Horse teeth

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The equine dental arcade, showing the front incisors, the interdental space before the first premolars Yawning horse, Scotland.jpg
The equine dental arcade, showing the front incisors, the interdental space before the first premolars

Horse teeth refers to the dentition of equine species, including horses and donkeys. Equines are both heterodontous and diphyodontous, which means that they have teeth in more than one shape (there are up to five shapes of tooth in a horse's mouth), and have two successive sets of teeth, the deciduous ("baby teeth") and permanent sets.

Contents

As grazing animals, good dentition is essential to survival. Continued grazing creates specific patterns of wear, which can be used along with patterns of eruption to estimate the age of the horse. [1]

Types of teeth

The skull of a horse. Crane cheval.jpg
The skull of a horse.
A view of the upper half of an immature horse's mouth. Palatum horse.JPG
A view of the upper half of an immature horse's mouth.

A fully developed horse of around five years of age will have between 36 and 44 teeth. All equines are heterodontous, which means that they have different shaped teeth for different purposes. All horses have twelve incisors at the front of the mouth, used primarily for cutting food, most often grass, whilst grazing. [2] They are also used as part of a horse's attack or defence against predators, or as part of establishing social hierarchy within the herd.

Immediately behind the front incisors is the interdental space, where no teeth grow from the gums. This is where the bit is placed, if used, when horses are ridden.

Behind the interdental space, all horses also have twelve premolars and twelve molars, also known as cheek teeth or jaw teeth. [2] These teeth chew food bitten off by incisors, prior to swallowing.

In addition to the incisors, premolars and molars, some, but not all, horses may also have canine teeth and wolf teeth. A horse can have between zero and four canine teeth, also known as tusks (tushes for the deciduous precursor), with a clear prevalence towards male horses (stallions and geldings) who normally have a full set of four. Fewer than 28% of female horses (mares) have any canine teeth. Those that do normally only have one or two, and these may be only partially erupted. [3]

Between 13 and 32% of horses, split equally between male and female, also have wolf teeth, which are not related to canine teeth, but are vestigial first premolars. Wolf teeth are more common on the upper jaw, and can present a problem for horses in work, as they can interfere with the bit. They may also make it difficult during equine dentistry work to rasp the second premolar, and are frequently removed. [2]

Tooth eruption

The "milk teeth" of a foal are short and oval-shaped Napping Colt.JPG
The "milk teeth" of a foal are short and oval-shaped
The incisors of a younger horse. Horse teeth.jpg
The incisors of a younger horse.

Horses are diphyodontous, erupting a set of first deciduous teeth (also known as milk, temporary, or baby teeth) soon after birth, with these being replaced by permanent teeth by the age of approximately five years old. The horse will normally have 24 deciduous teeth, emerging in pairs, and eventually pushed out by the permanent teeth, which normally number between 36 and 40. As the deciduous teeth are pushed up, they are termed "caps". Caps will eventually shed on their own, but may cause discomfort when still loose, requiring extraction.

It is possible to estimate the age of a young horse by observing the pattern of teeth in the mouth, based on which teeth have erupted, although the difference between breeds and individuals make precise dating impossible.

Common ages for tooth eruption. [2] [3]
Type of toothNumberDeciduousPermanent
IncisorFirst (central)birth to 8 days2.5 yrs
IncisorSecond (intermediate)4.5–6 weeks3.5–4 yrs
IncisorThird (corner)6–9 months4.5–5 yrs
CanineAbsent3.5–5 yrs, some around 6 yrs (if ever)
PremolarFirst (wolf)Absent6 months to 3 years (if ever)
PremolarSecondbirth to 2 weeks2–3 yrs
PremolarThirdbirth to 2 weeks2.5–3 yrs
PremolarFourthbirth to 2 weeks3–4 yrs
MolarFirstAbsent9–12 months
MolarSecondAbsent2 yrs
MolarThirdAbsent3–4 yrs

All teeth are normally erupted by the age of five, at which point the horse is said to have a "full mouth", but the actual age this occurs will depend on the individual horse, and also by breed, with certain breeds having different average eruption times. For instance, in Shetland ponies the middle and corner incisor tend to erupt late, and in both draft horses and miniature horses, the permanent middle and corner incisors are usually late appearing.

Tooth wear

The incisors, showing the wear and marks on their tables. Incisivi Pferd-16.jpg
The incisors, showing the wear and marks on their tables.

Horse teeth often wear in specific patterns, based on the way the horse eats its food, and these patterns are often used to conjecture on the age of the horse after it has developed a full mouth. As with aging through observing tooth eruption, this can be imprecise, and may be affected by diet, natural abnormalities, and vices such as cribbing.

The importance of dentition in assessing the age of horses led to veterinary dentistry techniques being used as a method of fraud, with owners and traders altering the teeth of horses to mimic the tooth shapes and characteristics of horses younger than the actual age of the equine. [4]

Equine teeth have evolved 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. In some cases, sharp edges can occur on the outside of the upper molars and the inside of the lower molars, as they are unopposed by an opposite grinding surface. These sharp edges can 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.[ citation needed ]

Typical wear patterns

Typical wear patterns in horses include:

Continuous eruption and loss

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's teeth are typically 4.5–5 inches long, but the majority of the crown remaining below the gumline in the dental socket. The rest of the tooth slowly emerges 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 to chew, may need soft feeds to maintain adequate levels of nutrition.

Older horses may appear to have a lean, shallow lower jaw, as the roots of the teeth have begun to disappear. [7] Younger horses may seem to have a lumpy jaw, due to the presence of permanent teeth within the jaw.

The teeth and the bit

Simple snaffle bit fitted to a horse, behind the incisors, but in front of the premolars Hunt bridle head.jpg
Simple snaffle bit fitted to a horse, behind the incisors, but in front of the premolars

If a bit is fitted to a horse, along with a bridle, the normally metal bar of the bit lies in the interdental space between the incisors (or canines, where present) and premolars. If the bridle is adjusted so that the bit rests too low, or too high, it may push against the teeth and cause discomfort.

Sometimes, a "bit seat" is filed in the first premolar, where the surface is rounded so that the flesh of the cheek is not pushed into the sharp edge of the tooth, making riding more comfortable for the horse, although the practice is controversial. [8]

Dental problems

Modern equine dentistry. This horse is heavily sedated and has been given analgesics, its head is supported by a sling. The mouth is kept open with a (horse) mouth gag, commonly referred to as a "speculum". Horse dentistry2003.jpg
Modern equine dentistry. This horse is heavily sedated and has been given analgesics, its head is supported by a sling. The mouth is kept open with a (horse) mouth gag, commonly referred to as a "speculum".

Like all mammals, horses can develop a variety of dental problems, with a variety of dental services available to minimise problems through reactive or prophylactic intervention.

Equine dentistry can be undertaken by a vet or by a trained specialist such as an equine dental technician, or in some cases is performed by lay persons, including owners or trainers.

Problems with dentition for horses in work can result in poor performance or behavioural issues, and must be ruled out as the cause of negative behaviours in horse. Most authorities recommend regular checks by a professional, normally six monthly or annually.

Problems due to wear patterns

A wolf tooth, located just in front of the premolars. Wolf tooth in horse.jpg
A wolf tooth, located just in front of the premolars.

The wear of the teeth can cause problems if it is uneven, with sharp points appearing, especially on the outer edge of the molars, the inner edge of the premolars and the posterior end of the last molars on the bottom jaw.

Other specific conditions relating to wear include a "step mouth", where one molar or premolar grows longer than the others in that jaw, normally because the corresponding tooth in the opposite jaw is missing or broken, and therefore could not wear down its opposite, a "wave mouth", where at least two molars or premolars 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, leading to periodontal disease and excessive wear of some of the teeth, and a "shear mouth" when the grinding surfaces of the molars or premolars 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), severely affecting chewing.

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. Horses also sometimes suffer from equine malocclusion where there is a misalignment between their upper and lower jaws.

The curvature of the incisors may also vary from the normal, straight bite. The curvature may be dorsal or ventral . These curvatures may be the result of an incisor malocclusion (e.g. ventral=overbite/dorsal=underbite). The curvature may also be diagonal, stemming from a wear pattern, offset incisors, 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 buildup. Wolf teeth may also cause problems, and are many times removed, as are retained caps.

Prevention of dental problems

Many veterinarians will use a Triadan chart to record the animal's dental problems for future reference. Triadan horse.gif
Many veterinarians will use a 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 vet or equine dental technician 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. 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 or equine dental technician. [9]

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 a horse 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 were purchasing. The saying is used in reference to being an ungrateful gift receiver. [10]

Related Research Articles

<span class="mw-page-title-main">Cattle age determination</span>

The age of cattle is determined chiefly by examination of the teeth, and less perfectly by the horn rings or the length of the tail brush; due to bang-tailing, which is the act of cutting the long hairs at the tip of the tail short to identify the animal after management practices, the last method is the least reliable.

<span class="mw-page-title-main">Human tooth</span> Calcified whitish structure in humans mouths used to break down food

Human teeth function to mechanically break down items of food by cutting and crushing them in preparation for swallowing and digesting. As such, they are considered part of the human digestive system. Humans have four types of teeth: incisors, canines, premolars, and molars, which each have a specific function. The incisors cut the food, the canines tear the food and the molars and premolars crush the food. The roots of teeth are embedded in the maxilla or the mandible and are covered by gums. Teeth are made of multiple tissues of varying density and hardness.

<span class="mw-page-title-main">Dentition</span> Development and arrangement of teeth

Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology of the teeth of an animal.

<span class="mw-page-title-main">Canine tooth</span> Long pointed tooth in mammals

In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, or fangs, eye teeth, vampire teeth, or vampire fangs, are the relatively long, pointed teeth. They can appear more flattened however, causing them to resemble incisors and leading them to be called incisiform. They developed and are used primarily for firmly holding food in order to tear it apart, and occasionally as weapons. They are often the largest teeth in a mammal's mouth. Individuals of most species that develop them normally have four, two in the upper jaw and two in the lower, separated within each jaw by incisors; humans and dogs are examples. In most species, canines are the anterior-most teeth in the maxillary bone.

<span class="mw-page-title-main">Incisor</span> Front teeth of most mammals

Incisors are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight. Opossums have 18, whereas armadillos have none.

Hypodontia is defined as the developmental absence of one or more teeth excluding the third molars. It is one of the most common dental anomalies, and can have a negative impact on function, and also appearance. It rarely occurs in primary teeth and the most commonly affected are the adult second premolars and the upper lateral incisors. It usually occurs as part of a syndrome that involves other abnormalities and requires multidisciplinary treatment.

<span class="mw-page-title-main">Deciduous teeth</span> First set of teeth in diphyodonts

Deciduous teeth or primary teeth, also informally known as baby teeth, milk teeth, or temporary teeth, are the first set of teeth in the growth and development of humans and other diphyodonts, which include most mammals but not elephants, kangaroos, or manatees, which are polyphyodonts. Deciduous teeth develop during the embryonic stage of development and erupt during infancy. They are usually lost and replaced by permanent teeth, but in the absence of their permanent replacements, they can remain functional for many years into adulthood.

<span class="mw-page-title-main">Wolf tooth</span>

Wolf teeth are small, peg-like horse teeth, which sit just in front of the first cheek teeth of horses and other equids. They are vestigial first premolars, and the first cheek tooth is referred to as the second premolar even when wolf teeth are not present. Torbjörn Lundström in Sweden reported that about 45-50% of 25000 horses had wolf teeth. They are much less common in the mandible than the maxilla although mandibular wolf teeth are found very occasionally.

<span class="mw-page-title-main">Maxillary canine</span>

In human dentistry, the maxillary canine is the tooth located laterally from both maxillary lateral incisors of the mouth but mesial from both maxillary first premolars. Both the maxillary and mandibular canines are called the "cornerstone" of the mouth because they are all located three teeth away from the midline, and separate the premolars from the incisors. The location of the canines reflects their dual function as they complement both the premolars and incisors during mastication, commonly known as chewing. Nonetheless, the most common action of the canines is tearing of food. The canines often erupt in the upper gums several millimeters above the gum line. The canine teeth are able to withstand the tremendous lateral pressure caused by chewing. There is a single cusp on canines, and they resemble the prehensile teeth found in carnivorous animals such as the extinct saber-toothed cat. Though relatively the same, there are some minor differences between the deciduous (baby) maxillary canine and that of the permanent maxillary canine.

<span class="mw-page-title-main">Permanent teeth</span> Second set of teeth in diphyodont mammals

Permanent teeth or adult teeth are the second set of teeth formed in diphyodont mammals. In humans and old world simians, there are thirty-two permanent teeth, consisting of six maxillary and six mandibular molars, four maxillary and four mandibular premolars, two maxillary and two mandibular canines, four maxillary and four mandibular incisors.

<span class="mw-page-title-main">Veterinary dentistry</span> Branch of veterinary medicine

Veterinary dentistry is the field of dentistry applied to the care of animals. It is the art and science of prevention, diagnosis, and treatment of conditions, diseases, and disorders of the oral cavity, the maxillofacial region, and its associated structures as it relates to animals.

<span class="mw-page-title-main">Dental arch</span> Arrangement and alignment of teeth

The dental arches are the two arches of teeth, one on each jaw, that together constitute the dentition. In humans and many other species; the superior dental arch is a little larger than the inferior arch, so that in the normal condition the teeth in the maxilla slightly overlap those of the mandible both in front and at the sides. The way that the jaws, and thus the dental arches, approach each other when the mouth closes, which is called the occlusion, determines the occlusal relationship of opposing teeth, and it is subject to malocclusion if facial or dental development was imperfect.

<span class="mw-page-title-main">Tooth eruption</span> Process in tooth development

Tooth eruption is a process in tooth development in which the teeth enter the mouth and become visible. It is currently believed that the periodontal ligament plays an important role in tooth eruption. The first human teeth to appear, the deciduous (primary) teeth, erupt into the mouth from around 6 months until 2 years of age, in a process known as "teething". These teeth are the only ones in the mouth until a person is about 6 years old creating the primary dentition stage. At that time, the first permanent tooth erupts and begins a time in which there is a combination of primary and permanent teeth, known as the mixed dentition stage, which lasts until the last primary tooth is lost. Then, the remaining permanent teeth erupt into the mouth during the permanent dentition stage.

Dental anatomy is a field of anatomy dedicated to the study of human tooth structures. The development, appearance, and classification of teeth fall within its purview. Tooth formation begins before birth, and the teeth's eventual morphology is dictated during this time. Dental anatomy is also a taxonomical science: it is concerned with the naming of teeth and the structures of which they are made, this information serving a practical purpose in dental treatment.

Occlusion, in a dental context, means simply the contact between teeth. More technically, it is the relationship between the maxillary (upper) and mandibular (lower) teeth when they approach each other, as occurs during chewing or at rest.

<span class="mw-page-title-main">Equine malocclusion</span>

An equine malocclusion is a misalignment between the upper and lower jaws of a horse or other equine. It results in a faulty bite with the upper and lower teeth failing to meet correctly. Malocclusions can cause pain to the horse and may also lead to weight loss and other eating problems related to poor chewing or loss of appetite. In addition, discomfort can lead to poor behavior when the animal is ridden or driven, particularly if a bit is used in the horse's mouth.

<span class="mw-page-title-main">Tooth</span> Hard, calcified structure found in the mouths of many vertebrates

A tooth is a hard, calcified structure found in the jaws of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tearing food, for defensive purposes, to intimidate other animals often including their own, or to carry prey or their young. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the outermost embryonic germ layer, the ectoderm.

<span class="mw-page-title-main">Odontometrics</span> Measurement and study of tooth size

Odontometrics is the measurement and study of tooth size. It is used in biological anthropology and bioarchaeology to study human phenotypic variation. The rationale for use is similar to that of the study of dentition, the structure and arrangement of teeth. There are a number of features that can be observed in human teeth through the use of odontometrics.

<span class="mw-page-title-main">Mammal tooth</span> Details of teeth found in many warm-blooded vertebrate animals

Teeth are common to most vertebrates, but mammalian teeth are distinctive in having a variety of shapes and functions. This feature first arose among early therapsids during the Permian, and has continued to the present day. All therapsid groups with the exception of the mammals are now extinct, but each of these groups possessed different tooth patterns, which aids with the classification of fossils.

Serial extraction is the planned extraction of certain deciduous teeth and specific permanent teeth in an orderly sequence and predetermined pattern to guide the erupting permanent teeth into a more favorable position.

References

  1. Ageing a Horse by its Teeth, England: Eventing Guide, 10 May 2020, retrieved 16 May 2020
  2. 1 2 3 4 Patricia Pence (2002), Equine Dentistry: A Practical Guide, Baltimore: Lippincott Williams & Wilkins, ISBN   0-683-30403-8
  3. 1 2 Al Cirelli, Equine Dentition (PDF), Nevada: University of Nevada, archived (PDF) from the original on 2016-02-25, retrieved 7 June 2010
  4. Harvey, C (1994). "The History of Veterinary Dentistry Part One: From the Earliest Record to the End of the 18th century". Journal of Veterinary Dentistry. 11 (4): 135–39. doi:10.1177/089875649401100401. PMID   9693612. S2CID   33259934.
  5. Lawrence, John (1796). A Philosophical and Practical Treatise on Horses: And on the Moral Duties of Man Towards the Brute Creation. Vol. 1. London: T.N. Longman. p.  116. OCLC   519860390.
  6. Clarke, William H. (1893). Horses' teeth: a treatise on their mode of development, anatomy, microscopy, pathology, and dentistry; compared with the teeth of many other land and marine animals, both living and extinct; with a vocabulary and copious extracts from the works of odontologists and veterinarians. New York: W. R. Jenkins. pp.  210–211. OCLC   9067598.
  7. "Managing the Changing Needs of Older Horses". Equisearch. Archived from the original on 8 March 2016. Retrieved 8 February 2016.
  8. Paul McGreevy, Janne Winther Christensen, Uta König von Borstel, and Andrew McLean, Equitation Science (London: John Wiley & Sons, 2018), 224-25. ISBN   1119241413, 9781119241416
  9. "Of horses' teeth, and liberty", The Economist , 10/27/07.
  10. "'Don't look a gift horse in the mouth' - the meaning and origin of this phrase".

Further reading