Rebonding strength of orthodontic brackets

Abstract

Clinicans have been advised to replace failing orthodontic brackets by repeating the original bonding procedure. However, the rebonding of a bracket to a resin-covered enamel may be different. The purpose of this study has been to examine systematically the parameters that control brackets rebonding and to compare rebonding procedures and determine the proper method for achieving optimal rebond strength. One hundred extracted human bicuspids were cleaned and mounted in resin bases. The buccal surface was etched and a bicuspid bracket was bonded. The strength of the bonded brackets were determined by shear stressing them in an Instron machine. A mean shear strength of 1657.8 [plus or minus] 289.4 P.S.I. was registered. Samples were divided into five groups. Group A: teeth were contaminated with saliva then washed with water and dried. A new bracket was bonded to the site; Group B; after salivary contamination, teeth were washed followed by pumicing with a bristle brush. A new bracket was bonded to the site; Group C: the resin was partially removed with a sand paper disc and a new bracket was bonded; Group D: the resin was totally removed with a disc. The surface was re-etched and a new bracket bonded; Group E: the resin was totally removed with a carbide bur. The surface was re-etched and a new bracket bonded. Analyses of the data revealed that the strength of the rebonded bracket may depend on the procedures used to prepare the surface. The mean rebond strength of the five groups were: Group A: 1208.9 [plus or minus] 410.5 P.S.I., Group B: 1663 [plus or minus] 342 P.S.I., Group C: 1573.6 [plus or minus]342 P.S.I., Group D: 1652.6 [plus or minus] 289.6 P.S.I., Group∴E: 1650 [plus or minus] 368.4 P.S.I.. The results indicate that the rebonding strengths obtained by procedure A were significantly weaker (P [less than] 0.1) whereas the rebonding procedures used in groups B, C, D E provided bond strengths equal to the initial bonding values.