OBJECTIVETo study the effect of pre-restoration bleaching treatment on tensile strength of resin bonding agents to deep enamel and its duration, and to estimate the optimal timing of porcelain veneers bonding operation after bleaching treatment.

METHODSA total of 96 extracted human permanent teeth were allocated into 6 groups, 16 teeth for each. In 5 study groups, 80 teeth were bleached using 35% hydrogen peroxide activated by cold light. Right after bleaching and at 1, 4, 7, and 14 days after bleaching, the teeth were prepared with removal of 0.6 to 0.8 mm depth of enamel respectively. And then each study group was divided into two subgroups and bonded with resin bonding agents A (One-step plus) and B (Single bond). In the control group, 16 unbleached teeth were divided into two subgroups and bonded with the two bonding agents respectively. The tensile bonding strength was measured.

RESULTSThe tensile strength was [(17.79 +/- 3.53) and (19.41 +/- 3.37) MPa], [(17.50 +/- 4.29) and (19.66 +/- 3.48) MPa], and [(18.39 +/- 3.58) and (19.53 +/- 3.21) MPa] right after bleaching 0 day, 1 day, and 4 days, which were significantly smaller (about 30%) than that of the control group [(25.94 +/- 4.88) and (28.02 +/- 4.36) MPa] (P < 0.001). At 7 days after bleaching the tensile strength [(22.46 +/- 3.98) and (23.74 +/- 5.04) MPa] reached 87% and 85% of that in the control(P > 0.01). At 14 days after bleaching treatment, the strength [(26.03 +/- 4.47) and (27.88 +/- 4.78) MPa] reached the same level as that in the control (P > 0.01). There was no significant difference in bonding tensile strength between the two resin bonding agents.

CONCLUSIONSThe bonding strength of resin bonding agents to deep enamel was low during 2 weeks after bleaching treatment. It is suggested that porcelain veneer bonding operation should be performed till 2 weeks after bleaching treatment.