The effects of orthodontic forces on the mechanical properties of the periodontal ligament in the rat maxillary molars.

Previous studies have shown that the mechanical strength of the periodontal ligament decreased markedly after the application of an orthodontic force to the rat mandibular first molar. However, the effects of orthodontic forces on the mechanical properties of the periodontal ligament of the other teeth in the same dental arch have not been examined. Furthermore, a detailed analysis of the mechanical parameters has not been made. The purpose of the present study was to analyze mechanical parameters such as maximum shear load, maximum deformation, elastic stiffness, and failure energy in shear, estimated from the load-deformation curves obtained by extracting the rat maxillary molars from their sockets after application of an orthodontic force for 5 days. It was found that the mechanical properties of the periodontal ligament of the rat maxillary molars varied considerably among control teeth in the same dental arch. Decreases in the mechanical properties of the periodontal ligament of the experimental teeth were greatest in the first, less in the second, and least in the third molars. Significant correlations were found between the maximum load and the failure energy and between the maximum deformation and the failure energy in all teeth. It was concluded that orthodontic force affected not only the mechanical properties of the periodontal ligament of the teeth to which the force had been applied but also the mechanical properties of distant teeth.