Abstract
Objectives
Evaluating the bond strength ( σ ) of resin cement systems (RXA – RelyX ARC; RXU – RelyX U100; and PF – Panavia F) to dentin and yttria-stabilized zirconia-based ceramic (YZ – In-Ceram YZ) after different surface treatments and aging.
Methods
Occlusal dentin of 54 human molars was exposed and conditioned following manufacturers’ instructions. Fifty-four YZ blocks were sintered and divided into two groups according to surface treatment: PA – airborne particle abrasion, and SC – tribochemical silica coating. All treated YZ blocks were cemented to dentin using one of the cement systems (RXA, RXU, and PF) following manufacturers’ recommendations, which includes specific silane agents. Teeth-cement-ceramic blocks were stored in 37 °C distilled water for 24 h before cutting into non-trimming bar-shaped specimens (adhesive area, A = 1 ± 0.1 mm 2 ). Specimens ( n ≥ 12) were assigned to one of the following conditions: N – no storage; W – stored in 37 °C distilled water for 60 days; and TC – thermal cycling (5–55 °C; 10,000 cycles). All specimens were loaded in tension ( F ) to failure using a universal testing machine. The σ ( F / A ) was calculated and data were statistically analyzed using ANOVA and Tukey tests ( α = 0.05). Fracture surfaces were examined to determine the failure mode.
Results
RXA-SC and PF-PA specimens showed the greatest mean σ values after N (13.9 and 13.0 MPa, respectively) and TC (12.9 and 14.8 MPa, respectively). SC-treated showed greater mean σ values than PA-treated YZ specimens after W.
Significance
Regardless of the cement used, W and TC did not significantly reduce the σ of SC-treated YZ resin bonded to dentin.
1
Introduction
The mechanical properties of zirconia are the highest reported for a dental ceramic. It presents high values of fracture strength (>1000 MPa) and toughness (5–10 MPa m 0.5 ) compared with other traditional ceramics .
Perhaps the most clinical relevant drawback of the zirconia-based restorations is the adhesion to resin-based cements. The reliable adhesion obtained between surface-treated acid sensitive ceramics and resin-based cements is not directly applicable to zirconia-based dental ceramics, since neither hydrofluoric acid conditioning nor silanization guarantee satisfactory adhesion between the zirconia and the resin-based materials . Thus, numerous cementation protocols have been proposed to modify the surface topography of acid-resistant high-crystalline content zirconia-based ceramics through airborne particle abrasion methods . These methods were criticized for favoring ceramic slow crack growth . Yet, mechanical test results showed greater ceramic strength compared with other framework ceramics, suggesting superior performance even after these ceramic surface treatments .
Cements containing bisphenol A diglycidylether methacrylate (Bis-GMA), 4 -methacryloxy-ethyl trimellitate anhydride (4-META) and methacryloxy decyl phosphoric acid (MDP) monomers show potential bond to zirconia and could reduce the need for additional ceramic surface treatments . One-step auto-adhesive cements have also been proposed for cementing zirconia-based restorations . The resin matrix of these cement systems is a multifunctional methacrylate acid that reacts with the substrate and contributes to the adhesion mechanism .
Nevertheless, it is unusual to find reports on tensile bond strength of zirconia-based ceramic resin bonded to dentin after aging. Thus, the objective of this study was to investigate the influence of ceramic surface treatments, resin cements and aging on tensile bond strength of resin-based cements to a zirconia-based ceramic (Y-TZP) and dentin, testing the hypothesis that aging (water storage or thermal cycling) reduces the resin bond strength of zirconia-based ceramic bonded to dentin, irrespective of the resin cement or ceramic surface treatment (airborne particle abrasion or tribochemical silica coating) used.
2
Materials and methods
This study was approved by the local Research Ethics Committee. Fifty-four caries-free human molars, extracted for periodontal or orthodontic reasons, were cleaned with periodontal scales, stored for less than 6 months in 5 °C distilled water and the roots were included in acrylic resin (Jet Clássico, Artigos Odontológicos Clássico Ltda, São Paulo, SP, Brazil). The crowns were cut flat with a diamond saw at low speed and water-cooling (Isomet 1000, Buehler, Lake Bluff, IL, USA), exposing the mid-coronal dentin. Dentin surfaces were inspected for absence of enamel. A smear layer was created by wet-grinding the dentin surface with 600-grit silicon carbide paper (Labpol 8–12, Extec, USA) for 60 s . The dentin surface was conditioned following the manufacturer’s recommendation of each resin-based cement system used. For RXA (RelyX ARC, lot # FY8HX, 3M ESPE, St. Paul, EUA) the adhesive was light activated for 10 s (SmartLite PS, Dentsply, Petropolis, RJ, Brazil, light intensity: 950 mw/cm 2 ). For PF (Panavia F, lot # 249D and 26D, Kuraray Medical Inc., Okayama, Japan) the adhesive was not light activated. No adhesive was used for RXU (RelyX U100, lot # CA3RW, 3M ESPE, St. Paul, EUA).
Fifty-four yttria partially stabilized tetragonal zirconia-based ceramic bocks (YZ – In-Ceram YZ, Vita Zanhfabrik, Bad Sackingen, Germany) were cut and surfaces were wet polished (Labpol 8–12 convertible grinding/polishing machine, Extec, Enfield, CT, USA) using 1200 grit silicon carbide paper before sintering following the manufacturer’s recommendations, resulting in 6.4 mm × 6.4 mm × 4.8 mm ceramic blocks. They were randomly divided into two groups according to the surface treatment:
-
PA – airborne particle abrasion using ≤45 μm alumina (Al 2 O 3 ) particles (Polidental Ind. e Com. Ltda, Cotia, SP, Brazil);
-
SC – tribochemical silica coating using 30 μm alumina particles modified by silica (CoJet Sand, ESPE Dental AG, Seefeld, Germany).
Prior to surface treatments, all ceramic blocks were sonically cleaned (Vitasonic, Vita Zanhfabrik) for 5 min in isopropyl alcohol bath. A chairside microblasting unit (Cojet Prep, 3M ESPE, St. Paul, EUA) was used for both PA and SC ceramic surface treatments. The unit was positioned perpendicularly to the cementation surface and used for 20 s with a pressure of 24–28 psi and at a working distance of 10 mm.
Three PA- and SC-treated ceramic blocks were randomly assigned to one experimental group according to the resin-based cement used (RXA, RXU and PF) and the aging treatment (N – no storage; W – wet storage in 37 °C distilled water for 60 days; and TC – thermal cycling, 10,000×, 5–55 °C) ( Fig. 1 ).
For RXA and RXU assigned ceramic blocks, a silane coupling agent (Rely X Ceramic Primer, Lot # 8YH, 3M ESPE, St. Paul, EUA) was applied to the treated ceramic surface. For PF, the silane coupling agent (Clearfil Porcelain Bond Activator, lot # 225AA) and the Clearfil SE Bond Primer (Lot # 896A, Kuraray Medical Inc., Okayama, Japan) were applied to the treated ceramic surface. Dentin treatment and cementation procedures were performed in accordance with the instructions from each resin-based cement system. The treated ceramic blocks were cemented to the treated dentin surfaces using a constant load (750 g) applied for 5 min at room temperature (23 ± 1 °C). Cement excess was removed with a brush. The resin-based cements were light-activated (SmartLite PS, Dentsply) for 40 s from each side of the blocks. All teeth-cement-ceramic blocks were stored in 37 °C distilled water for 24 h prior to specimen fabrication.
The blocks were attached to a cutting machine (Isomet 1000, Buehler, Lake Bluff, IL, USA) and cut with a diamond disc at low speed and water cooling to produce non-trimmed, bar-shaped specimens with a bonding area ( A ) of 1.0 ± 0.1 mm 2 . The outer specimens were discarded because of significant differences in A, presence of enamel and cement discrepancies. Therefore, only the inner specimens were used for the study .
The specimens from groups N were tested immediately after fabrication. Specimens from the remaining groups (W and TC) were tested after aging. W specimens were stored for 60 days in 37 °C distilled water. TC specimens were thermo-cycled (Model 521-4D, Nova Etica, Vargem Grande Paulista, SP, Brazil) 10,000×, from 5 °C to 55 °C, and dwell time of 30 s. All specimens were attached to the flat grips of the microtensile bond strength (MTBS) device (Odeme Equipamentos Méd. e Odont. Ltda, Joaçaba, SC, Brazil) using cyanoacrylate adhesive (Super Bonder – Flex Gel, Lot # MAI108V, Hentzel Ltda, Itapevi, SP, Brazil) and loaded in tension ( F ) to failure using a universal testing machine (EMIC DL-1000, EMIC, Sao Jose dos Pinhais, PR, Brazil) at a cross-head speed of 1 mm/min. Bond strength ( σ ) values were calculated ( σ = F / A , in MPa) and statistically analyzed using three- and two-way analysis of variance (ANOVA) and Tukey post hoc tests ( α = 0.05). Fracture surfaces were examined using optical microscopy (Microscope MF, Mitutoyo, Japan) and scanning electron microscopy (SEM – Jeol JSM-5310, Jeol, Japan) to determine the mode of failure. Fracture patterns were classified as follows: Acc – adhesive failure starting at the ceramic-cement interface; Acd – adhesive failure starting at the cement–dentin interface; Cc – cohesive failure of the resin-based adhesive-cement system; Cz – cohesive failure of the zirconia-based ceramic; and Cd – cohesive failure of the dentin.
In preparation for SEM examination, the specimen fractured surfaces were sputter-coated with gold–palladium (Polaron SC 7620 Sputter Coater, Quorum Technologies, Newhaven, UK) for 130 s, at a current of 10–15 mA and a vacuum of 130 mTorr.
2
Materials and methods
This study was approved by the local Research Ethics Committee. Fifty-four caries-free human molars, extracted for periodontal or orthodontic reasons, were cleaned with periodontal scales, stored for less than 6 months in 5 °C distilled water and the roots were included in acrylic resin (Jet Clássico, Artigos Odontológicos Clássico Ltda, São Paulo, SP, Brazil). The crowns were cut flat with a diamond saw at low speed and water-cooling (Isomet 1000, Buehler, Lake Bluff, IL, USA), exposing the mid-coronal dentin. Dentin surfaces were inspected for absence of enamel. A smear layer was created by wet-grinding the dentin surface with 600-grit silicon carbide paper (Labpol 8–12, Extec, USA) for 60 s . The dentin surface was conditioned following the manufacturer’s recommendation of each resin-based cement system used. For RXA (RelyX ARC, lot # FY8HX, 3M ESPE, St. Paul, EUA) the adhesive was light activated for 10 s (SmartLite PS, Dentsply, Petropolis, RJ, Brazil, light intensity: 950 mw/cm 2 ). For PF (Panavia F, lot # 249D and 26D, Kuraray Medical Inc., Okayama, Japan) the adhesive was not light activated. No adhesive was used for RXU (RelyX U100, lot # CA3RW, 3M ESPE, St. Paul, EUA).
Fifty-four yttria partially stabilized tetragonal zirconia-based ceramic bocks (YZ – In-Ceram YZ, Vita Zanhfabrik, Bad Sackingen, Germany) were cut and surfaces were wet polished (Labpol 8–12 convertible grinding/polishing machine, Extec, Enfield, CT, USA) using 1200 grit silicon carbide paper before sintering following the manufacturer’s recommendations, resulting in 6.4 mm × 6.4 mm × 4.8 mm ceramic blocks. They were randomly divided into two groups according to the surface treatment:
-
PA – airborne particle abrasion using ≤45 μm alumina (Al 2 O 3 ) particles (Polidental Ind. e Com. Ltda, Cotia, SP, Brazil);
-
SC – tribochemical silica coating using 30 μm alumina particles modified by silica (CoJet Sand, ESPE Dental AG, Seefeld, Germany).
Prior to surface treatments, all ceramic blocks were sonically cleaned (Vitasonic, Vita Zanhfabrik) for 5 min in isopropyl alcohol bath. A chairside microblasting unit (Cojet Prep, 3M ESPE, St. Paul, EUA) was used for both PA and SC ceramic surface treatments. The unit was positioned perpendicularly to the cementation surface and used for 20 s with a pressure of 24–28 psi and at a working distance of 10 mm.
Three PA- and SC-treated ceramic blocks were randomly assigned to one experimental group according to the resin-based cement used (RXA, RXU and PF) and the aging treatment (N – no storage; W – wet storage in 37 °C distilled water for 60 days; and TC – thermal cycling, 10,000×, 5–55 °C) ( Fig. 1 ).
For RXA and RXU assigned ceramic blocks, a silane coupling agent (Rely X Ceramic Primer, Lot # 8YH, 3M ESPE, St. Paul, EUA) was applied to the treated ceramic surface. For PF, the silane coupling agent (Clearfil Porcelain Bond Activator, lot # 225AA) and the Clearfil SE Bond Primer (Lot # 896A, Kuraray Medical Inc., Okayama, Japan) were applied to the treated ceramic surface. Dentin treatment and cementation procedures were performed in accordance with the instructions from each resin-based cement system. The treated ceramic blocks were cemented to the treated dentin surfaces using a constant load (750 g) applied for 5 min at room temperature (23 ± 1 °C). Cement excess was removed with a brush. The resin-based cements were light-activated (SmartLite PS, Dentsply) for 40 s from each side of the blocks. All teeth-cement-ceramic blocks were stored in 37 °C distilled water for 24 h prior to specimen fabrication.
The blocks were attached to a cutting machine (Isomet 1000, Buehler, Lake Bluff, IL, USA) and cut with a diamond disc at low speed and water cooling to produce non-trimmed, bar-shaped specimens with a bonding area ( A ) of 1.0 ± 0.1 mm 2 . The outer specimens were discarded because of significant differences in A, presence of enamel and cement discrepancies. Therefore, only the inner specimens were used for the study .
The specimens from groups N were tested immediately after fabrication. Specimens from the remaining groups (W and TC) were tested after aging. W specimens were stored for 60 days in 37 °C distilled water. TC specimens were thermo-cycled (Model 521-4D, Nova Etica, Vargem Grande Paulista, SP, Brazil) 10,000×, from 5 °C to 55 °C, and dwell time of 30 s. All specimens were attached to the flat grips of the microtensile bond strength (MTBS) device (Odeme Equipamentos Méd. e Odont. Ltda, Joaçaba, SC, Brazil) using cyanoacrylate adhesive (Super Bonder – Flex Gel, Lot # MAI108V, Hentzel Ltda, Itapevi, SP, Brazil) and loaded in tension ( F ) to failure using a universal testing machine (EMIC DL-1000, EMIC, Sao Jose dos Pinhais, PR, Brazil) at a cross-head speed of 1 mm/min. Bond strength ( σ ) values were calculated ( σ = F / A , in MPa) and statistically analyzed using three- and two-way analysis of variance (ANOVA) and Tukey post hoc tests ( α = 0.05). Fracture surfaces were examined using optical microscopy (Microscope MF, Mitutoyo, Japan) and scanning electron microscopy (SEM – Jeol JSM-5310, Jeol, Japan) to determine the mode of failure. Fracture patterns were classified as follows: Acc – adhesive failure starting at the ceramic-cement interface; Acd – adhesive failure starting at the cement–dentin interface; Cc – cohesive failure of the resin-based adhesive-cement system; Cz – cohesive failure of the zirconia-based ceramic; and Cd – cohesive failure of the dentin.
In preparation for SEM examination, the specimen fractured surfaces were sputter-coated with gold–palladium (Polaron SC 7620 Sputter Coater, Quorum Technologies, Newhaven, UK) for 130 s, at a current of 10–15 mA and a vacuum of 130 mTorr.
3
Results
Surface treatment ( F = 8.24; p < 0.0043), resin cement ( F = 8.19; p < 0.0003) and aging ( F = 5.66; p < 0.0038) significantly affected the mean σ values. Interactions between the factors were also significant ( F = 9.20; p < 0.00001). Mean σ values of all experimental groups are summarized in Table 1 .
| Resin cement a | Ceramic treatment b | Aging c | Mean (SD) (MPa) |
|---|---|---|---|
| RXA | PA | N | 8.9 (3.3) |
| W | 5.8 (2.7) | ||
| TC | 1.9 (0.6) | ||
| SC | N | 13.9 (6.0) | |
| W | 10.4 (4.3) | ||
| TC | 12.9 (4.7) | ||
| RXU | PA | N | 10.2 (2.6) |
| W | 7.0 (3.4) | ||
| TC | 9.9 (3.6) | ||
| SC | N | 6.0 (2.8) | |
| W | 10.4 (4.4) | ||
| TC | 7.2 (3.4) | ||
| PF | PA | N | 13.0 (3.9) |
| W | 6.9 (3.1) | ||
| TC | 14.8 (6.5) | ||
| SC | N | 9.7 (4.7) | |
| W | 10.3 (3.3) | ||
| TC | 9.2 (2.7) | ||
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