by Dr Shannon Lee BVSc
Dental care in the horse involves the same principles as human dentistry; many of the diseases seen in people's teeth are also diagnosed and treated in the horse. For example periodontal disease or disease of the structures surrounding the tooth is the number one cause of premature tooth loss in both horses and humans.
Just like people, horses experience dental pain. This pain comes from a number of sources. The maxillary branch of the infraorbital nerve innervates the teeth of the upper jaw of the horse, while the mandibular branch of the trigeminal nerve innervates teeth of the lower jaw. Horses certainly can experience severe pain caused by sensation to these nerves. Horses also experience pain due to oral ulcers, impacted teeth, feed packing into spaces (called diastema) between the teeth, fractured teeth, unopposed teeth erupting into soft tissues and tooth root infections causing abscesses. These are a few of the ways in which horses experience pain and discomfort due to dental disease.
Figure 1. Cheek ulcers caused by sharp points
Horses do have some important differences in the anatomy of their teeth. Horses are herbivores and their teeth are designed to grab and grind forage (grasses). Horses have two sets of teeth during their life and these teeth are constantly worn away by the actions of chewing and grinding. However the horse possesses extra tooth or reserve crown below the gumline in the jaw and this erupts at a similar rate to the rate at which tooth is worn away. Horses have enough reserve crown to last the average horse well into their twenties and certainly I personally have seen horses in their thirties that still had a functional mouth with all teeth present and were able to chew. However this system of tooth being erupted and worn away must stay perfectly in balance or problems will quickly occur. Pain is the most common reason why the system gets out of balance, because in response to pain the horse will alter the way it eats and chews and this rapidly affects the wear patterns of the teeth.
Figure 2. Large hook on first cheek tooth causing ulceration
Another very important component of how the mouth is balanced is the diet. Horses evolved to graze with their heads down at ground level eating grasses for many hours a day. By altering their living and feeding conditions we alter the way their teeth wear: by forcing them to eat with their head up; providing short feeding times; feeding grains, chaffs and pelleted feeds. When we do this we must be aware of the effects these changes have on the horses dentition.
Figure 3. Close-up of sharp points
Figure 4. Close up of tooth after removal of sharp points
Horses also have another important anatomical difference from people. Their upper jaw, when viewed from the front, is wider than their lower jaw, and this means that the outr surface of the upper cheek teeth (closest to the cheeks) is unopposed, as is the inner (closest to the tongue) surface of the lower cheek teeth. The edges or cingulae of these teeth grow through the continual process of eruption but are not worn away and these form razor sharp points (similar to the teeth of a saw blade) along the arcade of teeth. When the horse eats it is forced to bring its cheeks into contact with these points.
Because the horse chews in a complicated four part cycle, not simply side to side or up and down, these points then act on the cheeks and tongue of the horse like a saw blade causing ulceration, cuts and abscessation if bacterial infection occurs.
Equine teeth are made up of three tissues, enamel, cementum and dentine. Enamel is the hardest but most brittle and this is what the cingulae or sharp points are made of. Because of this brittleness these points can be removed relatively easily, providing relief for the horse and, all other things being equal, a return to a normal chewing cycle.
It is important that a thorough visual exam is made of a horse's mouth, as there are many other conditions that commonly occur in the mouth, many of which cannot be diagnosed without visualisation. These conditions are important and too complex to explain without a large amount of detail so I will not go into them here.
I encourage all horses owners to take responsibility for ensuring their horses receive proper dental care: do your research and chose a qualified experienced professional who can explain what procedures they are performing and why.
Figure 5. Series demonstrating removal of plaque from canine tooth; notice bleeding due to gingivitis and impacted feed material causing infection