Influences of aging changes in proliferative rate of PDL cells during experimental tooth movement in rats.

This study was designed to investigate the influences of aging changes in the proliferative activity of PDL cells during experimental tooth movement in rats. Young (6-week-old) and adult (14-week-old) Wistar strain rats were used as experimental animals. Light (10 g) or heavy forces (40 g) were applied to the maxillary first molars for periods of 1, 3, 7, or 14 days. Proliferative activity of the PDL cells was evaluated immunohistochemically in terms of the ratio of the number of labeled cells to the total number of PDL cells (labeling index) or the number of labeled cells. In the controls, cellular activity was significantly greater in the young than in the adult group (P < 0.05). Significant differences in the proliferative activity between young and adult groups were found in the tension and pressure areas during early stage of tooth movement (P < 0.05), which indicated a delay of biologic responses to orthodontic stimuli in adult rats. It is shown that aging changes substantially influence proliferative activity of the PDL cells and subsequent tooth movement during the initial phase in particular.