Horse Teeth Anatomy and Function [Pictures & Animations]

Having a basic understanding of horses’ dental terminology is the starting point of your journey to understand horse teeth anatomy and function.

Horses have four types of teeth: incisors, canines, premolars, and molars.

Each type of tooth has certain physical characteristics and specific functions.

Incisors grasp and cut food
Canines are for fighting
Premolars and molars are grinders
Wolf teeth are classified as premolar but are vestigial and have no function.

Horse Mouth Anatomy

The horse’s mouth anatomy is quite different from ours because they evolved to eat tough fibrous plants such as grass, and their mouth adapted to this diet.

The main adaptations are:

1- Incisors

Are specialized for grasping and cutting food, even very short grass.

2- Cheek teeth (molars and premolars)

Are very strong with wide graveled surfaces to effectively grind the grass into small pieces
Are tightly wedged together, to prevent food from getting in between the teeth.

3- Jaws

The upper and lower jaws have different widths (Anisognathia). The upper jaw (maxilla) is about 30% wider than the lower jaw (mandible). Also, the upper jaw teeth are slightly wider. This anatomy and the circular chewing motion enable an effective grinding of food.
The chewing surface of the upper and lower cheek teeth is not straight; it has an inclination of about 10 to15 degrees, formed by the chewing mechanism to help break down feed.
The presence of interdental space (“bars of mouth”) due to the evolutionary increase in face length allows horses to graze off the ground whilst being able to look out for predators.
Deeper jaw to accommodate the long hypsodont teeth.

4- Hypsodont

They have very long teeth (hypsodont = “high tooth”) that slowly erupt during their lifetime to compensate for wear 2-3mm a year, due to constant grinding.

Horse Teeth Structure

The horse’s tooth is made up of four layers with different characteristics: pulp, dentin, enamel, and cementum

The pulp is the innermost layer and contains vital parts such as nerves and blood supply. This structure is soft and sensitive, and so it is protected by the outer layers.
Dentin is the next layer and makes up most of the tooth structure. It essentially protects the pulp and is covered by enamel. Dentin also provides a sensory function for the tooth. The dentin along the edge of the pulp cavity has nerve endings within its tiny tubules.
Enamel is the hardest part of the tooth, but it is brittle. It is dead tissue and so cannot repair itself if damaged. It is located between the dentin and cementum layers to stay protected. It is layered in many folds to strengthen the teeth. You can see these folds on the tooth’s chewing surface.
Cementum is the tooth’s outermost layer covering the entire crown and filling the infundibulum (funnel cavity in the tooth’s crown). It is worn from the chewing surface after the tooth erupts. It is a cream-colored living tissue similar to bone. Its main function is to secure the tooth in its socket.
The infundibulum is an infolding of the enamel into the center of the tooth, forming a funnel-shaped cavity. It is filled with cementum.
Each incisor has one infundibulum commonly called “cup”. Each cheek tooth has 2 infundibula. During the horse’s lifetime, the infundibulum wears away until it completely disappears around 15 years of age.
During the horse’s lifetime, the infundibulum wears away until it completely disappears around 15 years of age.

Horse teeth anatomy - tooth structure. Showing crown, reserve crown, infundibulum, cementum, enamel, dentim and pulp

These three protective layers have different hardness; enamel is the hardest (96-98% mineralized), then comes dentin (70%), and finally cementum (65%)

These materials’ different hardness causes them to wear away at different rates (enamel slowest, dentin, and cementum fastest).

This explains why the teeth’ chewing surface has indentations, with the softer materials lying deeper in the surface than the harder ones. The result is a very irregular graveled surface, with relatively sharp edges perfect for crushing coarse fibrous feed.

Horse teeth chewing surface - Cementum, Enamel and Dentin

This rough chewing surface should not be smoothed out when floating a horse’s teeth (unless the tooth is abnormally long or the angle is wrong). The horse will feel pain and be unable to chew his food properly for some time.

Horse Hypsodont Teeth

Horses have very long hypsodont teeth (4 – 5 inches/ 10-12cm). Most of the tooth is a reserve hidden below the gum line. This reserve continually erupts during the horse’s lifetime as the teeth wear away due to the grinding of fibrous feed.

Many people are not aware of how much tooth is hidden below the gum line.

Horse teeth are very different from human teeth.

Horse teeth anatomy compared to human teeth anatomy

Horse Teeth	Human Teeth
Hypsodont type	Brachydont type
Crown is long and divided into a visible crown above the gumline and a reserve crown that is hidden below the gumline	Crown is short and ends at the gum
The root is short, so the reserve crown acts as a root to help stabilize the tooth inside the socket.	The root is long
Continuous growth during the horse’s lifetime	Stop growing after the crown has completely emerged

During the horse’s lifetime, their teeth slowly push (erupt) through the gum line at a rate of ⅛ inch / 2-3mm a year, which is similar to the rate of wear on the surface of the tooth.

The size of the tooth above the gumline (the visible crown) always remains the same. However, below the gum line, the tooth becomes shorter and shorter as the horse grows older.

Horse anatomy - Hypsodont teeth wear away as a horse ages.

The rate of eruption compensates for the rate of wear, as long as the horse is eating grass (or some alternative fibrous feed such as hay or silage).

If instead, he is being fed high quantities of concentrate food, then the rate of surface wear will be reduced. Also, the range of lateral chewing action will be more limited. This results in dental overgrowths such as sharp points and shear mouth.

Considering that horse’s teeth:

Have an initial length of approximately 4 inches (10-12cm)
Push through and wear away at a rate of 2 to 3mm per year

We can estimate that a healthy horse eating an ideal diet will have teeth that do not wear out completely for 25 to 30 years. After this age, the teeth will eventually “disappear.”

Triadan Tooth Numbering System – Horse Teeth

To avoid confusion when referring to specific teeth, a numbering system, called the Triadan system, was developed and is used worldwide.

The Triadan System is used for numbering teeth in different animal species, including equines.

It uses 3 digits to identify each tooth. The first digit refers to the quadrant: left and right maxilla, and left and right mandible.

The quadrants are numbered 1 to 4, starting at the right maxilla and ending at the right mandible in a clockwise direction, as seen in the image below. The deciduous teeth are identified similarly, but the quadrants are numbered 5 to 8.

The second and third digits identify the tooth position within the quadrant.

horse teeth anatomy - Triadan numbering system

The image shows the Triadan system for horses’ permanent teeth and horses’ deciduous teeth.

Horse Incisors

The horse´s incisors are the teeth at the front of the mouth. (Triadan 01’s to 03’s)

There twelve incisors: six on top, six on bottom
Incisors are used to tear off the grass and for grooming
Incisors first erupt as deciduous teeth and later replace with permanent teeth

Deciduous (baby) Incisors

The deciduous incisors erupt around the following ages:

Central (01’s) during the first week of age
Intermediate (02’s) between 4 and 6 weeks of age
Corner (03’s) erupt much later at 6 to 9 months of age.

Deciduous Teeth eruption charts can be seen in our article about how to tell a horse´s age by its teeth (before 5 years).

These baby incisors have a short crown and are wider and whiter than the permanent teeth that will later replace them. The deciduous incisors (caps) shed as the corresponding permanent incisors emerge.

Permanent (adult) Incisors

The permanent incisors erupt around the following ages

Central (01’s) at 2.5 years of age
Intermediate (02’s) at 3.5 years of age
Corner (03’s) at 4.5 years of age.

Permanent Teeth eruption charts can be seen in our article how to tell a horse´s age by its teeth (after 5 years).

Facts About Incisors

The dental eruption of the incisors happens throughout the horse’s lifetime. Normally the eruption rate corresponds to the wear rate.
In a young horse, the incisor teeth are curved in an almost semicircular shape, gradually becoming shallower with age due to progressive wear. This explains why incisors’ angle of incidence changes from an almost vertical position in a young horse to a sharper angle with age.
The horse’s incisors narrow down uniformly from the top surface to the apex. Thus with age, as they wear down, the portion of the tooth close to the apex emerges above the gumline, and so spaces start to appear between the incisors.
The chewing surface of the incisors gradually changes shape and indentations as the horse grows older.
Progressive wear-related changes of incisors are often used to estimate a horse’s age.

Horse Canine Teeth

The horse’s canine teeth (Triadan 04’s) are located between the incisors and premolars.

They were originally “fighting teeth”, and have no use in the eating process.

Deciduous (baby) Canines

In both male and female horses, the deciduous canines do not erupt above the gumline.

Permanent (Adult) Canines

Permanent canine teeth erupt between 4 and 6 years of age.

Facts About Canines

Male horses usually have 4 permanent canine teeth, but they typically are less developed or absent in female horses.
Canine teeth, commonly known as “tushes”, are curved and pointed. They are long (approx 6cm) but only a short length is visible above the gumline.
In some cases, the canines lie superficially below the gum and are called “blind canines.” These tend to be problematic because they can be painful if the overlying gum becomes swollen and sore.
The lower canines are positioned more to the front than the upper ones. Therefore, Canine teeth have no occlusal contact like other teeth do.
Horse Canine teeth do not continue to erupt over time as other teeth do, and so the long reserves of the crown are present throughout the horse’s lifetime. Due to the great length of these teeth, their extraction is a difficult process.

Horse Wolf Teeth

The horse´s wolf teeth (Triadan 05’s) are very small vestigial premolars located in front of the first cheek teeth.

Facts About Wolf Teeth

Technically they are classified as the first premolar, but unlike other cheek teeth, they do not continue to erupt throughout the horse´s lifetime and have no occlusal contact. These teeth are quite small (1 to 2 cm in length).
Wolf teeth are not used for eating and are also not used for fighting. In fact, they have no use at all for the horse today; they are just a prehistoric remnant.
Horses can have 0 to 4 wolf teeth or none at all. It is common for a horse to have 1 or 2 wolf teeth in the upper jaw, but they rarely appear in the lower jaw. They are not gender-related, so horses and mares are equally likely to develop wolf teeth.
Sometimes wolf teeth do not erupt through the gums, and are called “blind” wolf teeth.
Millions of years ago, they functioned as grinding teeth. Back then, horses were small brush eaters and had smaller cheek teeth like those of sheep today. But later, horses evolved to become pasture grazers. Chewing tough fibrous grass required stronger and larger teeth. The back six teeth gradually became larger while the first premolars (wolf teeth) shrunk and became redundant.
Wolf teeth can sometimes be problematic when using a bit. So to avoid problems and discomfort to the horse, they are usually removed. If horses are not ridden, such as breeding mares, there is no need to remove them because they do not cause any harm

Horse Cheek Teeth

Horse teeth anatomy - cheek teeth (molars and premolars)

The horse´s cheek teeth are the teeth at the back of the mouth. (Triadan 06’s to 11’s)

There are 24 cheek teeth (molars and premolars) in an adult horse. Each row has 6 teeth. The first 3 in each row are the premolars, and the last 3 are molars.

The cheek teeth, with strong graveled surfaces, are used for crushing and grinding the food.

Only the premolars have deciduous teeth.

Deciduous (Baby) Premolars

The deciduous premolars (06´s, 07’s, 08’s) have erupted at birth or erupt a few days later until 2 weeks of age.

The crowns of the deciduous premolars are very similar to the permanent premolars.

As the foal grows older, the crowns become thinner by wear (caps). Over time the caps loosen and fall off as the underlying permanent teeth erupt.

Permanent (Adult) Premolars

The permanent premolars erupt around the following ages:

(06’s) at 2.5 years of age
(07’s) at 3 years of age
(08’s) at 4 years of age.

The molars do not have deciduous precursors.

Permanent (Adult) Molars

The permanent molars erupt around the following ages:

(09’s) at 1 year of age
(10’s) at 2 years of age
(11’s) at 3.5 years of age.

Facts About Molars

The dental eruption of the cheek teeth happens throughout the horse’s lifetime. Normally the eruption rate corresponds to the wear rate (2-3mm a year).
Like the incisors, the cheek teeth have an infundibulum that wears out over time.
The upper cheek teeth usually have 3 roots but occasionally can have 4 roots. The lower cheek teeth usually have 2 roots.
The cheek teeth sit vertically, except for the first and last ones, which are tilted towards the middle ones. The purpose of these inclinations is to compress all six cheek teeth together at the chewing surface to prevent the development of spaces between the teeth (diastema).

Horse teeth Anatomy - cheek teeth compressed together

The upper an lower cheek teeth have the following differences:

The maxillary (upper jaw) cheek teeth are square-shaped (except for the first and the last, which are triangle-shaped).
The mandibular (lower jaw) teeth are rectangular shaped (except for the first and the last, which are triangle-shaped).
The maxillary cheek teeth are about 50% wider than the mandibular cheek teeth.

horse teeth anatomy - differences in upper and lower horse cheek teeth

The maxillary cheek teeth rows are wider apart (approx 30%) than the mandibular cheek teeth rows (this feature is called anisognathia). Consequently, the upper and lower cheek teeth do not completely contact each other transversely when the mouth is closed.
Additionally, the occlusal surfaces of the cheek teeth are not leveled but are instead angled (around 10 to 15 degrees), with the outer edge of the upper teeth being taller than the inner edge, and inversely the outer edge of the lower teeth being smaller than the inner edge.
When cheek teeth erupt, the chewing surface is flat, without any tilt. But the unequal arrangement of the upper and lower jaw (anisognathia), together with the side to side chewing motion cause the occlusal surface to become angled.

The Angulation Of Cheek Teeth Is Influenced By Diet

For a horse that eats a normal forage diet where the coarse fibrous feed requires a wide range of lateral chewing movement, the angle remains within the normal range.

For a horse that eats a diet based on concentrated feed, like processed grains, the chewing movement will be more vertical, will accentuate more the angle on the occlusal surface, and lead to a dental disorder called “shear mouth.”

How Does A Horse Chew?

Horses chew in a repetitive, cyclical motion with 3 phases: the mandible drops (opening stroke), then moves sideways and closes (closing stroke); finally, it slides sideways with cheek teeth in contact grinding the food (power stroke). The cycling motion can be clockwise or anti-clockwise as horses can be right-sided chewers, left-sided, or both.

The chewing process is crucial to prepare food for digestion. Throughout the whole digestive tract of the horse, there is no significant reduction in food size, which leaves chewing as the most important function to reduce food particle size.

How Anatomy Influences The Chewing Movement

To understand how a horse chews, let’s first take a quick look at the anatomy that impacts the chewing movement.

The upper jaw is larger than the lower jaw. So the lower teeth are positioned slightly to the inside of the upper teeth.
The upper cheek teeth are larger than the lower cheek teeth
The chewing surface of the upper and lower cheek teeth is not straight, it has an inclination.

The anatomy of the horse’s mouth influences the chewing movement as follows:

1- In the resting position the incisors are aligned while the back cheek teeth are not touching each other (not in occlusion).

horse chewing - in resting position the incisors are aligned while the back cheek teeth are not touching each other

2- As the lower jaw moves to the side, the cheek teeth touch each other.

horse chewing - As the lower jaw moves to the side, the cheek teeth touch each other

3- The incisors will need to separate to allow the check teeth to slide further laterally.

horse chewing - The incisors will need to separate to allow the check teeth to slide further laterally

The Horse’s Chewing Cycle

Chewing is a repetitive, cyclical motion that has three phases:

“O” – The opening stroke
“C” – The closing stroke
“P” – The Power stroke

The animation shows the complete chewing cycle in motion. Notice how the lower cheek teeth slide completely across the upper cheek teeth, wearing away the entire surface evenly.

Some horses are right-sided chewers, others are left-sided, and still, others chew on both sides.

In a study made of the chewing movements in of 400 horses the following was observed:

163 (41%) were right-sided
131 (32%) were left-sided
45 (11%) chewed on both sides
The remaining horses had incomplete observations

(source: Equine Dentistry – 3rd Edition, by Jack Easley, Padraic M. Dixon, James Schumacher)

How A Horse’s Diet Influences The Chewing Movement

Studies have shown that the chewing motion depends on the type of food being chewed.

Fiber Feed Requires more Movement Of The Jaw

When eating fiber feed such as grass or hay, there is a greater lateral movement of the lower jaw than when eating grains or pelleted food. This increased lateral movement will allow full contact of upper and lower cheek teeth during the chewing cycle.

When horses have free access to grass or hay and spend most of their day chewing this coarse feed, they will not develop significant wear abnormalities and so will have less need for dental treatments such as floating.

Grains and Pellets Requires Less Movement Of The Jaw

On the contrary, horses fed grains or pellets require less movement of the jaw (both side to side and front to back ) to chew this type of food. The limited motion influences teeth wear because there will only be partial contact with the upper and lower cheek teeth, and consequently, wear abnormalities such as “sharp enamel points” and “hooks” are frequent.

The animation shows how the reduced range of chewing motion does not completely wear the edges of the cheek teeth’ dental surface, causing sharp enamel points.

Watch this video on YouTube

However, we must understand that performance horses require a high caloric diet, which is more easily met with concentrated foods such as grains and pellets. To manage this, more frequent dental interventions may be necessary to prevent and fix abnormal teeth wear caused by the reduced range of chewing movement associated with this type of diet.

Another problem that can appear when horses do not have free access to hay is that the horse may start chewing on wood. Horses have a need to chew coarse fiber, and if they do not have access to it, they may search for alternatives such as wood.

So giving your horse free access to hay will avoid not only abnormal teeth wear but also bad habits such as chewing on wood.

Sources

The following sources were used to research this article:

The book: Equine Dentistry – by Jack Easley (Editor), Padraic M. Dixon (Editor), James Schumacher (Editor)

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