13 minute read
TMJ - the master link
TMJ – the master link A properly functioning temporo-mandibular joint is crucial to a horse’s well being and performance.
orses rely heavily on the proper function of the temporo-mandibular joint (TMJ). The ability to move the jaw correctly – side to side, forward and back, up and down – affects not only their ability to masticate, which is the very first step in proper digestion, but also body balance and biomechanics.
Yet proper TMJ function often gets overlooked by veterinarians. I practice and teach a dental paradigm based on the principle that the TMJ is the “master link” in equine biomechanics. In balanced equine dentistry, we work toward maintaining equilibrium or a balanced state of repose between two or more antagonistic forces that exactly counteract each other. In doing so, we adjust the angles and planes of the cheek teeth and incisors. This maximizes the surfaceto-surface contact between these biophysical planes and achieves optimal jaw biomechanics. Ultimately,
by Heather
K. Mack , VMD
we are looking to achieve three-point harmony between the incisors, molar tables and TMJ.
Anatomy The TMJ is a complex array of bones, muscles, ligaments, fascia, nerves and cartilage. It is a synovial joint between the condyles of the mandible and the temporal bone. It is a very strong, tight encapsulated joint with an articular disc that allows for the gliding movement of the condyle. The horse’s TMJ is considerably more complex than a human’s because of three factors:
1. It is connected to the ears and horses have movable ears with 20 or more muscles. 2. The hyoid bone articulates with the temporal bone. 3. Horses have teeth erupting continuously throughout their lives.
Bones
1The temporal bone is the most cranial bone in the TMJ mechanism. It is part of the maxilla. It is also home to the auditory or Eustachian tube. This is where balance and equilibrium are recorded through the vestibulocochlear nerve. Tightness in the muscles or temporo-mandibular joint disorder (TMD) can adversely affect the horse’s balance and proprioception. Also, the trigeminal nerve rests on the inside of the temporal bone. One of the three branches of the trigeminal nerve is the motor nerve to the muscles of mastication.
2The mandible at birth consists of left and right halves that have a cartilaginous joining at the center, much like the pubic bone of the pelvis. These two halves fuse together and become a complete jawbone when the horse is two to three months old. The mandible is considered one of the most important “pattern setters” in the body. A pattern setter is a body part or condition that sets up patterns of habitual compensatory movement in other parts of the body. The “right handedness” of a horse, for instance (see sidebar), can often be dissected back to TMJ dysfunction. I believe this is also why limited range of motion in the TMJ can cause limited or asymmetric pelvic movement.
3The hyoid apparatus is group of seven bones that cradles the larynx and pharynx, connects to the tongue and articulates with the temporal bone. Excessive tongue pulling, cribbing, throat surgery, and even chronic cough can create restriction in the hyoid apparatus, which can adversely affect the TMJ.
Muscles Though several muscles are responsible for jaw movement, I will review the three that are most influential and palpable.
• The masseter muscle is the largest. It can be easily observed while a horse is chewing. It brings the upper and lower jaws together. • The temporalis muscle is the next major muscle and also easily observable. It works in conjunction with the masseter muscle. Its primary function is to close the mandible. • The pterygoid muscles attach from the central bone of the cranium, or sphenoid bone, and insert onto the medial aspect of the mandible. The function of the pterygoid muscles is to pull the mandible from side to side. Horses with TMD often exhibit great discomfort when palpating the medial pterygiod muscle trigger point.
The horse by nature is a grazing animal, and will graze up to 16 hours a day if allowed. When the head is dropped down in the grazing position, the mandible comes down and forward in the joint capsule and the atlantoaxial joint opens. This relaxes the muscles and connective tissue around the TMJ, and the upper and lower molars achieve proper contact. Many performance horses are kept in stalls and fed from hay bags or elevated feeders. This does not promote healthy TMJs.
Symptoms of TMD These are many and varied and include low performance levels, imbalanced gaits or lameness, uneven tooth wear, head shaking, cribbing, teeth grinding, signs of headache, behaviors such as spookiness, ADD, ear sensitivity, head shyness and bitting difficulty, being a poor keeper, muscle wasting (especially on the top line), difficulty flexing the poll and engaging the hindquarters, and an unwillingness to change leads.
The right-handed horse
• Incisor wedge sending maxilla to right, mandible to left. • Atlas superior on left. • Horse camps on left front leg, has larger left foot, often more prominent shoulder muscles, often hollow behind left shoulder. • Pelvis is most often in reciprocal relation with the jaw, creating a right posterior ilium. In other words, the pelvis is rotated forward and upward on the right. • A full 75% of horses I see have a reciprocal pelvis to the incisor wedge; 25% mirror the wedge. Dr.
Judith Shoemaker taught me almost two decades ago that horses have different levels of proproiceptive awareness. Some try hard to correct their imbalances, while others just adapt to leaning. • Ribcage expanded on left, contracted on right. Already bending to right and very difficult to bend left. • Tail often held to left.
How it affects riding Most riders use reins to communicate with their horses. They expect the horse to interpret their signals. If there is pain or imbalance in the TMJ, the signals are polluted. Any deviation from normal will alter the rider’s communication. If she asks the horse to move to the left by picking up the rein and adjusting her body, and it causes him pain, it is actually telling him not to go forward. The horse starts to break down millisecond by millisecond. First he will perceive a physical inability which soon turns into an emotional situation. He will not feel good because he cannot do what the rider is asking.
The balance of the teeth determines the readiness of flexion which must be obtained and maintained to facilitate correct maneuvers. If a horse’s jaw is restricted in anterior-posterior (A/P) motion, he cannot drop his jaw into neutral, raise his withers to allow the head to go forward and down, lift the lower cervicals and engage his hindquarters. Pain in the jaw will likely kill the desire for specific movements and sometimes for any movement at all.
The most common causes of restricted A/P motion are: • Incisor abnormalities, especially overjet or overbite • ATRs (accentuated transverse ridges) • Hooks on lower 11s or upper 6s • Missing molars • Wave complexes
By paying closer attention to the balance and function of the TMJ in your equine patients, you can help preserve their overall health and performance levels.
Dr. Heather Mack graduated from the U i ersity of Pe syl a ia School of Veteri ary Medici e i 1991. I the early 1990s, she recei ed certificatio from both the I ter atio al Veteri ary Acupu cture Society (IVAS ) a d the America Veteri ary Chiropractic Associatio (AVCA ). She bega her studies of Traditio al Chi ese Medici e a d acupu cture i 1985 while atte di g Columbia College. She ru s a Equi e Sports Medici e practice a d has bee breedi g, raisi g, trai i g, obser i g herd dy amics a d heali g horses at her Mystic Ca yo Ra ch i Idaho for o er 14 years. b l nc quin lln ss.co
References
Gronberg, Pauli. (2002) ABC Of The Horse, A Handbook of Equine Anatomy, Biomechanics, and Conditioning. www.pg-team.fi.
May, Kevin J., DVM. (2008) Interrelationships Between Equine Acupuncture, Chiropractic And Dentistry. Procc. of 34th IVAS 2008 international congress, Keystone, CO, USA.
Rooney, James R. Clinical Neurology of the Horse. KNA Press Inc. 1971 June, First Edition.
Upledger, John E., DO, FAAP. Craniosacral Therapy II, Beyond The Dura. Eastland Press Inc. 1987
57th Annual AA EP Convention
November 18-22, 2011 San Antonio, TX Shift into the future of equine health care. Stay in-step with the best practices in your profession. Commit to growing alongside your colleagues during the AAEP’s 57th Annual Convention in San Antonio, Texas.
This year’s educational program presents opportunities to learn:
• New versatile skills for ambulatory scenarios, including needle-free injections and field anesthesia • How to apply breakthrough epidemiological research to your daily practice • Implications for the use of stem cell therapies and other biologic drugs to treat orthopedic problems • How to utilize imaging like the experts to improve diagnostic accuracy • How to utilize the latest reproductive techniques to optimize outcomes • Applying service excellence to your veterinary practice and its impact on your client’s satisfaction and your business success.
For more information: (859) 233-0147 aaepoffice@aaep.org www.aaep.org/convention.htm
Comprehensive Clinical Cardiology
December 3-4, 2011 Toronto, Ontario, Canada Join Sonya Gordon, DVM, DVSc, DACVIM (Cardiology) and Michael O’Grady, DVM, MS, DACVIM (Cardiology) for a two-day (12 hours of CE credit) in-depth training in canine and feline cardiology.
The program will utilize an interactive approach to provide an up-to-date, practical and clinically relevant review of heart disease in the dog and cat. The goal is to enhance clinical knowledge while augmenting participant abilities to identify the subtleties of diagnosis, prognosis and management strategy in clinical cardiology cases. Emphasis will be to facilitate the incorporation of these tools into clinical practice using a practical case-based approach.
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Timely Topics in Internal Medicine
December 4, 2011 Course Director: Linda Ross, DVM, DACVIM The 13th annual Timely Topics in Internal Medicine conference is scheduled for December 4, 2011 in the Agnes Varis Campus Center (Building O on the campus map) at Tufts University. Linda Ross, DVM, DACVIM and associate professor in the Department of Clinical Sciences at the Cummings School of Veterinary Medicine, will be the course director. This conference is 6 hours of Continuing Education credit.
The registration fee is $199. Registration includes lectures, laboratory and course notes on a CD (printed notes are available for an additional charge of $10.) Both online registration form and a PDF registration form are available.
For more information: (508) 839-5302 http://vet.tufts.edu/
Practical Veterinary Seminars
December 4, 2011 The Best Western Plaza Hotel – Honolulu, HA Surgery of the Anus, Ear and Stomach will be covered. These presentations will include conditions encountered; with the anal area of dogs. Perianal fistulas & anal sac disease; with the ear and surgical corrections including TICA and with the Stomach including GDV surgery. All will be covered in a practical descriptive manner, A “must hear” for all SA practitioners. Also new products will be discussed.
For more information: Dr. M. Joseph Bojrab (702) 219-2507 drbojrab@aol.com www.drbojrab.com
Can I Really Communicate with my Animal?
Wednesday, December 14, 7-8 p.m. ET & Thursday, January 5, 7-8 p.m. ET International Tele-seminar with Sue Becker Join Sue Becker for this one-hour FREE telephone seminar and discover what animal communication is all about. Is it really possible for you? What is involved? What can you learn from them? Can anyone connect telepathically with their animal buddy, or is it a special gift? What about wild, non-domesticated species? Get answers to these and many other questions in this fascinating class. Bring your own questions as well!
Sue Becker, BFRAP, BFRP, CTTP is an internationally known animal communicator and consultant, instructor and writer. She has worked with thousands of animals of many different species and holds recognized practitionerships in Bach Flower Remedies both for animals and humans, Tellington TTouch Method, Reconnective Healing, and has extensive training in many other physical and energy modalities.
For more information: 519-896-2600 suebecker@cyg.net www.suebecker.net
2012 AVMA Veterinary Leadership Conference
January 6-8, 2012 InterContinental Hotel – Chicago, IL
The VLC offers a robust three days of networking and workshop opportunities designed with you in mind. Tracks for current and emerging leaders, as well as state and allied representatives, are offered. This conference is also open to all veterinary professionals interested in learning more about leadership, team building and how the AVMA works with you and for you. New this year, receive continuing education credit for attending select sessions.
Registration Fee: $295/person Deadline: December 16, 2011
For more information: (800) 248-2862 www.avma.org/about_avma/governance/vlc/ default.asp
NAV C Conference 2012
January 14-18 2012 Orlando, Florida The NAVC Conference 2012 offers more than 1,300 hours of enriching CE opportunities, so whether you are a veterinarian, veterinary technician, practice manager or other staff, you will return home with new and practical knowledge designed just for YOU.
For more information: (800) 817.9928 www.navc.com/navc-conference
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See you at: NAVC Conference, Orlando, FL January 14-18See you at: NAVC Conference, Orlando, FL January 14-18
