Can teeth grinding (TMJ) be related to digestive problems? If we have TMJ, we will not be able to do oil pulling. Is there something similar to do instead of oil pulling?

Absolutely. Often clinically this is a sign of intestinal fungus, worms, or protozoa-- especially if you wake up multiple times throughout the night or have trouble falling asleep. TMJ can also be stress-related. If there is something going on in your personal life or inner world that is not being communicated, expiated, or expressed, it can show up this way as well. Journal, write, or talk to someone if that resonates with you. It can also be connected to fungus and parasites, both of which are more active at night. If you cannot do oil pulling, I'd suggest using a water pick and adding hydrogen peroxide to it 2-3x/week or gargling with it at the very least.