Effect of different attachment configurations and skeletal anchorage force application points on canines during...

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.