Figure 1. Monitoring of the estrous cycle in rats and design of the experiment on tooth movement. (A) Vaginal smears. P (pro-estrus): The smear was characterized by a moderate number of nucleated epithelial cells. E (estrus): Many cornified cells appeared in the smear. M (metestrus): The smear contained leukocytes as well as cornified cells. D (di-estrus): The smear was characterized by nucleated epithelial cells and a large number of leukocytes. Bar = 200 µm. (B) Representative cyclic change in vaginal impedance and design of the experiment on tooth movement. Rats that showed vaginal impedance greater than 3.0 k were defined to be in pro-estrus. The animals were divided into 4 groups based on the stage of the estrous cycle when the force was mainly applied. Animals in the Estrus, Metestrus, Di-estrus, and Pro-estrus groups received force for 2 days during every estrous cycle from late pro-estrus, late estrus, late metestrus, and late di-estrus, respectively. Animals in each group received no force for the remaining 2 or 3 days in each estrous cycle. The animals were examined for 5 consecutive estrous cycles and received the force 5 times for 2 days in each estrous cycle.
