it would be the same bad habit as biting your nails.... or smoking...
Nothing really can help unless you just stop doing it...
Maybe suck a lollipop or something :) or snack on biltong or chewing gum
Keep a journal... finding out what makes you feel "Stressed out" will help you decide what activities you are "up to doing" on a certain day. I have the same issue for many years now. For example if your mother in law who makes you crazy calls and asks you to lunch, you might say "Gee can we make it for another day when I have MORE time" or "thanks for the invite, I'd rather go see the new Tom Cruise movie with you" or even turn her down because YOU need to take care of yourself!! Also, check with your dentist. They may have an appliance for your mouth. I have an appliance to help me because I also GRIND my teeth. Try relaxing by taking a HOT bath, use techniques like Yoga or meditation, deep breathing, read a good book, watch a favorite movie, etc. In other words CUT BACK ON STRESS!! Blessings, MG