Dysfunctional Disturbance of the TMJ and Masticatory
Muscles (Etiology, Pathology, and Diagnosis)
The masticatory system consist of the skeletal component,
the muscle of mastication, the neural component, and the
teeth. The skeletal component consists of the jaw and the
temporomandibular joint (TMJ). The physiology of the masticatory
muscles and the neuromuscular activities associated with
mastication consists of cyclical movements produced by the
elevation and depression of the mandible as food is sheared
and formed into a bolus in preparation for swallowing. Controlled
movement of the mandible is used in biting, chewing, and
swallowing of food and fluids, and in the production of
speech sounds. Concurrent with the jaw movements are integrated
movements of the tongue and other muscles controlling the
perioral areas, pharynx and larynx. The TMJ acts as the
fulcrum of which the movement of mandible rotated and translate
in the horizontal, vertical, and sagittal plane. Together
with the masticatory muscle, the TMJ coordinated the skeletal
component of the masticatory system. Any functional disturbance
occurs to the TMJ will have an effect on the muscle of mastication
and vice versa, any disturbance occur to the muscle of mastication
will have an effect on the TMJ. Thus, functional disturbances
of TMJ and masticatory muscle must be located and diagnosed
as early as possible. The etiology and pathology must be
identified prior to select an appropriate therapy in treating
Numerous studies have been attempted to record the muscle
activity during masticatory cycle using electromyographic
recorder. Researcher have also identified the pattern of
chewing cycle, i.e., the envelope movement of mandible during
mastication. In this cycle, closing muscles are usually
inactive during jaw opening, whereas the jaw-opening muscles
are very active. Activity in jaw-closing muscles begins
to be apparent at the beginning of the jaw closing. Activity
of the jaw-closing muscles increases slowly as the teeth
begin to interdigitate or as soon as food is encountered
between the teeth. The closing muscles on the side where
food is being crushed (so-called working side) are more
active than the contralateral jaw-closing muscles. Any kind
of disturbance in masticatory muscle will result in splinting,
translated into clicking and poping of TMJ, and ultimately,
pain will occur.
The temporomandibular joints, as described by Harry Sicher,
is a bilateral articulation, right and left joints, though
anatomically separted, forming functionally one articulation.
There is only one position of the mandible in the dead that
imitates the position of the mandible in the living, that
is, the position of full occlusion. This centric occlusion
is established by intercuspation of the maxillary and mandibular
teeth. When the teeth in is CO, there is no bony contact
exists at the mandibular articulation of the skull. There
is always a space between mandibular condyles and the cranial
base at the articular tubercles. Normal physiologic CR position
of the jaws may be defined as the stable, comfortable, functional
craniomandibular relationship in which the condyles are
in their most superior position in intimate contact with
the thinnest central bearing area of their respective discs
against the distal surface of the articular eminences at
any vertical rotational postion of the mandible. CR is a
comfortable physiologic work position during mastication
and swallowing, provided there are no deflective interferences
from the teeth. It is not a rest postion; therefore when
the mandible is in CR, considerable electromyographic activity
may be observed. When CO = CR, CR is used during mastication
and swallowing about 5000 times a day. This position has
been found clinically to be the best location for the maximum
intercuspation of teeth. Clinically, CR may be defined as
the completely retruded position of the mandible with the
condyles in their most superior anterior postion at any
vertical rotational position of the mandible. As the jaw
open, the condyle brace themselves against the postglenoid
process as the mandible travels upward and backward. Studies
have shown that physiological bone remodelling observed
in the condyle has no orientation that could be related
to the changed occlusion. However, occlusal forces brought
about rebuilding of the bone in the neck of the condyle.
Longitudinal studies have shown that changes associated
with orthodontic treatment of class II malocclusion are
related mainly to altered growth patterns of the alveolar
processes rather than to joint changes. It appears that
the changes in temporomandibular joint morphology may be
the result of pathological rather than physiological processes.
Furthermore, there has been striking evidence of periodontal
trauma from occlusion and subsequent movement of teeth in
all studies of occlusal disharmony and TMJ morphology. The
clinical significance of these research findings to the
practice of dentistry should be the adaptation of the occlusion
to be in harmony with the TMJ rather than hoping for the
TMJ to adapt to the occlusion.
In discussing the disturbance involves the TMJ and the muscle
of mastication, we must examine the bruxism, the myofacial
pain syndrome (MPD), and the temporomandibular joint disorder
Bruxism is the most common disturbance of masticatory muscle.
As Karolyi have stated, " all person may at one time
or another grind their teeth". Etiology and nature
of bruxism have been explored in numerous studies. Researcher
have found that the major common denominator of all bruxing
patient is stress. Thus stress is the only proven factor
as to tip the neuromuscular balance and resulting in pathological
phenomena. Every body has some type of occlusal interference
and learn to compensate them with various tolerance level.
However, as the stress increase, this tolerance level may
be altered by psychic stress affecting the tonus activity
in the jaw muscles. It has also been shown that bruxism
can be reduced by biofeedback or by relief of stress, thus
demonstrating the strong central nervous system input in
this condition. The significance of bruxism in the cause
of periodontal disease depends on whether bruxism results
in trauma from occlusion. Since trauma from occlusion does
not cause periodontal disease but exacerbate this condition,
bruxism plays the similar role. Progressing of advanced
periodontal breakdown due to bruxism thus may necessitate
splinting of the teeth. Bruxism ultimately may lead to occurence
of dysfunctional muscle and temporomandibular joint pain.
Discomfort from the muscle, the teeth, the joints in association
with bruxism often increased the spychic tension and irritability,
and further increases muscle tonus and bruxism.
Myofacial pain-dysfunction syndrome is a psychophysiologic
disease that primarily involves the muscles of mastication.
The condition is characterized by dull, aching, radiating
pain that may become acute during use of the jaw, and mandibular
dysfunction that generally involves a limitation of opening.
Generally the condition involves only one side of the face
and, upon examination, tenderness can usually be elicited
in one or more of the muscles of mastication or their tendinous
attachments. Although MPD syndrome starts as a functional
disorder, it can ultimately lead to organic changes in the
temporomandibular joint (TMJ) and the masticatory muscles,
and even cause possible alterations in the dentition. MPD
syndrome is believed to be a stress-related disorder. It
is hypothesized that centrally induced increases in muscle
tension, frequently combined with the presence of parafunctional
habits such as clenching or grinding of the teeth, result
in muscle fatigue and spasm that produce the pain and dysfunction.
Similar symptoms, however, occasionally can also result
from muscular overextension, muscle overcontraction, or
trauma. Two major groups of conditions must be considered
in the differential diagnosis of MPD syndrome: the nonarticular
problems that can mimic MPD syndrome, and the various pathologic
disorders of the TMJ that may sometimes also produce similar
signs and symptoms. Nonarticular problems include conditions
that produce pain resembling that of MPD syndrome and those
that produce mainly limitation of jaw opening. Management
of MPD syndrome is founded on certain basic principles that
include the establishment of an accurate diagnosis, gradual
escalation of therapy, and avoidance of irreversible forms
of treatment. Several different treatments have been recommended
for MPD syndrome, ranging from structural alterations to
psychotherapy. These treatment modality will be discussed
in later seminars.
Patient with MPD must realize that this is a psychophysiologic
disease of which the psychologic stress can cause physical
disorders. Patient therefore must identify his or her stress
in life and converted these stress or adapt to it with a
healthier attitude. they must understand how stress can
result in centrally generated increases in muscle activity
and parafunctional habits such as clenching and grinding
of the teeth, and how this leads to muscle fatigue, spasm,
pain, and dysfunction. It may not be possible to provide
a permanent cure for the problem. The patient can learn
to manage it in a satisfactory manner by controlling stress
and by using the recommended forms of simple therapy at
the first sign of recurrent symptoms.
Temporomandibular disorders (TMD) should be viewed as a
group of related disorders in the masticatory system and
not as a single syndrome. The most common symptoms associated
with TMD are limited mandibular movement, joint sounds,
pain in the temporomandibular joint (TMJ) area, facial pain,
ear pain, temporal headaches, and neck aches. Symptoms usually
have a direct relationship to mandibular movement and function.
An increase in pain is often noted with palpation of the
joint or the masticatory muscles.
Successful management depends on an accurate determination
of the structures that are responsible for symptoms. Most
clinical problems emanate from the TMJs, masticatory muscles,
and cervical structures (which are all part of the musculoskeletal
system); however, other tissue systems may also be a source
of pain. Therefore, dentists who manage patient with TMD
must be aware of all the disorders that cause pain in the
craniofacial area, specially with respect to chronic pain
patients. These systems can be divided in extracranial,
intracranial, musculoskeletal, vascular, neurologic, and
The diagnosis and treatment of TMD requires the clinician
to use a full range of biological and clinical knowledge
and experience. It is essential to remember that, although
a variety of therapeutic modalities may prove to be effective,
there can only be one accurate diagnosis. No definitive
treatment should be initiated until the clinician has completed
all of the exploratory procedures and has made a presumptive
diagnosis. Nonetheless, it is often necessary to initiate
some emergency therapy to assist the acutely distressed
patient. Even if the emergency measures alleviate the acute
symptoms, they do not remove the responsibility of the clinician
to discover the etiology of the problem and seek its remedy.
It must always be remembered that many TMD patients have
psychologically contributing factors. It is often necessary
that some type of counseling support (conducted by an appropriate
mental health counselor) be administered simultaneously
with the dentist's treatment. The chronicity of pain in
many of these patients is extremely important. It means
that clinician must be aware that many of the patient's
complaints originate as part of the chronic pain pattern,
and are not related to actual TMD pathology. These symptoms
may continue to be manifested after all pathology in the
stomatognathic system has been eliminated. Reversible treatments,
when indicated, should be the initial treatment of choice.
Irreversible procedures should be initiated for the most
part after reversible procedures have not alleviated the
patient's discomfort and further intervention is necessary
for satisfactory treatment.
If the skeletal, traumatic, neurologic, neoplastic, internal
derangements, and infectious causes of dentofacial pain
are eliminated, there still remains 70% to 80% of patients
presenting with TMD symptomatology. These are the patients
with myospasm, trigger points, referred pain, occlusal disharmonies,
parafunctional occlusal habits, and emotional stress patterns.
The etiology of this TMD area is at present unresolved.
However, several etiologic theories have evolved. Five major
etiologic theories of myofacial pain disorder of the myospastic
category have been categorized. These are the mechanical
displacement theory, the muscle theory, the neuromuscular
theory, the psychophysiologic theory, and the psychological
Mechanical displacement theory is based on the observation
that some TMD patients have an overclosure of the mandible.
This may be caused by the loss or improper eruption of the
posterior dentition. The overclosure of the mandible is
thought to place undue pressure on the articulotemporal
and chorda tympani nerves and the Eustachian tube. Adherents
of this theory place great emphasis on the visualization
of equal anterior and posterior joint spaces on roentgenographic
examinations. The theory has been challenged on anatomic,
radiological, and clinical grounds.
The basis of this theory is muscle hyperactivity. The hyperactivity
serves as an initiator of myospasm, which then spreads to
its primary and secondary referred pain sites. Although
there is not a basis, at present, for the complete refutation
of this theory, some believe this theory is narrow and restrictive.
It does not take into account other variable causes of the
The neuromuscular theory is based on a functional disharmony
between the occlusal interface and a physiologic joint muscle
position. The incompatibility leads to parafunctional habits,
such as grinding and clenching of the dentition (bruxism).
The grinding and clenching may occur during daytime but
is most often manifested during sleep. The bruxism habit
leads to abnormal contractile states and, hence, myospastic
activity. The theory covers many of the clinical TMD problems
which are commonly seen and, indeed, may be the most popular
theory. Its major weakness is that it does not explain,
why many patients with abnormalities or variations from
the norms in the occlusal interface do not have TMD problems.
The basis of Physiologic and Psychophysiologic Theories
is that patients under stress have increased tension and
activity in the masticatory and associated musculature.
Some supporters of this school believe that the syndrome
is purely psychogenic and should be treated from a psychological
point of view. The psychophysiologic approach to TMD problems
states that myospastic activity is the primary cause of
TMD symptomatology. It is further believed that fatigue
caused by tension related oral habits is the major cause
of the abnormal myospastic activity. The theory does take
into account the necessity for physiologic harmony between
the components of the stomatognathic system as well as the
obvious influence that psychological factors have in the
TMD syndrome. At present there are too few data to unequivocally
support this theory. However, it is believed that its multifactorial
base is far more rational than the other existing theories
of TMD dysfunction.
It can be stated that the myofacial aspect of this syndrome
is multifactorial, and there can be little doubt that the
emotional status of the patient is one of the most important
of these factors. However, for any lasting improvement in
the patient's symptoms, all of the components of the stomatognathic
system must also be functioning within the physiologic parameters
of the patient. TMD has both a physical and emotional aspect.
Both must be accurately diagnosed and both must be accurately
In summary, essential signs and symptoms of the temporomandibular
joint and muscle dysfunction are : pain related to jaw movement
and palpation, the restriction of jaw movement, irregular
movement pattern, aches in the head, neck, and ears, clicking
which may or may not be related to dysfunction, prolonged
EMG silent periods, and signs and symptom of bruxism. Often,
patient with TMJ joint and muscle dysfunction may have episodes
of remission and recurrent exacerbations. These may occur
as the result of initial acute attack, or may have developed
gradually over the long time. These symptom must be treated
palliatively to relieve patient of pain, discomfort, and
ultimately psychic stress which can exacerbate the condition.
The practioner also must make a correct diagnosis as to
eliminate other disturbance which may produce the similar
sign or symptom such as Rheumatoid arthitis, infective arthritis,
neuralgias, myalgias, Meniere disease, rhematism, and neoplasm.
All these disorders leads to TMJ change and thus create
a need for a functional or occlusal therapy.
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