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The TMJ is
the “Master Link”
I have been practicing Equine Sports Medicine for 17 years and in
the last decade I have seen the horse market flooded with
supplements, blankets, lasers and various devices for physical
therapy. I am shocked at the influx of equine medications
manufactured for gastric ulcers, neurologic diseases and
inflammatory conditions. Why are our horses so out of balance and so
in need of all these medications? Is it environmental pressure, the
increased amount of travel to shows and events throughout the US and
Internationally? All of these things can add to the picture but I
believe many horsemen and women (the veterinary community included)
are unaware of the importance of the TMJ to a horse’s balance,
digestion, biomechanics and overall well being. I consider this the
“Master Link.” Restore this master link to optimal wellness and many
of the other psychological and physical issues, internal organ
imbalances and body compensations simply disappear.
The Temporomandibular Joint (TMJ) is critical for a horse’s survival
and well being. It has two primary functions, mastication or the
grinding of food and balance, i.e. its relationship with the ground
or posture. With a balanced jaw a horse’s body can achieve a state
of self perpetuating wellness, everything from digestion to cell
regeneration and rapid healing occurs easily, naturally.
ANATOMY: The TMJ connects the temporal bone which expands across the
horse’s forehead to the mandible, which is the lower portion of the
skull. It actually consists of two parts, an upper sliding joint and
the lower hinge joint. An articular disc separates the two
compartments and the entire joint is encapsulated and contains
synovial fluid. It is a very tight joint, reinforced by tendons,
ligaments and supported by an intricate array of muscles.
Many horses suffer from temporomandibular joint pain(TMJ) which is
articular and perhaps even more insidious is a condition called
temporomandibular dysfunction.(TMD) This involves more soft tissue
pain; myofascial and ligamentous. These horses’ adapt as the
inflammatory process slowly progresses, what starts as a bit of
discomfort becomes a raging headache. Once you have knowledge of
what to look for, you will be able to recognize it, the evaluation
is more subtle than just looking to see if they need their teeth
floated.
Evaluating for TMJ Pain or TMD:
1. Observation: Watch your horse chewing. Look for symmetry or
balance side to side. Does he swing his jaw to both sides? Does he
hold his head with a tilt while he eats? Is he dropping food? Does
he leave the stems of hay? Observe his head when he is not eating
and look straight at him face to face. Are the ears, eyes and
nostrils even or asymmetric? How about the bony prominence of the
jaw joint or the facial crest that runs down the side of the head?
Is one more prominent than the other? This is a good time to
evaluate the forehead or temporalis muscle and the cheek or masseter
muscle for symmetry also. The pterygoid muscle is equally important
but less noticeable on visual inspection.
2. Incisor Evaluation: The incisor pattern, length and angle
directly affect the biomechanics of the TMJ. Look straight at your
horse’s incisors; they should be aligned top to bottom. There is
pathology in the mouth and TMJ if they are off center or there is a
wedge sending them one direction and not the other.(figure 1) Now
look from the side is there an overbite or an overjet which is
really an incomplete overbite? (figure 2) If so chances are your
horse cannot put his head down and drop his mandible into a
comfortable or neutral position because anterior motion of his jaw
is impeded. Check for anterior and posterior motion visually or by
gently placing your finger at the incisor occlusal line(where the
front teeth meet). When the head is raised normal posterior motion
should pull the lower incisors slightly back. When you lower the
horses head the lower incisors should move forward if they have
healthy anterior motion of the jaw. The lack of anterior/posterior
motion indicates the biomechanics of the jaw can be improved.
 Figure
1
 Figure
2
3. Listen: There is a harmonic resonance in a healthy jaw that one
can hear. Listen to your horse grazing or eating hay with his head
down. All horses should be fed at ground level. With their head down
the atlanto-axial joint opens (C1-C2), the mandible comes down and
forward, the upper and lower cheek teeth meet at the optimal
occlusion and the muscles and soft tissues in the head and neck go
into the perfect balance of tension and relaxation for proper
chewing and neurological input. Wild horses graze for 15-20 hours a
day. All of the wild horse skulls I’ve found have nearly perfect
incisor and molar patterns. When you listen to your horse chewing
there should be a clear, clean sound if everything is healthy. It is
a resonance, which is also a frequency or vibration that is like a
lullaby to the nervous system. Squeaks, or pops or clicking sounds
could indicate TMJ or dental pathology.
4. Gentle palpation of the TMJ joint space can indicate asymmetry or
pain. One side may feel shallow and open while the other side might
feel tight and pinched. Palpation and observation of the muscle on
the forehead, the cheek muscle and the pterygoid muscle which is
difficult to observe but can be palpated on the medial aspect of the
mandible.
5. Palpation of acupoints- TH17, ST7, Bao-Sai, the facial crest
trigger points and the medial pterygoid muscle attachment- (see
figure 3) for those familiar with acupuncture or acupressure.
 Figure
3
After doing the above evaluation if you suspect your horse has some
TMJ dysfunction, please have a vet or a qualified equine dentist
perform an exam with a full mouth speculum. Many problems in the
rear molars cannot be assessed without one. Just be sure the
examiner does not keep the speculum on longer than necessary and
opens it only as wide as necessary.
I am an advocate and teacher of TMJ Awareness Dentistry. This is a
holistic approach to dentistry. I feel equine dentistry has advanced
too far toward the comfort of the dentist and less toward the
comfort and safety of the horse. The overuse of power dental
instruments is the primary reason I see and treat so many TMD
horses. Although a true artist can do the work correctly with power
instruments, it is so easy to over float with them. I have found
that a more accurate balance can be achieved with hand instruments.
If I find extreme pathology I will use my power instruments
judiciously, but I always finish with hand instruments.
My colleagues and I use hand instruments that are ergonomically
correct, specifically designed for a horse’s mouth. We use minimal
sedation, and are willing to add more if necessary. However, our
goal is to have the horse as aware as possible to the subtle changes
that are occurring to his nervous system as we make adjustments to
the teeth. This kind of TMJ Awareness Dentistry is really adjusting
the “gyroscope” and is often my first step in treating neurologic
diseases.
We have found that many power floaters take off too much clinical
crown, as well as they often obliterate the horse’s natural molar
table angles. Larger amounts of sedation are required to allow these
instruments into the oral cavity, then the head is hoisted or tied
up into a very unnatural position. Power floating can be so
excessive that it decreases the surface contact between molars that
a horse would naturally have. This leads to severe myofascial pain
syndrome (TMD) because the horse wants to get contact between his
molars so he clinches his jaw and constantly compresses his muscles
tendons and ligaments to try to get that contact. Sometimes it takes
years for that clinical crown to come back. Molar table angles and
surface contact is crucial to the guidance that relates to the
biomechanics of chewing as well as posture, balance, and
equilibrium.
The bottom line is, I believe power tools have allowed dentists to
become overly aggressive in equine dentistry and with one quick head
shake the proper table angles can be altered. Many dentists are more
concerned with eliminating sharp edges than restoring the proper
biomechanics to the jaw joint. Often practitioners float the molars
and either leave the incisors untouched or follow up with adjusting
the incisors to fit the work that was done on the molars. TMJ
awareness dentists start with a thorough examination of the head,
hyoid, poll and whole body for asymmetries and symptoms of TMD. We
address the incisors first. The length, angle, and balance of the
incisor tables are directly related to the TMJ. Sometimes incisor
pathology can only be reduced in increments while the horse adjusts
to the new TMJ alignment. Some pathology should not be corrected,
especially in aged horses that have been compensating for years and
have adapted, in these cases one does minimal work mostly to allow
more comfort and maximum surface to surface contact between the
teeth.
Once optimum incisor alignment has been achieved we then put the
speculum on and move to the molar tables. Remember we want the
horse’s participation and integration during the process and we
don’t hoist their head up with a hydraulic head lift or tie them to
an overhead beam. It is easy to create inappropriate changes to the
molar table angles with the head held high and the
neck hyper extended. We are willing to kneel on knee pads so that we
do the work with the horses head in a natural position, i.e. the
place were the horse spends most its time eating or being ridden.
(Figure 4) We leave as much clinical crown and table surface as
possible on the molars and pay close attention to table angles. This
is critically important in the rear most molars as they are closest
to the TMJ, brain, and central nervous system. Their occlusal
surface and angle is critical to proper guidance, body biomechanics
and balance. We always complete our dentistry with some stretching,
myofascial and trigger point release work, essential oils,
homeopathy and sometimes chiropractic and acupuncture.
 Figure
4
Even with the best of dental care, it takes a total holistic
approach to completely treat TMD issues. Dental work alone is a very
important starting point, but it will not completely resolve many
TMJ/TMD issues. This problem is often slow and insidious in its
occurrence; it does not happen over night. We often pull in the help
of cranio-sacral therapists, body workers who do extensive soft
tissue work, farriers to properly balance the feet, we use cyma
therapy, micro- current, laser, chiropractic, acupuncture,
homeopathy, bit changes, saddle changes, oral or injectable chondro
protective agents and sometimes anti inflammatory to get the horse
back to total balance and wellness.
I urge you to take a close look at your horses TMJ functioning. It
can be easily overlooked. As I said earlier in this article I
consider it the “Master Link” in the chain of healthy equine
biomechanics and movement. I see far too many hocks and backs get
injected that actually have TMD; although there will often be some
temporary improvement especially if corticosteroids are used, after
a while the imbalance shows up somewhere else, often the feet or
neck. Unkink the master link and be sure the feet are balanced and
you will see the life force flow through your horse’s entire body.
You may still have body work to do and old postural compensations to
correct, but it is much more possible for the horse to achieve a
state of self perpetrating wellness, vitality, and strength with a
healthy happy TMJ. This is homeostasis, every cell in the body has a
built in intelligence to allow well being, it is natural and it is
where they want and need to be.
MORE DETAIL ON TMJ Function & its RELATION TO THE WHOLE HORSE
A) Mastication and Digestion: Chewing the food properly is the very
first step in healthy digestion. A horse must be able to move his
jaw from side to side (lateral excursion), forward and back
(anterior/posterior movement) and up and down to reinforce the grind
in order to chew food properly. When dysfunction occurs a horse will
make many adaptations in order to survive, but these changes trickle
back into the entire body. We have all heard the old adage “no hoof
no horse,” the same goes for the teeth. Without the ability to chew
and digest food, chances for survival are slim.
B) Neurology and Balance: The jaw joint is highly innervated and
surrounded by structures that dictate the horse’s balance and
equilibrium. It is anatomically the closest joint in a horse’s body
to the brain and brainstem. Its proprioceptors tell the horse where
he is in space, or what his posture is, where
his right leg is placed in that sliding stop, over that jump or on
that rocky uneven trail. The neurology is intricate and beyond the
scope of this article, but be aware that the hyoid and cranial
nerves are intricately connected with the jaw. The hyoid apparatus
in the throatlatch is a group of 10 bones that give biomechanical
form and function to the larynx, pharynx and the tongue. Changes in
dental occlusion lead to stimulation of the periodontal ligaments or
lack of in the case of over floating. These ligaments sense tooth
strike and stimulate afferent nerve input through the trigeminal
nerve(one of the 5 cranial nerves involved with the TMJ). All of
this is an intricate web of information weaving the biomechanics and
neurology of the jaw together.
C) More Neurology: The TMJ is part of the stomatognathic system, a
neurological system that governs balance and equilibrium. All
components of the system are from the shoulder forward. “Where the
head goes the body goes.” This includes the eyes, hyoid apparatus,
proprioceptors and dural connections from the cervical spine which
connect all the way to the sacrum and pelvis. Changes in the muscle
tone in the head and neck increase dural tension all the way to the
sacrum. This is why we often see a reciprocal pattern in the pelvis
and sacrum to changes in the TMJ and pathology in the incisors.
D) Acupuncture Channels Convergence Point: There is another system
of vitality and connection in the body known as the acupuncture
meridians or channels. Vital life force or Chi flows along these
channels and maintain health when it is harmonious. If it is blocked
or altered in any way it can create dis-ease or dysfunction in the
body. Six different acupuncture channels converge on or very close
to the TMJ. Three travel to the front legs LI, SI, and TH, and three
to the hind legs GB, ST, and BL. This is another way to explain how
the hind legs pelvis and sacrum can be adversely affected by TMJ or
TMD.
Dr. Heather K. Mack
Mobile: 760-447-0776
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