Comparison of initial shear bond strengths of plastic and metal brackets.

The aims of this study were to compare initial and 24 hour shear bond strengths of plastic brackets with a mechanical base (Spirit MB) and metal brackets, using two different adhesives (System 1+ and Enlight), and to examine the modes of failure after debonding. Eighty extracted human premolars were used. After bonding, shear bond strengths in half the sample were tested within 30 minutes. The remaining 50 per cent were placed in a 37 degrees C distilled water bath for 24 hours before testing. The results showed that the effects of the two adhesives and the interaction of the two time intervals and the two bracket types on shear bond strength were significantly different (P < 0.05 and P < 0.0001, respectively). Six of the 10 groups were found to have less than 50 per cent of the adhesive remaining on the tooth surface after debonding in the 24 hour metal bracket-System 1+ group, but most specimens in the other seven groups had more than 50 per cent of the adhesive left. It is concluded that System 1+ cannot provide sufficient initial bond strengthfor Spirit MB and may increase the risk of enamel fracture for metal brackets.