COMPARISONS OF SHEAR BOND STRENGTH OF PRECOATED AND UNCOATED BRACKETS

In an attempt to save chairside time during bonding, orthodontists are using ceramic and metal brackets that have been precoated with the ad hesive material. The adhesive used on the precoated brackets is simila r in composition to that used for bonding uncoated brackets; the diffe rence is essentially in the percentages of the various ingredients inc orporated in the material. The purpose of this study is to determine w hether these changes in composition affect the shear bond strength and the site of bond failure when precoated and uncoated ceramic and meta l brackets are used. Eighty-five recently extracted human molars were bonded according to the manufacturer's instructions and mounted in phe nolic rings. An occlusogingival load was applied to the bracket, produ cing a shear force at the bracket-tooth interface with a Zwick Univers al Test Machine. After debonding, all teeth and brackets were examined under 10x magnification. Any adhesive remaining after bracket removal was assessed with the Adhesive Remnant Index (ARI). The current findi ngs indicated that: (1) Precoated ceramic brackets that used a slightl y modified adhesive have similar shear bond strengths as that provided by Transbond XT adhesive on uncoated brackets; (2) precoated metal br ackets that used the same adhesive have significantly lower shear bond strength than those obtained with Transbond XT on uncoated brackets. The differences in the bond strength between the ceramic and metal bra ckets were attributed to the combined effects of the changes in the co mposition of the adhesives used and in the retention mechanisms incorp orated in the bracket bases of the different types of brackets; (3) al l bracket/adhesive combinations tested provided clinically acceptable shear bond forces.