Shear bond strength comparison between direct and indirect bonded orthodontic brackets.

The purpose of this study was to compare the shear bond strength of orthodontic brackets bonded to teeth with either an indirect bonding technique and a new adhesive resin or a direct bonding technique and a light-activated adhesive. Fifty-four extracted premolars were mounted in acrylic blocks and randomly divided into 2 groups (n = 27). In one group, orthodontic brackets were bonded to premolars with an indirect bonding adhesive system; in the other, brackets were bonded with the direct method. Seventy-two hours later, the brackets were placed in a testing machine and subjected to a shear force with a crosshead speed of 1 mm/minute. The mean shear bond strengths for the indirect and direct groups were 11.2 and 10.9 MPa, respectively, both exceeding the minimum shear bond strength range of 5.9 to 7.8 MPa often cited in the literature for clinical success. Data were analyzed with Student t tests. No significant difference in shear bond strength between the 2 groups was detected (P =.76). Resin remnants on orthodontic bracket pads were observed with a dissecting microscope at 30x magnification and scored with a modified adhesive remnant index. There was no significant difference between groups (P >.05). There was also no correlation between shear bond strength and the percentage of adhesive resin remnants left on the orthodontic bracket. Under the conditions of this study, no evidence suggests a difference in shear bond strength of orthodontic brackets bonded to tooth enamel, whether they are bonded with the direct or indirect technique.