A review on nature, role and functions of dentin non-collagenous proteins. Part I: proteoglycans and glycoproteins.

Dentin is a collagen-based mineralized tissue consisting of inorganic apatite crystallites embedded in an extracellular matrix. In addition to type I collagen, the dentin organic matrix contains several proteins and proteoglycans, collectively referred as non-collagenous proteins, that play fundamental roles in actively promoting, controlling and regulating fibrillogenesis, crystal growth and mineralization during dentinogenesis. Similarly to collagen fibrils, non-collagenous proteins are synthesized and secreted by odontoblasts and some of them are detectable in both predentin and mineralized dentin, others only within the dentin layer. Non-collagenous components include proteoglycans (such as chondroitin-4/6-sulphate, decorin, biglycan, lumican, fibromodulin) and several glycoproteins such as: osteocalcin, osteonectin and the SIBLINGs proteins (i.e. osteopontin, bone sialoprotein, dentin matrix protein-1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein). The first part of this review offers an overview on the nature of the above mentioned non-collagenous proteins of the dentin organic matrix and their postulated functions, since a better understanding of the biological dynamics of the extracellular macromolecules is fundamental to clarify properties and function of the human mature sound dentin.