Last updated October 26, 2026
A dog has two carnassial teeth on each side of its mouth, the big fourth premolar on the top and the first molar on the bottom. They meet like a pair of scissors and do the heavy work of shearing meat and crushing hard things. Because they take that load, they are also the teeth that crack most often, and a cracked upper carnassial is the usual reason a dog turns up with a swelling under one eye.
This page explains which teeth they are, why they break, and what it means when one gets infected. A broken tooth or a facial swelling is a vet visit, so the last thing here is how a vet sorts it out, not a home fix.
What the carnassial teeth are and where they sit
Run a finger along the outside of your dog's upper back teeth and the largest one you reach, about level with the front of the eye, is the carnassial. In full it is the upper fourth premolar. Its partner sits just behind and below it on the lower jaw, the first molar. A dog has one pair on the left and one on the right, so four carnassials in all.
Vets label them by number. The upper fourth premolars are teeth 108 and 208, and the lower first molars are 309 and 409. You do not need the numbers, but they explain why a report after a dental might read "fractured 208" when the vet means the left upper carnassial.
These are cheek teeth, set back where the jaw muscles are strongest. That position is what makes them useful, and it is also what puts them at risk. To see where the carnassial sits among the rest of the teeth, our dog mouth anatomy guide walks through the whole set of 42 adult teeth.
Why these teeth shear and why they crack
The upper and lower carnassials pass each other like blades rather than meeting tip to tip. That shearing action lets a dog slice through meat and gristle and split hard material it could not grind with the flatter molars behind. It is the bite a dog uses when it turns a bone to the side and works it with the back of the mouth.
All that force runs through the upper carnassial, which is why it is one of the teeth that fractures most. The usual break is a slab fracture, where a slice of the outer wall of the tooth shears off, often taking the surface of the pulp with it. Tooth fractures are common in dogs overall, and the carnassials take more of this load than the teeth around them.
What breaks a carnassial is almost always something too hard to give. Cooked bones, dense weight-bearing leg bones like beef shin or marrow bones, antlers, hooves and hard nylon chews are the repeat offenders. A simple check is your own thumbnail. If you cannot dent the surface with it, the object is hard enough to crack a tooth.
Inside the tooth, three roots and an apical delta
The upper carnassial is not only the biggest cheek tooth, it is built to match. It has three roots, two at the front and one at the back, where most teeth have one or two. The lower carnassial has two. A study of 86 of each tooth in mixed-breed dogs and German Shepherds confirmed this three-and-two pattern and measured the roots in detail (Tandir and colleagues, 2024).
That same study found that each root does not end in a single neat hole. It finishes in an apical delta, a small spray of several tiny openings at the tip. For a dog owner the point is simple. Three long roots and a cluster of openings at each tip are why an infection in this tooth is stubborn, and why saving it takes a skilled vet rather than a quick pull.
When a crack becomes an abscess under the eye
A fresh slab fracture is painful because it exposes the pulp, the living core of nerve and blood vessels inside the tooth. Once that core is open to the mouth, bacteria travel down the root and settle at the tip, where they can build a tooth abscess. The abscess sits deep in the jaw, not on the gum where you would see it.
Here is the part that catches owners out. The roots of the upper carnassial reach high into the upper jaw, close to the eye socket and the nasal cavity. When the tip of a root becomes infected, the pressure often finds its way out through the skin, and it surfaces as a firm swelling or a weeping sore on the face just below the eye. Many owners treat it as an eye problem first. Antibiotic eye drops will not clear it, because the trouble is the tooth underneath.
A swelling under the eye, a sore that keeps draining, blood from the nose on one side, or a dog that suddenly chews on one side only all need a vet rather than watching. The tooth will not heal on its own, and nothing you sprinkle on food or rub on the gum will drain an infection at the root.
What a vet can do
The first step is to see the roots, which means dental X-rays with the dog under general anesthesia (AAHA Dental Care Guidelines, 2019). A cracked crown can look minor while the damage runs below the gum, and the only way to judge the roots is to image them.
From there a vet has two real choices. A root canal treatment cleans out the dead pulp and seals the tooth, which keeps a working carnassial in a dog that needs it. The other choice is extraction, which our guide to when a dog's tooth needs pulling covers in full. Because the upper carnassial has three roots, that is a surgical extraction, where the gum is lifted and the tooth is divided before it comes free. Either way the dog has pain relief, and sometimes antibiotics if there is active infection.
Losing a carnassial sounds drastic, but dogs cope well and go back to eating normally once the gum has healed. The choice between saving the tooth and removing it depends on how much tooth is left, what the X-rays show and the individual dog, and it is a conversation to have with the vet doing the work.
How to protect the carnassials
Most carnassial fractures come down to one thing a dog was given to chew. The thumbnail test does most of the work. If your nail cannot mark it, it is too hard, so cooked bones, dense leg bones, antlers, hooves, hard nylon and ice cubes are the ones to skip.
Soft, raw, non-weight-bearing bones such as chicken wings or necks, sized so the dog has to chew rather than gulp and always supervised, are gentler on teeth, though raw meat needs the same kitchen hygiene you would give your own chicken. Softer rubber chews that flex are a safer bet than anything rock hard.
None of this repairs a tooth that is already cracked. If you can see a broken carnassial, a worn flat surface with a dark dot in the middle, or a swelling on the face, book the vet. For the bigger picture of how broken teeth, gum infection and the problems that follow fit together, our guide to dental disease in dogs is the place to start.
Common questions
Which tooth is the carnassial in a dog?
There are two on each side. The large upper fourth premolar and the lower first molar behind it. They line up like scissor blades for shearing and are the teeth a dog uses on anything tough.
Can a dog live without its carnassial tooth?
Yes. Dogs manage well after a carnassial is removed and eat normally once the gum heals. Keeping the tooth with a root canal is sometimes an option, which is a decision for the vet based on the X-rays and how much sound tooth remains.
Is a broken carnassial tooth an emergency?
Treat it as a prompt vet visit rather than a wait-and-see. A fresh fracture hurts, and an exposed pulp lets infection in. A swelling under the eye, a draining sore or a one-sided nosebleed means the tooth needs attention soon.
What can my dog chew instead?
Use the thumbnail test. Skip anything you cannot dent, which rules out cooked and dense leg bones, antlers, hooves and hard nylon. Soft raw chicken wings or necks, sized and supervised, and chews that flex are kinder to the carnassials.
References
- Tandir F, Avdić R, Dučić N, Džanković A, Tandir R, Šaljić E, Vejzović A, Hadžiomerović N. Comparative morphology of the carnassial teeth root canals in mixed-breed dogs and German Shepherds. Animals (Basel). 2024;14(8):1138.
- Golden AL, Stoller N, Harvey CE. A survey of oral and dental diseases in dogs anesthetized at a veterinary hospital. J Am Anim Hosp Assoc. 1982;18:891-899.
- American Animal Hospital Association. Dental Care Guidelines for Dogs and Cats. 2019.
- American Veterinary Dental College. Nomenclature and position statements.