Effects of zinc and fluoride on the remineralisation of artificial carious lesions under simulated plaque-fluid conditions

Abstract

The aim was to study the effects of zinc and fluoride on remineralisation at plaque-fluid (PF) concentrations. Artificial carious lesions were created in two acid-gel demineralising systems (initially infinitely under-saturated and partially-saturated with respect to enamel) giving lesions with different mineral distribution characteristics (high- and low-R respectively) but similar integrated mineral-loss values. Lesions of both types were assigned to one of four groups and remineralised for 5 d at 37°C. Zinc and fluoride were added, based on PF concentrations 1 h post-application, to give four treatments; 231 µmol/L zinc (Zn), 10.5 µmol/L fluoride (F), zinc/fluoride combined (Zn/F) and an unmodified control solution (non-F/non-Zn). Subsequently remineralisation was measured using microradiography. High-R lesions were analysed for calcium, phosphorus, fluoride and zinc using electron-probe microanalysis (EPMA). All lesions underwent statistically-significant remineralisation. For low-R, remineralisation was in the order non-F/non-Zna < Fa < Znab < Zn/Fb, and for high-R, Fa < non-F/non-Znb < Znb < Zn/Fc (treatments with the same letter not significantly different (p < 0.05)). Qualitatively, remineralisation occurred throughout non-F/non-Zn and Zn, predominantly at the surface-zone (F) and within the lesion-body (Zn/F). EPMA revealed zinc in relatively large amounts in the outer regions (Zn, Zn/F). Fluoride was abundant not only at the surface (F) but also in the lesion-body (Zn/F). Calcium:phosphate ratios were similar to hydroxyapatite (all). To conclude, under static remineralising conditions simulating PF, Zn/F gave significantly greater remineralisation than did F, possibly because zinc in Zn/F maintained greater surface-zone porosity when compared with F, facilitating greater lesion-body remineralisation.