A modified direct technique versus conventional direct placement of brackets: in vitro bond strength comparison

Bond strength and failure location were evaluated in vitro for two methods of direct bracket bonding. Sixty human premolars were divided into two groups of 30 each. In group I the brackets were bonded with a two-paste adhesive by using the conventional direct method. In group II brackets were bonded with a newly developed modified direct technique. During the modified direct technique, unfilled resin catalyst liquid was applied to a bracket, which had a coating of hardened composite cured against a dental anatomic matrix (tooth). After the acid-etched tooth was coated with unfilled resin base liquid, the bracket was placed. Mixed unfilled resin liquid (sealant) was then placed at the periphery of the bracket/tooth interface. Thus the major modification of the direct technique would entail fabrication by the manufacturer of a bracket with prehardened bis-GMA composite resin on its backing. Bond strengths were 155.2 (SD = 35.7) and 140.6 (SD = 30.1) kg/cm2 for conventional and modified techniques, respectively. With the conventional method, failure occurred mainly at the tooth/composite interface. Failure seen with the modified technique was mixed, but the major mode was composite/bracket. Therefore this modified bonding method promises similar bond strengths and some advantages over the conventional method including, elimination of composite flash from around the brackets, ample working time, consistent adhesive thickness, and reduction of porosity.