Determination of the centre of resistance in an upper human canine and idealized tooth model

The purpose of this investigation was to analyse the influence of geometric and material parameters of a human canine on initial tooth mobility, and t he stress and strain profiles in the periodontal ligament. While the materi al parameters of tooth and bony structures are known within an uncertain li mit of approximately a factor of 10, values reported for the elasticity par ameters of the periodontal ligament differ significantly. In the course of this study, bilinear behaviour was assumed for the mechanical property of t he periodontium. The finite element model of an elliptical paraboloid was created as an appr oximation to the geometry of a human canine to reduce calculation time and to determine influences of the geometry on numerical results. The results w ere compared with those obtained for a realistic human canine model. The ro ot length of both models was 19.5 mm. By calculating pure rotational and pu re tipping movements, the centre of resistance (CR) was determined for both models. They were located on the long axis of the tooth approximately 7.2 mm below the alveolar crest for the idealized model and 8.2 mm for the cani ne model. Thus, the centre of resistance of a human canine seems to be loca ted around two-fifths of the root length from the alveolar margin. Using th ese results, uncontrolled tipping (1 N of mesializing force and 5 Nmm of de rotating momentum), as well as pure translation (additionally about 10 Nmm of uprighting momentum) were calculated. Comparing the idealized and the re alistic models, the uncontrolled tipping was described by the parabolic-sha ped model within an accuracy limit of 10 per cent as compared with the cani ne model, whereas the results for bodily movement differed significantly sh owing that it is very difficult to achieve a pure translation with the real istic canine model.