Structural organization of calcospherites in normal and rachitic human dentine.

The structure of human dentine affected by familial hypophosphataemic rickets was investigated by polarized light and electron microscopy. Within the calcospherites both radially-orientated and collagen-orientated crystals were present, in approximately equal numbers. This was so, but less distinctly, in the calcospherites of normal dentine. It is concluded that dentine mineralizes entirely by formation of calcospherities which coalesce. It is proposed that matrix vesicles are probably responsible for the initiation of mineralization, and that growth of the calcospherites may depend on scavenging of inorganic pyrophosphate by the first-formed crystals. Growth of these crystals is thus poisoned but the resulting removal of inhibition allows deposition of further crystals by precipitation and by nucleation on collagen. The rachitic structure of dentine appeared to be due to slow calcospherite growth, probably as a result of the depressed serum phosphate characteristic of the disease.