By Emily McNally, VMD, Rappahannock Equine Clinic

Equine odontoclastic tooth resorption and hypercementosis (EOTRH) is a disease that has just recently been properly identified and named in the horse population. First described in 2006, it is a painful condition affecting mainly the incisors and canine teeth of older horses.


Radiograph demonstrating the typical findings in horses with EOTRH. The lighter and moth-eaten appearance of the teeth is attributed to lysis and resorption and the bulbous appearance of the tooth roots is due to hypercementosis.

A horse’s tooth has an outer layer of enamel covered by cementum. The cementum gives grip for periodontal ligaments in the socket to keep the tooth in its place. Unlike humans and many other animals, horses’ teeth continuously erupt throughout life. They are able to do this through two steps: breakdown of the periodontal ligament attachment to allow the tooth to move and reproduction and subsequent re-attachment of the periodontal ligament. Odontoclasts are live cells in the tooth that cause lysis, or eating away, of cementum and tissues surrounding the tooth. When the attachment breakdown is overactive, the result is resorption or lysis of the tooth. Sometimes, other cells respond by exaggerating the re-attachment of the periodontal ligament, creating extra cementum on the tooth surface. Subsequent inflammation and infection of the teeth lead to decreased structural support which can result in gingivitis, pulpitis, and loose and fractured teeth.

The cause of EOTRH is not completely understood at this time. It is clear that chronic inflammation is somehow involved. One theory is that as a horse ages, the angulation of its incisor teeth puts more strain on the periodontal ligament, leading to increased inflammation. A study presented at the 2013 AAEP convention by Dr. Ann Pearson looked into associated risk factors of EOTRH. Excessive dentistry, periodontal disease, and horses fed alfalfa without pasture or grazing were more likely to have EOTRH, but more research is warranted.

This disease has a gradual progression with subtle initial clinical signs that may include nothing more than gingival inflammation. Many older horses are stoic and don’t always show outward signs of oral pain until the condition is quite advanced. Once the condition gets more painful, the horse can start losing weight and going off feed. Many horses lose their ability to grasp apples and carrots. Some horses become irritable, resistant and/or head shy when being bridled or ridden. When you look at the teeth, you may see cavities, excess tartar, painful swellings in the gum or jaw, gingival ulceration, loose teeth and bad smelling breath.

Photo Credit: Midwest Equine Services

Photo Credit: Midwest Equine Services

Diagnosis necessitates intraoral radiographs because most of the disease progression occurs underneath the gum line. Radiographs will demonstrate distinctive abnormalities of affected teeth. Where the tooth is dissolving, you will see resorptive lesions, and where there is excess cementum, the tooth will have a bulbous appearance.

Treatment has historically included antibiotics, oral mouth washes, anti-inflammatories, steroids injected around the teeth, and extraction of all loosened or badly infected teeth. Cases with only hypercementosis and/or mild subgingival resorption can be monitored with a yearly oral exam with radiographs. Once resorption of the reserve crown and root becomes extensive or a tooth fracture is observed, extraction is recommended. Extraction is the only curative treatment, with other treatments being only palliative and generally ineffective. Although extracting the teeth may seem like an aggressive treatment, it is really the only effective treatment for the advanced condition.  After extraction, these horses generally do very well with a lot less oral pain. If you have any questions about EOTRH or would like to schedule a dental for your horse, please call our office at 540-854-7171.