Biomechanical effects of attachment position and pressure ridge design on maxillary arch expansion with clear aligners: a finite element analysis

OBJECTIVES: To investigate the biomechanical effects of attachment position (buccal vs. palatal) and the integration of pressure ridges on maxillary arch expansion with clear aligners using finite element analysis. METHODS: Five 3D finite element models were constructed to simulate 0.2 mm of buccal expansion with different auxiliary configurations: (A) no attachment; (B) buccal attachments; (C) palatal attachments; (D) buccal attachments combined with palatal pressure ridges; and (E) palatal attachments combined with buccal pressure ridges. Biomechanical analysis quantified tooth displacement and stress distribution across tooth roots and periodontal ligament. RESULTS: Groups A-D exhibited significant buccal inclination in premolars and first molars, while second molar expansion remained limited. In contrast, Group E demonstrated a restricted expansion pattern. Regarding attachment position, palatal attachments (Group C) generated greater crown displacement in the mid-posterior segment (second premolar: 0.058 mm; first molar: 0.042 mm) compared to buccal attachments (Group B). Among the five groups, the buccal attachments combined with palatal pressure ridges (Group D) demonstrated superior biomechanical performance, achieving the greatest first molar expansion (0.057 mm) and favorable torque control (first molar: 3.42°/mm; second molar: 2.96°/mm). Notably, palatal attachments (Groups C and E) induced significantly higher von Mises stresses on the roots. CONCLUSIONS: Maxillary arch expansion with clear aligners is primarily achieved by buccal inclination of the posterior teeth. The configuration combining buccal attachments with palatal pressure ridges demonstrates biomechanical advantages, including enhanced crown displacement, better torque control, and favorable stress distribution.