Cavities or Dental Caries: Symptoms and Causes

Dental caries or cavities also known as tooth decay, is a breakdown of teeth due to acids made by specific types of bacteria.

Updated: June 16, 2022

Dental caries or cavities also known as tooth decay, is a breakdown of teeth due to acids made by specific types of bacteria. The acid produced by the bacteria destroys the tooth's enamel and the dentin. The cavities may be a number of different colors from yellow to black.
Different types of bacteria normally live in the human mouth which are build up on the teeth in a sticky film called plaque. This plaque also contains saliva, bits of food and other natural substances. Plaques can be formed most easily in certain places which include:

  • Between teeth
  • Around dental fillings or bridgework
  • Cracks, pits or grooves in the back teeth
  • Near the gum line

The bacteria turn sugar and carbohydrates in the foods we eat into acids.  Simple sugars in food are these bacteria's primary energy source and thus a diet high in simple sugar is a risk factor. The acids dissolve minerals in the hard enamel that covers the tooth's crown  which gradually destroys or develops pits. The pits are too small to see at first. But they get larger over time. Acid also can enter through pores in the enamel resulting in beginning of decay in the softer dentin layer. A cavity is created as the dentin and enamel break down.
If the decay is not treated, bacteria will continue to grow and produce acid that eventually will get into the tooth's inner layer which contains the soft pulp and sensitive nerve fibers.
Tooth roots exposed by receding gums can  also develop decay. The root's outer layer called cementum is not as thick as enamel and can be dissolved rapidly by acids produced from plaque bacteria.

Symptoms of Cavities:

A person experiencing cavities may not be aware of the disease. The earliest sign of a new carious lesion is the appearance of a chalky white spot on the surface of the tooth.  This is referred to as a white spot lesion or a microcavity. As the lesion continues to demineralize, it can turn brown but will eventually turn into a cavity.
The process is reversible before the cavity forms, but once a cavity forms, the lost tooth structure cannot be regenerated. Active decay is lighter in color and dull in appearance. As the enamel and dentin are destroyed, the cavity becomes more noticeable. The affected areas of the tooth change color and become soft to the touch.
Once the decay crosses the enamel, the dentinal tubules, which have passages to the nerve of the tooth become exposed, resulting in pain that can be transient, temporarily sensitive to heat, cold, or sweet foods and drinks. Sometimes a  tooth weakened by extensive internal decay can suddenly fracture under normal chewing forces.
A toothache can result when the decay has progressed enough to allow the bacteria to overcome the pulp tissue in the center of the tooth resulting in death of the pulp tissue and infection. The pain will become more constant and the tooth will no longer be sensitive to hot or cold.
Cavities can also cause bad breath and foul tastes. In highly progressed cases, an infection can spread from the tooth to the surrounding soft tissues. 

Cause of Cavities:

For cavities to be formed four things are required. These can be

  • enamel or dentin, a tooth surface
  • cavities causing bacteria
  • fermentable carbohydrates such as sucrose
  • time

Adherence of food to the teeth and acid creation by the bacteria build up the dental plaque. When the dental plaque lye on the teeth and mature, it become decay. Certain bacteria in the plaque produce acid in the presence of fermentable carbohydrates such as sucrose, fructose, and glucose which damage the enamel of the tooth.


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