What this means
A dog can open its mouth wide when yawning, taking a toy or allowing an examination. If you notice that the mouth opens only a little, your dog pulls away when you try to look at its teeth, or it seems to want to eat but cannot, that is not fussiness. Sometimes a dog even goes hungry because chewing hurts.
The causes vary. Pain can come from the teeth or inflammation in the mouth, and sometimes the chewing muscles or the jaw bones are affected. Some of these diseases appear in young dogs, others in middle age, and sometimes they affect not only the jaw but other parts of the body. The muscles may look shrunken or hollowed above the eyes, and the eyes can look sunken or red.
Never force the mouth open, because that can cause pain or harm. Note what has changed: whether your dog no longer chews hard food, takes only soft food, whether you hear clicking, whether it drools, whether the breath smells, and whether the shape of the head has changed. If you can, photograph your dog's head from the side and from above. It helps your vet decide which tests are needed.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your dog.
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Inflammation of the chewing muscles
When the immune system attacks the chewing muscles they may first swell and hurt and later shrink. Your dog cannot open its mouth, and the head begins to look narrow.
About the condition: Masticatory muscle myositis -
A disease of the jaw and skull bones
In young puppies of some breeds the bones can thicken and become painful. A puppy cannot open its mouth and the lower jaw looks swollen.
About the condition: Craniomandibular osteopathy (lion jaw) -
Dental and mouth disease
Painful teeth, an abscess or inflammation in the mouth can put a dog off opening wide. Bad breath and drooling often go with it.
About the condition: Dental and gum disease -
Inflammation of the skin and muscles
In dogs of some breeds inflammation affects both the skin and the muscles. Alongside the skin changes a dog may chew and swallow with difficulty.
About the condition: Dermatomyositis -
An injury or a problem of the jaw joint
After a blow or a fall the jaw may be broken or dislocated. The mouth stays half open or will not open.
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Something stuck in the mouth
A stick, a bone or another object can lodge between the teeth or across the roof of the mouth. Your dog may paw at its muzzle and drool.
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Whether the mouth opens only a little or not at all
- Whether your dog chews only soft food or avoids eating
- Whether it drools, has bad breath or paws at its muzzle
- Whether the chewing muscles look shrunken or the eyes sunken
- Whether the jaw looks swollen or the shape of the head has changed
- Whether your dog has a raised temperature, is dull or has skin changes
When to book a routine visit
If your dog has had trouble opening its mouth or chewing for some time, book a visit and do not try to force the mouth open. If your dog cannot eat, drink or swallow, go straight away.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Masticatory muscle myositis Nerves and muscles Masticatory muscle myositis is an autoimmune disease in which a dog's immune system attacks the chewing muscles on the head. The inflamed muscles are painful and swollen, and over time they can waste away and stiffen, making it harder and harder for the dog to open its mouth. The sooner a vet sees the dog, the better the chance of keeping the jaw moving.
- Craniomandibular osteopathy (lion jaw) Bones and joints Craniomandibular osteopathy is a disease of growing puppies in which extra bone builds up irregularly on the lower jaw and on some bones of the skull. The thickened bone is painful, and changes near the jaw joint can make it hard for the dog to open its mouth wide, chew and eat. The condition is thought to be inherited, and its course and how much it has affected the jaw are for a vet to assess.
- Dental and gum disease Digestion and liver Dental and gum disease starts with plaque that hardens over time into tartar, and the bacteria multiplying beneath it cause inflammation of the gums. Left alone, the inflammation can damage the tissues and bone that hold the tooth in place, so teeth loosen and fall out. A sore mouth troubles a dog every day, and infection in the mouth can affect other organs too.
- Dermatomyositis Skin and coat Dermatomyositis is an inherited inflammatory disease that affects the skin and sometimes the muscles. Its signs can appear at a young age, and it can range from barely noticeable skin changes to muscle wasting that makes eating and swallowing difficult. Damaged skin can leave lasting scars and bald patches.
Body systems: Nerves and muscles Bones and joints Digestion and liver Skin and coat