Anatomy of the tooth
The enamel is a dense protective covering of the tooth; it appears as a whiter shell around the tooth. The dentin is the inner part of the tooth; it appears as the light-gray part of the tooth. The nerve (pulp) of the tooth appears as a shadow inside the tooth.
No decay / healthy tooth
At this stage there is no tooth decay. There are no symptoms and no treatment is needed.
Incipient caries / baby cavity
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At this stage there is some enamel demineralization which is visible in the enamel if the cavity is between teeth. The actual extent of decay goes slightly beyond what is visible on the radiograph. If the cavity is on the top of the tooth, it will not be visible on the radiograph. Most patients experience no symptoms at this point.
Incipient lesions can be remineralized with good oral hygiene, good dietary habits, and fluoride (click here to read more about cavity prevention). Most patients do not require treatment at this point. Your doctor will recommend whether to treat or watch the area based on your personal caries risk.
Early stage cavity
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At this stage the decay has broken through the enamel into the dentin. The actual extent of decay goes slightly beyond what is visible on the radiograph. If the cavity is on the top of the tooth, it is usually not visible on the radiograph. Most patients experience no symptoms at this point.
Early stage lesions will not fully remineralize and should be treated with a filling to prevent further decay.
Medium-stage cavity
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Because dentin is softer than enamel, the cavity grows much faster in dentin. The actual extent of decay goes beyond what is visible on the radiograph. Most patients still experience no symptoms at this point.
These cavities should be treated with a filling to prevent further decay.
Late-stage cavity
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At this stage the decay is near or at the nerve. Some patients may experience a sharp pain to hot or cold. Some patients will not have any symptoms until the cavity is removed.
These cavities often need a root canal, build-up, and crown.
Late-stage cavity, dead nerve
If the pain to hot/cold is ignored, it will usually go away for a few months. At this stage the nerve is dead, and an infection is developing or present. When the pain returns, it is usually as a throbbing pain and/or pain to chewing.
These cavities need a root canal, build-up, and crown.
Non-restorable
If there is not enough tooth structure remaining, the tooth will need to be removed. Your doctor can discuss treatment options which may include an implant, bridge, or denture.