Rationalization of shape and related stress distribution in posterior teeth: a finite element study using nonlinear contact analysis

This study considered the loading configuration of intact teeth by using finite element analyses to rationalize the clinical and biologic advantage inherent to posterior tooth shape. The biomechanical behavior of opposing molars was investigated in consideration of different loadcases simulating working, nonworking, and vertical closing micromotions starting in a position close to maximum intercuspation. The resulting stress distribution was assessed in a numerical model, reproducing 2-D buccolingual cross sections of maxillary and mandibular molars. In each case (working/nonworking/closure), the stroke was applied to the mandibular tooth in a stepping procedure (nonlinear contact analysis) until a total external force of 200 N was attained on the contact nodes. The principal stress distribution and modified Von Mises stresses were extracted from the postprocessing files. Vertical loading of the teeth did not generate harmful concentrations of stress. More challenging situations were encountered during working and nonworking micromotions, both of which generated inverted stress patterns. Supporting cusps were generally well protected during both working and nonworking cases (mostly subjected to compressive stresses). Nonsupporting cusps tended to exhibit more tensile stresses. High stress levels were found in the central groove of the maxillary molar during nonworking micromotion and at the lingual surface of enamel of the mandibular tooth during single-contact working micromotion. The occlusal load configuration as well as geometry and hard tissue arrangement had a marked influence on the stress distribution within opposing molars. Additional computations demonstrated the essential role of enamel bridges and crests to protect the crown from harmful tensile stresses.