Dental Care in Horses
Dr. Philip Johnson
As in other herbivores, the premolar and molar teeth of horses are important for grinding herbaceous food (primarily grass) in order to maximize the extent to which the intestinal tract can obtain nutrients from it. The premolar and molar teeth are collectively referred to as the "cheek teeth" and, unlike the situation for humans, dogs and cats, these teeth are continually growing throughout the life of the horse.
In the young adult, the root of each of the cheek teeth is several centimeters in length, but they are progressively worn down by their grinding function, known as dental attrition. The age of horses can be defined by the length of the roots of their cheek teeth. By the age of 30 years, most horses have expended their cheek teeth by normal chewing activity throughout life; in the aged horse, the length of the roots of the cheek teeth might be less than 1.0 cm. They are not generally able to live beyond this point because, in the absence of effective cheek teeth, it is not possible to acquire sufficient nutritional value from food. The rate at which dental attrition occurs differs among horses based on genetic differences, such as the shape of the mouth, the type of food that the horse has been fed and the extent to which the horse's teeth have been cared for throughout life.
Grass-based diets increase the wear on teeth because of the abrasive content of silica in the dirt and grass, compared to the low silica content of grain. Therefore, the extent to which grain is used in a ration is an important predictor of early dental attrition. Veterinary dental health care for horse's teeth, when applied conservatively, can promote oral hygiene and possibly increase the useful life of horses.
However, excessive dental "treatments" may actually quicken the rate of dental attrition to the eventual demise of the patient. Currently, it is fashionable for horse "dental prophylaxis" programs to be undertaken regularly with little heed paid to the fact that these treatments may often be unnecessary and may undermine the true function of the cheek teeth.
Although some unusual horses are able to attain ages beyond 35 years, it's often the result of special diets. Many of these very old horses tend to have difficulty maintaining their body weight and they are at risk for other dental problems. As the horse ages and the cheek teeth become progressively worn down, the risk of secondary dental disease increases.
A very important contributor to normal oral hygiene is the movement of the tongue within the oral cavity. If the horse is unable to "clean" the interior surfaces of the oral with the tongue, food material will lodge and accumulate. If food material accumulates in the recesses between adjacent teeth or between the teeth and the lining of the cheek, bacterial infection occurs and leads to gingivitis. As with people, gingivitis progressively leads to other dental problems.
Rasping the Cheek Teeth
The on-going grinding process of the cheek teeth causes the cheek teeth to develop sharp edges. If these sharp edges are left unattended, the horse may experience pain during normal cleaning movements with the tongue that will lead to poor oral hygiene, food retention, and gingivitis. To prevent this sequence of events, the most common dental prophylaxis that is routinely afforded adult horses is "rasping" or "floating" the cheek teeth.
Dental rasping entails the use of "dental floats" – hand-held instruments that are comprised of a handle and a head. At the head is a grinding surface, often composed of carbide-tungsten. The grinding surface of the dental float is moved backwards and forwards along the sharp edges of the cheek teeth with the intention to smoothing off the sharp corners and improving the ease with which the tongue can be moved inside the oral cavity.
Remarkably, dental rasping is often accomplished in the standing horse with minimal restraint. For some horses, a light sedative may be useful to facilitate the procedure. Some dental rasping gear is powered so that the veterinarian's work in completing the procedure may be lessened. The use of powered gear is especially helpful when a large number of horses are being treated. Unfortunately, some veterinarians use the powered gear to excess and cause marked smoothing of the dental occlusal surfaces. Excessive rasping clearly quickens dental attrition and removes the important grinding surface of the cheek teeth to a detrimental extent (these surfaces are supposed to have a degree of irregularity to them).