If you have only mild to moderate hollows, then try the more robust forms of hyaluronic acid like Juvederm Ultra Plus or Perlane.   These should last 6-9 months the first time and slightly longer after that.  Generally, 1 syringe per cheek is average.  There is a longer lasting form in Europe made by Juvederm called Voluma but it is not FDA approved here so it's not yet available.  If your volume loss is more severe, then Sculptra will give you a very natural, long lasting correction without the stiffness.  Usually 2-3 treatments are needed to correct with 1 treatment a year for maintainance.   Dr. I