When I yawn my jaw muscles tense up and hurt why is this?

If your jaw muscles are irritated from doing a lot of chewing (gum, for example) or from clenching or grinding your teeth, yawning can overstimulate the muscles causing a spasm. This spasm leads to the feeling of tenseness and pain.

Try a soft diet for a week or so and see if this helps. You might want to see your dentist as well.

This has to do with the arrangements of the various ligaments in this area.

When you yawn, you are opening your mouth, and causing the mouth to open. This causes the ligaments and muscles to shorten, which can cause discomfort. Try moist heat when u get up in morning. Keep smiling!

One possibility is that your clench/grind your teeth which can cause problems with the jaw muscles.

To check out this problem, see an oral surgeon.