Sculptra comes in vials which are then reconstituted with sterile water and lidocaine. The number of vials that need to be injected depends on the amount of hollowness or atrophy that you are trying to correct, Because some patients have a considerable amount of atrophy it may take a total of four vials. However, you can not inject four vials in to the face at once because of risk of nodules. Furthermore, from experience, we know that spreading out the vials over time, for example two in the first treatment session, wait one month and then inject one vial, wait another month and then a third vial gives a nice gradual build up of collagen that peaks around 8 months and lasts at least two years from the first treatment. However, if you have minimal atrophy, you may only need two vials, so you could have your first treatment with one vial and your second treatment a month later with one vial and not need a third treatment. So in answer to your question, no, you do not always need three treatments to have lasting results especially if you are not that bad to begin with.