Effect of the transpalatal arch during extraction treatment.

INTRODUCTION The transpalatal arch (TPA) can be used as an adjunct during orthodontic treatment to help control the movement of the maxillary first molars in 3 dimensions, including producing molar rotation and uprighting, maintaining transverse dimensions posteriorly during treatment, and maintaining leeway spaces during the transition of the dentition. The purpose of this retrospective cephalometric study was to test an additional function of the TPA: its ability to enhance orthodontic anchorage during extraction treatment. METHODS Records consisting of pretreatment and posttreatment cephalograms were gathered from several orthodontic practices that used an .018 x .025-in preangulated appliance. All patients were white and had 4 first premolars extracted as part of their treatment protocol. Patients were treated either with or without a TPA of the soldered Goshgarian design. Patients were excluded if headgear or any other auxiliary anchorage device beside the TPA was used during treatment. Matched samples of 30 patients were identified based on sex, age at the start of treatment, treatment duration, and cervical vertebral maturation stage. Statistical comparisons were made with nonparametric statistical tests. RESULTS Analysis of the changes from pretreatment to posttreatment for the TPA and the no-TPA groups showed no statistically significant differences in any of the variables examined. The net difference for both vertical and mesial movement of the maxillary first molar in relation to the maxilla between the 2 groups was 0.4 mm, with the no-TPA group in a more downward and forward position. CONCLUSIONS Although the usefulness of the TPA for the abovementioned functions is not negated, it does not provide a significant effect on either the anteroposterior or the vertical position of the maxillary first molars during extraction treatment.