Multisite Mini-Implant Anchorage for Maxillary Intrusion With Clear Aligners: A Finite Element Analysis

OBJECTIVE: To investigate the biomechanical effects of various mini-implant anchorage configurations on maxillary full-arch intrusion with clear aligners and to propose an optimized protocol for vertical control in clinical orthodontics. METHODS: Based on cone-beam computed tomography data from an adult patient with Angle Class II high-angle malocclusion, three-dimensional finite element models of the maxillary arch, periodontal ligament (PDL), maxilla, clear aligner, mini-implants, and traction buttons were constructed. Simulations were performed for three anchorage categories: (1) intrusion without auxiliary anchorage (control group); (2) intrusion with posterior-only anchorage, comprising three groups - buccal-only, palatal-only, and bilateral - with mini-implants placed between the second premolar and first molar (#5/#6); and (3) intrusion with combined anterior-posterior anchorage, including a central incisor-posterior anchorage group (five implants) and a lateral incisor-posterior anchorage group (six implants). Outcomes included tooth displacement and PDL hydrostatic pressure distribution. RESULTS: Among the control group and the three posterior anchorage groups, bilateral posterior anchorage produced the most bodily posterior intrusion. Lateral incisor-posterior anchorage achieved the most optimal intrusion of the arch and mitigated the sagittal inclination of the anterior teeth. Posterior teeth in the second quadrant exhibited significantly smaller displacement and PDL hydrostatic pressure than those in the first quadrant, attributable to the fused, significantly thicker root morphology of the second-quadrant second molar (#27). CONCLUSION: Bilateral posterior anchorage effectively balances the buccal and palatal moments and is recommended for posterior intrusion. Strategic placement of mini-implants in the anterior region can prevent anterior tooth inclination and facilitate posterior intrusion, thereby achieving coordinated vertical control, although this approach carries an increased risk of root resorption. Individual anatomical features, particularly root morphology, should be considered in clinical vertical control protocols.