One injection is never enough when it comes to Radiesse. I always tell my patients that we are building the foundation of a house. The first injection is there to set the tone. I either add a second to achieve the desired effect at the same time, or might even tell the patient to come back in a week's time. I would not inject more than 3 in one setting, especially when it comes to a material that is not as forgiving as the HAs.
Unlike the work on Restylane where an injection 4 months after the initial showed a longevity of 18 months of the filler, there appears no study of such for Radiesse. A second injection, naturally, would build on what the first had already done and theoretically you should expect a longer effect.
Interestingly, I prefer using an HA filler after the Radiesse injection. First it is much more economical for the patient, plus longevity, in my experience is still maintained rather than with just Radiesse or HA alone.
