The prevalence of a serious dental disorder known as osteonecrosis of the jaw among people taking oral bisphosphonate medications is about 1 in 1,400, according to preliminary findings of a new study. The results will be presented Sunday, June 15, at The Endocrine Society’s 90th Annual Meeting in San Francisco.

The Predicting Risk of Osteonecrosis with Bisphosphonate Exposure, or PROBE, Study is being conducted at Kaiser Permanente Northern California, in collaboration with the U.S. Food and Drug Administration (FDA). The FDA and the National Institutes of Health provided funding support for this study.

“PROBE is one of the first U.S. observational studies with direct follow-up of patients who took oral bisphosphonates to determine how many developed osteonecrosis of the jaw,” said Joan Lo, MD, lead author and an endocrinologist at Kaiser Permanente Division of Research.

Jaw osteonecrosis is exposed bone in the lower and/or upper jaw in the absence of prior radiation or cancer in the jaw. Most reported cases of osteonecrosis of the jaw have occurred in cancer patients who received intravenous bisphosphonates, which are given at much higher doses than their oral counterparts, Fosamax, Actonel and Boniva, Lo said. However, cases of this condition have been reported in patients receiving oral bisphosphonate therapy, most commonly for long-term treatment of postmenopausal osteoporosis. According to the American Dental Association, most cases happened after an invasive dental procedure, such as a tooth extraction, but some occurred spontaneously, without any dental work.

The PROBE Study surveyed 13,946 members of Kaiser Permanente Northern California who were taking oral bisphosphonates for at least one year and had no record of ever receiving the intravenous form. Of these, 8,544 patients returned a mailed survey that asked about dental symptoms. Patients with symptoms either had a follow-up dental exam or had their dental records reviewed. An oral surgeon examined patients suspected of having osteonecrosis of the jaw. To receive a diagnosis of osteonecrosis, the patients must have had exposed bone for more than 8 weeks.

Among the 8,544 respondents who took oral bisphosphonates, Lo’s team has found six cases of jaw osteonecrosis so far, for an initial prevalence of 0.07 percent, or 7 in 10,000, Lo said. “Our final prevalence may be higher or lower upon completion of the study.” Lo said. “This prevalence is low but somewhat higher than previously estimated.”

Some of the patients had prior dental extractions at the diseased site and several had palatal tori, bony lumps on the roof of the mouth that are easily injured. The team also found a comparable number of patients with other jaw-related complications.

“I think the benefits of oral bisphosphonate therapy outweigh the risks for most patients with osteoporosis,” Lo said, “but it is important that we better understand who is at risk for jaw osteonecrosis and how we can prevent serious jaw-related complications.”

The authors continue to receive dental records and it is possible that they may identify a few more patients with the condition, she said.