Here is an article that gives the estimated half life of bisphosphonates, and factors unique to the oral cavity that may be linked to early manifestation of osteonecrosis in the mouth.
"In order to adequately caution our patients, we need to acknowledge that we are dealing with a condition characterized by a long latency period. That means that the pharmacologic effects of the oral bisphosphonates may not be seen for years, so now is the time to educate our patients."
"There is no current effective treatment for ONJ, even after the medication is withdrawn. Jaw reconstructive surgery, surgical debridements, hyperbaric oxygen therapy, reconstruction with plates, reconstruction with bone, antibiotic therapy, and other treatments have not been completely effective at eradicating the progression of necrotic bone." (biz.yahoo.com)