The finite element method was used to calculate temperature and thermal stress distribution as a result of hot/cold liquid in the mouth. This numerical study was carried out using axisymmetric finite element models and the tooth model was endodontically treated restored with cast post and cores. The two tooth models evaluated were Ti-Ti alloy and NiCr-AuPd alloy as post material and crown material with porcelain. First, temperature changes on the restored tooth as a result of hot/cold liquid in the mouth were calculated and then the thermal stress as a result of temperature changes were carried out. A FORTRAN computer program was developed for this study. The tooth was assumed isotropic, homogenous, elastic and symmetrical. The distribution of temperature and thermal stress versus time were plotted for four critical points.