The purpose of this study was to investigate the influence of the light-irradiation times on the bonding agent on the adhesion of the resin to the 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 times for the bonding agent were 10,20 and 30 seconds and the light-irradiation time for the composite resin was 40 seconds. Specimens were divided into the non-thermal cycled groups and the thermal cycled groups. In the thermal cycled groups, thermal cycling tests consisting of water baths with 10,000 temparature cycles between 60°C and 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) In the non-thermal cycled groups, the bond strength with 10 seconds (80.10±13.01 MPa) of light-irradiation on the bonding agent was significantly higher than those with 20 (45.35±16.24 MPa) and 30 seconds (49.91±8.58 MPa)of light-irradiation times.
2) In the thermal cycled groups, the bond strength with 10 seconds (78.99±10.93 MPa) of light-irradiation on the bonding agent was significantly higher than that with 20 seconds (56.85±14.94 MPa) of light-irradiation time. However, there was no significant difference between the bond strength with 10seconds of light-irradiation and the bond strength with 30 seconds (67.31±16.78 MPa) of light-irradiation.
3) In the case of 30 seconds of light-irradiation time on the bonding agent, 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 on the bonding agent.
5) The optimum light-irradiation time on Photo Bond was 10 seconds.