Effect of composite attachment on initial force system generated during canine rotation with plastic aligners: a threedimensional finite elements analysis

Objective: To establish a better understanding of the role of composite attachments in resultant displacement patterns during aligner-based rotational tooth movement. Methods: Computer assisted design (CAD) geometry of the upper right canine, the periodontal ligament (PDL), composite attachment and plastic aligner segment were digitally modelled and subsequently imported to ANSYS 16.1 finite element analysis (FEA) software. A 3-degree mesio-lingual rotation was imposed on the aligner segment, simulating aligner-based mechanics and clinical performance, with and without attachments. Results were compared to establish the role of composite attachments during aligner-based tooth rotation. Results: Intrusive displacement of canines was observed during aligner-based tooth rotation without attachment. The intrusive force was 2.5× greater when attachments were not included in simulation. A distinct "lag" was observed between aligner and tooth rotations, which reduced from 25% to 5% when attachments were added to the FEA simulation. Concentrated contact pressure areas were observed on the mesial and distal slopes of the incisal ridge. Conclusion: During aligner-based canine rotation, in the absence of attachments, intrusive forces as well as a "lag" between aligner rotation and the resultant movement of the tooth were observed. When specialised composite attachments were utilised, intrusive tendency and aligner-tooth rotational "lag" were significantly reduced, improving clinical predictability of aligner-based orthodontic systems. Keywords: aligner orthodontics, biomechanics, plastic aligners, rotation