The influence of PDL principal fibers in a 3-dimensional analysis of orthodontic tooth movement.

The effects of mechanical loads on the tooth-alveolus complex are of particular concern in orthodontics. The concepts of center of resistance (CRes) and center of rotation (CRot) are used to characterize tooth responses to orthodontic loads. The mechanical environment (stresses and strains) associated with orthodontic tooth movement is a unique model in bone adaptation physiology. Numerous finite element models of varying complexity have been developed to calculate tooth movements and stress distributions within the alveolar bone and the periodontal ligament (PDL). In general, the PDL has been idealized as a homogeneous isotropic material. For this project, a 3-dimensional tooth/PDL/mandible/finite element model was developed in which, for the first time in such an analysis, the PDL's principal-fiber structure was also incorporated. Parametric analyses showed that the fiber orientation and the mechanical properties do not exert much influence on the locations of the CRes and the CRot and on the stress patterns within the bone and the PDL matrix. However, the absence of principal fibers produces not only different stress magnitudes, but also differences in stress patterns. Furthermore, the no-fiber-associated CRes and CRot are considerably separated from the cluster of fiber-influenced centers. It was concluded that it may be more realistic to incorporate "generic" principal fibers into finite element models than not to include them at all, despite the lack of reliable information about fibers.