In vitro torque-deformation characteristics of orthodontic polycarbonate brackets.

The purpose of this study was to investigate the torque-deformation characteristics of the following four types of polycarbonate brackets: (1) pure polycarbonate, PPC (anterior Miura, RMO, Denver, Colo.), (2) ceramic reinforced polycarbonate, CRPC (Silkon bracket, American, Sheboygan, Wis.), (3) metal slot reinforced polycarbonate, MRPC (Plastic bracket, Tella Tech, Miami, Fla.), and (4) metal slot and ceramic reinforced polycarbonate, MCRPC (Spirit, Ormco, Glendora, Calif.). A stainless steel bracket, (Mini Diamond, Ormco, Glendora, Calif.), was used as a control. Ten brackets of each type were tested. Each bracket was bonded to a porcelain tooth and engaged in a torquemeter. The tooth-bracket assembly was made stationary by embeding it in die stone. Torsion was applied to the bracket at 4° per minute and the resultant torque (grams·centimeters) and deformation (degree) were measured. For optimum labiolingual tooth movement for a maxillary incisor at 175 grams·centimeters, the amount of angular dellection necessary for the different polycarbonate brackets was the following: (a) 15° for MRPC, (b) 17° for MCRPC, (c) 24° for CRPC, and (d)>30° for PPC. The amount of deformation at this deflection was the least for MRCP followed by MCRPC, CRCP, and PPC. When compared with the stainless steel bracket, all polycarbonate brackets showed significantly ( p p