Abstract:

Objective To investigate the effects of remineralization solutions with different calcium-to-phosphate ratios on the properties of the remineralized layer induced by phosphorylated polyamidoamine (P-PAMAM) dendrimers, to determine appropriate P-PAMAM mass concentrations and calcium-to-phosphate ratio, and to provide insights for the construction of an intraoral remineralization system. Methods Phosphoryl groups were used to modify PAMAM in vitro. The modification results were confirmed by attenuated total reflectance-Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. The mass concentration was screened by analyzing the ability of P-PAMAM to absorb hydroxyapatite(HAP) and its biocompatibility. Demineralized human enamel samples were prepared. The samples were divided into groups with remineralization conditions of 2∶1+P-P, 1.67∶1+P-P, 1.67∶1, 1∶1+P-P, and 0.5∶1+P-P. After 24 hours, 1 week, and 3 weeks of in vitro mineralization, the surface morphology was analyzed by scanning electron microscopy, the hardness of the remineralization layer was analyzed by micro Vickers hardness tester, and the crystal structure of the remineralization layer was analyzed by X-ray diffraction. Results Under a calcium-to-phosphate ratio of 1.67∶1 and the mediation of 4 mg/mL P-PAMAM, a dense and smooth remineralized layer formed on the demineralized enamel surface after 1 week, with a crystal structure similar to that of natural HAP. After 3 weeks, the surface micro Vickers hardness of the enamel was significantly higher than that of the other groups(P<0.000 1), and the enamel surface hardness could be restored to the level of healthy enamel. Although the remineralized layer formed in the absence of P-PAMAM reached a certain thickness, the disordered growth of numerous crystals resulted in defects in surface morphology and micro Vickers hardness. Under a high calcium-to-phosphate ratio (2∶1), the remineralization layer induced by P-PAMAM tended to be disordered in the later stage, which limited the recovery of the surface morphology and mechanical properties of the enamel. A low calcium-to-phosphate ratio (1∶1, 0.5∶1) limited the induction effect of P-PAMAM, resulting in poor formation of the remineralization layer and an increase in the content of carbonated hydroxyapatite and amorphous calcium phosphate in the remineralization crystals. Conclusion P-PAMAM-mediated remineralization achieves optimal efficacy when the calcium-to-phosphate ratio in the mineralization solution is 1.67∶1. Increasing or decreasing the ratio may reduce its effectiveness.

Key words: phosphorylated polyamidoamine dendrimers, human tooth enamel, remineralization, hydroxyapatite