Dentin is mineralized connective tissue, which consists of two parts, coronal dentin
covered by enamel and radicular dentin by cementum. Although both parts are formed by odontoblasts, biophysical and biochemical properties are indeed different, which evoke the specific system for radicular dentin formation. One of the critical factor of radicular dentin formation is Hertwig's epithelial root sheath (HERS), which leads proliferation and differentiation of odontoblasts under the control of TGF-β/BMP signaling, and the ablation or over-expression of constituent molecules showed the specific malformation of radicular dentin. Wnt/β-catenin signaling is the other candidate of dentin formation which may regulate differently on crown and root formation. Fibroblast growth factor (FGF) 18 is possible downstream molecule of this signaling. Interestingly, the expression of FGF18 transcripts was detected during root formation, but not crown formation in rat mandibular molar.
While possible receptors, FGFR2 and FGFR3, were continuously observed in both crown and root formation, those suggested that coronal and radicular dentin might be formed under the continuous and/or reciprocal control of different FGFs. The clarification of these systems may open new insight into the tissue regeneration and/or engineering of tooth and periodontium.