Hey Johanne-

I can't address your obturator questions, but if you will look further down in this same forum topic there is a topic "trismus questions". There is a lot of information there about the lovely jaw stretches. I don't know what my initial measurement was, but after surgery I was only 20. After working with a physical therapist and the high tech tongue blades I am up to 30. I made a pretty detailed entry of exactly what my PT has me doing under "trismus questions," so you might find something in there that would be of some help.
It does seem like I can usually open less wide in the mornings.