Equine dentistry is a major part of equine practice in the UK, accounting for an estimated 10–20% of practitioners’ time. A survey of horse owners in the UK has shown that 84% of owners elect to have prophylactic dental treatment performed at set time intervals, and guidance on horse ownership suggests that dental examination and treatment should be performed on a 6-monthly basis. The importance of equine dentistry worldwide may not be so large. However, an understanding of the basic anatomy of the equine head is very important for the equine practitioner.

The horse evolved in the Americas c.55 million years ago. The dawn horse (Hyracotherium) was a rabbit-sized animal that browsed on soft leaves. It had short brachydont (low-crowned) teeth similar to human or canine teeth. There then occurred climatic changes and hence a change in vegetation. The evolving horse developed a large caecum and colon for microbial digestion of cellulose. The brachydont teeth of the dawn horse changed to long-crowned hypsodont teeth to cope with eating an abrasive grass diet containing high levels of silica, for up to 18 h/day. As the horse evolved there was a migration from South America up through North America, across the Bering Strait to Asia. In central Asia there was an evolutionary branching, with the southern branch going to the Middle East and Africa; the northern branch went to Europe. Man first came into contact with horses at this period. There are drawings of wild horses in the Lascaux caves in south-west France dated c.15,000 BC. Horses were only a source of food then. However, the first evidence of equine domestication is bit-induced cheek teeth damage in a fossil equine skull dated c.4000 BC found near the Black Sea.

The main muscles are the temporalis and the internal and external masseter. These should be palpated and examined for symmetry. Directly in front of a horse is not a very safe place to stand, but it is the only real way that the practitioner can examine the differences between the two sides and assess symmetry or, in the event of a problem, asymmetry.

This is a very functional joint. Equine dental technicians (EDTs) would have horse owners believe that joint problems are common. This is not the case. Arthritis of the TMJ is extremely rare, and is normally a result of trauma and not the result of poor dental wear. The TMJs should be examined for lack of symmetry. If asymmetry is found then ultrasound is the best imaging modality for the TMJ. If using radiography, only skyline views are helpful. It should be stressed that major dental pathology might cause TMJ disease, but TMJ disease has not been shown to cause dental disease.

A horse has heterodont dentition. This means that it has different types of teeth. The canines and the first premolars are brachyodont teeth; the incisors and cheek teeth are hypsodont teeth. Hypsodont teeth have a long reserve crown, which is slowly worn down by the grinding of the occlusal surface of the tooth. The rate of attrition for the cheek teeth is approximately 2.5 cm over 10 years. At one time it was thought that the teeth of the donkey were harder than those of the horse, but this has been shown to be incorrect. The tooth length is finite: no further tooth is formed, unlike in rodents. The horse is also diphydont, having both deciduous and permanent teeth.

It appears complicated, but with repeated usage it becomes much simpler. There is general confusion if you describe a tooth as, e.g. the upper right second premolar. This is in fact the first cheek tooth in the cheek tooth row and may be the first premolar if the ‘wolf’ tooth is absent. If the practitioner is being very correct, the deciduous teeth should be numbered in quadrants of 5, 6, 7 and 8. Therefore, the central incisor in a yearling on the upper right-hand side would be 5/01. This would then be replaced by 1/01 at 2½ years of age. At the same stage another example would be the second premolar on the lower left arcade in a yearling, which would be 7/07; this would be replaced by 3/07 when the cap is shed.

The eruption of deciduous teeth in foals is fairly consistent. At birth they have two cheek teeth in each cheek tooth row, i.e. 06 and 07. The 08s erupt within 1 month. They have their central incisors at birth. The laterals erupt within 1 week and the corners in 1 month. These incisors are replaced, starting with the centrals, at 2½ years, the laterals at 3½ years and the corners at 4½ years. The permanent premolars, starting rostrally, erupt at 2½, 3 and 4 years. There is good evidence that the maxillary cheek teeth shed their caps up to 6 months before the mandibular cheek teeth. There is also evidence that colts shed their caps earlier than fillies. The molars, which by definition are permanent, erupt at 1, 2 and 3½ years. It is worth remembering that the first molars, the 09s, are the oldest teeth in a horse’s mouth. They are the most likely to give problems.

Like any veterinary examination the oral examination should be preceded by the taking of history. The age and use of the horse are then recorded. Any signs of dental disease should be noted. These may be related to eating, dysphagia, or grinding of the food, dysmastication. The position and carriage of the head should be noted, particularly in relation to the horse’s behaviour when being worked. Any problems with the bit should be noted.

A full examination of the outside of the head is the next stage. Particular attention should be given to any facial swellings, nasal discharge or smell. From a position in front of the horse the symmetry of the head is examined, with particular reference to the facial muscles, the masseters and temporalis, and the tempo-mandibular joints.

The area of cheek over the cheek teeth should be pushed in towards the cheek teeth to gauge a pain reaction. If such a pain response is initiated, it is advisable to rasp the buccal aspects of the upper cheek teeth at this point, as application of a gag will be resented by the horse.

Next, the head is examined from both sides and the lips curled back to examine the incisors. The bars of the mouth are then be examined and palpated. The movement of the jaw should be studied to estimate at what point the molar occlusal angle forces the incisors out of occlusion. At this stage it is useful to smell the horse’s breath, before washing out the oral cavity with a dilute solution of chlorhexidine.

Fig. 9.1. Oral examination of the horse, with a gag inserted.

Lastly, it is very important to record all the findings on a dental chart. The owner is then given one copy while the other is to be filed for your clinical records.

The canines or tushes occur in male horses, regardless of castration. They can also occur in approximately 10% of mares, then appearing small or even ‘blind’ when they actually do not erupt through the gingiva. However, in the male they provide a useful clue in ageing, as they erupt at 4½–5 years. It is the 5-year-old horse with a full set of permanent incisors that may be confused with the 2-year-old with a full set of deciduous incisors. If the canine is seen, the horse must be 5 years or older, rather than 2. The canines are brachydont teeth, and they should not be confused with the first premolar or ‘wolf’ tooth, which is also a brachydont tooth. In the UK the first premolars are commonly seen in the upper jaw, but are extremely rare in the lower. However, in Australia and the USA they are seen more commonly in Standardbreds in the lower jaw.

The deciduous incisors are replaced by the permanent incisors from a rostral direction, i.e. the central incisors are replaced first, followed by the laterals and then the corners. Occasionally, the deciduous teeth will remain in situ, and such a horse should be examined carefully; if the retained deciduous tooth is changing the direction of the permanent tooth, the former should be removed (in reality it may be that the permanent tooth is not erupting in quite the correct direction and so is not pushing out the deciduous tooth). Very rarely there are supernumary incisors present, and these are often extremely difficult to remove. Therefore, unless these are causing problems, they should be left alone. If incisors are fractured then the loose fragment should be removed. If both fragments are loose then they both should be removed. If food becomes packed between two incisors it should be regularly cleaned away from a caudal direction with a toothbrush. If the food has become tightly lodged, it should be removed with a dental pick and the diastema (gap between teeth, see below) should be widened with a hacksaw blade. Rarely, the incisors will have become covered by tartar, which should be removed with a small pair of extractors.

If an incisor has become excessively long it should be rasped down carefully, so that as soon as the pink stain of the pulp cavity is seen on the occlusal surface the rasping can stop. More rasping can be carried out in 3 months’ time. In cases of shear mouth (described below) the incisors will show a marked slant, if the condition is unilateral. Should gradual correction of shear mouth be carried out then the incisor slant will correct itself. If the condition is bilateral then the incisors will take on the shape of a smile, with the corners of the upper incisors shorter than the central incisors and the lateral incisors being of intermediate length. The lower incisors will show a mirror image. This configuration is often seen in the normal donkey.

The canines are brachydont teeth covered in an enamel layer. They are always present in male horses regardless of when castration has been performed. They erupt at 4½–5 years of age. They can cause problems on eruption, as the mucosa may be tender just before penetration of the tooth, but this is a short-lived phenomenon. They also appear in 5–10% of mares. They can cause problems if they do not perforate the mucosa, when they are termed ‘blind canines’. Owners often think they are a problem, but in reality they are not; they are often alleged to be a cause of head shaking, but this can be refuted by covering the mucosa with local anaesthetic gel. If the horse continues with its problems, then these are unlikely to be due to the canines.

The canines have long, curved roots which make extraction impossible except by using a buccostomy technique. However, there is actually no good reason to extract them. Owners complain sometimes that they are too long, but this does not actually cause any problems. They should not be clipped, cut or rasped as the enamel layer will be destroyed and the pulp may become infected. It is common for them to become covered in tartar, which should be removed regularly with a small pair of extractors to prevent gingivitis.

The task of removal should be viewed with caution. Sadly, there is often little evidence that the ‘wolf’ tooth is causing the problem. It is often extracted on the whim of the owner. The most frightening complication of removal is severance of the palatine artery, which runs palatally to the upper cheek teeth. If the palatine artery is accidentally severed, there will be a large amount of haemorrhage; it is alarming to the owner but not life threatening. The vessel is impossible to pick up with artery forceps and ligate, so this should not be attempted. Haemorrhage can be controlled by digital pressure. However, as soon as the finger is removed haemorrhage recommences. The horse should then be sedated. A towel, not cotton wool, which is always messy, should be rolled up into a tight roll, and this should be put in the mouth behind the incisors in between the cheek teeth. The jaws should then be clamped shut with a head collar that is a size too small for the horse, and this should then be left in place for at least 45 min. Next, the mess in the stable should be cleared up, and the horse led out into a paddock before the towel is carefully removed. There still may be some haemorrhage, but it will not be so noticeable.