Clear aligner orthodontic force and conformity during lateral expansion

Abstract

ABSTRACT Purpose: This study aimed to find the clear aligner form which buccal tipping is less likely to occur by experimentally comparing the marginal type of the aligners with the orthodontic force and conformity (flotation) on the first molars during lateral expansion. Materials and methods: Four different marginal types (conventional aligners with no palatal coverage, partial palatal coverage [with or without 2.0 mm buccal extension], and complete palatal coverage) and three levels of lateral expansion (no expansion, 0.25-mm expansion, and 0.50-mm expansion) were used. The force applied to the first molar was measured by attaching a pressure sensor to the palatal side of the left first molar on a modelled maxillary constricted dental arch. The conformity (flotation) was measured by micro-CT with each aligner attached to the model. Results: Conventional aligners showed no significant difference in force at 0.25-mm or 0.50-mm expansion, but significant flotation at the midpoint and cervical side. The force of all three types of palatal coverage aligners increased significantly (p < 0.01) with increasing expansion and showed less flotation (p < 0.01) compared to the conventional type. Complete palatal coverage aligners had little flotation at 0.25-mm expansion and no expansion. Conclusion: Conventional aligners should have greater buccal tipping of the molars due to increased flotation with expansion. Complete palatal coverage aligners with 0.25-mm expansion had the best conformity, suggesting that they may prevent unplanned buccal tipping of the molars and allow lateral expansion to occur as intended.