Figure 5: Demineralization of hydroxyapatite (HA) and remineralization with fluorapatite (FA) - depicted as stage 1-5 Stage 1: Fermentable sucrose intake. Stage 2: Microbes in cariogenic plaque metabolise them releasing acid in the biofilm-tooth interface. The pH in the interface drops below the critical pH of HA Stage 3: Phosphate ions from oral fluid buffer the acidic ions resulting in undersaturation. Stage 4: HA disintegrates to release the phosphate ions back to the oral fluid till it supersaturates-Demineralization Stage 5: Supersaturated oral fluid re precipitates the minerals onto the disintegrated enamel. If fluoride also deposits FA is formed on the superficial layer - Remineralization. Sub surface demineralization remains.