Effectiveness of different intrusion protocols with clear aligner for maxillary anterior teeth in periodontitis: a finite element analysis

BACKGROUND: Extrusion of anterior teeth is a common manifestation of periodontitis. Orthodontic intrusion is an effective approach for improving occlusion and periodontal health. This study aimed to identify the optimal protocols for maxillary incisor intrusion using clear aligner (CA) in patients with periodontitis. METHODS: A validated finite element model was established, including the CA, teeth, periodontal ligaments (PDLs), and alveolar bone with three levels of bone height (simulating mild to severe periodontitis). The intrusion angles were varied from 0° to 60° in 10° increments relative to each tooth's long axis. An intrusion of 0.1 mm was simulated for the maxillary incisors under each periodontal condition. Initial tooth movements and stress distributions of PDLs were evaluated. RESULTS: Both central incisors and lateral incisors exhibited absolute intrusion under all conditions, and the amount of intrusion decreased with increasing intrusion angle. At an intrusion angle of 0°, central incisors initially exhibited relative extrusion and lingual tipping, gradually transitioning to relative intrusion and labial tipping as the angle increased. In contrast, lateral incisors consistently displayed relative intrusion with less lingual tipping and earlier tipping transitions. These transitions occurred at lower angles in mild periodontitis. CONCLUSIONS: CA designed to intrude maxillary incisors along the tooth's long axis may not achieve bodily intrusion in periodontitis. Angulated intrusion designs appear to improve control of labiolingual tipping compared with axial designs under the simulated conditions.