The Journal of Adhesive Dentistry, 06/2016

Purpose: To evaluate the use of oxalic acid in restorations of noncarious cervical lesions. Materials and Methods: Twenty volunteers of both sexes between 24 and 55 years old, with at least two lesions that were restored with the techniques to be evaluated, were selected. Ninety teeth were randomly divided into two groups: group 1, two-step etch-and-rinse adhesive technique (control) and group 2, pretreatment with oxalic acid followed by the application of a two-step etch-and-rinse adhesive system. The adhesive system used was XP Bond (Dentsply) and the restorative composite resin was Durafill (Heraeus Kulzer). A modified USPHS method was employed for the clinical evaluation, taking into account the following criteria: retention (R), marginal integrity (MI), marginal discoloration (MD), postoperative sensitivity (S), caries (C), and anatomic form (AF). Clinical assessments were conducted by two examiners at baseline and after 6 months, 1 and 2 years. Results: After two years, the results of clinically satisfactory restorations (Alpha and Bravo) obtained for the control and experimental groups were: R (90.9%/93.33%), MI (100%/100%), MD (100%/100%), S (100%/100%), C (100%/100%), AF (100%/100%). Conclusion: Over a 2-year period, the use of oxalic acid as an agent of dentin pretreatment did not influence the clinical performance of restorations in noncarious cervical lesions. Keywords: adhesive, clinical trial, dentin hypersensitivity, oxalates

Purpose: To evaluate the effect of the etching strategy on the immediate and 1-year microtensile bond strength (μTBS) and structural reliability of a universal adhesive to sound and artificially-induced caries-affected dentin of primary teeth. Materials and Methods: Flat midcoronal dentin surfaces were exposed in 50 primary molars, which were then randomly assigned to 10 groups according to substrate (sound dentin [SD] and artificially-induced caries-affected dentin [CAD] with pH cycling for 14 days) and etching approach using Scotchbond Universal Adhesive (self-etching or dry or wet-bonding etch-and-rinse strategies) with Adper Single Bond Plus (two-step etch-and-rinse adhesive) and Clearfil SE Bond (two-step self-etching system) as controls. Composite buildups were constructed and sectioned to obtain bonded sticks (0.8 mm2) to be subjected to microtensile testing immediately or after 1 year of water aging. Data were analyzed using three-way repeated measures ANOVA and Tukey's test (α = 0.05). Weibull modulus and characteristic strength were also determined. Results: A decrease in bond strength was observed after 1 year of water aging, except when the universal adhesive was used in the dry-bonding etch-and-rinse and self-etching approaches. However, the self-etching approach resulted in lower μTBS values in SD, while no difference among experimental groups was observed in CAD. Overall, higher Weibull modulus values were achieved in the groups with higher bond strength. The relationship between characteristic strength and bond strengths was not linear for all groups. Conclusion: The bond longevity of the universal adhesive using the dry-bonding etch-and-rinse approach on sound and artificially-induced caries-affected primary dentin was better than the other bonding agents and approaches tested. Keywords: multimode adhesive, structural reliability, caries-affected dentin, deciduous tooth, durability, microtensile

Purpose: To evaluate the suitability of an ultra-short pulsed laser (USPL) to treat zirconia ceramic surfaces and increase their adhesion to dual-curing resin cement. Materials and Methods: Twenty 10 × 10 × 5 mm³ blocks were prepared from a zirconia ceramic (Y-TZP). The specimens were polished and randomly assigned to four groups (n = 5) which received the following surface treatments: sandblasting (SB) with Al₂O₃ particles and silica coating (SC) with SiO₂ particles as positive controls; two groups received USPL irradiation, one with 10 scan repetitions (L10) and the other with 20 (L20). Laser irradiation was performed at 1030 nm, 2.3 J/cm², 6 ps pulse duration. The ceramic blocks were duplicated in composite resin and cemented with a dual-curing resin cement. Half of the blocks were then stored in water (37°C) for 24 h and the other half for 1 month. At each time, 40 to 60 sticks per group were subjected to microtensile bond strength testing. Data were analyzed statistically using the Kruskal-Wallis test (α = 0.05). Results: Laser-treated zirconia presented statistically significantly higher roughness than did SB and SC. After 24 h, the highest bond strength means (MPa) were achieved by L10 (42.3 ± 10.8) and L20 (37.9 ± 14.4), and both of them were statistically significantly higher than SB (22.0 ± 5.3) and SC (20.8 ± 7.1) (p < 0.05). After 1 month of storage, L10- and L20-treated zirconia still showed significantly higher bond strengths than did SB- and SC-treated zirconia (p < 0.05). Conclusion: USPL irradiation significantly increases bond strength of zirconia ceramic to dual-curing resin cement and might be an alternative for improving adhesion to this material. Keywords: yttria-stabilized tetragonal zirconia polycrystal, luting, laser, sandblasting, silica coating, roughness

Purpose: This study evaluated the push-out bond strength (BS) of fiber posts in root canals and the nanoleakage (NL) pattern at the bonding interface when universal adhesives were applied in etch-and-rinse mode to root dentin using an oscillating sonic device. Materials and Methods: Fifty-four roots of human premolars were endodontically prepared and divided into 6 experimental groups according to the main factors: adhesive system/resin cement (Ambar Universal/AllCem, Scotchbond Universal/RelyX ARC, Prime&Bond Elect/Enforce) and application mode (vigorous manual or sonic). Fiber posts were cemented and roots were transversally sectioned into six 1-mm-thick serial slices, which were subjected to BS testing (n = 7 per group) at a crosshead speed of 0.5 mm/min, and the rest (n = 2 per group) were subjected to NL analysis using scanning electron microscopy after slice immersion in silver nitrate. Data were analyzed using two-way ANOVA and Bonferroni's post-hoc test (α = 5%). Results: Sonic application significantly increased BS only on the coronal third when Ambar Universal was used. When Scotchbond Universal was used, higher BS was observed when the adhesive was manually applied than when the sonic device was used. For Prime&Bond Elect, no significant difference in BS was noted when the application methods were compared. Manual application also produced lower NL values than did sonic application when Ambar Universal was used, while no significant difference in NL was noted using the other adhesive systems. Conclusion: Sonic application did not improve the bond strength of posts in root canals in comparison to vigorous, manual application. Keywords: fiber posts, root dentin, push-out bond strength, silver nitrate

Purpose: To use shear bond strength (SBS) and shear fatigue strength (SFS) testing to determine the influence of phosphoric acid pre-etching times prior to application of self-etch adhesives on enamel bonding. Materials and Methods: Two single-step self-etch universal adhesives (Prime&Bond Elect and Scotchbond Universal), a conventional single-step self-etch adhesive (G-ӕnial Bond), and a conventional two-step self-etch adhesive (OptiBond XTR) were used. The SBS and SFS were obtained with phosphoric acid pre-etching for 3, 10, or 15 s prior to application of the adhesives, and without pre-etching (0 s) as a control. A staircase method was used to determine the SFS with 10 Hz frequency for 50,000 cycles or until failure occurred. The mean demineralization depth for each treated enamel surface was also measured using a profilometer. Results: For all the adhesives, the groups with pre-etching showed significantly higher SBS and SFS than groups without pre-etching. However, there was no significant difference in SBS and SFS among groups with > 3 s of preetching. In addition, although the groups with pre-etching showed significantly deeper demineralization depths than groups without pre-etching, there was no significant difference in depth among groups with > 3 s of pre-etching. Conclusion: Three seconds of phosphoric acid pre-etching prior to application of self-etch adhesive can enhance enamel bonding effectiveness. Keywords: phosphoric acid pre-etching time, shear fatigue strength, self-etch adhesive, universal adhesive, demineralization depth

Purpose: To investigate the influence of 4-META concentration and type of solvent on the degree of conversion (DC%) and resin-dentin bond stability of experimental etch-and-rinse adhesives. Materials and Methods: Four different concentrations of 4-META (12 wt%, 20 wt%, 30 wt%, 40 wt%) were added to a model adhesive system consisting of TEG-DMA (25 wt%), UDMA (20 wt%), HEMA (30 wt%), water (4 wt%), camphorquinone (0.5 wt%), and tertiary amine (0.5 wt%) dissolved in 20% acetone (A12, A20, A30 and A40) or 20% ethanol (E12, E20, E30 and E40). DC% was evaluated by FT-IR spectroscopy. Human molars were wet ground until the occlusal dentin was exposed, the adhesive systems were applied after 37% phosphoric acid etching, and resin composite buildups were incrementally constructed. After storage in distilled water at 37°C for 24 h, the teeth were cut into resin-dentin beams (cross-sectional area 1 mm2). Microtensile bond strength (μTBS) was evaluated after 24 h, 6 months, and 1 year of water storage at 37°C. The failure mode was categorized as adhesive, mixed, or cohesive. Data were analyzed using ANOVA and Tukey's HSD test (α = 0.05). Results: A12 presented the lowest DC% (p < 0.05). All the other adhesive systems showed statistically similar DC% (p > 0.05). All adhesive systems maintained resin-dentin bond stability after 6 months of water storage, while only A40 and E40 maintained it after 1 year. Conclusion: Irrespective of the type of organic solvent, the incorporation of high concentrations of 4-META (40 wt%) improved the resin-dentin bond stability of the experimental etch-and-rinse adhesive systems over a period of 1 year. Keywords: adhesive systems, 4-META, degree of conversion, dentin bond stability

Purpose: The aim of this finite-element stress analysis (FEA) was to determine the effect of degradation due to water storage on stress distributions in root-filled premolar models restored with composite using either a self-etch (SE) or an etch-and-rinse (E&R) adhesive. Materials and Methods: Four premolar FEA models including root filling, MOD cavity, and composite restorations were created. The cavities were assumed to be treated by SE or E&R adhesives and stored in water for 18 months. The elastic properties of the adhesive-dentin interface after 24-h and 18-month water storage were obtained from the literature and applied to the FEA models. A 300-N load was applied on the functional cusps of the models. The SolidWorks/Cosmosworks structural analysis program was used and the results were presented considering the von Mises stresses. Results: Stresses in the cervical region increased over time on the load-application side of the main tooth models (SE: 84.11 MPa to 87.51 MPa; E&R: 100.24 MPa to 120.8 MPa). When the adhesive interfaces (hybrid layer, adhesive layer) and dentin were evaluated separately, the stresses near the root canal orifices increased over time in both models; however, this change was more noticeable in the E&R models. Stresses at the cavity corners decreased in the E&R model (within the adhesive layer), while SE models showed the opposite (within the hybrid layer). Conclusion: Change in the elastic modulus of the adhesive layer, hybrid layer, and dentin due to water storage has an effect on stresses in root-filled premolar models. The location and the level of the stresses differed depending on the adhesive used. Keywords: finite element analysis, dentin, elastic modulus, self-etch adhesive, etch-and-rinse adhesive, degradation

Purpose: To establish a fluorescence-based method to simultaneously assess micro-permeability and collagen cross-linking induced by chemical agents at the resin-dentin interface. Materials and Methods: Three chemical agents were investigated (proanthocyanidin-rich grape seed extract: GSE; carbodiimide hydrochloride/N-hydroxysuccinimide: EDC/NHS; glutaraldehyde: GD) along with a control (distilled water) as primers applied on flat occlusal dentin surfaces of 48 teeth and restored with two commercially available etch-and-rinse adhesives. Resin-dentin interfaces were polished and infiltrated with rhodamine-B solution for confocal laser scanning microscopy analysis. Parameters were chosen that would allow acquisition of a simultaneous appearance of collagen and interfacial micro-permeability (rhodamine-B). Fluorescence emission intensity (FEI) was converted into numerals and values were calculated for each group. Data were statistically analyzed using one-way ANOVA and post-hoc Scheffe's and multiple comparisons tests (α = 0.05). T-tests with Pearson correlations were used to investigate correlations between collagen cross-linking and micro-permeability. Results: The FEI of collagen was the highest for GD, followed by GSE, with no significant differences between EDC/ NHS and the control group (p > 0.05). Micro-permeability was significantly affected by the adhesives (p < 0.05). Micro- permeability was the lowest for GSE groups, regardless of the adhesives (p < 0.001). Weak correlations were found between micro-permeability and collagen auto-fluorescence. Conclusions: Non-enzymatic collagen cross-linking induced by GSE and GD can be detected by increased collagen auto-fluorescence, and results in reduced interfacial micro-permeability. Increased collagen auto-fluorescence was correlated with fluorescent collagen cross-links and decreased micro-permeability at the resin-dentin interface. Collagen auto-fluorescence is a useful tool to detect auto-fluorescent exogenous cross links and their potential impact on the quality of the resin-dentin interface. Keywords: dentin, collagen fluorescence, proanthocyanidins, dental adhesives, permeability

Purpose: To evaluate the effects of aqueous storage on shear bond strength (SBS) and monomer release of fiberreinforced composites (FRCs). Materials and Methods: Four unidirectional FRCs were tested, including one semi-interpenetrating polymer network (IPN) (ES, everStick) and three cross-linked polymer (CLP) FRCs (GT, GrandTec; TF, TenderFiber; DP, Dentapreg). The SBS of samples of original resin to fresh FRC with an intact oxygen inhibition layer (n = 30/group) and repair resin to FRC after surface treatment (n = 30/group) was evaluated after 6 and 12 months of storage in artificial saliva. Monomer release of polymerized resin-coated and uncoated FRCs was detected by high-performance liquid chromatography after immersion for 1 h, 1 day, and 7 days. Results: After 6 months, a significant decrease in SBS was seen with ES-repair (p < 0.0001). After 12 months, significant decreases were seen with ES-original (p < 0.0001), ES-repair (p < 0.0001), and TF-repair (p = 0.0003). A significant reduction was also found for GT-original (p = 0.0254) and GT-repair (p = 0.0176). At 6 and 12 months, GT showed the highest SBS values, with DP-repair being statistically similar to GT at 12 months. For UDMA and bis- GMA, the greatest amounts of release were seen in uncoated specimens, followed by flowable resin-coated and viscous resin-coated specimens. Conclusion: Matrix composition, interfacial bonding, and resin coverage seem to account for differences in the aging behavior of FRCs. The semi-IPN material is likely to suffer most from the challenging oral conditions. CLP FRCs might be more stable over the long term. Coverage of FRCs with viscous resin is highly recommended to reduce residual monomer release. Keywords: fiber-reinforced composites, aging, artificial saliva, aqueous solvent, shear bond strength, residual monomer release

Purpose: To evaluate the effect of a silicone disclosing procedure performed at different timepoints on the shear bond strength (SBS) of cements (self-adhesive composite cement, self-etch composite cement, resin-reinforced glass-ionomer cement) to different substrates (zirconia, lithium disilicate, bovine dentin). Materials and Methods: The substrate/cement combinations were assigned to two groups (n = 15) according to the timepoint, at which the vinyl polyether silicone disclosing agent was applied: after (experimental groups, EXP) or before (control groups, CTRL) specific micromechanical treatments of the substrate surface. To increase standardization, the cements were applied into rubber rings (2.2 mm diameter x 1.0 mm thickness) positioned on the substrate surface. After luting procedures, all specimens were stored in 37°C distilled water for 24 h, then subjected to SBS testing using a wire loop of 0.2 mm diameter at a crosshead speed of 1 mm/min until failure. Failure analysis was performed for all tested specimens. SBS data were submitted to Weibull analysis. Results: The silicone disclosing procedure performed after micromechanical surface treatment reduced the characteristic shear bond strength to zirconia and lithium disilicate when compared to CTRL. However, for dentin specimens, there was no significant difference between CTRL and EXP for any of the cements investigated. Failure analysis showed a predominance of interfacial failures. Conclusion: The silicone disclosing procedure performed after the micromechanical treatment of ceramic surfaces negatively affected the cement bond strength. Therefore, after using it to check the fit of a prosthesis, clinicians should carefully clean the ceramic surface. Keywords: dentin bond strength, luting, disclosing material, shear bond strength, Weibull analysis