Hi Kathy:  Great question...  Bisphosphonates are a class of drugs that have a very low risk of causing osteonecrosis of the jaw (ONJ).  Evista isn't a bisphosphonate.  Evista comes from the drug family called SERM's (selective estrogen receptor modulators).  From what I've read and understood, there isn't any incidence of osteonecrosis with Evista, but to be sure ask your Dr to explain this class of drug and their side effects.  Here's a link that explains all the osteo meds, explained by PJ Hamel in her excellent blog on these various treatments, that may help you to understand the difference between them all.

Good luck on your journey to better bone health.