Shear strength of brackets bonded to anterior and posterior teeth

A study was undertaken to determine the maximum shear strength of brackets bonded to anterior and posterior teeth. Brackets were bonded to two groups comprising 12 incisor and 12 molar teeth. After storage in water at 37 degrees C for 10 days, each bracket was tested to failure in a shear mode in a Instron machine. The mean value for the incisors was 164.3 +/- 35.1 kg/cm2 (16.1 +/- 3.4 MPa) and 115.7 +/- 41.1 kg/cm2 (11 +/- 4.0 MPa) for molars. These values, analyzed in a two-tailed test, were statistically different at the 0.01 level of confidence. It was concluded that differences in etching patterns do not necessarily affect shear bond strength and that the predominantly weak link in the bonding chain was at the bracket/resin interface. The lower values for molar teeth may relate to adaptation of the bracket and nonuniform resin thickness.