Dental caries is the medical term for tooth decay or cavities. It is caused by specific types of bacteria. They produce acid that destroys the tooth's enamel and the layer under it, the dentin.
Many different types of bacteria normally live in the human mouth. They build up on the teeth in a sticky film called plaque. This plaque also contains saliva, bits of food and other natural substances. It forms most easily in certain places. These include:
- Cracks, pits or grooves in the back teeth
- Between teeth
- Around dental fillings or bridgework
- Near the gum line
Some of the plaque bacteria turn sugar and carbohydrates (starches) in the foods we eat into acids. The acids dissolve minerals in the hard enamel that covers the tooth's crown (the part you can see). The enamel erodes or develops pits. They are too small to see at first. But they get larger over time.
Acid also can seep through pores in the enamel. This is how decay begins in the softer dentin layer, the main body of the tooth. As the dentin breaks down, the enamel over it can collapse, forming a cavity.
If the cavity is not fixed, bacteria will get into the tooth's inner layer. This contains the soft pulp and sensitive nerve fibers.
Tooth roots exposed by receding gums also can develop decay. The root's outer layer, cementum, is not as thick as enamel. Acids from plaque bacteria can dissolve it rapidly.
No one really knows what causes the pain people get with cavities that have not entered the pulp. Theories include:
- Inflammation caused by bacteria
- Exposure of the root surface
- Imbalance of fluid levels in tiny openings called tubules inside the dentin
Symptoms
Early caries may not have any symptoms. Later, when the decay has eaten through the enamel, the teeth may be sensitive to sweet, hot or cold foods or drinks.
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