Horse teeth

Horses' teeth are often used to estimate the animal's age, hence the sayings "long in the tooth" and "Don't look a gift horse in the mouth".

Types of teeth

At five years of age a horse has between 36 and 44 teeth. All horses have

* Twelve premolars and twelve molars commonly known as cheek teeth or jaw teeth.
* Twelve incisors, or front teeth.

Additionally, a horse may have:
* Between 4 and 5 canine teeth (tushes, tusks) between the molars and incisors. Generally all male horses have four canines. However, few female horses (less than 28%) have canines, and those that do usually have only one or two, which many times are only partially erupted.

* Between zero to four wolf teeth, which are vestigial premolars and "not" canines as the name may suggest. About 13-32% of all horses also are born with wolf teeth, with most of those having only one or two. They are equally common in male and female horses and much more likely to be on the upper jaw. If present these can cause problems in the bitting of the horse as they can interfere with the horse's bit contact, and may also make it difficult to rasp the second premolar. Therefore, wolf teeth are commonly removed.

Tooth growth

A horse's incisors, premolars, and molars, once fully developed, continue to erupt as the grinding surface is worn down through chewing. A young adult horse will have teeth which are 4.5-5 inches long, but the majority of the crown remaining below the gumline in the dental socket. The rest of the tooth will slowly emerge from the jaw, erupting about 1/8" each year, as the horse ages. When the animal reaches old age, the crowns of the teeth are very short and the teeth are often lost altogether. Very old horses, if lacking molars, may need to have their fodder ground up and soaked in water to create a soft mush for them to eat in order to obtain adequate nutrition. Commercially prepared hay pellets and Hay cubes can be moistened for this purpose. Beet pulp may also be a suitable feed.

The teeth and the bit

Contrary to popular belief, the bit of a bridle is not held between the horse's teeth, but lies in the "interdental space." This space lacks teeth, providing an area for the bit to rest without forcing the jaws open, and occurs between the cheek teeth and the incisors (or canines, should the horse have them).

However, if the bridle is adjusted so that the bit rests too low, or (more commonly) too high, it may push against the teeth and cause discomfort.

Sometimes, a "bit seat" is filed in the first cheek tooth. A veterinarian rounds the surface, so that, when the bit is pulled, the flesh of the cheek is not pushed into the sharp edge of the tooth. Although this practice is disputed, and most agree that an extreme bit seat can indeed be harmful, many veterinarians believe it makes riding more comfortable for the horse.

Estimating age using the teeth

It is possible to age a horse using signs of the tooth eruption and wear. However, this is not an exact science, and become increasingly difficult after the horse is "aged." Horses are individuals, and two horses of the same age may have difference wear patterns.

Estimating age using tooth eruption

There are 24 deciduous teeth (also known as milk, temporary, or baby teeth). These come out in pairs, and are pushed out later by the permanent teeth. The number of permanent teeth may vary, depending on if the horse has wolf teeth or canines. Most mares have 36, and most male horses have 40.

By age five, all permanent teeth have usually erupted. The horse is then said to have a "full" mouth.

However, individual horses will vary, and some breeds and types of horses are known to have differing eruption timelines. These include:

* Shetland ponies: The middle and corner incisor (both deciduous and permanent) usually erupt later than the average horse.
* Draft horses and miniature horses: the permanent middle and corner incisors usually erupt later than average.

Estimating age using wear patterns

After eight years, indeed good authorities say after five years, the age of a horse can only be conjectured. Dishonest dealers sometimes "bishop" the teeth of old horses, that is scoop them out, to imitate the mark: but this can be known by the absence of the white edge of enamel which always surrounds the real mark, by the shape of the teeth, and other marks of age about the animal. The wear of teeth may also be affected by diet, natural abnormalities, and cribbing.

* Cups: are hollow and rectangular or oval in shape, appearing on the tables of the permanent incisors, that wear away over time. In general, cups are worn away on the lower central inscisors by age 6, the lower intermediates by age 7, and corners at age 8. The cups of the upper central incisors are worn away by 9 years of age, the upper intermediate incisors by 10, and the corners by 11. When all the cups are gone, the horse is referred to as "smooth mouthed."

* Pulp mark/Dental star: After some wear has occurred on the teeth, the central pulp cavity is exposed, and the tooth is marked by a "dental star" or "pulp mark." These begin as a dark line in front of the dental cup, which grows in size and becomes more oval in shape as the cups are worn away. Dental stars are usually first visible at age 6, on the animal's lower central incisors, and very visible by age 8. They appear on the lower intermediates by age 9, and on the other incisors between the ages of 10-12 years.

* Hook/Notch: A hook appears on the upper corner incisor around age 7, and disappears by age 8. It reappears around age 13, again disappearing about 1 year later.

* Galvayne's Groove: The Galvayne's groove occurs on the upper corner incisor, producing a vertical line, and is helpful in approximating the age of older horses. It generally first appears at age 10, reaches half-way down the tooth by age 15, is completely down the tooth at age 20. It then begins to disappear, usually half-way gone by age 25, and completely gone by age 30.

* Lower jaw shape: Older horses may appear to have a lean, shallow lower jaw, as the roots of the teeth have begun to disappear. Younger horses may seem to have a lumpy jaw, due to the presence of permanent teeth within the jaw.

* Angle and Shape of the incisors: As the horse ages, the angle of the incisors generally becomes more acute, slanting forward. The incisors gradually change their form as the horse ages, becoming round, oval, and then triangular.

Dental problems

Like humans, horses can develop a variety dental problems, some which may be very serious and require surgery. It is therefore important that horse owners have a veterinarian check their animals' teeth regularly, to head off any potential issues, and examine the teeth should the horse exhibit any signs of dental problems. Abnormal teeth not only affect the horse's comfort while chewing, but also commonly manifest themselves as disobediences while the animal is ridden.

Problems due to wear patterns

Many dental problems in horses are related to the fact that their teeth grow continuously throughout their life. Horses are evolved to graze nearly continuously, often on rough forage in semi-arid climates. Their teeth are designed to wear against the tooth above or below as the horse chews, thus preventing excess growth. The upper jaw is wider than the lower one. Sharp edges occur on the outside of the upper molars and the inside of the lower molars, as they are unopposed by an opposite grinding surface.

There are many times when tooth wear is not even, and the horse may develop sharp edges on their teeth that reduce chewing efficiency of the teeth, interfere with jaw motion, and in extreme cases can cut the tongue or cheek, making eating and riding painful.

In the wild, natural foodstuffs may have allowed teeth to wear more evenly. Because many modern horses often graze on lusher, softer forage than their ancestors, and are also frequently fed grain or other concentrated feed, it is possible some natural wear may be reduced in the domestic horse. On the other hand, this same uneven wear in the wild may have at times contributed to a shorter lifespan. Modern wild horses live an estimated 20 years at most, while a domesticated horse, depending on breed and management, quite often lives 25 to 30 years. Thus, because domesticated animals also live longer, they may simply have more time to develop dental issues that their wild forebears never faced.Fact|date=March 2007

Hooks, or sharp points on a tooth, usually develop on the outside of teeth in the upper jaw, the inside of teeth in the lower jaw. They also commonly occur on the front of the first upper premolar, or last lower molar.

A step mouth occurs when one cheek tooth grows longer than the others in that jaw. This is usually because the tooth opposing that particular one, located in the opposite jaw, was missing or broken, and therefore could not wear down its opponent.

A wave mouth occurs when at least two of the cheek teeth are higher than the others, so that, when viewed from the side, the grinding surfaces produce a wave-like pattern rather than a straight line. This can make chewing very difficult for the horse.

A shear mouth occurs when the grinding surfaces of the cheek teeth are severely sloped on each individual tooth (so the inner side of the teeth are much higher or lower than the outer side of the teeth). This may result in an angle at 60-75 degrees, opposed to the normal 15 degree angle seen on most horses. Again, the chewing motion is severely affected.

Bite problems

Horses may also experience an overbite/brachygnathism (parrot mouth), or an underbite/prognathism (sow mouth, monkey mouth). These may affect how the incisors wear. In severe cases, the horse's ability to graze may be affected.

The curvature of the incisors may also vary from the normal, straight bite. The curvature may be dorsal (upper incisors grow faster than lower), or ventral (lower incisors grow faster than upper). These curvatures may be the result of a chewing pattern, or due to retained deciduous teeth. The curvature may also be diagonal, stemming from a wear pattern of or pain in the cheek teeth (rather than the incisors), which causes the horse to chew in one direction over the other.

Other dental problems

Other common problems include abscessed, loose, infected, or cracked teeth, retained deciduous teeth, and plaque build up. Wolf teeth may also cause problems, and are many times removed, as are retained caps.

igns of possible dental problems

* Reluctance to eat, does not finish food, or eats slowly
* Dull coat, weight loss, and loss of condition
* Quidding (horse drops partially chewed food while chewing), or chewing with the mouth open
* Turning of head to the side while chewing
* Excessive salivation while eating, blood in saliva
* Foul smell from mouth or nose
* Draining of abscess from the jaw
* Discharge from one nostril
* Undigested feed in manure
* Colic
* Excessive salivation
* Facial swelling

Additionally, many problems under saddle can be tooth-related, such as:
* head tossing
* difficulty in picking up the canter or in performing flying changes
* tilting of the head while riding or difficulty in bending
* refusal to collect
* bucking
* difficulty in getting the horse "on-the-bit" (especially if the horse tends to go behind the bit)
* gaping the mouth

For many performance-related problems, it is often best to check the teeth to rule out that factor.

Prevention of dental problems

[
Triadan chart to record the animal's dental problems for future reference.] To help prevent dental problems, it is recommended to get a horse's teeth checked by a veterinarian every 6 months. However, regular checks may be needed more often for individuals, especially if the horse is very young or very old. Additionally, the horse's teeth should be checked if it is having major performance problems or showing any of the above signs of a dental problem.

Many horses require floating (or rasping) of teeth once every 12 months, although this, too, is variable and dependent on the individual horse. In young horses, twenty four teeth are deciduous or "caps". These are the first three premolars of each arcade (not including wolf teeth) and all incisors. Caps are pushed out by the new permanent teeth, starting late in a horse's two year old year. Caps will eventually shed on their own, but may cause discomfort when still loose, requiring extraction. The first four or five years of a horse's life are when the most growth-related changes occur and hence frequent checkups may prevent problems from developing. Equine teeth get harder as the horse gets older and may not have rapid changes during the prime adult years of life, but as horses become aged, particularly from the late teens on, additional changes in incisor angle and other molar growth patterns often necessitate frequent care. Once a horse is in its late 20s or early 30s, molar loss becomes a concern. Floating involves a veterinarian wearing down the surface of the teeth, usually to remove sharp points or to balance out the mouth. However, the veterinarian must be careful not to take off too much of the surface, or there will not be enough roughened area on the tooth to allow it to properly tear apart food. Additionally, too much work on a tooth can cause thermal damage (which could lead to having to extract the tooth), or expose the sensitive interior of the tooth (pulp). A person without a veterinary degree who performs this service is called a "horse floater". [ [http://www.economist.com/world/na/displaystory.cfm?story_id=10024535 Of horses' teeth, and liberty] , The Economist, 10/27/07. ]

In popular culture

The common folk saying "don't look a gift horse in the mouth" is taken from the era when gifting horses was common. The teeth of horses are a good indication of the age of the animal, and it was considered rude to inspect the teeth of a gifted animal as you would one that you purchasing. The saying is used in reference to being an ungrateful gift receiver. [http://www.phrases.org.uk/meanings/117000.html]

References

*"The Household Cyclopedia of General Information", published in 1881.
*"Illustrated Atlas of Clinical Equine Anatomy and Common Disorders of the Horse, Vol. II". Riegel, Ronald J., and Susan E. Hakola. Equistar Publications, Limited. Copyright 1999.
*"Equus". "Healthy Teeth, Healthy Horse." November 2006, pp 31-39.

*"Sound Mouth-Sound Horse, The Gager Method of Equine Dental Care". Gager, E.R., and Rhodes, Bob. Emerson Publishing Company. Copyright 1983.