Effect of Bleaching on Shear Bond Strength of Composite Resins to Bovine Enamel Using Three Bonding Agents

In many studies reduction in bond strength of bleached enamel has been pointed out. The decrease in bond strength raised concern in cosmetic dentistry. However, there is little information about the effects of bleaching, on reduction of enamel bond strength in new bonding systems. This study aimed to investigate the effects of three dental bonding agents on shear bond strength of a composite to bleached enamel. In this in vitro study, sixty intact bovine mandibular incisors were collected and randomly divided into six groups (n=10). In group A, the facial enamel was etched with 35% phosphoric acid gel, then a single layer of bonding agent (SingleBond, 3M, ESPE) was applied and light-cured for 40 seconds by a light-curing device (ColtoluxII colten) with 400 mw/cm²light intensity according to the manufacturer’s instructions. In group B: after etching of enamel surfaces, Clearfil SE-Bond (Kuraray Medical Inc.) was used. In group C: after etching of enamel surface, Clearfil S3 Bond (Kuraray, Medical Inc.) was used. In groups D, E, and F 35% carbamide peroxide (Opalescence, Ultradent Products Inc.) was applied on the enamel surfaces for 5 hours according to the manufacturer’s recommendations. Afterwards the specimens were rinsed thoroughly with distilled water for 60 seconds and dried with compressed air. Immediately after bleaching, bonding regimes similar to groups A, B, and C were carried out in groups D, E, and F, respectively. Then, cylinders of hybrid composite were bonded to the facial enamel surface of all specimens, using 3 dental bonding agents. After 24 hours, the specimens were ther mo cycled (5–55°C, 1000cycles), and then subjected to shear bond testing by a universal machine Zwick (Zo20, Germany). The data were analyzed by one- and two-way ANOVA and post hoc tests. All statistical tests were performed with SPSS version 11. The mean shear bond strength of SingleBond to bleached and unbleached enamel was 8.36 ± 3.30 and 20.17 ± 6.52 MPa, respectively. For Clearfil SE bond, bleached enamel exhibited bond strengths of 12.25 ± 6.61Mpa and unbleached enamel exhibited a bond strength value of 17.66 ± 5.82 Mpa. The bond strength for Clearfil S3 bond was 6.66 ± 2.57 Mpa to bleached and10.40 ± 3.65Mpa to unbleached enamel. Shear bond strength of hybrid composite to bleached enamel in three experimental groups decreased but this reduction was not statistically significant for Clearfil SE bond.