Shearing strengths of recycled direct-bonding brackets.

One hundred twenty freshly extracted human incisor teeth were bonded with several different brands of direct-bonding brackets and tested for retention prior to and after recycling of the brackets by two different commercially available methods. Measurements of shearing strengths were performed to observe any possible changes in the retentive properties of the brackets. The teeth were preconditioned by the application of adhesive material, followed by scaling and pumicing to remove any visible signs of composite. After bonding of the teeth and recording of retentive strengths, the brackets were recycled and the same teeth (after scaling and pumice) were rebonded and tested once more. A decrease in retentive strength was noted in all types of recycled brackets. One type of bracket showed a statistically significant change in strength, depending on the process used in recycling, while the other brackets did not show any difference between the two processes. A control consisting of twenty teeth bonded only once and twenty teeth bonded several times showed no statistically significant change in retention of brackets.