Molecular Mechanisms of Dental Enamel Formation

Abstract

Tooth enamel is a unique mineralized tissue in that it is acellular, is more highly mineralized, and is comprised of individual crystallites that are larger and more oriented than other mineralized tissues. Dental enamel forms by matrix-mediated biomineralization. Enamel crystallites precipitate from a supersaturated solution within a well-delineated biological compartment. Mature enamel crystallites are comprised of non-stoichiometric carbonated calcium hydroxyapatite. The earliest crystallites appear suddenly at the dentino-enamel junction (DEJ) as rapidly growing thin ribbons. The shape and growth patterns of these crystallites can be interpreted as evidence for a precursor phase of octacalcium phosphate (OCP). An OCP crystal displays on its (100) face a surface that may act as a template for hydroxyapatite (OHAp) precipitation. Octacalcium phosphate is less stable than hydroxyapatite and can hydrolyze to OHAp. During this process, one unit cell of octacalcium phosphate is converted into two unit cells of hydroxyapatite. During the precipitation of the mineral phase, the degree of saturation of the enamel fluid is regulated. Proteins in the enamel matrix may buffer calcium and hydrogen ion concentrations as a strategy to preclude the precipitation of competing calcium phosphate solid phases. Tuftelin is an acidic enamel protein that concentrates at the DEJ and may participate in the nucleation of enamel crystals. Other enamel proteins may regulate crystal habit by binding to specific faces of the mineral and inhibiting growth. Structural analyses of recombinant amelogenin are consistent with a functional role in establishing and maintaining the spacing between enamel crystallites.

Hypomaturation Enamel Defects in Klk4 Knockout/LacZ Knockin Mice

“…It is believed that enamel proteins bind to the sides of enamel crystals, possible at kinks or similar growth sites, and inhibit the deposition of ions on the crystal surface (85). When maturation-stage enamel crystals are incubated in supersaturated solutions of calcium phosphate, no crystal growth is observed unless the maturationstage enamel is first pretreated with either 8 M urea or sodium hypochlorite to remove residual protein (86).…”

Ab initio modelling of protein–biomaterial interactions: influence of amino acid polar side chains on adsorption at hydroxyapatite surfaces

“…The HA (001) and (010) surfaces are the most relevant from a biological point of view: the (001) plane is the dominant surface in the thermodynamic morphology [52][53][54], whereas the crystal growth occurs overall through the c-direction during biomineralization, thereby the (010) face being very extended in the final HA crystal and often responsible for interaction with molecules [55][56][57]. These two surfaces were modelled within the slab approach by selective cuts of the optimized bulk structure.…”

The nucleation and growth of calcium phosphate by amelogenin

“…OCP is a common precursor phase for HAP in in vitro studies [38,39]. OCP formation is also relevant to enamel formation as it has been observed as a precursor phase in enamel [4,40] and has been used as a model system to study the effects of amelogenin on crystal growth [14]. OCP is favored in our solutions because the decrease in calcium concentration and pH with calcium phosphate formation stabilizes OCP [41].…”