Effect of the precrack preparation with an ultrasonic instrument on the ceramic bracket removal.

Background/purpose: In terms of fracture mechanics, a precrack preparation may facilitate the propagation of a break through the expected fracture plane during the bracket debonding process. The purpose of this study was to evaluate the effect of an ultrasonic precrack preparation on the debonding force and failure modes of ceramic bracket removal.

Methods: Eighty extracted premolars were assigned to four groups: Inspire, precrack Inspire, Clarity, and precrack Clarity groups, with each group containing 20 teeth. The precrack preparations were made at the mesial gingival line angle of Inspire brackets and on the mesial side of Clarity brackets with an ultrasonic tip. Debonding force, failure modes, and bracket breakage score were measured and recorded. Fracture surfaces after bracket debonding were observed with scanning electron microscopy (SEM).

Results: We found that the ultrasonic precrack preparation could significantly decrease the average debonding force and the mean bracket breakage scores of both kinds of ceramic brackets. After bracket debonding, 80% of brackets in the precrack Inspire group and 100% of brackets in the precrack Clarity group showed no bracket failure. However, only 25% of brackets in the Inspire group and 75% of brackets in the Clarity group showed no bracket failure. SEM micrographs showed a precrack notch at the adhesive resin after precrack preparation, and no enamel damage was noted after the bracket debonding.

Conclusion: The ultrasonic precrack preparation can significantly decrease the debonding force and may guide the bracket debonding through a favorable fracture plane without damage to either the bracket or the enamel.