Shear, torsional, and tensile bond strengths of ceramic brackets using three adhesive filler concentrations

The effect of changes in adhesive filler concentration on the shear, torsional, and tensile bond strength of a chemical, a mechanical, and a chemical/mechanical retained ceramic bracket was evaluated. Two hundred ten bovine teeth were bonded with one of three ceramic brackets using a 30%, 55%, or 80% filled adhesive. The brackets were debonded with a shear, torsional, or tensile force to test the bond strength and the site of bond failure. No significant difference was found in the shear, torsional, or tensile bond strength of each ceramic bracket type in relation to changes in the adhesive filler concentration. However, there was a trend toward increased bond strength with increasing filler concentration. Combining the data according to adhesive type revealed that the 80% filled adhesive displayed a significantly greater shear bond strength than the 30% or 55% filled adhesive and a greater torsional bond strength than the 30% filled adhesive. This supports the hypothesis of increased bond strength with increased adhesive filler concentration. The mechanically retained ceramic bracket showed greater shear bond strength and maximum shear bond strength in torsion than the chemical or chemical/mechanical retained ceramic bracket. The tensile bond strength of the mechanically retained ceramic bracket was similar to that of metal brackets reported in other studies, and the failure site was at the bracket-adhesive interface.