Effect of different concentrations and types of bleaching on the micro tensile bond strength to enamel, directly after bleaching, with and without sodium ascorbate: microtensile bond strenght

Description :

Aim: the purpose of the current research is to conduct an in vitro study to evaluate the neutralizing effect of 10% sodium ascorbate on the micro tensile bond strength of composite to enamel after bleaching with different concentrations and types of bleaching agents. Materials and methods: seventy-two human incisors, free from carious lesions, cracks, fractures or restorations, were extracted for periodontal reasons then cleaned with periodontal curettes and ultrasound to remove any residual tissue tags then pumiced and washed under running tap water. They were then stored in a solution of 0.1% thymol. A flexible diamond disc attached to a handpiece was used to cut the roots from the teeth 2mm apically to the cement-enamel junction. The teeth were then randomly divided into 9 groups (n=8): - Group 1: control group, no treatment. Specimens were not bleached and bonded with composite resin. - Group 2: specimens were bleached with 5% carbamide peroxide (white dental beauty) and immediately bonded with composite resin. - Groupe 3: specimens were bleached with 5% carbamide peroxide, treated with 10% sodium ascorbate and immediately bonded with composite resin. - Group 4: specimens were bleached with 10% carbamide peroxide (white dental beauty) and immediately bonded with composite resin. - Group 5: specimens were bleached with 10% carbamide peroxide, treated with 10% sodium ascorbate and immediately bonded with composite resin. - Group 6: specimens were bleached with 16% carbamide peroxide and immediately bonded with composite resin. - Group 7: specimens were bleached with 16% carbamide peroxide, treated with 10% sodium ascorbate and immediately bonded with composite resin. - Group 8: specimens were bleached with 6% hydrogen peroxide and immediately bonded with composite resin. - Group 9: specimens were bleached with 6% hydrogen peroxide, treated with 10% sodium ascorbate and immediately bonded with composite resin. Bleaching procedure: the home bleaching solutions of 5% 10% 16% carbamide peroxide and 6% hydrogen peroxide (white dental beauty, style italiano) were applied to the enamel surfaces for 30 minutes (6% HP), 60 minutes (16%CP), 2-4 hours (10% CP) and 2 hours (5%CP) per day for 2 weeks according to the manufacturer’s instructions. Application of sodium ascorbate gel: a solution containing 10% sodium ascorbate was prepared and applied to the enamel slabs for 10min following the bleaching process. The specimens were then rinsed with distilled water and dried with compressed air. Bonding procedure: the enamel surfaces was dried and etched with 35% phosphoric acid gel for 30s. Then the substrate was rinsed again for 10s and dried with compressed air spray. Two layers of bond adhesive (single bon, 3M Espe, St Paul, MN, USA) were applied to the enamel. We applied the resin composite (z250, 3M Espe, St Paul, MN, USA) into 2 layers of 2 mm each one and we polymerized using LED for 20s on each layer. The samples were cut to obtain sticks shape. Micro tensile bond strengths of the samples were analysed in a universal test machine at a crosshead speed of 1mm/min. The load required to dislodge each slab were recorded in MPa.