[Root resorption of vital and endodontically treated teeth in orthodontic movement]

Orthodontic tooth movement frequently induces the resorption of the tooth root, although valuable information concerning the relationship between the root resorption and force magnitude, duration and types of tooth movement and the condition of periodontium obtained. However, it is incompletely known that the situation of candidated tooth itself of orthodontic movement in which pulpectomized non-vital condition influence the process of root resorption and subsequent repairing. Thus, the study was conducted to clarify the effect by the pulpectomy accompanied with tooth movement on the process of root resorption and regeneration of periodontium. A hundred and fifty Wistar rats, weight 180-200 g, 6 weeks old, were used as experimental animals. Prior to experimental tooth movement, first molars of 50 rats were received pulpectomy on both sides followed by filling of root canal (first group) and those of another 50 rats on single side (second group). Maxillary first molars of the other 50 rats were saved as a vital dental pulp control (third group). The first and the third groups of animals were then subjected to experimental tooth movement with the interproximal insertion of elastic rubber as described by Waldo (1953) for 3 days, 1, 2, 3 and 4 weeks. After tooth movement was terminated, animals were sacrificed by ether inhalation or by perfusion of glutaraldehyde fixation solution. The upper jaw from each rat was dissected and prepared specimens for non-decalcified section and light microscopic section. Root resorption and regeneration of cementum were evaluated quantitatively using the modular system for semiautomatic quantitative evaluation of images on the light microscopic section. Occurrence of external root resorption with multinucleated odontoclast associated with experimental tooth movement in pulpectomized tooth were lesser and later than those of vital teeth. These findings suggest that the dental pulp plays an important role in the processes of root resorption and remodeling of cementum associated with orthodontic tooth movement.