A finite element model of apical force distribution from orthodontic toothmovement

This study was undertaken to determine the types of orthodontic forces that cause high stress at the root apex. A 3-dimensional finite element model o f a maxillary central incisor, its periodontal ligament (PDL), and alveolar bone was constructed on the basis of average anatomic morphology. The maxi llary central incisor was chosen for study because it is one of the teeth a t greatest risk for apical root resorption. The material properties of enam el, dentin, PDL, and bone and 5 different load systems (tipping, intrusion, extrusion, bodily movement, and rotational force) were tested. The finite element analysis showed that purely intrusive, extrusive, and rotational fo rces had stresses concentrated at the apex of the root. The principal stres s from a tipping force was located at the alveolar crest. For bodily moveme nt, stress was distributed throughout the PDL; however, it was concentrated more at the alveolar crest. We conclude that intrusive, extrusive, and rot ational forces produce more stress at the apex. Bodily movement and tipping forces concentrate forces at the alveolar crest, not at the apex.