Method: In the experiments, 60 mg calcium-release agent was added into 30 ml simulated oral fluid (SOF) which contained 100 mM glutamate (Glu) and then the human enamel specimens were incubated with the reaction solution for 24 hours at 37°C. Scanning electron microscope, Transmission electron microscope and Nano-indentation techniques were used to reveal the structure and mechanical properties of the new hydroxyapatite layer on enamel surface.
Result: The results revealed that the preferential orientation and mechanical strength of the newly formed hydroxyapatite crystals on enamel surface were similar to natural enamel. We noted that the enamel surface treated with the calcium-release agent and Glu had a hardness of 4.12 ± 0.53 GPa and elastic modulus of 95.16 ± 6.23 GPa. These values were similar to that of natural enamel (hardness of natural enamel: 4.56 ± 0.68 Gpa, elastic modulus: 98.04 ± 7.28 GPa). Moreover, we also found that Glu promoted the kinetics of the formation and crystallisation of hydroxyapatite. In contrast, SOF or the calcium-release agent without Glu could not provide a permanent repair, which showed no obvious promotion effect on the formation of ordered enamel-like hydroxyapatite layer on enamel surface.
Conclusion: The cooperation of calcium-release agent and Glu can result in the regeneration of enamel-like structure under physiological conditions. Importantly, the mechanical characteristics of the repaired enamel are maintained well by using this enamel model.