Dentin Matrix Proteins and Dentinogenesis

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Abstract
The precise mechanisms involved in dentinogenesis are not understood; however, the information to date suggests that a number of highly controlled extracellular events are involved. Mature odontoblasts secrete collagen at the cell border into predentin. They synthesize and secrete other non-collagenous proteins (NCPs) at the mineralization front, possibly through odontoblastic processes. A collagen-NCP complex is formed at the predentin-dentin border and apatite crystal initiation and growth takes place. One of the research needs is to uncover the nature of this dentin collagen-NCP complex and to understand how it controls mineralization. At least three dentin specific NCPs are known: phosphophoryn(s), dentin sialoprotein (DSP) and AG1 (Dmp1). Other macromolecules are commonly made by osteoblasts and odontoblasts and participate in bone and dentin formation. Some progress in understanding dentin mineralization has been gained by focusing upon the role of phosphophoryns. These highly phosphorylated proteins are secreted at the mineralization front, where a small portion binds in the gap region of type I collagen fibrils. This portion of phosphoproteins probably initiates formation of plate-like apatite crystals. Additional phosphophoryns in higher concentrations bind to the growing apatite crystals and slow their growth, possibly influencing their size and shape. Other areas which need careful investigations are those involving the mechanisms involved in odontoblast differentiation, how the synthesis of the dentin specific NCPs is controlled and the precise roles of these macromolecules in dentinogenesis. Future experimentation will focus on the gene structures for these NCPs and the mechanisms of tissue specific gene regulation. Tests for function can then be pursued in “gene knockout” experiments. There is no doubt that current “new” scientific approaches being utilized to answer many scientific questions in other fields will greatly impact our ability to answer the questions surrounding the process of dentinogenesis.