The Stomatognathic System and induced postural distortions

By Stuart Lawrence
BSc( Hons) MSc(Chiro) MSc (Eng) Process Safety PgD Animal Chiropractic MBVCA MIVCA

1.1 Position Statement

1.1.1 Introduction

The stomatognathic system is made up of a number of structures around the face, head and neck, centred around the Temporomandibular joint.

A literature review was carried out on the very limited information available. PubMed and other sites, all of which were in agreement, that due to neurological links, dysfunction of the stomatognathic system can cause postural and other neurological changes throughout the body.

This paper postulates that if the causative factors are not addressed by an appropriately qualified RAMP (Register of Animal Musculoskeletal Practitioners) and British Chiropractic Veterinary Association (BVCA) registered Animal/Veterinary Chiropractor, Stomatognathic dysfunction could lead to long term biomechanical degenerative conditions as described in the literature by Lantz, alongside chronic neurological disorders such as, (similar to those experienced by humans), headaches.

It is also postulated that use of poorly fitting bits, heavy handed bit used by either novice riders or overly zealous dressage riders or race jockeys, or repetitive actions that involve the jaw, such as fly ball in agility dogs, has a negative effect on the stomatognathic system. These hypotheses are made in the absence of any contrary evidence found to date.
It is considered that this subject requires further investigation as a matter of urgency.

2.1 Main Body

According to the Academy of Prosthodontics, the stomatognathic system is made up of a multitude of structures around the jaw region and by way of the muscular attachments to the skeleton, also include areas around the cervical region. The primary components consist of the maxilla and mandible, the dental arches, soft tissues nerves, blood vessels, and the Temporomandibular joint (TMJ) and the muscles associated with chewing, i.e. the masticatory muscles.

The Options for Animals UK: Animal Chiropractic course 2018, anatomy and neurology notes, include the tongue, hyoid bone and the long strap muscles associated with the neck, including the brachiocephalicus and sternocephalicus muscles as part of this system.

The relationship of the head, neck and tempero-mandibular joint (TMJ) and all the associated parts is known as the “cranio-cervico-mandibular system”. There are also significant neurological links between the afferent (sensory) and efferent (motor) innervations of the stomatognathic system and the motor and sensory areas of the cerebral cortex (Nakahara, H. et al. Journal of Dental Research, 83: pp307–11, 2004)

As far back as the 1800’s, it was discovered that stimulation of hemispheres of the brain (i.e. the motor cortex) could affect skeletal muscle groups and removal of said parts of the cortex caused functional disturbances of the same structural muscles. Ferrier (1876)

According to the meshb.nlm.nih.gov, the term stomatognathic system, first came into regular use around the late 1980’s, yet studies pertaining to the stomatognathic system did not take place, as far as can be determined, until the mid to late 90’s and even then, these were few and far between 90’s.

More recently the relationship between the stomatognathic system and postural issues has been made in a position statement to SOTO USA by Dr Charles Blum in 2008.

However, in the veterinary-chiropractic field, a search of PubMed reveals an absence of studies on the subject. In relation to equines and subsequently canines, there would appear to be even less research. There appears to be much human and animal work carried out into investigations of occlusional issues, yet investigation into problems that arise as a result of bit and bridle use, or in the case of dogs, muzzle, halti and lead use, appears to be very limited to the point of being non-existent.
Pet owners need to be made aware that certain methods of “controlling” their animals, by means of poor bit and bridle use, incorrectly measured and fitted muzzles, halti or even repetitive activities such as fly ball, can actually result in a range of physical problems. As such it is surely time to investigate the risks further and educate people of the risks in order to prevent their animals suffering unnecessarily.

According to the Oxford On-Line Dictionary, the definition of ‘posture’ is as follows:

“The position in which someone holds their body when standing or sitting. A particular pose adopted by a bird or other animal, interpreted as a signal of a specific pattern of behaviour.”

According to Loffe M., posture involves muscle activation, all controlled by the central nervous system. Any deviation from the neutral posture is driven by the cerebellum and transmitted by multisensory inputs from the visual, vestibular and somatosensory neurones.

Several studies such as those carried out by Gangloff (2000) and Milani (2000) have demonstrated how the trigeminal nerve is compromised upon dental occlusion, the trigeminal afferents then have an effect on maintenance of posture.
Another slightly more worrying concern is that of trigeminal vascular issues and cortical spreading depression. A paper written by Noseda and Burstein (2013), stated that:

“Evidence of altered brain excitability emerged from clinical and preclinical investigation of sensory auras, ictal and interictal hypersensitivity to visual, auditory, and olfactory stimulation, and reduced activation of descending inhibitory pain pathways. Data supporting the activation and sensitization of the trigeminovascular system include the progressive development of cephalic and whole-body cutaneous allodynia during a migraine attack. In addition, structural and functional alterations include the presence of subcortical white mater lesions, thickening of cortical areas involved in processing sensory information, and cortical neuroplastic changes induced by cortical spreading depression.”

Thankfully cortical spreading depression is relatively rare, but symptoms can include extreme shaking, ataxia and seizures.

Image 1 taken from drjomd.com

The image above, taken from drjomd.com, although human, has very close similarities to the neural pathways seen in a horse or dog. It demonstrates the close relationship between the TMJ and the surrounding neural structures. It is easy to see how, not only will the trigeminal nerve be affected but so will the facial nerve, glossopharyngeal nerve and to an extent the vagus nerve.
In the book Understanding Disease by John Bull, it is of interest that in children, irritation to the glossopharyngeal nerve has been linked to abdominal migraines and/or gastric sensitivities. This could theoretically be a reason for dogs and in particular horses, that suffer with repeated and unexplainable gastric issues, such as chronic colic.

Stress has been shown to markedly increase temporomandibular joint dysfunction in humans (Cestari 2002). In addition, it has been shown that high stress levels lead to clamping of the teeth, which affects local musculature and circulation around the jaw. The muscular tension that results causes a build-up of lactic acid in the muscles thus stimulating pain receptors around the area.
There is also evidence to suggest that both ascending issues from the feet, hip, pelvis, spine and neck can cause TMJ dysfunction “in the presence of occlusal issues” (Bergami 2008, Alkofide, 2007). Just as descending problems associated with TMJ dysfunction can subsequently affect the neck, spine, pelvis, hip and feet due to a change in posture and its subsequent effects on the body.
Esposito et al, 1993 writes that:

“Neurologically intact male and female TMJ dysfunction [human] patients with or without cervical spine involvement were examined using standard clinical neurologic testing for balance and coordination. Seventy percent of the TMJ patients without cervical involvement exhibited positive signs for balance, coordination, and/or ataxia found in response to having the patient’s mandible stressed by extending it as far as possible laterally, and also opened (as wide as possible) or closed (biting down). The performance of patients with cervical involvement was not significantly different than those without cervical involvement. Further examination of the relation between the TMJ and auditory, visual, cerebellar, and coordination mechanisms is therefore indicated.”

Other studies such as those carried out by Lippolda et al. (2006) demonstrate that changes to the thoracic, lumbar and pelvic angles can result from dental occlusions. D’Attilio et al (2005), showed how an induced dental occlusion in rats could give rise to cervico thoracic scoliotic changes after just one week; after removal of the occlusion only 83% of the tests rats returned to normal spinal stability. It is apparent that anything that effects the occlusion of the teeth will have an effect in changing the posture/spinal stability of an animal.

If we then look at the study by Zohreh et al (2009), it is apparent that dental occlusions can cause an anterior head carriage, this leads to an increase lordosis in the cervical spine so causing an anteriority of the posture.

Simmons et al (1999) have demonstrated that as the head becomes anteriorly displaced, there is an increased tension and shortening of the cervical extensor muscles, as well as shortening of the sternocleido mastoid muscle. In the horse these would be the long strap muscles such as the brachiocephalicus and sternocaphalicus muscles.

As the head is further displaced in an anterior direction, the cervical lordosis increases and increased tension is placed on the upper cervical spine, creating headaches (Fernandes-de-las-Penas et al. 2006).

This chain reaction travels further down the spine affecting the rest of the body and causing problems elsewhere within the spine, hips, pelvis and limbs as explained by Dr Charles Blum in his position statement to SOTO-USA 2008.

Lantz (1988), has even demonstrated that in humans changes in posture will lead to degenerative, or potentially osteoarthritic, changes in the areas of kinesiopathology.

2.2 Discussion

It is proposed that the change in jaw position and subsequent increased pressure around the soft tissues of maxilla facial region, due to improper or incorrect bit placement is causing a significant percentage of these problems identified in humans to occur in equines.

Information gathered during the RAMP registered “Options for Animal Chiropractic Course” makes a point of discussing some of the most recent research on bit and posture and its effects on the Stomatognathic system. Yet, it is of concern that many pet owners call out a non-registered or worse yet, poorly trained animal musculoskeletal practitioner who are likely to be unaware of the finer details of this issue.

If we assume that a bit gives the equivalent of an occlusal issue by the simple nature of it being in a horse’s mouth, especially with one that is either poorly fitted or designed as a more aggressive bit, we have to accept that regular and repeated use could potentially cause postural changes that when not regularly addressed, will lead to structural (physical) problems. We then have to consider that the more a bit is used (heavily by novice riders or during races, or when used to create excessive flexion by some dressage riders) the more postural distortion will occur and the worse the posture related symptoms will be.

Although Lantz’s findings in humans related to total immobilisation, to some degree they can occur with any level of kinesiopathology or hypomobility. His findings demonstrate that within 3 days of reduced movement, degenerative changes are apparent in the areas of contact opposition: within two weeks the opposing cartilaginous surfaces are starting to flatten; within 45 days adhesions form between the cartilaginous surfaces and cystic lesions form around the cartilage and menisci; within 90 days ulcerations have penetrated the subchondral bone and extra-articular adhesions are starting to form.

This would appear to suggest that after:
a) the heavy or prolonged use of a poorly fitting bit;
b) the use of a well-fitting bit in heavy hands;
c) or in the case of a dog, constant yanking around the jaw or neck by its collar or halti,
d) or, a repetitive action such as fly ball.

not only could these animals be suffering from headaches, but also dysfunctional joint movements throughout the spine and extremities could be being induced, which would subsequently promote ongoing or future degenerative changes.

Long term symptoms that could occur in a horse for example could be:
a) Reduced performance;
b) Abnormal posture;
c) Snapping and pinning back its ears when being saddled;
d) Insubordination when being ridden;
e) The attempt free itself by throwing its head back or up or by hollowing the back;
f) Swishing its tail and pinning back its ears;
g) Disobedience when jumping;
h) Difficulties with collected or lateral gaits;
i) Sensitivity to touch.

Or in dogs:
j) Reluctance to move;
k) Abnormal posture;
l) Disability to climb stairs or jump onto raised areas;
m) Signs of pain when performing certain movements or being lifted;
n) Disobedience when jumping;
o) Altered sitting position (so-called “puppy sitting”) or lying on one side only.

According to the International Veterinary Chiropractic Association, a pet owner should notice positive outcomes with 2 to 4 chiropractic sessions before ongoing, long-term maintenance care is required.

2.3 Conclusion and Further Work

It is obvious from the research papers investigated, that the stomatognathic system is only a relatively recently researched area and research in humans is somewhat limited, in animals however there are even fewer animal studies.

It is also clear from the lack of research that information pertaining to tacking up the horse and how this effects the horse’s posture and subsequent function is non-existent, in particular with regards to bit use in the case of horses, or repetitive jaw action in dogs, the use of collars, haltis and muzzles. These are all areas that it is considered warrant further investigation as a matter of urgency. The longer this matter is left un investigated, so the longer domestic animals will suffer.

I do however feel a short term, acutely dysfunctional stomatognathic system in a large animal such as a horse or dog, is unlikely to immediately cause the above problems as described in the discussion above, but long-term dysfunction through owner ignorance or not “reading” the behavioural cues and then subsequently not having them addressed by a RAMP registered and BVCA registered Veterinary Chiropractor, could well cause many of the long term degenerative conditions discussed throughout this paper.

However, I have to add a proviso here in that everything is linked. So just as a poorly shod horse, or a dog that trips when out on a run, could also suffer such problems, which need addressing by an appropriately qualified professional, there is an argument that from a neurological perspective, that what goes up, must come down.
Research results from the International Veterinary Chiropractic Association, suggests that both horses and dogs respond well to care and within 2 to 4 sessions a positive response should be seen. Ongoing care is dependent on the age, use or breed susceptibility to particular problems. Equally this should always take into account the research by Lantz. As such outcomes resulting from Animal Chiropractic care, both short and long term, would be an interesting mid to long term research project and warrants further investigation.