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.
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.