Over the past decade, the temporomandibular joint (TMJ) has become an area of interest for many equine clinicians. This small joint, located on each side of the jaw, is almost solely responsible for allowing mammals to open and close their mouths. Despite its obvious importance, little research has been done to determine how problems in this joint might impact a horse’s health.

At the 2015 American Association of Equine Practitioners’ Convention (Dec. 5-9) in Las Vegas, Travis Smyth (DVM) presented the results of a study evaluating the impact of unilateral (one-sided) TMJ inflammation on chewing performance in horses. Smyth, a surgical resident at the University of Saskatchewan’s Western College of Veterinary Medicine, in Saskatoon, Canada, is specializing in equine TMJ disease as part of a master’s thesis, under the supervision of James Carmalt, MA, MVetSc, VetMB.

During the conference, Smyth explained how chewing requires the jaw to move in three dimensions–not only vertically, but also horizontally and rostro-caudally (front to back). Only by having two functioning TMJs can horses be expected to perform this complex 3-D pattern.

Smyth said he and his colleagues are trying to determine what might lead to TMJ disease in horses; possible triggers include trauma, dental disease, and age-related arthritis. Clinical signs of TMJ inflammation might include quidding (dropping clumps of partially chewed, but undigested feed material from the mouth), anorexia, headshaking, head shyness, and fighting the bit.

Currently only a few cases of equine TMJ disease have been reported in published literature, all of which focus