Every dog does not grind their teeth, when they do there are few potential reasons:
Dogs grind their teeth as a response to pain or discomfort. Dogs don’t typically exhibit signs of pain the way humans do , they try to hide their pain by acting as normal as possible as a part of their survival instinct. A small behavior like teeth grinding may be the only hint you have that there is something wrong in your dog’s mouth. Causes of oral pain include periodontal disease, cavities, oral infections, fractured teeth, injury to the oral mucous membranes or tongue, and oral growths or tumors. Some puppies will grind their teeth while they are teething or when there is a loose tooth.
Like oral pain can make some dogs grind their teeth, pain or discomfort in the esophagus (muscular tube connecting throat with stomach), stomach, or intestines can do the same. Teeth grinding in response to pain are a way for dogs to self-soothe or distract from the pain.
A malocclusion occurs when the teeth’s are misaligned preventing the jaws from closing the teeth together properly and evenly. In dogs, it is sometimes called an “abnormal bite” and may be seen as an underbite or overbite. Malocclusions cause the teeth to grind against other teeth involuntarily as a part of normal mouth movement.
This type of teeth grinding may happen unconsciously while dogs sleep.