The Journal of Adhesive Dentistry, 04/2013

Purpose: This study evaluated whether air blasting or rinsing particle remnants with water would impair adhesion of resin composite to metal. Materials and Methods: Commercially pure titanium plates (1 mm x 25 mm x 50 mm) were wet polished down to 1200-grit silicone carbide abrasive and ultrasonically cleaned. They were then embedded in auto-polymerizing acrylic with the bonding surfaces exposed. Specimens were randomly assigned to one of the following particle deposition protocols (N = 60, n = 10 per group): group 1: particle deposition with aluminum trioxide (50 µm Al2O3) (AL) + air blasting + silane (ESPE-Sil); group 2: particle deposition with 30 µm SiO2 (CoJet) (CSC) + air blasting + silane; group 3: particle deposition with Rocatec Pre 110 µm Al2O3+Rocatec Plus 110 µm SiO2 (LSC) + air blasting + silane. In groups 4 (AL-W), 5 (CSC-W) and 6 (LSC-W), the same protocols were used, but instead of air blasting only, particle-deposited specimen surfaces were rinsed with water and air blasted. Adhesive resin (VisioBond) was applied and resin composite (Quadrant Posterior, Cavex) was bonded using polyethylene molds and photopolymerized. The specimens were then submitted to thermocycling (6000 cycles, 5°C-55°C, dwell time: 30 s, transfer time: 5 s). Pre-test failures during thermocycling were assigned a value of 0 MPa. Failure modes were identified using an optical microscope. SEM images of particles were obtained. Bond strength data (MPa) were statistically analyzed using two-way ANOVA and Tukey's post-hoc tests (a = 0.05). Results: Particle type significantly affected the bond results (p 0.001). AL groups presented significantly lower results (air blasting: 4.3 ± 3.3, rinsing: 11.8 ± 6.5) compared to those of CSC (air blasting: 27.7 ± 6.6, rinsing: 30.4 ± 9.3) and LSC (air blasting: 31.4 ± 8.7, rinsing: 28.7 ± 7.0). AL groups presented 5 spontaneous debondings during thermocycling in the air-blasted group. Rinsing with water as opposed to air blasting only did not decrease the results with any of the particle types (p > 0.05). While AL groups showed exclusively adhesive failure between the resin composite and the substrate, the incidence of cohesive failures in the composite was more frequent in groups CSC and LSC after either air blasting or rinsing. SEM images of particles showed sharp morphology of the particles in AL compared to CSC and LSC. Conclusion: Rinsing and air blasting following particle deposition methods did not impair adhesion of resin composite to titanium. Particle deposition with silica particles provided better adhesion of resin composite to this substrate compared to the use of alumina particles. Keywords: adhesion, air abrasion, bond strength, composite resin, particle deposition, repair, silane coupling agent, surface conditioning, titanium

Purpose: To evaluate an alternative device using starch tubes to build up resin composite specimens for microshear bond tests. Materials and Methods: Twenty human molars were selected and sectioned mesiodistally to obtain two sections. The teeth were randomly divided into 4 groups (n = 10) according to the adhesive system - a two-step etch-and-rinse adhesive (Adper Single Bond) and a two-step self-etching adhesive (Clearfil SE Bond) - and the type of tube, starch or polyethylene. The tubes were evaluated under a stereomicroscope at 25X magnification to observe the variation in internal diameter. The resin composite was bonded to flat enamel surfaces using one of the adhesive systems and tube types. After 24 h storage in distilled water, the microshear bond strength (µSBS) was determined and the fracture pattern was analyzed under a stereomicroscope (400X magnification). The microshear bond strength values were subjected to two-way ANOVA. The chi-square test was used to compare pre-test failures and fracture patterns between the groups (p 0.05). Results: The type of tube, the adhesive system, and their interaction did not influence the bond strength values (p = 0.062, p = 0.122, and p = 0.301, respectively). No significant differences were observed for pre-test failures or fracture patterns (p = 0.320 and p = 0.561, respectively). Conclusion: Using starch tubes is an alternative to build up composite resin specimens for microshear bond strength testing with the two tested adhesive systems. Keywords: microshear bond strength, enamel, adhesive system

Purpose: To evaluate the effect of smear-layer interposition on the bonding effectiveness of self-etching adhesives with different etching potential. Materials and Methods: Bur-cut dentin specimens were obtained from 25 human molars after preparation of the dentin surface with a medium-grit diamond bur (bur-cut). An additional 25 molars were fractured at the midcoronal dentin to create a smear-layer-free surface (smear-free dentin). The prepared teeth were assigned to 5 groups, according to the adhesive to be applied: a strong one-step self-etching adhesive (PLP, Adper Prompt L-Pop, 3M ESPE, pH = 0.8); two ultra-mild one-step self-etching adhesives (C3S, Clearfil Tri-S Bond, Kuraray, pH = 2.7; AEB, Adper Easy Bond, 3M ESPE; pH = 2.7 ); as the self-etching control, a mild two-step self-etching adhesive (CSE, Clearfil SE Bond, Kuraray, pH of primer = 1.9); and as the etch-and-rinse control, a three-step etch-and-rinse adhesive (OFL, Optibond FL, Kerr). After composite buildups were made, all specimens were stored in distilled water (24 h/37°C) prior to microtensile bond strength testing (µTBS). The failure mode was determined with a stereomicroscope at 50X magnification. Representative µTBS specimens were processed for analysis in a Feg-SEM. The Kruskal-Wallis test was performed to determine statistical differences (p 0.05). Results: Except for the strong one-step self-etching adhesive, all other self-etching adhesives (mild and ultramild) revealed a significantly lower bond strength to bur-cut dentin than to smear-free dentin. The etch-and-rinse adhesive presented the highest µTBS, which was not significantly different when bonded to bur-cut or smear-free dentin. Fracture analysis demonstrated a prevalence of adhesive failures for the self-etching adhesives, while OFL revealed more mixed failures. SEM revealed that smear debris remained part of the adhesive interfacial complex produced by the ultra-mild one-step self-etching adhesive C3S when applied on bur-cut dentin. Conclusion: Smear debris interferes with the interaction of mild and ultra-mild self-etching adhesives with dentin. Keywords: dentin bonding, smear layer, etch-and-rinse adhesive, self-etching adhesive, etching potential

Purpose: To evaluate the effect of the hydrophilicity of adhesives on the compatibility between one-bottle simplified adhesives and a dual-curing resin cement. Materials and Methods: Three experimental and two commercial adhesives (All-Bond Universal, OptiBond Allin- One) with the same or similar pH and various degrees of hydrophilicity were tested in this study. Extracted human dentin was treated with each adhesive and bonded with a dual-curing resin cement (Duolink), which was either light cured or chemically (self) cured (n = 10). Shear bond strength was tested using the Ultradent jig method, and failure modes were determined using a stereomicroscope. Water contact angle (as a measure of hydrophilicity/-phobicity) was measured on a fully cured adhesive (n = 10). The data were analyzed statistically by ANOVA and Tukey's test. The quantitative relationship between the hydrophilicity and bond strength differences was analyzed (confidence level 95%). Results: Among the experimental adhesives, differences in bond strengths between light-curing and self-curing modes were larger for the more hydrophilic adhesives. For the commercial adhesives, Optibond All-in-One had a lower contact angle than All-bond Universal (p 0.05). Bond strength (MPa) values for Optibond All-in-One and All-bond Universal were 29.6 and 31.5, respectively (light cured), and 1.9 and 30.0, respectively (self-cured). Adhesive failure was a predominant mode for all adhesives except for All-Bond Universal. Regression analysis indicated a linear correlation between adhesives' hydrophilicity and bond strength differences (p 0.05). Conclusion: The more hydrophilic adhesives were less compatible (larger bond strength differences between different curing modes) with this dual-curing resin cement. All-bond Universal is more hydrophobic than Optibond All-in-One and it is compatible with this self-/dual-curing resin cement. Keywords: dentin, shear bond strength, adhesive, dual curing, contact angle, hydrophilicity, compatibility

Purpose: To evaluate the effect of the alcohol wet-bonding technique on bond performance of the adhesive interface produced by two-step etch-and-rinse adhesive systems. Materials and Methods: Composite buildups were bonded to sectioned human third molars using Adper Single Bond 2 (SB) bonded to acid-etched dentin saturated with water (control) or ethanol, or XP Bond (XP) bonded to acid-etched dentin saturated with water (control) or tert-butanol. A simplified dentin dehydration protocol was performed using 100% ethanol or 99.5% tert-butanol directly applied to dentin for 60 s. Specimens were cut into nontrimming dentin-composite beams that were divided equally in two subgroups: immediately tested and after immersion in 10% NaOCl solution for 1 h. Specimens were tested in tension at a crosshead speed of 1 mm/ min until failure, and the failure mode was evaluated. Data were statistically analyzed with three-way ANOVA and Tukey's test (α = 0.05). Additional dentin disks were bonded using the same groups tested and examined for leakage under light microscopy after immersion in ammoniacal silver nitrate solution. Results: The SB control group showed significantly higher bond strength values than did SB used on ethanolsaturated dentin (p 0.05); this tendency was confirmed by the silver nitrate deposition. The use of tert-butanol did not influence XP bond strength values (p > 0.05) or silver nitrate penetration. NaOCl solution significantly reduced the bond strength of all groups tested (p 0.05) and also increased the interfacial silver nitrate penetration. Conclusion: The simplified alcohol wet-bonding technique used in the present study was not able to improve resin/dentin bond performance for simplified etch-and-rinse adhesive systems. Keywords: bond strength, ethanol wet-bonding, solvent, dentin

Purpose: To investigate how the incremental filling technique, elastic modulus, and post-gel shrinkage of different dental composite resins affect residual shrinkage stress in a restored premolar. Materials and Methods: Sixteen composites indicated for restoring posterior teeth were tested. Elastic modulus and Knoop hardness were measured using Knoop indentation tests (n = 10). A strain gauge test was used to measure the post-gel shrinkage (n = 10). Two incremental techniques, horizontal or oblique, were applied in a finite element model of a premolar in combination with the experimentally determined properties to assess the stress conditions along the interface of the restoration and within the material structures. Linear regressions were determined between residual shrinkage stress and the elastic modulus and post-gel shrinkage values. Results: The mechanical properties and the post-gel shrinkage varied significantly among the composites tested. The calculated shrinkage stress showed a strong correlation with post-gel shrinkage and a weaker correlation with elastic modulus. The oblique incremental filling technique resulted in lower residual shrinkage stress in the enamel and dentin and along the enamel/composite interface compared to the horizontal technique. Conclusion: Residual stress varied significantly among the contemporary dental composites indicated for restoring posterior teeth. Shrinkage stress in a restored tooth correlated with post-gel shrinkage. In general, oblique incremental filling resulted in lower residual stresses than did horizontal increments. Keywords: contraction, elastic modulus, filling technique, Knoop hardness, residual stress, resin composite

Purpose: To evaluate the influence of peripheral enamel bonding, chlorhexidine digluconate (CHX) pretreatment, and storage time on resin-dentin microtensile bond strength (µTBS) of a self-etching adhesive system and selfetching cement. Materials and Methods: Fifty-six noncarious human third molars were coronally sectioned to provide a flat dentin surface; the circumferential enamel was removed from half of these and the other half was left intact. Pretreatment with 0.2% or 2% CHX or none (control) was performed before bonding composite blocks with Panavia F2.0 or RelyX Unicem to dentin. Specimens were stored in 0.5% chloramine for 3 days (control) or 6 months. Bonded specimens were sectioned into 1-mm2 dentin-only beams and a tensile load was applied until failure. The resulting 14 test groups, defined by control group/storage time/cement/CHX application mode/enamel bonding, were analyzed using two-way and three-way ANOVA, as well as Tukey's HSD post-hoc test (α = 0.05). Failure patterns of the specimens were observed and measured using scanning electron microscopy. Results: The comparison of the control vs experimental subgroups with peripheral enamel bonding and without CHX pretreatment after six months found no significant differences regarding the µTBS between the cements (p > 0.05) but did for the storage time (p = 0.05). When storing the specimens for six months, the absence of peripheral enamel bonding significantly decreased the µTBS (p = 0.05). Panavia F2.0 specimens showed significantly higher µTBS values than RelyX Unicem specimens (p = 0.05). CHX pretreatment, regardless the concentration, showed a significant influence on the µTBS (p = 0.05). SEM revealed that peripheral enamel bonding reduced failures at the resin/dentin interface. Conclusions: The absence of peripheral enamel bonding and a longer storage time decrease the µTBS of twostep self-etching adhesive system and a one-step self-etching cement. CHX pretreatment of the dentinal surfaces seems to improve the durability of the bond to dentin. Keywords: microtensile testing, adhesive systems, chlorhexidine, dentin bonding, durability, composites, storage time

Purpose: This study evaluated the microtensile bond strength (µTBS) of 3 different resin cements to lithium-disilicate ceramic using two assemblies: ceramic-cement-ceramic (CCC) and ceramic-cement-dentin (CCD). Materials and Methods: The bonding surfaces of lithium disilicate ceramic blocks (5 × 5 × 4 mm) (Nblock = 90) were etched with 4% hydrofluoric acid for 20 s and silanized. Flat dentin surfaces of human third molars were conditioned according to the respective manufacturer's specifications for three types of resin cements (ML: Multilink, Ivoclar-Vivadent; PF: Panavia F, Kuraray; SB: Super Bond C&B, Sun Medical). While one set of ceramic blocks (n = 30) was cemented to another equal set (CCC assembly), another set of ceramic blocks (n = 30) was cemented on flat dentin (CCD assembly). The bonded specimens were stored in distilled water at 37°C for 24 h, and then sectioned along the x- and y-axes to obtain nontrimmed beam specimens. The beam specimens were randomly divided into two conditions: dry condition (DC - immediate testing); and aging condition (AC - thermocycling 12,000 times + water storage for 150 days). The µTBS bond strength test was performed using a universal testing machine (1 mm/min). After debonding, the substrate and adherent surfaces were analyzed using a scanning electron microscope to categorize the failure types. The data were statistically evaluated using 2-way ANOVA and Tukey's test (5%). Results: While the mean µTBS of CCC assemblies were significantly influenced by the cement type (p 0.05) and aging (p 0.05), CCD assemblies showed a significant effect of the cement (p 0.05) but not the aging (p > 0.05). Without aging (DC), the mean µTBS (MPa) of SB (26.9) and PF (26.9) were significantly higher than ML (18.5) (p 0.05). For CCC after aging (AC), SB (26.6) showed higher mean µTBS than those of PF (16.4) and ML (18.5) (p 0.05). However, in CCD after AC, no significant difference was found between the groups (p > 0.05). In both CCC and CCD assemblies, pre-test failures were the least with SB cement. Regardless of the resin cement type employed and storage conditions, adhesive failures ranged between 35.3% and 88.9%, cohesive failures in cement between 2.3% and 35.3%, and cohesive failures in ceramic between 3.3% and 6.8%. Conclusion: SB resin cement demonstrated the highest bond strength to a lithium disilicate ceramic in both tests assemblies with and without aging conditions. Keywords: adhesion, aging, bond strength, ceramic, dentin, lithium disilicate, microtensile bond strength

Purpose: Resin bonding of In-Ceram Zirconia (ICZ) ceramics is still a challenge, especially for minimally invasive applications. This study evaluated the adhesion of ICZ to enamel and dentin after different surface treatments of the ceramic. Materials and Methods: ICZ ceramic specimens (diameter: 6 mm; thickness: 2 mm) (N = 100) were fabricated following the manufacturer's instructions and randomly assigned to 5 groups (n = 20), according to the surface treatment methods applied. The groups were as follows: group C: no treatment; group SB: sandblasting; group SCS-S: CoJet+silane; group SCS-P: CoJet+Alloy Primer; group GE-S: glaze+ hydrofluoric acid etching (9.6%) for 60 s+silane. Each group was randomly divided into two subgroups to be bonded to either enamel or dentin (n = 10 per group) using MDP-based resin cement (Panavia F2.0). All the specimens were subjected to thermocycling (5000x, 5°C-55°C). The specimens were mounted in a universal testing machine and tensile force was applied to the ceramic/cement interface until failure occurred (1 mm/min). After evaluating all the debonded specimens under SEM, the failure types were defined as either "adhesive" with no cement left on the ceramic surface (score 0) or "mixed" with less than 1/2 of the cement left adhered to the surface with no cohesive failure of the substrate (score 1). The data were statistically evaluated using 2-way ANOVA and Tukey's tests (α = 0.05). Results: The highest tensile bond strength for the enamel surfaces was obtained in group GE-S (18.1 ± 2 MPa) and the lowest in group SB (7.1 ± 1.4 MPa). Regarding dentin, group CSC-P showed the highest (12 ± 1.3 MPa) and SB the lowest tensile bond strength (5.7 ± 0.4 MPa). Groups SB, CSC-S, CSC-P, and GE-S did not show significant differences between the different surface treatments on either enamel or dentin surfaces (p 0.05, p 0.001, respectively). Groups CSC-P and GE-S presented similar bond strength for both the enamel and dentin substrates (p 0.8 and p 0.9), respectively. While on enamel substrates, exclusively adhesive failures from ICZ (score 0) were found, on dentin exclusively mixed failures were observed (score 1). Conclusion: Adhesion of ICZ to both enamel and dentin can be improved when ceramics are glazed, etched, and silanized, or sandblasted, primed, and cemented with an MDP-based cement. Keywords: adhesion, adhesive cement, alloy primer, glaze, In-Ceram Zirconia, surface conditioning, tensile bond strength

Purpose: To evaluate in vitro the effect of using titanium tetrafluoride as an alternative etchant prior to the silanization of the bonding surface on the long-term resin bond strength to lithium disilicate ceramic. Materials and Methods: Disk-shaped specimens made of lithium disilicate ceramic were ground with abrasive paper, then etched with aqueous solutions (2.5% and 5%) of titanium tetrafluoride for 60 s, 120 s and 240 s. Positive control specimens were etched with 5% hydrofluoric acid for 20 s and negative control specimens were not etched. Afterwards, bonding surfaces of all specimens were silanized. Plexiglas tubes filled with a composite resin were bonded to the specimens using an alignment apparatus and a composite luting resin. After storage in 37°C tap water for three days (n = 8) and after storage in 37°C tap water for 150 days interrupted by 5 x 7500 thermal cycles (n = 8), tensile bond strength (TBS) was measured in a universal testing machine at a crosshead speed of 2 mm/min. Results: After artificial aging, all specimens etched with titanium tetrafluoride debonded spontaneously resulting in a TBS of 0 MPa. Therefore, statistical analysis revealed a highly significant difference between the positive control and the test groups after 150 days storage. Conclusion: Etching the bonding surface of lithium disilicate ceramic restorations with hydrofluoric acid is still a "gold standard" and cannot be replaced by titanium tetrafluoride. Keywords: tensile bond strength, etching, lithium disilicate ceramic, titanium tetrafluoride, artificial aging

Purpose: To determine the best-performing combination of three core buildup materials and three bonding materials based on their bond strength to ceramic blocks in vitro. Materials and Methods: The materials used for core buildup were a composite (Tetric EvoCeram), a compomer (Compoglass F), and a glass-ionomer cement (Ketac Fil Plus), and for bonding, a three-step etch-and-rinse adhesive (Syntac), a two-step etch-and-rinse adhesive (ExciTE), and a single-step system (RelyX Unicem). Bond strength to ceramic blocks was determined by shear bond strength testing. Fracture behavior was evaluated by scanning electron microscopy. Results: The highest adhesive values between buildup and ceramic were obtained using the materials Compoglass F and Syntac, followed by Compoglass F and ExciTE. Among the two other core buildups, Tetric EvoCeram performed better than Ketac Fil Plus, which was independent of the bonding materials. Adhesive fractures were characteristically observed with Syntac and ExciTE, and cohesive fractures were characteristically observed with RelyX Unicem. Conclusion: These data show that compomers bonded with a multistep adhesive system achieved statistically significantly higher shear bond strength than composites and glass-ionomer cements. Within the limitations inherent to this in vitro study, the use of compomers for core buildup can be recommended. Keywords: adhesive, core buildup, prosthodontic treatment, shear bond strength