You are correct a relaxed Embouchure would not cause teeth marks in the mouthpiece. I played the different Clarinets and Alto Saxophone as well as the Oboe. The botXXXXX XXXXXp should be relaxed when playing but the top teeth will put marks in the mouthpiece. I noticed some of my mouthpieces especially when I played the Alto Clarinet, I would make more teeth marks in my mouth piece
When playing a piece that has a lot of staccato notes I notice myself tightening up with my teeth on the top of the mouthpiece because of the tongueing of the notes. We hear more about a relaxed Embouchure when playing the Oboe or the brass instruments.
This link goes over the Embouchure: http://adamjberkowitz.com/?p=499
When you are first taught the Clarinet and Saxophone they have you resting your teeth on the top of the mouthpiece and your botXXXXX XXXXXp on the reed. When you start playing, and developing your style, it is hard not to tighten up around the mouthpiece.
I actually have played since I was in Junior High which is over 40 years and have gone through many mouthpieces in that time. My worst time was with the Oboe, where I would break the double reeds and that got quite expensive. Joan
Each person developes their individual style. I remember back when some of my band mates had braces and how that affected their Embouchure. Many had to put pieces of wax between their lips and teeth and that also affected the way they played. I know some of my mouthpieces had to be replaced along the way and to this day I still have some tucked away that have teeth marks form one time or another. Joan