OBJECTIVETo 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 for women's orthodontic treatment.

METHODS80 female 3-month-old Wistar rats, which had a stable and five-day estrous cycle, were used. They were randomly divided into control groups and loading-force groups. Each group was divided again into 4 sub-groups according to the different stages of the estrous cycle. The loading-force groups received repeated intermittent orthodontic force for four times seperately during the 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.

RESULTSThere were significant variations in the amount of tooth movement among the groups which received the mechanical force during the different stages of the estrous cycle (P <0.01). There were significant variations in the amount of tooth movement between the groups received force during pre-estrus and estrus (P <0.05). There were not significant variations between the groups received force during metestrus and diestrus (P > 0.05). The largest amount of tooth movement was in estrus group and smallest in pre-estrus one.

CONCLUSIONThe effect of tooth movement depended on which stage of estrous cycle was chosen to be the time of applying orthodontic force.