Could this be the result of jaw clenching?

yes most probably may be .

According to what you said it is a jaw joint disorder, may be due to disharmony between joint components, clenching may be the underlying cause, you may have sleeping clenching that means you may be clenching your jaws during sleeping, so for it is a simple problem that can be solved by simple night guard which an elastic cover of upper teeth preventing night clench, here is the picture of the Appliance

http://www.imageno.com/h47eb146c6bdpic.html

Could be. Your dentist would probably give you a night guard. You can buy one at your local pharmacy they sell tooth brushes,etc. Cost should be 20 - 30 dollars, not the 300.00 the dentist would charge you. I would suggest that you make it fit the lower teeth. f that doesn't help, see your dentist