In vitro comparison of the effects of direct attachment shape and location on forces and moments generated by thermoplastic aligners during simulated torque movement

Abstract

Introduction

The aim of this study was to investigate the effects of direct attachment shape and location on the forces and moments generated by thermoplastic aligners during simulated maxillary central incisor torque.

Materials and methods

A total of 7 typodonts were digitally printed with different attachment design and locations. Five clear aligners were fabricated for each typodont and placed on an orthodontic force tester (OFT) with the maxillary central incisor rotated palatally 1° around the incisal edge. Forces and moments were measured 2 times by the load cells. Analysis of variance (Anova) was used to determine the effects of group, tooth, and the group-by-tooth interaction on the outcomes; A two-sided 5% significance level was used for all tests. Analyses were performed using SAS version 9.4 (SAS Institute Inc., Cary, NC, USA).

Results

The two-way interactions between group and tooth were significant (P < 0.001) for all outcomes except facial/palatal moment around the X axis (M_x) (P > 0.05). The horizontal ellipsoid attachment at the middle third generated the highest M_x (−25.74 ± 8.93 Nmm) with facial crown/palatal root, while the rectangular attachment at the middle third yielded the lowest Mx (3.31 ± 12.92 Nmm).

Conclusions

Changing attachment shape and location had a significant effect on the forces and moments generated during simulated maxillary incisor torque. The best design for the incisor torque movement was found to be the horizontal ellipsoid attachment at the middle third. Besides the desired torque moment, all attachment shape and location combinations produced a vertical extrusive force as a side effect.