to outcome (Weislander, 1974; Baumrind et al., 1981; Watson, 1972; Firouz

et al., 1992), force of application (Ucem & Yiiksel, 1998; Tanne & Matsubara, 1996), and

optimum time of wear (Armstrong, 1971; Badell, 1976; Weislander, 1974; Watson,

1972).

Historical Overview

Monitoring of Time

One possible explanation for the uncertainty and disagreement with regards to the

force and duration of wear required to achieve effective molar distalization in various

studies, may be due to tooth movement measurement error, as well as the patient's wear

compliance and lack of effective active force estimation. Many such studies are

retrospective and estimation of patient wear compliance is therefore not applicable.

Prospective studies, for the most part, have generally relied on total patient cooperation

and did not specifically attempt to measure the amount of appliance wear time. The few

studies, which have made and attempt to record and quantify patients' compliance, have

done so through the use of a self-reported diary (Kirjavainen et al., 1997; Firouz et al.,

1992). While many researchers consider the self-reported patient diary as the gold









standard for compliance monitoring in orthodontic study design, there is no

published data supporting its reliability and validity.

There have been several attempts to combine a timing device into an orthodontic

headgear reported in the literature (Guray, 1997; Banks, 1987; Northcutt, 1976), as well as

one such device commercially available for headgear compliance monitoring (Affirm,

Ortho-Kinetics, Vista, CA). All of these timing devices, although varying in complexity

of design, operate on the same basic premise. When the force module exceeds a certain

preset destination the internal clock starts or resumes counting time, when the force

module is below the preset distention, the counting stops. In its simplest form, these

timing devices are basically modified stopwatches. Thus these devices lack the ability to

characterize the compliance pattern, such as time of day headgear is worn, days of week,

length of different wear periods, and other related parameters. Such parameters may

prove crucial in the interpretation of the data, particularly in a study set to correlate

treatment with treatment effects and outcomes. Furthermore, while few reports of a

timing device incorporated into an orthodontic headgear exist, no device which is capable

of monitoring the force of appliance application as well as monitoring of compliance has

yet to be reported on.

Monitoring of Force

The second component, which may have contributed to the large variations in the

results of different clinical studies, includes the monitoring of force of application in real

time.

The relationship between magnitude of orthodontic force application and rate of

tooth movement is a subject of controversy (Quinn & Yashikawa, 1985). Several









investigators have attempted to study the relationship between tooth movement and force

application in animal (Pilon et al., 1996; King et al., 1991) as well as human models (Lee,

1995; Andreasen & Zwanziger, 1980; Andreasen & Johnson, 1967; Boester & Johnston,

1974; Hixon et al., 1970, Hixon et al., 1969). While it is generally accepted that teeth

subjected to orthodontic forces will respond, the magnitude of optimal forces is unclear.

Optimal forces reported in the literature, vary from 140 grams (Boester & Johnston,

1974) to as much as 500 grams (Anreasen & Zwanziger, 1980). All the aforementioned

studies were conducted on teeth subjected to continuous forces. The study of optimal

forces required for maximal tooth movement using the orthodontic headgear would be

considerably more complex.

Studies measuring the forces produced by the headgear have been attempted both

in vitro (Tabash et al., 1984) as well as in vivo (Bratcher et al., 1985). These studies were

able to gauge the force of application only in static situations, a method that is of little use

in longitudinal clinical studies, due to the highly variable nature of the force of

application generated by the orthodontic headgear (Johnson et al., 1999).

Previous clinical studies involving the headgear have assumed constant force of

application, measured at time of appliance adjustment. The actual forces, however, may

be quite different then that anticipated by the clinicians and researchers, due to force level

variation. This potential error in force estimation during headgear wear, along with

compliance issues previously discussed, may have lead to misinterpretation of previously

reported data.

The required dynamic, real-time, monitoring of force of application in clinical

headgear studies has not yet been developed and addressed.









Measurement of Tooth Displacement

The final component of previous clinical studies involving the orthodontic

headgear, which may potentially have contributed to the wide variability in outcome

results, involves potential errors in the measurement of tooth displacement. Such errors in

measurement could lead to misinterpretation of the actual treatment effects by under- or

over-estimating the true molar displacement. There are several methods of measurement

of maxillary molar displacement. The three most popular techniques include:

radiographic measurements, photographic assessment, and molar cusp classification.

Radiographic measurements

This technique is by far the most popular method of measurement. This technique

utilizes digitized lateral cephalograms, and uses one of multiple available analysis

(Johnston, 1986; Baumrind et al., 1983; Riola et al., 1974). Using cephalometric

radiographs is probably the simplest and most convenient technique as these types of

radiographs are obtained as a standard part of regular orthodontic treatment. This

methodology is used extensively in both retrospective studies (Baumrind et al., 1983;

Derringer, 1990) as well as prospective clinical trials (Keeling et al., 1998). Briefly, the

lateral cephalometric radiographs are obtained before and after treatment. Predetermined

landmarks are then digitized, and, using one of several analyses, the maxillary molar

position is calculated with respect to stable craniofacial structures. The pre- and post-

treatment measurements are then compared to calculate the maxillary molar movement.

An alternative method of evaluating molar movement from radiographs involves

superimposing the pre- and post-treatment radiographs and directly measuring molar

movement (Isaacson et al., 1976).









There are several problems and difficulties associated with the radiographic

measurement technique:

1. The cephalometric radiographs are taken at 6 monthly intervals, in order to

minimize patient radiographic exposure. Consequently, short time

observations of molar movement are impossible.

2. Radiographs introduce artifacts and distortion. It is very difficult, if not

impossible, to position the patient's head exactly in the same orientation 6

months after the initial radiograph. Even small deviations would result in

erroneous measurements. Furthermore, any changes in the distance between

the patient's head and the film would cause magnification changes which,

compounded with any angular position differences add variability between the

radiographs. These variations are especially critical when small differences in

measurements are anticipated.

3. Measurement errors and variability are introduced during the tracing and

digitizing process (Keeling, 1993). Once again, these errors are critical when

small increments of movement are to be detected.

4. The cephalometric assessment only captures the craniofacial structures in a

two-dimensional plane: horizontal (anterior-posterior) and vertical. Any

changes in the transverse plane are overlooked and consequently lost. This

eliminates very important information on maxillary molar movement with

respect to expansion, constriction, rotation, and torque.









Photographic assessment

This technique obtains a photographic picture of the study model, by utilizing a

camera or a photocopy machine (Singh & Savara, 1971). In short, the pre- and post-

treatment study models are taken of the patient using routine alginate impressions. The

models are then trimmed and the occlusal surface is either photographed using a camera

placed perpendicular to the occlusal plane or by 'photocopying' the occlusal surface. The

photograph is then digitized, and, using the palatal rugae as a stable structure, tooth

displacement is measured from serial casts. Problems involved with this technique are the

following:

1. The technique relies on the occlusal plane, which would be changing

subsequent to orthodontic treatment.

2. The photograph of a three-dimensional study model converts the model into a

two-dimensional record.

3. Any changes in the vertical plane are undetectable due to the two-dimensional

transformation and are consequently lost. This eliminates important

information on maxillary molar movement with respect to extrusion,

intrusion, tip, and torque.

4. This technique relies on the structural stability of the palatal rugae for tooth

movement measurement. The palatal rugae, however, have been shown to

undergo significant changes in orthodontically treated cases (van der Linden,

1978).









Molar cusp classification

This particular technique is potentially the least reliable of all maxillary molar

displacement measurement techniques. This method evaluates the maxillary molar

displacement with respect to the lower first molar. For this method, maxillary and

mandibular study models are obtained and intercuspated, and the change of maxillary

molar position is observed, over time, by measuring points on the upper first molar with

respect to the lower first molar (Bondemark & Kurol, 1992). This method operates under

the premise that despite the documented imprecision in the research utilization of the

technique (Keeling et al., 1996), if appliances are not placed on the mandibular arch, no

appreciable changes should occur and so the mandibular molars could be used as a stable

point of reference. Such assumptions, however, are far reaching at best as significant

changes in the mandibular arch growth and development, using a headgear in the absence

of any mandibular arch appliances have been reported on (Tulloch et al., 1998; Keeling et

al., 1998; Kirjavainen et al., 1997).

Three-Dimensional Cast Analysis

Although this technique has been used in limited capacity in tooth movement

studies (Richmond 1987; Bhatia & Harrison, 1986), this system of measurements has the

potential, in theory, to be the most accurate (Jones, 1991). The analysis is achieved by

obtaining the three coordinates of several points on the model and then mathematically

orienting them in space (Bar-Zion et al., 1998). There are several approaches to obtaining

the spatial coordinates of the object surveyed including:

1. Reflex Metrograph (Swessi & Stephens, 1993; Richmond 1987; Bhatia &

Harrison, 1986). This instrument basically consists of a semi-reflecting









mirror; therefore, an object standing in front of the mirror has its image at an

equal distance behind the mirror. Working on this principle, a moving light

source connected to a three dimensional (X,Y,Z) slide system behind the

mirror can be used to record points corresponding to the image of the object.

The accuracy of the Reflex Metrograph has been tested by Richmond (1984,

1987) and the error found to be less then 0.27 mm. For linear distances,

however, Richmond (1987) reported mean errors as high as 1.06 mm.

2. Electronic Surveyor (Bar-Zion et al., 1998). This instrument is comprised of a

sliding table that measures linear displacement on the 'X' and 'Y' axis. A

vertical telescopic arm obtains the 'Z' axis. In a small sample study this

instrument proved to be accurate and reproducible in surveying dental casts to

about a 0.2mm error.

3. 3-D Digitizers. This technology is rather new and allows the three-

dimensional coordinates of an object to be imported directly into a personal

computer for further analysis. The computer program could then render the

object in virtual dimensions, allowing complex manipulations and

measurements, otherwise deemed impossible. There are three basic types of 3-

D digitizers, and they are classified according to their object capturing and

digital conversion approach. The different types include ultrasonic, magnetic,

and mechanical digitizers. Ultrasonic: Ultrasonic digitizers transmit sound

waves and triangulate coordinates in 3D space using transmitters mounted to

the wall or ceiling. Ultrasonic systems are deemed the least accurate and are

the most susceptible to geometric distortions. Under the best conditions,









ultrasonic systems do not typically provide accuracy better than 2mm

(manufacturer specifications, Artma, Utah, USA). Magnetic: Magnetic 3D

digitizers work on the same principle as ultrasonic systems, using a magnetic

field as the signal medium to triangulate spatial locations. These types of

digitizers are very sensitive to distortions resulting from nearby metal or

magnetic fields, and can generally produce resolution up to 1.5mm

(manufacturer specifications, Artma, Utah, USA). Mechanical: The

mechanical 3-D digitizer relates the stylus's position in space via a series of

mechanical arms which tracks its movement utilizing digital optical sensors at

each joint. Since this type of data capturing is strictly mechanical, it is

virtually unsusceptible to external interference and distortion, producing

digitizing data with accuracy of 0.25mm (manufacturer specifications,

Immersion Corporation, San Jose, CA).

The various studies which have utilized this type of three-dimensional surveying,

used either various teeth (Swessi & Stephens, 1993) or the palatal rugae (Bhatia &

Harrison, 1986) as the reference point for calculating dental displacement. This approach

may introduce much error and distortion for a tooth movement study as both the teeth and

the palatal rugae change their three dimensional conformation during orthodontic tooth

movement (van der Linden, 1978). Despite the fact that implementation of such three

dimensional cast analysis utilizing the palatal rugae, a structure with questionable

stability during tooth movement, may lead to some distortion of measurements, it still

may potentially offer a more accurate and reliable measurement of true displacement.









This technique has not yet been fully developed, tested, or implemented in a study of

dental changes subsequent to orthodontic headgear therapy.

Summary

When critically reviewing the present literature involving the orthodontic

headgear outcome effects, it is apparent that previous studies contain basic flaws that

could significantly affect the data and the interpretations of the results. Since the

headgear is indeed a popular appliance that has been used by orthodontists for over a

century, a close and careful evaluation of the treatment outcomes is warranted.

Addressing the potential confounding factors present in the previous studies,

namely the monitoring of compliance, force of application, and precise tooth

displacement measurement may provide a more objective insight into the therapeutic

potential of the orthodontic headgear. Furthermore, the development of methods and

protocols to accurately measure and record appliance compliance, force application, and

tooth displacement, could impact future studies by providing more effective and reliable

alternatives to the current methodology.















CHAPTER 3
MATERIALS AND METHODS


Orthodontic Time/Force Recording (OTFR) Headgear

To effectively evaluate the therapeutic effects of the orthodontic headgear

utilizing a clinical study, a dynamic system of accurately measuring compliance as well

as force of application in real-time is required.

Such novel timing headgear, capable of measuring compliance as well as force of

application (OTFR Headgear) has been recently developed in our laboratory (Figure 3-1).













Figure 3-1. Orthodontic Time / Force Recording Headgear.




The OTFR headgear is equipped with three unique components that not only

allow accurate data recording of force and time, but also innovative implements to

circumvent false data collection. The three basic components include the data capturing

microcomputer (Figure 3-1), a force encoder-probe that also doubles as a force module,

and a flexion switch concealed in the neck-strap.









The data capturing microcomputer, utilizes a compact (measures 1.8 in x 1.9 in x

0.6 in) commercially available data logger (StowAway-Volt) by Onset Computer

Corporation (Pocasset, MA). The data logger has on-board a 2.5 volt lithium cell (battery

has a two year life) to power a miniature reduced instruction set computing (RISC)

processor as a controller. Input to the logger is via an analog-to-digital converter, which

measures voltages and converts them to 8-bit results. The data is then stored in a 32

Kbytes EEPROM (non-volatile memory), allowing up to 32,000 samples measuring

voltages for different user determined monitoring periods (6 seconds to 24 minutes

between observations).

The OTFR headgear's force encoder-probe is attached to a custom-made force

module and uses a 100Kohm variable resistance linear potentiometer connected in

parallel with the headgear's spring mechanism (Figure 3-1). This potentiometer is

momentarily powered with voltage from the data logger during each of the 32,000

samples. The logger measures and stores the voltage existing across the potentiometer at

each sample time (Figure 3-2). As the headgear facebow is engaged on a patient, the

headgear spring will distend and the value of the voltage recorded will depend on this

distension. Since the resistance of the potentiometer varies linearly with the stretch of the

headgear spring, it is possible to calibrate the voltages measured by the data capturing

microcomputer with the force being exerted by the headgear spring.

The final component vital to the OFTR headgear's operation is the flexion switch,

concealed within the neck-strap (Figures 3-1, 3-2). The switch is activated when the neck

strap is bent or flexed signaling that the headgear is in fact being worn. The flexion

switch is integrated into the electronic circuitry to circumvent any potential false reading









when the headgear is not being worn. Such interceptive measure is necessary due to the

complexity of the force probe-encoder that may, due to hysteresis, mode of transport and

storage, or inadvertent as well as intentional manipulation of the headgear by the study

patient, encode a force measurement in the absence of wear. The flexion switch

completes the circuit (Figure 3-2) only when the OTFR headgear is being worn by the

patient, and therefore essentially eliminates all false positive force readings.





Jz ----U-----
Flexion Switch
Data Capturing Flexion Switch
Microcomputer V
2.5 V__ I v vAAAAAAAAAAAAA

33KQ 10KQ 100KQ variable resistor

Figure 3-2. Schematics of electronic circuitry of the OFTR headgear.


The data recording microcomputer is capable of data capturing at different preset

time intervals. Typically the time interval is set at two minutes, which allows sufficient

memory for 45 days of active data recording. At each appointment the data is

downloaded to a Pentium based personal computer, using a special program designed to

read the encoded data in terms of voltage, time, and date. The data capturing

microcomputer is then re-set and is thereafter ready for another 45-day session of data

recording. The data is initially reported as a series of values of voltage over date and time

recorded (Figure 3-3). Due to the linear fashion force-encoder potentiometer, the values

are readily converted into force units such as grams or ounces. The interpolation

conversion is facilitated by a data calibration set, performed by loading the force-







18



recording module with known weights at each appointment. These measurements of force


calibration can then be used to evaluate the reliability and consistency of the headgear's


force encoder. A recently developed algorithm, written specifically to calculate the total


wear-time as well as average force values then further interprets the data.




3-
/Flexion switch not activated

2 5 ----- ------



2 5

4J 1 5 -n---------


Flexion switch activated / Active data collection


0 (D CO 'T 0 0 CO 'T 0 0 CC CO 0 D V CO 0 V 0 CO 'T 0 V 0 CO 'V 0 CC
0 o (3 M 0 LO 0 'T 0 O LO '0 0 (0 M 0 01 (' 0 LO 0 'T LO 1 0
01 m m m 0 0 0 01 00. (0 m L o0





Figure 3-3. Three-day data capture of sample patient.





Development of Tooth Displacement Measurement


The second critical part of a study set to measure orthodontic headgear therapy


outcomes involves the physical measurements of change produced from treatment. As


previously discussed one main parameter of successful treatment is dental movement and


specifically maxillary molar distalization. Much of the body of literature reported on


headgear effects has measured this anticipated molar displacement in methods that, as


-1
0





05


0









described in chapter 2, are inaccurate, potentially distorting, difficult to measure, and not

practical or feasible in the measurement of very small dental movements.

Stable Reference Point

In order to characterize and measure an object's movement in space, a stable

landmark for three-dimensional superimposition is necessary. In this particular study,

characterizing the maxillary molar's movement would be feasible if a stable landmark

could be found or determined. Basically the landmark would have to be limited to the

maxilla, and be acquired via maxillary study model impressions.

A study reported by Almeida et al. (1995), set to determine the stability and

suitability of the palatal rugae as a stable landmark, has found significant dimensional

changes to occur at the lateral points of the rugae, particularly following headgear

treatment. The medial points of the second and third rugae, Almeida had suggested, were

an appropriate landmark for serial study-model longitudinal study, despite some

dimensional changes. Baily et al. (1996) repeated Almeida's protocol studying the

stability of the palatal rugae in a series of orthodontically treated patients. Baily's

findings showed that all rugae landmarks were statistically significantly different and

have altered during the course of treatment. Despite her findings, Baily has suggested that

perhaps due to the small changes in the rugae pattern, the changes may be too small for

clinical significance and could potentially be used as a stable landmark pending further

studies. Baily's findings were consistent with those of other investigators (Van der

Linden, 1978) who also reported significant changes in the palatal rugae' configuration

after orthodontic treatment. Although Almeida and Baily have suggested that small

changes in the rugae dimensional pattern may be acceptable, their suggestion could prove









quite contrary for the study of molar movement. Since the rugae would serve as a

landmark for superimposition, so that objects further away such as the maxillary molars

could be re-oriented in space, very small changes in the rugae could lead to very large

and significant errors in molar measurements when the rugae are superimposed.

Since all structures in the maxillary arch, soft as well as hard tissues, are likely to

undergo some dimensional change due to treatment or growth, an extra-dental stable

landmark needs to be defined. This stable extra-dental structure was accomplished

through the use of a Nance button by stabilizing several structures together minimizing

their overall individual displacement, and maximizing the differential displacement of the

objects of interest, the maxillary molars (Figures 3-4 and 3-5).


























Figure 3-4. Custom Nance appliance.




























Figure 3-5. Study model of Nance cemented in place.


Three-Dimensional Digitizing

Once the stable landmark is established, it, along with the object investigated

needs to be digitized; in this particular case, the Nance button and the maxillary molars.

The digitization process will render the selected landmarks, molars and Nance, in terms

of their three-dimensional coordinates for computational manipulations and spatial digital

reorientation. It is this digital reorientation that will allow the computer software to

superimpose all the stable landmarks in the series, and consequently calculate molar

movement, from several, serial superimpositions.

In order to mathematically compute movements of one object with respect to

another object in space, the location, and plane of each object is required. The minimal

amount of points that define a plane is three. Therefore, three points are needed for the









stable landmark's orientation, and three points are needed for the molar orientation

(Figures 3-6 and 3-7).


Figure 3-6. Templates placed on study model.


Figure 3-7. Centroid displacement and spatial analysis.









A reproducible and accurate system of designating the three points for both the

molar and the stable structure, was developed and shown to be a reliable method of data

point assignment (Bar-Zion et al., 1998). The system basically consists of well fitting

templates, one for the stable structure and one for the maxillary molar (Figure 3-6). These

templates are outfitted with three precision engraved marks, designating the three points

for data acquisition. The templates are transferred from each serial cast to the next, and

have proved to be rather stable due to their intimate adaptation to the maxillary molar's

occlusal table and the indexing marks on the stable structure (Figure 3-4).


Figure 3-8. MicroScribe 3DX.


Once the templates are made, the study models are secured in place utilizing a

modified vice grip. The templates are then placed on their perspective landmarks, and the

points on the templates are digitized using a mechanical 3-D scanner, MicroScribe-3DX







(Immersion Corporation, San Jose, CA). The MicroScribe-3DX (Figure 3-8) is connected
via a serial port to a Pentium based personal computer, and the data is uploaded directly
into an automated spreadsheet. The data points are stored in the spreadsheet as a series of
three-dimensional coordinates (Table 3-1). Once data is collection is complete, it is
interpreted using specially designed software.



Table 3-1. Sample of data captured spreadsheet.


Patient Name:
Sample Patient
x(mm)
palate 1 268.495
palate 2 273.771
palate 3 265.8814
molar 1-R 255.8717
molar 2-R 261.5681
molar 3-R 263.3255
molar 1-L 246.468
molar 2-L 250.1633
molar 3-L 252.9333


y(mm)
-158.613
-165.122
-168.257
-140.716
-142.661
-137.8
-183.142
-179.785
-185.782


z(mm)
80.9095
81.597
81.1651
87.1222
86.1361
85.9757
88.7872
89.4596
88.4936


Three-Dimensional Analysis
The final component in the characterization of dental displacement is the three
dimensional analysis of the data. As previously discussed, once the coordinates of the
stable landmark as well as the coordinates of the objects of interest in a complete series of
serial study models are obtained, the data is ready to be analyzed. To illustrate and









measure the object's movement in space over time, all different time points need to be

superimposed on the stable landmark (Figure 3-9). This will allow both qualitative and

quantitative characterization of the spatial displacement of the object of interest, in this

particular study the maxillary molar.




I'TI^l 1 I:i l. :l. :
i *
PaIaaIl CoajdLtjtkle
\

-- ', -
ibetween Clandmark and the maxillary molar l Can be calculat Ied and compared

STim3-10). Changes in the geometric ratios between the corresponding coordinates









Figcalculate the3-9. Fimagnitude and vectors of displacement (Figure 3-10).



To detect the overall molar displacement, changes in the centroid distance


between the stable landmark and the maxillary molar can be calculated and compared

(Figure 3-10). Changes in the geometric ratios between the corresponding coordinates

could be deciphered as three-dimensional spatial changes and could be resolved to

calculate the magnitude and vectors of displacement (Figure 3-10).

In order to discern and measure small spatial changes, the investigated object's

movement can be reduced to its finite elements of movement (Figure 3-11). These finite

elements are used to individually look at the various components of the overall spatial








displacement (Figure 3-11). The movement of any object in space is made up of travel in

the three planes: Sagittal (mesio-distal), transverse (bucco-lingual),

and vertical (intrusion-extrusion) (Figure 3-11). Any two of the three vector

resultants could then be used to calculate the angular change of the surveyed object:

Transverse and sagittal vector combination will render rotational changes; transverse and

vertical vectors combination will render tip and torque angular changes; sagittal and

vertical vectors combination will render tilt angular changes.


Figure 3-10. Centroid displacement
and spatial analysis.


Figure 3-11. Finite element analysis.


The maxillary molar's movement can also be evaluated qualitatively using three-

dimensional rendering software. This software can be specifically programmed to

digitally superimpose the data on the stable landmark, and subsequently render a

graphical representation of the displaced object. The rendered graphical illustration could

then be viewed from any position and angle in space, adding a new dimension to the data


F -i

r.r









interpretation. This represented data will be displayed in terms of triangular objects in

space each representing its respected object (Figure 3-12). Each digitized point is

represented as a point forming the vertex of a triangle. When a series of data points are

visualized in this manner, the graphical representation illustrates the spatial displacement

of the molar, over time, with respect to the Nance button (figure 3-13). Using specially

developed graphical software, the spatial displacement can potentially be viewed from

any angle.





Nance button coordinates Nance button coordinates





Occlusal view


Maxillary molar coordinates
Maxillary molar coordinates
at three simulated times


Figure 3-12. Sample object rendering Figure 3-13. Sample of serial
(simulation). superimposition object rendering
(simulation).





Once the three dimensional calculations are obtained, the software is able to

provide quantitative results in terms of angular and absolute displacement from the

perspective point of view. Furthermore, the computer can utilize substitutional emulation

to generate preset views along with a molar figure substitution to provide a more familiar

view of the molar's spatial displacement (Figure 3-14).











































Figure 3-14. Computer generated emulation of three-dimensional
displacement.





Clinical Data Collection

Subject Selection

To pilot test the study model developed, a sample size of five patients was

selected to participate in the study.









Inclusion criteria

1. Patient requires headgear therapy as part of orthodontic treatment.

2. At least 1/ cusp class II dental relationship.

3. First maxillary molars as well as first or second maxillary bicuspids fully

erupted (for the placement of the Nance button).

4. Patient agrees to wear special timing headgear for 6 month

5. Patient is able to present to the clinic for records at monthly intervals

6. Patient is in good health and free of dental disease

Exclusion criteria

Patients not fitting inclusion criteria

Study Design

A flow chart representing the study protocol is depicted in figure 3-15.

In order to test the validity of the timing devices, one of the patients' mothers was

asked to personally place and remove her daughter's headgear as well as record the time

of wear episodes in the assigned log-book. With the single exception of the compliance

diary entries recorded by her mother, this patient followed the same protocol as the other

subjects.















1. Informed consent
2. Separators placed for maxillary molars and Second premolars (First premolars are
used if second premolars unerupted)


One week

3. Bands are cemented on first maxillary molars
4. Bands are fitted for maxillary premolars and picked-up for custom Nance button
5. Maxillary premolars separators are replaced

One week

6. Nance button is cemented to premolars, anterior prongs are bonded to the
maxillary central incisors
7. Maxillary facebow is selected and fitted

One month

8. Cephalometric radiograph taken
9. OTFR headgear calibrated and set to capture data at 2 minute intervals
10. Commercially available timing module is re-set and place on contralateral side of
neck-strap
11. Patient compliance diary is dispensed
12. Two maxillary alginates are taken
13. Intra- and extra-oral photographs taken



4 X one month Repeated four times

14. Data from OTFR headgear is downloaded and saved
15. Data from alternative timing module is downloaded
16. Patient compliance diary is collected
17. Steps 9-13 are repeated

One month

18. Steps 9-17 repeated
19. Cephalometric radiograph taken
20. Conventional headgear dispensed
21. Continued standard orthodontic treatment


Figure 3-15. Study design flow chart.









Initial appointment: After obtaining an Institutional Review Board approved

informed consent from the patient, orthodontic separators were placed in preparation for

banding of the maxillary first molars as well as the banding of the second premolars. In

cases where the second premolars had not yet erupted, the first premolars were used.

Second appointment: Bands were fitted for the maxillary first molars as well as

the selected premolars. The premolar bands were then picked-up utilizing an alginate

impression, poured up, and a modified Nance button was later fabricated (Figure 3-5).

The maxillary bands were cemented at this appointment, and the premolars orthodontic

separators are re-placed in preparation for the Nance button delivery in one-weeks time.

Third appointment: The Nance appliance is cemented in place, and the anterior

stabilizing wires are bonded to the maxillary central incisors for added stabilization of the

Nance (Figures 3-4, 3-5), which will serve as the stable landmark in the tooth movement

part of the study. Maxillary facebow is selected and is passively fitted into the maxillary

molars' headgear tubes. A cephalometric radiograph is taken of the patient. The patient

returns to the clinic in one month, allowing any inadvertent forces applied to the

premolars due to the Nance appliance cementation to be expressed. This step is taken to

avoid any potential tooth movement due to the Nance button. Such initial tooth

movement artifact could potentially distort the findings.

Fourth to tenth appointments: At each monthly appointment, for the next six

months, data collection records are taken. Upon patient arrival the data form the OTFR

and the commercially available timer (Affirm, Ortho-Kinetics, Vista, CA) are

downloaded and stored, The patient's self reported compliance diary is retrieved and

filed, The OTFR headgear is calibrated using known weights ranging from 100 to 800









grams. The calibration data is then downloaded and stored, and the OTFR timing

microcomputer is set to record at two-minute intervals. The commercially available timer

is reset and placed on the contra-lateral side of the OTFR headgear's force probe. Two

maxillary alginate impressions are taken and are later poured in lab stone. Intra- as well

as extra-oral pictures are taken. The patient's diary is collected and a new diary is given

to the patient for self-reported compliance. The headgear is adjusted and set clinically to

16 ounces per side using a Dontrix gauge (ETM Corp, Glendora, CA). The patient is

reminded to wear the headgear for 12 hours per day, and is to return to the clinic in one

month for the next appointment.

Eleventh appointment: Following the final record appointment, the patient was

given a conventional headgear, the Nance button was removed (if necessary) and

orthodontic treatment was continued.

Data Analysis

Testing of the Three-Dimensional Molar Measurement System (objective 1)

Before the tooth displacement measurement methodology is used to analyze the

collected study models, the developed analysis system needs to be implemented on a set

of study models that had undergone visible dental change. This is necessary to determine

the feasibility of the system to analyze data when change is obviously apparent. Should

none of the study patients experience any measurable dental changes, it could be

ascertained that the system is in fact capable of characterizing molar displacement when

such displacement is present, and an estimate of the technique sensitivity could be

established.









A set of study models, obtained from a patient undergoing headgear therapy who

exhibited significant apparent dental change, was selected from our dental clinic. Since

this set of models was selected retrospectively, it lacks the stable landmark created by the

Nance button. We felt that for this preliminary examination of the molar displacement

measurements system, the palatal rugae could be used. This determination was based on

the facts that the amount of apparent dental movement was so large, that the sensitivity of

the technique of measurement would overwhelm distortion arising from the palatal rugae

deformation, and the technique feasibility could therefore be examined.

The initial and final maxillary models of this selected patient would be digitized

and analyzed according to the methods described above. The results of this section of the

study would be reported and illustrated both as qualitative visual representation of the

gross movement, and also as quantitative linear and angular changes.

Analysis of Timing Data (objectives 2 and 3)

The timing data can be separated into four parts:

1. OTFR headgear data

2. Affirm (commercially available timer) data

3. Actual time of appliance recorded by patient's mother in assigned logbook

4. Patients' self reported compliance recorded in assigned diary

This data will be correlated to answer the various objectives. In order to test the

validity of the OTFR the total time of wear recorded using the OTFR will be correlated

with the known total time of wear recorded by the mother. The data from the Affirm

timer would be correlated with the known time of wear as well as the OTFR. If three sets

of time recordings exhibit statistically significant correlation and their values are similar









in magnitude, we can assume with reasonable certainty that the OTFR headgear

microcomputer along with its interpolating algorithm is valid in the estimation of wear

time and evaluation of compliance.

Should the OTFR and the Affirm timing data prove valid, the total time of wear

will be correlated with the patients' self reported compliance diary. This will provide an

insight into the reliability of such compliance monitoring method previously utilized in

published clinical headgear studies yet never validated. If the self reported diary does in

fact correlate with statistical significance with the OTFR and Affirm timing data, it would

provide support for the continued use of this popular method in future clinical studies.

Analysis of Force Data (objective 4)

The force data will be used to evaluate the reliability of the OTFR in force

recording measurement utilizing the calibration data, as well as calculating the average

force of application during each period of wear.

Intra-reliability: The calibration data obtained at each monthly visit from each

OTFR headgear would be statistically evaluated to ascertain the ability of the headgears'

force probe to record the same known force levels over time. This particular analysis will

provide insight into the longevity of the OTFR headgears' components, and will

influence future designs. Furthermore, this data will be used to convert the voltage

reading captured by the ORFR microcomputer into the clinically relevant force values.

Inter-reliability: The calibration data from each headgear set will then be averaged

and correlated across all other OTFR headgears in this study. This analysis will determine

if each individual headgear requires its own calibration data-set or if a single calibration









set will suffice for all manufactured headgear, saving time and resources when the OTFR

headgear is implemented in a large clinical study.

Analysis of Tooth Displacement (objective 5)

All collected study models would be scanned and analyzed for three-dimensional

molar displacement using the newly developed methodology described above. The results

would be evaluated both qualitatively and quantitatively.

Qualitative results would provide insight into the general pattern of maxillary

molar displacement following headgear therapy, should such a pattern in fact exist.

Quantitative results would be described in terms of overall displacement in each plane of

space, as well as respected angular changes. The results will be further reported in terms

of displacement from time-point to time-point, as well as overall changes, further

assisting in detecting a possible pattern of displacement, should one in fact exist.

Should a pattern of maxillary molar spatial displacement be detected, it will be

correlated and related to the time and force of application. Such findings will suggest the

significance that force and time of application bear on tooth movement, as well as

provide insight into the potential of future investigations to determine the ideal force

levels and time of applications necessary for optimal outcomes.















CHAPTER 4
RESULTS AND DISCUSSION


Tooth Displacement Characterization of a Selected Study Model

Study models of a nine-year old orthodontic patient undergoing headgear therapy

were selected to test the tooth displacement model. The patient's pretreatment (Figure 4-

1) and post-treatment (Figure 4-2) models had exhibited an apparent large maxillary

molar displacement. This could be visibly noted by the space apparently created between

the first molars and the maxillary second primary molars. These study models were

selected retrospectively, and so they lacked the fabricated stable landmark developed for

the subjects enrolled in the prospective study. It was determined to use the palatal rugae

as the stable landmark for the analysis of these study models. This was done with two

considerations:

1. The stability of the palatal rugae could be evaluated using the three-

dimensional analysis software for their suggested stability (Baily, 1997;

Almeida, 1995).

2. It was determined that despite potential deformation in the palatal rugae

secondary to treatment, the apparent large magnitude of maxillary molar

displacement could still be detected.


























Figure 4-1. Pretreatment models. Figure 4-2. Post-treatment models.








The models were digitized and analyzed as described in chapter three. Each

model was digitized five consecutive times, and the means were used with three-

dimensional analysis software to produce quantitative and qualitative results of maxillary

molar displacement (Tables 4-1 and 4-2).


Table 4-1. Pretreatment averaged
digitized values.

Time 1 X (mm) Y (mm) Z (mm)
palate 1 264.7176 -148.7966 92.54328
palate 2 268.1068 -140.5322 88.9753
palate 3 261.1059 -131.3662 93.40006
molar 1-R 242.099 -123.398 100.9215
molar 2-R 244.7412 -117.8221 100.382
molar 3-R 249.381 -118.8547 99.96186


Table 4-2. Post-treatment averaged
digitized values.

Time 2 X (mm) Y (mm) Z (mm)
palate 1 260.7638 -152.242 88.82768
palate 2 264.8879 -143.3413 85.91742
palate 3 256.9131 -133.9568 89.893
molar 1-R 234.9356 -126.9538 95.98292
molar 2-R 237.2209 -120.5735 95.86216
molar 3-R 241.7571 -121.1681 96.4798
























Figure 4-3. Digital conversion of pre-treatment structures into three-dimensional
graphics.


Figure 4-4. Digital conversion of post-treatment structures into three-dimensional
graphics.


10. 4k


MMOOO.









Values were entered into the digital graphic rendering software, which used the

three-dimensional coordinates to generate two triangles, each positioned in space at its

digitized spatial location. One triangle represented the palatal rugae triangle, and the

other represented the molar occlusal table triangle (Figure 4-3).

Both models were digitally converted into a three-dimensional graphical

representation in the manner described above. Post-treatment models (Figure 4-2) digital

conversion is illustrated in figure 4-4. Once both models were in digital form, the

software identifies each set of palatal and molar triangles (Figures 4-3, 4-4), and

mathematically grouped them together in space. The computer then treated each set of

triangles as a separate object, such that when each object was manipulated in space, its

related structures and their spatial relationships remained static. This procedure was

crucial in preparation for the next step of palatal superimposition (Figure 4-5).






Initial Final Superimposition










Digital conversion of Digital conversion of Digital superimposition of pre-
pre-treatment post-treatment and post-treatment structures

Figure 4-5. Digital superimposition of digitized structures on palatal rugae.









The palatal triangle of each set of related structures was then identified, and the

analysis software mathematically found the best-fit spatial capture for the palatal

triangles. The best-fit algorithm was designed to place both palatal triangles on the same

spatial plane, simultaneously altering their corresponding molar triangle to its

interpolated spatial position, and then rotate the triangles until geometrical best fit was

achieved.

The resolved molar triangles were then graphically rotated to obtain the desired

views (Figures 4-6, 4-7, and 4-8). Both qualitative and quantitative evaluations were

performed in this manner. To aid in the measurement and visualization of the spatial

displacement the software was programmed to calculate the geometric centroid of each

molar triangle and place a vertical line perpendicular to each molar's occlusal table

through its geometric centroid. Magnitude of spatial displacement as well as angular

changes were then calculated and reported in orthodontic terms, to provide clinically

useful information (Figures 4-6, 4-7, and 4-8).


Figure 4-6. Occlusal view, calculations and graphical emulation.


9.54- Mesiobuccal rotation
2.676 mm Distal
0.759 mm Buccal

Palatal triangle


Molar initial


C- Molar final

















Palatal triangle


Molar final






Molar initial '


5.050 Buccal crown torque
0.759 mm Buccal expansion
0.312 mm Extrusion


ApiciI1


Figure 4-7. Posterior view, calculations and graphical emulation.


Figure 4-8. Buccal view, calculations and graphical emulation.


O(cclIuiI,


Molar initial

Palatal triangle



Molar final

4.960 Distal crown tip
2.676 mm Distalization
0.312 mm Extrusion


Apical


(O)cclIul











The newly developed analysis system was capable of providing both quantitative

as well as qualitative measurements of the spatial molar displacement. This analysis

system, though employed utilizing the palatal rugae, was still capable of producing

results with reasonable resolution. The palatal rugae, as anticipated, underwent some

dimensional deformation evident by the slight differences in the palatal triangles

representation (Figure 4-5). The use of the Nance button as the stable landmark would

have afforded more accurate superimposition for even greater resolution in detecting yet

smaller spatial displacements. The ability of this system of analysis to successfully utilize

the palatal rugae as a stable landmark further suggests the future potential of this system

in retrospective studies as well as prospective studies. Though the resolution may have

been compromised due to the somewhat dimensionally unstable nature of the palatal

rugae, the time points of interest were spaced far enough apart, allowing a larger

displacement to be detected using less resolution. By utilizing the palatal rugae in future

clinical studies, the study design could be simplified, eliminating the Nance button

fabrication and all related steps.

The data output of this system was unique and provided clinically relevant and

applicable information. The quantitative results were described in orthodontically

relevant planes of space, as well as applicable angular and linear dimensions. The data

could then be exported into a spreadsheet, allowing for further analysis when related to

time and magnitude of force application, as well as statistical modeling of the pattern and

rate of molar movement. The qualitative results available through the use of this system

provided virtually unlimited views of the treatment effects, from all planes of space. This









visualization potential could allow researchers as well as clinicians an insight into the

true three-dimensional changes that occur during treatment. Changes in the various

planes that were previously undetectable and went unnoticed could now be visualized

from a different plane of space, and their significance could further be explored.

This three-dimensional analysis system is not limited for the detection of molar

movements from study models, but for spatial analysis of virtually any tooth following

small modifications to the data capture protocol. Such application may include the study

of canine retraction, space closure, incisor intrusion, growth and development, or any

such study in which the spatial displacement of one object with respect to another is of

interest.

Timing Data

Timing data collected during this study can be separated into four groups, OTFR,

Affirm, third-person logbook, and patients' diary. Each set of data collected was

imported into a spreadsheet, the third-person logbook and the compliance diaries were

manually entered into a database, the total time of wear was calculated, and results were

imported into the main spreadsheet (Table 4-3). Due to some OTFR malfunctions some

data for several time points were not available. The same held true for some of the diary

data, in which the patient did attempted to record the length of wear or had lost the diary,

and for the Affirm time recorder that experienced some software failure later revised by

the manufacturer.

OTFR malfunctions included situations in which some of the wiring solder joints

came loose during routine headgear wear, force-probe module failure, and some cases of

unintentional breakage due to improper headgear storage and handling.










In performing the correlation estimates, both the Pearson correlation and the

Spearman rank correlation tests were performed. The Pearson correlation test assumes

normal distribution of the actual values and is therefore influenced by extreme values.

The Spearman rank correlation test is a non-parametric test that does not assume a normal

distribution of the data values. Each value is assigned a rank and therefore, the estimation

of the correlation coefficient is not influenced by extreme values. The Spearman rank test

for non-parametric values was determined to be the more appropriate test for analysis of

this data due to the nature of the data set. For the sake of completeness both correlation

coefficients were reported.


Table 4-3. Timing data spreadsheet summary.
Patient ID Start Date End Date Hrs-comp Hrs-affirm Hrs-diary
1 1/28/99 3/3/99 273.3 305.5
1 3/4/99 4/1/99 125.9 126.1 125.25
1 4/1/99 5/13/99 148.6 149.1 149
1 5/20/99 6/8/99 90.7 90.6
1 6/8/99 7/1/99 102.9 103.3
1 5/20/99 5/26/99 39.6 39.5
1 6/12/99 6/13/99 5.9 6.1

2 10/1/98 10/29/98 324.7 285.4
2 10/29/98 12/15/98 428.25
2 12/15/98 1/14/99 258.5 261
2 1/14/99 2/17/99 160.8 191.1
2 2/18/99 3/18/99 87.56 86.7 197
2 3/21/99 5/2/99 122.1 123.6 316

3 12/17/98 1/19/99 112.1 117.5
3 1/28/99 3/4/99 252.1 241.4 302
3 3/4/99 4/1/99 102.3 190.2
3 4/1/99 4/20/99 148 146.5 52.5
3 4/20/99 5/27/99 215.1 217.4 73.6
3 6/1/99 6/30/99 161.1 137.1

4 10/17/98 10/28/98 12.4
4 12/30/98 1/20/99 0.25

5 3/18/99 4/14/99 178.4 192
5 4/15/99 6/13/99 190.8 176.5
5 6/14/99 7/22/99 123.1
5 7/27/99 8/19/99 87 95.2









Correlation of the OTFR Headgear with Third-Person Log Book

To evaluate the validity of the OTFR headgear's ability to record and report the

correct time of appliance wear, the timing data recorded by the OTFR needed to be

evaluated against the actual time of wear. The actual time of appliance wear is difficult to

determine in this type of studies due to the inability of the investigator to physically

observe and record compliance over the study period. In order to acquire this data, we

asked one of the patients' mothers to place the headgear on her daughter and personally

record the wear period in a logbook (third-person logbook). The data from this third-

person logbook was then entered into a database, total time of wear per period was

calculated, and then correlated with the OTFR total time data (Table 4-4).




Table 4-4. OTFR and third party logbook correlation.
Start Date End Date Hrs-diary Hrs-comp
3/4/99 4/1/99 125.25 125.9 Correlation
4/1/99 5/13/99 149 148.6 r(s)=1.00 p=0.0001
5/20/99 5/26/99 39.5 39.6 r(p)=1.00 p=0.0001
6/12/99 6/13/99 6.1 5.9_


The highly significant correlation r= 1.00, p=0.0001 using both the Spearman and

the Pearson correlation test, suggested that the OTFR headgear was in fact accurate in

estimating true time of wear. This was based on the assumption that the patient's mother

actually recorded the true time of wear in the third party logbook. Three factors could

support the validity of the third-person logbook. The first factor involves the pattern of

the entry points. The third-person logbook was very detailed in its recordings of the wear

periods. Some entries were as short as a few minutes, detailing removal of appliance for









tooth brushing, eating, and various other such episodes. The logbook also revealed

placement and removal of headgear at various times which appeared to correlate with the

careful interview of the patient and the mother with respect to wear patterns. The second

factor supporting the third-party logbook validity was its high statistical correlation with

the OTFR headgear. Although such correlation could potentially be due to chance, in

reality the total time value of both were so close that it seems unlikely. Finally, the third-

party logbook was also correlated with the total time of wear recorded by the Affirm

timing device (Table 4-5). The reliability of the Affirm timing device has not previously

been reported on in the literature, however the manufacturer's independent evaluation

estimates the device tolerance at 2%. The Affirm total time recorded was highly

correlated with the third-party logbook r=1.00, p=0.0001 for both the Pearson and the

Spearman rank correlation tests further supporting the validity and reliability of the

OTFR headgear in measuring and estimating appliance wear as well as compliance.




Table 4-5. Affirm and third party logbook correlation.

Start Date End Date Hrs-affirm Hrs-diary
3/4/99 4/1/99 126.1 125.25 Correlation
4/1/99 5/13/99 149.1 149 r(s)=1.00 p=0.0001
5/20/99 6/8/99 90.7 90.6 r(p)=1.00 p=0.0001
6/8/99 7/1/99 102.9 103.3_


Correlation of Timing Headgear with Commercial Timing Device

To further test the reliability of the newly developed OFTR headgear, the

recorded time data was also correlated with the commercially available headgear time

monitor Affirm. As previously mentioned, although not reported on in the literature, the









Affirm's reliability according to the manufacturer's independent testing is high with

tolerance as low as 2%. The correlation of the OFTR with the Affirm was important not

only to help evaluate and support the OTFR's reliability and vice versa, but also to

establish the two as reasonably similar in their ability to estimate time of wear. This

would allow us to compensate and substitute missing data points due to appliance

malfunction for establishment of a more complete timing data set. The recorded data

from the two appliances were evaluated and appeared to be highly correlated r=1.00,

p=0.0001 using both the Pearson and the Spearman rank correlation tests (Table 4-6).




Table 4-6. Affirm and OTFR correlation.

Start Date End Date Hrs-affirm Hrs-comp
3/4/99 4/1/99 126.1 125.9 Correlation
4/1/99 5/13/99 149.1 148.6 r(s)=1.00 p=0.0001
2/18/99 3/18/99 86.7 87.56 r(p)=1.00 p=0.0001
3/21/99 5/2/99 123.6 122.1
1/28/99 3/4/99 241.4 252.1
4/1/99 4/20/99 146.5 148
4/20/99 5/27/99 217.4 215.1


The significant correlation between the OTFR and the Affirm, further supported

the validity and reliability of the newly developed appliance. In addition it also

documented the reliability of the Affirm module. Being relatively inexpensive and

reliable in its ability to record total time of wear, the Affirm module could potentially be

used in various clinical applications of compliance monitoring. The OTFR, however,

with its ability to characterize the wear pattern, as well record force levels, makes it much

more suitable for research applications. The characterization of the wear time is made

possible with the OTFR due to its unique data recording microcomputer, which records a










date and time signature for each data point. This allows a graphical representation of the

wear pattern as well as highly intensive analysis of the data for detection of different

patterns of wear, such as time of day, days of week, length of each period of wear, and

similar parameters.

Correlation of Timing Headgear with Commercial Timing Device and Patient Diary

Monitoring of compliance in previous clinical studies evaluating the treatment

effect of orthodontic headgear was attempted using patient self-reported compliance diary

(Kirjavainen et al., 1997; Firouz et al., 1992). While many researchers consider this

method of compliance monitoring as the gold standard, its validity and reliability has not

yet been evaluated. To evaluate the reliability of the patient's diary as a potential source

for estimating headgear compliance, the diary data was entered into a database, calculated

for total time of wear per period and compared with both timing devices, the OTFR and

the Affirm timer (Table 4-7).






Table 4-7. Patient's diary, Affirm, and OTFR headgear data.
Start Date End Date Hrs-affirm Hrs-diary Hrs-comp I


4/15/9~ 6/13/9~ 190.~ 176.5


10/1/98 10/29/98 285.4 324.7
12/15/98 1/14/99 261 258.5
1/14/99 2/17/99 160.8 191.1
2/18/99 3/18/99 86.7 197 87.56
3/21/99 5/2/99 123.6 316 122.1
12/17/98 1/19/99 117.5 112.1
1/28/99 3/4/99 241.4 302 252.1
3/4/99 4/1/99 102.3 190.2
4/1/99 4/20/99 146.5 52.5 148
4/20/99 5/27/99 217.4 73.6 215.1
6/1/99 6/30/99 137.1 161.1
3/18/99 4/14/99 178.4 192


Correlation affirm and diary ->
r(p)=0.12, p=0.75
r(s)=-0.04, p=0.91

Correlation OTFR and diary ->
r(p)=0.39, p=0.30
r(s)=-0.27, p=0.49


4/15/9


6/13/9


190.8


176.5









Analysis of the data revealed no statistically significant correlation between the

patients' self-reported compliance and either the OTFR r(p)=0.39, p=0.30 / r(s)=-0.27,

p=0.49 or the Affirm timer r(p)=0.12, p=0.75 / r(s)=-0.04, p=0.91. This suggested that

although the assumption in the literature that the daily diary is a reliable method for

securing data on headgear compliance, we found no statistical correlation to support this

assumption. In fact the patients' diary both over- as well as underestimated true total

wear time as measured by the electronic timers, without any decipherable systematic

error.

When carefully reviewing the patient's diary entries it became apparent that many

of the entries for several days were entered at a single time, further supporting the noted

discrepancy. When the patients' were asked about it the common reply was that they had

forgotten to provide entries for a few days and entered them in bulk a few days later.

Some of the patients had worn the headgear and forgot to enter the wear period in the

diary causing an underestimation of true wear time. Others had reported a wear time that

was in actuality interrupted by several hours of non-wear (specifically detected by the

OTFR) thereby overestimating the true wear time. The errors in entries were not

consistent however, such that each patient may have overestimated or underestimated the

true wear-time without any particular trend.

The use of a patient's diary to record and monitor compliance has been used not

only in dentistry and orthodontics (Kirjavainen et al., 1997; Firouz et al., 1992) but also

in other fields of medicine including pulminology (Berg et al., 1998; Malo, 1996),

cardiology (Torrisi et al., 1997), oncology (Lee et al., 1992), neurology (Neugebauer,

1989), and particularly in pharmacology (van Berge Henegouwen et al., 1999; Straka et









al., 1997; Olivieri et al., 1991). While many studies have relied on the diary for

compliance, only one reported study had set to study the reliability of self-reported drug

regimen compliance using electronic monitoring in pharmacology (Straka et al., 1997). In

his study, Straka's findings suggested poor correlation between the patients' self-reported

compliance and true drug compliance.

Our findings of poor correlation between self-reported and true compliance is

consistent with findings of other researchers (Straka et al., 1997) evaluating similar

parameters in somewhat different fields. The use of such a method for the monitoring of

compliance appears to be unjust and may in fact contribute to the large inconsistencies

reported in the various headgear clinical studies. The implementation of a digital timing

device, such as the OTFR headgear in future clinical studies will provide a true and

reliable measure of compliance. Such data, along with force recordings will provide

invaluable data for the establishment of dose-response evaluation for force, time, and

tooth movement.

Force Data

The second component of the OTFR headgear data includes the recording of force

measurements. The OTFR's force recording capability makes it a novel measurement

device, incorporating newly developed technology for research application; this pilot

study is the first long-term implementation and testing of such device in a clinical trial.

In order to utilize and interpret the force measurements recorded by the OTFR, a

series of base-line force calibrations were taken at each appointment (Figure 4-8). The

calibrations were accomplished by placing a series of known weights in a cradle

suspended from the end of the force-probe module, such that as the weight increased, the














distension was greater, altering the voltage recordings. The voltage recordings were then


plotted against the known force values. Since we anticipate that the resistance across the


variable resistor is linear, and that the spring force distention constant is linear, we should


be able to plot the weight against voltage and attain a line with a particular slope and


intercept. The slope and intercept values could then be used to interpolate the real-time


force data.


600gm
1 353V

500gm
1 225V

400gm
1 098V






300 m
77



Time 1


700gm
1 755V



600gm
1 48V
500gm
1 372V

400gm
1 304V 3










200gm
823V





Time 2


700gm
1 706V



600gm
1 539V

500gm
1 392V




400gm
1 108V
300gm
1 049V



200g
863V





Time 3


800gm
1 559V
700gm
1 5V


600gm
1 304V
500gm
1 245V2




400gm
98V

300gm
823V
200gm
804V
80 V-- Voltage (V)



Time 4


Figure 4-9. Patient RS Force calibration recording.













The calibrations performed at each appointment served two functions: obtain data


necessary to convert voltage values into force values and secondly, as part of this pilot


study, evaluate the ability of the electronic force-probe encoder to provide consistent and


1 8




1 6




1 4








1 2




08




06











reliable force measurements over time. To determine this reliability, the various force-


voltage plots were evaluated for serial time points, and their variability was assessed.


This variability was also evaluated across all force encoders to determine the inter-force


encoder reliability. A sample of the force calibration recording is presented in Figure 4-9


and the force-voltage plot is illustrated in Figure 4-10. Similar plots were performed for


all calibration data sets.


18



16



14



12 -


/F / ^ -time 1
1 ^ /^ ^ time 2
/ /^ time 3
^^_ ^rtme 4
08



06
200gm 300gm 400gm 500gm 600gm 700gm 800gm
Weight

Figure 4-10. Patient RS Force / Voltage plots.


When the various plots of the serial time points were evaluated (Figure 4-10), it


became apparent that the force-voltage relationship was not consistent over time. Similar


trends were noted for the other data sets as well. For better visualization of the variation









in voltage recordings between times for the same calibrated weight, as well as

visualization of the variability across different OTFR headgears, each patient data-set was

assigned a symbol designation, and the entire data was plotted (Figure 4-11).


A Subject 1
El Subject 2
+ Subject 3
m Subject 4
S 0 Subject 5 *

+















Figure 4-11. Scatter plot of force/voltage data of entire calibration set.
Figure 4-11. Scatter plot of force/voltage data of entire calibration set.


The scatter plot (Figure 4-11) further illustrates the force recording variability

within each OTFR headgear, for example subject #4 calibration for 600gm. Figure 4-11

also points out the inter-headgear variability for force recordings. It is interesting to note

that despite the intra-headgear variability, two distinct patterns of force/voltage trends

became apparent; one pattern includes subjects 1 and 4, while the other pattern includes









subjects 2,3, and 5. The generalized inter- and intra-headgear variability rendered the data

of voltage readings exceedingly difficult to interpolate into meaningful force values,

since the true conversion factor necessary to convert voltage into force values remained

uncertain.

In order to determine factors contributing to the variability in an attempt to isolate

its source, modeling of voltage as a function of force (weight) was performed for each of

the subjects' recorded data set. Since the force-probe encodes the force data in a linear

fashion, three linear models of voltage as a function of weight were developed.

Model 1: voltage = intercept + Bl grams

Here, voltage is a linear function of grams, such that the intercept

estimates the "baseline" voltage when grams=0

Model 2: voltage = intercept + Bl menih, + B2 grams Here, months is coded

as 1,2, or 3; this term allows for a consistent shift over time, in a positive

or negative direction.

Model 3: voltage = intercept + Bl month] + B2 month + B3 month + B4

grams

Here, the model is set to allow the 'correction' to vary from month to

month; monthly is coded as 0 if not month 1, or as 1 if it is month 1.

Since we had observations from 4 months, we only needed the 3 month

variables above. The correction for the 4th month would be the intercept

term, since all other month terms would be 0.

From this analysis, the coefficient for grams (B 1 in model 1, B2 in model 2, B4 in

model 3) should give us an idea of the consistency of the voltage / force relationship










between subjects, and the months or monthly to month coefficients, and their

significance, will indicate important departures from the basic linear model. The results

of the models are presented in tables 4-8 to 4-12.






Table 4-8. Subject 1 Modeling voltage as a function of force (weight).

Model 1: Overall model: p=0.0001
intercept grams R =0.966
estimate 0.081 0.001
p-value 0.0016 0.0001
s.e. 0.00004
Model 2: intercept months grams R =0.974
estimate 0.034 0.018 0.001
p-value 0.26 0.0454 0.0001
s.e. 0.00004
Model 3: intercept month month month grams R =0.983
estimate 0.084 -0.044 -0.018 0.037 0.001
p-value 0.0018 0.08 0.46 0.1 0.0001
s.e. 1 0.00004


The modeling results suggested a significant role for the intercept value as a

contributor for the departure from the anticipated basic linear model for all subjects

except subject #3. For model 2, with the exception of subject #3, and for all subjects of

models 3, significant finding were detected, suggesting the months term as well as the

changes from one month to the next, as important contributors to the detected variation

from the anticipated linear model.

Variations between Headgears

The intercept estimate, the largest contributing factor to the apparent variability

from the linear model, represents the voltage value when the force or weight is zero.










Table 4-9. Subject 2 Modeling voltage as a function of force (weight).

Model 1: Overall model: p=0.0001
1 intercept _grams R =0.851
estimate 0.459 ___0.0016
p-value 0.0001 0.0001
s.e. 0.00015
Model 2: intercept months grams R =0.856
estimate 0.504 -0.018 0.0016
p-value 0.0001 0.46 0.0001
s.e. 0.00015
Model 3: intercept month month month grams R =0.937
estimate 0.355 0.021 0.173 0.184 0.0016
p-value 0.0001 0.7 0.0025 0.0011 0.0001
s.e. 0.00011






Table 4-10. Subject 3 Modeling voltage as a function of force (weight).
Model 1: Overall model: p=0.0127
intercept _grams R=0.478
estimate 1 0.129 0.0019
p-value 0.63 0.0127
s.e. 0.0006
Model 2: intercept months grams R =0.899
estimate -0.244 0.326 0.0012
p-value 0.11 0.0002 0.0042
s.e. 0.00032
Model 3: intercept month month month grams R =0.990
estimate 0.553 -0.625 -0.062 0.0014
p-value 0.0001 0.0001 0.13 0.0001
s.e. 0.00011


Variations of such sort can be contributed to inconsistencies in the fabrications of

the force encoders. Since each one the OTFR headgears in this pilot study was

individually manufactured, it is likely that each force probe would have a unique initial

rest position and therefore some resistance would be measured across the encoder. To

circumvent this problem in future OTFR headgear manufacturing, the initial resistance of

each encoder could be set at zero or another predetermined resistance, making the










intercepts uniform across all headgears. Establishing uniform force-encoders would allow

the replacement of OTFR headgear in mid-treatment due to potential headgear loss,

damage, or malfunction without significant data collection differences, an important

consideration in future large clinical studies. Also, the establishment of uniformity across

all force encoders, would ease the use of this device by eliminating the need for intensive

calibration data collection and analysis, as well as make the isolation of inaccurate data

collection to a malfunctioning headgear reasonably simple.


Table 4-11. Subject 4 Modeling voltage as a function of force (weight).

Model 1: Overall model: p=0.0049
__intercept I__grams R =0.363
estimate 0.262 0.0009
p-value 0.0485 0.0049
s.e. 0.00027
Model 2: intercept months grams R2=0.756
estimate 0.569 -0.134 0.001
p-value 0.0001 0.0001 0.0001
s.e. 0.00017
Model 3: intercept month month month grams R =0.973
estimate 0.04 0.503 0.036 0.006 0.0011
p-value 0.23 0.0001 0.23 0.83 0.0001
s.e. 0.00006





Table 4-12. Subject 5 Modeling voltage as a function of force (weight).
Model 1: Overall model: p=0.0001
__ intercept ___grams R[=0.906
estimate 0.065 ___0.0011
p-value 0.188 0.0001
s.e. 0.0001
Model 2: intercept months grams R2=0.906
estimate 0.064 0 0.0011
p-value 0.32 0.98 0.0001
s.e. 0.0001
Model 3: intercept month month month grams R2=0.912
estimate 0.059 -0.004 0.026 0.0011
p-value 0.28 0.91 0.49 0.0001
s.e. _0.0001









Variations within Headgears over Time

The second important finding using modeling of the pilot data is the detection of

variations in force to voltage conversion factors from month to month. Such intra-

headgear calibration data variations occurring over time could potentially impact the data

in a more significant manner then inter-headgear variations due to intercepts. Since the

calibration data is used to develop the conversion factors to interpolate the voltage

measurements into meaningful force values, changes in the calibrations and consequently

the conversion factors would make the force recording indecipherable. This uncertainty

arises since we cannot precisely determine when during the course of the recording

period the changes in calibration values occurred nor can we predict the pattern of

change.

Two factors may have contributed to this intra-force encoder variability, both are

associated with the encoder's design and fabrication. The first factor is related to the

force probe intrinsic hysterisis, resulting from binding and friction within the internal

components. The described hysterisis could lead to inaccuracies in measurements since

the headgear's force probe undergoes some internal bindings under function. These

bindings would lead to the generation of different voltage readings under similar force

levels. In our calibration data collection great care was taken to avoid artifacts due to

hysterisis, by loading and unloading the force-probe's spring in a uniform and consistent

fashion throughout the study. While hysterisis cannot be entirely eliminated due to the

nature of the device's operation, it can be greatly reduced by modifying the force encoder

to undergo less friction, and altering the force module to allow less binding during

function.









The second potential component leading to intra-force encoder variability is

alteration in resistance across the variable resistor over time. Such changes in resistance

can be brought forth due to increased function of the resistor beyond it's designed

tolerance, introduction of contamination such as sweat onto the resistor's contact surface,

flexion of the sliding components, and other such time related resistance altering factors.

Basically, if resistance were altered across the variable resistor over time it would make

data interpolation highly inaccurate, since the rate and pattern of such change is likely to

be random and unpredictable. This problem, although critical, could be corrected and

circumvented with fairly minor apparatus revisions. The resistor itself could be replaced

with one of higher tolerance and durability, the entire force-encoder should be encased in

a protective casing, and other such implementations to increase the force-encoder's

durability and consistency.

Despite the presently reported problems, the OTFR has been successful in the

collection of the voltage recordings, which makes its design, for the most part, effective

and functional. The main problems with this unique device stem from the durability of its

components rather then its novel concept design. Following revisions of the force-probe

encoder, it is likely that the OTFR headgear force recordings be relatively consistent,

both within and across headgears, making the use of the OTFR in large clinical study

invaluable for the collection of time and force data.

Tooth Movement Data

The final component of this pilot study involved the measurement of the

maxillary molar displacement using the newly developed analysis system described in










chapter 3. The serial study models were digitized, analyzed, and their centroid

displacements were evaluated for the detection of tooth movement (Table 4-13).

The centroid displacement data was then mathematically analyzed with respect to

time, looking at total as well as annualized displacement for the left and right maxillary

molars (Table 4-14). Descriptive statistics of the data was performed and is represented in

Table 4-15.

The Changes in molar displacement are presented in graphical form (Figures 4-12

to 4-16). Each line was then tested for linear trend, to detect if the distances were

changing over time in a uniform linear manner; the p-values and R2 values are listed in

table 4-16).




Table 4-13. Serial study models centroid distance data.

Subject 1 Centroid results:
date 12/17/98 01/28/99 03/04/99 04/01/99 04/20/99 05/27/99 07/01/99
p-mR 26.01375 25.8385 25.71792 25.63614 25.35939 25.40421 25.44911
p-mL 25.05825 24.97996 24.86637 24.7285 24.75937 24.48681 24.64375
Subject 2 Centroid results:
date 10/01/98 10/29/98 12/15/98 01/14/99 02/18/99 03/18/99 05/03/99
p-mR 28.32946 28.33766 28.18476 27.88086 27.87187 27.88454 27.7989
p-mL 30.61198 30.73332 30.85037 30.47233 30.21945 30.46612 30.52185
Subject 3 Centroid results:
date 10/15/98 11/12/98 12/17/98 02/02/99 03/18/99 04/15/99 05/27/99
p-mR 31.8815 31.64829 31.52422 31.68327 31.4617 31.59308 31.59813
p-mL 31.96796 31.78871 31.79189 31.87752 31.76298 31.65795 31.8449
Subject 4 Centroid results:
date 03/18/99 04/15/99 06/14/99 07/22/99
p-mR 27.73471 27.49168 27.44613 27.36195
p-mL 29.60711 29.52234 29.21378 29.145
Subject 5 Centroid results: ________
date 01/28/99 03/04/99 04/01/99 05/20/99 07/01/99
p-mR 25.89126 25.97744 26.06482 25.54013 25.66678
p-mL 28.61314 28.26028 28.23787 28.2145 28.3037_

p-mR centroid distance between palate and right maxillary molar
p-mL centroid distance between palate and left maxillary molar













Table 4-14. Summary of total and annualized centroid change.
Subject Days TCh-Right TCh-Left ACh-Right ACh-Left
1 196 0.56465 0.41450 0.0028809 0.0021148
2 214 0.53055 0.09012 0.0024792 0.0004211
3 224 0.28337 0.12306 0.0012650 0.0005494
4 126 0.37275 0.46211 0.0029584 0.0036675
5 154 0.22448 0.30944 0.0014577 0.0020094

TCh Total change in centroid distance
Ach Annualized change in centroid distance






Table 4-15. Descriptive statistics of molar displacement.

Variable N Mean Std. Dev. Minimum Maximum
Days 5 182.8000000 42.5355270 126.0000000 224.0000000
TCh-R 5 0.3951603 0.1493228 0.2244790 0.5646470
TCh-L 5 0.2798457 0.1679301 0.0901217 0.4621081
ACh-R 5 0.0022082 0.0079710 0.0012650 0.0029584
ACh-L 5 0.0017524 0.0013308 0.0004211 0.0036675

Days # of days from initial to final visit
TCh Total change in centroid distance
Ach Annualized change in centroid distance / per day


Evaluation of the descriptive statistics revealed a linear trend of molar movement

for four molar teeth (subject 1 right and left, subject 2 right molar, and subject 4 left

molar). While some linear trends were statistically significant, the magnitude of the total

displacement was particularly small (<0.57mm) over the six months of treatment and can

likely be considered not clinically significant. The small magnitude of displacement

bordered on the lower extreme of the system resolution, as these values were somewhat

within the error of measurement envelope. Due to the unexpectedly small displacement,












three-dimensional characterization of the slight molar movement was not practical or

feasible since the apparent spatial displacement was within the specified error of

measurement. It is interesting to note that none of the patients exhibited any visible dental

changes following the headgear trial, and all but one patient maintained the same

anterior-posterior dental classification. The one patient who experienced some molar

correction had lost her mandibular primary second molars, which we suspected was the

source of her correction mechanism.








Subject 1 Left molar -----
Right molar-- .




_. Subject 2 Left molar -----
--, .... Right molar-



Days Days

Figure 4-12. Subject 1 Centroid graph. Figure 4-13. Subject 2 Centroid graph.













Subject 4 Left molar -----
Right molar-

a -

i3 .


Days


Figure 4-14. Subject 3


Centroid graph.


Figure 4-15. Subject 4 Centroid graph.


Subject 5 Left molar -----
a Right molar-










Days

Figure 4-16. Subject 5 Centroid graph.


Table 4-16. Linear trends of centroid graphs.
Right Left
Subject p-value R2 p-value R2
1 0.0041 0.83 0.0036 0.84
2 0.0025 0.86 0.22 0.28
3 0.18 0.32 0.26 0.24
4 0.11 0.80 0.0129 0.97
5 0.20 0.48 0.29 0.35


S- Subject 3 Left molar -----
Right molar-






Days











Our findings of virtually undetectable molar movement following orthodontic

headgear treatment were not consistent with those of others (Ucem, 1998; Tanne, 1996;

Firouz, 1992; Baumrind, 1981; Weislander, 1974; Watson, 1972). One of three potential

scenarios or some combination of each could potentially explain this apparent

disagreement. 1- all previously reported literature on headgear treatment effect grossly

overestimated the maxillary molar displacement, which in fact does not exist. 2- the

patients in our study had experienced molar movement but we were not able to detect it

due to our method of measurement. 3- while the orthodontic headgear is capable of

displacing maxillary molars, our patients did not experience any detectable displacement

due to factors independent of appliance potential or measurement technique.

The first possible scenario is highly unlikely. Despite systematic errors in molar

displacement measurement, the body of literature supporting maxillary molar

displacement is highly comprehensive, and while previous studies have relied on

inaccurate measurement techniques, it is reasonable to assume that some molar

displacement could potentially occur following headgear therapy. This notion is further

supported by our initial experiment, in which we have detected considerable molar

movement subsequent to headgear wear.

The second possible scenario that our patients did in fact experience some molar

displacement subsequent to treatment yet our system of measurement was incapable of

detecting the change is also somewhat unlikely. This scenario is doubtful as our newly

developed system has been tested and was in fact capable of characterizing molar

movement on a selected study model. Our lack of molar movement detection is consistent









with our visual findings, both intra-oral and from study models, further supporting the

findings or our measurement technique.

The most likely explanation for the lack of molar displacement in our patients

involves several factors independent of the appliance treatment potential or the

measurement technique. Factors that could have potentially contributed to the

exceedingly small or otherwise undetectable molar movement in our sample include the

presence of second molars as well as the use of the Nance button to the second premolars.

All of the patients in our study were either in the late mixed dentition or early

permanent dentition, and all had erupted second permanent molars. The feasibility of

molar distalization with the use of orthodontic headgear in the presence of erupted second

molars has been shown to be less effective (Battagel & Ryan, 1998). By actively

selecting patients with fully erupted permanent premolars for the utilization of the Nance

button, the patients effectively also had second permanent molars, a factor which could

have contributed to the lack of clinically significant molar movement.

The Nance button, the appliance specifically placed for the establishment of a

stable landmark, may have inadvertently contributed to the lack of detectable molar

displacement. Two potentially related problems may have been brought forth through the

use of the Nance button in our patients. Both involve the fact that by essentially

stabilizing the second premolars using the Nance, the interseptal and interdental

periodontal fibers may have hindered the molar's movement. Such potential mechanism

is supported by the work of Gianelly et al. (1989), as well as others (Bondemark & Kurol,

1992; Muse et al., 1993), who have demonstrated the spontaneous distal migration of

maxillary second premolars following maxillary molar distalization. This finding was









attributed to the intersepteal and interdental periodontal fibers pulling on the second

premolar as the adjacent molar was distalized. The same concept could also be applied to

suggest that if the second premolars are held in place through the use of the Nance

appliance, their static position could potentially hinder the maxillary molar distalization.

The second potential problem involving the Nance button's possible role in

obscuring the results, involved the same periodontal fiber mechanism in an alternative

manner. In a similar manner to that which could contribute to restrictive molar

movement, the entire dentition, from second premolar to second premolar could be driven

back along with the molars (Figure 4-17).















Inital Distalization Final

Figure 4-17. Mechanism of potential en-mass distalization.





This distal en-mass movement of the entire dentition has been previously

observed following the use of appliances that hold the maxillary teeth together (Weiland,

1997;Orton, 1996). Such conceivable scenario could potentially lead to an undetectable

molar movement by any intra-arch measurement technique since all objects would









experience the same spatial displacement. These potential problems could be minimized

by placing the Nance button on the first premolars or circumvented altogether by using

the palatal rugae as presented earlier in the chapter. While the use of the Nance button is

likely to increase the resolution, if the absence of it will allow for more subsequent tooth

movement and more clinically relevant findings, its elimination should be evaluated in

future studies pending further investigation.

In the absence of tooth movement it was not possible to draw any conclusions or

correlations with respect to force and time of application, although it is conceivable that

this study design would facilitate such analysis in the presence of tooth movement.















CHAPTER 5
SUMMARY AND CONCLUSIONS


This pilot study is the first of its kind with respect to data collection and analysis.

It incorporates novel technology specifically designed for research implementation, and

highly computer intensive graphical analysis of the data, previously unattainable.

As with every clinical study, data interpretation is highly dependent on the quality

of the data collected, and the strength of the data analysis. Our newly developed materials

and methods for clinical headgear studies add a new dimension to the data acquisition

and outcome analysis. The OTFR headgear's ability to collect force as well as

compliance data in real time allows for calculations and analysis never before possible

due to data collection shortcomings.

Lessons learned from this pilot study will lead to improvement of the OTFR and

allow the reliable use of such device in future clinical studies. Furthermore, this study

was the first of its kind to test the validity of the patient's self-reported diary for

monitoring of compliance. While such method is considered the gold standard in clinical

orthodontic studies, we have shown that such assumptions are without scientific basis and

do not correlate with true compliance. This is a very important finding as it not only

scrutinizes results of previous studies, but also suggests the necessary use of real-time

compliance monitoring device in clinical research.

The testing of the three-dimensional analysis system has been shown to provide

qualitative as well as quantitative results with respect to the molar spatial displacement









subsequent to headgear use. The use of this system offers the investigator the ability to

view dental changes from different planes of space, and could potentially visualize

important dimensional changes previously overlooked. It is encouraging to discover that

the palatal rugae could potentially be used as a stable landmark for three-dimensional

superimposition studies, although further investigation is warranted. Should the palatal

rugae prove to be useful for such purpose in future studies, our analysis system would

prove invaluable not only in prospective clinical trials but also in retrospective ones as

well.

Although the tooth movement component of this pilot study has not detected any

clinically significant displacement, it provides much insight into potential problems with

this type of design in future studies. While the Nance button provides and excellent stable

landmark for three-dimensional model analysis, it may interfere with the clinical effects

potentially occurring in its absence. This finding of potential molar movement restraint

due to the application of a Nance button on the adjacent premolars warrants future

investigation, not only for the purpose of stable structure establishment, but also to

provide further insight in to the dynamics of tooth movement.

Future studies using this novel design should be implemented following

correction of the encountered problems. Only through the use of such real-time data

acquisition headgear, capable of collecting force as well as compliance data, and the

implementation of advanced three-dimensional analysis to accurately measure the

outcomes would we be able to appreciate the true treatment effects of the orthodontic

headgear. An appliance of enormous popularity and use spanning back over a century,

yet still to date its effects and underling mode of action remain virtually unknown.









Conclusions:

1. The three-dimensional study model analysis system was successful in the

characterization of spatial molar displacement.

2. The palatal rugae' potential as a stable structure for spatial superimposition

appears favorable pending further investigation.

3. The orthodontic time/force recording (OTFR) headgear appears valid for the

monitoring of compliance.

4. The OTFR headgear's force encoder was inconsistent in its force recording yet its

data acquisition potential was shown to be successful.

5. The use of patients' self-report logbook does not appear to correlate with true

compliance as measured using two separate digital timing devices. The future use

of such logbooks for the monitoring of compliance does not appear to be

warranted in clinical orthodontic research.

6. Limited tooth movement (< 0.56mm) was noted for patients in our pilot study

subsequent to headgear therapy. The apparent small movement may be related to

the presence of erupted permanent second molars and the Nance stabilizing

appliance.















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BIOGRAPHICAL SKETCH


Yossi Bar-Zion was born in Israel and raised in southern California. He attended

the University of California at Irvine for his undergraduate study and then the State

University of New York at Buffalo for his dental education. At Buffalo Dr. Bar-Zion was

engaged in several research projects that had earned him multiple awards, including the

American Association for Dental Research student fellowship award, Quintessence award

for outstanding achievement in research, Omicron Kappa Upsilon research award, and

the Hinman's most outstanding presentation in basic science research award. Dr. Bar-

Zion was distinguished for his academic achievements as well, and received several

recognition including the Edwin C. Jauch award for the most outstanding completed

comprehensive dental restoration case, the Alpha Omega scholastic achievement award,

the American Academy of Orofacial Pain award, the Omicron Kappa Upsilon scholastic

award, the Oral Surgery Society award, and the Barrett Foundation award for highest

scholastic average for four years of dental study. Dr. Bar-Zion graduated summa cum

laude from the State University of New York at Buffalo in 1997, obtaining a Doctor of

Dental Surgery degree. Following graduation, Dr. Bar-Zion continued his dental

education at the University of Florida to complete a degree of Master of Science with a

certificate in orthodontics. At the University of Florida Dr. Bar-Zion was involved in

clinical research as well as the applications of computers in the field of orthodontics.




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