Accuracy of dental arch form in customized fixed labial orthodontic appliances

Introduction: This study evaluated arch form accuracy with or without premolar extraction in customized fixed labial orthodontic appliance treatment. Methods: Setup and posttreatment digital models of 27 samples (15 extractions and 12 nonextractions) were selected and superimposed by best-fit surface-based registration in both the maxilla and the mandible. The facial axis points were identified and converted into Cartesian coordinates. A sixth-order polynomial equation was used to fit dental arches. Arch discrepancies (the mean distance between 2 arch forms) and similarities were compared between extraction and nonextraction groups, maxilla and mandible, and anterior and posterior arches. Results: The arch discrepancy between extraction and nonextraction groups showed no statistically significant difference, but a statistically significant difference in arch similarity was found in the mandible. There were statistically significant differences between anterior and posterior arch discrepancies in the extraction (mandible) and the nonextraction (maxilla and mandible) groups. However, no statistically significant correlation was shown between anterior and posterior arch discrepancies. The arch similarities were 96.18% and 97.38% in the maxilla and 96.01% and 97.49% in the mandible between extraction and nonextraction groups. Arch form discrepancies and similarities showed a moderate correlation but no statistically significant differences between the maxilla and the mandible. Conclusions: In customized fixed labial orthodontic appliance treatment, arch form setup can be accurately achieved with and without premolar extraction. Anterior arch form acquires fewer discrepancies than the posterior arch, and overcorrection should be added to the end of the customized archwire to reduce posterior arch discrepancies. The discrepancy of the maxillary and mandibular arches is interrelated, and adjustments should be made on both maxillary and mandibular archwires to correct single-jaw transverse malposition.