Influence of third molar eruption status on the biomechanical environment of the temporomandibular joint: An in silico evaluation

Third molar (M3) may potentially cause occlusal interference, disrupt occlusal balance, alter temporomandibular joint (TMJ) loading, and impair the functional homeostasis of the stomatognathic system. This study conducted finite element method (FEM) on seven typical M3 conditions, analyzed its effects on occlusal and joint loading, and built an analytic biomechanical model to explore the regulatory mechanism of mandibular morphological parameters. Results revealed that (1) the presence of M3 would elevate TMJ functional load for all seven cases, in comparison to congenital absence case (control model [CM]). (2) Moreover, both occlusally functional (four erupted) and non-occluded (three impacted) cases of M3 presence could shift bite force to the posterior dentition and TMJ. (3) With constant masticatory muscle force, greater relative occlusal plane height (h) and length (L) would reduce TMJ loading. However, the load trends between dentition and TMJ could be reversed in consideration of periodontal ligament (PDL) negative feedback, wherein the load tendency is consistent with clinical data. In conclusion, the M3 presence would hinder the dispersion of occlusal forces in the stomatognathic system, and consequently aggravate stress environments in TMJ. The extraction of M3 could be potentially beneficial for alleviating the stress situation in TMJ due to the increase of relative occlusal plane height.