The mutual effects between orthodontic tooth movement and estrous cycle or estrogen

The mutual effects between orthodontic tooth movement and estrous cycle or estrogen of female rats were studied. Animals were randomly divided into control group, force-loading for one time group, force-loading for five times group and sham groups. Each group included four subgroups, based on the estrous cycle stage. Serum estradiol, the change of estrous cycle, and tooth movement distance were measured. Significant variations in the estradiol level were found among the groups receiving force during the same stage of the estrous cycle (p < 0.01) and among the subgroups within each group (p < 0.01). The experimental treatments affected the estrous cycle of the groups receiving force in metestrus and diestrus. There were significant variations in the amount of tooth movement among the groups receiving force during different stages of the estrous cycle (p < 0.01). The largest amount of tooth movement was in the estrus group. The results show it was more desirable to wear appliances and apply force during estrus.