What are you using the erbium yag for is the first question. Are you doing a superficial peel, a fractionated ablation or a deeper peel? Silicone is a permanent filler. If you are using the laser to try to remove the permanent filler I am not sure that this is a good approach. In most cases the silicone is placed in the deeper layers of the lip and most lasers will not reach them easily. If your question is more about safety or will the laser harm the underlying silicone the same response is true that in most cases the filler is deep and the laser does not need to go that deep to achieve its results. Your doctor should be able to know where they put the silicone, look at your lips and decide whether the laser depth they are planning will effect the silicone. As a disclosure, I do not inject silicone and so one of the responding plastic surgeons who does may be able to give you better insight into this subject. However, my experience is with other fillers such as Radiesse, Restylane, Perlane, Cosmoderm, Cosmoplast, Juvederm, Zyplast, Zyderm, Hyalaform, etc and for these I would be comfortable with specific erbium yag laser settings over these fillers.