Analysis of stress in the periodontium of the maxillary first molar with athree-dimensional finite element model

The aim of this study was to simulate the stress response in the periodonti um of the maxillary first molar to different moment to force ratios, and to determine the moment to force ratio for translational movement of the toot h by means of the finite element method. The three-dimensional finite eleme nt model of the maxillary first molar consisted of 3097 nodes and 2521 isop arametric eight-node solid elements. The model was designed to dissect the periodontal ligament, root, and alveolar bone separately. The results demon strate the sensitivity of the periodontium to load changes. The stress patt ern in the periodontal ligament for a distalizing force without counterbala ncing moments showed high concentration at the cervical level of the distob uccal root due to tipping and rotation of the tooth. After various counterr otation as well as countertipping moments were applied, an even distributio n of low compression on the distal side of the periodontal ligament was obt ained at a countertipping moment to force ratio of 9:1 and a counterrotatio n moment to force ratio of 5:1. This lower and uniform stress in the period ontal ligament implies that a translational tooth movement may be achieved. Furthermore, high stress concentration was observed on the root surface at the furcation level in contrast with anterior teeth reported to display hi gh concentration at the apex. This result may suggest that the root morphol ogy of the maxillary first molar makes it less susceptible to apical root r esorption relative to anterior teeth during tooth movement. The stress patt erns in the periodontal ligament corresponded with the load types; those on the root appeared to be highly affected by bending and the high stiffness of the root.