|Dentition In The Horse|
By Stephen Champion, BSc (Hons) BVM&S MRCVS,
The dentition of the horse has evolved over millions of years to cope with the fibrous nature of its diet, which is a particularly abrasive material. In simplest terms the teeth comprise the incisors at the front, which prehend the food and the cheek teeth, which masticate, or grind up, the food. The cheek teeth are the combined premolars and molars, which provide the horse with a continuous grinding surface.Both incisors and cheek teeth are high-crowned, or hypsodont, teeth. This ensures a long working life, despite considerable wear at the occlusal surfaces, the areas of the teeth which grind together. Delayed formation of the roots allows for the cheek teeth to grow for some years after they come into wear. Since the teeth are worn down at two to three mm each year, the greater part of the crown of the tooth is embedded within the jaw and appears only slowly to compensate for the loss. The extremely hard enamel casing of the incisor and cheek teeth is folded uniquely within the structure of the equine teeth. Furthermore it stands proud of the surface of the tooth and thus provides a highly effective grinding surface. The incisor teeth form an arch in both upper and lower jaws and are curved lengthways and outwards. Together, as they wear, the upper and lower teeth meet at an increasingly pronounced angle. The occlusal surface becomes more triangular and less oval as the horse ages and the teeth are worn down. During this time the appearance of the occlusal surface of the incisors changes. The identification of these changes allows an approximation of the horse’s age to be made once all the permanent incisors have erupted. Hence, horses can usually be accurately aged to within one to two years of their documented age up to about the age of ten years. After this time, the ageing of horses becomes a less reliable process. During the first five years of life, the horse’s milky white temporary or deciduous teeth erupt, followed by their permanent teeth. Usually the temporary incisors have all erupted by 9 months, the temporary cheek teeth being in by two weeks old. Permanent incisors do not finish erupting until about four and a half years old, when the corner incisors have come through. Permanent cheek teeth are usually through by four years old. Hence it is usually relatively straightforward to age a horse accurately to within six months of its true age, until about five years old. Although canine teeth or tushes generally form in both sexes, they are rudimentary and commonly fail to erupt in mares. In males they are low cones situated in the diastemas between the incisors and the cheek teeth. The first premolar is known as the wolf tooth in the horse. It often does not develop at all and when present it is small and usually confined only to the upper jaw. It can be a potential nuisance if it shifts under the pressure of the bit and thus irritates the gum. If this becomes a problem it is relatively straightforward for your vet to extract. The cheek teeth possess up to four roots each, which serve to embed them securely in the jawbone. In the upper arcade of teeth, these roots lie very closely to the hollow cavities in the skull of the horse, the so-called para-nasal sinuses. Relatively common infections involving the tooth roots can spread upward into the sinuses to cause chronic sinusitis in the horse, a frustrating disease which is often difficult to cure. Throughout your horse’s life, your vet should check his teeth on a regular basis, at least once a year. Horses with known dental problems or predisposition to aberrant growth should be checked every 6 months. Newborn foals should have their mouths checked for any abnormalities. This also ensures that they become accustomed to having their mouths handled. Two to four year old horses start to produce their permanent teeth. They should be checked to see if they are coming out properly and not causing irritation to the surrounding gums. Five-year-old horses have all their permanent teeth and these should be checked at this stage. Your vet may start to rasp them at this age to ensure there are no uncomfortable sharp edges. Horses over five years old should be checked ideally every six to 12 months by your vet to look for any sharp edges, hooks, decay or damage. Horses will often receive a routine rasping or floating at this time. Abnormalities that go unnoticed can cause serious damage to the soft tissues inside your horse’s mouth, with consequent pain and reluctance to chew properly. It is worth remembering that a horse receiving regular dental care will keep his teeth for up to five years longer than a horse that does not. And that’s from the horse’s mouth!