Disease Du Jour: EOTRH 

In this episode, Dr. Amelie McAndrews discusses equine odontoclastic tooth resorption and hypercementosis (EOTRH).
A mild case of EOTRH
A mild case of equine odontoclastic tooth resorption and hypercementosis (EOTRH). | Courtesy Garden State Equine Dentistry

In this episode, Amelie McAndrews, DVM, DAVDC-Eq, of Garden State Equine Dentistry, joined us to talk about equine odontoclastic tooth resorption and hypercementosis (EOTRH). She discussed the prevalence of the disease and described common clinical signs, management options, and more. 

What Is EOTRH? 

McAndrews described EOTRH as “a painful and progressive condition in middle-aged to older horses.” While it mostly affects the incisors and canine teeth, there are some reports of affected cheek teeth as well.  

“Tooth resorption starts on the periphery of the tooth, usually in the root or reserve crown of the tooth, and then that tooth resorption progresses toward the pulp,” McAndrews explained. When that tooth resorption happens, inflammatory cells cause fibrosis of the gingiva and periodontal ligament. The horse also experiences lysis of the alveolar bone and distortion of the vascular channels around the tooth. Tooth resorption by odontoclastic cells occurs, followed by hypercementosis.  

“The way I explain this to owners is the tooth starts to resorb or basically dissolve, and then the body tries to repair those defects, that tooth resorption, by laying down cementum,” McAndrews said. The problem is, the cementum is laid down in places it’s not supposed to be, and it’s more brittle than the dental tissue it is replacing.  

“It sort of becomes this self-perpetuating process where the teeth are getting more and more resorptive, they lay down this cementum, which doesn’t have the same properties as the dental tissue it’s replacing, and the disease process progresses that way,” she said.  

Horses subsequently get periodontal disease and osteomyelitis around the affected teeth. McAndrews noted that this disease process is different than tooth resorption in both cats and people.  

How Prevalent Is Tooth Resorption in Horses?  

A moderate case of EOTRH
A moderate case of EOTRH. | Courtesy Garden State Equine Dentistry

In recent studies of horses 5 years and older, radiographic surveys have identified a very high incidence of tooth resorption, said McAndrews. “They found that 88% of horses and 49% of teeth had radiographic evidence of tooth resorption,” she said.  

Furthermore, the studies revealed 20% of horses and 7.6% of teeth had hypercementosis, and almost 16% of incisors in asymptomatic horses had tooth resorption at a high enough stage to warrant extraction. Age correlated with increasing rates of tooth resorption, with horses older than 15 having a higher stage of tooth resorption on their corner incisors. 

While these are shockingly high percentages, McAndrews said the tricky part is determining when tooth resorption is getting to a level that’s pathologic and causing the horse pain.  

What Causes EOTRH?  

Researchers still don’t know what causes EOTRH, but they have a few theories. McAndrews said the most prevalent theory currently is biomechanical stresses on the tooth are potentially causing the condition. Horses’ incisors start getting shorter at ages 13-15, which causes a decreased surface area for the periodontal ligament attachment. Because there’s less surface area, there’s more focal stress on certain parts of the tooth, which causes a release of cytokines. Those cytokines release clastic cells, which triggers the tooth resorption.  

Once tooth resorption starts, the horse will experience concurrent periodontal disease. This leads into another theory that bacterial infections could potentially cause EOTRH.  

Others speculate that iatrogenic dental procedures like over-floating potentially cause the condition. In another recent study, researchers looked at trace minerals in hypercementosis.   

“The long and short of it, unfortunately, is we don’t know,” McAndrews said. “And without knowing what causes it, it’s harder for us to stop the disease process, because we don’t know exactly what we’re trying to stop other than tooth resorption and hypercementosis.” 

Clinical Signs of EOTRH 

McAndrews said EOTRH takes many years to develop, and veterinarians usually don’t diagnose it until the horse is in the later stages of the disease when it starts to affect the crowns of the teeth. She said clinical signs can be subtle, even if the horse has significant radiographic changes, and it can be difficult to correlate radiographic changes with pain.  

Common clinical signs can include gingivitis, periodontitis, small pits in the teeth calculus, and a bulbous appearance of the incisors from hypercementosis. If the disease is advanced enough, it can progress to fracture, tooth mobility, and periodontal pockets. Horses can be sensitive to the speculum and noncompliant for oral exams. They might display weight loss, quidding, halitosis, and bitting problems. Some horses rub their incisors on the wall. Others have essentially no clinical signs, likely because they have learned to live with the discomfort because of its gradual onset.  

Diagnosing EOTRH 

radiographs of horses with EOTRH
Radiographs of a moderage case of EOTRH (left) and a severe case (right). | Courtesy Garden State Equine Dentistry

EOTRH requires a radiographic diagnosis guided by a clinical exam. “What you’ll see on your radiographs is there’ll be ovular bone loss paired on a ligament widening or condensing osteitis,” McAndrews said. “That will lead to periapical abscess. They can get osteomyelitis, you can see tooth fracture, and then, of course, tooth resorption.”  

McAndrews said it is helpful to owners to grade the tooth resorption. Grade 1 involves the cementum and a little bit of the enamel; Grade 2 involves the dentin; Grade 3 is tooth resorption that’s into the pulp, which is the stage when veterinarians typically recommend tooth extraction; Grade 4 is when the tooth loses its structural integrity; and Grade 5 is when only remnants of tooth remain.  

Treating EOTRH 

A severe case of EOTRH
A severe case of EOTRH, for which tooth extraction would be required. | Courtesy Garden State Equine Dentistry

McAndrews said veterinarians have tried all kinds of treatments for EOTRH, from tooth brushing to steroids to antimicrobials to splinting the teeth. These have all been unsuccessful for long-term management. Because veterinarians still don’t know what causes the disease, they don’t know how to stop the disease process. That leaves tooth extraction as the most effective option.  

“This is a really tricky thing client-communication-wise, especially if the owner wasn’t expecting it,” McAndrews said. “I try to put myself in owners’ shoes and validate all their concerns.” 

McAndrews goes over radiographs with owners and shows them normal vs. abnormal, which can be helpful for visual learners. She sometimes has clients talk to other owners whose horses have had the procedure for reassurance. She never forces owners to make the decision, and she is a listening ear for all their questions.  

For the extraction process, McAndrews said it is important to extract all the incisors, especially because it is difficult to correlate radiographic changes with pain to understand which teeth are most painful. She also said veterinarians must be prepared to extract the whole tooth, even if it fractures, which is likely if there is a lot of tooth resorption. “They will continue to be painful and develop draining tracks and develop more hypercementosis if you leave bits of tooth in there,” she explained.  

McAndrews further noted that veterinarians should be good at doing nerve blocks and prepared to take post-extraction radiographs. Many of these extractions can be performed on the farm by general practitioners, but some cases might be easier to treat in stocks at the clinic.  

Following the procedure, McAndrews said the extraction sites will look awful for a while but ultimately heal great. “Any complications associated with the procedure are mostly related to the effects of needing to sedate the horse,” she said.  

Prognosis for Horses Following Extraction  

McAndrews mentioned a recent study conducted by Bo Rainbow, DVM, who sent a survey to owners whose horses had undergone this procedure. The owners reported their horses showed improvements in body condition, dropping hay, speed of eating, general behavior, resistance to bridling, and headshaking. Overall, the owners said their horses seemed happier and had an improved quality and length of life. More than 90% of respondents said they would have done the procedure again and would do the procedure on another horse in the future.  

“I think that really shows how much we can improve horses’ lives by addressing these really painful teeth,” McAndrews said. “When you remove this source of pain, they tend to have a new lease on life. It can be a really, really rewarding procedure.” 

About Dr. Amelie McAndrews 

Amelie McAndrews, DVM, DAVDC-Eq, is a Board Certified Equine Dentist™ and a Diplomate of the American Veterinary Dental College. There are only a handful of Board Certified Equine Dentists™, and she is the only practicing equine dental specialist in the mid-Atlantic region and Eastern Pennsylvania. Besides owning Garden State Equine Veterinary Dentistry, she is a clinical associate at University of Pennsylvania’s New Bolton Center and manages the referral dentistry caseload there. 
​Originally from Connecticut, McAndrews completed an internship before spending five years at a general equine practice in New Jersey. During her time as a general practitioner, her interests and caseload became increasingly focused on equine dentistry. She found she could significantly improve her patients’ quality of life by addressing problems found through a comprehensive oral exam. Garden State Equine Veterinary Dentistry was founded in 2015, with the goal of helping more horses through better oral health. She uses minimally invasive techniques for improved outcomes in equine oral surgery. 
McAndrews regularly presents to equine veterinarians on dental disease and teaches equine dentistry to veterinarians and veterinary students. A graduate of the United States Pony Clubs, she enjoys teaching local pony clubbers horse management skills and horse owners about equine dentistry. 

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