LOCALIZATION OF UNCALCIFIED CEMENTUM IN ADULT-RAT MOLAR ROOTS AND ITSRELATION TO PHYSIOLOGICAL TOOTH MOVEMENT

The study was designed to elucidate the effect of physiological tooth movement on cellular cementum, using the upper molar roots of 10-week- old rats. Paraffin sections stained with haematoxylin and eosin displa yed two types of cellular cementum, lightly and darkly staining. The l ightly stained was present on the distal half of all molar roots excep t the mesial root of the first molar. The alveolar bone facing the lig htly stained cementum showed resorption lacunae and multinucleated ost eoclasts, while the opposite bone surface was lined with osteoblasts. In contact microradiographs of undemineralized ground sections, the X- ray density of the lightly stained cementum was similar to that of the periodontal ligament and pulp, while the X-ray density of the darkly stained cementum was similar to that of alveolar bone. Tetracycline la belling lines were seen at the interface between the two types of cell ular cementum as well as on surfaces of bone and cementum located mesi ally to the root dentine. The results suggest that the mechanical stre ss of tooth movement differently affects the alveolar bone and cellula r cementum; the bone is resorbed whereas the cementum resists resorpti on and its calcification is inhibited under the compressive force of t ooth movement.