I have some kind of $20-30 shockdoctor boil-and-bite mouthguard I picked up at Dick's Sporting goods. My question is how tightly I should bite into it when I am forming it. There are two main layers, the softer layer that moves around when you bite into it after boiling, and a harder layer. I notice if I bite solidly that a lot of the lower layer is showing, which makes me think that I might be biting too hard. However, after I recently reshaped it, biting less hard, I also noticed that I have to use my lower teeth somewhat to keep the mouth guard to stay in consistently, which doesn't seem very good either. Is the mouth guard supposed to always stay in, without assistance from the lower teeth? Should the lower layer of the plastic be showing, or is the upper layer merely for getting a good tight mold rather than providing support? Answers from mouthguard experts would be particularly appareciated.