In Vitro Comparison of the Effectiveness of Different Attachment Shapes and Locations on Extrusion of the Upper Left Lateral Incisor Using Thermoplastic Aligners

Objectives: The aim of this study was to compare the effectiveness of different attachment shapes and locations on the extrusion of the upper left lateral incisor (UL2) using thermoplastic aligners.

Materials and methods: Seven typodonts were digitally printed with hemi-ellipsoid or rectangular attachments in the incisal, middle or cervical third of the UL2. Five clear aligners were fabricated for each typodont; each was tested twice. Forces and moments were measured with an orthodontic force tester during 0.2 mm simulated extrusion of the UL2. 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.

Results: Altering attachment shape and location had a statistically significant effect on the forces and moments generated in each trial (p < 0.01), except for rectangular incisal and hemi-ellipsoid cervical (p > 0.05). The rectangular middle attachment generated the highest extrusive force (Fz = 7.498 N), followed by hemi-ellipsoid cervical (Fz = 6.338 N) and rectangular incisal (Fz = 5.948 N).

Conclusions: Varying direct attachment shape and location on the UL2 during extrusion has a significant effect on the forces and moments generated by thermoplastic aligners. The rectangular attachment located in the middle third generated the most effective extrusive force and least unwanted moment. For anchorage teeth, hemi-ellipsoid attachments located in the cervical third were found to be the most effective in minimising the reciprocal intrusive forces and unwanted moments.