A cavity is a tiny hole that forms on the surface of the tooth. It is caused by the mixture of sugars in the food we eat and bacteria that are in our mouth, producing a mild acid that attacks the hard outer layer of teeth (called enamel). Cavities are more common in children. But adults can also be affected. Mostly on the 2 categories in adults:
1. Cavities that form around a filling cavities or "recurrent" means the surface of a tooth restored is not as smooth as that of a natural tooth. Small food particles and bacteria may remain stuck at the edge of the shutter, thus promoting the formation of a new cavities. In addition, the exposed part of a tooth filling which is broken is more susceptible to cavities. 
2. Cavities that form the root of tooth decay or "root" years of brushing too hard, even aging may push back the gums, exposing the roots. The latter have no enamel to protect them and are therefore more susceptible to cavities. During the dental examination, in addition to search for signs and symptoms of decay as brown or black spots, your dentist also checks the status of your fillings. It may suggest that you replace those who are mobile or broken. It may also decide to take an X-ray to examine more closely the problem areas. If you have cavities, your dentist can decide either to monitor its evolution (if the cavity is small), or is to restore the tooth immediately. If it does not restore a large cavities, it can get bigger and cause pain. It may even have to extract the tooth and replace it with a false tooth (or artificial tooth).