Amelogenin-guided Crystal Growth on Fluoroapatite Glass-ceramics

Abstract

The formation of aligned fibrous apatite crystals in enamel is predominantly attributed to the involvement of amelogenin proteins. We developed a model to study interactions of matrix proteins with apatite mineral in vitro and tested the hypothesis that amelogenin solubility affects the ability to induce protein-guided mineralization. Crystal growth experiments were performed on fluoroapatite (FAP) glass-ceramics in mineralizing solutions containing recombinant full-length amelogenin (rH174) at different concentrations. Using atomic force microscopy, we observed that mineral precipitated randomly on the substrate, but also formed thin layers (height, 10 nm) on FAP within 24 hrs. This growth pattern was unaffected when 0.4 mg/mL of rH174 was added. In contrast, crystals grew on FAP at a rate up to 20 times higher, at 1.6 mg/mL protein. Furthermore, nanospheres and mineral bound specifically to FAP and aligned in strings approximately parallel to the c-axis of FAP, leading us to the conclusion that amelogenin proteins indeed control direction and rate of growth of apatite in enamel.

Electromechanical imaging of biomaterials by scanning probe microscopy

“…Interestingly, several isolated regions with a high-piezoresponse signal are observed in the enamel region, indicative of the presence of a low fraction of protein Wbers. Although it is recognized that enamel of a fully developed tooth does not contain proteins, the early stages of tooth development require the presence of amelogenins to guide the HAP crystal growth (Habelitz et al, 2004;Ishiyama et al, 1999). No protein inclusions were observed in the outer layers of enamel.…”

Mimicking the Self-Organized Microstructure of Tooth Enamel

“…The technical difficulties involved in directly evaluating the crystal nucleation rate have led to other approaches to initial crystallization events, and one of the most common ways to characterize the kinetics of nucleation is to measure the induction period (t s ) prior to nucleation at different supersaturations. The induction period can be expressed as eq 9: 19,52 (9) where κ [= 16πγ 3 Ω 2 /3(kT) 3 ] remains constant under a given set of conditions. V is the volume of the system, R s and N 0 are the radius of curvature and the density of the additives/substrates, respectively, and B is a kinetic constant.…”

Effects of Fluoride on the Interactions between Amelogenin and Apatite Crystals

“…To determine further the nature of amelogenin binding to fluoride-containing apatite, we used a polished fluorapatite-ceramic disc with oriented rod-like fluorapatite crystals (0.7-1.0 μm wide) embedded in a glass ceramic (Habelitz et al, 2004). These discs were first treated with 200 μL of binding buffer (20 mM Tris-HCl, pH 7.5) containing NaF/NaCl (1000 ppm F − ), allowing either the fluoride or chloride in the solutions to bind to positive sites on the apatite crystal surface.…”