Force systems and the function of attachments in aligner biomechanics: an analytical approach

The growing adoption of aligners contrasts with the lack of clear foundation in the literature regarding their activation methods. Studies often focus on effectiveness or estimated forces, lacking rational standardization and frequently presenting results that conflict with clinical practice.

This article analyzes the theoretical inconsistencies about how aligners work and proposes an alternative analytical approach to understand the force system they generate. It also explores how the use of attachments can modulate the direction of these forces to enable specific orthodontic movements.

To assess aligner activation, a two-dimensional model representing a maxillary central incisor was developed. This model, using palatal tipping and extrusion movements, enabled analysis of the aligner's activation mechanism and the influence of attachments on force redistribution.

The analysis showed consistency with previous studies, providing a rational explanation for aligner activation in these movements. Attachments proved essential in modifying force distribution, enabling displacements beyond the buccolingual axis.

In their current configuration, aligners predominantly generate normal buccal and lingual compressive forces through flexion, lacking intrinsic capacity to produce orthodontically useful forces such as traction, torsion, or shearing in the buccal and lingual planes. However, the strategic use of attachments allows interception of the aligner's deactivation and redirection of a fraction of the original forces, making other types of orthodontic movements feasible. This highlights the need for a rigorous biomechanical approach for each necessary movement for each tooth, to optimize aligner efficiency in clinical treatments.