Objective To explore the effects of applying force during the different stages of estrous cycle on orthodontic tooth movement of rats, so as to offer an experimental princinple forwomen′s orthodontic treatment.Methods 80 female 3-month-old Wistar rats, which had a stable and five-day estrous cycle, were used. Theywere randomly divided into control groups and load- ing-force groups. Each group was divided again into 4 sub-groups according to the different stages of the estrous cycle. The load- ing-force groups received repeated intermittent orthodontic force forfourtimes seperately duringthe same stage of the estrous cycle. The distance between upper incisor and the first molar on the left was measured. The data were analyzed by One-way ANOVA, S-N-K.Results Therewere significant variations in the amount of toothmovement amongthe groupswhich received the mechani- cal force duringthe different stages of the estrous cycle (P0·05). The largest amount of tooth movement was in estrus group and smallest in pre-estrus one.Conclusion The effect of tooth movement depended on which stage of estrous cycle was chosen to be the time of applying orthodontic force.
