Statistical evaluation of torque angles in reference to straight-wire appliance (SWA) theories

Inconsistency in torque data on diverse straight-wire appliance (SWA) attachments calls for reassessment of the SWA theories. This study evaluates the SWA theories and suggests predictive torque models. A custom-made torque angle gauge was used on models from 54 ideal occlusion subjects (34 orthodontically treated and 20 untreated cases). This study is in close agreement with Andrews' mean torque values except those for the upper incisors. No agreement is found with Ricketts' torque data. A SD of +/- 5 degrees is characteristic for all teeth. Therefore, the maximal arch wire in a 0.018-inch slot that will not produce deleterious effects is 0.016 X 0.022 inches using Andrews' data and 0.016 X 0.016 inches with Ricketts' data. Neither the setup procedure nor the morphometric parameters predict individual torque data. Intertooth torque correlations indicate that the first premolar in each arch is the tooth of choice for predictive purposes, with unpredictability in the upper arch. Intertooth torque correlations demonstrate a systematic arrangement defined as follows: (1) a lower torque value for a known tooth indicates a lower value for a predicted tooth, (2) neighboring teeth show the strongest coefficient of correlation, and (3) intertooth torque correlations are ranked according to dental fields, showing a similar genetic pattern to tooth morphology.