A Curious Case of Equine Compound Odontoma

If your horse is dropping food, head-tilting or -tossing, and/or eating slower than normal, he might be experiencing tooth-related pain. While these signs of dental problems are typically easy to spot, serious issues often lurk out of sight. Take, for example, a 2-year-old gelding who arrived at Idaho Equine Hospital (IEH), in Nampa, for a checkup in August 2021.

The gelding’s owner reported finding a firm swelling on his lower right jaw but no problems eating and no signs of pain. Treating veterinarian and surgeon Pete Knox, DVM, Dipl. ACVS, started his assessment with an oral exam and, at first glance, all looked normal.

The next step was taking radiographs of the affected area. The results showed what looked to be many disorganized tooth roots—288 unattached tooth roots in the horse’s right mandible, to be precise. Compare that to an average adult horse’s teeth: Stallions and geldings have 40 permanent teeth, while mares have 36 to 40.

A Curious Case of Equine Compound Odontoma

The young gelding had compound odontoma, or a benign tumor of dental origin, a condition rarely reported in veterinary literature, said Knox. Neither he nor any other vets at IEH recall having seen a case.

Few studies have reported on the condition in recent years, but a 2004 paper and a 2008 clinical commentary highlight cases similar to the one Knox received.

After making the diagnosis, Knox recommended surgery to remove the offending tooth roots. The gelding went under general anesthesia so Knox could remove part of the lower jaw to expose the cavity holding the teeth. He used a saline flush to clean most of the teeth out of the mandible cavity and a bone curette to cut out the remaining roots.

“The roots were contained within the cavity along with gelatinous tissue, and some were adhered to the surrounding bone,” he said.

The pile of teeth looked sizeable post-surgery, but Knox said they were relatively small—each about the size of a peanut.

In the seven months since the procedure, the horse has recovered well. His skin has healed, the bump is less noticeable, and the owner has reported no other dental issues to this point, Knox said.

“Hopefully, we will have the chance to monitor him over the next few years due to the possibility of damage to the roots of the permanent teeth,” he said.

Knox said they did not find a specific cause linked to the development of compound odontoma during the diagnosis and treatment.

Fortunately, compound odontoma is extremely rare, Knox said. He encouraged horse owners not to worry about this condition developing in their young horses. However, when it does occur, the signs are easily visible.

“They would see a large bony bump on the lower jaw, which is much more prominent than the normal eruption cysts young horses develop as their permanent teeth come in,” he said. “While it is a rare and dramatic condition, surgical treatment has a good chance of success.”