The Impact of the Orthodontic Forces on the Internal Resorptive Process for Intact Periodontium: A Finite Element Analysis

Background/Objectives: This numerical (finite element analysis/FEA) study aimed to analyze the internal stress distribution patterns caused by a 4 N orthodontic force during intrusion, extrusion, rotation, tipping, and translation, using four common failure criteria, in intact periodontium. Additionally, based on these stress patterns, the study sought to establish correlations between these failure criteria to determine the most appropriate one—brittle-like or ductile-like. The orthodontically induced internal resorption was also assessed, along with the influence of orthodontic movements on the topography of the resorptive processes. Methods: A total of 180 numerical simulations on nine 3D anatomically accurate models containing the second lower premolar (manually reconstructed, CBCT-based) were performed. The brittle-like Maximum Principal, Minimum Principal, and ductile-like Von Mises and Tresca criteria were employed for the numerical analyses. Results: Translation and rotation more frequently cause internal pulp chamber resorption (vestibular, occlusal, lingual–mesial walls). In rotation, the stress was directly caused by the force applied to the bracket, while in translation, the origin of the stress was from the lingual third cervical area. Intrusion and extrusion movements are most likely to cause resorption in the root canal’s cervical and middle thirds (vestibular and proximal walls) due to high stresses induced by movement at the external cervical vestibular region. Tipping seems to be least prone to internal resorption. Conclusions: A 4 N orthodontic force can induce internal resorption in the pulp chamber and in the middle and cervical thirds of the root canals. The ductile-like failure criteria appear to provide a more accurate assessment of internal orthodontically induced resorption than the brittle-like criteria.