effect of adhesives on bond strength of porcelain veneer to
TRANSCRIPT
Prosthodontics
Effect of adhesives on bond strength of porcelain veneer to base metal alloy
Reza Goharian, DDS, MSVFatemeh Maleknejad, DDS /Taghi Saiari,DDS3/ Marjaneh Ghavamnasiri, DDS- /Mohammad Derhami,
Objective: The purpose of this in vitro study was to evaluate the bond strength of porcelain veneer to base metal alloy using different adhesive systems. Method and materials: Eighty cylindrical models were cast in a nlckel-chromium-beryIlium base metal alloy. After they were mounted in self-cured acrylic resin, the surfaces of the specimens were air abraded. Specimens were divided into four groups of 20, Control porcelain disks were baked on the base metal. For the experimental groups, 60 porcelain disks were made. After öO-pm aluminum oxide sandblasting, a silane coupling agent was applied to the surface of the porcelain. The experimental groups were based on the type of adhesive used to bond porcelain to metal: Scotchbond Multipurpose and Duo Cement; One Coat Bond and Duo Cement; or Panavia 21 Ex, After 500 thermal cycles, the bonded porcelain specimens were placed under a continuous shear load of 2 mm/min until fracture occun-ed. Results: Mean values for bond strength were 25,39 (control), 19.10 ¡Panavia 21 Ex), 15,81 (Scotchbond Multipurpose), and 13,69 MPa (One Coat Bond], Statistically significant differ- ences in bond strength were noted between tfie control group and all the experimental groups, A statisti- cally significant difference was observed between Panavia 21 Ex specimens and One Coat Bond speci- mens. Conclusion: Panavia 21 Ex provided an effective bond strength between a porcelain veneer and a base metal alloy, the closest of all the experimental groups to that of the control group, (Quintessence int 2002:33:595-599)
Key words: adhesive, base metal alloy, bond strength, porcelain veneer
CLINICAL RELEVANCE: The repair of a fractured metal- ceramic crown with a porcelain veneer cemented to the base metal substructure is a possible treatment alterna- tive, Panavia 21 Ex may be a suitable resin cement for bonding the porcelain veneer to the base metal.
Metal-ceramic crowns are the most widely used type of complete veneer restoration. Considering
the large difference in modulus of elasticity hetween
'Associate Professor, Departmenl ol Prostlioöondcs, Faoulty of Dentistry,
Mashhad Unrversity, Mashrtad, Iran.
^Assistant Professor, Department of Piosthodonlcs, Faculty of Dentistry,
Mashhad Univeisify, Mashhad, Iran.
Reprint requests: Or M. Ghavamnasiri, Associate Professor, Department ol Operative Dentistry, Mashhad University, Mashhad, Iran. E-maii; dr_Marjaneh @yahoo,com
metal and porcelain, it is not surprising that mechani- cal faiiures of the metal-ceramic bond can occur. Causes of metal-ceramic faiiure include unsuitable de- sign of metal coping, tecbnical errors, contamination, physical trauma, and premature occlusal contact.
Porcelain fracture does not necessarily mean failure of the restoration. It may pose only an esthetic and/or a functional dilemma for the patient and dentist. If the restoration is to be repaired, the bond strength of the repair must be strong and dtirable.' Types of failure in metal-ceramic cro«Tis include fracture only in porce- lain without metal exposure, fracture with partial metal exposure, and fracture with complete metal exposure.-
Various methods have been introduced for repair- ing fractured porcelain with resin composite. Sandblasting with aluminum oxide is one method of surface roughening.^ The porcelain can also be etched with hydrofluoric acid to facilitate mlcromechanical retention of resin composite,'"^ Use of an intraoral sandblaster is an alternative way to provide microme- chanical retention, although the roughening of the ce- ramic surface by the sandblaster may be less than that produced by hydrofluoric acid,'
Quintessenc 595
• Goharian et ai
Mechanical roughening of the fractured surface fol- lowed by application of a silane coupling agent can enhance the resin-to-porcelain bond,' Phosphoric acid etching does nol increase the porcelain-resin compos- ite bond strength,' It was recognized that roughening and etching of porcelain are more important for me- chanical retention than are silane coupling agent and chemical retention.^ Appeldoorn et al"* found the bond strength of resin composite to porcelain was 23.5 MPa; after thermocycling, the bond strength de- creased. Chung and Hwang' showed that aluminum oxide sandblasting and hydrofiuoric acid treatment followed by application of Scotchbond can result in a porcelain repair bond strength of 14.7 MPa.
Surface treatment of base metal alloys with alu- minum oxide sandblasting is a valuable procedure for increasing roughness."-'^ A previous study reported that tbe aluminum oxide content of base metal alloys increases up to 30 vt Vo after sandblasting. Ultrasonic cleaning resulted in only minor removal of the embed- ded aluminum oxide, which can create chemical bonds with adhesives and enhance bond strength.'^
Further improvements in adhesion of resin compos- ite to base metals have recently been reported by the following
1. Multipurpose resins such as Scotchbond Multi- purpose (3M Dental), for which a bond strength of 30 MPa to Rexillium cast metal alloy (feneric/ Pentron) has been quoted by the manufacturer. ""
2. All-Bond 2 {Bisco Dental), for which a bond strength of 21.8 MPa to Rexillium III cast metal alloy has been reported.^
3. Panavia Ex (Kuraray), a dimethacrylate in wbich phosphate ester groups are incorporated in a bis- GMA resin. Aboush and Jenkins'** have reported bond strengths of up to 28 MPa between Panavia Ex and sandblasted nickel-chromium alloy,
A number of studies on porcelain repair by resin composite have been published,^'^-^' but, when metal is completely exposed, tbere seem to be two ways to solve the problem: (1) bonding a resin composite ve- neer to base metal (2) bonding a porcelain veneer to base metal. Only two clinical reports have been pub- lished ahout bonding of a porcelain veneer to exposed metal. ' ^ Therefore, the aim of the present study was to evaluate the effect of adhesives on tbe bond strength of a porcelain veneer to a base metal alloy.
METHOD AND MATERIALS
Eighty cast specimens were made in a nickel- chromium-beryllium alloy (Super Cast MP, Therma-
bond Alloy). All the manufacturer's re ¡.cndations for the burnout and casting proced ^ • were fol- lowed. The specimens consisted of twi. 'lisiiS, one (11 mm in diameter and 3 mm thick) for porcelain veneer application and the other (8 mm in ditimeter and 3 mm thick) for mounting in a self-cured acrylic resin mold (Formatray, Kerr/Sybron). The surfaces of all specimens were air abraded with 50-[¡m aluminum oxide (Micro-etcher, Model ERC, Danville Engin- eering) used with a pressure of 50 kg/cm^ at a dis- tance of 5 mm.
Specimens were divided into four groups of 20. In the control group (C), 20 specimens were selected for firing of porcelain (Vita Omega A-2 Metalkeramic, Vita Zahnfabrik). A piece of platinum foil was pre- pared, with a hole (4 mm in diameter) punched ap- proximately at its center, and adapted on the cast- metal disk to create a standardized area for porcelain application. Porcelain firing was carried out in a porcelain oven (Vita Vacumat 300, Vita Zahnfabrik). After 24 hours, specimens underwent 500 thermal cy- cles from 500"C to 55''C,
In the experimental groups, 60 cast specimens were maintained at 96O''C for 5 minutes, which was similar to the firing cycle for the metal-ceramic specimens. The base metal surtaces were then roughened with a coarse diamond bur, rinsed in tap water, and subjected to 50-ijm aluminum oxide sandblasting. Holes were created in a piece of platinum foil (4 mm in diameter), which was then adapted to a piece of mica. In this way, the porcelain disks were fired in a porcelain oven.
After the bonding surface of the porcelain disks was sandblasted, a 9.50/0 hydrofiuoric acid gel (Ultradent) was applied to this surface for 4 minutes. A frosted ap- pearance was observed after the surface was rinsed with water and dried. The ceramic primer was applied to the bonding surface of the porcelain disks. The manufacturer's directions for each system were fol- lowed when the porcelain was bonded to the base metal. Tbc experimental groups of specimens were di- vided into three groups of 20, based on tbe type of ad- hesive. Scotchbond Multipurpose {group S) is a dentin bonding agent. After application of activator on the metal surface, Scotchbond primer was applied and dried after 5 seconds until a glossy appearance was observed. The catalyst was applied to the primed sur- face. Duo Cement (Coltene/Whaledent) was used as a luting cement. Duo Cement was applied first to the porcelain bonding surface and then to the metal sur- face and light cured with the Coltene light-curing unit (Coltene/Whaledent) from each side for 60 seconds.
One Coat Bond (group O) is a dentin bonding agent {Coltene/Whaledent). One drop of the adhesive was applied to the bonding surface of porcelain and light cured for 20 seconds with the Coltene light-ciiring
596 Volume 33, Number 8, 2002
• Gotiarian et al
unit. The rest of the procedure was similar to that de- scribed for group S.
Panavia 21 Ex (group P) is a resin cement. The base and catalyst were mixed and applied to the porcelain disk. The disk was Immediately placed on the bonding surface of metal and mild finger pressure was main- tained until the cement set.
Thermocycîing was performed for the experimental groups in a manner similar to that used for the control group. An Instron testing machine (Model 8500. Instron Engineering) was equipped with a chisel- shaped rod with a shearing force along the interface between metal and porcelain. The bonded porcelain cylinders were placed under sustained, continuous loading at 2 mm/min until fracture occurred (Fig 1). Sbear bond strengths were calculated and recorded in megapascals.
Statistical analysis of data was accomplished by analysis of variance. The Duncan multiple range test and / test were used for all post hoc pairwise compari- sons at the QS /o confidence level.
DISCUSSION
Previous studies have indicated that, for repair of porce- lain, etching with hydrofluoric acid and application of a süane coupling agent in combination with an unfilled resin could create a suitable bond strength.-*- The pre- sent smdy evaluated the effect of adhesives on the bond strengths of porcelain veneers to base metal alloys.
It was not surprising that the metal-ceramic speci- mens (controi) displayed tbe higbest bond strength. Miller et al--' found that metal-ceramic bond strength was 720 psi in axial loading. The most important causes of higher bond strengths in metaj-ceramic are:
1. The surface roughness of the ailoy. which is filled and wetted by porcelain during sintering.
2. Tbe creation of a chemical bond between porcelain and metal oxides.
3. Tbe compact bond between the ceramic and the base metal. =
RESULTS
The mean bond strength values for each group are listed in Table 1. The bond strength values ranged from 13.69 ± 6.62 MPa to 25.39 ± 6.68 MPa. One-way analysis of variance for the experimental groups re- vealed a stadstically significant difference among them (P < .05). Duncan's mulfiple range test revealed a sta- tistically significant difference (P < .05) between groups P and O. Tbere was no statistically significant difference between the bond strengths of Scotchbond Multipurpose and Panavia 21 Ex. The t test reveaied a statistically significant difference (P < .01) between the mean bond strengtb of group C and tbe mean bond strengths of all three experimental groups (Fig 2).
— Shea nng device
-Embedded material
Fig 1 Positioning of test specimer>s in the tesling apparatus.
TABLE 1 Shear bond strength (MPa)
Group Mean SD
Scotchbond Muftipurpose (S) 15.81 7.50 Panavta 21 Ex (P) 19.10 8.90 One Coat Bond (0) 13.69 6.62 Control (C) 25 39 6.68
'S Q-
H•—•—^M c
Fig 2 Sheaf txind strengths ot experimental groups and control; (S) Scotchbond Multipurpose; (P) Panavia 21 Ex; (O) One Coat Bond; (C) controE.
Quintess 597
• Goharian et al
Among experimental groups, the highest bond strengtb was observed in group P altbougb it was not significantly different from group S, Panavia 21 Ex re- portedly adheres to sandblasted base metal alloy,"'' '"* The manufacturer also has recommended this proce- dure, Williams et al" found that, after 1,080 thermal cycles, Panavia demonstrated higher bond strengths to sandblasted metal than did Super-Bond B&C, Omura et al ^ found tbe best base metal surface treatment for Panavia was aluminum oxide sandblasting, which re- sulted in minor roughness and embedding of the alu- minum oxide in metal surface. ' Phosphate groups in Panavia could react with metal oxides and create both mechanical and chemical bonds,"
Tbe mean bond strength of group S was not signifi- cantly different tban tbat of Panavia, but its bond strengtb was lower tban enamel to resin composite bond strength,- ' ^ Tbe ceramic primer in this adbesive could act as adhesion promoter on the metal sur- face,^^^ However, when paired with Duo Cement dual-cured resin cement, Scotchbond Multipurpose did not achieve a high bond strength.
Film tbickness of tbe luting cement is a very impor- tant factor in bond strengtb; the lower the thickness, the greater the bond strengtb, "' i Tbe film tbickness of adhesive resins such as Panavia is in the range of 13 to 20 pm,'^ It is thought that tbe lower bond strengtb of Duo Cement could be attributed to the greater film thickness of this resin cement (about lOf) ]im}.'^^ This may be the reason that the eombination of Scotcb- bond Multipurpose and Duo Cement achieved a lower mean bond strength tban Panavia,
Chung and Hwang' found that Liner M repair sys- tem sbowed significantly greater bond strength tban did resin composite to metal surfaces, with or without sandblasting. Their suggestion for treatment of ex- posed metal before bonding of resin composite was only sandblasting of alloy, Tbey showed that, after sandblasting and application of Seotchbond Multi- purpose, bond strength with resin composite was 10.2 MPa, lower than tbe finding in the present study.
One Coat Bond accompanied by Duo Cetitent achieved a mean bond strengtb of 13.6 MPa, wbieh was the lowest of the four groups. This adhesive did not have an adhesion promoter for metal surfaces. In addition, the combination with Duo Cement did not create a suitable bond.
Long-term studies are not available to evaluate ail tbe factors contributing to success or failure of porce- lain veneer-base metal bonds. Further clinical studies are indicated.
CONCLUSION
1, The mean bond strengths of groups C, P, S, and 0 were 25,39, 19,10, 15,81 and 13,69 MPa, respec- tively,
2, The metal-ceramic control specimens showed the greatest bond strength,
3, Among the experimental groups, Panavia 21 Ex achieved tbe greatest bond strength, whieh was sig- nificantly greater than that of One Coat Bond,
ACKNOWLEDGMENTS
Tiiis study was supported by a grant from the Research Council of Mashhad Universily of Medical Science, Mashhad, Iran,
REFERENCES
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2, Bertolotti RL, Lacy AM, Watanabe LG. Adhesive monomers for porcelain repair, Int J Prosthodont 1989;2: 483-4S9,
3, Simonsen RJ, Calamia ]R, Tensile bond strength of etched porcelain [abstract 1154], J Dent Res 1983;62:297,
4, Stangcl I, Nathanson D, Shear bond strength of composite hond to etched porcelain. J Dent Res 1987;66:1460-1465.
5, Tylka DF, Stewart CR Comparison of acidulated phosphate fluoride gel and hydrofluoric acid etchants for porcelain composite repair, J Prosthet Dent 1994;72:12I-127.
6, Delia Bona A, Van Noort R, Shear vs tensile hond strength of resin composite bond to ceramic, J Dent Res 1995;74: 1591-1596.
7 Burke FJT, Grey NJA, Repair of fractured porcelain units; alternative approaches, Br Dent [ 1994;l76:251-256.
S. Kamada K, Yoshido K, Atsuta M, Effect of surface treat- ments on the bond of four resin luting agents to a ceramic material. J Prosthet Dent 1998;79 508-513.
9, Bello JA, Myers ML. Gräser GN, Jamis RH, Bond strength and microleakage of porcelain repair materials, J Prosthet Denl 1985;45:788-797,
10, Appeldoorn RE, Wilwerding TM, Barkmeier WW, Bond strength to composite resin of porcelain with newer genera- tion porcelain repair system, ) Prosthet Dent 1993;7O:6-I1,
11. Willams VD. Arnold AD, Aquilino SA. Bond versus rebond strengths of three luting agents for resin bonded fixed par- tial dentures, J Prosthet Dent 1992;67:289-292,
12, el-Sherif MH, el-Messery A, Halhoul MN, The effect of alloy surface treatments and resins on the retention of resin- bonded retainers, ] Prosthet Dent 1991;65:782-78e,
13. Ozcan M, Pteiffer P, Nergiz I, A brief historji of current status of metal and ceramic surface conditioning concepts for resin honding in dentistry. Quintessence Int 1998;29:713-724,
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M. Pegoraro LF, Barrack GA. Comparison of bond strength of adhesive cast restorations using different designs, bonding agents, and luting resins. | Prosthel Dent 1987:57:133-138.
15. Czera- RJ, Wakefield CW. Robbins |W, Fuikenion MS, Shear bond strength of composite resin to microelched metal with five newer-generation bonding agents, Oper Dent 1995:20: 58-62.
16. Scotchbond Multipurpose Product Profile. Si Paul, MN: 5M,
D. Silva E. Souza MG, Retief DH. Russell CM. Denys FR, Shear bond strength and microleakage of All-Bond. Am J Dent 1993:6:148-154.
18. Aboush YEY. Jenkins CGB. Tensile strength of enamel-resin metal, J Proslhet Dent 1989:61:688-694.
19. Frankenberge R, Kramer N, Sindle J, Repair strength of etched vs silica-coated metal ceramic and all-ceramic restorations. Oper Dent 200025:209-213,
20. Pameijer CH. Louw NP, Fischer D, Repairing fracture porcelain: How surface preparation affects shear force resis- tance. J Am Dent Assoc 199 6 127:2 03-2 09.
21. Badaw i BA, Sherif AH. Microleakage of oral microflora for porcelain and some porcelain repair materials-in vitro study. Egypt Dent J 1994:40:617-624.
22. Lacy .AM. Clinical techniques for intraorai repair of frac- tured porcelain when metal is exposed. Quintessence Int 1989:2:595-598,
23. Burke FJT. Evtending tbe use of a 4-META material: Repair of fractured melal/ceramic crowns and bridges. Dent Update 1998:25:124-128.
24. Miller A, Miller B. Cole J. Comparison of Ihe fracture strengths of ceramometal versus several all ceramic crowns. J Prosdiet Dent 1992:68:38^1,
25. Wiltshire WA_ TensQe bond strengths of various alloy sur- face treatments for resin bonded bridges. Quintessence DentTechnol 1986:10:227-232.
26. Omura 1, Yamauchi J, Harada I, Wada T. Adhesive and me- chatiical properties of a new dental adbesive [abstract 561]. J Dent Res 1984:63:233.
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32. Craig RG. Restorative Dental Materials, ed 10. St Louis: Mosby, 1997:737.
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Effect of adhesives on bond strength of porcelain veneer to base metal alloy
Reza Goharian, DDS, MSVFatemeh Maleknejad, DDS /Taghi Saiari,DDS3/ Marjaneh Ghavamnasiri, DDS- /Mohammad Derhami,
Objective: The purpose of this in vitro study was to evaluate the bond strength of porcelain veneer to base metal alloy using different adhesive systems. Method and materials: Eighty cylindrical models were cast in a nlckel-chromium-beryIlium base metal alloy. After they were mounted in self-cured acrylic resin, the surfaces of the specimens were air abraded. Specimens were divided into four groups of 20, Control porcelain disks were baked on the base metal. For the experimental groups, 60 porcelain disks were made. After öO-pm aluminum oxide sandblasting, a silane coupling agent was applied to the surface of the porcelain. The experimental groups were based on the type of adhesive used to bond porcelain to metal: Scotchbond Multipurpose and Duo Cement; One Coat Bond and Duo Cement; or Panavia 21 Ex, After 500 thermal cycles, the bonded porcelain specimens were placed under a continuous shear load of 2 mm/min until fracture occun-ed. Results: Mean values for bond strength were 25,39 (control), 19.10 ¡Panavia 21 Ex), 15,81 (Scotchbond Multipurpose), and 13,69 MPa (One Coat Bond], Statistically significant differ- ences in bond strength were noted between tfie control group and all the experimental groups, A statisti- cally significant difference was observed between Panavia 21 Ex specimens and One Coat Bond speci- mens. Conclusion: Panavia 21 Ex provided an effective bond strength between a porcelain veneer and a base metal alloy, the closest of all the experimental groups to that of the control group, (Quintessence int 2002:33:595-599)
Key words: adhesive, base metal alloy, bond strength, porcelain veneer
CLINICAL RELEVANCE: The repair of a fractured metal- ceramic crown with a porcelain veneer cemented to the base metal substructure is a possible treatment alterna- tive, Panavia 21 Ex may be a suitable resin cement for bonding the porcelain veneer to the base metal.
Metal-ceramic crowns are the most widely used type of complete veneer restoration. Considering
the large difference in modulus of elasticity hetween
'Associate Professor, Departmenl ol Prostlioöondcs, Faoulty of Dentistry,
Mashhad Unrversity, Mashrtad, Iran.
^Assistant Professor, Department of Piosthodonlcs, Faculty of Dentistry,
Mashhad Univeisify, Mashhad, Iran.
Reprint requests: Or M. Ghavamnasiri, Associate Professor, Department ol Operative Dentistry, Mashhad University, Mashhad, Iran. E-maii; dr_Marjaneh @yahoo,com
metal and porcelain, it is not surprising that mechani- cal faiiures of the metal-ceramic bond can occur. Causes of metal-ceramic faiiure include unsuitable de- sign of metal coping, tecbnical errors, contamination, physical trauma, and premature occlusal contact.
Porcelain fracture does not necessarily mean failure of the restoration. It may pose only an esthetic and/or a functional dilemma for the patient and dentist. If the restoration is to be repaired, the bond strength of the repair must be strong and dtirable.' Types of failure in metal-ceramic cro«Tis include fracture only in porce- lain without metal exposure, fracture with partial metal exposure, and fracture with complete metal exposure.-
Various methods have been introduced for repair- ing fractured porcelain with resin composite. Sandblasting with aluminum oxide is one method of surface roughening.^ The porcelain can also be etched with hydrofluoric acid to facilitate mlcromechanical retention of resin composite,'"^ Use of an intraoral sandblaster is an alternative way to provide microme- chanical retention, although the roughening of the ce- ramic surface by the sandblaster may be less than that produced by hydrofluoric acid,'
Quintessenc 595
• Goharian et ai
Mechanical roughening of the fractured surface fol- lowed by application of a silane coupling agent can enhance the resin-to-porcelain bond,' Phosphoric acid etching does nol increase the porcelain-resin compos- ite bond strength,' It was recognized that roughening and etching of porcelain are more important for me- chanical retention than are silane coupling agent and chemical retention.^ Appeldoorn et al"* found the bond strength of resin composite to porcelain was 23.5 MPa; after thermocycling, the bond strength de- creased. Chung and Hwang' showed that aluminum oxide sandblasting and hydrofiuoric acid treatment followed by application of Scotchbond can result in a porcelain repair bond strength of 14.7 MPa.
Surface treatment of base metal alloys with alu- minum oxide sandblasting is a valuable procedure for increasing roughness."-'^ A previous study reported that tbe aluminum oxide content of base metal alloys increases up to 30 vt Vo after sandblasting. Ultrasonic cleaning resulted in only minor removal of the embed- ded aluminum oxide, which can create chemical bonds with adhesives and enhance bond strength.'^
Further improvements in adhesion of resin compos- ite to base metals have recently been reported by the following
1. Multipurpose resins such as Scotchbond Multi- purpose (3M Dental), for which a bond strength of 30 MPa to Rexillium cast metal alloy (feneric/ Pentron) has been quoted by the manufacturer. ""
2. All-Bond 2 {Bisco Dental), for which a bond strength of 21.8 MPa to Rexillium III cast metal alloy has been reported.^
3. Panavia Ex (Kuraray), a dimethacrylate in wbich phosphate ester groups are incorporated in a bis- GMA resin. Aboush and Jenkins'** have reported bond strengths of up to 28 MPa between Panavia Ex and sandblasted nickel-chromium alloy,
A number of studies on porcelain repair by resin composite have been published,^'^-^' but, when metal is completely exposed, tbere seem to be two ways to solve the problem: (1) bonding a resin composite ve- neer to base metal (2) bonding a porcelain veneer to base metal. Only two clinical reports have been pub- lished ahout bonding of a porcelain veneer to exposed metal. ' ^ Therefore, the aim of the present study was to evaluate the effect of adhesives on tbe bond strength of a porcelain veneer to a base metal alloy.
METHOD AND MATERIALS
Eighty cast specimens were made in a nickel- chromium-beryllium alloy (Super Cast MP, Therma-
bond Alloy). All the manufacturer's re ¡.cndations for the burnout and casting proced ^ • were fol- lowed. The specimens consisted of twi. 'lisiiS, one (11 mm in diameter and 3 mm thick) for porcelain veneer application and the other (8 mm in ditimeter and 3 mm thick) for mounting in a self-cured acrylic resin mold (Formatray, Kerr/Sybron). The surfaces of all specimens were air abraded with 50-[¡m aluminum oxide (Micro-etcher, Model ERC, Danville Engin- eering) used with a pressure of 50 kg/cm^ at a dis- tance of 5 mm.
Specimens were divided into four groups of 20. In the control group (C), 20 specimens were selected for firing of porcelain (Vita Omega A-2 Metalkeramic, Vita Zahnfabrik). A piece of platinum foil was pre- pared, with a hole (4 mm in diameter) punched ap- proximately at its center, and adapted on the cast- metal disk to create a standardized area for porcelain application. Porcelain firing was carried out in a porcelain oven (Vita Vacumat 300, Vita Zahnfabrik). After 24 hours, specimens underwent 500 thermal cy- cles from 500"C to 55''C,
In the experimental groups, 60 cast specimens were maintained at 96O''C for 5 minutes, which was similar to the firing cycle for the metal-ceramic specimens. The base metal surtaces were then roughened with a coarse diamond bur, rinsed in tap water, and subjected to 50-ijm aluminum oxide sandblasting. Holes were created in a piece of platinum foil (4 mm in diameter), which was then adapted to a piece of mica. In this way, the porcelain disks were fired in a porcelain oven.
After the bonding surface of the porcelain disks was sandblasted, a 9.50/0 hydrofiuoric acid gel (Ultradent) was applied to this surface for 4 minutes. A frosted ap- pearance was observed after the surface was rinsed with water and dried. The ceramic primer was applied to the bonding surface of the porcelain disks. The manufacturer's directions for each system were fol- lowed when the porcelain was bonded to the base metal. Tbc experimental groups of specimens were di- vided into three groups of 20, based on tbe type of ad- hesive. Scotchbond Multipurpose {group S) is a dentin bonding agent. After application of activator on the metal surface, Scotchbond primer was applied and dried after 5 seconds until a glossy appearance was observed. The catalyst was applied to the primed sur- face. Duo Cement (Coltene/Whaledent) was used as a luting cement. Duo Cement was applied first to the porcelain bonding surface and then to the metal sur- face and light cured with the Coltene light-curing unit (Coltene/Whaledent) from each side for 60 seconds.
One Coat Bond (group O) is a dentin bonding agent {Coltene/Whaledent). One drop of the adhesive was applied to the bonding surface of porcelain and light cured for 20 seconds with the Coltene light-ciiring
596 Volume 33, Number 8, 2002
• Gotiarian et al
unit. The rest of the procedure was similar to that de- scribed for group S.
Panavia 21 Ex (group P) is a resin cement. The base and catalyst were mixed and applied to the porcelain disk. The disk was Immediately placed on the bonding surface of metal and mild finger pressure was main- tained until the cement set.
Thermocycîing was performed for the experimental groups in a manner similar to that used for the control group. An Instron testing machine (Model 8500. Instron Engineering) was equipped with a chisel- shaped rod with a shearing force along the interface between metal and porcelain. The bonded porcelain cylinders were placed under sustained, continuous loading at 2 mm/min until fracture occurred (Fig 1). Sbear bond strengths were calculated and recorded in megapascals.
Statistical analysis of data was accomplished by analysis of variance. The Duncan multiple range test and / test were used for all post hoc pairwise compari- sons at the QS /o confidence level.
DISCUSSION
Previous studies have indicated that, for repair of porce- lain, etching with hydrofluoric acid and application of a süane coupling agent in combination with an unfilled resin could create a suitable bond strength.-*- The pre- sent smdy evaluated the effect of adhesives on the bond strengths of porcelain veneers to base metal alloys.
It was not surprising that the metal-ceramic speci- mens (controi) displayed tbe higbest bond strength. Miller et al--' found that metal-ceramic bond strength was 720 psi in axial loading. The most important causes of higher bond strengths in metaj-ceramic are:
1. The surface roughness of the ailoy. which is filled and wetted by porcelain during sintering.
2. Tbe creation of a chemical bond between porcelain and metal oxides.
3. Tbe compact bond between the ceramic and the base metal. =
RESULTS
The mean bond strength values for each group are listed in Table 1. The bond strength values ranged from 13.69 ± 6.62 MPa to 25.39 ± 6.68 MPa. One-way analysis of variance for the experimental groups re- vealed a stadstically significant difference among them (P < .05). Duncan's mulfiple range test revealed a sta- tistically significant difference (P < .05) between groups P and O. Tbere was no statistically significant difference between the bond strengths of Scotchbond Multipurpose and Panavia 21 Ex. The t test reveaied a statistically significant difference (P < .01) between the mean bond strengtb of group C and tbe mean bond strengths of all three experimental groups (Fig 2).
— Shea nng device
-Embedded material
Fig 1 Positioning of test specimer>s in the tesling apparatus.
TABLE 1 Shear bond strength (MPa)
Group Mean SD
Scotchbond Muftipurpose (S) 15.81 7.50 Panavta 21 Ex (P) 19.10 8.90 One Coat Bond (0) 13.69 6.62 Control (C) 25 39 6.68
'S Q-
H•—•—^M c
Fig 2 Sheaf txind strengths ot experimental groups and control; (S) Scotchbond Multipurpose; (P) Panavia 21 Ex; (O) One Coat Bond; (C) controE.
Quintess 597
• Goharian et al
Among experimental groups, the highest bond strengtb was observed in group P altbougb it was not significantly different from group S, Panavia 21 Ex re- portedly adheres to sandblasted base metal alloy,"'' '"* The manufacturer also has recommended this proce- dure, Williams et al" found that, after 1,080 thermal cycles, Panavia demonstrated higher bond strengths to sandblasted metal than did Super-Bond B&C, Omura et al ^ found tbe best base metal surface treatment for Panavia was aluminum oxide sandblasting, which re- sulted in minor roughness and embedding of the alu- minum oxide in metal surface. ' Phosphate groups in Panavia could react with metal oxides and create both mechanical and chemical bonds,"
Tbe mean bond strength of group S was not signifi- cantly different tban tbat of Panavia, but its bond strengtb was lower tban enamel to resin composite bond strength,- ' ^ Tbe ceramic primer in this adbesive could act as adhesion promoter on the metal sur- face,^^^ However, when paired with Duo Cement dual-cured resin cement, Scotchbond Multipurpose did not achieve a high bond strength.
Film tbickness of tbe luting cement is a very impor- tant factor in bond strengtb; the lower the thickness, the greater the bond strengtb, "' i Tbe film tbickness of adhesive resins such as Panavia is in the range of 13 to 20 pm,'^ It is thought that tbe lower bond strengtb of Duo Cement could be attributed to the greater film thickness of this resin cement (about lOf) ]im}.'^^ This may be the reason that the eombination of Scotcb- bond Multipurpose and Duo Cement achieved a lower mean bond strength tban Panavia,
Chung and Hwang' found that Liner M repair sys- tem sbowed significantly greater bond strength tban did resin composite to metal surfaces, with or without sandblasting. Their suggestion for treatment of ex- posed metal before bonding of resin composite was only sandblasting of alloy, Tbey showed that, after sandblasting and application of Seotchbond Multi- purpose, bond strength with resin composite was 10.2 MPa, lower than tbe finding in the present study.
One Coat Bond accompanied by Duo Cetitent achieved a mean bond strengtb of 13.6 MPa, wbieh was the lowest of the four groups. This adhesive did not have an adhesion promoter for metal surfaces. In addition, the combination with Duo Cement did not create a suitable bond.
Long-term studies are not available to evaluate ail tbe factors contributing to success or failure of porce- lain veneer-base metal bonds. Further clinical studies are indicated.
CONCLUSION
1, The mean bond strengths of groups C, P, S, and 0 were 25,39, 19,10, 15,81 and 13,69 MPa, respec- tively,
2, The metal-ceramic control specimens showed the greatest bond strength,
3, Among the experimental groups, Panavia 21 Ex achieved tbe greatest bond strength, whieh was sig- nificantly greater than that of One Coat Bond,
ACKNOWLEDGMENTS
Tiiis study was supported by a grant from the Research Council of Mashhad Universily of Medical Science, Mashhad, Iran,
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Quintessen
HoUiston L. Riviere
128 pp (spii3Í binding) 2 )5 color illustrations ISBN 0-86715-386-5 US 534
This lab manual of color oral histo]oa\ photographs is designed to aid dental and dental hygiene students in identifying tho salient feauires of microscopic anatomv of oral tissLies. It presents large, clear, identi- fiable photos af normal oral tissues and developing teeth accompanied by brief descriptions highlighting the special fea- tures of each.
Contents
Chapter I Iboth Development Chapter 2 Enamel Chapter 3 Dendn Chapter 4 Pulp Chapter 5 Cementum Chapter 6 Periodontal Ligament and
Den togiiigival Junction Clinpler 7 .\lveolar Bone Chapter S Tooth Emption and Shedding Chapter 9 Mticosa Chapter 10 Salivary Glands Chapter 1! Temporomandibuiar Joint
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