When fermentable carbohydrates are introduced into the oral cavity, lactic acid production occurs as an end-product of S. mutan bacteria, causing the saliva pH to drop from a neutral pH slightly below 7 to an acidic pH of 4.5-5.5. This metabolizing acidogenic bacteria’s lactic acid production is what demineralizes (removes calcium and phosphate ions) from enamel. Common reasons for the prolonged acid conditions include: consistent carbohydrate intake, reduced clearance of lactic acid due to low saliva content (hyposalivation or xerostomia), impaired saliva pH buffer capacity, and biofilm accumulation due to insufficient oral hygiene care. The more acidogenic bacteria that are present, the more lactic acid produced.
When saliva is released into the oral cavity, in the absence of fermented carbohydrates, the pH of the saliva returns to normal or an approximate pH of 7 and a period of remineralization (repair) occurs. This process is facilitated if fluoride and/or calcium and phosphate are present locally. The balance between demineralization and remineralization is crucial. If the balance is not maintained and demineralization occurs too frequently, then an incipient lesion may occur. This incipient or ‘white spot’ lesion may take up to approximately nine months or more to be seen radiologically as radiolucent (dark spot) on a dental image.