[Resin adhesion to the ground enamel. Influence of the ground depths of the enamel and etching times (1)].

The purpose of this study was to investigate the influence of the ground depths of the enamel and etching times on the adhesion of the resin on the ground enamel. Seventy-five extracted and frozen bovine mandibular young permanent incisors were used. The etchant used in this study was 40% phospholic acid gel and the etching times were 0, 10, 20, 30 and 60 seconds. All of the specimens were washed with an air water spray for 30 seconds after etching. The bonding agent and composite resin used in this study were Photo Bond and Photo Clearfil A (Kuraray Co.). Shear bond strengths to the outer enamel layers and inner enamel layers of the same teeth were measured. After the shear bond strength test, all the test surfaces of the enamel and resin specimens were observed using the SEM. The following conclusions were obtained. 1) The etching times which showed the highest bond strength were 20 seconds on the outer enamel layers (bond strength: 35.25 +/- 6.60 MPa) and 30 seconds on the inner enamel layers (bond strength: 40.15 +/- 6.59 MPa). 2) When the enamel was etched with all of the etching times, the bond strengths were significantly higher than those of the enamel without etching on the outer and inner enamel layers. 3) In the etched groups, significant differences between the bond strengths were not obtained among the different etching times on the outer and inner enamel layers. 4) In the comparison of the bond strengths between the outer enamel layers and the inner enamel layers, the bond strengths of the inner enamel layer were higher than those of the outer enamel layer with 0, 10, 30 and 60 seconds of etching times. However, a significant difference between the bond strengths was obtained only in the cases with 30 seconds of etching time. 5) In the etched groups, such a tendency toward a higher bond strength was observed in cases which showed poor enamel prism structures and poor resin tags, and resin widely adhered on the enamel surface. 6) Thirty seconds is a sufficient time for etching on the ground young permanent enamel using Photo Bond and Photo Clearfil A.