In rare cases, bisphosphonates, the class of medicines to which Fosamax belongs, have been linked to the death of jaw bone tissue. But the bisphosphonates mostly likely to cause this tissue death are the intravenous forms, such as Zometa or Aredia, which are given to cancer patients to retard the spread of tumors in the bone.

The pill form of bisphosphonates like Fosamax, Actonel and Boniva, used to treat osteoporosis, may also raise the risk of jaw necrosis, but extremely rarely.I’ve heard that Fosamax, the osteoporosis drug, can damage the jaw. Is that true?

Bisphosphonate drugs block the normal “turnover” of bone cells, the process by which bone is continuously destroyed, then re-made. With this turnover blocked, tiny fractures may not be able to heal after trauma — whether it’s trauma from chewing hard or from tooth extraction. And because bone is not turning over, infections in the mouth (which is loaded with bacteria), may not heal properly, further damaging the jaw.

In a paper published in May in the Annals of Internal Medicine, researchers from Brigham and Women’s Hospital and elsewhere searched the medical literature for cases of jaw necrosis linked to bisphosphonates. The team identified 368 cases in the last couple of years — 94 percent of which occurred in patients taking the intravenous drugs. Most of these people had breast cancer that had spread, or multiple myeloma, another type of cancer.

Still, because the link has only recently come to light, “the concern is that the 368 figure is an underestimate” of the problem, said Dr. Sundeep Khosla, an endocrinologist at the Mayo Clinic in Minnesota and chairman of a task force recently convened by the American Society for Bone and Mineral Research to look into the issue.

Some patients are suing Merck & Co., the maker of Fosamax. But the company, on its website, noted that as of March, 2006, jaw necrosis probably occurs in less than one in every 100,000 patient-treatment years. Last year, the US Food and Drug Administration asked Merck, and the other makers of oral bisphosphonates to mention the jaw necrosis risk on its product labels.

If you are already taking bisphosphonates and are worried about jaw necrosis, consult a dentist. If you are about to start taking bisphosphonates, try to get dental work done before you start, said Dr. Jon Giles, an instructor in rheumatology at Johns Hopkins University.