Effect of Enamel Matrix Derivative on Biomimetic Mineralisation of Enamel

Objective:  Enamel matrix derivative (EMD) has been shown to promote periodontal regeneration but its effect on biomimetic mineralisation of enamel is unknown. To investigate the effect of EMD on biomimetic mineralisation of demineralised enamel. Method: Enamel slices prepared from extracted sound human molars were demineralised with 37% phosphoric acid for 1 minute. The slices were put into polyethylene tubes and covered with a 2-mm-thick EMD-calcium chloride (CaCl₂) agarose hydrogel, which was created by mixing EMD (Emdogain, Straumann, Basel, Switzerland) with CaCl₂ agarose hydrogel. Another 2-mm-thick pure agarose hydrogel was added on top of the EMD-CaCl₂ agarose hydrogel. After gelation, they were immersed in phosphate solution containing 500ppm fluoride and incubated at 37°C for 4 days. The slices treated with CaCl₂ agarose hydrogel without EMD were used as control specimen. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray Diffraction (XRD) were used to evaluate the crystals formed on enamel surface. The elastic modulus and nanohardness of the regenerated enamel, natural enamel and etched enamel were evaluated with nanoindentation test. Result: SEM showed the formation of enamel prism-like crystals on demineralised enamel. The crystal prisms consisted of typical apatite hexagonal structures which was similar to enamel microstructure. EDX revealed the presence of calcium, phosphorus and fluorine ions in the formed crystals. XRD also confirmed the crystals formed were fluorinated hydroxyapatite. The crystals formed in the control specimens were loosely packed crystal bundles which did not resemble natural enamel structure. The elastic modulus before and after remineralization were 59.1GPa and 78.5GPa (p<0.001), respectively; whereas their nanohardness were 1.1GPa and 2.2GPa, respectively (p<0.001). Conclusion:  EMD can promote in-vitro biomimetic mineralisation and facilitate enamel prism-like tissue formation on demineralised human enamel. This study is first to report using EMD in biomimetic mineralisation, which may serve as a biomaterial for enamel repair.