Detection of apoptosis during orthodontic tooth movement in rats

Experimental evidence suggests that cellular changes and tissue turnover occurs in the periapical tissue during tooth movement. The possible role of apoptosis in tooth movement has never been investigated. The purpose of this study was to show whether apoptosis plays any role in orthodontic tooth movement. A sample of 21 adult male Sprague-Dawley rats was divided into 4 groups. Orthodontic appliances were attached to the rats for various times-to group I (n = 6) for 3 days, to group II (n = 6) for 1 week, and to group III (n = 6) for 2 weeks. Rats in group IV (n = 3) had appliances but no force and served as the control group. At the end of the observation period, the animals were killed and tissue blocks of involved teeth were processed and prepared for TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) reaction. TUNEL-positive cells from selected areas on each slide were counted and compared by means of an analysis of variance. Group I demonstrated a significantly higher (P <.05) number of positive cells. This suggests that the maximum apoptosis occurs approximately 3 days after the application of the appliance.