Role of Premolar Extraction in Overbite Treatment With Clear Aligner: A Biomechanical Study

Abstract Premolar extraction is often used in clear aligner (CA) therapy for teeth retraction. However, concerns such as anchorage loss leave clinicians divided on its drawbacks. This study aims to investigate the effect of premolar extraction on the mechanical response of teeth, including displacement pattern, force distribution, and hydrostatic stress stimuli in the periodontal ligament (PDL) using finite element analysis (FEA). The same aligner design was applied onto two teeth models, one with the first premolar extracted (EX case) and one without extraction (NE case). The EX case produced greater distal movement of anterior teeth, mesial displacement of posterior teeth, and up to 94% higher root forces compared with the NE case. In contrast, the NE case exhibited elevated interproximal contact pressures, particularly between the lateral incisor and canine, up to 1.39 MPa, which contributed to buccal displacement and less predictable tooth movements. Additionally, the PDL hydrostatic stress differs between EX and NE cases in both spatial distribution and magnitude, indicating variations in bone remodeling. These results shed light on the tradeoffs between extraction and nonextraction strategies in CA therapy and underscore the importance of anchorage management and force transmission in therapy planning.