Transient amorphous calcium phosphate in forming enamel

Abstract

Enamel, the hardest tissue in the body, begins as a three-dimensional network of nanometer size mineral particles, suspended in a protein gel. This mineral network serves as a template for mature enamel formation. To further understand the mechanisms of enamel formation we characterized the forming enamel mineral at an early secretory stage using x-ray absorption near-edge structure (XANES) spectromicroscopy, transmission electron microscopy (TEM), FTIR microspectroscopy and polarized light microscopy. We show that the newly formed enamel mineral is amorphous calcium phosphate (ACP), which eventually transforms into apatitic crystals. Interestingly, the size, shape and spatial organization of these amorphous mineral particles and older crystals are essentially the same, indicating that the mineral morphology and organization in enamel is determined prior to its crystallization. Mineralization via transient amorphous phases has been previously reported in chiton teeth, mollusk shells, echinoderm spicules and spines, and recent reports strongly suggest the presence transient amorphous mineral in forming vertebrate bones. The present finding of transient ACP in murine tooth enamel suggests that this strategy might be universal.

Hierarchical self-assembly of amelogenin and the regulation of biomineralization at the nanoscale

“…Our observations correlate well with the initial mineralization events in vivo. Our earlier studies of amelogenesis demonstrate that the first mineral deposited is amorphous and it is comprised of elongated mineral particles organized into parallel arrays similar to those observed in our mineralization experiments with full-length amelogenin (26). The fact that the shape and organization of the mineral particles in vivo is determined prior to their crystallization indicates that the enamel formation occurs via nonclassical crystallization pathway and that organic matrix plays the major role in the regulation of mineral phase shape and structural organization.…”

“…Our earlier studies have shown that phosphorylated amelogenin is a very strong inhibitor of mineralization and can stabilize amorphous calcium carbonate for relatively long periods of time (8,17). Hence, although recombinant nonposphorylated amelogenin in vitro seems to recapitulate some aspects of in vivo enamel formation, such as transient stabilization of ACP and formation of parallel arrays of crystallites (1,8,26), native phosphorylated protein behaves very differently. At this point, we can only surmise that other proteins in forming enamel modify the strong inhibitory potential of the phosphorylated amelogenin.…”

“…The idea of roughly spherical clusters, 9.5 Å in diameter, with the chemical formula of Ca 9 ðPO 4 Þ 6 was originally proposed by Posner and Betts in the 1970s based upon their studies of calcium phosphate mineralization using the X-ray radial distribution method (24). These clusters, often identified as Posner clusters, are thought to be building blocks of both amorphous calcium phosphate as well as apatitic mineral phases (24,25), which is of particular importance for biomineralization systems where metastable amorphous phases often serve as precursors to crystalline minerals (26,27). After 10 min in the presence of rM179, similar prenucleation clusters formed, which often assembled into small groups (Figs.…”

Elucidation of differential mineralisation on native and regenerated silk matrices

“…Moreover, the decreased tortuosity index of the braided structures (Figure 1) ensured effective permeability and higher contact with supersaturated solution which would subsequently precipitate Ca and P along the structure. Researchers have also acknowledged the existence of another mineralisation mechanism explicitly established in zebra fish bone [38], as well as in human enamel [39], where the nucleation was initiated not through the ions in solution but via an intermediary amorphous calcium precursor. However, lack of sufficient knowledge in this realm makes the generality of this pathway debatable [40,41].…”

The Influence of Amorphous Calcium Phosphate Addition on Mechanical Properties of the Experimental Light-Cured Dental Composite

“…Badania pokazują również, że ACP może brać udział w mineralizacji włókien kolagenowych przez różne mechanizmy [4,5]. Beniash et al [6] wykazali istotny udział przejściowych nierozpuszczalnych faz ACP w mineralizacji szkliwa siekaczy żuchwy myszy. Amorficzny fosforan wapnia jest związkiem szeroko stosowanym w biomedycynie dzięki swojej doskonałej bioaktywności, wysokiej adhezji komórek, regulowanemu poziomowi biodegradacji oraz dobrej osteokondukcji [7].…”