In-vitro subsurface remineralisation of artificial enamel white spot lesions pre-treated with chitosan

To test the null hypothesis that chitosan application has no impact on the remineralisation of artificial incipient enamel white spot lesions (WSLs).

66 artificial enamel WSLs were assigned to 6 experimental groups (n=11): (1) bioactive glass slurry, (2) bioactive glass containing polyacrylic acid (BG+PAA) slurry, (3) chitosan pre-treated WSLs with BG slurry (CS-BG), (4) chitosan pre-treated WSLs with BG+PAA slurry (CS-BG+PAA), (5) remineralisation solution (RS) and (6) de-ionised water (negative control, NC). Surface and cross-sectional Raman intensity mapping (960cm^-1) were performed on 5 samples/group to assess mineral content. Raman spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were used to identify the type of newly formed minerals. Surface and cross-sectional Knoop microhardness were implemented to evaluate the mechanical properties after remineralisation. Surface morphologies and Ca/P ratio were observed using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Data were statistically analysed using one-way ANOVA with Tukey's test.

BG+PAA, CS-BG, RS presented significantly higher mineral regain compared to NC on lesion surfaces, while CS-BG+PAA had higher subsurface mineral content. Newly mineralised crystals consist of type-B hydroxycarbonate apatite. CS-BG+PAA showed the greatest hardness recovery, followed by CS-BG, both significantly higher than other groups. SEM observations showed altered surface morphologies in all experimental groups except NC post-treatment. EDX suggested a higher content of carbon, oxygen and silicon in the precipitations in CS-BG+PAA group. There was no significant difference between each group in terms of Ca/P ratio.

The null hypothesis was rejected. Chitosan pre-treatment enhanced WSL remineralisation with either BG only or with BG-PAA complexes. A further investigation using dynamic remineralisation/demineralisation system is required with regards to clinical application.