Periodontal disease is defined as the destruction of tooth attachment (periodontal ligament and jaw bone), caused by bacteria. It begins when bacteria form on teeth in a substance called plaque. If plaque is not removed immediately, two things occur. First, the plaque is calcified by the minerals in saliva to become calculus (or tartar). This is the brown substance on teeth that many people mistakenly equate with periodontal disease, but the truth is that calculus does not result in periodontal disease.

The other thing that occurs with chronic plaque formation is that it will start to move under the gumline. Once the plaque gets under the gum, it starts causing inflammation, which is called gingivitis. Gingivitis is the initial, reversible form of periodontal disease. If this inflammation is not controlled, the bacteria within the gingiva change to a more virulent type. These more virulent species create more severe inflammation. Eventually, the body responds to this inflammation. Part of this response is bony destruction, which continues until the tooth is lost. However, in most cases, periodontal disease causes problems long before this happens. (See above, Is dental disease really a big deal?)