# Effect of different attachment configurations and skeletal anchorage force application points on canines during distalization of maxillary second molars with clear aligners: a finite element study

## TL;DR

This study used computer models to explore how different attachment setups and anchoring points affect tooth movement during molar distalization with clear aligners.

## Contribution

The study introduces a finite element analysis of attachment configurations and skeletal anchorage effects on canine movement during molar distalization.

## Key findings

- Distalization of upper second molars caused anchorage loss in all models.
- Models without attachments showed a lower anchorage loss ratio compared to those with attachments.
- Most models showed tooth intrusion and movement toward the midsagittal plane, except for one extrusion case.

## Abstract

This study investigated the influence of attachments on the maxillary posterior teeth using aligners and extra alveolar skeletal anchorage applied to precision cuts (PC) or buttons (BT) on the upper canines.

3D virtual models were created from a tomography of a young adult Class II, division 1 Caucasian patient with healthy and non-restored full complement of permanent teeth (except third molars) was used. Six finite element models of the maxillary teeth with aligners and extra alveolar screw anchorage to simulate second molar distalization with three attachment configurations were used (NA, no attachments; VA, vertical attachments; VHA, vertical and horizontal attachments). PC or BT was used to transfer a anchoring force of 1.66 Newtons (N) on the canines. A 0.2mm of distalization activation was used between molars. Tooth displacements were measured in millimeters (mm) at the cusp tip of the second molar, canine, and central incisor in the coronal (X), sagittal (Y), and vertical (Z) axes.

The upper second molar distalized in all models resulting in anchorage loss of anterior teeth. In models without and with attachments, the distalization/anchorage loss ratio was 5:1 and 4:1, respectively. In most models, the teeth evaluated intruded and moved towards the midsagittal plane. The exception was model 3 (PC + VA), in which the molars were extruded.

The distalization of upper second molars results in anchorage loss, whether attachments are present or not, despite the presence of skeletal anchorage. Its occurrence tends to be lower in the absence of attachments.