Resin adhesion to the primary enamel: influence of light-irradiation times.

The purpose of this study was to investigate the influence of the light-irradiation times to the bonding agent and the composite resin on resin adhesion to the primary enamel. One hundred bovine mandibular ground primary incisors were used. Materials used in this study were 40% phosphoric acid gel, Photo Bond and Photo Clearfil A (Kuraray Co., Kurashiki, Japan). The etching time was 30 seconds. The light-irradiation times for the bonding agent were 10, 20 and 30 seconds and the light-irradiation times for the composite resin were 20, 40 and 60 seconds. Specimens were divided into the non-thermal cycled groups and the thermal cycled groups. Shear bond strengths were tested. After the shear bond strength test. the test surfaces of the enamel and the resin specimens were observed using the SEM. The optimum light-irradiation time on the bonding agent was 10 seconds. Both in the non-thermal cycled group and the thermal cycled group, the light irradiation time on the composite resin which showed the significantly higher bond strength was 40 seconds. Higher bond strength was not always obtained with the longer light-irradiation time on the bonding agent and the composite resin.