Accuracy in tooth positioning with a fully customized lingual orthodontic appliance

Abstract

Introduction: To understand orthodontic tooth movement, a method of quantification of tooth position discrepancies in 3 dimensions is needed. Brackets and wires now can be fabricated by CAD/CAM technology on a setup made at the beginning of treatment, so that treatment should produce a reasonably precise duplicate of the setup. The extent of discrepancies between the planned and actual tooth movements can be quantified by registration of the setup and final models. The goal of this study was to evaluate the accuracy of a CAD/CAM lingual orthodontic technique.

Methods: Dental casts of 94 consecutive patients from 1 practice, representing a broad range of orthodontic problems, were scanned to create digital models, and then the setup and final models for each patient were registered individually for the maxillary and mandibular dental arches. Individual tooth discrepancies between the setup and actual outcome were computed and expressed in terms of a six-degrees-of-freedom rectangular coordinate system.

Results: Discrepancies in position and rotation between the setup and outcome were small for all teeth (generally less than 1 mm and 4°) except for the second molars, where some larger discrepancies were observed. Faciolingual expansion in the posterior teeth was greater in the setup than in the final models, especially at the second molars. Linear mixed models showed that age, type of tooth, jaw, initial crowding, time in slot-filling wire, use of elastics, days in treatment, interproximal reduction, and rebonding, were all influences on the final differences, but, for most of these factors, the influence was small, explaining only a small amount of the discrepancy between the planned and the actual outcomes.

Conclusion: These fully customized lingual orthodontic appliances were accurate in achieving the goals planned at the initial setup, except for the full amount of planned expansion and the inclination at the second molars. This methodology is the first step toward understanding and measuring tooth movement in 3 dimensions.