Dear Adventurous528225: Great question! No scientific answer. History has developed the experiential use of this medication. From the beginning of bone healing with the use of PLLA in the 1940’s, to the nodular complications in the facial cheeks during the 1990’s (with greater volumes and concentrations) to the current cosmetic surgery dilutions; I will provide my theoretical stab at your question. In the face, I have found the recommended dilution of Sculptra powder (PLLA) to be adequate given the volume of each facial side. I have estimated this to be 10 cc. Elsewhere, I have used (off-label) dilutions elsewhere in order to diminish cost but lengthen the number of sessions to achieve the goals of the patient. That being, firming of the underlying subcutaneous tissues and evening of dimples and irregularities by tightening the dermal skin. I believe it takes about 2 weeks for the fibroblasts (forming collagen and other essential structural skin molecules) to kick in. Thereafter, I have found a exponential growth of contour improvement peaking at 12 weeks. I therefore, re-inject 1 vial of half strength Sculptra per 20 cc of estimated volume. If each gluteal-cheek area is estimated at 60 cc; then 3 vials per cheek; re-injected at 6 – 12 weeks to maintain the growth. Thereafter, the residual PLLA particles will continue to stimulate at a more linear rate for 8 to 12 months. I, therefore recommend a yearly booster injection once you have reached the desired firmness and fullness for maintanence. The risk of nodular complications occurs when the concentration of the suspension is unable to be properly distributed throughout the desired volume. This occurred during the 1990’s developing not granulomas (foreign body reactive lumps) but collagenomas due to over stimulation of the fibroblasts and dense collagen formation. I hope this has been helpful.