Bone loss caused by our own immune system

May 1, 2000
If this complex immune response is not interrupted, bone loss will continue until significant support is destroyed and the teeth are lost.

If this complex immune response is not interrupted, bone loss will continue until significant support is destroyed and the teeth are lost.

Trisha E. O`Hehir, RDH, BS

Bacteria are considered to be the cause of periodontal disease. But bacteria do not destroy the bone and connective tissue - the body does! It seems strange to think a person`s own defense system causes the breakdown associated with periodontal disease. But that really is what happens.

Toxins produced by bacteria in the sulcus penetrate the junctional epithelium and trigger the immune response, ultimately destroying the bone and supporting tissues around the teeth. If the immune system doesn`t get too excited about the bacteria, connective tissue and bone remain intact. When the immune system goes wild, connective tissue and bone are destroyed until the teeth are lost.

Looking first at the bacterial biofilm, it begins as gram-positive rods and cocci. Depending on oral hygiene - and the immune system - the sulcus may be an incubator allowing the biofilm to mature.

With routine mechanical disruption of the biofilm and an effective immune system, the biofilm will remain gram-positive and the tissue response will remain one of reversible gingivitis. With inadequate mechanical disruption of the biofilm, an overgrowth of gram-negative anaerobes will occur. If this patient`s gingival tissue becomes highly inflamed, the substances produced by the inflammation will nourish the bacterial biofilm and allow maturation of gram-negative, black-pigmented, anaerobic species. In the presence of gingival inflammation, these bacteria are nurtured.

Bacteria release lippopolysaccharide (LPS), which then passes through the epithelial attachment and triggers the immune system. In response to LPS, the body sends white blood cells to the area to fight the infection. In children, the response to LPS is very weak. This explains why children experience gingivitis that rarely progresses to periodontitis.

LPS stimulates release of histamine from mast cells near the blood vessels in the connective tissue. Dilation of the blood vessels allows for the release of white blood cells (neutrophils). Ideally, the white blood cells will travel through the connective tissue to the site of the bacteria. They mark the bacteria for consumption by phagocytic cells. This sounds simple, clean, and easy. When biofilm growth is controlled, the immune system can handle the level of LPS released. The tissue response remains at a level of reversible gingivitis.

During gingivitis, neutrophils move to the sulcus to fight the bacteria. This phase can be measured in gingival crevicular fluid by a breakdown product of neutrophils, leukotriene B4. As the biofilm becomes more gram-negative, bleeding upon probing increases rapidly.

A gingival crevicular fluid-marker for prostaglandin E2 becomes evident. This signals that the level of LPS has exceeded the body`s neutrophil defense. The amount of LPS penetrating the tissues is significantly increased, triggering even more substances that break down the connective tissue and bone.

Here`s what happens. As neutrophils move from the connective tissue to the sulcus, they release substances to destroy the connective tissue. It`s almost as though each white blood cell has its own machete to cut through the tough underbrush of the connective tissue which blocks the path to the sulcus. The cytokines/machete destroy the connective tissue, allowing the blood cells to reach the sulcus more quickly. As the connective tissue is destroyed, epithelial cells move into the area, creating pocket epithelium.

The cytokines you will hear most about are interleukin-1ß (IL-1ß), tumor necrosis factor alpha (TNF) and prostaglandins (most often PG-E2). Interleukins stimulate the release of prostaglandins and matrix metalloproteinases. Tumor necrosis factor acts in a similar way to interleukin. IL-1ß and TNFσ act synergistically, causing the release of histamine and seratonin, platelet-activating factor, and prostaglandins. Prostaglandins are noted for breaking down bone and stimulating the production of other bone-destroying substances, such as osteoclasts. Tissue redness and edema are attributed to the ability of prostaglandin-E2 to induce vascular permeability and dilation. PG-E2 also stimulates monocytes and fibroblasts to release matrix metalloproteinases. It is definitely a complex series of events.

If this complex immune response is not interrupted, bone loss will continue until significant support is destroyed and the teeth are lost. This entire process begins with bacterial plaque biofilm, but each person`s oral hygiene and immune response actually determine the eventual outcome. To summarize this process for patients, the body`s defense system destroys the bone around the teeth in an attempt to stop the disease process. Professional and daily removal of the bacterial biofilm will allow the body to re-establish a healthy balance, preserve bone around the teeth, and contribute to a healthy body.

Trisha E. O`Hehir, RDH, BS, is a senior consulting editor of RDH. She also is editor of Perio Reports, a newsletter for dental professionals that addresses periodontics. The Web site for Perio Reports is She can be reached by phone at (800) 374-4290 and by e-mail at [email protected].