Abstract
The purpose of this study was to investigate the influence of the light-irradiation times on the adhesion of the resin on primary ground enamel.
Labial surfaces of 60 extracted and frozen bovine mandibular primary incisors were used. The bonding agent and composite resin used in this study were Photo Bond and US shade color Photo Clearfil A (Kuraray Co. ). The etchant used in this study was 40% phospholic acid gel and the etching time was 30 seconds. Light-irradiation time for the bonding agent was 10 seconds and the light-irradiation times for the composite resin were 20,40 and 60 seconds. Specimens were divided into the non-thermal cycled group and the thermal cycled group. In the thermal cycled groups, thermal cycling tests consisting of water baths with 10,000 temparature cycles between 60°Cand 4°C were attempted. The shear bond strength was tested. After the shear bond strength test, the test surfaces of the enamel and the resin specimens were observed using the SEM.
The following conclusions were obtained.
1) Both in the non-thermal cycled group and the thermal cycled group, the lightirradiation time which showed the highest bond strength was 40 seconds (80.10±13.01 MPa,78.99±10.93 MPa).
2) Both in the non-thermal cycled group and the thermal cycled group, the bond strength with 40 seconds of light-irradiation was significantly higher than those with 20 and 60 seconds of light-irradiation time, and the bond strength with 60 seconds of light-irradiation was significantly higher than that with 20 seconds light-irradiation.
3) In the 20 second light-irradiation time, the bond strength with the thermal cycled group was significantly higher than that with the non-thermal cycled group.
4) Higher bond strength was not always obtained with the longer light-irradiation time.
5) In the 20 seconds of short light-irradiation time, fracture of the resin easily occurred on tne enamel by the shear strengtn and the bond strengtns were low.
