Cavities, as we know them in people, are not common in dogs and are quite rare in cats. Many "holes" in teeth are assumed to be "cavities" but they are, in reality, the opened pulp chambers of broken teeth. Other "holes" are due to the reabsorption of tooth structure. These resorptive lesions are very painful and should be evaluated promptly. When cavities do develop, they result from bacterial decay of the tooth structure. The decay usually starts in the pits and fissures on the flatter surfaces of molars in dogs. Cavities found early can be drilled and filled just as in people. If the decay has extended into the pulp, then a root canal procedure must be done to salvage the tooth. Often the problem is not discovered until major tooth destruction has occurred and extraction is the only option.