Effects of clear aligner-assisted miniscrew intrusion in mandibular anterior teeth: a three-dimensional finite element study

This study aimed to systematically investigate the biomechanical effects of mandibular dentition during anterior intrusion with clear aligners assisted with miniscrews, employing three-dimensional finite element analysis (3D-FEA). We specifically measured the effect of traction direction (buccal vs. lingual side), traction force values (30 g to 250 g), and intrusion strategies (en masse and two-step intrusion). By incorporating teeth, periodontal ligament (PDL), mandibular alveolar bone, miniscrews, and clear aligners, a 3D finite element model was developed in this study. Mandibular tooth displacement and stress distribution were simulated under 0.2 mm anterior intrusion activation. The study assessed three biomechanical variables: (1) Traction force values: 0 g, 30 g, 50 g, 100 g, 150 g, 200 g, and 250 g. (2) Traction approaches: buccal and lingual traction. (3) Intrusion strategies: en masse intrusion and two-step intrusion. In all experimental groups, increasing traction forces consistently enhanced vertical displacement of central and lateral incisors, which was accompanied by labial tipping. Unwanted extrusion was observed in premolars during en masse intrusion. Unwanted extrusion was also detected in canines and in premolars during two-step intrusion at force values less than 150 g. Compared to buccal traction, lingual traction produced more bodily movement of incisors, with two-step intrusion exhibiting better controlled tipping compared to en masse intrusion. Stress concentrations in the PDL and alveolar bone are predominantly localized at the cervical third of the labial surface of anterior teeth. Specifically, lingual traction revealed a more homogeneous stress distribution than buccal traction. Miniscrew-assisted buccolingual traction significantly affects the movement of the mandibular anterior tooth. To achieve biologically efficient intrusion, the following protocols are suggested: en masse intrusion with 200 g buccal traction or 250 g lingual traction; and two-step intrusion with 100 g buccal traction or 150 g lingual traction. Based on a comprehensive evaluation of posterior anchorage and bodily intrusion movement, a two-step intrusion with lingual traction at approximately 150 g may provide more favorable biomechanical conditions, although clinical validation is required. Registry: Chinese clinical trial registry; Trial registration number: ChiCTR2400092922; Date of registration: 2024/11/26.