Does the mouth speculum hurt your horse's TMJ? Here's what the science actually says

It's a question that comes up more often than you'd expect, when someone mentions that the jaw looks a little tense, or a therapist flags the TMJ (temporomandibular joint) as sensitive.

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Could the speculum have caused that?

It's a fair question. And because we believe horse owners deserve honest, science-backed answers we wanted to share what the research actually says.

What is the TMJ?

The temporomandibular joint is the hinge joint connecting your horse's lower jaw (mandible) to the skull. It enables the complex side-to-side grinding motion horses use to chew.

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Because this joint sits close to where the bit, bridle, and dental equipment all interact with the horse's head, it has become a frequent talking point in equine health discussions.

Riders, therapists, and owners increasingly mention the TMJ when a horse shows resistance, head sensitivity, or changes in performance.

Which brings us to something the research addresses head-on.

TMJ: the "trendy diagnosis"

In 2024, equine specialist James Carmalt published a paper in the Journal of the American Veterinary Medical Association that pulled no punches. He wrote that equine TMJ disease has become "the trendy diagnosis" in certain disciplines, and that a logical, systematic diagnostic workup is often lacking.

Many of the clinical signs being attributed to TMJ problems, he noted, can be readily explained by other, far more common conditions. This is compounded, he added, by a LACK of extensive scientific evidence actually linking TMJ disease to behavioural or performance changes.

This is a peer-reviewed specialist, in one of the most respected veterinary journals in the world, saying that TMJ is being over-diagnosed, and that when a horse shows a problem, jumping straight to the TMJ as the cause often means skipping the proper diagnostic steps.

What does palpation of the TMJ tell you?

Finding sensitivity on palpation of the TMJ is NOT A DIAGNOSIS.

Proper diagnosis of equine TMJ disease requires advanced imaging. The 2025 systematic review of equine TMJ diseases published in the Equine Veterinary Journal found that CT imaging was used in 92.2% of confirmed TMJ disease cases, and radiography in 84.4%. These are the tools that can actually show what's happening inside the joint. Pulpation on the outside of the jaw cannot.

This matters enormously when someone, whether a therapist, chiropractor, or even a vet palpates your horse's TMJ after a dental visit and suggests the dentist caused a problem.

Sensitivity on palpation is a starting point for investigation, not a conclusion. And it is certainly not evidence of cause.

So what about the speculum? What does the research say?

A peer-reviewed study published in the Journal of Veterinary Dentistry (Pereira et al., 2016) investigated this directly.

Researchers applied a full-mouth speculum to horses for 60 continuous minutes, far longer than any routine dental procedure, and measured the effect on the TMJ using clinical assessment, thermography, and synovial fluid analysis.

They looked specifically at the biological markers that would indicate cartilage breakdown and the early stages of degenerative joint disease.

Their findings were clear. Even at 60 uninterrupted minutes at full aperture, there was NO INCREASE in extracellular matrix degradation products in the synovial fluid, the markers that would indicate actual joint damage.

Key indicators including total protein, chondroitin sulphate, hyaluronic acid, and the pain-mediating compound prostaglandin E2 showed no significant change.

The 2025 Equine Veterinary Journal systematic review confirmed it: these biomarkers remain unchanged with speculum use in routine dental practice. And critically, the review noted that the hypothesis linking routine speculum use to TMJ osteoarthritis was specifically tested and rejected in the experimental literature.

A routine dental procedure, where the speculum is opened conservatively and closed between each phase of treatment, does not cause TMJ damage. The science is clear on this.

What a routine dental procedure looks like

The 60-minute stress test used in the Pereira study was a deliberate extreme. Routine equine dental work looks nothing like that.

A standard dental examination and float typically takes between 20 to 35 minutes in total.

A trained equine dental practitioner opens the speculum only as much as needed, and closes it regularly between rinsing, instrument changes, and rest phases. Most horses have their mouths open for only a few minutes at a time during active treatment.

References: Carmalt, J.L. (2024). Equine poor performance: the logical, progressive, diagnostic approach to determining the role of the temporomandibular joint. Journal of the American Veterinary Medical Association, 262(3). Jasiński et al. (2025). Equine temporomandibular joint diseases: A systematic review. Equine Veterinary Journal. Pereira, T.P. et al. (2016). Effects of the Oral Examination on the Equine Temporomandibular Joint. Journal of Veterinary Dentistry.

Want to learn more about your horse's dental health?

Our Horse Aging Guide is a practical, professionally written booklet covering how your horse's teeth change at every life stage and what to watch for as they age. Available in our online shop for R120.

And if your horse is due for a check-up, or you have questions about a recent procedure, we'd love to hear from you. (marlise@horse-dentist.co.za)