En-Masse Distalization of the Maxillary Dentition Studied with Finite Element Analysis

Abstract

Introduction: En-masse distalization of the maxillary dentition is a widely used technique in orthodontics for correcting Class II malocclusions. While various force magnitudes and directions are employed in clinical practice, their precise effects on stress distribution and displacement remain inadequately understood. Also, variations in force magnitude and distalization modality may significantly affect biomechanical outcomes. Finite element analysis (FEA) offers a powerful tool for simulating orthodontic forces and assessing biomechanical responses in a controlled setting.

Aims: To compare stress distribution in the PDL and displacement patterns of the studied maxillary dentition under 200 g and 300 g of force. To evaluate the effects of buccal, palatal, and bucco-palatal distalization modalities on tooth movement. To determine which of the studied dentition experiences the highest stress levels and greatest displacement in response to distalization forces. To analyze the influence of cortical bone thickness and stiffness on resistance to tooth movement.

Materials and methods: A three-dimensional finite element model of the maxillary dentition was generated using data from cone-beam computed tomography. Variations in cortical bone thickness and stiffness were incorporated across 13 and 11 models, respectively. Three distalization modalities were analyzed: buccal force (from a buccal miniscrew), palatal force (from a palatal miniscrew), and combined bucco-palatal force. Two force magnitudes (200 g and 300 g) were applied to the maxillary canines, with stress evaluated at the periodontal ligament (PDL) and displacement assessed at the occlusal surfaces of crowns and apices of roots. The models were meshed and analyzed using ABAQUS software, and statistical comparisons were made between different force magnitudes, distalization modalities, and cortical bone variations.

Results: Force magnitude and application method significantly influenced stress distribution and tooth displacement. The 300 g force led to greater displacement than the 200 g force but also generated higher stress levels on the PDL. Buccal force application resulted in the greatest displacement among the studied dentition, while palatal force produced tipping of the canine crown in the opposite direction. The combined bucco-palatal force modality facilitated a more balanced distalization. Moreover, the central incisor underwent the greatest displacement compared to all other teeth. In contrast, the molar exhibited the least displacement across all distalization modalities. The canine experienced the highest stress levels, followed by the lateral incisor. Additionally, cortical bone stiffness affected tooth movement; models with stiffer cortical bone exhibited lower displacement and higher stress concentrations, indicating greater resistance to distalization.

Conclusion: • The canine experienced the highest stress, followed by the lateral and central incisors. The central incisor showed lower stress, and higher displacement compared to the others. The lateral incisor and canine had higher stress but less displacement, suggesting greater resistance to movement, influenced by anatomical factors like tooth position, root length, and bone structure. • Anchorage modality significantly affects stress distribution and displacement. Buccal anchorage caused the highest displacement, followed by bucco-palatal and palatal modalities. The palatal modality led to canine tipping, requiring clinical control or compensation. • Applying 300g of force resulted in greater displacement of maxillary teeth and higher stress recorded in the periodontal ligament. • The model's strength lies in incorporating individual variations in mechanical properties, showing that stiffness has a greater impact on resistance to displacement than thickness. • Future studies should investigate the long-term effects of stress distribution on bone remodeling using CT scans of multiple individuals and time-dependent simulations for continuous tooth movement. Clinical validation via patient-specific finite element modeling would enhance the findings' applicability.