Deposition of Amelogenin--Apatite Composite on Human Tooth Enamel

Background: Synthesis of enamel-like biocomposites provides a promising approach for development of new generation of dental restorative materials with improved esthetic and mechanical properties. Objectives: To implement a biomimetic approach for the growth of calcium phosphate layers on human dental enamel surface, in the presence of amelogenin and fluoride. Methods: Mineral deposition took place on the exposed surface of enamel from extracted human third molars. Thin sliced samples were soaked in supersaturated calcium phosphate solution at 37^oC, pH 7.4-7.6 in the presence of varying amounts (5-100 mg/mL) of recombinant porcine amelogenin (rP172) and fluoride (0.01-2 ppm), for 2-24 hours. The samples were rinsed with deionized water and air-dried. Mineral phase was analyzed by ATR-FTIR and micro-Raman spectroscopy. Morphology and orientation of the crystals were examined by SEM and TEM. Results: In the control, octacalcium phosphate (OCP) plates with dimensions of 2-10 mm in width and about 50 nm in thickness were formed creating a surface with porous structures. In the presence of amelogenin (30-70 mg/mL) the coating was still porous and smaller OCP crystals with curved-flake morphology were formed. In the presence of 0.5-2 ppm fluoride and without amelogenin rod-like fluoridated apatite crystals having high aspect ratio, with diameters of 20-30 nm and length of more than 500 nm were formed. In the presence of both amelogenin (50-100 mg/mL) and fluoride (1ppm), bundles of oriented rod-like fluoridated apatite crystals were formed creating a dense coating on the enamel substrate. Such bundles were not formed at low concentrations of rP172 (< 30 mg/mL). Conclusion: Amelogenin and fluoride played a key role in the in vitro synthesis of organized nano-rod bundles formed on pre-existing enamel surface. Such protein-mineral composite has a potential for the design and future development of improved dental restorative material.

NIH-NIDCR grants DE-13414, DE-15332