Ó 2013 Eur J Oral Sci
Eur J Oral Sci 2014; 122: 84–88 DOI: 10.1111/eos.12109 Printed in Singapore. All rights reserved
European Journal of Oral Sciences
Short Communication
Surface modification with alumina blasting and H2SO4–HCl etching for bonding two resin-composite veneers to titanium
Yohsuke Taira1, Takafumi Egoshi2, Kohji Kamada1, Takashi Sawase1 1
Department of Applied Prosthodontics, Graduate School of Biomedical Sciences, Nagasaki University; 2Department of Prosthetic Dentistry, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
Taira Y, Egoshi T, Kamada K, Sawase T. Surface modification with alumina blasting and H2SO4–HCl etching for bonding two resin-composite veneers to titanium. Eur J Oral Sci 2014; 122: 84–88. © 2013 Eur J Oral Sci The purpose of this study was to investigate the effect of an experimental surface treatment with alumina blasting and acid etching on the bond strengths between each of two resin composites and commercially pure titanium. The titanium surface was blasted with alumina and then etched with 45wt% H2SO4 and 15wt% HCl (H2SO4–HCl). A light- and heat-curing resin composite (Estenia) and a light-curing resin composite (Ceramage) were used with adjunctive metal primers. Veneered specimens were subjected to thermal cycling between 4 and 60°C for 50,000 cycles, and the shear bond strengths were determined. The highest bond strengths were obtained for Blasting/H2SO4-HCl/Estenia (30.2 4.5 MPa) and Blasting/Etching/ Ceramage (26.0 4.5 MPa), the values of which were not statistically different, followed by Blasting/No etching/Estenia (20.4 2.4 MPa) and Blasting/No etching/Ceramage (0.8 0.3 MPa). Scanning electron microscopy observations revealed that alumina blasting and H2SO4–HCl etching creates a number of micro- and nanoscale cavities on the titanium surface, which contribute to adhesive bonding.
With the advent of computer-aided design/computeraided manufacturing (CAD/CAM) systems, titanium has become widely used for crowns, fixed partial dentures, and implant-supported superstructures. Titanium frameworks are usually veneered with resin-composite materials to fulfill the aesthetic demands of patients. However, most CAD/CAM systems cannot shape microretention devices because the milling drill is too large. Consequently, strong and durable bonding between resin composites and titanium CAD/CAM frameworks are required for veneered prostheses to withstand the severe environment in the oral cavity. Several surface-modification techniques, such as high-energy abrasion (1), silica coating (2–4), plasma irradiation (5), alkaline treatment (6), acid etching (7,8), and fluoride treatment (9–11), have been investigated with the aim of improving the adhesive bonding of resin to cast or machine-milled titanium. With regard to acid etching, HF, H3PO4, H2SO4, and HCl were individually used to modify the titanium surface to improve the bond strength to resin (7,8). A commercially pure titanium (cpTi) etched with 48% H2SO4 at 60°C for 60 min was reported to exhibit a high bond strength (7). The authors had previously used (NH4)FHF or NaFHF to roughen cpTi surfaces on a
Yohsuke Taira, Department of Applied Prosthodontics, Graduate School of Biomedical Sciences, Nagasaki University, 1-7-1 Sakamoto, Nagasaki 852-8588, Japan E-mail: [email protected] Key words: adhesive bonding; computeraided design/computer-aided manufacturing; surface treatment; titanium Accepted for publication November 2013
submicron scale (9–11). Moreover, a mixture of concentrated H2SO4 and HCl has been used to modify the surface of titanium implant bodies (Straumann, Basel, Switzerland), and this modified surface is known as a sandblasted large-grit acid-etched (SLA) surface. The surface roughness of cpTi was improved by sandblasting with alumina particles of 250–500 lm in size and etching with a mixture of H2SO4 and HCl (12,13). Little attention has been directed toward modification of the SLA surface for adhesive bonding. In addition to modification of the substrate, the type of functional monomers applied to the substrate is an important factor in bonding metal alloys, including cpTi (14–19). A primer containing 10-methacryloxydecyl dihydrogen phosphate (MDP) exhibited better bonding durability than did primers containing carboxylic acidderivative monomers (16,19). It was also reported that priming with 6-methacryloxyhexyl phosphonacetate (6-MHPA) improved the bonding of resin to aluminablasted titanium alloy to a level comparable with that observed with MDP (21). The combination of alumina blasting, etching at 70°C for 10 min with a mixture of 45wt% H2SO4 and 15wt% HCl (H2SO4–HCl), and application of primer containing MDP significantly improved initial bond strength (20). However, it was
Blasting and acid etching for titanium adhesion
unknown whether 6-MHPA promoted durable bonding as well as MDP did when the titanium surface was chemically etched with H2SO4–HCl. The purpose of the present study was to evaluate the effect of H2SO4–HCl etching, in conjunction with alumina blasting and primer application, on the bond strength between each of two veneering resins and cpTi. The null hypothesis was that neither the etching nor the type of resin affects the bond strengths.
Material and methods Specimen preparation The specifications of the titanium, etching agents, primers, and resin composites used in the present study are listed in Table 1. A total of 32 titanium specimens were machine milled to a diameter of 10 mm and a thickness of 3 mm. All disks were ground with #600 and #1,000 silicon-carbide papers and were blasted (Pen-Blaster; Shofu, Kyoto, Japan) with alumina (Hi-Aluminas; Shofu) for 15 s. The air pressure for sandblasting was 0.45 MPa, and the nozzle was located approximately 10 mm from the metal surface. Two commercially available resin-composite veneers were used: Estenia C&B (Estenia; Kuraray Noritake Dental, Tokyo, Japan) and Ceramage (Shofu). The Estenia system is composed of light- and heat-curing resin composites and a primer containing MDP, whereas the Ceramage system is composed of light-curing resin composites and a primer containing 6-MHPA. The specimens were divided into four groups of eight specimens (Blasting/No etching/Estenia; Blasting/Etching/ Estenia; Blasting/No etching/Ceramage; and Blasting/ Etching/Ceramage). In the Blasting/Etching/Estenia and Blasting/Etching/Ceramage groups, specimens were immersed in the experimental H2SO4–HCl liquid at 70°C for 10 min, rinsed with tap water for 15 s, and then air dried for 5 s.
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An acrylic ring (inside diameter = 6 mm; height = 2 mm) was placed in such a way that it surrounded the bonding area and was then filled with one of the two resin veneering systems (Estenia or Ceramage) according to the manufacturer’s instructions. Shear bond-strength tests After leaving the bonded specimens at room temperature for 30 min, all specimens were immersed in distilled water at 37°C for 24 h and then thermocycled for 50,000 cycles between water baths held at 4 and 60°C, with a dwell time of 1 min in each bath. The specimens were embedded in an acrylic resin mould and fitted to a shear-testing jig (Wago Industrial, Nagasaki, Japan) that was used to apply a shearing load parallel to the bonded interface. Shear bond strengths were determined using a universal testing machine (AGS-10kNG; Shimadzu, Kyoto, Japan) at a cross-head speed of 0.5 mm min 1. The mean bond strength and SD of eight specimens were calculated for each test group. Homoscedasticity of variances was analysed using Levene’s test. When the homoscedasticity assumption was invalid, all pairs of the test groups were compared using a non-parametric (SteelDwass) test at a statistical significance of 0.05. After shear testing, the titanium surfaces of the debonded specimens were observed by optical microscopy (SMZ-10; Nikon, Tokyo, Japan) at a magnification of 920 to determine the type of bond failure. The failure mode was categorized as adhesive failure at the resin composite– titanium interface (A), cohesive failure in the resin composite (C), or complex adhesive failure and cohesive failure (A/C). Scanning electron microscopy Two specimens of titanium – one treated with Blasting/No etching and the other treated with Blasting/Etching –were prepared for microscopic observation. The surface structure
Table 1 Titanium, etching agent, primers, and resin composites used in the present study Name (abbreviation)
Components
Commercially pure titanium grade 4 (cpTi) Ti, ≥99.4578%; O, 0.32–0.36%; Fe, 0.16–0.17%; H, 0.001–0.0012%; N, 0.005%; C, 0.006% Etching agent 45wt% sulfuric acid H2SO4–HCl 15wt% hydrochloric acid, water Veneering resin Estenia C&B Opaque Primer: MDP, methacrylate, solvent, others (Estenia) Body Opaque OA3: Bis-GMA, methacrylate, photoinitiator, Dentin DA3: urethane methacrylate, methacrylate, photoinitiator, surface-treated alumina microfiller, silanated glass ceramic filler, pigment, others Ceramage M.L. Primer: 10-MDDT, 6-MHPA, acetone Pre-Opaque: UDMA, aluminum silicate, HEMA, glass, pigment, others Opaque A3O: UDMA, aluminum silicate, HEMA, glass, pigment, others Body A3B: UDMA, urethane diacrylate, zirconium silicate, pigment, others
Manufacturer
Kobe Steel, Hyogo, Japan Wako Pure Chemical, Osaka, Japan Wako Pure Chemical
Lot no.
1039C65001
DCF1559 DCR1606
Kuraray Noritake Dental, Tokyo, Japan
00176A 00115A 00086A
Shofu, Kyoto, Japan
071261 071243 051254 051234
MDP, 10-methacryloxydecyl dihydrogen phosphate; Bis-GMA, bisphenol A-glycidyl methacrylate; 10-MDDT, 10-methacryloxydecyl-6,8dithiooctanate; 6-MHPA, 6-methacryloxyhexyl phosphonacetate; UDMA, urethane dimethacrylate; HEMA, 2-hydroxymethacrylate.
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of the titanium specimens was observed by scanning electron microscopy (S-3500N; Hitachi, Tokyo, Japan) at a magnification of 94,000.
A
Results and discussion The Levene test showed no homoscedasticity of variances among the test groups (P = 0.0256). The mean shear bond strengths, SD values, and failure modes are listed in Table 2. The mean bond strength ranged from 0.8 to 30.2 MPa. Blasting/Etching/Estenia and Blasting/Etching/Ceramage exhibited the highest bond strengths and no significant difference (P = 0.3628). No significant difference was found between Blasting/No etching/Estenia and Blasting/Etching/Ceramage (P = 0.0843). The bond strength of Blasting/Etching/Estenia was significantly higher than that of Blasting/No etching/Estenia (P = 0.0105). Blasting/No etching/Ceramage resulted in the lowest bond strength for all groups tested (P = 0.0052). With regard to the failure mode, all Blasting/No etching/Ceramage specimens exhibited complete adhesive failure at the resin composite–titanium interface (A). With the exception of the Blasting/No etching/ Ceramage specimen, all specimens exhibited complex adhesive failure at the resin composite–titanium interface and cohesive failure in the resin composite (A/C). No complete cohesive failure of the resin composite (C) was observed. Scanning electron microscopy images of the cpTi surface observed at 94,000 magnification showed the surface texture of the specimen treated with alumina blasting and H2SO4–HCl etching (Fig. 1). The surface of the specimen treated with alumina blasting and H2SO4–HCl etching (Fig. 1B) was clearly different from the surfaces of the specimens treated with alumina blasting alone (Fig. 1A). Many microcavities, and several-hundred nanoscale cavities with sharp edges like torn cotton, were observed (Fig. 1B). In contrast, no such nanoscale cavities were obtained for alumina blasting alone (Fig. 1A). Thus, modification of the titanium surface by alumina blasting and H2SO4–HCl etching significantly
B
Fig. 1. Scanning electron microscopy micrographs of (A) the titanium specimen blasted with alumina alone and (B) the titanium specimen blasted with alumina and etched with H2SO4–HCl. Original magnification, 94,000.
improved the shear bond strengths of the two veneering resins to cpTi. Therefore, the null hypothesis was rejected. Thermocycling in water is considered to accelerate aging and is often used for comparing the role of adhesive systems as a screening tool. The number of cycles was set to 50,000, in accordance with literature evaluating titanium adhesion (15,19). Without thermocycling, the mean SD shear bond strengths corresponding to Blasting/No etching/Estenia and Blasting/Etching/Estenia were reported to be 20.3 1.3 MPa and 29.9 4.1 MPa, respectively (20). These values are close to
Table 2 Shear bond strength after 50,000 thermocycles and failure mode
Shear bond strength values are given as mean SD. Asterisks (*) indicate that the values are statistically different (P < 0.05). A, adhesive failure at the resin composite–titanium interface; A/C, complex adhesive failure and cohesive failure within the resin composite.
Blasting and acid etching for titanium adhesion
those of the present study, of 20.4 2.4 MPa for Blasting/No etching/Estenia and 30.2 4.5 MPa for Blasting/Etching/Estenia after thermocycling for 50,000 cycles (Table 2), suggesting bonding durability. With regard to the alumina grain size used for sandblasting, the SLA surface was blasted with alumina particles of 250–500 lm before etching with a mixture of H2SO4 and HCl (12,13). In the present study, we used smaller alumina particles in an attempt to create small cavities in the cpTi for adhesive bonding. The grain sizes of 500 alumina particles were measured using a color-laser three-dimensional profile microscope (VK-8500; Keyence, Osaka, Japan) in a preliminary experiment and this confirmed the mean grain size, SD value, and range as 50.8 38.0 (range, 3.6–249.7) lm. The surface structure is considered to be important for improving micro- and nano-mechanical retention, which contributes to the high bond strength. The scanning electron microscopy images suggested that alumina blasting with H2SO4–HCl etching (Fig. 1B) produced more undercuts compared with alumina blasting without H2SO4–HCl etching (Fig. 1A). The components of the etching agent (45wt% H2SO4 and 15wt% HCl), temperature (70°C), and etching time (10 min) were selected based on those used in previous experiments (20). We speculated that effective mechanical interlocking was generated when diffused monomers were polymerized in the micro- and nanoscale cavities created (11). The M.L. Primer contains 10-methacryloxydecyl-6,8dithiooctanate (10-MDDT) and 6-MHPA. A primer containing MDP or 6-MHPA has been reported to play an essential role in the bonding of adhesive to titanium or titanium alloys (15,16,21,22). The dihydrogen phosphate group of MDP and the phosphonacetate group of 6-MHPA may react chemically with the titanium oxide layer. Another difference in the molecular structures of MDP and 6-MHPA is the length of hydrocarbon connecting segment. The longer hydrocarbon-connecting segment in MDP may extend the durability of the bond compared with that in 6-MHPA. The bond strengths for blasted but non-etched surfaces were dramatically different (Blasting/No etching/Estenia and Blasting/No etching/Ceramage), which suggests that MDP is superior to 6-MHPA as an adhesion-promoting monomer for alumina-blasted cpTi. We speculate that the primed functional monomer promotes both chemical bonding and diffusion of the other monomers into the nano-undercut. In addition to the type of functional monomer, the viscosity, the wetting characteristics, the filler particle size, the polymerization, and the mechanical properties of the resin composite may be related to micro- and nano-mechanical retention. Therefore, further studies are needed to determine whether the primed functional monomer alone or both the functional monomer and the resin composite affect the bond strength. High durability of bond strength is required in order for prostheses to function for a long time in the oral environment. The combined use of alumina blasting and H2SO4–HCl etching would be useful for reducing
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clinical complications, such as fracture or debonding of veneered resin composite from titanium frameworks. Careful handling in a fume chamber is necessary to prevent the vapors of the evaporated acids from being inhaled. Within the limits of the present study, the following conclusions are drawn. First, when cpTi was blasted with alumina without additional etching, the shear bond strength of the light- and heat-curing resin composite veneer (Estenia) to alumina-blasted grade-4 cpTi was significantly higher than that of the light-curing resin composite veneer (Ceramage). Second, the shear bond strengths were significantly improved by additional etching with 45% H2SO4 and 15% HCl at 70°C for 10 min, and no significant difference in bond strength was observed between Estenia and Ceramage when both alumina blasting and H2SO4–HCl etching were applied. Finally, a number of submicron cavities were observed on the cpTi specimen that was modified successively by alumina blasting and H2SO4–HCl etching, which suggests micro- and nano-mechanical retention. Conflicts of interest – The authors report no conflicts of interest.
References 1. WHITE SN, YU Z, ZHAO XY. High-energy abrasion: an innovative esthetic modality to enhance adhesion. J Esthet Dent 1994; 6: 267–273. 2. KERN M, THOMPSON VP. Durability of resin bonds to pure titanium. J Prosthodont 1995; 4: 16–22. 3. FUJISHIMA A, FUJISHIMA Y, FERRACANE JL. Shear bond strength of four commercial bonding systems to cpTi. Dent Mater 1995; 11: 82–86. 4. MATINLINNA JP, LASSILA LVJ, VALLITTU PK. The effect of five silane coupling agents on the bond strength of a luting cement to a silica-coated titanium. Dent Mater 2007; 23: 1173–1180. 5. KIBAYASHI H, TERAOKA F, FUJIMOTO S, NAKAGAWA M, TAKAHASHI J. Surface modification of pure titanium by plasma exposure and its bonding to resin. Dent Mater J 2005; 24: 53–58. 6. BAN S. Effect of alkaline treatment of pure titanium and its alloys on the bonding strength of dental veneering resins. J Biomed Mater Res 2003; 66A: 138–145. 7. BAN S, TANIKI T, SATO H, KONO H, IWAYA Y, MIYAMOTO M. Acid etching of titanium for bonding with veneering composite resins. Dent Mater J 2006; 25: 382–390. 8. TSUCHIMOTO Y, YOSHIDA Y, TAKEUCHI M, MINE A, YATANI H, TAGAWA Y, VAN MEERBEEK B, SUZUKI K, KUBOKI T. Effect of surface pre-treatment on durability of resinbased cements bonded to titanium. Dent Mater 2006; 22: 545–552. 9. TAIRA Y, YANAGIDA H, MATSUMURA H, ATSUTA M. Effects of a metal etchant and two primers on resin bonding durability to titanium. Eur J Oral Sci 2004; 112: 95–100. 10. YANG L, TAIRA Y, ATSUTA M. Effect of an acidulated fluoride etchant on bonding between titanium and two luting materials. J Biomed Mater Res 2006; 78B: 161–166. 11. TAIRA Y, YANG L, ATSUTA M. Comparison of four fluoride etchants in bonding between titanium and a self-curing luting agent. Dent Mater J 2006; 25: 345–351. 12. BUSER D, NYDEGGER T, OXLAND T, COCHRAN DL, SCHENK RK, HIRT HP, SNETIVY D, NOLTE LP. Interface shear strength of titanium implants with a sandblasted and acid-etched sur-
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Taira et al. face: a biomechanical study in the maxilla of miniature pigs. J Biomed Mater Res 1999; 45: 75–83. COCHRAN DL, SCHENK RK, LUSSI A, HIGGINBOTTOM FL, BUSER D. Bone response to unloaded and loaded titanium implants with a sandblasted and acid-etched surface: a histometric study in the canine mandible. J Biomed Mater Res 1998; 40: 1–11. TAIRA Y, IMAI Y. Primer for bonding resin to metal. Dent Mater 1995; 11: 2–6. TAIRA Y, MATSUMURA H, YOSHIDA K, TANAKA T, ATSUTA M. Adhesive bonding of titanium with a methacrylate-phosphate primer and self-curing adhesive resin. J Oral Rehabil 1995; 22: 409–412. TAIRA Y, YANAGIDA H, MATSUMURA H, YOSHIDA K, ATSUTA M, SUZUKI S. Adhesive bonding of titanium with a thionephosphate dual functional primer and self-curing luting agents. Eur J Oral Sci 2000; 108: 456–460. OHKUBO C, WATANABE I, HOSOI T, OKABE T. Shear bond strengths of polymethyl mathacrylate to cast titanium and cobalt-chromium frameworks using five metal primers. J Prosthet Dent 2000; 83: 50–57.
18. 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: 385–388. 19. 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: 1614–1616. 20. EGOSHI T, TAIRA Y, SOENO K, SAWASE T. Effects of sandblasting, H2SO4/HCl etching, and phosphate primer application on bond strength of veneering resin composite to commercially pure titanium grade 4. Dent Mater J 2013; 32: 219–227. 21. KOIZUMI H, FURUCHI M, TANOUE N, YANAGIDA H, YONEYAMA T, MATSUMURA H. Bond strength to primed Ti-6Al-7Nb alloy of two acrylic resin adhesives. Dent Mater J 2006; 25: 286–290. 22. TAIRA Y, ODATSU T, SAWASE T. Effects of a fluoride etchant and a phosphate primer on bonding of veneering composite to Ti-6Al-4V alloy for CAD/CAM restorations. J Prosthodont Res 2013; 57: 30–35.
Eur J Oral Sci 2014; 122: 84–88 DOI: 10.1111/eos.12109 Printed in Singapore. All rights reserved
European Journal of Oral Sciences
Short Communication
Surface modification with alumina blasting and H2SO4–HCl etching for bonding two resin-composite veneers to titanium
Yohsuke Taira1, Takafumi Egoshi2, Kohji Kamada1, Takashi Sawase1 1
Department of Applied Prosthodontics, Graduate School of Biomedical Sciences, Nagasaki University; 2Department of Prosthetic Dentistry, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
Taira Y, Egoshi T, Kamada K, Sawase T. Surface modification with alumina blasting and H2SO4–HCl etching for bonding two resin-composite veneers to titanium. Eur J Oral Sci 2014; 122: 84–88. © 2013 Eur J Oral Sci The purpose of this study was to investigate the effect of an experimental surface treatment with alumina blasting and acid etching on the bond strengths between each of two resin composites and commercially pure titanium. The titanium surface was blasted with alumina and then etched with 45wt% H2SO4 and 15wt% HCl (H2SO4–HCl). A light- and heat-curing resin composite (Estenia) and a light-curing resin composite (Ceramage) were used with adjunctive metal primers. Veneered specimens were subjected to thermal cycling between 4 and 60°C for 50,000 cycles, and the shear bond strengths were determined. The highest bond strengths were obtained for Blasting/H2SO4-HCl/Estenia (30.2 4.5 MPa) and Blasting/Etching/ Ceramage (26.0 4.5 MPa), the values of which were not statistically different, followed by Blasting/No etching/Estenia (20.4 2.4 MPa) and Blasting/No etching/Ceramage (0.8 0.3 MPa). Scanning electron microscopy observations revealed that alumina blasting and H2SO4–HCl etching creates a number of micro- and nanoscale cavities on the titanium surface, which contribute to adhesive bonding.
With the advent of computer-aided design/computeraided manufacturing (CAD/CAM) systems, titanium has become widely used for crowns, fixed partial dentures, and implant-supported superstructures. Titanium frameworks are usually veneered with resin-composite materials to fulfill the aesthetic demands of patients. However, most CAD/CAM systems cannot shape microretention devices because the milling drill is too large. Consequently, strong and durable bonding between resin composites and titanium CAD/CAM frameworks are required for veneered prostheses to withstand the severe environment in the oral cavity. Several surface-modification techniques, such as high-energy abrasion (1), silica coating (2–4), plasma irradiation (5), alkaline treatment (6), acid etching (7,8), and fluoride treatment (9–11), have been investigated with the aim of improving the adhesive bonding of resin to cast or machine-milled titanium. With regard to acid etching, HF, H3PO4, H2SO4, and HCl were individually used to modify the titanium surface to improve the bond strength to resin (7,8). A commercially pure titanium (cpTi) etched with 48% H2SO4 at 60°C for 60 min was reported to exhibit a high bond strength (7). The authors had previously used (NH4)FHF or NaFHF to roughen cpTi surfaces on a
Yohsuke Taira, Department of Applied Prosthodontics, Graduate School of Biomedical Sciences, Nagasaki University, 1-7-1 Sakamoto, Nagasaki 852-8588, Japan E-mail: [email protected] Key words: adhesive bonding; computeraided design/computer-aided manufacturing; surface treatment; titanium Accepted for publication November 2013
submicron scale (9–11). Moreover, a mixture of concentrated H2SO4 and HCl has been used to modify the surface of titanium implant bodies (Straumann, Basel, Switzerland), and this modified surface is known as a sandblasted large-grit acid-etched (SLA) surface. The surface roughness of cpTi was improved by sandblasting with alumina particles of 250–500 lm in size and etching with a mixture of H2SO4 and HCl (12,13). Little attention has been directed toward modification of the SLA surface for adhesive bonding. In addition to modification of the substrate, the type of functional monomers applied to the substrate is an important factor in bonding metal alloys, including cpTi (14–19). A primer containing 10-methacryloxydecyl dihydrogen phosphate (MDP) exhibited better bonding durability than did primers containing carboxylic acidderivative monomers (16,19). It was also reported that priming with 6-methacryloxyhexyl phosphonacetate (6-MHPA) improved the bonding of resin to aluminablasted titanium alloy to a level comparable with that observed with MDP (21). The combination of alumina blasting, etching at 70°C for 10 min with a mixture of 45wt% H2SO4 and 15wt% HCl (H2SO4–HCl), and application of primer containing MDP significantly improved initial bond strength (20). However, it was
Blasting and acid etching for titanium adhesion
unknown whether 6-MHPA promoted durable bonding as well as MDP did when the titanium surface was chemically etched with H2SO4–HCl. The purpose of the present study was to evaluate the effect of H2SO4–HCl etching, in conjunction with alumina blasting and primer application, on the bond strength between each of two veneering resins and cpTi. The null hypothesis was that neither the etching nor the type of resin affects the bond strengths.
Material and methods Specimen preparation The specifications of the titanium, etching agents, primers, and resin composites used in the present study are listed in Table 1. A total of 32 titanium specimens were machine milled to a diameter of 10 mm and a thickness of 3 mm. All disks were ground with #600 and #1,000 silicon-carbide papers and were blasted (Pen-Blaster; Shofu, Kyoto, Japan) with alumina (Hi-Aluminas; Shofu) for 15 s. The air pressure for sandblasting was 0.45 MPa, and the nozzle was located approximately 10 mm from the metal surface. Two commercially available resin-composite veneers were used: Estenia C&B (Estenia; Kuraray Noritake Dental, Tokyo, Japan) and Ceramage (Shofu). The Estenia system is composed of light- and heat-curing resin composites and a primer containing MDP, whereas the Ceramage system is composed of light-curing resin composites and a primer containing 6-MHPA. The specimens were divided into four groups of eight specimens (Blasting/No etching/Estenia; Blasting/Etching/ Estenia; Blasting/No etching/Ceramage; and Blasting/ Etching/Ceramage). In the Blasting/Etching/Estenia and Blasting/Etching/Ceramage groups, specimens were immersed in the experimental H2SO4–HCl liquid at 70°C for 10 min, rinsed with tap water for 15 s, and then air dried for 5 s.
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An acrylic ring (inside diameter = 6 mm; height = 2 mm) was placed in such a way that it surrounded the bonding area and was then filled with one of the two resin veneering systems (Estenia or Ceramage) according to the manufacturer’s instructions. Shear bond-strength tests After leaving the bonded specimens at room temperature for 30 min, all specimens were immersed in distilled water at 37°C for 24 h and then thermocycled for 50,000 cycles between water baths held at 4 and 60°C, with a dwell time of 1 min in each bath. The specimens were embedded in an acrylic resin mould and fitted to a shear-testing jig (Wago Industrial, Nagasaki, Japan) that was used to apply a shearing load parallel to the bonded interface. Shear bond strengths were determined using a universal testing machine (AGS-10kNG; Shimadzu, Kyoto, Japan) at a cross-head speed of 0.5 mm min 1. The mean bond strength and SD of eight specimens were calculated for each test group. Homoscedasticity of variances was analysed using Levene’s test. When the homoscedasticity assumption was invalid, all pairs of the test groups were compared using a non-parametric (SteelDwass) test at a statistical significance of 0.05. After shear testing, the titanium surfaces of the debonded specimens were observed by optical microscopy (SMZ-10; Nikon, Tokyo, Japan) at a magnification of 920 to determine the type of bond failure. The failure mode was categorized as adhesive failure at the resin composite– titanium interface (A), cohesive failure in the resin composite (C), or complex adhesive failure and cohesive failure (A/C). Scanning electron microscopy Two specimens of titanium – one treated with Blasting/No etching and the other treated with Blasting/Etching –were prepared for microscopic observation. The surface structure
Table 1 Titanium, etching agent, primers, and resin composites used in the present study Name (abbreviation)
Components
Commercially pure titanium grade 4 (cpTi) Ti, ≥99.4578%; O, 0.32–0.36%; Fe, 0.16–0.17%; H, 0.001–0.0012%; N, 0.005%; C, 0.006% Etching agent 45wt% sulfuric acid H2SO4–HCl 15wt% hydrochloric acid, water Veneering resin Estenia C&B Opaque Primer: MDP, methacrylate, solvent, others (Estenia) Body Opaque OA3: Bis-GMA, methacrylate, photoinitiator, Dentin DA3: urethane methacrylate, methacrylate, photoinitiator, surface-treated alumina microfiller, silanated glass ceramic filler, pigment, others Ceramage M.L. Primer: 10-MDDT, 6-MHPA, acetone Pre-Opaque: UDMA, aluminum silicate, HEMA, glass, pigment, others Opaque A3O: UDMA, aluminum silicate, HEMA, glass, pigment, others Body A3B: UDMA, urethane diacrylate, zirconium silicate, pigment, others
Manufacturer
Kobe Steel, Hyogo, Japan Wako Pure Chemical, Osaka, Japan Wako Pure Chemical
Lot no.
1039C65001
DCF1559 DCR1606
Kuraray Noritake Dental, Tokyo, Japan
00176A 00115A 00086A
Shofu, Kyoto, Japan
071261 071243 051254 051234
MDP, 10-methacryloxydecyl dihydrogen phosphate; Bis-GMA, bisphenol A-glycidyl methacrylate; 10-MDDT, 10-methacryloxydecyl-6,8dithiooctanate; 6-MHPA, 6-methacryloxyhexyl phosphonacetate; UDMA, urethane dimethacrylate; HEMA, 2-hydroxymethacrylate.
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of the titanium specimens was observed by scanning electron microscopy (S-3500N; Hitachi, Tokyo, Japan) at a magnification of 94,000.
A
Results and discussion The Levene test showed no homoscedasticity of variances among the test groups (P = 0.0256). The mean shear bond strengths, SD values, and failure modes are listed in Table 2. The mean bond strength ranged from 0.8 to 30.2 MPa. Blasting/Etching/Estenia and Blasting/Etching/Ceramage exhibited the highest bond strengths and no significant difference (P = 0.3628). No significant difference was found between Blasting/No etching/Estenia and Blasting/Etching/Ceramage (P = 0.0843). The bond strength of Blasting/Etching/Estenia was significantly higher than that of Blasting/No etching/Estenia (P = 0.0105). Blasting/No etching/Ceramage resulted in the lowest bond strength for all groups tested (P = 0.0052). With regard to the failure mode, all Blasting/No etching/Ceramage specimens exhibited complete adhesive failure at the resin composite–titanium interface (A). With the exception of the Blasting/No etching/ Ceramage specimen, all specimens exhibited complex adhesive failure at the resin composite–titanium interface and cohesive failure in the resin composite (A/C). No complete cohesive failure of the resin composite (C) was observed. Scanning electron microscopy images of the cpTi surface observed at 94,000 magnification showed the surface texture of the specimen treated with alumina blasting and H2SO4–HCl etching (Fig. 1). The surface of the specimen treated with alumina blasting and H2SO4–HCl etching (Fig. 1B) was clearly different from the surfaces of the specimens treated with alumina blasting alone (Fig. 1A). Many microcavities, and several-hundred nanoscale cavities with sharp edges like torn cotton, were observed (Fig. 1B). In contrast, no such nanoscale cavities were obtained for alumina blasting alone (Fig. 1A). Thus, modification of the titanium surface by alumina blasting and H2SO4–HCl etching significantly
B
Fig. 1. Scanning electron microscopy micrographs of (A) the titanium specimen blasted with alumina alone and (B) the titanium specimen blasted with alumina and etched with H2SO4–HCl. Original magnification, 94,000.
improved the shear bond strengths of the two veneering resins to cpTi. Therefore, the null hypothesis was rejected. Thermocycling in water is considered to accelerate aging and is often used for comparing the role of adhesive systems as a screening tool. The number of cycles was set to 50,000, in accordance with literature evaluating titanium adhesion (15,19). Without thermocycling, the mean SD shear bond strengths corresponding to Blasting/No etching/Estenia and Blasting/Etching/Estenia were reported to be 20.3 1.3 MPa and 29.9 4.1 MPa, respectively (20). These values are close to
Table 2 Shear bond strength after 50,000 thermocycles and failure mode
Shear bond strength values are given as mean SD. Asterisks (*) indicate that the values are statistically different (P < 0.05). A, adhesive failure at the resin composite–titanium interface; A/C, complex adhesive failure and cohesive failure within the resin composite.
Blasting and acid etching for titanium adhesion
those of the present study, of 20.4 2.4 MPa for Blasting/No etching/Estenia and 30.2 4.5 MPa for Blasting/Etching/Estenia after thermocycling for 50,000 cycles (Table 2), suggesting bonding durability. With regard to the alumina grain size used for sandblasting, the SLA surface was blasted with alumina particles of 250–500 lm before etching with a mixture of H2SO4 and HCl (12,13). In the present study, we used smaller alumina particles in an attempt to create small cavities in the cpTi for adhesive bonding. The grain sizes of 500 alumina particles were measured using a color-laser three-dimensional profile microscope (VK-8500; Keyence, Osaka, Japan) in a preliminary experiment and this confirmed the mean grain size, SD value, and range as 50.8 38.0 (range, 3.6–249.7) lm. The surface structure is considered to be important for improving micro- and nano-mechanical retention, which contributes to the high bond strength. The scanning electron microscopy images suggested that alumina blasting with H2SO4–HCl etching (Fig. 1B) produced more undercuts compared with alumina blasting without H2SO4–HCl etching (Fig. 1A). The components of the etching agent (45wt% H2SO4 and 15wt% HCl), temperature (70°C), and etching time (10 min) were selected based on those used in previous experiments (20). We speculated that effective mechanical interlocking was generated when diffused monomers were polymerized in the micro- and nanoscale cavities created (11). The M.L. Primer contains 10-methacryloxydecyl-6,8dithiooctanate (10-MDDT) and 6-MHPA. A primer containing MDP or 6-MHPA has been reported to play an essential role in the bonding of adhesive to titanium or titanium alloys (15,16,21,22). The dihydrogen phosphate group of MDP and the phosphonacetate group of 6-MHPA may react chemically with the titanium oxide layer. Another difference in the molecular structures of MDP and 6-MHPA is the length of hydrocarbon connecting segment. The longer hydrocarbon-connecting segment in MDP may extend the durability of the bond compared with that in 6-MHPA. The bond strengths for blasted but non-etched surfaces were dramatically different (Blasting/No etching/Estenia and Blasting/No etching/Ceramage), which suggests that MDP is superior to 6-MHPA as an adhesion-promoting monomer for alumina-blasted cpTi. We speculate that the primed functional monomer promotes both chemical bonding and diffusion of the other monomers into the nano-undercut. In addition to the type of functional monomer, the viscosity, the wetting characteristics, the filler particle size, the polymerization, and the mechanical properties of the resin composite may be related to micro- and nano-mechanical retention. Therefore, further studies are needed to determine whether the primed functional monomer alone or both the functional monomer and the resin composite affect the bond strength. High durability of bond strength is required in order for prostheses to function for a long time in the oral environment. The combined use of alumina blasting and H2SO4–HCl etching would be useful for reducing
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clinical complications, such as fracture or debonding of veneered resin composite from titanium frameworks. Careful handling in a fume chamber is necessary to prevent the vapors of the evaporated acids from being inhaled. Within the limits of the present study, the following conclusions are drawn. First, when cpTi was blasted with alumina without additional etching, the shear bond strength of the light- and heat-curing resin composite veneer (Estenia) to alumina-blasted grade-4 cpTi was significantly higher than that of the light-curing resin composite veneer (Ceramage). Second, the shear bond strengths were significantly improved by additional etching with 45% H2SO4 and 15% HCl at 70°C for 10 min, and no significant difference in bond strength was observed between Estenia and Ceramage when both alumina blasting and H2SO4–HCl etching were applied. Finally, a number of submicron cavities were observed on the cpTi specimen that was modified successively by alumina blasting and H2SO4–HCl etching, which suggests micro- and nano-mechanical retention. Conflicts of interest – The authors report no conflicts of interest.
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