In vitro analysis of mandibular arch response to canine distalization with aligners at varying initial angulations

The purpose of this research was to analyze the three-dimensional forces acting on the mandibular teeth with aligner activation for distalization and an antitipping design of the mandibular canines, based on various pretreatment canine tips in vitro.

Five sets of clear aligners were designed to produce the same 0.25 mm distalization forces, with/without the 2° antitipping design, and were applied to canines with three initial angulations. Each group consisted of 12 aligners. Aligner forces were measured in real time using a force transducer measurement system.

In the mesial group, the canines mainly received distal and extrusive forces; labial and intrusive forces were observed on the incisors, and the second premolar received mesial forces. In the upright and distal groups, the canines were subjected to distal and intrusive forces, while the incisors were subjected to lingual and extrusive forces. Greater mesial forces on the second premolars were also observed. In the upright and distal groups, the distal and intrusive forces on the canines, and the lingual and extrusive forces on the incisors, were reduced by adding a 2° antitipping design to the canines; however, the mesial and intrusive forces on the second premolars increased.

With clear aligners, the "bowing effect" is aggravated when the initial angulation of the canines is distal. This effect can be partially relieved by implementing an antitipping design on the canines, although greater attention should be paid to posterior anchorage control.