Cavities (cont.)

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How does a cavity form?

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Two main factors contribute to tooth decay -- bacteria in the mouth and a diet high in sugar and starch. There are over 500 different types of bacteria that are normally present in the mouth. These bacteria combine with food and saliva to form a sticky substance called plaque that attaches to teeth. Foods rich in starches add to the stickiness of the plaque, which begins to get hard if it remains on the teeth after a couple of days and turns into tartar or calculus. Bacteria in the plaque convert sugar into acid that dissolves the tooth structure, causing holes, or cavities. Because of these two contributing factors, dental caries have been described as a "dietobacterial" disease.

The parts of teeth that are most vulnerable to tooth decay are areas where plaque can accumulate most easily. Plaque tends to settle into the pits and fissures in the tops of teeth, into the areas in between the teeth, and next to the gum line. Where there is plaque, there are bacteria and acid, and eventually destruction of the tooth surface. The cavity starts in the outer layer of the tooth (enamel) and as it gets deeper, penetrates into the softer inner layer of the tooth (dentin). Typically, it isn't until the decay reaches the dentin that a person will start to notice signs and symptoms of the cavity.

What risk factors contribute to tooth decay?

Saliva helps prevent plaque from attaching to teeth and helps wash away and digest food particles. A low salivary flow or dry mouth leaves the teeth more vulnerable to tooth decay. This is particularly common in patients with diseases that feature dryness of the mouth, such as Sjögren's syndrome and other diseases of the salivary glands. Genetic factors that affect tooth decay are the following:

  • Tooth size and shape: Small teeth with numerous deep pits and grooves will be more vulnerable to cavity formation than large teeth with fewer and shallower grooves. The grooves and pits provide areas for plaque to build up and are difficult to brush thoroughly.
  • Thickness of enamel: Enamel is the tooth's main defense against cavities, so the more of it a person has, the longer it will take for a cavity to break through to the inside of the tooth.
  • Tooth position and bite: Crooked, overlapped teeth provide more areas for plaque to accumulate and are harder to keep clean. Many problems can occur if the bite is poorly aligned. Poor alignment of the bite can cause the enamel on certain teeth to wear down rapidly, leaving soft dentin exposed. Orthodontics is a great cavity-prevention measure because straight teeth that are in a proper bite position tend to stay cleaner and more cavity-free throughout a person's lifetime.
  • Tooth eruption time and sequence: People who get their permanent teeth earlier in life are at greater risk for cavities because oral hygiene practices may not be developed yet.
Medically Reviewed by a Doctor on 7/2/2014

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