I feel your pain. Literally.
I learned to play from teachers that never mentioned pressure either. I am amazed that I was able to play without pain when I was in high school. When I started playing again I resorted to pressure and used the same embouchure I used in high school; the old "smile" embouchure. Unfortunately, my mouth and teeth didn't seem to be inpervious to it the way they did in high school. I used so much pressure that I had sore and loose teeth! The only thing I can think of is that my teeth and my trumpet playing both grew up together and were used to each other.
I didn't take long until I decided that there had to be a better way
and decided to find it. Mostly I listened to the discussions on the
TPIN. Methods like Mark Van Cleave's, Clyde Hunt's and The Maggio system
all stress the use of a dynamic embouchure and tongue level to adjust pitch.
While there are many proponents and oponents of these methods, I believe
that methods are all generally correct (IMHO). I had been trying
to make the change on my own using Schlossberg and Arban's but the method
that really showed my how to make my embouchure work was Clyde Hunt's.
Getting your embouchure to work is, I believe, the key. It should
not be static. Right now your embouchure is not doing the work, your
arm is. Once you experience playing with an embouchure that adjusts
for each note and see how it can be done with little pressure, you will
be amazed. I know I was. It is difficult to leave the pressure
It takes constant awareness. Once you are able to get the feel of how it is done, it really helps. You can then strive for that feeling as you play. The Maggio system is also (IMHO) good for this (I like the monkey).
One aspect that has also helped me quite a bit to understand was playing softly in the upper register while consciously adjusting my embouchure with as little pressure as possible (M. Van Cleave stresses this). This really shows you how to use your embouchure should move to achieve the results and leave pressure behind. Good luck. It can be done.
Tim "IMHO" Hutson