Peritubular dentin formation: Crystal organization and the macromolecular constituents in human teeth

Peritubular dentin (PTD) is a relatively dense mineralized tissue that surr ounds the tubules of coronal tooth dentin. It is composed mainly of crystal s of carbonated apatite together with a small amount of collagen. Its mode of formation has been investigated by studying the relatively dense particl es isolated from a powdered preparation. Electron microscopic examination o f the PTD particles, including 3-dimensional image reconstruction and elect ron diffraction, shows that the organization of the crystals of PTD is very similar to that of the adjacent intertubular dentin (ITD). The latter cont ains relatively large amounts of collagen and the carbonated apatite crysta ls are closely associated with the collagen matrix. The proteins present in the PTD particles are soluble after decalcification and stain with Stains All. The principal protein has higher molecular weight and a quite differen t amino acid composition than the phosphophoryns of the intertubular dentin . The interface between the PTD and the ITD shows structural continuity. Th ese data show how two distinct carbonated apatite-based mineralized tissues can be organized and formed contiguously within the same organ by utilizin g different sets of matrix proteins. (C) 1999 Academic Press.