This is my main issue with Radiesse and why I don't use it much.  In my opinion, the longevity of it is less predictable than with the Juvederm/Restylane products.   In some patients the Radiesse seems to last what the manufacturer claims - about 9 months (ish) and, in others, it seems to be gone in 3 months.   I can only guess (since there are no studies on this) that it's because we have variable levels of the enzymes that break it down.  For more see my article on dermal fillers.   Dr. I