EFFECT OF VARYING ETCHING TIMES ON THE BOND STRENGTH OF CERAMIC BRACKETS

Damage to the enamel surface when debonding orthodontic ceramic bracke ts has been a clinical concern. Ideally, bond failure at the bracket-a dhesive interface should occur without damaging the enamel surface. Th e purpose of this study was to determine the shear bond strength and d ebonding failure modes of ceramic brackets with varying etching times. Sixty freshly extracted human premolars were pumiced and divided into six groups of 10 teeth. Each group was assigned an etching time inter val of either 30, 20, 15, 10, 5, or 0 seconds with 37% phosphoric acid . Ceramic orthodontic brackets were bonded to each etched tooth by usi ng the same orthodontic bonding system. The teeth were mounted in phen olic rings and stored in deionized water at 37 degrees C for 48 hours. A Zwick universal testing machine (Zwick GmbH and Co., Ulm, Germany) was used to determine shear bond strengths. The residual adhesive on t he enamel surface was evaluated with the Adhesive Remnant Index. The r esults of the analysis of variance indicated that there were significa nt differences in bond strengths between the various etching times (p = 0.0001). The Duncan multiple range test revealed that the Ei-second and no etch group exhibited significantly lower bond strengths. The re sults of the Chi square test evaluating the residual adhesives on the enamel surfaces also revealed significant differences (p = 0.0001). Ho wever, when the 5- and 0-second groups were dropped from the test, the Chi square test revealed no significant differences between the 30-, 20-, 15-, and 10-second groups (p = 0.211). In conclusion, decreasing etching time between 30 and 10 seconds does not significantly affect e ither bond strength or the site of bond failure.