Compromised bonding to bleached enamel can be reversed with sodium ascorbate as an antioxidant. This study evaluated the effect of hydrogel and solution of sodium ascorbate on enamel-resin composite shear bond strength after bleaching. Sixty buccal enamel surfaces obtained from human, sound third molars were randomly divided into 4 groups (n=15). Enamel surfaces were subjected to different treatments: 1) bleaching (10% carbamide peroxide gel); 2) bleaching + 10% sodium ascorbate solution; 3) bleaching + 10% sodium ascorbate hydrogel and 4) bleaching + 20% sodium ascorbate hydrogel. The specimens were bonded with Single Bond and restored with a composite. The specimens were prepared for shear bond testing. The data was evaluated using ANOVA and Tukey tests. Bond strengths were significantly increased following hydrogel and solution of sodium ascorbate treatments (p<0.05). Also, there was no significant difference among the different forms of sodium ascorbate preparations.

Based on the results of this study, Er, Cr: YSGG laser was confirmed to be as effective as air-abrasion for laboratory composite repair.

Bleaching significantly decreased the bracket bond strength. Compromised bonding was reversed with a three-hour application of both forms of SA.

Aim: Adhesion of composite resin and pulp capping biomaterials remarkably influences treatment outcomes. This in vitro study aimed to compare the shear bond strength of composite resin to calcium enriched mixture (CEM) cement, mineral trioxide aggregate (MTA) and resin modified glass ionomer (RMGI) with or without acid etching. Materials and methods:A total of 90 cylindrical acrylic blocks containing a central hole, measuring 4 mm diameter and 2 mm height were prepared. The blocks were randomly divided into three experimental groups based on being filled with CEM, MTA or RMGI. Samples in each group were then randomly divided into two subgroups, i.e. with or without phosphoric acid etching. Placing composite resin cylinders on the samples, shear bond strengths were measured using a universal testing machine. Failure modes of the samples were evaluated under a stereomicroscope. Data were analyzed using two-way ANOVA and Tukey tests.Results: Shear bond strengths in the etched and nonetched samples were not significantly different (p = 0.60). There was a significant difference in shear bond strength values of the three experimental materials (p < 0.001) and RMGI showed the highest strength values (p < 0.001); no significant difference was observed between MTA and CEM (p = 0.51). The interaction of the type of material and surface etching was statistically significant (p < 0.001). All of the samples showed cohesive failure mode. Conclusion:Acid etching of MTA, CEM and RMGI do not improve the shear bond strength of these materials to composite resin. Besides, shear bond strength values of MTA and CEM to composite resin, are favorable due to their cohesive mode of failure.Clinical significance: When MTA and CEM biomaterials are used in vital pulp therapy, it is advisable to cover these materials with RMGI. In addition, if it is not possible to use RMGI, the surface etching of MTA and CEM biomaterials is not necessary prior to composite restoration using total-etch adhesive resin.

BackgroundThe use of composites in dental restoration has been commonly criticized, due to their underwhelming mechanical properties. This problem may be solved partially by preheating. The present research aims to determine the effect of preheating on the mechanical properties of two different classes of composites. Material and Methods A Silorane-based (Silorane) and a Methacrylate-based (Z250) composite were preheated to different temperatures (25, 37, and 68 °C) and afterwards were tested with the appropriate devices for each testing protocol. The material’s flexural strength, elastic modulus, and Vickers microhardness were evaluated. Two-way ANOVA, and Tukey’s post hoc were used to analyze the data. Results Microhardness and elastic modulus increased with preheating, while flexural strength values did not increase significantly with preheating. Furthermore the methacrylate-based composite (Z250) showed higher values compared to the Silorane-based composite (Silorane) in all the tested properties. Conclusions Preheating Silorane enhances the composite’s microhardness and elastic modulus but does not affect its flexural strength. On the other hand, preheating Z250 increases its microhardness but does not change its flexural strength or elastic modulus. In addition, the Z250 composite shows higher microhardness and flexural strength than Silorane, but the elastic modulus values with preheating are similar. Therefore Z250 seems to have better mechanical properties making it the better choice in a clinical situation. Key words:Composite, elastic modulus, flexural strength, microhardness, preheating.

Objectives: The effect of 15% carbamide peroxide bleaching gel on color stability and surface topography of a giomer and a microfilled composite resin was evaluated in the present in vitro study. Study design: Forty discs measuring 10 mm in diameter and 1 mm in thickness were prepared from a giomer and a microfilled composite resin. Each material yielded 20 discs with completely smooth surfaces. Then a spectrophotometer was used to measure L* (lightness), a* (redness, greenness) and b* (blueness, yellowness) color coordinates of all the discs. Subsequently, the specimens were subjected to 15% carbamide peroxide bleaching gel. After measuring the color coordinates once again, color changes (ΔE*) were calculated by the CIELAB system. Six specimens from each material (three specimens before bleaching agent application and three specimens thereafter) were viewed under an atomic force microscope (AFM) for surface topography evaluation. Data were analyzed by Mann-Whitney U and Kruskal-Wallis tests at α=0.05. Results: There were no statistically significant differences in color changes (ΔE*) between the two materials (P>0.05). In addition, no significant differences were detected in surface roughness between composite resin and giomer discs before and after bleaching (P>0.05 for both). However, in both materials the differences in surface roughness were significant before and after bleaching procedures (P<0.001). Conclusions: Based on the results of the present study it was concluded that 15% carbamide peroxide does not induce clinically detectable color changes in composite resin and giomer despite an increase in surface roughness. Key words:Bleaching, color stability, giomer, microfilled composite.

This study compared the effects of two mechanical surface preparation techniques, air abrasion and Nd:YAG laser, with the use of two adhesive systems, self-etch and etch and rinse, on the repair bond strengths of an indirect composite resin. One hundred fifty cylindrical samples of an indirect composite resin were prepared and randomly divided into six groups (n = 25). In groups 1-3, the composite resin surfaces were respectively prepared as follows: no roughening, roughening by air abrasion, and roughening by Nd:YAG laser, followed by application of an etch-and-rinse adhesive. In groups 4-6, the preparation techniques were respectively the same as those in groups 1-3, followed by application of a self-etch adhesive. Subsequently, a direct composite resin was added and repair bond strengths were measured. Data were analyzed with two-way ANOVA and post hoc Tukey's test. Mean bond strength value was significant based on the preparation technique (P < 0.001), i.e., in air abrasion and Nd:YAG laser groups, bond strengths were significantly higher compared to no-preparation groups (P < 0.0005). There were significant differences in bond strength values between air abrasion and Nd:YAG laser groups, with significantly higher values in air abrasion groups (P < 0.0005). However, there were no significant differences in bond strength values between the adhesive systems. Furthermore, the cumulative effects of the adhesive system and the surface preparation technique were not significant. Surface preparation of the indirect composite resin with air abrasion and Nd:YAG laser resulted in a significant increase in the repair bond strength, with air abrasion being more effective. There were no significant differences in bond strength between the two adhesives.

The aim of this study was to compare the effects of solution and different sodium ascorbate hydrogels on dentin-resin composite shear bond strength subsequent to a bleaching procedure with 10% carbamide peroxide. Methods and Materials: Sixty buccal dentin surfaces obtained from intact human third molars were randomly divided into five groups (n=12). Dentin surfaces received different treatments: (1) no treatment; (2) bleaching (10% carbamide peroxide gel); (3) bleaching + 10% sodium ascorbate solution; (4) bleaching + 10% sodium ascorbate hydrogel, and (5) bleaching + 20% sodium ascorbate hydrogel. Dentin surfaces were bonded with Single Bond™ and restored with a composite (Z100). The samples were tested for shear bond strengths. Data was analyzed using analysis of variance (ANOVA) and Tukey tests. Results: Significantly higher bond strengths were observed subsequent to treatment with hydrogel and solution forms of sodium ascorbate (p<0.05). No significant differences were demonstrated between different forms of sodium ascorbate preparations. In addition, no significant differences were observed among groups with antioxidant treatment (Groups 3, 4, and 5) and Group 1 (no treatment). Conclusion: Reduced bond strength to bleached dentin can be amended by the use of sodium ascorbate as an antioxidant.