How Long Does Stitches On Lip Take To Dissolve?

I had some stitches put in on the inside of my bottom lip, it has been 3 wks, and no sign of dissolving, I went to the ER to have them removed and the Doc said that they were dissolving stitches and he did not want to go on a digging expetidion to remove them, how long will it take them to dissolve?