Comparing Distalization Modalities in Minimizing Compact Bone Resistance: A Finite Element Analysis

Abstract

Introduction: Orthodontic mini-implants have been utilized for Class II malocclusion correction by distalizing the maxillary dentition through direct anchorage, where forces are applied directly from the mini-implant to the teeth. Anatomical factors, such as compact bone, have shown to create resistance to movement. A previous study by our group suggested palatal placement of TADs to overcome this resistance. Finite element analysis (FEA) provides a robust framework for simulating orthodontic forces and evaluating biomechanical responses under controlled conditions. Aims: • Evaluate stress distribution within the periodontal ligament (PDL) and displacement of teeth under three different TAD-supported distalization setups. • Determine the setup that produces the greatest displacement while avoiding high stresses. • Determine the effect of adding a palatal force in reducing unwanted dental side effects. • Evaluate the impact of cortical bone properties, including stiffness, on stress distribution and 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. A force magnitude of 200 grams was applied to the maxillary posterior segment, 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 application method significantly influenced stress distribution and tooth displacement. Across all modalities, stress levels were highest at the canine and gradually decreased posteriorly. The buccal modality resulted in greatest stress values on all studied teeth, followed by the bucco-palatal, and then the palatal modality. Buccal force application resulted in the least displacement among the studied dentition with the greatest buccal tipping of the canine and posterior teeth, while palatal force produced palatal tipping of the canine crown in the opposite direction. The combined bucco-palatal force modality produced the greatest distalization with the least side effects. Additionally, cortical bone stiffness affected tooth movement; models with stiffer cortical bone exhibited lower displacement and higher stress concentrations, indicating greater resistance to distalization. Conclusions: • The bucco-palatal modality demonstrated stress values at all teeth surfaces intermediate between the buccal and palatal modalities, and greater displacement than either of these setups. Accordingly, this combination would favor the bucco-palatal approach to distalization of the maxillary teeth. • While the buccal modality led to undesirable buccal tipping of the teeth, particularly the canine, and the palatal modality yielded palatal crown and buccal root tipping of the canine, combining buccal and palatal forces in the BP modality resulted in a more controlled displacement pattern by reducing those side effects. • The incorporation of individual mechanical properties in this study buttressed the finding that cortical bone stiffness was a limiting factor in tooth distalization, further underscoring the importance of steering the teeth away from cortical bone. This tenet was achieved more with the BP modality. Moreover, thickness of the cortical bone did not present resistance similar to bone stiffness. • The application of 200 grams distalization force, compared with 150 grams in a prior study by our research group, confirmed that greater forces lead to higher stress levels, particularly in the posterior teeth and improved molar distalization. • Future studies should focus on alternate distalization modalities in individualized CT scans and time-dependent simulations. Clinical validation integrating finite element analysis (FEA) with clinical data should allow for precise individualized predictions of treatment outcomes.