FRACTURE-RESISTANCE OF CERAMIC BRACKETS DURING ARCH WIRE TORSION

The purpose of this study was to determine the fracture resistance of commercially available ceramic brackets during arch wire torsion. Lingual root torque was applied at the distal side of upper central incisor brackets with 0.022-inch slots by means of a 0.0215 x 0.028-inch arch wire. A specially designed apparatus was used to test six types of ceramic bracket in sample groups of 30. The amount of torque and degrees of torsional rotation at fracture were measured. The ceramic brackets could be separated into three statistically different groups with mean torques at fracture ranging from 3,706 to 6,177 gm-mm. The mean torsional rotation at fracture ranged from 9.5-degrees to 17.8-degrees. The single-crystal alumina bracket had the most intragroup variation. Eight to ten degrees of torsional rotation of the arch wire produced sufficient orthodontic force to achieve the torque. The fracture resistance of the ceramic brackets appears to be adequate for clinical use. The Starfire, Allure III, and Transcend brackets had the highest fracture resistance values.