A. STIEFENHOFER 1*, H. RICHTER 2 (1 Poliklinik fur Zahnärztliche Prothetik, Universität Würzburg, 2 Fa. CAD-FEM GmbH, Grafing b. München)
2-dimensional Finite-Element-Analysis (FEA) of reconstructed teeth utilizing endodontic post and core systems has shown a significant correlation between post geometry, horizontal level of alveolar bone, post fixation and mechanical stress of post and remaining tooth substance. In accordance with clinical practice 2-dimensional FEA has shown reduction of mechanical stress for the root by using long and thick endodontic dowels. The influence of taper seemed to be of minor importance. An influence on the mechanical stress on both tooth substance and endodontic post is given by the horizontal level of alveolar bone. Stress increases nonlinearely with loss of alveolar bone level. Mechanical stress for the endodontic dowels is reciprocal to the stress of the remaining tooth substance when varying post geometry. The use of a 2-dimensional FEA offered the possibility to calculate high numbers of different models with reasonable hardware capacities and processing time. To proof this investigation technique further analysis on a 3-dimensional Finite-Element-Model were carried out. A model of the upper front tooth segment was digitalized to get the coordinates and functions of tooth and bone surfaces. ProEngineer CAD- Software was used to reconstruct the model with a fine tethrahedal mesh for further FEA using ANSYS 5.2. The mechanical stress on remaining tooth substance and endodontic dowel was investigated by calculation of von- Mises-Stresses on two different post lengths assuming an ideal adhesive bond between post and tooth surface. The results show a good correlation between 2- and 3-dimensional FEA regarding stress distribution. Significant differences resulted in the absolute values of the calculated von-Mises-Stresses due to radial tensions in the 3- dimensional model. Regarding the necessary hardware capacities and processing time the 2-dimensional Finite- Element-Model seems to be sufficient for qualitative investigations of geometric influences of post and core design.