COMPOSITE RESIN BOND STRENGTH AFTER ENAMEL BLEACHING

This study evaluated the effect of enamel bleaching with a commercial product on the sheer bond strength of a composite resin. A total of 45 human extracted permanent molars were used. A flat enamel surface was obtained with 600-grit SiC paper. The teeth were then randomly distri buted into three groups of 15 teeth each: Group 1: Enamel etching with 37% phosphoric acid gel (Coe) for 60 seconds, placement of an unfille d resin (Coe) thinly applied with a brush and a composite resin (Occlu sin); Group 2: Enamel bleaching (Rembrandt Lighten Bleaching Gel, Den- Mat) for one hour, etching for 60 seconds and placement of unfilled an d composite resins. Group 3: Enamel bleaching for 24 hours, etching fo r 60 seconds, and placement of unfilled and composite resins. A nylon ring over the etched enamel retained the composite resin. The teeth we re thermocycled (X100) and sheared with a knife-edged blade in an Inst ron machine running at a cross-head speed of 1 mm/min. The results in MPa were: Group 1: 12.86 +/- 4.83, Group 2: 12.33 +/- 2.95, and Group 3: 7.67 +/- 1.98. An ANOVA revealed that Groups 1 and 2 were significa ntly different from Group 3 (P < 0.001). Fracture within the enamel oc curred in 53% in Group 1, 33% in Group 2, and 0% in Group 3. The study reveals that the shear bond strength of composite resins is significa ntly reduced after enamel bleaching for 24 hours.