Midwest Equine

Feature Article

Equine Odontoclastic Tooth
Resorption and Hypercementosis

By Dr. Ruedi Steiger, DACVIM Swissvet Veterinary Products

Article Archives LinkEquine Odontoclastic Tooth Resorption and Hypercementosis

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Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) is a relatively newly described condition that affects incisor and canine teeth of older horses over the age of 15 years. The key findings of EOTRH are resorption of dental tissue (odontoclastic) and sometimes excessive proliferation of cementum around the tooth roots (hypercementosis). A number of predisposing factors are suspected, but the full etiology of the disease is unknown. Extraction of affected teeth is currently the only treatment option to alleviate horses from the significant pain associated with EOTRH. There is no indication that the condition can spread to other animals, and horses typically recover quickly after incisor or canine tooth extraction. Early detection and treatment using proper instrumentation are key in dealing with EOTRH.

EOTRH typically starts at the third incisors (103/203 and 303/403) slowly spreading mesially to the other incisors, or less frequently to the canines. Affected teeth start with an uncontrolled periodontal inflam-mation resulting in resorptive lesions, essentially dissolving the tooth roots. As the anchoring roots resorb, the dental structure tries to stabilize the tooth with the formation of excessive external cementum. This results in the formation of the diagnostically typical pain and bulbous swelling under the gums.

Despite the distinct clinical signs there is a surprising lack of older recordings of the condition. It almost looks like EOTRH is a new syndrome and it has not been studied in great detail. As a result, the cause of EOTRH is poorly understood.


Dr. C. Stazyk from Europe who marked the term EOTRH in 2008, speculated early on that mechanical stress might be the triggering factor. So does Dr. D. Klugh who theorizes that its origin in the '3s may provide a clue: 'As incisors age they normally undergo a rostrally directed tipping movement. The 3s are the most dramatically tipped teeth, and the biomechanical forces are exacerbated by mastication. These forces may be sensed by the cell rests and set off a cascade of events that lead to the disease.' Occlusal forces directed to a tipping tooth may lead, for unknown reasons, in some horses in the development of the disease. He further suggests that the spread of the disease may be due to an uncontrolled inflammatory reaction and cytokine recruitment.

There are similar resorptive conditions in humans and cats, but with a less dramatic proliferative component. It might be the increased regenerative properties of the equine periodontal ligament and its interaction with the peripheral cementum is responsible for the hypercementosis in horses. There are reports where researchers have studied possible contributing factors for EOTRH. Dr. Ann Pearson reported that excessive dentistry, periodontal disease, a low grazing diet and endocrine disease are potential risk factors being associated with EOTRH.

I think that we should consider the possibility that EOTRH might be associated with the use of power instruments. It is quite striking that we describe these lesions only after the introduction and broad use of power instruments after 2000 (Swissfloat and Powerfloat were introduced at the AAEP in 1999). It is possible that excessive removal of cheek tooth material results in increased occlusive forces to the incisor teeth or that there is a direct damage to incisor teeth after incisor work. In any case, more research is needed to determine the cause of EOTRH.

Symptoms and Diagnosis

Whatever the cause, EOTRH is believed to be a painful disease. Because pain in the incisors may cause difficulty in grasping apples and carrots, owners may complain that their horse has lost interest in treats. In fact, watching a horse's eating habits may be a good way to gauge the stage of the disease. Horses suffering from EOTRH may begin to use their lips to slide grass and feed past their incisors to avoid pain. Other early signs of EOTRH may include a loss of appetite, irritability when being bridled, halitosis, excessive saliva, resisting turning during training, and head shaking.

Oral examination of horses suffering from EOTRH can prove quite difficult. Patients generally shy away from manipulation of the affected region and even under sedation may display dangerous alert behavior in response to the placement of an oral speculum. Despite the challenges, an oral exam and radiography are both necessary for a definitive diagnosis of the disease. Possible oral exam findings include: bulb-like swelling around the roots of incisors, edema, hyperemic and receding gingiva, and excessive calculus, decreased incisor angle, swelling of the mandibular lymph nodes, apical fistulae, and varying degrees of tooth mobility.

Eibrich Instruments, Germany; Extraction of third incisor

Extraction of a third incisor using a strong gouge (Erbrich Instruments, Germany) and a mallet. The alveolar bone is partially removed on the vestibular side to loosen the periodontal ligament.


Once EOTRH is suspected, radiography is necessary to diagnose the spread and severity of the disease. Radiographs may show moderate to severe resorptive lesions and bulbous hypercementosis, alveolitis, tooth fractures, and osteomyelitis.

However, since most of these horses are older, the anesthetic risk must be carefully weighed against these possible disadvantages of the standing procedure. The combination of Detomidine and Butorphanol, either as injections or as a CRI is typically sufficient that a horse that can be treated in a standing position. When choosing to perform the procedure in the standing horse, blocking the mandibular and maxillary nerves will provide local anesthesia to both the cheek teeth and incisors. One can also block just the mental nerve and the infraorbital nerve, but this may prove more difficult particularly on horses who are already shy about the head.

Details about extractions of incisor teeth or canines are described elsewhere. It is important to have the proper equipment ready, including a good set of elevators and strong gouges to elevate the tooth and remove the periodontal and alveolar support as well as having the instruments to deal with possible fragments of fractured tooth roots. The surgical site needs to be thoroughly lavaged with an antiseptic solution (or just tap water) and curettage is performed carefully to avoid damage to the remaining teeth.

Filling of the alveolus is not needed, the resulting blood clot is left in place which soon will be replaced by reparative tissue. Suturing the gingiva can be attempted but often results in dehiscence. Postoperative radiographs are recommended to check that the entire affected tooth has been removed, and horses should be put on post-operative pain medicine but only rarely on antibiotics. Surgical sites should be rinsed twice daily with either warm water or a warm antimicrobial rinse for a few days.

In cases where not all incisors are removed the veterinarian might consider floating the remaining incisor teeth slightly below normal contact to relieve physical stress to the incisor teeth.


Recovery from extraction is usually quick and complete. Horses should be fed a soft diet for several weeks and shouldn't be ridden with a bit for a while, but most will recover fully and experience a significantly higher quality of life once the pain from EOTRH is alleviated.

Since cheek teeth are responsible for grinding, not incisors, even patients who have had all incisors extracted are able to go back to grazing with little difficulty (though owners may want to keep some hay around, just in case).

Most will learn to grasp apples and carrots with their lips so that their owners can once again reward them for an excellent day's work!

Dr. Ruedi Steiger About the Author
Dr. Ruedi Steiger, Diplomat of the American College of Veterinary Internal Medicine (Large Animal), graduated from the University of Zurich, Switzerland in 1987. After working in private practice, he completed a residency in internal medicine in Auburn Alabama. He worked at Oklahoma State university and later in a private equine clinic in Tennessee. He had a special interest in equine dentistry and started a distribution business of equine dentistry instruments (Swissvet) in 1999. He enjoys his equine dentistry practice, as well as teaching and lecturing and has been a frequent contributor for the equine solution.