Causes:

Periodontal disease is marked by bacterial overgrowth. However, a persistent immune response to chronic infections in the mouth is believed to play a major role in gum destruction.

Bacterial Culprits

Reachers have found more than 350 species of microorganisms in the typical healthy mouth. Periodontal infections are linked to fewer than 5% of these species. Healthy and disease-causing bacteria can generally be grouped into two categories:

• The harmless or helpful bacteria are usually known as gram positive aerobic bacteria.
• In periodontal disease, the bacterial balance shifts over to gram negative anaerobic bacteria. Inflammatory disease and injury cannot develop without these bacteria.

Following are some of the bacteria most implicated in periodontal disease and bone loss:

• Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis. These two bacteria appear to be particularly likely to cause aggressive periodontal disease. Both P. gingivalis and A. actinomycetemcomitans, along with multiple deep pockets in the gum, are associated with resistance to standard treatments for gum disease. P. gingivalis may double the risk for serious gum disease. P. gingivalis produces enzymes, such as one called arginine-specific cysteine proteinase, that may disrupt the immune system and lead to subsequent periodontal connective tissue destruction.
• Bacteroides forsythus is also strongly linked to periodontal disease.
• Other bacteria associated with periodontal disease are Treponema denticola, T. socranskii, and P. intermedia. These bacteria, together with P. gingivalis, are frequently present at the same sites, and are associated with deep periodontal pockets.

Some bacteria are related to gingivitis, but not plaque development. They include various streptococcal species.

The Autoimmune and Inflammatory Response

Evidence indicates that periodontal disease is an autoimmune disorder, in which immune factors in the body attack the person's own cells and tissue -- in this case, those in the gum. It appears to work like this:

• The bacteria that form plaque and tartar release toxins that stimulate the immune system to overproduce powerful infection-fighting factors called cytokines.
• Ordinarily, cytokines are important for healing. In excess, however, they can cause inflammation and severe damage.
• In addition, white blood cells produced by the immune response to bacteria also release a family of enzymes called matrix metalloproteinases (MMPs), which break down connective tissue.

Studies suggest that this inflammatory response may have damaging effects not only in the gums but also in organs throughout the body, including the heart.

Viral Causes

Certain herpes viruses (herpes simplex and varicella-zoster virus, the cause of chickenpox and shingles) are known causes of gingivitis. Other herpes viruses (cytomegalovirus and Epstein-Barr) may also play a role in the onset or progression of some types of periodontal disease, including aggressive and severe chronic periodontal disease. All herpes viruses go through an active phase followed by a latent phase and possibly reactivation.

These viruses may cause periodontal disease in different ways, including release of tissue-destructive cytokines, overgrowth of periodontal bacteria, suppressing immune factors, and initiation of other disease processes that lead to cell death.