Caries is the chemical dissolution of the hard tooth structures - enamel and dentin - by the acid created as the bacteria in dental plaque ferment carbohydrates. The development of caries is dependent on the interplay between processes that cause demineralization of tooth enamel, and those which cause remineralization: Only when factors favor the high acidity that leads to demineralization does caries occur. In this section, the dynamic process of demineralization and remineralization is discussed, paying particular attention to tooth hard tissue structure, the role of acid production by cariogenic bacteria, and the critical pH at which tooth enamel begins to dissolve. The role of acid-reducing bacteria, saliva, and fluoride in tooth hard tissue remineralization will also be explained.

Clinical Significance Snapshots

How does understanding the demineralizing-remineralizing cycle help me prevent or arrest the caries process in my patients?

The ‘demin-remin’ cycle is like the ebb and flow of money in a checking account. If too many withdrawals are made and too few credits received, then the account becomes overdrawn. Credits that match or exceed the debits leads to a healthy financial situation. The same applies to calcium ions entering and exiting the tooth. Some loss of calcium inevitably occurs at mealtimes, as the cariogenic bacteria in the biofilm on the surface of the tooth metabolize the sugars in the diet via glycolysis. This creates a low pH or acidic environment that is capable of driving demineralization. Between meals, the saliva brings the pH back to safe levels (above pH 5.5) when the calcium ions can return to the tooth (remineralization). If there is not enough time for sufficient remineralization, then there is an overall loss of calcium from the tooth, the subsurface lesion may develop, bacteria enter the tooth material and the cavitation process commences. To prevent the occurrence of caries in your patients, it is important to include information about foods that lead to demineralization in oral health counseling, and note that saliva needs time between food intakes to restore any loss of calcium by sugar-containing foods and beverages. Foods rich in calcium and that stimulate saliva flow are very beneficial at the end of any meal. Examples would be yogurt, cheese, or milk (super-saturated with calcium) or a sugar-free chewing gum (saliva stimulation).

Why is the use of fluoride agents so prominent in the prevention of dental caries?

Hydroxyapatite crystals in enamel are impure, due to the presence of carbonate ions. Carbonate ions make the carbon-hydroxyapatite weak and much more easily dissolved by acids. Fluoride ions can replace some of the carbonate and hydroxyl ions to create fluorapatite. Fluorapatite is physically much stronger than carbon-hydroxyapatites, and more resistant to acid dissolution. Essentially, fluoride tips the demin/remin balance in favor of remin. Fluoride should be applied daily in low concentration via the use of toothpaste that has proven bioavailability of fluoride (ADA Seal of Acceptance). Additional forms of fluoride application should be considered for patients more at risk of caries due to frequent consumption of sugars or poor saliva flow. These would include fluoride rinses (daily or weekly depending upon strength), and professional application of gels or foams rich in fluoride.