Fig. 1

The dentinogenesis starts at the late bell stage. The inner dental epithelium induced by various signalling molecules such as Wnt, Runx-2, and TGF-β differentiate into pre-ameloblast and subsequently become secretory ameloblast. Whilst, the ectomesenvhymal cells reside in dental papilla becomes the pre-odontoblast and the other cells remain undifferentiated. Pre-odontoblast develop into tall and polarized with the nucleus away from the dental membrane known as Tomes fibers. Tomes fibers connect with the cells at surface of dentin and continuously secrete organic matrix which composed of proteoglycans, glycoproteins, and collagens. The matrix accumulates as unmineralized layer (pre-dentin) and gradually mineralizes to form dentin