Objective: The purpose of this study was to develop a new method to change a bracket position without debonding the metal bracket that was bonded with a polymethyl methacrylate (PMMA) orthodontic adhesive resin by using an ultrasonic device. Materials and Methods: An originally designed scaler tip was developed for a piezoelectric ultrasonic scaler. The adhesive turned to melting state by thermal heat that was generated by ultrasonic frictional heat. When the adhesive was in melting state, the bracket was rotated approximately 20° and held in this position until the adhesive hardened again by air cooling. Shear bond strengths were measured on each sample in the control and the repositioning groups. To evaluate the thermal effects of the increased temperature on the enamel surface and pulpal cavity, extracted human lower premolars were monitored during the repositioning time. Results: The time required for the repositioning procedures was approximately 7 s. The temperature of the enamel surface increased by 53°C and the pulpal wall increased by 0.5°C during the repositioning procedures. The bonding strength showed no significant difference between the control and repositioning groups. Conclusion: This method for bracket repositioning without debonding using an ultrasonic device proved to be a new method for bracket repositioning.

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