Forces and moments on a maxillary lateral incisor using 3D-printed aligners with pressure points: an in vitro study

Abstract

Purpose: This study aimed to compare the initial forces and moments exerted by 3D-printed clear aligners on a maxillary left lateral incisor during distal rotation using pressure points and/or relief channels.

Materials and methods: An in vitro setup using multi-axis force/moment transducers measured forces and moments on tooth 22, rotated 3° distally. Six experimental groups were tested, using TC-85 clear resin aligners with varying pressure points (PP) and relief channel configurations: Group 1 (CON): Control with no PPs or channels; Group 2 (FP): Facial PP on the distofacial aspect; Group 3 (LP): Lingual PP on the mesiolingual aspect; Group 4 (DBL): Combined facial and lingual PPs; Group 5 (FWR): FP with a distolingual relief channel; and Group 6 (LWR): LP with a mesiofacial relief channel.

Results: Adding PPs generally increased the desired distal rotational moment, with LP showing the highest and CON the lowest rotational moment. However, relief channels yielded mixed outcomes. CON, FP, and FWR showed significant lingual forces, while LP, DBL, and LWR produced facial forces. All groups exhibited distal forces, except for CON and FP which generated mesial forces (p < 0.001). Also, all groups demonstrated intrusive forces except for the DBL group, which showed significant extrusive forces (p < 0.001). CON, FP and LP produced facial torque, whereas DBL, FWR, and LWR resulted in lingual torque. Groups without relief channels (e.g. FP, LP) demonstrated no significant differences in faciolingual or incisogingival forces compared to their relief-channel counterparts (FWR, LWR), though FP showed a significantly lower distal rotational moment than FWR and LP produced significantly higher rotational moments than LWR. DBL showed no significant difference in faciolingual and mesiodistal forces compared to LP but showed significant opposite forces when compared to FP. Moreover, DBL showed a significantly higher distal rotational moment than FP but lower than LP (p < 0.001).

Conclusions: Pressure points in 3D-printed aligners create rotational moments on maxillary lateral incisors without the need for attachments. These findings highlight the clinical potential of direct-printed aligners to deliver customized biomechanics for improved predictability.

Keywords: biomechanics; clear aligners; direct 3D printing; maxillary lateral incisor; orthodontic force; tooth rotation.