The dentin formation and mineralization proceeds in the defined, matrix-mediated manner. It begins from the secretion of the organic matrix and ends with the complete mineral deposition. The dentin apposition takes place when odontoblasts begin the secretion of type I collagen into the extracel- lular compartment. Type I collagen is the main component of the dentin extracellular organic matrix and forms the specific scaffold for the deposition of dentin hydroxyapatite crystals.