Are dermal fillers safe?

Hi there. I'm 38 and getting very fine lines on my upper lips. Would like to consider fillers, however, I am concerned that they may migrate or cause cell death. I have also had filler in my nasolabial folds (juvederm or restylane, can't remember) which has lasted 2 years. I have read that it is not usual for it to last this long and am concerned.