Effects of dental arch size variation on orthodontic forces delivered by preformed Ni-Ti archwires

ABSTRACT Purpose The purpose of the present study was to investigate the effect of the size variation of the mandibular dental arch on the magnitude and direction of orthodontic forces delivered by a variety of commercially available preformed rectangular Ni-Ti archwires. Materials and methods The means and standard deviations (SDs) of intercanine and intermolar widths and the means of dental arch depths at the canines and first molars were established based on our previous studies of subjects with untreated normal occlusions. The mandibular dental arch of a multi-sensor measuring system was adjusted to the mean, enlarged to +1SD and reduced to −1SD sizes of the normal dental arch. Fifty-nine types of 0.019 × 0.025-inch NiTi archwires were selected, and the intercanine and intermolar widths of the archwires were measured. Delivered forces were measured at the central incisors, canines, and first molars for each dental arch condition. Results Significant correlations were found between archwire width and forces at all examined teeth for all dental arch widths. Significantly greater facial direction forces were delivered at the central incisor for the large dental arch condition than for the small and mean dental arch conditions. Significantly greater facial direction force was delivered at the canines for the small dental arch than for the large dental arch condition. Conclusion Possible risks of clinically significant magnitudes of orthodontic force in the facial direction at the central incisors and canines were observed when using preformed rectangular NiTi archwires for patients with relatively large and small dental arches, respectively.