Evaluation of shear bond strength with different enamel pre-treatments

The purpose of this study was to investigate the shear bond strengths of two adhesives, Panavia-21 and a composite resin (Transbond XT), with different enamel pre-treatments, acid etching (37 per cent phosphoric acid) and grit blasting (50 microm aluminium oxide particles). The mode of bond failure was also assessed using the modified adhesive remnant index (ARI). Ninety freshly extracted non-carious human premolar teeth were randomly divided into the following groups: (1) Transbond XT, acid-etched enamel surface; (2) Panavia-21, acid-etched enamel surface; (3) Transbond XT, grit-blasted enamel surface; (4) Panavia-21, grit-blasted enamel surface; (5) Transbond XT, acid-etched enamel surface with grit-blasted brackets; (6) Panavia-21, acid-etched enamel surface with grit-blasted brackets. All groups had stainless steel brackets bonded to the buccal surface of each tooth. An Instron universal testing machine was used to determine the shear bond strengths at a crosshead speed of 0.5 mm/second. Statistical analysis was undertaken using analysis of variance and the Tukey test. The mean bond strength values were as follows: group 1, 135.7 +/- 23.0 N; group 2, 181.5 +/- 18.4 N; group 3, 38.4 +/- 27.5 N; group 4, 59.1 +/- 24.1 N; group 5, 106.7 +/- 21.5 N; group 6, 165.3 +/- 21.4 N. Panavia-21 with the acid-etched enamel surface had a significantly higher shear bond strength than the other groups (P < 0.001). This was followed by the composite group with the acid-etched enamel surface. This group differed significantly from the composite and Panavia-21 groups with the grit-blasted tooth surface (P < 0.001) and from the composite and Panavia-21 groups with the acid-etched enamel surface and grit-blasted brackets (P < 0.01). The current findings indicate that Panavia-21 is an excellent adhesive and produces a bond strength that is clinically useful. Enamel surface preparation using grit blasting alone results in a significantly lower bond strength and should not be advocated for clinical use.