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Chairside Repair of All-Ceramic Crowns

Permanent Link: http://ufdc.ufl.edu/UFE0022701/00001

Material Information

Title: Chairside Repair of All-Ceramic Crowns
Physical Description: 1 online resource (50 p.)
Language: english
Creator: Jragh, Adel
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: acid, ceramic, chairside, chipped, hydrofluric, repair, sandblast, zirconia
Dentistry -- Dissertations, Academic -- UF
Genre: Dental Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The objective of this study was to determine whether similar repair approaches should be used for different all-ceramic crowns. To perform such an evaluation, HeraCeram (HC), IPS Empress Esthetic (IE), Procera? Crown Alumina(PC), and Cercon? Zirconia (CE) were compared. Seventy-two specimens of HC, IE, PC, and CE were fabricated, embedded in self-curing methylmethacrylate, then grounded flat with sandpapers (240, 400 and 600 grits) until one surface was completely exposed and smooth. Each material was divided into three groups. Each group received surface treatments of: (F) finished only, no additional treatment received, (AC) acid etching with 9.6% hydrofluoric acid, and (SB) sandblasting with 50 ?m Al2O3. Each of these groups was divided into 4 subgroups. Each subgroup was bonded to composite cylinders using either Clearfil Ceramic Primer (CE), silane and Optibond FL Adhesive(SO), Calibra and XP Bond(SXP ), or 904 Zirconia adhesive with Optibond FL Adhesive(ZR) and then stored 7 days in water at 37 degrees C before shear strength tested. HC ceramic performed better on both etched and sandblasted surfaces than finished surfaces. Of the three adhesive systems, CE gave the highest mean strength values independent of surface treatments. There was no significant difference in bond strength between etched and sandblasted surface in any adhesive systems. The IP results revealed that surface etching with 9.6% hydrofluoric acid gave the highest shear bond strength of the other treated groups. There was no significant difference in CE performance when compared to etched or sandblasted SO, or etched SXP adhesive systems. PC had the highest shear bond strength when the surface had been sandblasted. CE and SXP showed no significant differences when it come to surface treatments. For CZ, sandblasting gave the highest shear bond strength, and when it comes to adhesive systems on CZ, SXP appeared to have the highest bond strength independent of surface treatment. It can be concluded from this study that in order to repair a fractured or chipped all ceramic crown, one needs to know the composition of the core ceramic structures.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Adel Jragh.
Thesis: Thesis (M.S.)--University of Florida, 2008.
Local: Adviser: Soderholm, Karl J.
Local: Co-adviser: Clark, Arthur E.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022701:00001

Permanent Link: http://ufdc.ufl.edu/UFE0022701/00001

Material Information

Title: Chairside Repair of All-Ceramic Crowns
Physical Description: 1 online resource (50 p.)
Language: english
Creator: Jragh, Adel
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: acid, ceramic, chairside, chipped, hydrofluric, repair, sandblast, zirconia
Dentistry -- Dissertations, Academic -- UF
Genre: Dental Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The objective of this study was to determine whether similar repair approaches should be used for different all-ceramic crowns. To perform such an evaluation, HeraCeram (HC), IPS Empress Esthetic (IE), Procera? Crown Alumina(PC), and Cercon? Zirconia (CE) were compared. Seventy-two specimens of HC, IE, PC, and CE were fabricated, embedded in self-curing methylmethacrylate, then grounded flat with sandpapers (240, 400 and 600 grits) until one surface was completely exposed and smooth. Each material was divided into three groups. Each group received surface treatments of: (F) finished only, no additional treatment received, (AC) acid etching with 9.6% hydrofluoric acid, and (SB) sandblasting with 50 ?m Al2O3. Each of these groups was divided into 4 subgroups. Each subgroup was bonded to composite cylinders using either Clearfil Ceramic Primer (CE), silane and Optibond FL Adhesive(SO), Calibra and XP Bond(SXP ), or 904 Zirconia adhesive with Optibond FL Adhesive(ZR) and then stored 7 days in water at 37 degrees C before shear strength tested. HC ceramic performed better on both etched and sandblasted surfaces than finished surfaces. Of the three adhesive systems, CE gave the highest mean strength values independent of surface treatments. There was no significant difference in bond strength between etched and sandblasted surface in any adhesive systems. The IP results revealed that surface etching with 9.6% hydrofluoric acid gave the highest shear bond strength of the other treated groups. There was no significant difference in CE performance when compared to etched or sandblasted SO, or etched SXP adhesive systems. PC had the highest shear bond strength when the surface had been sandblasted. CE and SXP showed no significant differences when it come to surface treatments. For CZ, sandblasting gave the highest shear bond strength, and when it comes to adhesive systems on CZ, SXP appeared to have the highest bond strength independent of surface treatment. It can be concluded from this study that in order to repair a fractured or chipped all ceramic crown, one needs to know the composition of the core ceramic structures.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Adel Jragh.
Thesis: Thesis (M.S.)--University of Florida, 2008.
Local: Adviser: Soderholm, Karl J.
Local: Co-adviser: Clark, Arthur E.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022701:00001


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1 CHAIRSIDE REPAIR OF ALL-CERAMIC CROWNS By ADEL K. JRAGH A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2008

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2 2008 Adel K. Jragh

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3 To my wife and all who ma de this milestone possible

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4 ACKNOWLEDGMENTS First, I would like to acknowledge my wife fo r her love and encouragem ent throughout my studies. I would like to give a special thanks to my supervisory committee chairman, Dr. KarlJohan Sderholm, for his guidance and support. Dr.Soderhoms motivati on and leadership has made this endeavor successful. I would also like to thank my supervisory committee cochair, Dr. Buddy Clark, for his support and time. I am also gr ateful to my mentor, Dr. Edgar ONeill, for his inspiration to complete this work. I thank fa culty, Dr. Lucius Battle, my colleague residents, and the Department of Prosthodontics for their encouragement. Also, I would like to thank Ivoclar/Vivodent and Dentsply/DeTrey for supporting this project with the ceramic samples; Dentsply/DeTrey for providing Calibra and XP Bond; Kuraray for providing Clearfil Ceramic Primer; Kevin P. Parekh for his lab assistance; and Dr Mark Yang from the Department of Statistics for his time and explanations. Last but not least, I thank my parents for their love and support.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4LIST OF TABLES................................................................................................................. ..........7LIST OF FIGURES.........................................................................................................................8ABSTRACT.....................................................................................................................................9CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW..............................................................11Introduction................................................................................................................... ..........11Repairing a Chipped Ce ramic Restoration............................................................................. 12Surface Roughening........................................................................................................12Coupling Agents..............................................................................................................13Composite Resin Application.......................................................................................... 13Commonly Used Ceramic Ma terials in Dentistry.................................................................. 14Feldspathic Ceramic........................................................................................................ 15Leucite-Reinforced Ceramic (Hot-Pressed Systems)......................................................15High-Alumina Reinforced Ceramics............................................................................... 15Zirconia Reinforced Ceramics.........................................................................................16Novelty, Scope, and Goal of Study........................................................................................172 MATERIALS AND METHODS........................................................................................... 21Ceramic Materials and Their Preparation............................................................................... 21Bonding Procedure 1 (CE).............................................................................................. 22Bonding Procedure 2 (SO).............................................................................................. 22Bonding Procedure 3 (SXP)............................................................................................ 23Bonding Procedure 4 (ZR).............................................................................................. 23Shear Bond Strength Testing..................................................................................................23Statistical Evaluation......................................................................................................... .....243 RESULTS AND DISCUSSION............................................................................................. 27Results.....................................................................................................................................27Feldspathic Ceramic (HC)............................................................................................... 27Leucite-Reinforced Ceramic Systems (IP)...................................................................... 28High-Alumina Reinforced Ceramics (PC)......................................................................29Zirconia Reinforced Ceramics (CZ)................................................................................30Modes of Failure..............................................................................................................32Discussion...............................................................................................................................32

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6 Statistical Evaluation....................................................................................................... 32Surface Treatment........................................................................................................... 32Adhesive..........................................................................................................................35Modes of Failure..............................................................................................................364 SUMMARY AND CONCLUSIONS.....................................................................................44LIST OF REFERENCES...............................................................................................................46BIOGRAPHICAL SKETCH.........................................................................................................50

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7 LIST OF TABLES Table page 2-1 Description of ceramic m aterials used in study................................................................. 252-2 Description of adhesive materials used in study................................................................ 253-1 Feldspathic ceramic T-test comparison and significant differences of different surface treatments and adhesive bond materials................................................................ 413-2 IPS Empress ceramic T-test comparison and significant differences of different surface treatments and adhesive bond materials................................................................ 413-3 Procera ceramic T-test co mparison and significant diffe rences of different surface treatments and adhesive bond materials............................................................................ 413-4 Cercon ceramic T-test comparison and si gnificant differences of different surface treatments and adhesive bond materials............................................................................ 42

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8 LIST OF FIGURES Figure page 1-1. Fracture toughness of ceram ic materials.46........................................................................201-2. Formation of covalent bond between the silica surface and the silane (Courtesy by KJ Sderholm)......................................................................................................................202-1 Shear bond testing device with bonded specimen. Metal ring used to shape the composite was kept in place during the test....................................................................... 263-1. Shear bond strength of HeraCeram.................................................................................... 393-2. Shear bond strength of IPS Empress.................................................................................. 393-3. Shear bond strength of the Cercon Zirconia...................................................................... 403-4. Shear bond strength of Procera Crown Alumina............................................................... 403-5. Type of HeraCeram ceramic adhesive failures of acid etched surface treatment.............. 423-6. Type of HeraCeram ceramic adhesive failures of sandblast surface treatment................. 423-7. Type of IPS Empress ceramic adhesive failures of acid etched surface treatment............ 433-8. Type of IPS Empress ceramic adhesive failures of acid etched surface treatment............ 433-9. Failure of IPS Empress ceramic (left). No such failures occurred in any of the Cercon Zerconia (right)............................................................................................................... ...43

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9 Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science CHIARSIDE REPAIR OF ALL-CERAMIC CROWNS By Adel K Jragh August 2008 Chair: Karl-Johan Sderholm Cochair: Buddy Clark Major: Dental Sciences The objective of this study was to determine whether similar repair approaches should be used for different all-ceramic crowns. To pe rform such an evaluation, HeraCeram (HC), IPS Empress Esthetic (IE), Procera Crown Alum ina(PC), and Cercon Zirconia (CE) were compared. Seventy-two specimens of HC, IE, PC and CE were fabricated, embedded in selfcuring methylmethacrylate, then grounded flat with sandpapers (240, 400 and 600 grits) until one surface was completely exposed and smooth. Each material was divided into three groups. Each group received surface treatments of: (F) finished only, no additional treatment received, (AC) acid etching with 9.6% hydrofluoric aci d, and (SB) sandblasting with 50 m Al2O3. Each of these groups was divided into 4 subgroups. E ach subgroup was bonded to composite cylinders using either Clearfil Ceramic Primer (CE), sila ne and Optibond FL Adhesive(SO), Calibra and XP Bond(SXP ), or 904 Zirconia adhesive with Optibond FL Adhesive(ZR) and then stored 7 days in water at 37 C before shear strength tested. HC ceramic performed better on both etched and sandblasted surfaces than finished surfaces. Of the three adhesive systems, CE gave the highest mean strength values independent of surface treatments. There was no significant di fference in bond strength between etched and sandblasted surface in any adhesive systems. The IP results revealed that surface etching with

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10 9.6% hydrofluoric acid gave the highest shear bond strength of the other treated groups. There was no significant difference in CE performance when compared to etched or sandblasted SO, or etched SXP adhesive systems. PC had the highest shear bond strength when the surface had been sandblasted. CE and SXP showed no significant differences when it come to surface treatments. For CZ, sandblasting gave the highest shear bon d strength, and when it comes to adhesive systems on CZ, SXP appeared to have the highest bond strength independent of surface treatment. It can be concluded from this study that in order to repair a fractured or chipped all ceramic crown, one needs to know the composition of the core ceramic structures.

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11 CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW Introduction During the past 10 to 20 years, patient dem and for esthetic and metal-free restorations and the use of all-ceramic crown/brid ge restorations have increased.1 As a result of the increased use of these ceramic materials, the number of failu res can also be expected to increase because of dentists and technicians attempts to achieve es thetic design, particularly of complex multi-tooth bridges, where the ceramic materials cannot withstand the required loading conditions.2 Other failures result because of high lo calized stresses genera ted by hard particulates caught between the teeth during chewing. Poor adhesion betw een the ceramic restoration and the underlying tooth is an additional cause for failure.3 Today, the greatest shortcoming with all-ceramic dental restorations is the tendency to chip or fracture.4 To decrease the fracture risk, ceramics su ch as alumina and zirconia are now used,5 which provides superior fracture toughness compared to more trad itional dental ceramics (Figure 1-1).6 However, despite the superior fracture toughness of alumina and zirconia, it is unlikely that the use of these materials will decrease the risk for chipping of the outer layer of the restoration as long as the entire restoration is not made from these ceramics. This is because both alumina and zirconia are too opaque and whitish in color to serve as ideal aesthetic materials. Therefore, to overcome the problem with their ae sthetic limitations, these materials are used as core substrates and as such, are usually covered with layers of feldsp athic veneering porcelain with superior aesthetic properties.7 Unfortunately, these outer ceramic layers have properties similar to those used in dentistry for the past fifty years. Consequently, it seems reasonable to suspect th at even though fractures of the ceramic core-structures may decrease as a result of using alum ina and zirconia, the

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12 tendency for chipping in the veneering layer should remain the same. Based on available information, it is known that failures resulting fr om ceramic fractures range from ~ 2 to 4% for ceramic fused-to-metal crowns between seven and ten years old,8 while with an Allceram crowns, the failure rate between five a nd ten years is ~ 2% and 6.5% respectively.9 Replacement of chipped ceramic restoration is not always necessary. The most practical solution, considering the replacement cost of an additional tooth structure and additional trauma to the tooth during the rem oval of a core structure, is to repair the crown.10 As a result, in determining the ability to chair-si de repair chipped or partly fract ured ceramic restorations, it is important to consider reparabili ty when an all-ceramic dental material is being selected.11, 12 Repairing a Chipped Ceramic Restoration The treatm ent of a chipped ceramic restorati on depends on the size of the chip. In some cases with smaller degrees of chipping, the onl y treatment possibly needed is to smooth and finish the sharp edges of the fractured surface. If the fractured surface is isolated to the outer ceramic or if the core material has been expos ed, it can be repaired with a composite resin bonded to the ceramic surface. 13 This type of repair consists of three steps: A) surface roughening, B) placement of coupling agent, and C) placement of composite resin. Surface Roughening To succeed with such a repair, the ceram ic su rface is etched with a hydrofluoric acid and rinsed.14, 15 If the exposed ceramic surface is not acid re sistant, the acid removes the least acidresistant phases of the ceramic and creates an irregul ar and rough surface.16 The rough surface formed by acid etching facilitates the formation of micromechanical retention of composite resin to the ceramic surface.17-20 In addition to hydrofluoric ac id etching, air abrasion with 50-m aluminum oxide (Al2O3) particles under air pressure is another method of surface roughening.21 The impact from the

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13 abrasive particles knocks away the weaker phase s of the ceramic and creates an irregular and rough surface, which increases the bondable surf ace area. The roughness, however, in contrast to the etched surface, is not associated with true micromechanical retention, as sandblasting causes an overall surface chipping while etchi ng results in micro-cavity formation.22 Coupling Agents The etched or sandblasted surface is then silane coated and dried.22,23 The silane treatment forms covalent bonds to the ceramic surface 24-26 and to the methylmethacrylate groups of the methacrylate-based composite resin molecules (Figure 1-2). Also, it enhances the composite resin wetting of the ceramic surface.2729 A regular bonding resin is placed on the silane-coated surface and cured, whereupon the composite is pl aced and cured. If, however, a core structure such as alumina or zirconia is exposed, the bon ding process becomes more complicated because hydrofluoric acid is not capable of form ing a rough alumina or zirconia surface.30 Besides, the silane may not act as an efficient coupling agent on those surfaces as it is on regular silica-based ceramic surfaces. Composite Resin Application When a chipped ceram ic surface repair us es a composite resin, thermal expansion coefficient and modulus of elasticity are importa nt properties to consider. The benefit with low thermal expansion coefficient is that it better ma tches the ceramic, while a lower modulus results in lower stress levels introduced during curing. In addition, a lower modulus also decreases the stress level induced in that pa rticular region if one assumes th at the region deforms a certain amount during chewing, independent of compos ite (e.g., primary contact in occlusion). Unfortunately, thermal expansion coefficient and modulus of elasticity are opposite properties to each other. Low thermal expansion is associated with high modulus and vice versa. Besides, low modulus also is associated with lower filler fraction and higher polymerization shrinkage.

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14 Because of the latter, a safer option is to move toward a composite with higher filler fraction and thus higher modulus and lower thermal expansion co efficient. Unfortunatel y, no clinical data is available today determining the superiority of any particular composite type, and as a consequence, no simple selection process exists. Perhaps the most important considerations are the aesthetic appear ance and the ease of manipulation. Some in vitro studies have tried to address the selection of composite for ceramic repairs. Accordingly, the bond between the ceramic surf ace and the composite restoration must be sufficiently strong to with stand the functional loads.13 Therefore, a minimal coefficient of thermal expansion and polymerization shrinkage are considerations when choosing the repair materials. Bond strength is also dependent on the type of the composite resin used. According to Gregory and Moss (1990),31 repairs with larger particle-si zed composite, hybrid type at the porcelain interface and overlaid with micro-f illed composites resulted in higher bond strength values than when a homogeneous small particle -sized composite was used. Hybrid composite resin increases strength and decreases stress compared with a micro-filled composite.14 If a micro-filled composite resin is used, the loaded restoration should not be exposed to fatigue loading.32, 33 Commonly Used Ceramic Materials in Dentistry The success of repairing chippe d ceram ics depends on the surface treatment of the ceramic surface as well as on the coupling ag ent (silane or adhesive) used.21, 34 In addition, the composition of the ceramic affects the surface treatment 35, 36 as well as the way a coupling agent interacts with the ceramic surface.2 The following section focuses on four commonly used ceramic systems. These systems include the trad itional feldspathic ceram ics, pressable leucitebased ceramics, alumina-based cera mics, and zirconia-based ceramics.

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15 Feldspathic Ceramic The Chinese were the leaders in the development of the ceramics materials in the seventeenth and eighteenth centuries.37 The composition of these ceramics was around fifty percent kaolinite, 25 percent feldspar, and 25 percent quartz. The first single-tooth ceramic material was introduced to dentistry in the 1880s and was used to make full porcelain jacket crowns and porcelain inlays. The co mpositions of these early dental ceramics were very close to the composition of the Chinese porcela ins which were rich in mullite (Al6Si2O13). 37 Another name for mullite is porcelainite, from which the word porcelain originated. Over the years, the compositions of dental ceramics have changed. Mullite and free quartz were removed, while the Na2O, K2O and the leucite (AlSi2O6) contents were increased. The change in the composition improved the transl ucence and the strength of the material.38, 39 Leucite-Reinforced Ceramic (Hot-Pressed Systems) Leucite-reinforced ceramic was developed by Wohlwend in 1983 at th e Dental Institute, Zurich University. In 1986, Ivocla r Vivadent bought the patent and presented it to the market as IPS Empress in 1990.40 In this system, leucite crystals measuring 1-5 m is added to the dental ceramic to enhance flexural strength and fracture resistance.41, 42 The leucite crystals reinforce the material by preventing crack propagation and failure. Also, by heat-pressing the ceramic, large pores are avoided. Heat-pressing also promotes a good dispersion of the crystalline phase within the glassy matrix, and it reduces the amount of ceramic shrinkage, which results in higher flexural strength.40, 42 High-Alumina Reinforced Ceramics High-purity alumina coping s were described by Andersson and Oden in 1993.43 This system was marketed as the Procera AllCeramic System (Procera-Sandvik, Stockholm, Sweden). Procera all-ceramic copings are manufactured by using a dry-pressing technique

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16 against enlarged models of the tooth prepar ation to compact a high-purity alumina powder (A12O3 > 99.9%).1 The enlarged dies are made by the Procera system, which utilizes a computer-aided manufacturing (CAM) and comput er-aided design (CAD) technology to mill the dies used to press the Al2O3 framework. After the frameworks are pressed, they are heat processed and shrunk to their final size. The Al2O3 structure has no glassy phase between their particles; 38 however, because of the far-fromideal aesthetic properties of Al2O3, the core structure is veneered with an aesthetic ceramic. This process is completed by firing feldspathic veneering porcelains such as NobelRondo Alumin a onto the alumina core to provide the color and form of the restoration. Zirconia Reinforced Ceramics During the past few years, several dif ferent zirconia-based core products were introduced. One such system is the Cercon Zi rconia System, which like Procera, uses a CAM/CAD process. After the tooth has been pr epared and an impression and a gypsum model made, a wax reconstruction is made on the die. The wax model placed on the gypsum model is transferred to the Cercon Ceramic System, in wh ich the model is scanned with and without the wax pattern. The computer then an alyzes the two scans and constr ucts a three-dimensional model of the wax pattern. The coordinates of the model are transferred to a milling unit, and a core structure is milled in partly-sintered zirconia. In order to produce a dense structure, the partlysintered zirconia structure is transferred to a co mputerized oven in which the core finally is sintered. During the sintering process, the core structure shrinks. To overcome the shrinkage, the milled framework must be oversized to a size determined by the computer when the scanned information is processed. In addition to Cercon, zirconia frameworks are made by systems such as Lava and Denzir. Lava uses similar technology to Cercon, while Denzir mills the core structure directly from

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17 industrially processed and sinter ed zirconia. Thus, in the cas e of Denzir, no sintering is performed after the milling process is completed. However, independent of which process is used, the aesthetic properties of zirconia are not ideal, and therefore, a ve neering ceramic is used to finalize the ceramic reconstruction, like in the case of Al2O3 cores. Novelty, Scope, and Goal of Study Because of an increased use of different allceram ic restorations, it is predicted that the interest in repairing such restorations will increase in the future. It is expected that clinicians will find themselves in situations where they are uns ure of which ceramic system they are repairing. Such situations will be common in states such as Florida, where patients received their restorations in other states at a younger age and then retired in Fl orida. Under such conditions, if a ceramic failure occurs, the dentist in Florid a may not have access to information about the ceramic system used when the ceramic restoratio n is made. In such a situation, how should the dentist treat the ceramic surface and pick a coupling agent with the highest likelihood of being successful? Also, if the most likely treatment is picked, which ceramic system can cause the biggest problem? Furthermore, if the dentist ha ppens to know the ceramic type, which treatment should then be used to optimize the outcome? To address these questions, a comparison of composite repair stre ngth of different ceramics after they have been surface treated and then bonded with a composite was arranged. The ceramic materials tested in this study were regular feldspat hic ceramics, pressed ceramics, alumina, and zirconia. The ceramic materials were surface treated wi th either 9.6 percent hydrofluoric acid, sandblasted, or finished before composite cylinders were bonded with four different adhesive systems to these surfaces. The hypothesis is that the best bonding would occur to ceramics that responded most to the hydrofluoric acid treatment. By acid etching the surface, it shoul d be possible to selectively

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18 dissolve less acid resistant phases and there by form micro-mechanic al retention sites.22 The hydrofluoric acid treatment was hyp othesized to work best on feldspathic and pressed ceramics because studies by Borges et al. 2003 have show n that alumina and zirconia do not respond well to such an acid treatment.30 In addition to hydrofluoric acid et ching, surface roughening can also be achieved by sandblasting the ceramic surface. During sandblasting, microchips are knocked away from the ceramic surface as a result of the impact from the abrasive particles. Air abrasion was hypothesized to be the optim al surface treatment to roughen zirconia and alumina compared to hydrofluoric acid. In order to determine whet her etching or sandblastin g would perform best, a comparison of these two treatments with fini shed surfaces serving as controls was used. When it came to comparing feldspathic and pr essed ceramics with alumina and zirconia, the hypothesis was that sandblasted feldspathic and pressed ceramics would probably provide better bonding conditions. The reason was that due to the lower fracture toughness of feldspathic and pressed ceramics,44 these two ceramics would respond more extensively to sandblasting than alumina and zirconia.30 Of the investigated ceramics, the zirconia-based core material has the highest fracture toughnesstwice as high as th e second toughness ceramic investigated, the alumina core material.45 Thus, the higher fracture toughness of alumina and zirconia (Figure 1-1) suggests that these two ceramics would not micr ochip as much as the feldspathic and pressed ceramics during the sandblasting process. Regarding the use of different adhesives, th e hypothesis was that the similarities between the silica structure and the silane molecules woul d result in better compatibility bonding between the silane and the feldspathic and pressed ceramics with their SiO2 content in contrast to the alumina and zirconia ceramics with their Al2O3 or ZrO2 groups. Even though silane treatment enhances bonding, such a treatment may not contribu te as much to retention as micromechanical

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19 retention. The reason may simply be that only a maximum of one-third of all SiOH groups present on a silica surface interact s with the silane molecules.26 Such a limited chemical bond formation supports the assumption that the hydrofluoric-etched or sandblasted feldspathic and pressed specimens would form stronger composite bond strength values than the smoothest surfaces. If silane is the key bond mechanism, s ilane-treated finished specimens would perform as well as etched or sandblasted. In fact, both etching and sandblas ting would increase the probability for the introduction of defects at th e interface, suggesting that a reliable silane bonding on a finished surface should perform bette r than a silane bonding on a defect rich surface. Thus, it is hypothesized that because of th e 1/3 SiOH interaction, silane treatment is just a supplement to an etched or sandblasted surfac e, and by comparing the overall results, it is expected to find the best adhesion to surfaces wi th the highest micromechanical retention ability. In this case, this would be etched surfaces fo llowed by sandblasted surfaces with the lowest bond strength values being the finished surfaces. To summarize, it was hypothesized that: a) Hydrofluoric acid treatment would work be st on feldspathic and pressed ceramics. b) Air abrasion would provide better surface roughening on alumina and zirconia ceramics, and therefore provide better bonding on thes e two ceramics than hydrofluoric acid. c) Regarding the use of different adhesives, incl uding the silane treatment, the similarities between the silica structure and the silane molecules would result in better bonding between the silane and the feldspathic and pressed ceramics than with the Al2O3 and ZrO2 ceramics. d) Because only 1/3rd of the SiOH groups on a silica surface react with silane, silane treatment is just a supplement to an etched or sandblasted surface. Consequently, it was expected that the best adhesion would occur to surfaces with the hi ghest micromechanical retention ability. Thus, it was expected that etched surfaces should be followed by sandblasted surfaces, while the lowest bond strength values would be found for the finished surfaces.

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20 Figure 1-1. Fracture toughne ss of ceramic materials.46 Figure 1-2. The formation of covalent bond between the silica surface and the silane (Courtesy by K-J Sderholm).

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21 CHAPTER 2 MATERIALS AND METHODS Ceramic Materials and Their Preparation Four ceram ic materialsfeldspathic (HeraC eram [HC], lot # 1602, Heraeus Kulzer, Inc. Armonk, NY, USA), leucite-reinfor ced glass (IPS Empress Esthetic Rohling [IE], batch JM0639, Ivoclar Vivadent, Schaan, Lichtenstein), aluminum oxide (Procera Crown Alumina [PC], Nobel Biocare, Sweden), and yttria-stabili zed zirconia (Cercon Zirconia [CZ], lot # 20020089, DeTray, Konstantin, Germany)were prepared as follows. The HC samples consisted of 72 ceramic blocks, ~ 5 x 5 x 5, and were made by Pr ecision Dental Lab, Gaines ville, Florida, USA. The manufacturer of IE donated sixteen pressed cylinders, ~ 25 mm long with a diameter of 5 mm. From these cylinders, 72 cylinders, ~ 5 mm long, were cut. The 72 PC samples were donated several years ago by the manufacturer of PC. These samples consisted of disks, 16.4 mm in diameter and 1.5 mm thick. Th e manufacturer of CZ provided 72 processed cylinders of CZ used to evaluate their product. These cylinders were ~ 8 mm in diameter and ~ 5 mm long. All 288 ceramic samples were imbedded in self-c uring methylmethacrylat e (Technovit 4004, lot # 64708471, Heraeus Kulzer GmbH, Germany) cylinders (30 mm diameter x 30 mm height), with one of the ceramic surfaces exposed. After the methylmethacrylate set, the exposed ceramic surface was ground flat with sa ndpaper (240, 400 and 600 grits). The 72 specimens per ceramic group were divided into three groups of 24 specimens each. One of these main groups, the finished group (F ), was not processed further before bonding was performed, while the other two groups were ac id etched (AE) with 9.6% hydrofluoric acid (Porcelain Etch Gel, Pulpdent Corporation, Wa tertown, MA, USA) for two minutes and then rinsed with water for thirty seconds just befo re different bonding procedures were performed or were sandblasted (S) with 50 m Al2O3 for five seconds under a pres sure of two bars with the

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22 nozzle held 10 mm away from the ceramic surf ace just before the different bonding procedures were performed. Each of these main groups was in turn divided into four subgroups, each consisting of six specimens. Each of these subg roups was treated with one of the following bonding procedures. Bonding Procedure 1 (CE) The ceram ic surface was coated with Clearfil Ceramic Primer (lot # 00003A, Kuraray America, Inc. NY, USA) and then dried by blowi ng mild oil-free air for five second. A stainless still disk, 2 mm thick, 12 mm wide, and with a central hole 3 mm in diameter, was used as a mold for the composite cylinder bonded to the ad hesive. The surface of the disk contacting the ceramic surface was covered with a double adhe sive tape. The adhesive-coated surface was placed in contact with the flat ceramic-methylme thacrylate surface with the central hole over the ceramic surface only. A small increment of a composite material (Venus, A2, lot# 010118, Heraeus Kulzer GmbH, Germany) was inserted to half the height of the cylinder. The composite then was adapted to the ceramic surface to s ecure a good composite/adhesive contact and was light-cured (Translux Power Blue, Heraeus Kulz er GmbH, Germany) for twenty seconds. The power density of the light source was ~ 1000 mW/cm2 determined with a light meter (Cure Rite, Dentsply Caulk, Milford, DE, USA). After the first increment was cured, a second increment was added to fill the entire mold, and this layer was cured for another twenty seconds. Bonding Procedure 2 (SO) A ceram ic surface was coated with Dry-Rite (D rying Agent, Pulpdent Corporation), and air dried for five seconds, whereupon a silane c oupling agent (Calibra, lot # 070215, Dentsply, Caulk) was placed and dried five seconds. One coat of OptiBond FL Adhesive (lot # 4XX233, Kerr Corporation, Orange, CA, USA) was placed over the silane and lightly air thinned for five

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23 seconds after which it was cured for ten sec onds. A composite cylinder was then bonded as described above. Bonding Procedure 3 (SXP) The ceram ic surface was dried and silane trea ted as described above, whereupon a coating of XP Bond (lot # 0609001329, De ntsply, DeTray, Konstantin, Germany) was placed and allowed to interact for twenty seconds before it was air thinned five seconds and light cured for ten seconds. Following these steps, a compos ite cylinder was bonded as described above. Bonding Procedure 4 (ZR) The adhesive used in this experim ent was a zirconia adhesive called 904 Zirconia (lot # 722842, Cotronics Corporation, Brooklyn, NY, USA) and is used within the electronic/electrical industry. One drop of the 904 adhesive and one drop of the 904 thinner/hardener (lot # 722844, Cotronics Corporation, Brooklyn, NY, USA) were mixed for fifteen seconds and then placed on the exposed ceramic surface. The coating was ligh tly air-thinned for ten seconds and heated to 50C with a hairdryer for thirty seconds, wher eupon one coat of Optibond FL Adhesive was placed and lightly air-thinned for five seconds after which it was light-cured for ten seconds. Following these steps, the metal molds were placed as described and filled with composite as described earlier. After bonding was completed, the specimens were immersed into tap water and stored for one week at 37 C before they were tested in shear. Shear Bond Strength Testing The specim ens with the metal rings surrounding the composite cylinders were secured in a guillotine-like specimen holder attached to a universal testing machine (Model 1125, Instron, Canton, MA). The blade of the guillotine-like specim en holder was placed on top of the edge of the metal disk surrounding the bonded composite cy linder and then loaded under the load cell

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24 with a cross-head speed of 0.5 mm/min (Figure 21). At a certain load, th e metal disk with its composite cylinder was separated in shear from the ceramic surface. The shear load at failure was then divided by the cross-s ectional area of the cylindrical composite sample, providing the shear stress level at failure. The fractured surfaces then were evaluated in an attempt to determine where the failures occurred. Statistical Evaluation The experim ental treatments formed a balanced 3 x 4 factorial design with six replicates per treatment combination. Because the distri bution of shear bond strength exhibited strong skewness and a non-constant variance, a natural-logarithm scale was used for the analysis. A paired t-Test with modified degrees of fr eedom was used; this test is known as the Satterthwaites approximation.47 A P-value less than 0.05 was cons idered as significant. Because it was clear at this point that the 904 adhesive with Optibond FL Adhesive (ZR) was not working as it failed even during storage in water or pla cement in the testing device, the ZR group was not included in the final analysis.

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25 Table 2-1. Description of ceramic materials used in study Ceramic Code Type Composition Manufacturer HeraCeram HC Feldspathic SiO2 (6072%), Al2O3 (812%), K2O (11-17%), Na2O (4-9%), Li2O (0.3-1.2%), CeO2 (0.5-3.0%), F (0.1-1.5%), CaO (0.1-3.0), B2O3 (0.2-1.2%), SnO2, ZrO2, Y2O3, Li2O, Inorganic pigments (0.0-3.5%). Heraeus Kulzer Inc. Armonk, NY, USA IPS Empress IE Leucite-reinforced SiO2 (63%), Al2O3 (17.7%), K2O (11.2%), Na2O (4.6%), CeO2 (1.6%), B2O3, CaO, BaO, TiO2 ( 1%) Ivoclar Vivadent, Schaan, Lichtenstein Procera Crown Alumina PC High-alumina reinforced Al2O3 (99.5%) Nobel Biocare, Sweden Cercon Zirconia CZ Zirconia reinforced ZrO2, Y2O3 (5%), Hf2O3< 2%, Other oxides < 1% DeTray, Konstantin, Germany Table 2-2. Description of adhesive materials used in study Adhesive Code Composition Manufacturer Clearfil Ceramic CE ethanol 80-100%, trimethoxysilylpropyl methacrylate < 5%, 10-Methacryloyloxydecyl dihydrogen phosphate ( MDP) Kuraray America, Inc. NY, USA Optibond FL Adhesive SO Uncured Methacrylate Ester Monomers 50-60%, Triethylene Glycol Dimethacrylate 5-10%, Ytte rbium rifluoride 12-17% Kerr Corporation, Orange, CA, USA XP Bond SXP TCB resin, PENTA, UDMA, TEGDMA, HEMA, Butylated benzenediol (stabilizer), Ethyl-4dimethylaminobenzoate, Camphorquinone, Functionalised amorphous silica, t-butanol DeTray, Konstantin, Germany 904 Zirconia ZR Composition was not available from the company Cotronics Corpotation, Brooklyn, NY, USA

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26 Figure 2-1. Shear bond testing device with bond ed specimen. Metal ring used to shape the composite was kept in place during the test.

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27 CHAPTER 3 RESULTS AND DISCUSSION Results Results of the m ean shear bond strength valu es and standard deviations for the study ceramics groups are shown in Figures 3-1 to 34. The significance leve ls between pairs are shown in Tables 3-1 to 3-11. Fi gures 3-1 to 3-4 show numerical results for the ZR adhesive. while ZR is not included in the tables because of its inferior results. The ZR results are not included in the tables because of the numerous spontaneous fa ilures during storage in water. suggesting that ZR was so inferi or to the other adhesives that there was no need for further analyses of that product. Feldspathic Ceramic (HC) Surface tr eatment: Figure 3-1 and Table 3-1 show that both etched and sandblasted surfaces performed better than finished surfaces However, regarding separating etching and sandblasting, a certain interacti on exists between the surface treat ments and the used adhesives, making it impossible to identify one of these two treatments as the one to recommend independent of adhesive selection. Adhesive materials: Of the three adhesive systems, CE gave the highest mean strength values independent of surface treatments. The highest strength values with CE were for sandblasted surfaces even though it was not signif icantly higher than the etched surface. Sandblasting gave significantly higher bond st rength than with finished surfaces, while no significant difference between etched and finished surfaces was determined (Table 3-1). The trends were somewhat different for the SO and SXP adhesives. The etched surfaces had the highest bond strength values and the fini shed surfaces the lowest values for these

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28 adhesives. Table 3-1 shows that there is no significant difference in bond strength between etched and sandblasted surfaces in any adhesive system. SummaryHC: The best treatment for the HC is either sandblasted or etched the surface, and any of the three adhesives can be used (T able 3-1). Because of these findings, the first hypothesis that hydrofluoric acid treatment would work best on fe ldspathic ceramics could not be supported since sandblasting performed equally well in this type of ceramic. However, the fourth hypothesis that silane treatment is just a supplement to microm echanical retention is supported, because the best adhesion occurred on etched and sandblasted surfaces. The lowest bond strength values were found on the finished surfaces. Leucite-Reinforced Ceramic Systems (IP) Surface tr eatment: Figure 3-2 and Table 3-2 reveal that surface etching with 9.6% hydrofluoric acid resulted in the highest shear bond strength, followed by sandblasting and then a finished surface. However, it is important to note that interactions exist between surface treatments and adhesives, making it difficult to compare sandblasted and finished surfaces without considering the adhesive used. Adhesive materials: Of the three adhesives, CE result ed in the highest mean shear bond strength value independent of surface treatment. Of the three surface treatments, CE bonded best to etched surfaces and weakest to finished su rfaces. However, the differences between these three surface treatment groups were too small to be statistically sign ificant (Table 3-2). Comparing SXP and SO revealed that both ha d the highest values when bonded to etched surfaces, while SXP had the lowest value when bonded to sandblasted surfaces, and SO had its lowest value when bonded to finished surfaces. The strength value for the etched surfaces treated with SXP was significantly higher than the sandblasted or fini shed surfaces. The difference between the sandblasted and finished surfaces treated with SXP was not significant (Table 3-2).

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29 The SO groups had the same pattern as th e CE groups, showing the highest strength values for the etched surfaces and the lowest for the finished surfaces. When bonded to etched or sandblasted surfaces, however, SO produced sign ificantly higher values than when bonded to finished surfaces while showing no significant di fference between the etched and the sandblasted surfaces (Table 3-2). SummaryIP: The best treatment according to these re sults is to etch an IP surface with 9.6% hydrofluoric acid. Of the adhesives, CE ga ve similar results independent of surface treatment, while SXP produced comparably good results to CE when the surface was etched (Table 3-2). However, SXP gave significantly lower values than CE when the surfaces were sandblasted or finished. For this type of ceramic, the first hyp othesis that hydrofluoric acid treatment would perform best is weakly supported. The interaction between adhesive and surface treatment is too strong to str ongly support that hypothe sis. The fourth hypothesis that silane treatment is just a supplement to micromechan ical retention is weak ly supported. The weak support relates to the performance of CE that c ontains silane and gave only a non-significant difference between the different surface treatments. High-Alumina Reinforced Ceramics (PC) Surface tr eatment: Sandblasting resulted in the highest shear bond strength values (p < 0.05) (Figure 3-3 and Table 3-3). The other two treatments, etchi ng or finishing, did not differ from each other (p > 0.05). Adhesive material: Figure 3-3 shows that SXP always produced the highest shear bond strength values of the three adhesives, independent of surf ace treatment. Figure 3-3 also determines that SXP had the highest value for th e sandblasted surfaces and the lowest values for the etched surfaces. However, no significant difference in bond strength was determined when SXP is used on etched, finished, or sandblasted surfaces, as is depicted on Table 3-3. Figure 3-3

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30 shows that the bond strength values of the sandbl asted treatment combined with SXP adhesive were significantly higher than the other groups. Product CE followed the same pattern as SXP regarding the highest mean strength value for sandblasted surfaces and the lo west for etched surfaces. Also, the differences in strength between the three su rface groups were not significan t (p > 0.05) (Table 3-3). Of the three adhesives, the SO adhesive deviated from the other two adhesives considering surface treatments and bond strength values. The trend for SO was to have the highest shear bond strength for the sandblasted surface and the lowest for the finished surface, a difference that was significant. The SO adhesive gave the lowest shear bo nd strength values for PC treated with either etch ing or finishing treatment. Summary PC: The best treatment according to these results is to sandb last PC and use SXP or CE as the adhesive system (Table 3-3). The second hypothesis, suggesting that air abrasion would provide better surf ace roughening on alumina and therefore would provide better bonding than hydrofluoric acid was supported. Th e third hypothesis suggesting that due Al2O3 (or ZrO2) surfaces would be less compatible with the silane than a SiO2 surface is supported. All the adhesive contained silane, but in contrast to SO, both SX P and CE contained other active coupling agents. It seems as these active component improved the adhesion. Zirconia Reinforced Ceramics (CZ) Surface tr eatments: Figure 3-4 and Table 3-4 show that sandblasting produced the highest shear bond strength (p < 0.05). The other two treatments, etching or finishing, did not differ significantly from each other (p > 0.05). Adhesive material: Figure 3-4 shows that SXP, independent of a surface treatment, always resulted in the highest shear bond strength value of the three adhesive s. Figure 3-4 also reveals that SXP has the highest value for the sa ndblasted surfaces and the lowest value for the

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31 etched CZ surface. However, by looking at Ta ble 3-4, there was no significant difference in shear bond strength between the etched or finished surfaces when SXP was used, while SXP in combination with sandblasted surf aces resulted in significantly higher shear bond st rength values than the other two surface treatments (p < 0.05). The result of Figure 3-4 shows that the bond strength of a sandblasted treatment combined with SXP adhesive was significantly higher than the other groups. Adhesive CE followed the same trend as SXP regarding the highest mean strength value for sandblasted surfaces and the lowe st for etched surfaces (Figure 3-4). However, that trend was not significant because there were no significant differences in strength between the three surface groups (p > 0.05) (Table 3-4). Of the three adhesives, SO deviated from the other two adhesives considering surface treatments and bond strength values. The trend for SO was to have the highest shear bond strength for the sandblasted surface and the lo west for the finished surface, a significant difference (Table 3-4). The etched surface, though, was not significantly stronger than the finished surface and not significantly w eaker than the sandblasted surface. Summary CZ: The best treatment according to these results is to sandblast CZ and use SXP or CE as the adhesive system (Table 3-4) Also for CZ, the second hypothesis, suggesting that air abrasion would provide better surf ace roughening on alumina and therefore would provide better bonding than hydrofl uoric acid was supported. The same was true for the third hypothesis, suggesting that Al2O3 and ZrO2 surfaces would be less compatible with the silane than a SiO2 surface, was supported. The two adhesives that contained other active components than silane (SXP and CE) performed better than th e adhesive system that just relied upon silane (SO).

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32 Modes of Failure Alm ost all failures were adhesive in nature. Only IP and HC failed cohesively, and these failures occurred mainly in the surface-etched groups even though some failures could also be seen in the sandblasted groups (Figures 3-5 to 3-8). Not a single failure in the ceramic was noticed for any of the CZ or PC specimens, i ndependent of surface treatment (Figure 3-9). Discussion Statistical Evaluation Most studies sim ilar to this study use one -way, two-way, or three-way ANOVA. However, these results showed to have standard deviations between the different groups too large to make such an approach suitable. In order to run a reliable ANOVA evaluation on this data, more than six specimens per experimental group were needed as well as standard deviations of similar sizes. Because the key factor regarding bonding is to avoid failures, we felt that low strength values were of greater importance than the highest values. Because of that as well as the skewed distribution, the statistical eval uations were performed on the l ogarithm of the strength values. By using such an approach, the low values co uld be emphasized on the expense of the highest strength values. However, in Figures 3-1 to 3-4, decimal numbers were used to present the experimental results. The reason is simply that such a presentation helps the reader to understand the magnitude of the values generated for the different groups. Surface Treatment To better un derstand the effects of the different surface treatments, it is important to look at the different ceramics and their compositions. As s een from Table 2-1, there is a clear difference between the four ceramics. The HC and IP ceramics contain many different components, 35, 36 while PC and CZ ceramics are primarily comprised of either Al2O3 or ZrO2 with some yttrium. It is often assumed that hydrofluoric acid does not etch Al2O3 or ZrO2 in contrast to ceramics such

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33 as feldspathic porcelain and leucite. Re view of the literature reveals that Al2O3 and ZrO2-based ceramics are acid resistant and perform better when their surfaces are sandblasted. 30, 35, 48 By etching feldspathic ceramic with 9.6% hydr ofluoric acid, the acid dissolves the glassy phase of the feldspathic ceramic, which results in a micro-undercut forma tion at the surface of the ceramic. These micro-undercuts are then filled by the adhesive resin, resulting in micromechanical interloc king within the ceramic.22, 49 Leucite in the IPS Empress ceramic showed a morphological surface change when treated with 10% hydrofluoric acid.30 Etching the HC and IP groups with 9.6% hydrofluoric acid resulted in the highest bond strength values. This finding is in agreement with the earlier works.22, 50, 51 However, with both alumina and zirconia the etching reaction may be different. For example, alumina consists mainly of Al2O3 and zirconia mainly of ZrO2 (Table 2-1). Because of these rather homogeneous compositions, no preferential etching may occur, and as a consequence, the contribution from micromechan ical retention may be significantly reduced when compared to the other two ceramics. These results may be explained by assuming that such a difference exists between HC and IP ceramics on one hand and the PC and CZ ceramics on the other hand. When it comes to alumina and zirconia, both are significantly toughe r than the other two ceramics. Comparing zirconia with alumina reveal s that zirconia-based material is the toughest of all the investigated ceramics (Figure 1-1). The high fracture toughness of zirconia is understood by examining the structure of zirconia. Zirconia may be present in a number of crystal phases, depending on the presence of small amounts of components such as calcia, magnesia, yttria (Y2O3), or ceria. A tetragonal precipitate of ZrO2 is achieved by Y2O3 additions, while an alternative approach is used to produce a different micr ostructure. For example, a very

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34 fine powder (<0.03 m) containing 2 to 3 mol % Y2O3 and 97 to 98 mole % ZrO2 can be densified completely in the tetragonal phase fi eld to yield a fine-gra ined microstructure consisting almost totally of tetra gonal grains. Each grain in this ma terial can transform to another phase near a crack tip to inhi bit propagation of the crack. When that happens, the ZrO2 goes through a martensitic phase transformation from the tetragonal-to-monoclinic crystal form, causing the material to expand in front of the crack tip and induce a compressive stress in that region that hinders the crack to propagate. Partly stabilized zirconia contains yttria, and its tetragonal zirconia phase is stabilized at room temperature.36 Under such conditions, etching w ill not produce a surface capable of forming a significant level of micromechanical retention, explaining w hy the bond strength of CZ treated with 9.6% hydrofl uoric acid were lower within the same groups. From this observation, it can be determined that the 9.6% of hydrofluoric acid does not have a selective phase or is not strong enough to etch the zirconia-based ceramics. H ydrofluoric acid may just be an ineffective etchant on this type of ceramic.30, 52 Besides etching a ceramic surface, such a su rface can also be sandblasted. By mixing air under pressure with a hard particulate abrasive, the ceramic material can be abraded or worn away from the surface of the ceramic. By using su ch an approach, a rough ceramic surface with a frosted appearance is produced during sandblasting. The longer time the abrasive stream targets the surface of the ceramic and the larger the size of the abrasive particulates, the more material will be removed.53 In this study, airborne Al2O3 particles, 50 m in diameter, were used for five seconds with a pressure of two bars. By sandblas ting the HC and IP ceramics, it is known that Al2O3 particles produce a uniform pee ling appearance of the feldspathic ceramics or increase the number of pits per unit area of the IPS Empress ceramic.30 Such a treatment increases the

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35 mechanical retention and the bond strength.54 Regarding the HC ceramic, there was no significant difference (P > 0.05) between sandblasted or acid etching. On that ceramic, it did not seem to matter which one of the resinous adhesives was used. IP showed almost the same results except that SXP resulted in the (P < 0.05) highest bond strength significantly when used on the etched IP surfaces. For the PC and CZ ceramics, the shear bond strength values of th e sandblasted surface were higher than the etched or finished surface treatments, which supports the hypothesis that air abrasion is the optimal surface treatment to roughen alumina and zirconia ceramic. This result was similar to Madanis in 2000; 55 however, these values were lower when compared to HC or IP ceramics. This differen ce may be related to the Al2O3 particles used during sandblasting having a higher fracture toughness than the HC or IP ceramics but having a similar fracture toughness as PC and lower than CZ. As a conseq uence, the lowest level of abrasion may have occurred on CZ followed by PC, while the highes t abrasion occurred on HC and IP ceramics. In other words, the composition of the ceramic materi als plays an important role when it comes to surface roughening ability. Adhesive The shear b ond strength depends on the ceramic composition and the surface treatment of the ceramic. The silane enhances the wetting ability of the ceramics. When silane is applied to a ceramic surface and then dried, a condensation re action occurs that results in a covalent bond formation with the glass surface. The silane-treat ed ceramic with its methacrylate groups present in the silane creates a bond with the methacrylate groups in the composite resin when the composite is cured (Figure 1-2).24 CE is a single-component adhesive primer containing both silane and a phosphate monomer, 10-Methacryloyloxydecyl dihydrogen phosphate (MDP). When placed on a basic

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36 surface, this phosphate monomer acts as an acid, loosens protons, and forms a negative backbone structure that reacts with positive charge site s on the ceramic surface. The silane also forms bonds to the ceramic surface. According to the manufacturer, phosphate monomer will bond directly to metal, alumina, or zirconia oxides, and as well as a silane coupler to bond with SiO2 based ceramics. MDP provides a long term-ter m stable bond to alumina and zirconia-based ceramics.48, 56 Regarding SXP, the surface treatment consis ted of first a separate silane coating and then a coating with XP Bond. XP B ond contains dipentaerytritolpentacrylatephosphoricacid-monomer (PENTA-P) among other mono mer systems, which reacts in the same way as MDP and bonds to positive charge sites present on a ceramic surface. However, Raffaelli (2004) concluded in his study that XP Bond was outperform ed when compared to the control group.57 A possible explanation why Raffaelli (2004) did not succeed as well with XP Bond could simply be that he did not combine it with silane. Considering these aspects, both CE and SXP can be described as both silane and acidic monomer treatments. Thus, both the silane and the acidic monomer will bond to ceramic surfaces and contribute to their good bondi ng abilities. Considering that SO does not contain any acidic monomer like MDP or PENTA-P, it seems reasona ble to suggest that th e higher bond strength values of CE and SXP are due to the pres ence of the acidic monomer components. Modes of Failure The clin ical failure of all-ceramic restorations is very often associated with their brittleness and low fracture toughness. Recent studies show th at the zirconia-based core material has the highest fracture toughness44twice that of alumina cores,45 which in turn is tougher than pressed leucite and feldspathic ceramics (Figure 1-1). Fracture toughness is an important material property and represents the ability of the material to resist brittle failure. The lower the fracture

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37 toughness, the lower the clinical reliability of the ceramic rest oration. The higher the fracture toughness, the better the material deflect s a crack and distributes its energy.58 The dominating failure mode occurred in the adhesive. Because of a lack of information (no SEM evaluation or microanalysis of surface compositions), researchers do not know whether failures occurred at the ceramic-adhesive interface, within the adhesive, or at the adhesivecomposite interface. However, visual inspections indicate that most failures occurred within the adhesive film or at the adhesi ve-composite interface. The conc lusion is based on the impression that a resin film was left on th e ceramic surfaces after testing. In addition to the adhesive failures, the HC a nd IP ceramics showed some cohesive failures occurring in the ceramic. These failures are attr ibuted to high resin-ceramic bond strength values and sufficiently high stress levels transferred to the ceramic surface. In such situations, cracks that started at the interface could be diverted into the ceramic surface and result in a cohesive failure of the ceramic region in contact with the bonded composite surf ace. Such cohesive failures were seen in HC and IP, especially af ter surface etching, while no such failure was seen in any of the CZ or PC specimens. The goal of this study was to determine the best method of repairing chipped ceramic veneering. Based on the results, the first recomm endation, if possible, is that the clinician identifies the ceramic that has been used. If th e chipped veneer is a FELD crown, the clinician should sandblast it and bond it with CE. In the case of an IP, the crown should be acid-etched and bonded with SXP. With CZ and PC, however the ceramic should be sandblasted and bonded with SXP, as it preformed best in this study. If the ceramic re storation cannot be determined, repair of the chipped ceramic should utilize a univ ersal system that works for all ceramics. Based on this study, the recommendation is to sandblas t the ceramic surface and then use CE as the

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38 bonding agent, as this method proved effective on each ceramic system tested. An interesting observation was that CZ had a higher shear strength value than the PC ceramic, when sandblasted with Al2O3. Since the fracture toughness of ZrO2 is higher than the Al2O3, one would expect that sandblasting with Al2O3 should have less effect on ZrO2 than on Al2O3. The reason would simply be that the Al2O3 particles rather than the zircon ia surface should break during the impact. As a consequence, the zirconia surf ace should be less rough th an the alumina surface after sandblasting and result in rather a lower than a higher b ond strength than the alumina surface. However, the opposite was observed justifyi ng future studies dealing with the impact of different sandblasting parameters.

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39 Figure 3-1. Shear bond strength of HeraCeram Figure 3-2. Shear bond strength of IPS Empress

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40 Figure 3-3. Shear bond strength of the Cercon Zirconia Figure 3-4. Shear bond strength of Procera Crown Alumina

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41 Table 3-1. Feldspathic ceramic T-test comparison and significant differences of different surface treatments and adhesive bond materials. Column1 E/CE E/SO E/SXP F/CE F/SO F/SXP S/CE S/SO S/SXP E/CE not not not + S + S Not not not E/SO not not + S + S + S Not not not E/SXP not not + S + S + S Not not not F/CE not S S + S not S not not F/SO S S S S not S S S F/SXP S S S not not S S S S/CE not not not + S + S + S not not S/SO not not not not + S + S Not not S/SXP not not not not + S + S Not not Table 3-2. IPS Empress ceramic T-test comparis on and significant differences of different surface treatments and adhesive bond materials. Column1 E/CE E/SO E/SXP F/CE F/SO F/SXP S/CE S/SO S/SXP E/CE not not not not + S Not not + S E/SO not not not + S + S Not not + S E/SXP not not not + S + S Not not + S F/CE not not not not not Not not not F/SO not S S not not Not S not F/SXP S S S not not S S not S/CE not not not not not + S not + S S/SO not not not not + S + S Not + S S/SXP S S S not not not S S Table 3-3. Procera ceramic T-test comparison and significant differences of different surface treatments and adhesive bond materials. Column1 E/CE E/SO E/SXP F/CE F/SO F/SXP S/CE S/SO S/SXP E/CE not not not not not Not not not E/SO not S S + S S S S S E/SXP not + S not + S not S not not F/CE not + S not + S not Not not not F/SO not S S S S S S S F/SXP not + S not not + S Not not not S/CE not + S + S not + S not + S not S/SO not + S not not + S not S not S/SXP not + S not not + S not Not not

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42 Table 3-4. Cercon ceramic T-test comparison an d significant differences of different surface treatments and adhesive bond materials. Column1 E/CE E/SO E/SXP P/CE P/SO P/SXP S/CE S/SO S/SXP E/CE not not not not S S not S E/SO not not not not not S not S E/SXP not not not + S not not not S P/CE not not not + S not not not S P/SO not not S S S S S S P/SXP + S not Not not + S not not S S/CE + S + S Not not + S not not not S/SO not not Not not + S not not S S/SXP + S + S + S + S + S + S not + S Figure 3-5. Type of HeraCeram ceramic adhesi ve failures of acid etched surface treatment. Figure 3-6. Type of HeraCeram ceramic adhe sive failures of sandbl ast surface treatment.

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43 Figure 3-7. Type of IPS Empress ceramic adhesive failures of acid etched surface treatment. Figure 3-8. Type of IPS Empress ceramic adhesive failures of acid etched surface treatment. Figure 3-9. Failure of IPS Empress ceramic (IP) which had been etched before bonding (left). No such failures occurred in any of the Cerc on Zerconia specimens (CZ), independent of surface treatment (right).

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44 CHAPTER 4 SUMMARY AND CONCLUSSIONS The four formulated hypotheses showed to be difficult to reject or strongly support because of the interactions that o ccurr ed between ceramics, surface treatments and adhesives. The first hypothesis suggesting that hydroflu oric acid treatment would work best on feldspathic and pressed ceramics, was only supported for the pr essed ceramic. The second hypothesis suggesting that air abrasion would provide better surface roughening on zircon ia and alumina and therefore provide better bonding on these two ceramics than hydrofluoric acid was indirectly supported by the strength measurement and needs to be supplemented by surface roughness measurements. The third hypothesis suggesting that similarities between the silica structure and the silane molecules, should result in be tter bonding between the silane and feldspathic and pressed ceramics than with the Al2O3 and ZrO2 ceramics was supported. The fourth hypothesis, suggesting that silane treatment is just a suppl ement to an etched or sandblasted surface was partly supported because in general the best adhesion occurred to surfaces with micromechanical retention ability. However, to prove this hypothesis, unsilanated specimens should have been included in the experimental design. The key objective with this project was to determine how a clinician should repair a chipped ceramic restoration. The results revealed that different ceramics require different repair approaches and repair systems in orde r to perform best. The results suggest: a) feldspatic ceramics performs equally well if sandblasted or etched. b) IPS Empress performs best if etch ed with 9.6% hydrofluoric acid. c) zirconia and alumina materials such as CE R and PROC are best repaired by use of sandblasting. d) Of the different adhesives, SXP and CE pe rformed best on feldspathic, alumina and zirconia based ceramics, even though a more traditional treatment with SO performs equally well when used on feldspathic and pressed.

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45 e) An important observation was that for sa ndblasted IPS Empress, the CE adhesive performed better than SXP. IPS Empress perfor med best after hydrofluoric acid treatment and when CE was used as adhesive. In a situation, when the dentis t does not know what kind of ceramics was originally used, sandblasting and use of CE will most likely give the best result.

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46 LIST OF REFERENCES 1. McLean JW. Evolution of dental ceram ics in the twentieth century. J Prosthet Dent 2001;85:61-6. 2. Fischer H, Marx R. Fracture toughness of dental ceramics: comparison of bending and indentation method. De nt Mater 2002;18:12-9. 3. Thompson JY, Anusavice KJ, Naman A, Morri s HF. Fracture surface characterization of clinically failed all-ceramic crowns. J Dent Res 1994;73:1824-32. 4. Moffa JP. Porcelain materials. Adv Dent Res 1988;2:3-6. 5. Kelly JR. Dental ceramics: current thinki ng and trends. Dent Clin North Am 2004;48: 513-30. 6. Guazzato M, Albakry M, Ringer SP, Swain MV. Strength, fracture toughness and microstructure of a selection of all-ceramic materials. Pa rt II. Zirconia-based dental ceramics. Dent Mater 2004;20:449-56. 7. Lee YK, Cha HS, Ahn JS. Layered color of all-ceramic core and veneer ceramics. J Prosthet Dent 2007;97:279-86. 8. Coornaert J, Adriaens P, De Boever J. L ong-term clinical study of porcelain-fused-togold restorations. J Pros thet Dent 1984;51:338-42. 9. Odman P, Andersson B. Pro cera AllCeram crowns followed for 5 to 10.5 years: a prospective clinical stud y. Int J Prosthodont 2001;14:504-9. 10. Zhukovsky L, Godder B, Settembrini L, Schere r W. Repairing porcelain restorations intraorally: techniques and materials. Compend Contin Educ Dent 1996;17:18, 20, 22. 11. Latta MA, Barkmeier WW. Approaches for intraoral repair of ceramic restorations. Compend Contin Educ Dent 2000;21:635-44. 12. Ozcan M, Niedermeier W. Clinical study on th e reasons for and location of failures of metal-ceramic restorations and survival of repairs. Int J Prosthodont 2002;15:299-302. 13. Ozcan M. Evaluation of alternative intra-oral repair techniques for fractured ceramicfused-to-metal restorations. J Oral Rehabil 2003 ;30:194-203. 14. Stangel I, Nathanson D, Hsu CS. Shear strength of the composite bond to etched porcelain. J Dent Res 1987;66:1460-5. 15. Canay S, Hersek N, Ertan A. Effect of different acid treatments on a porcelain surface. J Oral Rehabil 2001;28:95-101. 16. Beiran I, Miller B, Bentur Y. The efficacy of calcium gluconate in ocular hydrofluoric acid burns. Hum Exp Toxicol 1997;16:223-8.

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47 17. Zachrisson Y O, Zachrisson B U, Buyukyilm az T. Surface preparation for orthodontic bonding to porcelain. American Journal of Orthodontics and Dentof acial Orthopedics 1996;109:420 430. 18. Kocadereli I, Canay S, Akca K. Tensile bond strength of ceramic orthodontic brackets bonded to porcelain surfaces. American J ournal of Orthodontics and Dentofacial Orthopedics 2001;119:617. 19. Harari D, Shapira-Davis S, Gillis I, Ro man I, Redlich M. Tensile bond strength of ceramic brackets bonded to porcelain facets. Am J Orthod Dentofacial Orthop 2003;123:551-4. 20. Gler AU, Yilmaz F, Ural C, Gler E. Eval uation of 24-hour shear bond strength of resin composite to porcelain according to surface treatment. Int J Prosthodont 2005;18:156-60. 21. Thurmond JW, Barkmeier WW, Wilwerding TM. Effect of porcelain surface treatments on bond strengths of composite resin bonded to porcelain. J Prosthet Dent 1994;72:355-9. 22. Roulet JF, Sderholm KJ, Longmate J. Eff ects of treatment and storage conditions on ceramic/composite bond streng th. J Dent Res 1995;74:381-7. 23. Newburg R, Pameijer CH. Composite resin bond ed to porcelain with silane solution. I Am Dent Assoc 1978;96:288-291. 24. Plueddemann, EP. Silane Coupling Agents. New York: Plenum Press; 1982. 25. Hayakawa T, Horie K, Aida M, Kanaya H, Kobayashi T, Murata Y. The influence of surface conditions and silane agents on the bond of resin to dental porcelain. Dent Mater 1992;8:238-40. 26. Sderholm KJ, Shang SW. Molecular orientatio n of silane at the surface of colloidal silica. J Dent Res 1993;72:1050-4. 27. Bascom WO. Structure of sila ne adhesion promoter films on glass and metal surfaces. Macromol 1972;5:792-798. 28. Marsden JG. Organofunctional silane coupling agents. In: Skeist I, editor. Handbook of adhesion. New York: Van Nostrand Reinhold; 1990. 29. Matinlinna JP, Heikkinen T, Ozcan M, Lassila LV, Vallittu PK. Evaluation of resin adhesion to zirconia cerami c using some organosilanes. Dent Mater 2006;22:824-31. 30. Borges GA, Sophr AM, de Goes MF, Sobrinho LC, Chan DC. Effect of etching and airborne particle abrasion on the microstructu re of different dental ceramics. J Prosthet Dent 2003;89:479-88. 31. Gregory WA, Moss SM. Effects of heteroge neous layers of composite and time on composite repair of porcela in. Oper Dent 1990;15:18-22.

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48 32. Creugers NH, Snoek PA, Kyser AF. An expe rimental porcelain repair system evaluated under controlled clinical conditions. J Prosthet Dent. 1992 Nov;68(5):724-7. 33. Llobell A, Nicholls JI, Kois JC, Daly CH. Fa tigue life of porcelain repair systems. Int J Prosthodont 1992;5:205-13. 34. Jardel V, Degrange M, Picard B, Derrien G. Correlation of to pography to bond strength of etched ceramic. Int J Prosthodont 1999;12:59-64. 35. Ozcan M, Vallittu PK. Effect of surface c onditioning methods on the bond strength of luting cement to ceramics Dent Mater 2003;19:725-31. 36. Giordano R. Materials for chairside CAD/CA M-produced restorations. J Am Dent Assoc 2006;137 Suppl:14S-21S. 37. Jones DW. Development of dental ceramics. An historical perspective. Dent Clin North Am 1985;29:621-44. 38. Ironside J G, and Swain M V. Ceramics in De ntal Restorations A Review and Critical Issues. Journal of the Australa sian Ceramic Society 1998;34:78-91. 39. Kon M, O'Brien WJ, Rasmussen ST, Asaoka K. Mechanical properties of glass-only porcelains prepared by the use of two feldspathic frits with different thermal properties. J Dent Res 2001;80:1758-63. 40. Dong JK, Luthy H, Wohlwend A, Schrer P. Heat-pressed ceramics: technology and strength. Int J Pr osthodont 1992;5:9-16. 41. Deany IL. Recent advances in ceramics for dentistry. Crit Rev Oral Biol Med 1996;7:134-43. 42. El-Mowafy O, Brochu JF. Longevity and clinical performance of IPS-Empress ceramic restorations--a literature revi ew. J Can Dent Assoc 2002;68:233-7. 43. Andersson M, Oden A. A new all-ceramic crown. A dense-sintered, high-purity alumina coping with porcelain. Acta Odont Scand 1993;51:59-64. 44. Yilmaz H, Aydin C, Gul BE. Flexural stre ngth and fracture toughne ss of dental core ceramics. J Prosthet Dent 2007;98:120-8. 45. Richerson DW Modern ceramic engineer ing. Marcel Dekker Inc., New York 1992; p.360. 46. Lthy H, Filser F, Loeffel O, Schumacher M, Gauckler LJ, Hammerle CH. Strength and reliability of four-unit all-ceramic pos terior bridges. Dent Mater 2005;21:930-7. 47. Ott L. First Course in Statistical Methods. 2003.

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49 48. Kern M, Wegner SM. Bonding to zirconia ceramic: adhesion methods and their durability. Dent Mater 1998;14:64-71. 49. Chen JH, Matsumura H, Atsuta M. Effect of different etching periods on the bond strength of a composite resin to a machinable porcelain. J Dent 1998;26:53-8. 50. Akova T., Aytutuldu a N. and Yoldas b O. The evaluation of different surface treatment m ethods for porcelaincomposite bonding. In ternational Journal of Adhesion and Adhesives 2007;27:20-25. 51. Trk T, Sara D, Sara YS, Elekda -Trk S. Effects of surface conditioning on bond strength of metal brackets to allceramic surfaces. Eur J Orthod 2006;28:450-6. 52. Terki R, Bertrand G, Aourag H, Coddet C. Stru ctural and electronic pr operties of zirconia phases: A FP-LAPW investigations. Mate rials Science In Semiconductor 2006;9:10061013. 53. Kern M, Thompson VP. Sandblasting and sili ca coating of a glass-infiltrated alumina ceramic: volume loss, morphology, and changes in the surface composition. Journal of Prosthetic Dentistry 1994;74:145. 54. Gillis I, Redlich M. The effect of differ ent porcelain conditioning techniques on shear bond strength of stainless steel brackets. Am J Orthod Dentofacial Orthop 1998;114:38792. 55. Madani M, Chu FC, McDonald AV, Smales RJ. Effects of surface treatments on shear bond strengths between a resin cement and an alumina core. J Prosthet Dent 2000;83:644-7. 56. Kern M, Thompson VP. Bonding to glass infi ltrated alumina ceramic: adhesive methods and their durability. J Prosthet Dent 1995;73:240-9. 57. Raffaelli O, Cagidiaco MC, Goracci C, Ferrari M. XP BOND in self-curing mode used for luting porcelain restorati ons. Part A: Microtensile te st. J Adhes Dent 2007;9 Suppl 2:275-8. 58. Thompson JY, Anusavice KJ, Balasubram aniam B, Mecholsky JJ. Effect of microcracking on the fracture toughness and fr acture surface fractal dimension of lithiabased glassceramics. J Am Ceram Soc 1995;78:3045-9.

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50 BIOGRAPHICAL SKETCH I was born in 1974 and grew up in Kuwait City, Kuwait. I graduated from Bayan High School in Kuwait City in 1992. In 1993, I enrolled at the University of Miss ouri-Kansas City to pursue a deg ree in biology of arts and scienc e. In 1996, I was accepted at the University of Missouri-Kansas City School of Dentistry. In 1997, I married my beautiful wife, Dalal. In 2001, I graduated from the University of Missouri-Kansas City School of Dentis try with a Doctor of Dental Surgery degree. I have three children, two girls and a boy. I retu rned home to Kuwait and worked for the public health system of Kuwa it from 2001 to 2005, before deciding to pursue a dental specialty degree in the Un ited States. I enrolled in the gr aduate prosthodontics program at the University of Florida. After graduation with a Master of Science in dental sciences with specialization in prosthodontics from the University of Florida in July 2008, I will be enrolled in the same program as Implant Fellow for one ye ar. On completion of the implant fellowship position, my wife and I plan to return to Kuwait and work for the public health system for the betterment of the dental service of our beloved country. This will be the beginning of the rest of our lives.