Combined effects of nano-hydroxyapatite and Galla chinensis on remineralisation of initial enamel lesion in vitro

Objectives: The aim of the present study was to investigate the combined effects of nano-hydroxyapatite and Galla chinensis on remineralisation of initial enamel lesion. Methods: Bovine enamel blocks with in vitro produced initial lesion were used. The lesions were subjected to a pH-cycling regime for 12 days. Each daily cycle includes 4 x 3 min application with one of five treatments: NaF (positive control), deionised water (negative control), crude aqueous extract of G. chinensis (GCE), nano-hydroxyapatite (nano-HA) and GCE with nano-HA. The samples were subsequently evaluated using a microhardness tester, polarised light microscopy (PLM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results: Surface hardness measurements and integrated mineral recovery value obtained from cross-sectional microhardness test (CSMH) revealed that all the treatment groups had significantly greater effect on enhancing remineralisation than that of the negative control group. Detailed investigation of both CSMH and PLM indicated that nano-HA would only help mineral deposition predominate in the outer layer of lesion and had limited capacity to reduce the lesion depth significantly. In GCE-nano-HA combined treatment group, more mineral deposition occurred in the lesion body and lesion depth was reduced significantly. Meanwhile, significantly greater mineral deposition in the outer portion of the lesion was also observed in comparison with GCE group. The results of XRD and SEM also showed that GCE could influence the deposition and adsorption of nano-HA. Conclusion: There was a significant synergistic effect of combined GCE and nano-HA treatment on promoting the remineralisation of initial enamel lesion. (C) 2010 Elsevier Ltd. All rights reserved.