Jawbone Enlargement in Dogs

4 min read

Craniomandibular Osteopathy in Dogs

A dog’s mouth is made up mainly of two bones, the mandible (lower bone) and the maxilla (upper bone). These two bones come together at a joint called the temporomandibular joint (TMJ). The TMJ is the joint that allows the jaw to open and close. Dogs use their cheek muscles to move the TMJ in order to open and close their mouths.

Craniomandibular osteopathy is a condition by which extra bone forms along the mandible and TMJ, making it painful and difficult for the affected dog to open its mouth and eat. Signs are usually seen in puppies that are four to eight months of age, and it is seen more in some breeds of dogs than others. Breeds that are the most commonly affected are Scottish Terriers, Cairn Terriers, and West Highland White Terriers. Breeds with a lesser incidence of this condition, but which also have a higher than normal diagnosis are Labrador Retrievers, Great Danes, Boston Terriers, Doberman Pinschers, Irish Setters, English Bulldogs, and Boxers.

Symptoms and Types

  • Pain when opening the mouth
  • Difficulty opening the mouth
  • Difficulty picking up food
  • Difficulty chewing and concurrent loss of appetite
  • Pain and difficulty eating get worse with time
  • Fever that comes and goes
  • Eyes that seem to bulge out (exophthalmos), due to swelling within the skull
  • Swelling in jaw
  • Excessive drooling


Inherited. The genetic predisposition is strongest with West Highland white terriers.


Your veterinarian will need a thorough history of your dog's health leading up to the onset of symptoms. Paying careful attention to your dog's head during the examination. your veterinarian may be able to feel a decrease in the amount of muscle on the sides of your dog's head, along with a thickening of the bone along the sides of the jaws. There will also be obvious pain when trying to open your dog's mouth, and it may not even open all the way.

A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and biochemistry levels. These will be used to identify whether there are any abnormalities in your dog's bones. Further blood tests may help to rule out or verify fungal or other types of infection. The most precise diagnostic tool for this condition will be x-rays images taken of your dog's head, which will show the abnormal bone growth. In most cases these will be all of the tests that need to be done, but for some cases, your veterinarian may also want to get a sample of the bone (bone biopsy) to make sure your dog's symptoms are not caused by a tumor or bone infection.

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