Dental Formulas in Animals: Dog, Cat, Horse, Cow, Pig

An adult dog's dental formula is 2(I 3/3, C 1/1, P 4/4, M 2/3) = 42. That is 20 teeth in the upper jaw and 22 in the lower jaw. A puppy has 28 baby teeth: 2(I 3/3, C 1/1, P 3/3) = 28, with no molars at all.

A dental formula is shorthand for the teeth on one side of the mouth. Once you can read one, you can work out the tooth count for any species in a few seconds, and you will spot the animals that break the pattern: mares that skip their canines, cows with no upper front teeth, rabbits with a hidden second pair of upper incisors. This page shows how to read the notation, gives verified formulas for the common domestic species, and covers the details that trip up students.

How to read a dental formula

Each letter is a type of tooth:

• I = incisors, the small front teeth
• C = canines, the long pointed teeth
• P = premolars, the cheek teeth behind the canines
• M = molars, the cheek teeth at the back

Each pair of numbers is written as a fraction. The top number is the count in the upper jaw (maxilla) and the bottom number is the count in the lower jaw (mandible), on one side only. The 2 in front doubles everything, because the left and right sides match.

Here is the dog worked through:

20 upper plus 22 lower gives 42 teeth. Merck lists the same mouth as 12 incisors, 4 canines, 16 premolars and 10 molars.

Baby teeth get their own formula. The letters are usually prefixed with D for deciduous (Di, Dc, Dp) or written in lowercase. Deciduous is the correct scientific term for baby teeth; the American Veterinary Dental College accepts "primary" when talking with clients. In dogs there are no baby molars, and the first premolar has no baby tooth before it. Those teeth come in once, as permanent teeth.

Dental formulas by species

Dog, cat, horse, ruminant and pig formulas are from the Merck Veterinary Manual table of dental formulas. The small-mammal, ferret and human sources are linked in their sections below. Each total is the formula added up, so you can check the arithmetic yourself.

Most mammals grow two sets of teeth in a lifetime: a deciduous set, then a permanent set. A few do it differently. Elephants, kangaroos and manatees grow more than two sets over a lifetime, according to Merck.

Dogs

Most dogs have 28 deciduous teeth and 42 permanent teeth. The baby teeth start to come through at 3 to 5 weeks of age. Permanent teeth usually begin to appear at around 4 to 5 months, and all of them are in by 7 months, per the Merck Veterinary Manual. That stretch is the teething phase most owners notice; our guide to puppy teething covers what it looks like at home.

Compared with people, a dog has 3 incisors in each quarter of the mouth where we have 2, and 4 premolars where we have 2. That adds 4 incisors and 8 premolars. Dogs have 2 fewer molars than an adult human, though, so the net difference is 10 teeth: 42 against 32.

The big shearing cheek teeth in dogs and cats are the carnassials: the upper fourth premolar and the lower first molar.

Cats

An adult cat has 30 teeth and a kitten has 26. The deciduous incisors erupt at 2 to 4 weeks and the deciduous premolars at 5 to 6 weeks. Permanent teeth usually start appearing at around 4 to 7 months (Merck).

The Ohio State University veterinary skills handbook sums up the difference from the dog in one count. Cats are missing 12 of the dog's teeth:

• the first premolar in every quadrant (4 teeth)
• the lower second premolar on each side (2)
• the upper second molar on each side (2)
• the lower second and third molars on each side (4)

That leaves one molar per quadrant. It also means the small tooth just behind a cat's upper canine is the second premolar, not the first; the first was lost during evolution. Merck adds that the upper second premolar and the upper first molar are absent in some cats.

Big cats follow the same plan. Adult lions have 30 teeth, according to the University of Michigan's Animal Diversity Web, the same count as the cat on your sofa. For the rest of the feline body, see our cat anatomy guide.

Horses

There is no single tooth count for horses. The permanent formula runs from 36 to 44 because two kinds of teeth may or may not be there:

• Canines. They usually appear only in male horses, at around 4 to 5 years of age, and are usually small or absent in mares.
• Wolf teeth. These are small first premolars, usually in the upper jaw and sometimes in the lower. Not every horse has them.

So a gelding or stallion without wolf teeth has 40 teeth, 2(I 3/3, C 1/1, P 3/3, M 3/3), and a mare without canines or wolf teeth has 36. Merck's horse-owner page gives mature stallions 40 to 44 teeth and mature mares 36 to 40.

Foals have 24 deciduous teeth. The first ones appear early, usually within 2 weeks of birth. Wolf teeth erupt at about 5 to 6 months, the permanent molars at about 1, 2 and 4 years, and the swap from baby incisors and premolars to permanent ones starts at about 2.5 years. Most horses have their full permanent set by 5 years (Merck).

Horse cheek teeth are hypsodont: long-crowned teeth that keep erupting through life as the grinding surface wears down. Dog and cat teeth are brachydont, with short crowns that stop erupting once they are in place. More on the horse's head and body is in our horse anatomy article.

Cows, sheep and goats

Cattle, sheep and goats share one formula, with 32 permanent teeth and 20 baby teeth. They have no upper incisors. A firm dental pad on the front of the upper jaw takes their place, and the lower incisors work against it (Cooperative Extension).

Merck writes the formula as 2(I 0/3, C 0/1, P 3/3, M 3/3) = 32: three lower incisors and one lower canine on each side. Some texts write it as 2(I 0/4, C 0/0, P 3/3, M 3/3) instead, because the lower canine sits in line with the incisors and looks like a fourth one. Both versions describe the same mouth and both add up to 32, so check which convention a chart uses before you compare it with another.

Like horses, ruminants have hypsodont cheek teeth that keep erupting as they wear.

Pigs

Pigs have the highest count in the table, 44 permanent teeth: 2(I 3/3, C 1/1, P 4/4, M 3/3). Piglets have 28 deciduous teeth.

A pig's tusks are its canine teeth, upper and lower. Merck describes the canines of male pigs as continuously erupting and growing, which is why boars develop long tusks, while females have smaller canines. Pig cheek teeth have low, rounded cusps, a type Merck calls bunodont.

Rabbits and rodents

Rabbits are not rodents, but both groups have teeth that keep growing throughout life. How many of them keep growing is where they differ.

Rabbits have 28 teeth, 2(I 2/1, C 0/0, P 3/2, M 3/3). They have two pairs of upper incisors. The second pair, the small "peg teeth", sits directly behind the big front pair, and there is one pair of lower incisors (Merck). Some references give 2 or 3 upper molars per side, so a rabbit may have 26 teeth instead of 28 (Suckow and colleagues, Laboratory Animal Medicine). Rabbit baby teeth are not functional and are shed shortly before or after birth. All rabbit teeth keep growing throughout life, peg teeth included.

Guinea pigs and chinchillas have 20 teeth, 2(I 1/1, C 0/0, P 1/1, M 3/3): 4 incisors and 16 cheek teeth (De Boer, IVIS; the chinchilla formula is from Derbaudrenghien and colleagues, listed in the sources). Their teeth are open-rooted and grow throughout life, and Merck notes that a hay-based diet helps keep them worn to the right length.

Rats and golden hamsters have 16 teeth, 2(I 1/1, C 0/0, P 0/0, M 3/3), with no canines or premolars. Here only the incisors grow continuously. The cheek teeth have roots and do not keep growing, unlike in guinea pigs and chinchillas, where every tooth does (Mancinelli and Capello, Veterinary Clinics of North America: Exotic Animal Practice).

That constant growth only works when the teeth wear evenly. Overgrown or misaligned teeth in a rabbit or rodent need a veterinarian, ideally one who sees exotic pets.

Ferrets and people, for comparison

Ferrets have 34 permanent teeth, 2(I 3/3, C 1/1, P 3/3, M 1/2): four more than a cat and eight fewer than a dog (Primožič and colleagues, Frontiers in Veterinary Science).

Adult humans have 32 teeth: 8 incisors, 4 canines, 8 premolars and 12 molars (Smiles for Life). Per side of each jaw that is I 2, C 1, P 2, M 3, so the formula is 2(I 2/2, C 1/1, P 2/2, M 3/3) = 32. A dog has 10 more teeth than you do; a cat has 2 fewer.

Why vets care: charting and the Triadan system

The formula tells the dental team what a normal mouth should contain. During an oral exam and on the dental chart, anything that does not match is worth recording. The AVDC uses specific terms for the common mismatches:

• Persistent deciduous tooth: a baby tooth still present when it should have fallen out.
• Supernumerary tooth: an extra tooth.
• Hypodontia: a few teeth that never developed.

To record which tooth is affected, veterinary dental charts commonly use the modified Triadan system, which the AVDC calls the numbering system of choice. Every tooth gets a 3-digit number:

• The first digit is the quadrant: 1 = upper right, 2 = upper left, 3 = lower left, 4 = lower right. Baby teeth use 5 to 8 in the same order.
• The last two digits are the tooth's position from the midline: 01 is the central incisor, 04 is always the canine and 09 is always the first molar.
• Missing teeth are skipped, not renumbered. The first upper premolar a cat actually has is therefore 106 or 206; there is no 105 or 205.

So a dog's lower left first molar is 309, and a horse's lower left second premolar is 306, per Merck.

If a puppy or kitten still has a baby tooth next to the adult tooth that replaced it, or a tooth seems to be missing, ask your veterinarian to take a look. For year-round care ideas, see our post on Pet Dental Health Month.

Sources

• Merck Veterinary Manual: Dental Formulas of Various Animal Species
• Merck Veterinary Manual: Dentition and Dental Nomenclature of Animals
• Merck Veterinary Manual: Dental Development in Animals
• Merck Veterinary Manual: Dental Development of Dogs
• Merck Veterinary Manual: Dental Development of Cats
• Merck Veterinary Manual: Dental Development of Horses
• Merck Veterinary Manual: Description and Physical Characteristics of Rabbits
• Merck Veterinary Manual: Description and Physical Characteristics of Guinea Pigs
• American Veterinary Dental College: AVDC Nomenclature
• Ohio State University College of Veterinary Medicine: Modified Triadan System and Dental Formulas
• dvm360: Tighten your dentistry knowledge (Proceedings)
• Suckow MA et al.: Biology and Diseases of Rabbits, Laboratory Animal Medicine (PMC)
• De Boer E-J: Guinea pig dentistry (IVIS)
• Derbaudrenghien et al.: Dental pathology in chinchillas, Vlaams Diergeneeskundig Tijdschrift
• Mancinelli E, Capello V: Anatomy and Disorders of the Oral Cavity of Rat-like and Squirrel-like Rodents (PMC)
• Primožič et al.: Simple Extraction of Fractured Maxillary Canine Teeth in Domestic Ferrets, Frontiers in Veterinary Science (2021)
• Cooperative Extension: Goat Dentition
• Smiles for Life: Adult Dentition
• Animal Diversity Web, University of Michigan: Panthera leo

This article is for general information and is not a substitute for advice from your veterinarian.