THE DEVELOPING ENAMEL MATRIX - NATURE AND FUNCTION

The hydroxyapatite crystals of mature enamel are unusually large, unif orm and regularly disposed within the tissue, implying that their deve lopment is a highly controlled process. The organic matrix of developi ng enamel is presumed to play an important role in the modulation of m ineral deposition and growth during tooth morphogenesis but the precis e functions of individual matrix proteins remain unclear. The aim of t his review was to survey the current knowledge of enamel matrix protei ns with a view to suggesting possible functions. The organic matrix is highly heterogeneous, comprising proteins derived from a number of di fferent genes, including amelogenin, enamelin, ameloblastin (amelin/sh eathlin), tuftelin, dentine sialophosphoprotein, enzymes and serum pro teins such as albumin. Each of these classes appears to undergo post-s ecretory sequential degradation which contributes further towards matr ix heterogeneity. Possible functions of these proteins include de novo mineral nucleation/initiation (dentine sialophosphoprotein, tuftelin) , mineral ion binding as crystal precursors (amelogenin, enamelin), co ntrol of crystal growth (amelogenin, enamelin, ameloblastin), support of growing crystals (amelogenin, enamelin), determination of prismatic structure (ameloblastin), cell signalling (tuftelin, ameloblastin), c ontrol of secretion (breakdown products) and protection of the mineral phase (amelogenin, enamelin). Failure of these mechnisms could lead t o incomplete maturation of the enamel and the eruption of dysplastic t issue.