Fig 1: The images of H.E. staining and immunohistochemistry staining for prenatal rat dental germs. H.E. staining demonstrated that the rat dental germs entered the early cap stage at E14.5 d, the cap stage and early bell stage at E16.5 d, and the bell stage at E18.5 d. The separation between the pre-odontoblast and pre-ameloblast layers occurred in all E18.5 d species. Immunohistochemistry staining revealed that Clock, Per1, and Col1 were detected in the epithelial-mesenchymal interaction area, dental follicle, and dental papilla at E14.5 d, and became stronger at E16.5 d when p75NTR, Bmal1, and ALP were detected. All the factors were expressed at E18.5 d, but Cry1 showed the weakest expression. All experiments were repeated three times independently. op: oral epithelium; dp: dental papilla; iee: inner enamel epithelium; oee: outer enamel epithelium; sr: stellate reticulum. The scale bar represents 50 μm, respectively.