Equine Odontoclastic Tooth Resorption and Hypercementosis…..EOTRH for Short!

Equine odontoclastic tooth resorption and hypercementosis. A long name for a complicated disease. Thankfully, we shorten the name to EOTRH (or “E-roth” as we say). EOTRH is a degenerative disease that affects the incisors and canines, in most cases. There have been a few select reports of it also involving the first premolars, but it is rare. Horses aged 12 years and older are affected, and it can be seen in any breed. However, it has been more commonly reported in Thoroughbreds and Warmbloods1.

First, a short course in the structure of a tooth. Teeth are made up of cementin, dentin, and enamel, with a pulp cavity(or cavities) in the middle to supply nutrients. There is also a ligament that holds the tooth in the socket.  EOTRH is characterized by resorption of tooth structures, often with simultaneous excessive production of cementin on the surface of the tooth root. Once the process begins, it continues until the tooth breaks or is completely resorbed. This process is EXTREMELY painful. Horses with EOTRH often resent the pressure caused by the speculum we use to open their mouth, and need more sedation as a result. EOTRH can involve anywhere from one tooth, to the entirety of both the upper and lower incisors and canines. It has been noted that the disease seems to start with the outer 03 incisors and work towards the middle1. Due to the painful nature of the disease, the only current treatment is to remove all affected teeth. Although it seems barbaric, owners have noted a complete change in their horses’ demeanor after removing the teeth. The horses are much more comfortable and happier once the extractions have healed.

A normal tooth on X-ray (2nd from left) and a tooth showing advanced resorption and hypercementosis (2nd from right)

So, what are some signs to look for? Each horse has a different way of displaying the pain associated with EOTRH. Some horses will continue on like nothing is wrong, despite having advanced disease. Others will stop eating or start resisting the bridle, or just start acting cranky. A common test is what we call “the carrot test.” Offer your horse a carrot to bite. If he bites through it with no problem, it’s all good. But, if he starts to hesitate or can’t bite through it, this is a sign that his teeth hurt and he may have EOTRH. Some owners notice pustules forming on the gums and/or gingival recession. This is due to infection surrounding the tooth. The gums can also look bumpy or swollen if there is hypercementosis associated with the disease. Sometimes, we don’t know they have it until they break a tooth and we take an X-ray. 

A pustule above an affected tooth, with concurrent gingival recession  

Unfortunately, no distinct cause has been identified at this time. There is ongoing research to determine if EOTRH has a singular cause or is the result of many factors over the life of the horse. It is suspected that inflammation of the periodontal ligament surrounding the tooth plays a roll in initiating the disease1. This can lead to secondary infection by different bacteria, which help progress the resorption of the tooth structures and cause visible infection around the tooth. The hypercementosis is suspected to be the body trying to repair the resorption; it just goes out of control1. Not every case has hypercementosis associated with it. As stated earlier, the only treatment is to remove the affected teeth. This is done with the horse sedated and standing, and can take up to 4 hours. Nerve blocks with lidocaine or carbocaine help to numb the entire affected area, and we also numb around each tooth with lidocaine. The disease is progressive and painful, and if left alone, causes profound discomfort and stress to the horse. Regular dental check ups can help to identify suspicious lesions and track the progression of the disease, if previously identified. The best way to determine the extent of disease is to take an X-ray of both the upper and lower incisors and canines. We have documented numerous cases of EOTRH within our practice, and regularly remove affected teeth. If you suspect your horse may have something wrong, don’t hesitate to give us a call. X-rays are a quick and easy way to determine if your horse is suffering from EOTRH.

Written by: Dr. Morgan Bosch, DVM


1. Vahideh Rahmani, Lotta Häyrinen, Ilona Kareinen and Mirja Ruohoniemi. History, clinical findings and outcome of horses with radiographical signs of equine odontoclastic tooth resorption and hypercementosis. https://veterinaryrecord.bmj.com/content/185/23/730

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