Bruxism (teeth grinding) is indeed associated with stress. But it's also associated with insufficient quantities of some nutrients. Make sure you are getting sufficient quantities of B vitamin, magnesium, and vitamin C as these three are most associated with bruxism. If you still eat some fruit, then the C vitamin should be fine. As for B vitamins, most paleo eaters get sufficient, but B5 supplementation is especially associated with improvement in bruxism so might be worth a shot. And then there is magnesium for which even paleo eaters often do not meet the RDA, so definitely look into that one. Personally, I suspect that most people meet a lot of their magnesium needs via potatoes so cutting those out probably causes problems for some if they don't compensate by eating other high magnesium foods (of which there are not many). Keep in mind that some research says it can take up to 5 weeks of supplementation for the effects to kick in. My advice would be to go to fitday.com and see what nutrients you might not be taking in enough of and consider those as likely candidates. Anyway, it doesn't hurt to make sure all your nutrient intake is at healthy levels.

Intake of alcohol is another factor that sometimes contributes to tendency towards bruxism. And one other is hypoglycemia and blood sugar swings. If you have any issues with hypoglycemia, then try to find a diet that controls that. CUtting out sugar and starch doesn't always make hypoglycemia go away immediately for some people. They are then left with a tricky business of carefully parsing out food intake to dodge hypoglycemia but also dodge blood sugar swings. Bruxism is not only painful but can cause serious teeth and jaw damamge so you should do what you can to prevent it.

Shortly after I stopped eating grains, my tooth-grinding stopped. I suspect, but do not know, that it had something to do with gluten.

You might have tooth pain -- try fluoride toothpaste if you have been avoiding it. Stress is possible too.

Magnesium and B-5 might help.

Don't supplement with "B vitamins" as that would include folic acid, which seems to cause cancer.

I have a similar issue (I'm not sure if I grind or just clench my teeth), which leaves me with tension headaches and a constantly popping jaw. Unfortunately, I tend to also clench my jaw when awake and I have to consciously remind myself to relax. I have even started a weird habit of keeping my tongue or cheeks in between my teeth so I know when I starting to clench.

I am new to paleo/primal and have been easing into it. I have cut out sugars and most processed foods. I just finished a 30-day wheat-free challenge and, to see if I noticed any affects, allowed myself to have a few meals with wheat in them.

Two days after my first meal that reintroduced wheat, I woke up with a sharp pain in my jaw and it was so sore I didn't want to open my mouth. It was that morning that I realized I hadn't had much jaw pain and the frequency of headaches had tapered off during my wheat-free challenge.

While I know stress and other variables can play a role, I am cutting out wheat again because I feel that wheat intake negatively affects this issue. Life without jaw pain and with fewer headaches? Sign me up!

If improving your diet and reducing stress doesn't help, another possible cause might be misaligned teeth and or bones in the head. Functional orthodontics and appliances such as ALF lightwire, SOMA, etc. can realign teeth and improve related conditions such as TMJ and grinding. A well designed appliance though can not make up for poor technique so research carefully for a good practitioner. This is a good start: link (look under 'Find an Holistic "Orthodontist"')