There are many different types of fillers injected into the lips. The most popular is the hyaluronic acid filler. There are also a number of factors which determine how long lip fillers last. It depends on the type of filler being used, your immune system, your doctor, and mouth movement. Juvederm is known to be the longest lasting lip filler and can last anywhere from 12-18 months. If you received a Juvederm lip filler, which is very possible, it is normal that it hasn't dissolved. However, if you wish that your filler dissolves, that are treatments to reverse lip fillers.