The changes in shear bond strength due to repeated bonding - an in vitro study

Orthodontist face a range of problems during treatment, one commonly being bracket failure. The reason for this occurrence is usually either because of the patient's inadvertently applying improper forces to the bracket or of a poor bonding technique. As a result of this a significant amount of precious clinical time is wasted in rebonding brackets in a busy orthodontic practice. This study evaluates the effect of repeated bonding on the shear bond strength of orthodontic brackets. Thirty freshly extracted human premolars were collected and stored in a solution of 0.1% (wt/vol) thymol. The teeth were cleaned, polished, and etched with a 37% phosphoric acid gel. The brackets were bonded with the adhesive and light cured for 40 seconds. The teeth were sequentially bonded and debonded 3 times with the same composite orthodontic adhesive. The results of the analysis of variance comparing the shear bond strength at the 3 debonding attempts indicated that, the highest values for shear bond strength were obtained after the initial bonding. Rebonded teeth have considerably lower and inconsistent shear bond strength. The shear bond strength after two debonding procedures significantly decreased, but was still above the recommended required bond strength.