Equine odontoclastic tooth resorption and hypercementosis (EOTRH) is a progressive and painful dental condition that occurs in some horses.

Primarily affecting senior horses, it typically involves the gradual degeneration of the incisors and canine teeth. Over time, the roots of these teeth are resorbed or dissolved.

The teeth also become excessively calcified with the buildup of cementum, sometimes resulting in a bulb-like appearance. The weakened teeth may fracture or may need to be extracted to prevent discomfort for your horse.

Horses affected by EOTRH may demonstrate a resistance to biting or chewing hard feeds. [9] They may become generally irritable and experience other behavioural changes due to the pain caused by the condition.

EOTRH can also result in poor appetite or weight loss linked to difficulty with chewing and eating. [9] Horses diagnosed with this condition should work with a nutritionists to design a feeding plan that takes into account their dental health and chewing ability.

If your horse has EOTRH, submit their diet for analysis online and our nutritionists can help you design a diet for free.

What is EOTRH?

Equine odontoclastic tooth resorption and hypercementosis is a condition that typically affects the equine canine and incisor teeth positioned at the front of the mouth on the upper and lower jaws.

It has also been reported to occur in the cheek teeth (molars and premolars) positioned at the sides of the mouth. [1][2]

EOTRH typically affects multiple teeth and negatively impacts the entire external and internal structure of the tooth. It also compromises the periodontal ligament that connects the roots of each tooth to the gums (gingiva). [1]

Tooth roots affected by EOTRH are dissolved or broken down via resorption by cells called odontoclasts.

Odontoclasts are cells that are responsible for the breakdown of the roots of teeth. In humans, they are responsible for resportion of the roots of baby teeth so they can fall out and make way for permanent adult teeth.

EOTRH can also cause an overproduction of the hard material (cementum) that covers the roots, a process referred to as hypercementosis. [3][4][5]

Eventually, EOTRH leads to additional changes in the gum tissues and bone surrounding the teeth. [6][7] Bacteria will subsequently infiltrate the compromised tooth structure and surrounding bone, contributing to the disease process and the destruction of the teeth. [8][9]


Although EOTRH was initially observed in clinical settings, it was first identified in dental tissue specimens in 2008 and is associated with periodontic disease. [3][4]

The condition is believed to be underdiagnosed since it can progress without significant symptoms. It may go undetected for months or years until at which time it may have reached an advanced state. [5]

Older horses appear to be at a greater risk for developing EOTRH. A study of 142 horses with an average age of 21 found that 94% had minor and 64% had moderate to severe indications of EOTRH, upon radiological examination of their teeth during a routine dental check. [6]

The Progression of EOTRH

Teeth affected by EOTRH display one of three patterns of disease progression: tooth root resorption as the dominant process, hypercementosis as the dominant process, or a combination of these two processes. [9]

When resorption is the dominant process, odontoclasts are continuously being activated by a type of immune signalling molecule known as a cytokine. This activation is in response to mechanical stress exerted on the periodontal ligament.

Cytokine activity is also stimulated by an invasion of microorganisms that cause infection in the periodontal ligament. [9]

When hypercementosis is the dominant process, an abnormal amount of cementum (calcified tissue) is deposited on teeth and their roots. This process is considered a responsive action in an attempt to stabilize the damaged tooth. [9]

In all three types of EOTRH reported, resorption and hypercementosis are both evident to some degree in affected teeth when analyzed microscopically. [9] It is believed that resorption happens inside the tooth pulp cavity in advance of hypercementosis which occurs on the outer surface of the teeth.

EOTRH most commonly progresses from the incisors positioned at the corner of the mouth, to the middle and central incisors at the front of the mouth. [5]

Signs and Symptoms of EOTRH

The clinical symptoms of EOTRH can vary significantly between horses. It is common for some horses to show little or no visible indication of the disease even when they have advanced areas of breakdown in the tooth structure, known as dental lesions.

EOTRH affected horses may have difficulty biting, chewing, and swallowing due to pain. [9] They may also experience a reduction in appetite and weight loss due to difficulty eating normally. [9]

Other signs of EOTRH include: [9]

  • Refusing to bite hard treats
  • Drooling
  • Bad breath
  • Behavior changes
  • Irritability or discomfort
  • Increased head shaking
  • Hay dunking
  • Resistance to dental exams

During dental work, horses with EOTRH may exhibit signs of discomfort with the dental speculum and require additional sedation.

Severe Symptoms

When EOTRH becomes severe, several physical manifestations of the disease are typically evident and include:

  • Inflammation in the gum tissues (gingivitis) at the base of the teeth and gum recession. [5]
  • Sores (fistulas) that appear as red dots may develop in the gums and small drainage tracts may be visible if infection is present. [5]
  • The teeth may display an excessive buildup of cementum on their surface. Cementum accumulation can also extend under the gums causing the area of the gums above the tooth roots to have a bulbous appearance. [5]
  • Tooth displacement, fracture, and loss are all commonly associated with EOTRH. [5]

Risk Factors and Causes

EOTRH typically affects horses over the age of 15, although x-ray images have indicated signs of the condition in middle-aged horses of 11 to 13 years of age. [5]

Geldings are more likely to be affected by EOTRH than mares and stallions. [5]

Multiple types of horses including warmbloods, Thoroughbreds, Icelandic horses, Haflingers, and Arabians are affected by EOTRH. [5]

The exact cause of EOTRH is not yet known, although multiple factors are believed to be involved with the development and progression of the condition. [9]

Biomechanical stress on the periodontal ligament is thought to contribute to the development of the disease. [9] Mechanical stress can result from chewing forces over time.

Areas of stress are more commonly observed in older rather than younger incisor teeth and might contribute to the development of lesions. These damaged areas could permit bacterial micro-organisms to propagate or grow inside the teeth. [9]

Excessive dental work may promote EOTRH if the periodontal roots of teeth have been damaged. [10]

Oral Bacteria

At this time, there is a limited understanding of the differences in the oral microbiome of horses with a healthy dental status and those affected by EOTRH. However, research has found that bacterial microorganisms including Treponema and Tannerella contribute to infection in EOTRH affected teeth. [8]

In one study, the DNA of Treponema species was present in 78.2% of horses with EOTRH and only in 38% without the condition. [8] The DNA of Tannerella species was present in 38.4 percent of horses with EOTRH and only in 19% without the condition. [8]

Pituitary Pars Intermedia Dysfunction

EOTRH is more prevalent in horses with the endocrine condition Pituitary Pars Intermedia Dysfunction (PPID; Equine Cushing’s disease). It is also more prevalent in horses with other metabolic disorders, presumably due to hormonal abnormalities. [5]

Research indicates that small animals affected by Cushing’s disease are more likely to have loose periodontal ligaments due to the effects of the hormone cortisol. In excess, this hormone weakens the periodontal ligaments thus contributing to the development of periodontitis. [5]

Some researchers propose that EOTRH affected horses with abnormal cortisol, insulin, and glucose levels are at a greater risk of periodontal disease because of the effects of these imbalances on the periodontal ligament.

Horses with PPID are known to be more vulnerable to infections in general, including in their teeth.

Other Causes

A form of autoimmune disease affecting the teeth has also been suspected of contributing to EOTRH and is known to occur in humans and felines. [9]

Other proposed but unproven causes of EOTRH include genetic factors, parathyroid abnormalities, low blood calcium levels, vitamin A toxicity, and poor blood supply to the bone surrounding teeth.

Diagnosing EOTRH

Microscopic evaluation of the teeth of EOTRH-affected horses is valuable since it can aid in distinguishing EOTRH from other dental diseases.

However, EOTRH is primarily diagnosed by clinical examination of the mouth and with dental radiographs (x-ray images).

The most reliable method for accurately diagnosing EOTRH is via radiography. Clinical examination may not be sufficient to detect the disease if no dental lesions are present.

Portable x-ray machines can be used to take radiographs of the head to gain a comprehensive understanding of the horse’s dental status, so the most appropriate therapy can be chosen.

Radiographs capture multiple aspects of dental resorption and hypercementosis that occur with EOTRH. The most common features of EOTRH observed on radiographs include:

  • Fractured teeth [9]
  • Enlarged tooth roots [9]
  • Resorption lesions on the crown, the apex of affected teeth, and in the bone surrounding the teeth. [9]
  • Widening of the periodontal ligament in affected teeth due to inflammation. [9]

EOTRH Management and Tooth Extractions

A range of strategies including the use of antibiotics, anti-inflammatory drugs, and oral rinses have been employed to attempt to manage EOTRH. At best, they offer temporary relief of the condition and have not been proven to stop the progression of the disease.

Nutraceutical combinations of mushrooms have been shown in a small number of case studies to improve some manifestations of the disease and slow its progression. Cordyceps, Reishi, Polyporus, Pleurotus, Antrodia, Hericium and Maitake mushrooms have all been tested. [11]

The only successful treatment known for EOTRH to date is the extraction of the affected teeth. Removing these teeth can eliminate the pain associated with the condition and may lead to an improved quality of life. [9]

EOTRH-affected horses who undergo multiple tooth extractions typically tolerate the procedure well since they are administered heavy sedation, regional or local anesthetics, and nerve blocks. Most extraction techniques can be performed while the horse is in a standing position.

A veterinary surgeon with expertise in performing dental surgery should be consulted for EOTRH affected horses requiring extraction of multiple teeth as the procedure can be complicated.

A surgeon will typically review radiographs before the procedure to assess the horse’s current dental status. Radiography may be repeated afterwards to ensure any fragments from EOTRH affected teeth have been completely removed.

Horses are administered non-steroidal anti-inflammatory drugs to manage pain and antibiotics to prevent infection. These medications are given for approximately seven to ten days post-extraction surgery.

Most horses are eating before they leave the veterinary hospital. Horses with extracted canines and incisors can resume a normal diet after healing is completed since they use their cheek teeth to grind their food. Healing may take four to six weeks.

Without incisors and canine teeth, horses can still effectively use their lips and tongue to pick up grain and hay. They can also feed on grass that is a sufficient length for them to grasp.

However, some horses may need additional feed sources such as forage cubes and pellets consisting of shorter fibers, to maintain their weight.

After undergoing a full mouth extraction, horses may have a protruding tongue since there are no teeth left to maintain the position of the tongue in the mouth. This is considered a cosmetic concern only.

Horses that have their affected teeth removed are typically significantly more comfortable than they were prior to having extraction surgery. Reported improvements include being less withdrawn, happier overall, and able to eat their food more easily. [5]

If you have a horse with dental issues, you can consult with an equine nutritionist by submitting your horse’s diet online to formulate a nutritional plan that allows them to eat comfortably and ensures they are getting all the nutrients they need.

Important Considerations for Horse Owners

Further research is required to broaden the current limited understanding of EOTRH and its serious health implications. There are several relevant factors for horse owners to consider when managing horses with the condition as outlined below.

When to Extract Teeth Affected by EOTRH

One of the most difficult questions related to managing EOTRH-affected teeth is when to remove them. Severely affected teeth may only show radiographically observable changes but appear relatively normal upon inspection of the mouth.

Unfortunately, there is a lack of research related to dental pain in horses. The true level of pain horses may be experiencing is not always evident to owners or veterinary professionals; horses may be suffering more than is realized. [5]

Digestive Complications

As EOTRH progresses, it can become severe enough to cause significant destruction to the teeth, promote weight loss, and compromise nutrition status. The role of EOTRH in colic should also be considered.

Although research on EOTRH and its relation to colic is currently lacking, horses with dental abnormalities including sharp enamel points and tooth decay are known to have an increased risk for colic.

A study that examined 74 horses with colic and 71 without, found that 38 horses from the colic group had dental irregularities, whereas only 22 horses from the non-colic group had such irregularities. [12]

Healthy dental status plays a role in the prevention of colic. Reducing complications resulting from any dental condition, including EOTRH, is an important consideration for horse owners.

Regular Dental Exams

Veterinarians typically recommend that horses have an annual dental exam to prevent and treat dental problems which may compromise the animal’s overall health.

However, in some cases involving dental abnormalities that are already present, a dental exam may be recommended on a more frequent basis.

In between dental visits from the veterinarian, owners of horses with EOTRH should inspect their horse’s gums and teeth regularly to note any changes occurring over time. Treating EOTRH before it reaches an advanced and painful stage is vital for ensuring the health and well-being of the horse.

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  1. Smedley, R.C. et al. Equine odontoclastic tooth resorption and hypercementosis: histopathologic features. Vet Pathol. 2015.
  2. Moore, N.T. et al. Equine odontoclastic tooth resorption and hypercementosis affecting all cheek teeth in two horses: clinical and histopathological findings. Equine Vet Educ. 2016.
  3. Carsten, S. et al. Equine odontoclastic tooth resorption and hypercementosis. The Veterinary Journal.
  4. Smedley, R.C. et al. Equine Odontoclastic Tooth Resorption and Hypercementosis: Histopathologic Features. Vet Pathol. 2015.
  5. Rahmani, V. et al. History, clinical findings and outcome of horses with radiographical signs of equine odontoclastic tooth resorption and hypercementosis. Veterinary Record. 2019.
  6. Rehrl, S. et al. Radiological prevalence of equine odontoclastic tooth resorption and hypercementosis. Equine Vet J. 2018.
  7. Lee, S. Equine odontoclastic tooth resorption and hypercementosis. Aust Vet J. 2010.
  8. Sykora, S. et al. Isolation of Treponema and Tannerella spp. from equine odontoclastic tooth resorption and hypercementosis related periodontal disease. Equine Vet J. 2014.
  9. Hole, S.L. and Staszyk, C. Equine odontoclastic tooth resorption and hypercementosis. Equine Vet Educ. 2018.
  10. Pearson, A.M. et al. Associated risk factors of equine odontoclastic tooth resorption and hypercementosis. In: Proceedings of the 59th annual convention of the American association of equine practitioners. 2013.
  11. Thiede, S. Case Studies on the Application of Medicinal Mushrooms in Veterinary Medicine. (Translated from German) J Holistic Vet Med. 2017.
  12. Olusa, T. and Akinrinmade, J.F. Do dental abnormalities predispose horses to colic? J Vet Med Anim Health. 2014.