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Phosphate and thiophosphate primers for bonding prosthodontic luting materials to titanium
THE JOURNAL OF PROSTHETIC DENTISTRY
TAIRA ET AL
Phosphate and thiophosphate primers for bonding prosthodontic luting materials to titanium Yohsuke Taira, DDS, PhD,a Keiichi Yoshida, DDS, PhD,b Hideo Matsumura, DDS, PhD,c and Mitsuru Atsuta, DDS, PhDd Nagasaki University School of Dentistry, Nagasaki, Japan Statement of problem. When resin-bonded prostheses are constructed with titanium, they must be strongly bonded with luting materials for the prostheses to withstand the oral environment over the long term. However, limited information is available about the bond durability between luting materials and titanium. Purpose. This study determined whether a phosphate and two thiophosphate primers increase bond strength and durability between a commercially available pure titanium and four luting agents. Material and methods. Three primers and four luting agents were divided into three groups according to the type of acidic monomers: carboxylic acid derivatives (4-META, 4-AET, and MAC10), a phosphoric acid derivative (MDP), and a thiophosphoric acid derivative (MEPS). Disk specimens were bonded with 16 combinations of 3 primers and 4 luting agents, including 4 controls. Shear bond strengths were determined after 1-day immersion in water and after thermocycling for 100,000 cycles. Results. Bond strengths were influenced by thermocycling, primer, luting agent, and their combinations. After thermocycling, the groups that demonstrated the highest bond strengths were six combinations of two primers (Cesead Opaque Primer and Metal Primer II) and three luting agents (Imperva Dual, Panavia 21, and Super-Bond C&B). (J Prosthet Dent 1998;79:384-8.)
CLINICAL IMPLICATIONS In this study, the highest bond strengths were achieved with the six combinations of two primers (CP and MP II) and three adhesive resins (Imperva, Panavia 21, and Super-Bond). This simple technique combining adhesive primers and self-curing luting materials is applicable for prosthodontic practice without the need for complicated surface preparation.
T
itanium is an ideal material for use in prosthodontics because of its biocompatibility, corrosion resistance, and mechanical strength compared with light weight. There are some approaches for using titanium as a resin-bonded fixed partial denture,1,2 but limited information is available about the bond durability between luting materials and titanium. Although attempts to increase mechanical retention, that is, electrolytic etching3 and chemical etching,4 have been introduced to enable metal alloys to be bonded mechanically with luting materials, traditional resin-bonded prostheses still suffer from rather high rates of debonding.5-8 When resinbonded prostheses are constructed with titanium, the titanium must be strongly bonded with luting materials through a chemical bonding system. Prosthodontic resin cements are usually composed of a
Instructor, Department of Fixed Prosthodontics. Assistant Professor, Department of Fixed Prosthodontics. c Associate Professor, Department of Fixed Prosthodontics. d Professor and Chair, Department of Fixed Prosthodontics. b
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base monomers, fillers, polymerization initiators, and functional monomers. The importance of the functional monomer has been emphasized,9-11 and these monomers also seem to play a critical role in bonding systems appropriate for titanium.12-15 Previous investigations16,17 in the quest of adhesive systems for pure titanium have demonstrated that the application of primers containing either carboxylic, phosphoric, or thiophosphoric acid derivative monomer resulted in increased bond strengths of tri-n-butylboraneinitiated luting materials. In contrast to the purity of the other functional monomers, however, the synthesized thiophosphoric primer contained an unpurified mixture of various thiophosphate compounds, which in turn affected bond strengths.13 Recently, a slightly refined thiophosphoric methacrylate monomer (MEPS) has become commercially available as a primer for bonding base and noble metal alloys.18 This study describes experiments designed to determine whether a phosphate and two thiophosphate primVOLUME 79 NUMBER 4
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THE JOURNAL OF PROSTHETIC DENTISTRY
Table I. Primers and luting agents used Material
Primer
Luting agent
Trade name
Cesead Opaque Primer Metal Primer Metal Primer II Super-Bond C&B Imperva Dual Bistite Resin Cement Panavia 21
Abbreviation
Manufacturer
CP MP MP II Super-Bond Imperva Bistite Panavia 21
Lot no.
Kuraray Co., Ltd., Okayama, Japan GC Corp., Tokyo, Japan GC Corp., Tokyo, Japan Sun Medical Co., Ltd., Moriyama, Japan Shofu Inc., Kyoto, Japan Tokuyama Soda Co., Ltd., Tokyo, Japan Kuraray Co., Ltd., Okayama, Japan
00260 181131 210261 60101 0593 20009X 11223
Functional monomer
MDP MEPS MEPS 4-META 4-AET MAC10 MDP
MDP: 10-methacryloyloxydecyl dihydrogen phosphate; MEPS: methacrylate with thiophosphoric acid moiety; 4-AET: 4-acryloyloxyethyl trimellitate; MAC10: 11methacryloyloxyundecan 1,1-dicarboxylic acid; 4-META: 4-methacryloyloxyethyl trimellitate anhydride.
Table II. ANOVA results for shear bond strengths Source of variation
Thermocycling Luting agent Primer* Thermocycling × luting agent Luting agent × primer Thermocycling × primer Thermocycling × luting agent × primer Residual
df
Sum of squares
Mean squares
F-value
P-value
573.8 1996.1 2781.0 327.6 898.0 987.2 1099.8 4333.8
573.8 665.4 927.0 109.2 99.8 329.1 122.2 33.9
16.9 19.7 27.4 3.2 2.9 9.7 3.6
0.0001 0.0001 0.0001 0.0248 0.0033 0.0001 0.0005
1 3 3 3 9 3 9 128
*Three primers and a control.
ers increase bond strength and durability between a commercially available pure titanium and four luting agents.
MATERIAL AND METHODS Three primers and four luting agents were tested. Their trade names, abbreviations, manufacturers, lot numbers, and functional monomers contained are listed in Table I. Two types of disks (10 mm in diameter by 2.5 mm thick and 6 mm in diameter by 2.5 mm thick) of “Pure Titanium A” (Ti >99.66%, O = 0.15%, Fe = 0.15%, N = 0.03%; J. Morita Corp., Suita, Japan) were cast into an alumina-magnesia investment (Titavest CB, J. Morita Corp., Suita, Japan) according to the manufacturer’s specifications by using an arc casting apparatus (Cyclarc, J. Morita Corp., Suita, Japan). After the disk specimens had been ground with No. 600 silicon-carbide paper, the surfaces were sandblasted with 50 µm alumina for 10 seconds (Pen-Blaster, Shofu, Inc., Kyoto, Japan). The pressure was 0.5 MPa with the nozzle held 5 mm from the specimen surface. A piece of tape (50 µm thick) with a circular hole 5 mm in diameter was positioned on the surface of each 10 mm diameter specimen to delineate the area of the bond. After the primer was applied to the titanium surfaces, specimen pairs (6 mm diameter and 10 mm diameter) were joined with luting agent. Five pairs of specimens were prepared in this way for each combination of primer and luting agent, as well as five pairs of specimens without primer as controls for each luting agent. APRIL 1998
After the elapse of 1 hour from preparation, the specimens were immersed in water at 37° C for 24 hours. This state was defined as thermocycle 0. The specimens were then placed in a thermocycling machine (Rika Kogyo, Hachioji, Japan) and alternated between 4° C and 60° C water for 1-minute periods for 100,000 cycles. Shear bond strength was determined on a universal testing device (AGS-10kNG, Shimadzu Corp., Kyoto, Japan) at a crosshead speed of 0.5 mm/minute. The means and standard deviations of the five specimens were calculated for each group. All data were analyzed by three-factor analysis of variance (ANOVA), and the mean values were compared by a post hoc Fisher’s protected LSD test, for which significant levels were set at p < 0.01. After shear testing, debonded surfaces were examined with an optical microscope (SMZ-10, Nikon Corp., Tokyo, Japan) ×4 to evaluate failure modes. These were classified into (a) resin-metal interface (adhesive failure), and (b) mixture of adhesive failure and cohesive failure (mixed failure, adhesive plus cohesive).
RESULTS The mean bond strengths and standard deviations before and after thermocycling are graphed in Figure 1. Bond strengths ranged from 35.5 to 45.1 MPa before thermocycling, and values varied from 13.8 to 50.7 MPa after 100,000 thermocycles. Table II shows the shear testing results evaluated according to three-factor ANOVA. The bond strength was 385
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TAIRA ET AL
Fig. 1. Shear bond strength results.
Fig. 2. Failure modes after shear testing.
influenced by thermocycling, luting agent, primer, and their interactions. No significant interaction was found between thermocycling and luting agent. The results of Fisher groupings are presented in Table III. No significant differences in bond strengths were found among the 16 groups at thermocycle 0. After 100,000 thermocycles, bond strengths among the nonprimed groups, presented in increasing order, were Bistite, Super-Bond, Imperva, and Panavia 21. The six combinations of two primers (CP and MP II) and three luting agents (Imperva, Panavia 21, and Super-Bond) showed the greatest bond strength, and demonstrated the same statistical level. The mode of bond failure for each specimen is listed in Figure 2. With the exception of three groups that showed only mixed adhesive and cohesive failure (groups 2, 4, and 12), all groups showed an increase in complete adhesive mode failure after thermocycling.
DISCUSSION Previous reports 17 have shown the application of a primer containing a phosphoric acid derivative monomer to be effective in improving the bond strength of resin to 386
machine milled pure titanium. The findings of the current study indicate that the phosphoric primer is effective in the bonding of luting agents to cast pure titanium, and further, that a primer containing MEPS is also effective. To determine an acidic monomer that contributes to adhesive bonding, we divided three primers and four luting agents into three groups according to the type of acidic monomers: carboxylic acid derivatives (4-META, 4-AET, and MAC10), a phosphoric acid derivative (MDP), and a thiophosphoric acid derivative (MEPS). It has been shown that metal specimens bonded to an acrylic rod decreased in bond strength within a short period as a result of thermocycling, as opposed to the metal-to-metal adhesion.12,18-20 The mechanical stresses induced by thermocycling may be minimized when the adhesive cements are interposed between two pieces of like material. However, loss of bond strength due to the accumulation of thermal cycles can be evaluated within a shorter period compared with prolonged storage in water,21 and it is difficult to successfully bond most prosthodontic composite materials to an acrylic resin rod; hence, we examined adhesive bonding durability by means of metal-to-metal adhesion. The period of 100,000 thermocycles was selected on the basis of our previous findings.16,17 Although three-factor ANOVA analysis (Table II) showed significant interactions among all three main effects, certain trends could be found with the help of comparisons with the Fisher test. As shown in Figure 1 and Table III, the bond strength of titanium joined with Super-Bond was considerably improved with CP primer or MP II primer. Super-Bond contains 4-META as a functional monomer, but these findings suggest that MDP and MEPS are superior to 4-META as an adhesive bonding promoter for titanium. In bonding with Imperva, which contains 4-AET, or with Bistite, which contains MAC10, the bond strengths were also improved by means of CP and/or MP II primers. Taking these findings into consideration, monomers derived from phosphoric or thiophosphoric acid probably VOLUME 79 NUMBER 4
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Table III. Statistical analysis results Thermocycle
Luting agent
Primer
Mean (SD) (MPa)
100,000 100,000 100,000 100,000 100,000 100,000 0 100,000 0 100,000 100,000 0 0 0 100,000 0 0 0 0 0 0 0 100,000 0 0 100,000 0 0 100,000 100,000 100,000 100,000
No primer MP MP CP No primer MP No primer MP MP MP II No primer MP II MP No primer No primer No primer No primer CP CP MP MP II CP CP CP MP CP MP II MP II MP II CP MP II MP II
Bistite Imperva Super-Bond Bistite Super-Bond Panavia 21 Bistite Bistite Super-Bond Bistite Imperva Bistite Bistite Imperva Panavia 21 Super-Bond Panavia 21 Super-Bond Bistite Imperva Super-Bond Panavia 21 Imperva Imperva Panavia 21 Super-Bond Panavia 21 Imperva Super-Bond Panavia 21 Panavia 21 Imperva
13.8 (1.0) 26.7 (6.2) 28.3 (2.8) 29.5 (3.7) 29.7 (3.1) 34.1 (3.6) 35.5 (6.5) 36.3 (2.0) 36.5 (1.3) 36.5 (8.4) 36.9 (5.1) 37.0 (2.3) 37.2 (1.9) 37.7 (6.2) 38.5 (2.5) 38.8 (2.0) 39.7 (5.7) 40.1 (6.0) 40.9 (6.3) 42.4 (4.6) 43.2 (3.1) 43.9 (5.0) 44.1 (7.5) 44.4 (6.3) 44.5 (8.3) 44.6 (4.9) 44.6 (2.8) 45.1 (7.1) 45.1 (3.8) 45.9 (7.6) 50.0 (6.8) 50.7 (7.3)
Fisher grouping
a ab abc abc abcd abcde abcdef abcdef abcdef abcdef abcdef ab c d e f abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef
g gh gh gh gh gh gh gh gh gh gh gh gh gh
Identical letters indicate that the mean values are not statistically different at p = 0.01.
enable titanium to be bonded more strongly with polymeric materials than do monomers derived from carboxylic acid. We speculate that MDP and MEPS can react with the thin oxide film produced on the titanium surface, contributing to increased bond strength and durability. The efficacy of MDP or MEPS was also reported with regard to the bonding of Co-Cr alloy.13,22 After 100,000 thermocycles, the bond strengths of 4-META/MMATBB resin joined to Co-Cr alloy were measured at 43.4 and 37.0 MPa with and without MDP primer, respectively.13 These values were comparable to those measured in this study. The disagreement in results between MP and MP II may be due to the concentration of MEPS in these primers. Although both MP and MP II contain MEPS, the concentration of MEPS in MP II primer was greater than that in MP primer. The influence of concentration of MEPS in primer has already been ascertained.19,23 In the cases of Imperva and Panavia 21 materials, the differences between MEPS and MDP were detected after thermocycling. These luting materials bonded more APRIL 1998
strongly to the MP II-primed specimens than to the nonprimed groups, whereas no significant differences were detected between CP-primed groups and nonprimed groups. However, the mechanism of the improved durability obtained by modification of the MP II primer remains unclear. Interestingly, the CP-primed Panavia 21 group demonstrated better bonding durability than the nonprimed Panavia 21 group, although both used MDP as a functional monomer. The greater bond strength of the CPprimed group may be due to the high concentration of free phosphate at the resin-metal interface. When amine dissolved in Panavia 21 material exists at the interface, the effect of MDP may be weakened by acid-base reaction. Although clear differences were lacking in original failure modes, a trend could be identified with the help of thermocycling (Fig. 2). After thermocycling, the resin composite materials (Imperva, Bistite, and Panavia 21) showed more adhesive failure than the unfilled type luting material (Super-Bond). This may be because the composite type luting materials have higher mechanical 387
THE JOURNAL OF PROSTHETIC DENTISTRY
strengths compared with the unfilled type luting material Super-Bond.24 In summary, the surface treatment of titanium with primers containing either MDP or MEPS demonstrated high bond strengths and bonding durability. This simple technique combining primers (CP and MP II) and luting materials (Imperva, Panavia 21, and Super-Bond) will enable prostheses to withstand the oral environment in the long term.
CONCLUSIONS Within the limits of this study, the following conclusions were drawn. 1. Bond strengths of luting agents joined to a commercially available pure titanium were influenced by type of primer, type of luting agent, thermocycling, and their combinations. 2. Bond strengths ranged from 35.5 to 45.1 MPa before thermocycling, and values varied from 13.8 to 50.7 MPa after 100,000 thermocycles. 3. The highest bond strengths (44.1 to 50.7 MPa) after 100,000 thermocycles were obtained with combinations of two primers (Cesead Opaque Primer and Metal Primer II) and three adhesive resins (Imperva Dual, Panavia 21, and Super-Bond C&B). REFERENCES 1. Peters D, Marx R. Titanium in adhesive bridge technic: adhesive-metal-bond. Z W R 1989;98:966-74. 2. Lorey RE, Edge MJ, Lang BR, Lorey HS. The potential for bonding titanium restorations. J Prosthodont 1993;2:151-5. 3. Livaditis GJ, Thompson VP. Etched castings: an improved retentive mechanism for resin-bonded retainers. J Prosthet Dent 1982;47:52-8. 4. Love LD, Breitman JB. Resin retention by immersion-etched alloy. J Prosthet Dent 1985;53:623-4. 5. Besimo C. Resin-bonded fixed partial denture technique: results of a medium-term clinical follow-up investigation. J Prosthet Dent 1993;69:144-8. 6. Boyer DB, Williams VD, Thayer KE, Denehy GE, Diaz-Arnold AM. Analysis of debond rates of resin-bonded prostheses. J Dent Res 1993;72:1244-8. 7. Verzijden CW, Creugers NH, Mulder J. A multi-practice clinical study on posterior resin-bonded bridges: a 2.5-year interim report. J Dent Res 1994;73:529-35. 8. de Rijk WG, Wood M, Thompson VP. Maximum likelihood estimates for the lifetime of bonded dental prostheses. J Dent Res 1996;75:1700-5.
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9. Ekstrand K, Ruyter IE, Øysæd H. Adhesion to titanium of methacrylate-based polymer materials. Dent Mater 1988;4:111-5. 10. Matsumura H, Yoshida K, Tanaka T, Atsuta M. Adhesive bonding of titanium with a titanate coupler and 4-META/MMA-TBB opaque resin. J Dent Res 1990;69:1614-6. 11. Fujishima A, Fujishima Y, Ferracane JL. Shear bond strength of four commercial bonding systems to cp Ti. Dent Mater 1995;11:82-6. 12. Tanaka T, Fujiyama E, Shimizu H, Takaki A, Atsuta M. Surface treatment of nonprecious alloys for adhesion-fixed partial dentures. J Prosthet Dent 1986;55:456-62. 13. Matsumura H, Tanaka T, Taira Y, Atsuta M. Bonding of a cobalt-chromium alloy with acidic primers and tri-n-butylborane-initiated luting agents. J Prosthet Dent 1996;76:194-9. 14. Yoshida K, Kamada K, Tanagawa M, Atsuta M. Shear bond strengths of three resin cements used with three adhesive primers for metal. J Prosthet Dent 1996;75:254-61. 15. Salonga JP, Matsumura H, Yasuda K, Yamabe Y. Bond strength of adhesive resin to three nickel-chromium alloys with varying chromium content. J Prosthet Dent 1994;72:582-4. 16. Taira Y, Matsumura H, Atsuta M. Bonding of titanium with acidic primers and a tri-n-butylborane-initiated luting agent. J Oral Rehabil 1997;24:385-8. 17. Taira Y, Matsumura H, Yoshida K, Tanaka T, Atsuta M. Adhesive bonding of titanium with a methacrylate-phosphate primer and self-curing adhesive resins. J Oral Rehabil 1995;22:409-12. 18. Ikeda Y. Influence of resin cements on durability of metal-resin adhesion. J Jpn Dent Mater 1995;14:42-51. 19. Taira Y, Imai Y. Primer for bonding resin to metal. Dent Mater 1995;11:2-6. 20. Taira Y, Matsumura H, Yoshida K, Tanaka T, Atsuta M. Influence of surface oxidation of titanium for adhesion. J Dent 1998;26:69-73. 21. Tanaka T, Nagata K, Takeyama M, Atsuta M, Nakabayashi N, Masuhara E. 4META opaque resin—a new resin strongly adhesive to nickel-chromium alloy. J Dent Res 1981;60:1697-706. 22. Yoshida K, Taira Y, Sawase T, Atsuta M. Effects of adhesive primers on bond strength of self-curing resin to cobalt-chromium alloy. J Prosthet Dent 1997;77:617-20. 23. Ueno T, Kumagai T, Hirota K, Saitoh Y, Kojima I. The characteristic of metal adhesion primer “GC METAL PRIMER II”. J Dent Res 1997;76(Special Issue):312. 24. White SN, Yu Z. Physical properties of fixed prosthodontic, resin composite luting agents. Int J Prosthodont 1993;6:384-9. Reprint requests to: DR. YOHSUKE TAIRA DEPARTMENT OF FIXED PROSTHODONTICS SCHOOL OF DENTISTRY NAGASAKI UNIVERSITY 1-7-1, SAKAMOTO NAGASAKI 852-8588 JAPAN Copyright © 1998 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/98/$5.00 + 0. 10/1/87982
Availability of JOURNAL Back Issues As a service to our subscribers, copies of back issues of The Journal of Prosthetic Dentistry for the preceding 5 years are maintained and are available for purchase from the publisher, Mosby, until inventory is depleted, at a cost of $12.00 per issue. The following quantity discounts are available: 25% off on quantities of 12 to 23, and one third off on quantities of 24 or more. Please write to Mosby, Inc, Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, or call (800)453-4351 or (314)453-4351 for information on availability of particular issues. If unavailable from the publisher, photocopies of complete issues may be purchased from UMI, 300 N. Zeeb Rd., Ann Arbor, MI 48106, (313)7614700.
388
VOLUME 79 NUMBER 4
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Phosphate and thiophosphate primers for bonding prosthodontic luting materials to titanium Yohsuke Taira, DDS, PhD,a Keiichi Yoshida, DDS, PhD,b Hideo Matsumura, DDS, PhD,c and Mitsuru Atsuta, DDS, PhDd Nagasaki University School of Dentistry, Nagasaki, Japan Statement of problem. When resin-bonded prostheses are constructed with titanium, they must be strongly bonded with luting materials for the prostheses to withstand the oral environment over the long term. However, limited information is available about the bond durability between luting materials and titanium. Purpose. This study determined whether a phosphate and two thiophosphate primers increase bond strength and durability between a commercially available pure titanium and four luting agents. Material and methods. Three primers and four luting agents were divided into three groups according to the type of acidic monomers: carboxylic acid derivatives (4-META, 4-AET, and MAC10), a phosphoric acid derivative (MDP), and a thiophosphoric acid derivative (MEPS). Disk specimens were bonded with 16 combinations of 3 primers and 4 luting agents, including 4 controls. Shear bond strengths were determined after 1-day immersion in water and after thermocycling for 100,000 cycles. Results. Bond strengths were influenced by thermocycling, primer, luting agent, and their combinations. After thermocycling, the groups that demonstrated the highest bond strengths were six combinations of two primers (Cesead Opaque Primer and Metal Primer II) and three luting agents (Imperva Dual, Panavia 21, and Super-Bond C&B). (J Prosthet Dent 1998;79:384-8.)
CLINICAL IMPLICATIONS In this study, the highest bond strengths were achieved with the six combinations of two primers (CP and MP II) and three adhesive resins (Imperva, Panavia 21, and Super-Bond). This simple technique combining adhesive primers and self-curing luting materials is applicable for prosthodontic practice without the need for complicated surface preparation.
T
itanium is an ideal material for use in prosthodontics because of its biocompatibility, corrosion resistance, and mechanical strength compared with light weight. There are some approaches for using titanium as a resin-bonded fixed partial denture,1,2 but limited information is available about the bond durability between luting materials and titanium. Although attempts to increase mechanical retention, that is, electrolytic etching3 and chemical etching,4 have been introduced to enable metal alloys to be bonded mechanically with luting materials, traditional resin-bonded prostheses still suffer from rather high rates of debonding.5-8 When resinbonded prostheses are constructed with titanium, the titanium must be strongly bonded with luting materials through a chemical bonding system. Prosthodontic resin cements are usually composed of a
Instructor, Department of Fixed Prosthodontics. Assistant Professor, Department of Fixed Prosthodontics. c Associate Professor, Department of Fixed Prosthodontics. d Professor and Chair, Department of Fixed Prosthodontics. b
384
THE JOURNAL OF PROSTHETIC DENTISTRY
base monomers, fillers, polymerization initiators, and functional monomers. The importance of the functional monomer has been emphasized,9-11 and these monomers also seem to play a critical role in bonding systems appropriate for titanium.12-15 Previous investigations16,17 in the quest of adhesive systems for pure titanium have demonstrated that the application of primers containing either carboxylic, phosphoric, or thiophosphoric acid derivative monomer resulted in increased bond strengths of tri-n-butylboraneinitiated luting materials. In contrast to the purity of the other functional monomers, however, the synthesized thiophosphoric primer contained an unpurified mixture of various thiophosphate compounds, which in turn affected bond strengths.13 Recently, a slightly refined thiophosphoric methacrylate monomer (MEPS) has become commercially available as a primer for bonding base and noble metal alloys.18 This study describes experiments designed to determine whether a phosphate and two thiophosphate primVOLUME 79 NUMBER 4
TAIRA ET AL
THE JOURNAL OF PROSTHETIC DENTISTRY
Table I. Primers and luting agents used Material
Primer
Luting agent
Trade name
Cesead Opaque Primer Metal Primer Metal Primer II Super-Bond C&B Imperva Dual Bistite Resin Cement Panavia 21
Abbreviation
Manufacturer
CP MP MP II Super-Bond Imperva Bistite Panavia 21
Lot no.
Kuraray Co., Ltd., Okayama, Japan GC Corp., Tokyo, Japan GC Corp., Tokyo, Japan Sun Medical Co., Ltd., Moriyama, Japan Shofu Inc., Kyoto, Japan Tokuyama Soda Co., Ltd., Tokyo, Japan Kuraray Co., Ltd., Okayama, Japan
00260 181131 210261 60101 0593 20009X 11223
Functional monomer
MDP MEPS MEPS 4-META 4-AET MAC10 MDP
MDP: 10-methacryloyloxydecyl dihydrogen phosphate; MEPS: methacrylate with thiophosphoric acid moiety; 4-AET: 4-acryloyloxyethyl trimellitate; MAC10: 11methacryloyloxyundecan 1,1-dicarboxylic acid; 4-META: 4-methacryloyloxyethyl trimellitate anhydride.
Table II. ANOVA results for shear bond strengths Source of variation
Thermocycling Luting agent Primer* Thermocycling × luting agent Luting agent × primer Thermocycling × primer Thermocycling × luting agent × primer Residual
df
Sum of squares
Mean squares
F-value
P-value
573.8 1996.1 2781.0 327.6 898.0 987.2 1099.8 4333.8
573.8 665.4 927.0 109.2 99.8 329.1 122.2 33.9
16.9 19.7 27.4 3.2 2.9 9.7 3.6
0.0001 0.0001 0.0001 0.0248 0.0033 0.0001 0.0005
1 3 3 3 9 3 9 128
*Three primers and a control.
ers increase bond strength and durability between a commercially available pure titanium and four luting agents.
MATERIAL AND METHODS Three primers and four luting agents were tested. Their trade names, abbreviations, manufacturers, lot numbers, and functional monomers contained are listed in Table I. Two types of disks (10 mm in diameter by 2.5 mm thick and 6 mm in diameter by 2.5 mm thick) of “Pure Titanium A” (Ti >99.66%, O = 0.15%, Fe = 0.15%, N = 0.03%; J. Morita Corp., Suita, Japan) were cast into an alumina-magnesia investment (Titavest CB, J. Morita Corp., Suita, Japan) according to the manufacturer’s specifications by using an arc casting apparatus (Cyclarc, J. Morita Corp., Suita, Japan). After the disk specimens had been ground with No. 600 silicon-carbide paper, the surfaces were sandblasted with 50 µm alumina for 10 seconds (Pen-Blaster, Shofu, Inc., Kyoto, Japan). The pressure was 0.5 MPa with the nozzle held 5 mm from the specimen surface. A piece of tape (50 µm thick) with a circular hole 5 mm in diameter was positioned on the surface of each 10 mm diameter specimen to delineate the area of the bond. After the primer was applied to the titanium surfaces, specimen pairs (6 mm diameter and 10 mm diameter) were joined with luting agent. Five pairs of specimens were prepared in this way for each combination of primer and luting agent, as well as five pairs of specimens without primer as controls for each luting agent. APRIL 1998
After the elapse of 1 hour from preparation, the specimens were immersed in water at 37° C for 24 hours. This state was defined as thermocycle 0. The specimens were then placed in a thermocycling machine (Rika Kogyo, Hachioji, Japan) and alternated between 4° C and 60° C water for 1-minute periods for 100,000 cycles. Shear bond strength was determined on a universal testing device (AGS-10kNG, Shimadzu Corp., Kyoto, Japan) at a crosshead speed of 0.5 mm/minute. The means and standard deviations of the five specimens were calculated for each group. All data were analyzed by three-factor analysis of variance (ANOVA), and the mean values were compared by a post hoc Fisher’s protected LSD test, for which significant levels were set at p < 0.01. After shear testing, debonded surfaces were examined with an optical microscope (SMZ-10, Nikon Corp., Tokyo, Japan) ×4 to evaluate failure modes. These were classified into (a) resin-metal interface (adhesive failure), and (b) mixture of adhesive failure and cohesive failure (mixed failure, adhesive plus cohesive).
RESULTS The mean bond strengths and standard deviations before and after thermocycling are graphed in Figure 1. Bond strengths ranged from 35.5 to 45.1 MPa before thermocycling, and values varied from 13.8 to 50.7 MPa after 100,000 thermocycles. Table II shows the shear testing results evaluated according to three-factor ANOVA. The bond strength was 385
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Fig. 1. Shear bond strength results.
Fig. 2. Failure modes after shear testing.
influenced by thermocycling, luting agent, primer, and their interactions. No significant interaction was found between thermocycling and luting agent. The results of Fisher groupings are presented in Table III. No significant differences in bond strengths were found among the 16 groups at thermocycle 0. After 100,000 thermocycles, bond strengths among the nonprimed groups, presented in increasing order, were Bistite, Super-Bond, Imperva, and Panavia 21. The six combinations of two primers (CP and MP II) and three luting agents (Imperva, Panavia 21, and Super-Bond) showed the greatest bond strength, and demonstrated the same statistical level. The mode of bond failure for each specimen is listed in Figure 2. With the exception of three groups that showed only mixed adhesive and cohesive failure (groups 2, 4, and 12), all groups showed an increase in complete adhesive mode failure after thermocycling.
DISCUSSION Previous reports 17 have shown the application of a primer containing a phosphoric acid derivative monomer to be effective in improving the bond strength of resin to 386
machine milled pure titanium. The findings of the current study indicate that the phosphoric primer is effective in the bonding of luting agents to cast pure titanium, and further, that a primer containing MEPS is also effective. To determine an acidic monomer that contributes to adhesive bonding, we divided three primers and four luting agents into three groups according to the type of acidic monomers: carboxylic acid derivatives (4-META, 4-AET, and MAC10), a phosphoric acid derivative (MDP), and a thiophosphoric acid derivative (MEPS). It has been shown that metal specimens bonded to an acrylic rod decreased in bond strength within a short period as a result of thermocycling, as opposed to the metal-to-metal adhesion.12,18-20 The mechanical stresses induced by thermocycling may be minimized when the adhesive cements are interposed between two pieces of like material. However, loss of bond strength due to the accumulation of thermal cycles can be evaluated within a shorter period compared with prolonged storage in water,21 and it is difficult to successfully bond most prosthodontic composite materials to an acrylic resin rod; hence, we examined adhesive bonding durability by means of metal-to-metal adhesion. The period of 100,000 thermocycles was selected on the basis of our previous findings.16,17 Although three-factor ANOVA analysis (Table II) showed significant interactions among all three main effects, certain trends could be found with the help of comparisons with the Fisher test. As shown in Figure 1 and Table III, the bond strength of titanium joined with Super-Bond was considerably improved with CP primer or MP II primer. Super-Bond contains 4-META as a functional monomer, but these findings suggest that MDP and MEPS are superior to 4-META as an adhesive bonding promoter for titanium. In bonding with Imperva, which contains 4-AET, or with Bistite, which contains MAC10, the bond strengths were also improved by means of CP and/or MP II primers. Taking these findings into consideration, monomers derived from phosphoric or thiophosphoric acid probably VOLUME 79 NUMBER 4
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Table III. Statistical analysis results Thermocycle
Luting agent
Primer
Mean (SD) (MPa)
100,000 100,000 100,000 100,000 100,000 100,000 0 100,000 0 100,000 100,000 0 0 0 100,000 0 0 0 0 0 0 0 100,000 0 0 100,000 0 0 100,000 100,000 100,000 100,000
No primer MP MP CP No primer MP No primer MP MP MP II No primer MP II MP No primer No primer No primer No primer CP CP MP MP II CP CP CP MP CP MP II MP II MP II CP MP II MP II
Bistite Imperva Super-Bond Bistite Super-Bond Panavia 21 Bistite Bistite Super-Bond Bistite Imperva Bistite Bistite Imperva Panavia 21 Super-Bond Panavia 21 Super-Bond Bistite Imperva Super-Bond Panavia 21 Imperva Imperva Panavia 21 Super-Bond Panavia 21 Imperva Super-Bond Panavia 21 Panavia 21 Imperva
13.8 (1.0) 26.7 (6.2) 28.3 (2.8) 29.5 (3.7) 29.7 (3.1) 34.1 (3.6) 35.5 (6.5) 36.3 (2.0) 36.5 (1.3) 36.5 (8.4) 36.9 (5.1) 37.0 (2.3) 37.2 (1.9) 37.7 (6.2) 38.5 (2.5) 38.8 (2.0) 39.7 (5.7) 40.1 (6.0) 40.9 (6.3) 42.4 (4.6) 43.2 (3.1) 43.9 (5.0) 44.1 (7.5) 44.4 (6.3) 44.5 (8.3) 44.6 (4.9) 44.6 (2.8) 45.1 (7.1) 45.1 (3.8) 45.9 (7.6) 50.0 (6.8) 50.7 (7.3)
Fisher grouping
a ab abc abc abcd abcde abcdef abcdef abcdef abcdef abcdef ab c d e f abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef
g gh gh gh gh gh gh gh gh gh gh gh gh gh
Identical letters indicate that the mean values are not statistically different at p = 0.01.
enable titanium to be bonded more strongly with polymeric materials than do monomers derived from carboxylic acid. We speculate that MDP and MEPS can react with the thin oxide film produced on the titanium surface, contributing to increased bond strength and durability. The efficacy of MDP or MEPS was also reported with regard to the bonding of Co-Cr alloy.13,22 After 100,000 thermocycles, the bond strengths of 4-META/MMATBB resin joined to Co-Cr alloy were measured at 43.4 and 37.0 MPa with and without MDP primer, respectively.13 These values were comparable to those measured in this study. The disagreement in results between MP and MP II may be due to the concentration of MEPS in these primers. Although both MP and MP II contain MEPS, the concentration of MEPS in MP II primer was greater than that in MP primer. The influence of concentration of MEPS in primer has already been ascertained.19,23 In the cases of Imperva and Panavia 21 materials, the differences between MEPS and MDP were detected after thermocycling. These luting materials bonded more APRIL 1998
strongly to the MP II-primed specimens than to the nonprimed groups, whereas no significant differences were detected between CP-primed groups and nonprimed groups. However, the mechanism of the improved durability obtained by modification of the MP II primer remains unclear. Interestingly, the CP-primed Panavia 21 group demonstrated better bonding durability than the nonprimed Panavia 21 group, although both used MDP as a functional monomer. The greater bond strength of the CPprimed group may be due to the high concentration of free phosphate at the resin-metal interface. When amine dissolved in Panavia 21 material exists at the interface, the effect of MDP may be weakened by acid-base reaction. Although clear differences were lacking in original failure modes, a trend could be identified with the help of thermocycling (Fig. 2). After thermocycling, the resin composite materials (Imperva, Bistite, and Panavia 21) showed more adhesive failure than the unfilled type luting material (Super-Bond). This may be because the composite type luting materials have higher mechanical 387
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strengths compared with the unfilled type luting material Super-Bond.24 In summary, the surface treatment of titanium with primers containing either MDP or MEPS demonstrated high bond strengths and bonding durability. This simple technique combining primers (CP and MP II) and luting materials (Imperva, Panavia 21, and Super-Bond) will enable prostheses to withstand the oral environment in the long term.
CONCLUSIONS Within the limits of this study, the following conclusions were drawn. 1. Bond strengths of luting agents joined to a commercially available pure titanium were influenced by type of primer, type of luting agent, thermocycling, and their combinations. 2. Bond strengths ranged from 35.5 to 45.1 MPa before thermocycling, and values varied from 13.8 to 50.7 MPa after 100,000 thermocycles. 3. The highest bond strengths (44.1 to 50.7 MPa) after 100,000 thermocycles were obtained with combinations of two primers (Cesead Opaque Primer and Metal Primer II) and three adhesive resins (Imperva Dual, Panavia 21, and Super-Bond C&B). REFERENCES 1. Peters D, Marx R. Titanium in adhesive bridge technic: adhesive-metal-bond. Z W R 1989;98:966-74. 2. Lorey RE, Edge MJ, Lang BR, Lorey HS. The potential for bonding titanium restorations. J Prosthodont 1993;2:151-5. 3. Livaditis GJ, Thompson VP. Etched castings: an improved retentive mechanism for resin-bonded retainers. J Prosthet Dent 1982;47:52-8. 4. Love LD, Breitman JB. Resin retention by immersion-etched alloy. J Prosthet Dent 1985;53:623-4. 5. Besimo C. Resin-bonded fixed partial denture technique: results of a medium-term clinical follow-up investigation. J Prosthet Dent 1993;69:144-8. 6. Boyer DB, Williams VD, Thayer KE, Denehy GE, Diaz-Arnold AM. Analysis of debond rates of resin-bonded prostheses. J Dent Res 1993;72:1244-8. 7. Verzijden CW, Creugers NH, Mulder J. A multi-practice clinical study on posterior resin-bonded bridges: a 2.5-year interim report. J Dent Res 1994;73:529-35. 8. de Rijk WG, Wood M, Thompson VP. Maximum likelihood estimates for the lifetime of bonded dental prostheses. J Dent Res 1996;75:1700-5.
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9. Ekstrand K, Ruyter IE, Øysæd H. Adhesion to titanium of methacrylate-based polymer materials. Dent Mater 1988;4:111-5. 10. Matsumura H, Yoshida K, Tanaka T, Atsuta M. Adhesive bonding of titanium with a titanate coupler and 4-META/MMA-TBB opaque resin. J Dent Res 1990;69:1614-6. 11. Fujishima A, Fujishima Y, Ferracane JL. Shear bond strength of four commercial bonding systems to cp Ti. Dent Mater 1995;11:82-6. 12. Tanaka T, Fujiyama E, Shimizu H, Takaki A, Atsuta M. Surface treatment of nonprecious alloys for adhesion-fixed partial dentures. J Prosthet Dent 1986;55:456-62. 13. Matsumura H, Tanaka T, Taira Y, Atsuta M. Bonding of a cobalt-chromium alloy with acidic primers and tri-n-butylborane-initiated luting agents. J Prosthet Dent 1996;76:194-9. 14. Yoshida K, Kamada K, Tanagawa M, Atsuta M. Shear bond strengths of three resin cements used with three adhesive primers for metal. J Prosthet Dent 1996;75:254-61. 15. Salonga JP, Matsumura H, Yasuda K, Yamabe Y. Bond strength of adhesive resin to three nickel-chromium alloys with varying chromium content. J Prosthet Dent 1994;72:582-4. 16. Taira Y, Matsumura H, Atsuta M. Bonding of titanium with acidic primers and a tri-n-butylborane-initiated luting agent. J Oral Rehabil 1997;24:385-8. 17. Taira Y, Matsumura H, Yoshida K, Tanaka T, Atsuta M. Adhesive bonding of titanium with a methacrylate-phosphate primer and self-curing adhesive resins. J Oral Rehabil 1995;22:409-12. 18. Ikeda Y. Influence of resin cements on durability of metal-resin adhesion. J Jpn Dent Mater 1995;14:42-51. 19. Taira Y, Imai Y. Primer for bonding resin to metal. Dent Mater 1995;11:2-6. 20. Taira Y, Matsumura H, Yoshida K, Tanaka T, Atsuta M. Influence of surface oxidation of titanium for adhesion. J Dent 1998;26:69-73. 21. Tanaka T, Nagata K, Takeyama M, Atsuta M, Nakabayashi N, Masuhara E. 4META opaque resin—a new resin strongly adhesive to nickel-chromium alloy. J Dent Res 1981;60:1697-706. 22. Yoshida K, Taira Y, Sawase T, Atsuta M. Effects of adhesive primers on bond strength of self-curing resin to cobalt-chromium alloy. J Prosthet Dent 1997;77:617-20. 23. Ueno T, Kumagai T, Hirota K, Saitoh Y, Kojima I. The characteristic of metal adhesion primer “GC METAL PRIMER II”. J Dent Res 1997;76(Special Issue):312. 24. White SN, Yu Z. Physical properties of fixed prosthodontic, resin composite luting agents. Int J Prosthodont 1993;6:384-9. Reprint requests to: DR. YOHSUKE TAIRA DEPARTMENT OF FIXED PROSTHODONTICS SCHOOL OF DENTISTRY NAGASAKI UNIVERSITY 1-7-1, SAKAMOTO NAGASAKI 852-8588 JAPAN Copyright © 1998 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/98/$5.00 + 0. 10/1/87982
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