Osteonecrosis of the jaw (ONJ) is, simply put, the death of a portion of the bone in the maxilla (upper jaw) and / or mandible (lower jaw). The most obvious symptom is the visibility of diseased bone through a lesion in the gum tissue. Nutritional improvement, oral antimicrobial treatments, and even surgery can be required to treat this often painful and unsightly ailment.
ONJ has been in the news a great deal over the past several years because of its link to bisphosphonate treatments. Any drug or chemical that suppresses the body's ability to turn over bone tissue can cause ONJ, as can toxic agents such as lead and cadmium, and even infectious agents. However, with the development of bisphosphonate drugs to treat osteoporosis and the entrance of Baby Boomers into menopause, more individuals -- particularly women -- are exposed to a potential risk factor for ONJ.
Bisphosphonates are drugs that inhibit the body's ability to turn over bone tissue. In a healthy human, osteoclasts break down bone cells and osteoblasts grow new bone cells; bisphosphonates cause osteoclasts to self-destruct. The goal of bisphosphonate therapy is to increase bone mineral density. Popular bisphosphonates include zoledronic acid (marketed by Novartis as Zometa or Reclast), pamidronic acid (marketed by Novartis as Aredia), alendronic acid (marketed by Merck as Fosamax), risedronic acid (marketed by Warner-Chilcott and Sanofi-Aventis as Actonel), and ibandronic acid (marketed by Roche as Boniva).
Bisphosphonates are prescribed both for women suffering osteoporosis as a side effect of chemotherapy and for women experiencing the common bone mineral density loss of menopause. For several years, the medical community has been aware of bisphosphonate-related ONJ, or BRONJ, and hundreds of lawsuits against Merck, the manufacturer of Fosamax, are approaching trial in the United States. Two cases have already been decided in favor of the plaintiffs by federal judge John Keenan.
Attempts to measure the increased risk of BRONJ as compared with ONJ are ongoing. The CONDOR dental study, the results of which are included in the April 2013 issue of Texas Dental Journal, found that intravenous bisphosphonate users were 29,950% as likely and oral users were 1200% as likely as non-bisphosphonate users to develop ONJ. Other researchers estimate the relative risk differently; a Kaiser Permanente study published in the same issue of the same journal found that oral bisphosphonate users were 1550% more likely than non-users to develop ONJ. Swedish researchers writing in the August 2013 issue of the Journal of Oral and Maxillofacial Surgery note that the "background incidence" of ONJ is low in Sweden (roughly 0.1 case per 100,000 person-years), individuals are more than 100 times more likely to develop BRONJ than ONJ.
Researchers have hypothesized that osteoclast percursors residing in jaw bone marrow absorb more bisphosphonates than the osteoclast precursors in other types of bone, which could explain the particularly pernicious effect bisphosphonates on jaws. Lower levels of pH in the mouth, which makes conditions ripe for infection, may also be a factor in the pathology of BRONJ. In any case, both doctors and patients are cautioned by the drug manufacturers regarding this risk of BRONJ.