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Therapeutic effect of chitosan on remineralisation of enamel carious lesions by bioglass-based biomaterials

Student thesis: Doctoral ThesisDoctor of Philosophy

Objectives: To investigate the effect of chitosan (CS) on subsurface remineralisation in vitro of incipient human enamel carious lesions by bioglass-based materials. Materials and methods: Artificial enamel white spot lesions (WSLs) were formed using a methylcellulose gel (8 wt.%)/lactic acid (pH 4.60) demineralisation system for three weeks. Lesions were subjected to static and/or dynamic remineralisation regimes in each study. For dynamic investigations, the feasibility of a modified 7-day pH-cycling regime was validated by using simulated plaque fluid. Chitosan was prepared and applied as solution for pre-treatment or as chitosan-bioglass complexes slurry. For the pre-treatment study, the lesion surfaces were pre-treated with chitosan and remineralised using bioglass (BG) or bioglass-polyacrylic acid (BG-PAA) slurry and compared to those without pre-treatment. To further simulate oral conditions, an in vitro pellicle layer was formed for three minutes and the efficacy of chitosan pre-treatment was again evaluated. Chitosan-bioglass complexes were prepared by mixing chitosan solution and bioglass powder to form a slurry and the remineralisation potential was compared to chitosan pre-treatment. The artificial lesions were characterised by optical coherence tomography (OCT, lesion depth), tandem scanning confocal microscopy (TSM, surface morphology), Raman intensity mapping (mineral content), Knoop microhardness (KHN, structural strength), and scanning electron microscopy (SEM, ultrastructural morphology). The chitosan-bioglass complexes were characterised using infrared spectroscopy (IR) to evaluate their chemical composition. All comparisons were considered statistically significant if p < 0.05. Results: Artificial WSLs were formed successfully using the acidic gel after three weeks demineralisation. Lesions had a relatively intact surface layer and revealed structural similarities to natural lesions, as shown by SEM. The modified pH-cycling regime led to remineralisation either by simulated plaque fluid or 1450 ppm fluoride as revealed by the thickened surface layer compared to the negative control (12.64 ± 3.22, 22.02 ± 3.14 and 7.32 ± 2.07 μm, respectively). Notable surface depositions were found after pH-cycling in all groups, suggesting toothbrushing was required for the subsequent study. Chitosan pre-treatment improved the subsurface remineralisation after both static and dynamic treatment with either BG slurry only or BG+PAA, as subsurfaces showed in increase in mineral content and Knoop microhardness and denser morphology at least down to 20 µm depth. SEM images showed irregular depositions covering the lesion surface after static remineralisation, which disappeared in the dynamic studies. The pellicle layer was formed successfully on the lesion surface after three minutes and shown to cover the surface porosities in SEM observations. The existence of the pellicle had an impact on the remineralisation, as the surface had a significant mineral regain in a standard remineralisation solution (RS) group but the subsurface remained porous. The surface mineral regain was significantly lower (p < 0.05) in BG+PAA groups regardless of chitosan pre-treatment, but the subsurface microhardness was greater than the negative control. BG group with pre-treatment exhibited greater subsurface microhardness and denser morphologies compared to the non-pretreated BG group, suggesting the pellicles had less impact on the potential of chitosan on enhancing subsurface remineralisation with BG. In the study of chitosan-bioglass complexes, SEM images and IR spectra suggested that amorphous calcium phosphate was formed after the preparation of the slurry. RS had more surface mineral regain than other groups due to the pellicle after static remineralisation. The tendency was reversed using the dynamic regime, as the complexes group showed a significantly greater mineral regain than RS (p < 0.05). Hardness results implied that the complexes improved the surface and subsurface microhardness better than chitosan pre-treatment. SEM observations found that the lesions treated by chitosan-bioglass complexes had a denser surface and subsurface than other groups in both static and dynamic studies. It was also found that the remineralisation deteriorated in pH-cycling in all investigations. Conclusions: Chitosan shows potential in enhancing subsurface remineralisation by bioglass-based materials either in the form of pre-treatment or as chitosan-bioglass complexes in clinically simulated conditions.
Original languageEnglish
Awarding Institution
Award date2018


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