The mechanical conditions associated with orthodontically induced bone formation and resorption were studied in rat molar periodontium using the finite element method. The model simulated mesial tipping of a maxillary first molar. Elevated strain energy densities were noted in the central regions of the Periodontal Ligament (PDL) at sites where osteoblast histogenic activity occurs. These results suggest that elevated strain energy is related to the induction of osteoblast differentiation in the perivascular areas of the PDL. Calculations also revealed high tensile, compressive, and shear stress gradients in the PDL and adjacent alveolar bone in areas of bone resorption and formation.