Would one syringe of Bellafill be enough to treat small smile lines?

An examination or photographs of you would be needed to give you the best advice in regards to possibly using Bellafill to improve your smile lines.  I would say it is possible that one syringe would be enough to treat both smile lines, but this would be for one treatment only.  Bellafill is a stimulating agent and normally requires several treatment sessions to gradually produce the desired effect.  

It really depends on the degree of correction needed. I can't guide you without pictures. I will place Bellafill in this area using cannulas for increased safety and less downtime. If after 4 months, you feel you need more, another syringe or 2 can be added.

How many vials you use of Bellafill will depend on how deep your lines are.  There is no absolute minimum nor maximum for how many vials you will need.  However, you can always add one vial at a time until your desired correction is achieved.  It can help stimulate collagen for many years so it is ok to start with one vial.

of course a photo would be needed to tell how much material will be needed.. smile lines can be easily filled but since they move so much during facial expression i would not expect the results to last as long as an injection in a non moving area such as the cheek bone or in an acne scar

While it is hard to say how much you will need without seeing any photos the good news is that it does not matter.  One of the beauties of Bellafill is that Bellafill is a long term filler.  It is, in fact essententially permanent, so if one syringe does not get you the results that you are looking for, it will be an improvement and you can always add more at some point in the future.  If you compare Bellafill to the other fillers, you will always have to come back for more with all of the others.  I hope that helps.Best regards.