The Journal of Adhesive Dentistry, 01/2014

Purpose: This study compared the microtensile bond strengths (μTBS) of two different self-etching (SE) and etchand- rinse (ER) adhesive systems to enamel affected by hypoplastic amelogenesis imperfecta (HPAI) and analyzed the enamel etching patterns created by the two adhesive systems using scanning electron microscopy (SEM). Materials and Methods: Sixteen extracted HPAI-affected molars were used for the bond strength tests and 2 molars were examined under SEM for etching patterns. The control groups consisted of 12 healthy third molars for μTBS tests and two molars for SEM. Mesial and distal surfaces of the teeth were slightly ground flat. The adhesive systems and composite resin were applied to the flat enamel surfaces according to the manufacturers' instructions. The tooth slabs containing composite resin material on their mesial and distal surfaces were cut in the mesio-distal direction with a slow-speed diamond saw. The slabs were cut again to obtain square, 1-mm-thick sticks. Finally, each stick was divided into halves and placed in the μTBS tester. Bond strength tests were performed at a speed of 0.5 mm/min. Data were analyzed with two-way ANOVA and Tukey's tests. Results: There was no significant difference between the bond strength values of ER and SE adhesives (p > 0.05). However, significant differences were found between HPAI and control groups (p < 0.05). HPAI-affected enamel surfaces exhibited mild intra- and inter-prismatic enamel etching patterns after orthophosphoric acid application, while conditioning of HPAI-affected enamel with SE primer created a slightly rough and grooved surface. Conclusion: SE and ER adhesive systems provide similar bond strengths to HPAI-affected enamel surfaces. Keywords: Amelogenesis imperfecta, bond strength, microtensile, self-etch adhesive, etch-and-rinse adhesive

Purpose: To evaluate the relationship between biocompatibility and degree of monomer conversion of composites used to bond brackets to enamel, porcelain, resin, or metal surfaces at different time intervals. Materials and Methods: Twenty-four male Wistar rats were used, divided into 4 groups (n = 6) as follows: group C (control, polyethylene), group TCC (Transbond Color Change), group QC (Quick-Cure), and group EB (Eagle Bond). These substances were inserted into subcutaneous tissue. The events of inflammatory infiltrate, edema, necrosis, granulation tissue, multinuclear giant cells, young fibroblasts, and collagen formation were analyzed. The degree of conversion was evaluated by the Fourier method using infrared spectroscopy. Biocompatibility and degree of conversion were statistically analyzed using the Kruskal-Wallis and Dunn tests, and ANOVA and Tukey's test, respectively (p < 0.05). Results: The composites caused a small amount of inflammatory infiltrate, edema, and granulation tissue at all experimental time intervals, showing a gradual reduction over time (p > 0.05). Group TCC showed the highest amount of fibroblasts and EB the smallest at the time interval of 15 days (p = 0.035). Group TCC showed the highest amount of collagen fibers and EB the smallest throughout the experiment; there was a significant difference in terms of collagen fibers between groups QC and EB, which differed from the control at 7 days (p = 0.006), and between groups EB and TCC (p = 0.018) at 30 days. Monomer conversion ranged from 64.1% in group EB at 7 days to 85.3% in group TCC at 30 days. Conclusion: Transbond Color Change composite showed a higher degree of conversion and a better healing process compared to Eagle Bond composite at 15 and 30 days. Quick-cure composite demonstrated a better degree of conversion and healing process than that of Eagle Bond, but this was not statistically significantly different. Keywords: composites, biocompatibility, adhesive dentistry

Purpose: To evaluate the effect of saturation of demineralized dentin with aqueous and alcoholic excipients of chlorhexidine (CHX) on the exposure of collagen fibrils in resin-dentin bonds in sound and caries-affected dentin. Materials and Methods: Flat midcoronal dentin surfaces were prepared from 24 noncarious molars, and artificial caries was induced in half of the sample. For each substrate, the surfaces were assigned to 4 groups (n = 3) according to the saturation solution of the dentin: water, ethanol, 1% CHX aqueous or alcoholic solution. Infected dentin was removed by abrasive papers. After acid etching, the dentin surface was saturated with each solution for 60 s followed by application of Single Bond. The specimens were processed for Goldner's trichrome staining and the thickness of the exposed collagen zone (ECZ) at the resin/dentin interfaces was measured under optical microscopy. Data were analyzed statistically by Kruskal-Wallis and Mann-Whitney tests (α = 0.05). Results: Regardless of the saturation solution, caries-affected dentin presented a thicker ECZ at the bottom of the hybrid layer than did sound dentin. For both substrates, 100% ethanol had a negative influence on collagen exposure in comparison with water, but the same was not observed for the CHX alcoholic solution. CHX solutions did not differ significantly from each other or from their respective solvents. Conclusion: The saturation of phosphoric acid-demineralized dentin with either CHX aqueous or alcoholic solutions did not affect the exposure of collagen fibrils in the resin-dentin bonds produced in sound and caries-affected dentin. A thicker zone of exposed collagen was found in hybridized caries-affected dentin compared to noncarious dentin. Keywords: dental caries, dentin bonding agents, dentin, ethanol, chlorhexidine

Purpose: To compare marginal microleakage in porcelain veneer restorations following dental finishing using two types of instruments to test the hypothesis that microleakage will be less when teeth are prepared with sonic oscillating burs than when prepared with high-speed rotating burs. Materials and Methods: Fifty-six extracted human maxillary central incisors were selected and divided randomly into two groups. Group 1 samples underwent dental finishing using high-speed rotating diamond burs, while group 2 used sonic oscillating diamond burs. Buccal chamfer preparation was carried out for both groups. Fortyeight of the samples (24 per group) were restored using IPS Empress ceramic veneers. 2% methylene blue was used to evaluate microleakage at the tooth/composite veneer interface. Teeth were sectioned lengthwise into three parts and microleakage was measured at two points - cervical and incisal - on each section. Before bonding, four teeth per group underwent SEM examination. Results: Evaluation of microleakage at the cervical dentin margin showed a value of 10.5% in group 1 and 6.6% in group 2, which was statistically significantly different (p < 0.05). Incisal microleakage was 1.3% for group 1 and 1.2% for group 2, which was not significantly different. SEM revealed different patterns of surface texture in both areas according to the instrument used. Group 1 exhibited parallel horizontal abrasion grooves with a milled effect and thick smear layers; group 2 showed abrasive erosion, discontinuous perpendicular depressions, and thin smear layers. Conclusion: Tooth preparations finished with sonic burs produced significantly less microleakage in the cervical dentin area of bonded veneer restorations. No differences were found in the incisal enamel area. Keywords: porcelain veneer, microleakage, dentin adhesion, enamel adhesion, oscillating burs

Purpose: To evaluate the influence of long-term water storage and thermocycling on the shear bond strength of a glass-ionomer cement to Er:YAG-irradiated and bur-prepared dentin. Materials and Methods: Fifteen bovine incisors were selected and the roots removed. Crowns were sectioned into four pieces, resulting in 60 samples that were individually embedded in polyester resin (n = 15) and ground to plane the enamel and expose the dentin. The bonding site was delimited and samples were randomly assigned according to the method of cavity preparation: Er:YAG laser (250 mJ/4 Hz) or high-speed handpiece (diamond bur #2096). Samples were fixed to a metallic device, where glass-ionomer cement (GIC) cylinders were prepared. Subsequently, they were subdivided according to the duration of water storage (WS) and number of thermocycles (TCs) - 24 h WS/no TCs and 6 months WS/12,000 TCs - and subjected to a shear bond strength test (500 N at 0.5 mm/min). Results: The duration of water storage and number of thermocycles tested had no statistically significant effect on the shear bond strength to laser-irradiated dentin (p > 0.05). For bur-prepared substrate, the long-term degradation process promoted a decrease in shear bond strength values (p < 0.05). Conclusion: Long-term water storage and thermocycling did not affect shear bond strength of glass-ionomer cement bonded to Er:YAG laser-prepared dentin. Keywords: glass-ionomer cement, shear bond strength, Er:YAG laser, dentin

Purpose: To study the effect of addition of poly(acrylamide-co-sodium acrylate) copolymer and/or TiO2 nanoparticles on the mechanochemical properties of conventional glass ionomer (GIC)-based restorative materials. Materials and Methods: The copolymer was prepared, characterized and then added, either separately or in combination with different proportions of TiO2 nanoparticles to the conventional GIC powder. The developed composites were characterized using FTIR spectrometry, x-ray diffraction, and scanning electron microscopy. The mechanical properties of the obtained series of modified GIC formulations were investigated in comparison with other formulations containing only TiO2 nanoparticles through testing their compressive strength, flexural strength, and dentin shear bond strength. Results: The preliminary data of the study showed a significant increase in the compressive strength of the conventional GIC after addition of 3% and 5% TiO2 nanoparticles by weight, but 7% decreased it. Upon addition of copolymer, the compressive strength was lower than that of the conventional GIC. The highest average compressive strength value was obtained upon incorporation of 7% 1:1 combination of copolymer-TiO2 nanoparticles. The results also demonstrated a significant increase in the flexural strength values after addition of both copolymer and TiO2 nanoparticles to the GIC powder. In addition, the results revealed a significant increase in values of dentin shear bond strength after copolymer addition with the highest value noted upon addition of 7% by weight of copolymer. Conclusion: The new series of modified glass ionomers developed here can be tailored to act as restorative materials with high quality performance in high stress-bearing areas. Keywords: glass ionomer, nanoparticles, TiO2, copolymer, restorative material, compressive strength, flexural strength, dentin shear bond strength

Purpose: The purpose of this in vitro study was to evaluate the bond strength of a resin luting cement to zirconia surfaces that had received two novel surface pretreatment methods: etching of a pre-fired overglaze or paste liner on the zirconia substrate. Materials and Methods: Fully sintered zirconia disks were assigned to 6 groups according to the surface pretreatment: firing of 2 layers of paste liner which was then etched with hydrofluoric acid and treated with silane (Liner group); firing of 2 layers of overglaze which were then etched with hydrofluoric acid and treated with silane (glaze group); Rocatec treatment and silane application (Rocatec group); Rocatec treatment followed by ultrasonic cleaning and silanization (ultrasonic-Rocatec group); sandblasted with alumina (alumina group); as-sintered with no pretreatment (control group). Twenty composite resin cylinders were bonded to each group with Panavia F 2.0. Each group was further divided into 2 subgroups (n = 10) for 2 different storage conditions: 24 h water storage or 3 weeks water storage plus 6000 thermocycles between 5°C and 55°C. The shear bond strength was then determined. Statistical analyses with two-way ANOVA were conducted; the level of significance was set at p < 0.05. Results: At 24 h, the shear bond strength values of all groups except the control showed no statistically significant difference. After artificial aging, the mean bond strength of all groups dropped, but the decrease in the glaze group was not statistically significant. The glaze group showed the highest shear bond strength. However, that was not statistically different from the liner or the Rocatec group without ultrasonic cleaning (p < 0.05). All the control specimens debonded spontaneously after aging. Ultrasonic cleaning after Rocatec treatment caused a reduction in shear bond strength, but the difference was not statistically significant. Conclusion: Both the fired paste liner and overglazed ceramic treated zirconia surfaces provided a strong and durable bond to resin cement under the conditions tested. Keywords: zirconia, silica coating, resin cements, silane, surface treatment of zirconia

Purpose: To evaluate the influence of the number of porcelain layers on its cohesive strength and on bonding to zirconia. Materials and Methods: Y-TZP blocks were cut into 1 cm3 specimens (n = 30). The feldspathic porcelain (V9) was applied to the zirconia in different numbers of layers up to 1 cm total thickness (n = 10): ZP1 - one layer; ZP2 - two layers; ZP3 - three layers. Ten specimens with V9 were prepared following the same protocols of groups 1 (P1) and 3 (P3). All study specimens were sintered three times. The specimens were cut into 1 mm2 microbars and tested under tension in a universal testing machine (0.5 mm/min). We calculated strength (σ, in MPa) by dividing the fracture load (N) by the fractured area (mm2). The failure mode was classified as cohesive (used to calculate the cohesive strength, σc) or adhesive (bond strength, σa). The data were analyzed by Kruskal-Wallis and Dunn's tests (α = 0.05) or ANOVA and Tukey's test (α = 0.05), according to their distribution parameters. Results: The ZP1 group presented the highest values for σa data, compared with other groups, which were statistically similar. The predominant failure mode for the bonded specimens was cohesive. With regard to the cohesive strength (σc), ZP1 presented the highest values. Conclusion: It can be concluded that the presence of more than one porcelain layer decreases its cohesive strength and its bonding strength to zirconia. Keywords: dental porcelain, zirconia, sintering, tensile strength

Purpose: This study evaluated the repair bond strength of differently surface-conditioned press-on-metal ceramic to repair composites and determined the location of the accumulated stresses by finite element analysis. Materials and Methods: Press-on-metal ceramic disks (IPS InLine PoM, Ivoclar Vivadent) (N = 45, diameter: 3 mm, height: 2 mm) were randomly divided into 3 groups (n = 15 per group) and conditioned with one of the following methods: 9.5% hydrofluoric acid (HF) (Porcelain etch), tribochemical silica coating (TS) (CoJet), and an unconditioned group acted as the control (C). Each group was divided into three subgroups depending on the repair composite resins: a) Arabesk Top (V, a microhybrid; VOCO), b) Filtek Z250 (F, a hybrid;3M ESPE); c) Tetric EvoCeram (T, a nanohybrid; Ivoclar Vivadent) (n = 5 per subgroup). Repair composites disks (diameter: 1 mm, height: 1 mm) were photopolymerized on each ceramic block. Microshear bond strength (MSB) tests were performed (1 mm/min) and the obtained data were statistically analyzed using 2-way ANOVA and Tukey's post-hoc test (α = 0.05). Failure types were analyzed under SEM. Vickers indentation hardness, Young's modulus, and finite element analysis (FEA) were performed complementary to MSB tests to determine stress accumulation areas. Results: MSB results were significantly affected by the surface conditioning methods (p = 0.0001), whereas the repair composite types did not show a significant effect (p = 0.108). The interaction terms between the repair composite and surface conditioning method were also statistically significant (p = 0.0001). The lowest MSB values (MPa ± SD) were obtained in the control group (V = 4 ± 0.8; F = 3.9 ± 0.7; T = 4.1 ± 0.7) (p < 0.05). While the group treated with T composite resulted in significantly lower MSB values for the HF group (T= 4.1 ± 0.8) compared to those of other composites (V = 8.1 ± 2.6; F = 7.6 ± 2.2) (p < 0.05), there were no significant differences when TS was used as a conditioning method (V = 5 ± 1.7; F = 4.7 ± 1; T = 6.2 ± 0.8) (p > 0.05). The control group presented exclusively adhesive failures. Cohesive failures in composite followed by mixed failure types were more common in HF and TS conditioned groups. Elasticity modulus of the composites were 22.9, 12.09, and 10.41 GPa for F, T, and V, respectively. Vickers hardness of the composites were 223, 232, and 375 HV for V, T, and F, respectively. Von Mises stresses in the FEA analysis for the V and T composites spread over a large area due to the low elastic modulus of the composite, whereas the F composite material accumulated more stresses at the bonded interface. Conclusion: Press-on-metal ceramic could best be repaired using tribochemical silica coating followed by silanization, regardless of the repair composite type in combination with their corresponding adhesive resins, providing that no cohesive ceramic failure was observed. Keywords: ceramic repair, finite element analysis, hydrofluoric acid, microshear bond strength, press-on-metal ceramic, surface conditioning method, tribochemical silica coating

Purpose: To evaluate the effect of the resin cement thickness (RCT) on bond strength (BS) and gap formation (GF) of fiber posts bonded to root dentin. Materials and Methods: The roots of 24 extracted human mandibular premolars were treated endodontically and the post spaces were prepared using drills with different diameters according to the following groups (n = 8): well adapted (WA), moderately well adapted (MA) and poorly adapted (PA). The fiber glass posts were cemented (Excite DSC and Variolink II) in accordance with the manufacturer's instructions. After 1 week, the roots were transversely sectioned into six 1-mm-thick disks and photographed using an optical microscope to determine the RCT. After this, epoxy resin replicas of each sample were observed using SEM, and the mean length and width of the gaps formed in the cement/dentin/post interface were measured. Finally, each sample was subjected to the push-out test (0.5 mm/min), and the data were statistically analyzed using one-way ANOVA and Tukey's tests at the 5% level of significance. Results: The lowest RCT (μm) was observed for WA and the highest for PA. The group MA showed an intermediate value. Significantly higher push-out BS values were observed for WA compared to the other groups. The MA and PA groups were statistically similar. The highest mean gap length (%) and width (μm) were observed for PA. The groups MA and WA were statistically similar. Conclusion: Lower resin cement thickness resulted in better fiber post adhesion, that is, in higher bond strength and less gap formation. Keywords: bond strength, fiber posts, gap, resin cements, root dentin, scanning electron microscopy

Purpose: To evaluate the effect of solvent removal and light-curing methods on the push-out bond strength of fiber posts to root canal dentin using a one-step self-etching adhesive. Materials and Methods: Eighty single-rooted, single-canal human mandibular premolars were used in this study. After removal of the crown, the pulp was extirpated and the post space was prepared. The teeth were divided into two main groups according to the solvent removal method, either using the paper point or the air-drying method. Each of the above main groups was further subdivided into 4 subgroups according to the light-curing method: group 1: both adhesive and resin cement were cured from the top of the post in the same step (cocuring) for 40 s; group 2: the adhesive was light cured for 20 s and the resin cement for 40 s; group 3: the adhesive was light cured for 40 s as was the resin cement; group 4: an intracanal tip was used to cure the adhesive inside the post space for 20 s. In groups 1 to 4, the solvent was evaporated using oil-free compressed air for 5 s from the root surface and excess adhesive was removed from inside the canal using a paper point. In groups 5 to 8, the adhesive and cement were applied and light cured as in groups 1 to 4, except the solvent was evaporated (air dried) from inside the post space using an intra-canal disposable plastic tip attached to the tip of a 3-way syringe. After 24 hours, three 2-mm-thick root slices were obtained from each root. Each slice was subjected to the push-out bond strength test at a crosshead speed of 0.5 mm/min. Factorial analysis (two-way ANOVA) was run to test the effect of solvent evaporation method, light-curing method, and their interactions on bond strength. One-way ANOVA followed by Duncan's Multiple Range Test were used to test the effect of lightcuring method on bond strength within each solvent evaporation method. Student's t-test was performed to compare the effect of solvent evaporation method on bond strength within each light-curing method. Results: Two-way ANOVA revealed that the solvent removal method had a significant effect on the bond strength of fiber post to root canal dentin. Neither the light-curing method nor the interaction between the two independent variables had a significant effect on the push-out bond strength. Conclusions: Only air drying the one-step self-etching adhesive could influence the bond strength of the fiber post to root canal dentin. Keywords: fiber post, self-etching adhesive, solvent removal method, push-out bond strength

Purpose: To investigate the effects of pretreatment with 2% chlorhexidine in a gel base (CHX) and 100% ethanol (EtOH) on the bond strength between fiber posts relined with resin composite and root dentin under cyclic loading. Materials and Methods: Forty bovine incisor roots were divided into four groups after phosphoric acid etching: group 1 (control), irrigation with physiological saline solution; group 2, 5 min pretreatment with CHX; group 3, 1 min pretreatment with EtOH; group 4, 5 min pretreatment with CHX followed by 1 min with EtOH. Fiber posts relined with resin composite were cemented with RelyX ARC and the etch-and-rinse adhesive system Scotchbond Multi-Purpose. Each group was randomly divided into two subgroups: 24 h of storage (immediate groups) and cyclic loading (loading groups) with 250,000 cycles in a controlled chewing simulator. All roots were sectioned transversely and push-out tests were performed. Failure modes were observed and the bond strength means were analyzed using ANOVA and Tukey's test (a = 0.05). Results: The mean values for the bond strength test (MPa) in immediate groups were: group 1, 5.44 ± 1.48; group 2, 5.57 ± 1.41; group 3, 5.49 ± 1.48; group 4, 5.57 ± 1.42. Immediate groups showed similar bond strength values (p > 0.05). In the cyclic loading groups, the bond strength values were: group 1, 2.80 ± 0.79; group 2, 4.02 (1.30); group 3, 4.50 ± 1.67; group 4, 4.97 ± 2.00. After cyclic loading, a significant decrease in the control group was observed (p < 0.05), while CHX pretreatment resulted in intermediate values (p < 0.05) and EtOH alone or associated with CHX preserved the bond strength values (p > 0.05). Conclusion: Chlorhexidine and/or ethanol pretreatment preserved the bond strength of the fiber post after cyclic loading. Keywords: bond strength, chlorhexidine, cyclic loading, ethanol, fiber post, root canal