Shear bond strength of ceramic orthodontic brackets to enamel

The recent introduction of ceramic orthodontic brackets has generated interest among orthodontists. The aim of this investigation was to evaluate the in vitro shear bond strengths to enamel of four ceramic orthodontic brackets and one stainless steel bracket in trials with two separate acid-etching times for enamel. Eighty extracted human central incisors were prepared for bonding to Starfire, Allure, Transcend, Quasar, and stainless steel (in the control group) orthodontic bracket systems. Enamel etching times of 15 seconds and 60 seconds were used. There was a total of 10 groups. After acid etching, one coat of low-viscosity bonding agent was applied and the brackets were bonded to etched enamel with Concise orthodontic bonding resin. The bonded test specimens were stored in distilled water at 37° C for 14 days, after which they were thermocycled for 500 cycles (5° C to 60° C). The bonds were stressed to failure in an Instron machine at a crosshead speed of 0.02 inch per minute. The shear bond strengths were calculated and Weibull analysis was used to obtain a shape factor (the slope of the straight line and a measure of predictability) and the characteristic level (the 63.2% bond strength value of median rank on the straight line) for each group. Predictability and high bond strength, along with other factors, are important in the clinical selection of a bracket system. When either predictability or bond strength was considered independently, several bracket systems, coupled with a particular etch time, had either high predictability or high bond strength. The highest predictability and the highest bond strength were both found with the Allure bracket system.