I got my lips done, they used Princess Voluma. I want to get them done again but I want to do Juvederm -- can I mix the product?

Yes you can have juvederm even if the Princess Volume it has not completely dissolved. They will dissolve at different rates however meaning you may need another injection when the Princess volume completely dissolves but at one year it probably is already gone. So nothing to worry about. 

Yes, you can have a different filler.  I prefer to use a micro cannula to inject the lips to prevent bruising.I hope this helps.

Yes, it is fine to have a different type of filler for lip augmentation. Keep in mind, results take 1-2 weeks. Best, Dr. Emer

It is fine to proceed with further injections.  Typically you only need to wait two weeks between injections just to give the bruising and swelling a chance to resolve.  It is fine to mix the two products.

Typically, lip filler results last between 6-12 months depending on the product used. Yes, it is ok for you to get Juvederm at this point. 

I have used other filler in the same location as filler placed using a different product. It has not been a problem for me.

Juvederm Line Products can generally be mixed rather well. If it's been a year, it's probably time for you to top off your lips. Good luck from New York City