Some people can do significant damage to their teeth from grinding them in their sleep. Sometimes it is a daytime habit. This can lead to abnormal wear, cracked teeth, pain in the teeth and even tooth loss.
Below are pictures of a person I saw not long ago and you can see how far over they move the jaw.
This movement outside the normal range of chewing is called Parafunction. We know this must be from habitual chewing (like nail biting) or from bruxing during sleep, because people just don’t chew their food on the front teeth in such an uncomfortable position.
A night splint can help protect the teeth from damage while the patient is asleep.