I think the get a life comment was a little harsh, nothing wrong with what he's doing. The only time I think you should begin biting hard is for altissimo, if not you might be playing on too hard of a setup (mouthpiece and reed)? 3-4 Hours straight is pretty bad, without any breaks I can play for maybe 40mins. You could try a thinner reed, unless your already pretty thin or else your intonation will start to fail.. Or you could try not practicing EVERY single day, maybe take a break? I practice for an hour (besides the 2 hours during school) at home like once every 2-3 days. Muscles get stronger by tearing and then healing, but if you dont let them heal then your not gaining much...the mouth has a bunch of muscles (more than just 2 muscles like big foot ball players, embrochure is a lot harder to get stronger :P), it takes time to get use to.

Well I don't bite at all and still my teeth cut into my lips. They just are a bit sharp. After all they were built to cut into meat and my lips are meat. I have seen 3 solutions: Paper (works for me) Dental Wax (worked for my teacher but keeping it clean and stuff. too much work compared to papper) Have the dentist file your teeth. I know a guy who had that done. Sounds crazy to me but he was happy. Keep practicing

i agree with everyone when they say that your embochure is the problem. you mouth should be round like you're saying the letter "o" and the bottom lip should form some sort of a cushion for the mouthpiece to rest on. after you get used to this embochure, your lip muscle should build up and you probably won't have trouble with tired lips again.

I was really bad at biting my lip back in school. The best thing that could have happened to me was to put hte horn down for a few years. I've been playing with the correct one since, now that I picked it back up a few years ago. I'm not great, and can't play for a long time (I'm still nto in shape) but at least now I'm doing things the right way.