Regeneration of biomimetic hydroxyapatite on etched human enamel by anionic PAMAM template in vitro

To repair the demineralized enamel by biomimetic method, and the effect of Poly (amido amine) (PAMAM) dendrimers on the crystallization of hydroxyapatite on etched enamel surface is investigated.

PAMAM dendrimers were synthesized step by step following the classical method and modified with the carboxylic acid groups (COOH) on the surface. Demineralized human enamel samples were immersed in 10,000ppm PAMAM-COOH solution for 30min and then in calcium phosphorous solution with or without fluoride under near-clinical conditions for 20h. Other samples without PAMAM-COOH were immersed in calcium phosphorous solution as the control group. After the immersion, the micro structure, morphology and composition of the regrown crystals on the longitudinal and transversal enamel surfaces were investigated by SEM, XRD and FTIR, and the results were compared with etched enamel and intact enamel.

With the PAMAM-COOH templates, well-arranged rod-like crystals were formed and they were parallel to the long axis of enamel crystals, which was more obvious on the longitudinal enamel surface. Otherwise, irregular flake-like crystals were obtained without PAMAM-COOH. Fluorapatite was not influenced by the PAMAM-COOH but its specific distribution also shown the patterns of the PAMAM-COOH temples XRD spectra showed that the main phase of the obtained crystals with PAMAM-COOH was hydroxyapatite and their morphology and structure were close to the intact enamel. Amide I band and two bands of methylene groups of PAMAM-COOH detected by FTIR demonstrated the presence of PAMAM-COOH within the biomimetic coating.

It was concluded that PAMAM-COOH can play as the organic template on the demineralized enamel surface to induce the formation of HAP crystals with the same structure, orientation and mineral phase of the intact enamel in relatively short time.