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Equine Odontoclastic Tooth Resorption and Hypercementosis


Equine odontoclastic tooth resorption and hypercementosis is a very painful dental disease veterinarians have begun to diagnose in older horses. Dental care is essential to our horses’ well-being—healthy teeth ensure horses digest their food properly and tolerate a bit when ridden. Sources of dental pain are the molars (cheek teeth) that wear into sharp points, long hooks, and ramps as they grow and the incisors and canines. A relatively newly named dental disease (EOTRH) can be responsible, sometimes causing severe consequences.

What Is It?

Equine odontoclastic tooth resorption and hypercementosis (EOTRH) is a dental disease that has just recently been described in veterinary literature.  This does not mean that it must be a new disease. We know that there are similar poorly understood dental conditions reported in humans (multiple idiopathic root resorption) and in cats (feline odontoclastic resorptive lesions). The disease process that we call EOTRH has probably been with horses throughout history.

Veterinarians are recognizing the disease now because horses are living much longer than in the past and veterinarians are scrutinizing their mouths more closely.The EOTRH disease process occurs in older horses when their body resorbs the bone and tissue surrounding the incisor (and sometimes canine) roots. As a horse loses more and more of his dental papillae (the gingiva, or gums, between each incisor), feed accumulates and paves the way for infection in the gingival pockets. This can destroy the periodontal ligament, which helps hold each tooth in place, as well as the alveolar bone that surrounds the tooth root. Following tissue resorption and inflammation and infection in the pulp (the part of the tooth’s center that contains sensitive connective tissues), periodontal ligament, and alveolar bone, cementum—the enamel-like material that covers the horse’s tooth—proliferates near the gumline. Researchers believe that cementum proliferation is the body’s way of trying to stabilize the tooth as the normal structures deteriorate. As the disease progresses, the gingival degradation only worsens and the support structures continue to diminish. The weakened areas of the teeth can even fracture. The entire process is quite painful and can lead to changes in the horse’s ability or desire to eat and drink.

We don’t yet know why EOTRH occurs. Some researchers blame age-related changes in the mouth, such as natural loss of a tooth’s reserve crown (the portion of the tooth hidden by the gum). Dental trauma and not enough time spent masticating (chewing) could also be inciting factors. Ann Pearson, MS, DVM, of Reata Equine Veterinary Group, in Tucson, Arizona, points out that when horses lower their heads to graze, saliva bathes their incisors, moving food particles and bacteria through the mouth naturally. She and others theorize that if horses do not chew enough, especially when grazing, food particles might stagnate in the mouth.

Alternatively, other groups (Schrock et al., 2013) suggest that the stresses and strain that chewing puts on the incisors and canine teeth, especially in older horses, plays a role in EOTRH development.

Finally, in a study published in a 2014 edition of Equine Veterinary Journal, Sykora et al. identified Treponema and Tannerella spp bacteria in the mouths of 100% of the horses with EOTRH that they studied. They also identified these bacteria in more than 50% of normal horses and concluded that their proliferation in diseased mouths might be significant in the development of the disease.



Who’s At Risk?

This condition mainly occurs in horses older than 15. Warmbloods and Thoroughbreds are more commonly affected than other breeds, though in Pearson’s study she showed that Arabians tend to be more predisposed to EOTRH than other breeds. Stallions might be more susceptible than mares or geldings. Horses with a history of dental care performed by a lay dentist or those that have undergone aggressive procedures such as incisor reduction were more than five times more likely to develop EOTRH, says Pearson. Horses with limited pasture access or consuming feedstuffs that did not require a lot of chewing, such as those on alfalfa-based diets, were also at risk. Finally, horses with endocrine conditions such as equine metabolic syndrome (EMS) or Cushing’s disease were 50% more likely to develop EOTRH than healthy horses. Pearson believes the high circulating levels of insulin and glucose seen in horses with EMS might be associated with periodontal disease. Dogs with Cushing’s disease, for instance, have a higher prevalence of ligament laxity, a phenomenon that might be similar to the resorptive process veterinarians see with the periodontal ligament in horses. Additionally, horses with Cushing’s disease are known to have impaired immune function, making them more susceptible to infection.



What to Look For

EOTRH takes years to develop into its highly destructive and most painful stages. The changes to the teeth and the horse’s demonstration of pain can be quite subtle in the early stages. Owners often attribute these signs to the horse just aging and getting a little grumpy. Many caring and attentive owners miss these slowly developing signs. This is an excellent reason for the value of having a veterinarian perform annual oral exams on your horses.

One of the earliest signs is related to incisor pain. Some owners report their horses being unable or unwilling to grasp hard treats, such as apples or carrots. The animals try to use their lips instead of their teeth to grasp hay and grass, and they might spend an abnormal amount of time mouthing at their water bucket. In Pearson’s study she surveyed owners of EOTRH horses, and they reported horses exhibiting a “smiling” behavior, pulling the lips back at both rest and work. Owners might also note nonspecific signs of dental pain, such as headshaking, resistance to the bit, hypersalivation, poor appetite, and weight loss. These horses might become resistant to having their mouth handled or their teeth examined.

Once the resorption process has begun, you might notice the physical loss of the dental papillae. The cementum overgrowth will make the affected teeth appear bulbous and discolored near the root, and the gumlines will appear to be receding. The tissue surrounding the top of the teeth might become enlarged and inflamed. If tooth roots are infected, you might also notice small red dots above the gumline. These areas can even open up to form draining tracts that produce discharge. Because of the tooth roots’ structure loss, the incisors might shift or become noticeably loose.

How is it Diagnosed?

Owner recognition is the first step toward an EOTRH diagnosis, because it’s likely you will notice your horse’s subtle behavior and eating pattern changes before others do. Shannon Lee, BVSc, MANZCVSc, MICEVO, of Advanced Equine Dentistry in New South Wales, Australia, says your veterinarian can confirm an EOTRH diagnosis based on both a physical examination of the teeth and intraoral radiographs (X rays), the latter of which are essential to revealing the destructive process hidden beneath the gumline. Using these images your veterinarian will view the roots of the upper and lower incisors as well as the canines. He or she will also look for loss of the periodontal ligament space, changes in the bone surrounding the tooth roots, and any evidence of osteomyelitis (infection in the bone) or fractured teeth.

What Can be Done?

Unfortunately, there is little you can do to slow EOTRH progression once it has begun. In mild cases horses benefit from having a veterinary dentist address the early stages of periodontal disease. You can also keep the incisors free of feed material by flushing the mouth with water daily or even brushing the teeth. Additionally, antibiotic treatment might help prevent excessive bacteria accumulation and local infection contributing to the resorption and damage. Once radiographic changes and pain occur, however, most practitioners recommend that they extract the affected teeth. Removing the teeth relieves the pain associated with each tooth and might even prevent the process from expanding to nearby incisors. Most equine practitioners are experienced in dental care and capable of removing loose incisors. If the disease is advanced and your horse requires complete removal of the incisors, however, he might need to be referred to a veterinary dentist or surgeon, as the retrieval of all infected material, fractured tooth shards, or severely resorbed teeth can be quite technically challenging. Postoperatively, horses receive a course of pain management and antibiotics. Most veterinarians recommend taking serial radiographs to ensure they completely removed affected teeth and to monitor the remaining incisors’ progress.

While incisor extraction might seem like a radical procedure, Lee notes that “with ongoing management, horses affected by EOTRH who have had incisor teeth or canine teeth removed cope very well.”

Going forward, these horses typically receive a soaked pelleted feed for the first few days after surgery but can quickly transition to soaked hay or a hay stretcher—a complete pelleted feed that serves as a forage alternative. Horses learn to use their lips and their tongue to prehend grass and hay, and because incisors were never intended to grind food in the first place, these horses are still able to eat hard feeds. Some older horses might benefit from a senior feed to help them maintain a normal daily caloric intake.

It appears that the removal of the incisors of horses afflicted with EOTRH improves their quality of life. Until we can prevent or cure EOTRH, removal of the incisors of diseased horses seems to be the best treatment.

Take-Home Message

What veterinarians know about this disease has expanded rapidly over the past few years, but more research is needed to identify a cause. They hope that further studies will lead to better treatment options and even preventive measures.

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