The Effect of Varying Occlusal Loading Conditions on Stress Distribution in Roots of Sound and Instrumented Molar Teeth: A Finite Element Analysis

This study aimed to investigate whether the direction of force applied to the occlusal surface influenced the pattern of tensile stresses in roots of sound and root canal-prepared mandibular molar teeth. The effect of obturation forces on the development of apical stress was also investigated. To this end, models were constructed using micro-computed tomographic imaging and investigated using finite element analysis.Micro-computed tomographic data established boundaries of internal and external model surfaces to allow finite element analysis. Individually segmented components were modeled based on mechanical properties in precedent literature. The following conditions were considered: axial force directed over the mesial marginal ridge, a mesial or a distal tipping force, a combination of both a torquing force and axial loading, and hydrostatic pressure. The maximum principal stresses were determined.The highest root stress occurred in the cervical third of root surfaces (ie, not apically) under all loading conditions. Importantly, mesial tipping forces resulted in tension on distal roots, whereas distal tipping resulted in tension in the mesial roots. Intracanal pressures produced tensile stress on the internal root canal walls in the cervical third of the root. Stresses were calculated to be less than the fatigue tensile strength of dentin.Static loading, under the conditions modeled, does not result in stress concentration at the root apices that would cause root fracture under normal masticatory loads. Stress patterns developing from mesial and distal tipping forces help to explain the appearance of vertical root fractures reported in sound nonrestored molar teeth.