- Email: [email protected]
Tensile bond strengths of composites to a gold-palladium alloy after thermal cycling
Tensile bond strengths of composites to a gold-palladium alloy after thermal cycling Jeffrey Chai Chang, DDS, MS,a Sheila H. Koh, DDS,b John M. Powers, PhD,c and Joseph H. Duong, BDSd University of Texas-Houston Dental Branch, Houston, Texas Statement of problem. Many different materials and methods have been used to fabricate or repair veneer facings with composites, but only a few of these have been studied.
Purpose. This study compared the tensile bond strengths of composites to a gold-palladium alloy with the use of several surface treatment methods. Material and methods. Forty alloy specimens were cast in Eclipse (52% gold and 37.5% palladium) in the form of truncated cones. These specimens were divided equally into 4 groups. In group I, the bonding surfaces of the metal cones were treated with Silicoater MD. Truncated cones of Dentacolor composite were bonded to the metal surfaces and light-polymerized. In group II, the bonding surfaces of the metal cones were air-particle abraded with 50 µm aluminum oxide and coated with C&B Metabond. Truncated cones of Epic-TMPT composite were bonded to the metal surfaces and light-polymerized. In group III, the bonding surfaces of the metal cones were air-particle abraded with CoJet-Sand. Truncated cones of Pertac-Hybrid composite were bonded to the metal surfaces and light-polymerized. In group IV, the bonding surfaces of the metal cones were air-particle abraded with CoJet-Sand. Truncated cones of Visio-Gem were bonded to the metal surfaces and light-polymerized. After 24 hours of water immersion at 37°C and 1000 thermal cycles in water at 5°C and 55°C, tensile forces were applied to all specimens with a universal testing machine. Analysis of variance was applied to the data (P<.05), and differences among means were determined with a Tukey-Kramer interval of 5.4 MPa. Results. Tensile bond strengths in MPa were as follows: Dentacolor, 14 ± 5; Epic-TMPT, 12 ± 4; Pertac-Hybrid, 13 ± 5; and Visio-Gem, 18 ± 4. The tensile bond strength of Visio-Gem was significantly higher than that of Epic-TMPT, but no differences were found among Dentacolor, Pertac-Hybrid, and Epic-TMPT (P<.05). Conclusion. Within the limitations of this study, all 4 bonding systems tested produced high bond strengths between composites and a gold-palladium alloy after thermal cycling. (J Prosthet Dent 2002;87:271-6.)
CLINICAL IMPLICATIONS The results of this in vitro study indicate that all 4 composites tested, when applied with the techniques described, are strong enough for the repair and fabrication of veneer facings.
I
n the 1960s, porcelain-fused-to-metal veneer crowns were introduced to dentistry. Dental porcelain can be used to manufacture esthetic fixed restorations.1 High-fusing porcelain, which is used mainly in porcelain teeth, is composed of feldspar (70% to 90%), quartz (11% to 18%), and kaolin (1% to 10%). Noble metals have been used for the copings. Because gold is
aAssociate
Professor, Department of Prosthodontics. Professor and Director, Advanced Education in General Dentistry Program, Department of Restorative Dentistry and Biomaterials. cProfessor and Vice Chair, Department of Restorative Dentistry and Biomaterials; Director, Houston Biomaterials Research Center. dDental Lab Technician. bAssistant
MARCH 2002
expensive, nickel-chromium also has been used in porcelain-fused-to-metal crowns. Although porcelain is quite esthetic, it is also brittle. Repair with composite is necessary for fractured porcelain crowns. Veneer facings can be fabricated from laboratory composites and bonded to an alloy with the application of a pyrolytic silica surface treatment, which was introduced to the United States in 1985. The mechanism of adhesion consists of the heat fusion of a microscopic layer of glass beads to the metal, after which composite is bonded with a silane coupling agent. This process, which is known as pyrolytic silanization,2 requires equipment such as Silicoater, Silicoater MD, or the latest version, Siloc (Kulzer Inc, Irvine, Calif.). All 3 systems use 250 µm aluminum THE JOURNAL OF PROSTHETIC DENTISTRY 271
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Table I. Materials used in this study Commercial name
Alloy Eclipse Composite Dentacolor Epic-TMPT Visio-Gem Pertac-Hybrid Visio-Gem Alloy Treatment CoJet-Sand Silicoater MD C&B Metabond Opilux 401
Material
52% Au, 37.5% Pd
Ney Dental International, Bloomfield, Conn.
Composite Composite Opaque Composite Composite
Kulzer Inc, Irvine, Calif. Parkell, Farmingdale, N.Y. ESPE America, Plymouth Meeting, Pa. EPSE America ESPE America
Air-particle abrasion material Polymerization unit Luting cement Polymerization light
ESPE America Kulzer Inc Parkell Demetron Corp, Danbury, Conn.
oxide for air-particle abrasion, but they differ in the heating of the metals. The original Silicoater uses an open flame, whereas Silicoater MD and Siloc use an oven. These systems can be used to bond composite to any metal surface. In previous studies, silicoated metals produced 25% more initial strength than etched metals,3 higher bond strengths after 3 days of water storage,4 and mixed results after thermocycling.5-7 The Rocatec System (ESPE America, Plymouth Meeting, Pa.) deposits a microscopic ceramic layer on the metal and bond composite to it with a silane coupling agent. In this system, high heat is eliminated by the use of air-particle abrasion under pressure (tribochemical coating). With the silane coupling agent, a chemical bond is formed between the ceramic silicate layer on the metal surface and the resin, which produces gap-free bonding of the veneer material to the metal frame. The size of the abrasion material is approximately 110 µm. The latest version of this system is the Rocatec Junior, which makes abrasion material approximately 50 µm in diameter. Recently, the same company introduced CoJet-Sand, an air-particle abrasion material that is also approximately 50 µm in diameter and that can be used to fabricate or repair veneer facings. Because this material is relatively new to the market, research data on its use are limited. Adhesive bonding also can be used to fabricate or repair veneer facing. With advances and improvements in adhesive resins, this method has become popular in recent years. One advantage of this system is that expensive lab equipment is not required. However, reported disadvantages include low bond strength with base metal after 6 months of water storage6 and with noble metal7 compared to pyrogenic silanization and tribochemical coating. Adhesive resins such as C&B Metabond (Parkell, Farmingdale, N.Y.) and Super-Bond C&B (Sun Medical Co, Kyoto, Japan) bond well to both base and noble metals.8-19 The objective of this study was to evaluate the ten272
Manufacturer
sile bond strengths of 4 types of veneer facing materials used with 4 different surface treatment techniques: Dentacolor composite and Silicoater MD, Epic-TMPT composite and C&B Metabond, Pertac-Hybrid composite and CoJet-Sand, and Visio-Gem composite and CoJet-Sand. All composites were bonded to a goldpalladium alloy.
MATERIAL AND METHODS Forty alloy specimens were cast with Eclipse (Ney International, Bloomfield, Conn.), a 52% gold and 37.5% palladium alloy, in the form of truncated cones 3 mm in diameter at the bonding surfaces and 5 mm in diameter at the base. These specimens were divided into 4 groups of 10 each. Each group was treated with 1 of 4 composite bonding systems according to the manufacturer’s directions. Composite truncated cones were formed on the metal with a split mold and then polymerized. All materials and their manufacturers are listed in Table I. In group I, the bonding surfaces of the metal cones were air-particle abraded with 250 µm aluminum oxide for 15 seconds. The specimens then were washed with Siliclean (Kulzer Inc) for 30 seconds and air dried for 5 minutes. Sililink (Kulzer Inc) was applied and dried for 2 minutes, followed by heat treatment in the Silicoater MD unit for 4 minutes. This unit consists of a heating chamber and was used to burn the Sililink (silicate coated in metal oxide) into the surface of the alloy at a temperature of 320°C. The specimens were cooled for 5 minutes before Siliseal was applied and air dried for 2 minutes. Two layers of Dentacolor Opaque (Kulzer Inc) were applied to the bonding surfaces and light-polymerized for 90 seconds twice in a photopolymerization unit (Dentacolor XS; Kulzer Inc) with a xenon strobe light chamber. The wavelength with a heat protection filter is 320 to 520 nanometers, and the minimum light intensity within the polymerization chamber is 250 mW/cm2. Dentacolor, a veneering composite composed of 51% VOLUME 87 NUMBER 3
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Fig. 1. Custom mounting jig for testing.
by weight pyrogenic silicium dioxide and 48.5% by weight methacrylic ester, was added in increments to form the truncated cones with a split mold. Each layer was light-polymerized for 90 seconds twice in the photopolymerization unit. In group II, the bonding surfaces of the metal cones were air-particle abraded with 50 µm aluminum oxide for 15 seconds and then cleaned for 3 minutes in distilled water and dried. One drop of catalyst was mixed with 4 drops of monomer of C&B Metabond (Parkell) and used to wet the bonding surfaces. The mixture was combined with 2 scoops of powder, brought to a creamy consistency, and applied to the bonding surface. Epic-TMPT (Parkell), a microfill composite that contains trimethylol propane and trimethacrylate, was used to form a truncated cone on the metal with a split mold. Each of the 3 sides was light-polymerized for 30 seconds in a visible light unit (Optilux 401; Demetron Research Corp, Danbury, Conn.) at an intensity of 450 to 500 mW/cm2. In group III, the bonding surfaces of the metal cones were air-particle abraded with CoJet-Sand (ESPE America). ESPE-Sil (ESPE America) then was applied with a brush and allowed to dry for 5 minutes. A thin layer of the Visio-Gem Opaque (ESPE America) was brushed onto the bonding surface and light-polymerized for 5 seconds twice. Pertac-Hybrid, a universal radiopaque hybrid composite that contains methacrylates and 61% inorganic fillers by volume, was added in increments to form the truncated cones with a split mold. Each layer was light-polymerized for 30 seconds with the visible light unit (Optilux 401) at an intensity of 450 to 500 mW/cm2. In group IV, the bonding surfaces of the metal cones were air-particle abraded with CoJet-Sand, and MARCH 2002
ESPE-Sil was applied with a brush and allowed to dry for 5 minutes. A thin layer of Visio-Gem Opaque was brushed onto the bonding surface and light-polymerized for 5 seconds twice in a halogen light unit (Visio Alpha; ESPE America) at an intensity of 300 mW/cm2. Visio-Gem, a paste that contains 34% acrylate and that is used mainly for veneer facings, was added in increments to form the truncated cones with a split mold. Each layer was light-polymerized for 15 minutes with another unit (Visio Beta Vario; ESPE America) that uses halogen light in the polymerization chamber at an intensity of 380 mW/cm2. The polymerization unit was connected to a vacuum pump with a pumping speed of 1.5 m3 per hour to decrease porosity and increase density of the resin. Fifteen minutes were needed for 1 cycle of light and vacuum. After 24 hours of water immersion at 37°C and 1000 thermal cycles in water at 5°C and 55°C, each specimen was mounted on the split Assembly B of a custom mounting jig (Fig. 1). Tensile forces were applied to Assembly A with the use of a universal testing machine (4465; Instron Corp, Canton, Mass.) at a crosshead speed of 0.5 mm/minute. Analysis of variance was applied to the data (P<.05). Differences among means were determined by a Tukey-Kramer interval of 5.4 MPa at the .05 level of significance. Differences larger than the calculated Tukey-Kramer interval were considered statistically significant.
RESULTS Visio-Gem had the highest mean tensile bond strength to Eclipse (18.0 ± 3.8 MPa), followed by Dentacolor (14.4 ± 4.9 MPa), Pertac-Hybrid (13.3 ± 5.3 MPa), and Epic-TMPT (12.2 ± 3.7 MPa) (Fig. 2). The tensile bond strength of Visio-Gem was 273
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Fig. 2. Mean tensile strengths of composites to gold-palladium.
Fig. 3. Types of bond failures.
Table II. Analysis of variance of bond strength data Source
Df
Product Residual
3 36
Sum of squares
192.0 728.7
Mean square
64.0 20.2
F value
P value
3.16
.036
Dependent: Bond strength (MPa).
significantly higher than that of Epic-TMPT, but the bond strengths of Dentacolor, Pertac-Hybrid, and Epic-TMPT were not significantly different (P<.05) (Table II). Bond failure types are reported in Figure 3. In group I, 60% of the bond failures were adhesive and occurred between Dentacolor Opaque and Eclipse, 27.5% were adhesive between Dentacolor Opaque and Dentacolor composite, 7.5% were cohesive in Dentacolor composite, and 5% were cohesive in Dentacolor Opaque. In group II, 92.5% of the bond failures were adhesive between C&B Metabond and 274
Eclipse, and 7.5% were adhesive between C&B Metabond and Epic-TMPT. In group III, 57.5% of the bond failures were cohesive in the Visio-Gem Opaque layer, and 42.5% were adhesive between VisioGem Opaque and Eclipse. In group IV, 67.5% of the bond failures were cohesive in the Visio-Gem Opaque layer, and 32.5% were adhesive between Visio-Gem Opaque and Eclipse.
DISCUSSION The purpose of this study was to evaluate different methods of fabricating and repairing veneer facings. In group I, Silicoater MD produced high bond strengths (14.4 MPa) between composite and metal. However, Silicoater requires bulky equipment to produce intense heat on the metal to form the oxide layer for bonding; this method therefore cannot be used intraorally. Similar drawbacks can be attributed to group IV. The Visio-Gem polymerization unit and CoJet-Sand also produced high bond strengths (18.0 MPa) between VOLUME 87 NUMBER 3
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composite and metal, but the polymerization instrument is bulky and uses heat and pressure to bond and polymerize the composite. These two methods of repairing or fabricating of veneers can be used only outside the mouth. The use of C&B Metabond in group II and CoJetSand in group III required no bulky equipment, no heat, and no pressure. These methods can be used intraorally or extraorally. However, the tensile bond strengths recorded for these groups were lower than for the other 2 groups because heat and pressure is required for a strong, consistent bond between composite and gold. This finding supports a previous study6 in which Rocatec and Silicoater produced stronger and more consistent bond strengths than adhesive resins and bonding agents. In the present study, the bond strengths of resins and gold-palladium were lower than those reported in a study on resins and a nickel-chromium alloy.6 This discrepancy can be attributed to the fact that, because gold is a noble metal, the optimal oxide layer required for bonding does not form adequately. Observation of the bond failure types (Fig. 3) shows that the Visio-Gem group, which produced the highest tensile strengths, exhibited the majority of bond failures cohesively in the Visio-Gem Opaque layer; the C&B Metabond and Pertac-Hybrid groups, which produced lower tensile strengths, exhibited the majority of bond failures adhesively at the metal/resin interface. These results again highlight the importance of optimal metal oxide layer formation and metal surface treatments. Additional research should be performed in this area. In a study by Chung and Hwang,20 the bond strengths of porcelain repair systems bonded to base metal with various surface treatments were investigated. The LinerM/Superbond system (4-META) (Sun Medical Co) demonstrated the highest strength values. No significant difference in bond strengths was found with air-particle abrasion and hydrofluoric acid etching surface treatments. Hydrofluoric acid, like Silicoater and Rocatec, is hazardous and should not be used intraorally. In a study by Petridis et al,21 the shear bond strength between esthetic veneers and a gold-palladium alloy was evaluated. In group 1, a traditional method of porcelain fused to metal was used to fabricate the veneers. In group 2, Artglass composite was bonded to metal treated with the Siloc unit. In group 3, the opaque ceramic layer was etched for 2 minutes with 6% hydrofluoric acid before 3 layers of Artglass dentin were bonded to it. After thermocycling, porcelain-fused-to-metal veneers exhibited the highest mean shear strength (23 MPa), followed by the Siloc system (18 MPa); the etched porcelain demonstrated the lowest bond strength (16 MPa). These bond strengths are MARCH 2002
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comparable to those recorded in the present study, which also evaluated a noble metal bonded to composite. The porcelain-fused-to-metal and Siloc systems require heat treatment for the metal, which confirms that heat or pressure is required for a strong, consistent bond.
CONCLUSIONS Within the limitations of this study, the following conclusions were drawn: All 4 bonding systems produced high bond strengths (12.2 to 18.0 MPa) between composites and Eclipse after thermal cycling. Visio-Gem exhibited the highest bond strength to gold-palladium. The tensile bond strength of VisioGem was significantly higher than that of Epic-TMPT. No significant differences among Dentacolor, PertacHybrid, and Epic-TMPT were observed. The majority of the failure modes were adhesive at the junction of the metal and opaque or cement. We sincerely thank Dr C. David Taylor, Director of Educational Assessment and Technology, University of Texas-Houston Dental Branch, for his editorial assistance. We also thank Ney Dental International, Jelenko/Kulzer Lab Products, Parkell, and ESPE America for their material support.
REFERENCES 1. Shillingburg HT, Hobo S, Whitsett LD, Jacobi R, Brackett SE. Fundamentals of fixed prosthodontics. 3rd ed. Chicago: Quintessence; 1997. p. 433-83. 2. Albers HE. Adept Report. Santa Rosa: Adept Institute; 1991. p. 25. 3. Re GJ, Kaiser DA, Malone WF, Garcia-Godoy F. Shear bond strengths and scanning electron microscope evaluation of three different retentive methods for resin-bonded retainers. J Prosthet Dent 1988;59:568-73. 4. Tenjoma LT, Nicholls JI, Townsend JT, Harper RJ. Chemical retention of composite resin to metal. Int J Prosthodont 1990;3:78-88. 5. Schneider W, Powers JM, Pierpont HP. Bond strength of composites to etched and silica-coated porcelain fusing alloys. Dent Mater 1992;8:211-5. 6. Chang JC, Powers JM, Hart D. Bond strength of composite to alloy treated with bonding systems. J Prosthodont 1993;2:110-4. 7. Laufer BZ, Nicholls JI. Time delay effects on the tensile bond strength developed by the Silicoater. Quintessence Dent Technol 1987;11:199203. 8. Lo CS, Millstein PL, Nathanson D. In vitro shear strength of bonded amalgam cores with and without pins. J Prosthet Dent 1995;74:385-91. 9. Donald HL, Jeansonne BG, Gardiner DM, Sarkar NK. Influence of dentinal adhesives and a prefabricated post on fracture resistance of silver amalgam cores. J Prosthet Dent 1997;77:17-22. 10. NaBadalung DP, Powers JM, Connelly ME. Comparison of bond strengths of three denture base resins to treated nickel-chromium-beryllium alloy. J Prosthet Dent 1998;80:354-61. 11. van Putten MC Jr, Culbertson BM. Adhesion promotion between metadent and a high palladium alloy with a pyrolytically fused porcelain opaque layer. J Prosthodont 1994;3:79-87. 12. Bahannan S, Lacefield WR. An evaluation of three methods of bonding resin composite to stainless steel. Int J Prosthodont 1993;6:502-5. 13. Suliman AH, Swift EJ Jr, Perdigao J. Effects of surface treatment and bonding agents on bond strength of composite resin to porcelain. J Prosthet Dent 1993;70:118-20. 14. Moser JB, Brown DB, Greener EH. Short-term bond strengths between adhesive cements and dental alloys. J Dent Res 1974;53:1377-86. 15. Watanabe F, Powers JM, Lorey RE. In vitro bonding of prosthodontic adhesives to dental alloys. J Dent Res 1988;67:479-83. 16. Penugonda B, Scherer W, Cooper H, Kokoletsos N, Koifman V. Bonding
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17.
18.
19.
20. 21.
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Ni-Cr alloy to tooth structure with adhesive resin cements. J Esthet Dent 1992;4Suppl:26-9. Hunsaker KJ, Christensen GJ, Christensen RP, Cao D, Lewis RG. Retentive characteristics of dental cementation materials. Gen Dent 1993;41:464-7. Matsumura H, Salonga JP, Taira Y, Atsuta M. Effect of ultrasonic instrumentation on bond strength of three dental cements bonded to nickel-chromium alloy. J Prosthet Dent 1996;75:309-13. Diaz-Arnold AM, Mertz JM, Aquilino SA, Ryther JS, Keller JC. A comparison of the tensile strength of four prosthodontic adhesives. J Prosthodont 1993;2:215-9. Chung KH, Hwang YC. Bond strengths of porcelain repair systems with various surface treatments. J Prosthet Dent 1997;78:267-74. Petridis H, Hirayama H, Kugel G, Habib C, Garefis P. Shear bond strength of techniques for bonding esthetic veneers to metal. J Prosthet Dent 1999;82:608-14.
O
Reprint requests to: DR JEFFREY C. CHANG DEPARTMENT OF PROSTHODONTICS UNIVERSITY OF TEXAS-HOUSTON DENTAL BRANCH 6516 JOHN FREEMAN AVE HOUSTON, TX 77030 FAX: (713)500-4353 E-MAIL: [email protected] Copyright © 2002 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2002/$35.00 + 0. 10/1/121583
doi:10.1067/mpr.2002.121583
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Purpose. This study compared the tensile bond strengths of composites to a gold-palladium alloy with the use of several surface treatment methods. Material and methods. Forty alloy specimens were cast in Eclipse (52% gold and 37.5% palladium) in the form of truncated cones. These specimens were divided equally into 4 groups. In group I, the bonding surfaces of the metal cones were treated with Silicoater MD. Truncated cones of Dentacolor composite were bonded to the metal surfaces and light-polymerized. In group II, the bonding surfaces of the metal cones were air-particle abraded with 50 µm aluminum oxide and coated with C&B Metabond. Truncated cones of Epic-TMPT composite were bonded to the metal surfaces and light-polymerized. In group III, the bonding surfaces of the metal cones were air-particle abraded with CoJet-Sand. Truncated cones of Pertac-Hybrid composite were bonded to the metal surfaces and light-polymerized. In group IV, the bonding surfaces of the metal cones were air-particle abraded with CoJet-Sand. Truncated cones of Visio-Gem were bonded to the metal surfaces and light-polymerized. After 24 hours of water immersion at 37°C and 1000 thermal cycles in water at 5°C and 55°C, tensile forces were applied to all specimens with a universal testing machine. Analysis of variance was applied to the data (P<.05), and differences among means were determined with a Tukey-Kramer interval of 5.4 MPa. Results. Tensile bond strengths in MPa were as follows: Dentacolor, 14 ± 5; Epic-TMPT, 12 ± 4; Pertac-Hybrid, 13 ± 5; and Visio-Gem, 18 ± 4. The tensile bond strength of Visio-Gem was significantly higher than that of Epic-TMPT, but no differences were found among Dentacolor, Pertac-Hybrid, and Epic-TMPT (P<.05). Conclusion. Within the limitations of this study, all 4 bonding systems tested produced high bond strengths between composites and a gold-palladium alloy after thermal cycling. (J Prosthet Dent 2002;87:271-6.)
CLINICAL IMPLICATIONS The results of this in vitro study indicate that all 4 composites tested, when applied with the techniques described, are strong enough for the repair and fabrication of veneer facings.
I
n the 1960s, porcelain-fused-to-metal veneer crowns were introduced to dentistry. Dental porcelain can be used to manufacture esthetic fixed restorations.1 High-fusing porcelain, which is used mainly in porcelain teeth, is composed of feldspar (70% to 90%), quartz (11% to 18%), and kaolin (1% to 10%). Noble metals have been used for the copings. Because gold is
aAssociate
Professor, Department of Prosthodontics. Professor and Director, Advanced Education in General Dentistry Program, Department of Restorative Dentistry and Biomaterials. cProfessor and Vice Chair, Department of Restorative Dentistry and Biomaterials; Director, Houston Biomaterials Research Center. dDental Lab Technician. bAssistant
MARCH 2002
expensive, nickel-chromium also has been used in porcelain-fused-to-metal crowns. Although porcelain is quite esthetic, it is also brittle. Repair with composite is necessary for fractured porcelain crowns. Veneer facings can be fabricated from laboratory composites and bonded to an alloy with the application of a pyrolytic silica surface treatment, which was introduced to the United States in 1985. The mechanism of adhesion consists of the heat fusion of a microscopic layer of glass beads to the metal, after which composite is bonded with a silane coupling agent. This process, which is known as pyrolytic silanization,2 requires equipment such as Silicoater, Silicoater MD, or the latest version, Siloc (Kulzer Inc, Irvine, Calif.). All 3 systems use 250 µm aluminum THE JOURNAL OF PROSTHETIC DENTISTRY 271
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Table I. Materials used in this study Commercial name
Alloy Eclipse Composite Dentacolor Epic-TMPT Visio-Gem Pertac-Hybrid Visio-Gem Alloy Treatment CoJet-Sand Silicoater MD C&B Metabond Opilux 401
Material
52% Au, 37.5% Pd
Ney Dental International, Bloomfield, Conn.
Composite Composite Opaque Composite Composite
Kulzer Inc, Irvine, Calif. Parkell, Farmingdale, N.Y. ESPE America, Plymouth Meeting, Pa. EPSE America ESPE America
Air-particle abrasion material Polymerization unit Luting cement Polymerization light
ESPE America Kulzer Inc Parkell Demetron Corp, Danbury, Conn.
oxide for air-particle abrasion, but they differ in the heating of the metals. The original Silicoater uses an open flame, whereas Silicoater MD and Siloc use an oven. These systems can be used to bond composite to any metal surface. In previous studies, silicoated metals produced 25% more initial strength than etched metals,3 higher bond strengths after 3 days of water storage,4 and mixed results after thermocycling.5-7 The Rocatec System (ESPE America, Plymouth Meeting, Pa.) deposits a microscopic ceramic layer on the metal and bond composite to it with a silane coupling agent. In this system, high heat is eliminated by the use of air-particle abrasion under pressure (tribochemical coating). With the silane coupling agent, a chemical bond is formed between the ceramic silicate layer on the metal surface and the resin, which produces gap-free bonding of the veneer material to the metal frame. The size of the abrasion material is approximately 110 µm. The latest version of this system is the Rocatec Junior, which makes abrasion material approximately 50 µm in diameter. Recently, the same company introduced CoJet-Sand, an air-particle abrasion material that is also approximately 50 µm in diameter and that can be used to fabricate or repair veneer facings. Because this material is relatively new to the market, research data on its use are limited. Adhesive bonding also can be used to fabricate or repair veneer facing. With advances and improvements in adhesive resins, this method has become popular in recent years. One advantage of this system is that expensive lab equipment is not required. However, reported disadvantages include low bond strength with base metal after 6 months of water storage6 and with noble metal7 compared to pyrogenic silanization and tribochemical coating. Adhesive resins such as C&B Metabond (Parkell, Farmingdale, N.Y.) and Super-Bond C&B (Sun Medical Co, Kyoto, Japan) bond well to both base and noble metals.8-19 The objective of this study was to evaluate the ten272
Manufacturer
sile bond strengths of 4 types of veneer facing materials used with 4 different surface treatment techniques: Dentacolor composite and Silicoater MD, Epic-TMPT composite and C&B Metabond, Pertac-Hybrid composite and CoJet-Sand, and Visio-Gem composite and CoJet-Sand. All composites were bonded to a goldpalladium alloy.
MATERIAL AND METHODS Forty alloy specimens were cast with Eclipse (Ney International, Bloomfield, Conn.), a 52% gold and 37.5% palladium alloy, in the form of truncated cones 3 mm in diameter at the bonding surfaces and 5 mm in diameter at the base. These specimens were divided into 4 groups of 10 each. Each group was treated with 1 of 4 composite bonding systems according to the manufacturer’s directions. Composite truncated cones were formed on the metal with a split mold and then polymerized. All materials and their manufacturers are listed in Table I. In group I, the bonding surfaces of the metal cones were air-particle abraded with 250 µm aluminum oxide for 15 seconds. The specimens then were washed with Siliclean (Kulzer Inc) for 30 seconds and air dried for 5 minutes. Sililink (Kulzer Inc) was applied and dried for 2 minutes, followed by heat treatment in the Silicoater MD unit for 4 minutes. This unit consists of a heating chamber and was used to burn the Sililink (silicate coated in metal oxide) into the surface of the alloy at a temperature of 320°C. The specimens were cooled for 5 minutes before Siliseal was applied and air dried for 2 minutes. Two layers of Dentacolor Opaque (Kulzer Inc) were applied to the bonding surfaces and light-polymerized for 90 seconds twice in a photopolymerization unit (Dentacolor XS; Kulzer Inc) with a xenon strobe light chamber. The wavelength with a heat protection filter is 320 to 520 nanometers, and the minimum light intensity within the polymerization chamber is 250 mW/cm2. Dentacolor, a veneering composite composed of 51% VOLUME 87 NUMBER 3
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Fig. 1. Custom mounting jig for testing.
by weight pyrogenic silicium dioxide and 48.5% by weight methacrylic ester, was added in increments to form the truncated cones with a split mold. Each layer was light-polymerized for 90 seconds twice in the photopolymerization unit. In group II, the bonding surfaces of the metal cones were air-particle abraded with 50 µm aluminum oxide for 15 seconds and then cleaned for 3 minutes in distilled water and dried. One drop of catalyst was mixed with 4 drops of monomer of C&B Metabond (Parkell) and used to wet the bonding surfaces. The mixture was combined with 2 scoops of powder, brought to a creamy consistency, and applied to the bonding surface. Epic-TMPT (Parkell), a microfill composite that contains trimethylol propane and trimethacrylate, was used to form a truncated cone on the metal with a split mold. Each of the 3 sides was light-polymerized for 30 seconds in a visible light unit (Optilux 401; Demetron Research Corp, Danbury, Conn.) at an intensity of 450 to 500 mW/cm2. In group III, the bonding surfaces of the metal cones were air-particle abraded with CoJet-Sand (ESPE America). ESPE-Sil (ESPE America) then was applied with a brush and allowed to dry for 5 minutes. A thin layer of the Visio-Gem Opaque (ESPE America) was brushed onto the bonding surface and light-polymerized for 5 seconds twice. Pertac-Hybrid, a universal radiopaque hybrid composite that contains methacrylates and 61% inorganic fillers by volume, was added in increments to form the truncated cones with a split mold. Each layer was light-polymerized for 30 seconds with the visible light unit (Optilux 401) at an intensity of 450 to 500 mW/cm2. In group IV, the bonding surfaces of the metal cones were air-particle abraded with CoJet-Sand, and MARCH 2002
ESPE-Sil was applied with a brush and allowed to dry for 5 minutes. A thin layer of Visio-Gem Opaque was brushed onto the bonding surface and light-polymerized for 5 seconds twice in a halogen light unit (Visio Alpha; ESPE America) at an intensity of 300 mW/cm2. Visio-Gem, a paste that contains 34% acrylate and that is used mainly for veneer facings, was added in increments to form the truncated cones with a split mold. Each layer was light-polymerized for 15 minutes with another unit (Visio Beta Vario; ESPE America) that uses halogen light in the polymerization chamber at an intensity of 380 mW/cm2. The polymerization unit was connected to a vacuum pump with a pumping speed of 1.5 m3 per hour to decrease porosity and increase density of the resin. Fifteen minutes were needed for 1 cycle of light and vacuum. After 24 hours of water immersion at 37°C and 1000 thermal cycles in water at 5°C and 55°C, each specimen was mounted on the split Assembly B of a custom mounting jig (Fig. 1). Tensile forces were applied to Assembly A with the use of a universal testing machine (4465; Instron Corp, Canton, Mass.) at a crosshead speed of 0.5 mm/minute. Analysis of variance was applied to the data (P<.05). Differences among means were determined by a Tukey-Kramer interval of 5.4 MPa at the .05 level of significance. Differences larger than the calculated Tukey-Kramer interval were considered statistically significant.
RESULTS Visio-Gem had the highest mean tensile bond strength to Eclipse (18.0 ± 3.8 MPa), followed by Dentacolor (14.4 ± 4.9 MPa), Pertac-Hybrid (13.3 ± 5.3 MPa), and Epic-TMPT (12.2 ± 3.7 MPa) (Fig. 2). The tensile bond strength of Visio-Gem was 273
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Fig. 2. Mean tensile strengths of composites to gold-palladium.
Fig. 3. Types of bond failures.
Table II. Analysis of variance of bond strength data Source
Df
Product Residual
3 36
Sum of squares
192.0 728.7
Mean square
64.0 20.2
F value
P value
3.16
.036
Dependent: Bond strength (MPa).
significantly higher than that of Epic-TMPT, but the bond strengths of Dentacolor, Pertac-Hybrid, and Epic-TMPT were not significantly different (P<.05) (Table II). Bond failure types are reported in Figure 3. In group I, 60% of the bond failures were adhesive and occurred between Dentacolor Opaque and Eclipse, 27.5% were adhesive between Dentacolor Opaque and Dentacolor composite, 7.5% were cohesive in Dentacolor composite, and 5% were cohesive in Dentacolor Opaque. In group II, 92.5% of the bond failures were adhesive between C&B Metabond and 274
Eclipse, and 7.5% were adhesive between C&B Metabond and Epic-TMPT. In group III, 57.5% of the bond failures were cohesive in the Visio-Gem Opaque layer, and 42.5% were adhesive between VisioGem Opaque and Eclipse. In group IV, 67.5% of the bond failures were cohesive in the Visio-Gem Opaque layer, and 32.5% were adhesive between Visio-Gem Opaque and Eclipse.
DISCUSSION The purpose of this study was to evaluate different methods of fabricating and repairing veneer facings. In group I, Silicoater MD produced high bond strengths (14.4 MPa) between composite and metal. However, Silicoater requires bulky equipment to produce intense heat on the metal to form the oxide layer for bonding; this method therefore cannot be used intraorally. Similar drawbacks can be attributed to group IV. The Visio-Gem polymerization unit and CoJet-Sand also produced high bond strengths (18.0 MPa) between VOLUME 87 NUMBER 3
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composite and metal, but the polymerization instrument is bulky and uses heat and pressure to bond and polymerize the composite. These two methods of repairing or fabricating of veneers can be used only outside the mouth. The use of C&B Metabond in group II and CoJetSand in group III required no bulky equipment, no heat, and no pressure. These methods can be used intraorally or extraorally. However, the tensile bond strengths recorded for these groups were lower than for the other 2 groups because heat and pressure is required for a strong, consistent bond between composite and gold. This finding supports a previous study6 in which Rocatec and Silicoater produced stronger and more consistent bond strengths than adhesive resins and bonding agents. In the present study, the bond strengths of resins and gold-palladium were lower than those reported in a study on resins and a nickel-chromium alloy.6 This discrepancy can be attributed to the fact that, because gold is a noble metal, the optimal oxide layer required for bonding does not form adequately. Observation of the bond failure types (Fig. 3) shows that the Visio-Gem group, which produced the highest tensile strengths, exhibited the majority of bond failures cohesively in the Visio-Gem Opaque layer; the C&B Metabond and Pertac-Hybrid groups, which produced lower tensile strengths, exhibited the majority of bond failures adhesively at the metal/resin interface. These results again highlight the importance of optimal metal oxide layer formation and metal surface treatments. Additional research should be performed in this area. In a study by Chung and Hwang,20 the bond strengths of porcelain repair systems bonded to base metal with various surface treatments were investigated. The LinerM/Superbond system (4-META) (Sun Medical Co) demonstrated the highest strength values. No significant difference in bond strengths was found with air-particle abrasion and hydrofluoric acid etching surface treatments. Hydrofluoric acid, like Silicoater and Rocatec, is hazardous and should not be used intraorally. In a study by Petridis et al,21 the shear bond strength between esthetic veneers and a gold-palladium alloy was evaluated. In group 1, a traditional method of porcelain fused to metal was used to fabricate the veneers. In group 2, Artglass composite was bonded to metal treated with the Siloc unit. In group 3, the opaque ceramic layer was etched for 2 minutes with 6% hydrofluoric acid before 3 layers of Artglass dentin were bonded to it. After thermocycling, porcelain-fused-to-metal veneers exhibited the highest mean shear strength (23 MPa), followed by the Siloc system (18 MPa); the etched porcelain demonstrated the lowest bond strength (16 MPa). These bond strengths are MARCH 2002
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comparable to those recorded in the present study, which also evaluated a noble metal bonded to composite. The porcelain-fused-to-metal and Siloc systems require heat treatment for the metal, which confirms that heat or pressure is required for a strong, consistent bond.
CONCLUSIONS Within the limitations of this study, the following conclusions were drawn: All 4 bonding systems produced high bond strengths (12.2 to 18.0 MPa) between composites and Eclipse after thermal cycling. Visio-Gem exhibited the highest bond strength to gold-palladium. The tensile bond strength of VisioGem was significantly higher than that of Epic-TMPT. No significant differences among Dentacolor, PertacHybrid, and Epic-TMPT were observed. The majority of the failure modes were adhesive at the junction of the metal and opaque or cement. We sincerely thank Dr C. David Taylor, Director of Educational Assessment and Technology, University of Texas-Houston Dental Branch, for his editorial assistance. We also thank Ney Dental International, Jelenko/Kulzer Lab Products, Parkell, and ESPE America for their material support.
REFERENCES 1. Shillingburg HT, Hobo S, Whitsett LD, Jacobi R, Brackett SE. Fundamentals of fixed prosthodontics. 3rd ed. Chicago: Quintessence; 1997. p. 433-83. 2. Albers HE. Adept Report. Santa Rosa: Adept Institute; 1991. p. 25. 3. Re GJ, Kaiser DA, Malone WF, Garcia-Godoy F. Shear bond strengths and scanning electron microscope evaluation of three different retentive methods for resin-bonded retainers. J Prosthet Dent 1988;59:568-73. 4. Tenjoma LT, Nicholls JI, Townsend JT, Harper RJ. Chemical retention of composite resin to metal. Int J Prosthodont 1990;3:78-88. 5. Schneider W, Powers JM, Pierpont HP. Bond strength of composites to etched and silica-coated porcelain fusing alloys. Dent Mater 1992;8:211-5. 6. Chang JC, Powers JM, Hart D. Bond strength of composite to alloy treated with bonding systems. J Prosthodont 1993;2:110-4. 7. Laufer BZ, Nicholls JI. Time delay effects on the tensile bond strength developed by the Silicoater. Quintessence Dent Technol 1987;11:199203. 8. Lo CS, Millstein PL, Nathanson D. In vitro shear strength of bonded amalgam cores with and without pins. J Prosthet Dent 1995;74:385-91. 9. Donald HL, Jeansonne BG, Gardiner DM, Sarkar NK. Influence of dentinal adhesives and a prefabricated post on fracture resistance of silver amalgam cores. J Prosthet Dent 1997;77:17-22. 10. NaBadalung DP, Powers JM, Connelly ME. Comparison of bond strengths of three denture base resins to treated nickel-chromium-beryllium alloy. J Prosthet Dent 1998;80:354-61. 11. van Putten MC Jr, Culbertson BM. Adhesion promotion between metadent and a high palladium alloy with a pyrolytically fused porcelain opaque layer. J Prosthodont 1994;3:79-87. 12. Bahannan S, Lacefield WR. An evaluation of three methods of bonding resin composite to stainless steel. Int J Prosthodont 1993;6:502-5. 13. Suliman AH, Swift EJ Jr, Perdigao J. Effects of surface treatment and bonding agents on bond strength of composite resin to porcelain. J Prosthet Dent 1993;70:118-20. 14. Moser JB, Brown DB, Greener EH. Short-term bond strengths between adhesive cements and dental alloys. J Dent Res 1974;53:1377-86. 15. Watanabe F, Powers JM, Lorey RE. In vitro bonding of prosthodontic adhesives to dental alloys. J Dent Res 1988;67:479-83. 16. Penugonda B, Scherer W, Cooper H, Kokoletsos N, Koifman V. Bonding
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Ni-Cr alloy to tooth structure with adhesive resin cements. J Esthet Dent 1992;4Suppl:26-9. Hunsaker KJ, Christensen GJ, Christensen RP, Cao D, Lewis RG. Retentive characteristics of dental cementation materials. Gen Dent 1993;41:464-7. Matsumura H, Salonga JP, Taira Y, Atsuta M. Effect of ultrasonic instrumentation on bond strength of three dental cements bonded to nickel-chromium alloy. J Prosthet Dent 1996;75:309-13. Diaz-Arnold AM, Mertz JM, Aquilino SA, Ryther JS, Keller JC. A comparison of the tensile strength of four prosthodontic adhesives. J Prosthodont 1993;2:215-9. Chung KH, Hwang YC. Bond strengths of porcelain repair systems with various surface treatments. J Prosthet Dent 1997;78:267-74. Petridis H, Hirayama H, Kugel G, Habib C, Garefis P. Shear bond strength of techniques for bonding esthetic veneers to metal. J Prosthet Dent 1999;82:608-14.
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Reprint requests to: DR JEFFREY C. CHANG DEPARTMENT OF PROSTHODONTICS UNIVERSITY OF TEXAS-HOUSTON DENTAL BRANCH 6516 JOHN FREEMAN AVE HOUSTON, TX 77030 FAX: (713)500-4353 E-MAIL: [email protected] Copyright © 2002 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2002/$35.00 + 0. 10/1/121583
doi:10.1067/mpr.2002.121583
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