According to the Research: Trisha E. O’Hehir, RDH, BS
Editorial Director, Hygienetown Magazine

According to the research, periodontal disease is a bacterial infection. However, the destruction of connective tissue and bone that qualify the infection as periodontitis rather than gingivitis is not caused directly by bacteria or viruses. It’s due to the immune system. That’s right, our own immune system causes destruction of connective tissue and bone, all in an attempt to stop the bacterial infection.

Bacterial infection

Bacteria are normal in the mouth and are needed to begin the digestive process. In health, there is a balance of many bacteria, but when this balance changes, then the problems begin. One change is an increase in all the bacteria seen when someone doesn’t ever clean interproximally and the plaque level is high. Another change occurs when the bad bacteria outnumber the good bacteria. Both changes can take place at the same time. As the bacterial plaque level increases, so does the level of bacterial toxins the body must defend against.

Permeability of the junctional epithelium

The inflammatory response is triggered when the junctional epethelium (JE) becomes more permeable, thus allowing bacterial toxins to pass through. The JE is made more permeable by the presence of volatile sulphur compounds (VSC), which are released with the breakdown of protein and bacteria, and responsible for the odors of bad breath. The cell turnover rate in infected areas is much more than in healthy sites, thus the distinctive odor of periodontal disease. In fact, bad breath also may be a precursor to periodontal disease. If the bad breath is due to high plaque levels on the tongue and teeth, the VSC level can go up and this leads to increased permeability of the JE.

Bacterial antigens trigger immune response

Toxins passing through the JE travel through the epithelium and then into the connective tissue where they activate the immune response in two important ways. First comes chemotaxis, or the migration of white blood cells – polymorphonuclear leukocytes (PMN). At the first sign of bacterial toxins, the immune system immediately sends PMN to the area to wipe out the bacteria.

Secondly, the toxins prompt the mast cells around the blood vessels to release histamine. This causes vasodilation, the step needed to allow the PMN to move to the sides of the blood vessels and begin their journey through the vessel walls and out into the surrounding connective tissue and eventually to the site of the bacteria – the sulcus.

PMN produce chemical machetes

Now remember, the connective tissue around the blood vessels is healthy. The problem is in the sulcus. As the PMN make their way through healthy tissue to the sulcus, they release cytokines, chemical machetes that destroy healthy connective tissue, thus allowing the PMN to pass through more quickly.

The goal of the PMN is to kill the bacteria; they don’t really pay attention to the destruction they cause on the way. In a healthy person, the body balances the destruction/repair interaction. This first alert system and attack by the PMN effectively destroys the invading bacteria and the body heals in the effort. If the immune system is healthy, this destruction is a small price to pay for effectively controlling the bacteria in the sulcus. Such equilibrium can be seen in individuals who develop gingivitis, yet never progress to periodontitis with loss of connective tissue and bone. That’s because the body is able to balance destruction and repair.

Compromised immune system is overactive, yet not effective

In an immunocompromised individual, the PMN aren’t efficient at wiping out bacteria nor do they efficiently eat up dead bacteria (phagocytosis). As the bacterial toxins continue to pass through the JE and trigger the immune system, the body keeps sending more PMN to the area to get rid of the bacteria. More chemical machetes are released and more healthy connective tissue is destroyed. The immune system keeps trying, but as more and more PMN arrive at the area, more tissue is damaged and the bacteria are not eliminated by the PMN. The balance is now in favor of tissue destruction, not tissue repair.

The immune response is much more complex, but this snapshot of infection and the immune response can provide a framework for understanding the process. Understanding the complexity of the disease process reinforces the value of your treatment and patient education. So, the next time you examine puffy, red, bleeding tissue, remember the roles of the bacteria and viruses that trigger the infection and the immune system’s part in the destruction of underlying connective tissue.