Biomechanical effects of attachment designs on maxillary molar expansion with clear aligners: A 3-dimensional finite...

The aim of this study is to determine, using finite element analysis (FEA), attachment configurations that minimize adverse biomechanical effects on the molars during posterior expansion with clear aligners and support biomechanical interpretation for treatment planning. Using FEA, the Invisalign G8 protocol (Align Technology, San Jose, Calif) and conventional attachment designs were compared.

Seven FEA models with attachments placed on the maxillary posterior teeth were created: (1) group 0: control group; (2) group 1: buccal horizontal rectangular attachment; (3) group 2: buccal gingivally-beveled rectangular attachment; (4) group 3: buccal-optimized expansion support attachment; (5) group 4: optimized attachment combined with an occlusally-beveled palatal attachment; (6) group 5: optimized attachment combined with a palatal horizontal rectangular attachment; and (7) group 6: palatal horizontal rectangular attachment without a buccal attachment. In the loading method, the deformation occurring in the clear aligner geometry and the contact forces resulting from the deformation were applied in the opposite direction.

In all groups, expansion was observed to occur in the form of buccal displacement of the crown and palatal displacement of the root. Optimized attachment configurations were associated with greater buccal crown displacement relative to palatal root displacement. In group 4, the highest expansion values and the lowest palatal root displacement were identified.

Simulation results indicated that parallel tooth displacement was not achieved with maxillary molar expansion using clear aligners, and buccal tipping predominated. Optimized attachments demonstrated a biomechanical tendency toward greater expansion efficiency. The combined use of optimized and palatal attachments showed increased buccal crown displacement with reduced palatal root displacement.