A controversial breed, the pit bull has long been the face of ‘vicious dog attacks’ and many gruesome tales: some true, some fictional.
It has even been said that once a pit bull bites you, its jaws will lock into place, remaining in place until it decides to let go or is beaten off. However, is there any sort of truth to this? Can pit bulls lock their jaws? Where did this rumor come from?
The Anatomy of Canine Skulls
Like most animals, pit bulls have an upper and lower jaw.
The upper jaw connects directly to their skull, and the lower jaw, or ‘mandible,’ connects to their skull with a joint on each side of their head. This mandible is held tight by a number of muscles and tendons that give pit bulls the freedom to chew, yawn, and open and close their mouths.
Dog skulls can vary depending on the breed, but these are usually cosmetic differences. For example, the skull of a pug is very small and round, with a short snout, compared to other breeds. However, the structure of the skulls mostly stays the same. 
Animals that can lock their jaws, such as the crocodile, have a secondary joint in their skull. This allows the force of the bite to be spread out, meaning that the crocodile can hold the bite for longer without getting tired, effectively ‘locking its jaws.’
It's important to note…No dog breeds, including the pit bull, have this secondary joint. This means pit bulls DO NOT have the biological ability to lock their jaws.
There is also no veterinary evidence to support that there is a specific enzyme unique to pit bulls or any other dog breed that could stiffen their tendons and lock up their jaws. It would also be impossible to produce this supposed enzyme on command.
So, where did this rumor come from?
The Bite of a Pit Bull…
Purpose and Nature
One of the places this rumor could have started is with the pit bull’s origin. Pit bulls were originally bred to be bull-baiting dogs - meaning that they had to be able to hold on tightly to large animals, like bulls or bears, without being thrown off.
A pit bull needed strong jaws to help it hold on for its life.
This ability to hold on was bred into them, both purposefully by breeders and unintentionally, as the dogs that held on would survive longer.
Pit bulls are also noted for being very stubborn and strong; this, combined with their breed purpose, makes it difficult to shake a pit bull off. While other dog breeds may bite and let go, a pit bull is likelier to try and hold on.
The Strength of Their Bite
So if pit bulls can’t lock their jaws but can still hold on, that must mean they have a powerful bite force, right?
Measuring bite force is not an exact science and depends a lot on a dog’s age, temperament, and the cause of the bite (a playful nip vs a hunting bite). Bite force is measured in PSI (Pound Force per Square Inch), a unit for determining pressure.
It is also quite tricky to get several dog breeds and mixes to bite the same object with force. So, therefore, most of these studies produce varied results and we can only guess the averages these dogs can bite at.
The American pit bull terrier seems to be the pit bull with the highest bite force, and in most studies…didn’t even crack the top ten.
Most pit bulls have a bite force PSI between 270 - 300 PSI, meaning that they are outranked by German Shepards, most Mastiff breeds, Akitas, and the most powerful dog bite in the world…The Turkish Kangal which has a whopping bite force of around 731 PSI. 
So, not even the powerfully strong American pit bull terrier can compare to the true big-league biters of the dog world.
Interesting fact! - The saltwater crocodile, an animal that does possess the ability to lock its jaws, was recorded as having a bite force of around 3700 PSI, with some Nile Crocodile going way further than that.
Therefore, the difference between locking and regular jaws is quite clear - as well as what side the pit bull sits on.
Pit bulls have a lot of tenacity and a high prey drive from their terrier ancestors compared to other dog breeds. A lot of damage from pit bull bites is from them shaking their prey rather than anything to do with locking jaws.
A real cause of ‘lockjaw’ in pit bulls, and all other breeds, is the dangerous disease ‘tetanus.’ While dogs don't contract tetanus as often as humans, it can still be a real issue.
Tetanus is the name given to a condition caused by the bacterium Clostridium tetani. This bacterium causes a build-up of tetanus toxins in the body that can affect muscles, nerves, the spine and the brain.
Tetanus bacteria are also widely available in the environment, and a dog can easily contract it from having an open wound or being bitten by another dog.
When really bad, Tetanus can cause extreme muscle tension, causing a dog to walk stiffly. It can also cause muscles in the face to seize up, leaving a dog unable to open its mouth and causing locking jaws, which may be more common with bites to the face.
It is possible that, as fighting dogs, pit bulls were more susceptible to being bitten in the face than some other breeds, causing them to contract tetanus more often.
This misunderstanding may have led to the belief that pit bulls have locking jaws that they can lock on command - rather than the dog suffering from a painful disease.
Tetanus does not make a pit bull dangerous and does not affect its bite force, but severe cases can make eating, drinking, and breathing difficult. It's best to take your pit bull to a veterinarian who can assess the right treatment for your pit bull’s jaw.
Other symptoms of Tetanus can include forehead ridges (from muscle spasms), excessive drooling from being unable to swallow, a stiff walking pattern, a rigid tail, and a fever from the infection.
Vets don’t normally give Tetanus injections to dogs, so the best treatment normally involves prompt wound care. You can flush out a wound on your dog’s body and apply antibacterial cream to the affected area to reduce the chance of infection.
How To Get a Pit Bull to Let Go
The biggest weapon against dog bites is prevention. Owners of pit bulls should begin training when their dogs are still young. Pit bulls are not naturally aggressive, as some claim, but they may require more training due to their stubborn nature.
Young pit bulls should be well-socialized with humans, dogs, and other animals. This means giving them access to social areas such as parks and helping them keep calm in tense situations. Pit bull puppies should also be discouraged from ‘play biting’ too much, as they can keep this behavior into adulthood.
Pit bulls that are actively attacking can sometimes be discouraged by throwing a blanket or jacket over their heads or squirting them with water. If you see a pit bull attacking another dog or animal, it's usually best to try and distract them using the methods above. Otherwise, do not risk your own safety by trying to get involved. If you have been gripped, you can try to hit them sharply on the nose.
What You Should Take Away…
Despite being a common myth, even among pit bull lovers, pit bulls are completely biologically incapable of locking their jaws on command. They have no unique jaw structure or enzyme that would allow them to lock their jaws.
This rumor may have started since pit bulls have historically needed to hold onto prey to save their lives and because they can be pretty stubborn in refusing to let go.
A pit bull’s jaws can be very strong, but they don’t have that much bite force. The American pit bull terrier is the pit bull with the strongest bite force, and even they rank far below many larger dogs such as alsatians and mastiffs.
The false ‘fact’ that pit bulls have an uncanny ability to lock their jaws can and has been used to contribute to the stigma surrounding them. That said, pit bull bites can be dangerous, as they can cause quite a bit of damage with their bite. The best solution is prevention. Train your pit bull to follow your commands and to be calm in hairy situations.
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Keeping owners and their pit bulls safe - as well as reducing stigma - is a priority for us. Feel free to check out our Harness Collection here.