Neuromuscular disturbances causing temporomandibular dysfunction and pain

Temporomandibularjoint

Neuromuscular dysfunction

disturbances and

causing

temporomandibular

pain

Sebastian A. Bruno, D.M.D.* Columbia University School of Dental New York, N. Y.

and Oral Surgery,

0

ne of the most perplexing problems dentists encounter is dysfunction of the temporomandibular joint (TM J) associated with myofascial pain. This problem arises from disturbances in the neuromuscular system. This article deals with the diagnosis of the neuromuscular disturbances which interfere with the complex normal movements of the mandible. It demonstrates how pain perceived in the TMJ may be referred from certain muscles. A treatment plan designed to regain a relaxed healthy musculature is discussed. The complaints of patients who show no apparent reason for their TMJ dysfunction and pain are quite often dismissed as having a psychosomatic illness. Upon examination, these patients demonstrate certain irregular mandibular movements which indicate the presence of neuromuscular dysfunction. To analyze the process by which this dysfunction arises, one must study the complex masticatory system. TMJ DYSFUNCTION The temporomandibular joint is but one unit of the masticatory system; its functional integrity depends upon the soundness of the other components. Dysfunction of any one unit in the system is reflected in all the other units. One of the most common afflictions of the TMJ is traumatic arthritis which most often is caused by occlusal disharmony. Pain which results from this disharmony may be perceived in the TM J and in certain areas of the head and neck. The security of the TMJ rests mainly on the closing muscles of the jaws. These powerful antigravity muscles cross the temporomandibular articulation from their origin to insertion. The ligaments of the mandible serve to reinforce these muscles to maintain the integrity of the TMJ. Read before Greater New York Academy *Adjunct Professor of Dentistry.

of Prosthodontics,

Nov. 30, 1969.

387

388

.I. l’lostbet. October.

Bruno

NEUROMUSCULAR

Derrt. 1971

SYSTEM

by these powerful elt~vatori. The closing movement of the mandible is executed The eccentric movements are produced by the external pterygoid muscles. ‘l’h(* infra- and suprahyoid muscles serve to open the jaws during the full cycle of mandibular motion. The muscles of the back of the. neck, by maintaining lht> also enter into masticatory flmction. ~111 position of the head during mastication, of these muscles, including their intricate nervous system with its extrcnlel) SVIISItive receptors, are known collectively as the neuromuscular system. Neuromuscular function is most eficirnt whcrl the centric relation coincidcas motion with the maximum intercuspal occlusion. The critical point of mandibular intcrct+\-r. or occurs at the precise moment of intercuspal contart. Dcflectivez gliding contacts at this moment will introduce noxious impulses into some or all of the mandibular muscles, and these impulses will introduce changes it1 the XWUICmuscular system which controls mandibular Irtotiorl. NEUROMUSCULAR

SPASM

Travelll points out that, ‘
OF REFERRED PAIN

Skeletal muscles characteristically have a specific pattern of referred pain: excitation of these trigger areas gives rise to essentially the same distribution of referred pain in all subjects. Fixed anatomic pathways link the trigger areas directly with the reference zones. Whether the noxious stimuli are applied directly to th(, muscle or reach the muscle indirectly from the viscera or brain via the central nervous system, the same pathway leads from the trigger area to the region interpreted as painful. Travelll has mapped out the patterns of referred pain in

z%:‘4”

Fig.

Neuromuscular

1. Mandibular

Fig. 2. Insertion

Table

deviation

disturbances

389

to the left upon opening movement.

of a dry needle into a spastic muscle.

I. Distribution

of referred

myofascial

pain

Area stimulated Masseter muscle Anterior border and upper part Lower part Mandible Angle Short deep layer Temporal muscle Anterior section Most posterior section Intermediate section Deepest layer Internal and external pterygoid muscle Internal pterygoid muscle Neck muscles

Area to which

Pain was referred

Jaws, molar teeth, gums Upper molars Lower molars Temple, outer corner of eyebrow TMJ, inner ear Above supraorbital ridge, upper incisor teeth Upper molars, back of head Cuspids, bicuspids, temple, TM J Mandibular articulation

TMJ Mouth, tongue, hard palate Side of head, jaws, TMJ”

*Spastic disorders may also be seen. These plus the referred complain of the “stiff neck” syndrome.

pain cause the patient

to

patients with myofascial pain syndrome by inserting a needle into the trigger areas which appeared spontaneously in mandibular muscles (Fig. 2). A needle inserted into normal muscle produced no painful reference, but injection of hypertonic saline solution into normal muscle evoked transient referred pain. In this manner, the distribution of referred myofascial pain was mapped out (Table I). The significance of these experiments is that many normal teeth are in danger of being condemned because of pain referred to them by neuromuscular disturbances. Dentists must recognize the pain symptoms of neuromuscular origin and be familiar with the precise patterns of referred pain. Many painful symptoms arthritis of the spine, migraine, and that are diagnosed as trigeminal neuralgia, tension headaches might be due to myofascial pain resulting from spasticity of the masticatory muscles. It is imperative to recognize the subjective symptoms as well

390

1 l’rosthet. Dwr. October, I’fi!

Bruno

Fig. 3. Procaine (0.25 per cent). Fig. 4. An anterior

HCI

(2 per cent)

maxillary

as the clinical symptoms corrections are anticipated. ALLEVIATION

combined

with

isotonic

saline produce5

procairw

wIntin::

bite plane.

of neuromuscular

disturbances,

especially

Mhcn 0ccluSal

OF SPASM

When a patient has had an acute spastic experience associated with myofascial pain, it is possible by one of three methods to return the mandibular musculature to a temporary resting state by reducing the spasm and abolishing the myofascial pain symptoms. Method I. Insert a dry needle deep into the spastic muscle in the region of the trigger mechanism. This procedure brings about a release of cellular potassium which breaking the spastic cycle, and has the capacity of interruptin, u nerve conduction. thus expending the electric potential within the muscle1 (Fig. 2) . Method 2. Spray ethyl chloride intermittently across the areas of the spastic muscle about 18 inches from the face, taking care to protect the eyes, ears, and nose of the patient. The quick chilling, followed by the sudden rise in temperature, elicits a tremendous number of sensory impulses. Since pain travels along the same pathways as the sensations of heat and cold, the excessive loading with other sensory imp&es blocks the conduction of pain. Method 3. Inject a solution of 0.25 procaine in isotonic saline into the area of the trigger mechanism of the spastic muscle; this will cause a more prolonged interruption of the noxious stimuli which originally induced the spasm into the muscle (Fig. 3). Repeat this procedure for each trigger area until the m)rofascial pain disappears. These three methods may serve as diagnostic procedures to indicate whether the pain is of muscular or dental origin. If the pain disappears but returns in four to five days (the time it takes the spasm to recur), a diagnosis of neuromuscular disturbance is almost certain. If the pain persists, other causes must be sought. These methods also afford irnrnediate relief of the unrelenting painful myofascial symptoms. AIong with patient comfort there is a return of more normal mandibular motion, permitting a better evaluation of the degree of neuromuscular disturbance.

Neuromuscular

Fig. 5. Restricted

mandibular

Fig. 6. Isometric

exercise.

Fig. 7. Isometric

opening. The fingers

Note the deviation are applying

exercise. The thumb is applying

391

to the right.

downward

upward

disturbances

pressure on the mandible.

pressure.

TREATMENT Records necessary to determine the etiology of neuromuscular dysfunction may be obtained at this stage of treatment. Unfortunately, radiographic studies of the TMJ of patients with muscle spasm causing joint dysfunction have been very unrewarding. Diagnostic casts made and mounted on an adjustable or semiadjustable articulator by means of a face-bow and interocclusal records will serve to determine the presence of gross discrepancies between centric relation and centric occlusion. A return of normal mandibular movement and a dynamic centric occlusion which is in harmony with the neuromuscular system must first be obtained before the occlusal components may be corrected. To accomplish this objective quickly, a maxillary anterior bite plane is used to keep the posterior teeth out of occlusion. This eliminates the improper occlusal contacts which overload the neuromuscular system (Fig. 4). The anterior platform of the bite plane must be slanted upward to encourage a more posterior position of the mandible and to restore the full length of the external pterygoid muscles. The wear facets on the occlusal surfaces of teeth which exactly match antagonistic wear facets indicate conclusively that bruxism is a factor. The patient will report restricted mandibular opening, TMJ pain, and tiredness of the masespecially during the morning hours (Fig. 5). Bruxism is ticatory musculature, indicative of the patient’s psychic tension and emotional stress. The administration of 200 mg. of Soma (N-isopropyl-2-methyl-2-propyl-1,3-propanediol dicarbamate) before bedtime serves to reduce nocturnal bruxing and clenching which perpetuates and accentuates adverse neuromuscular changes. The prevention of clenching and bruxing by use of the anterior bite plane, both day and night, will restore normal muscle length to the mandibular muscles and permit the full limit of mandibular opening with little or no deviation. A statistical study has placed the normal vertical opening at 4.5 cm. for women and 5 cm. for

392

J. Ptorthet. Dent October, 1971

Bruno

men.lm3 The use of the bite plane for several weeks combined with conscientious home care, consisting of application of wet heat to the affected muscles followed by isometric exercises four to five times a day, will prepare the patient for mole intensive corrective therapy. The adminstration of two tablets of Equagesic (meprobamate and ethoheptazine citrate with acetylsalicylic acid) every four hours during the acute phase and one tablet three times a day during the subacute phnsc! will serve to keep the muscles in a resting, relaxed state during the day. The isometric exercises are as follows: The mandible is placed under tension fol the count of one through seven in opposing positions: opening and closing (Figs. 6 and 7) ; side to side (Figs. 8 and 9) ; and in and out (Figs. 10 and 11 j . Thesr exercises are designed to force relaxation upon the antagonist muscle IO impro\;ca its tone and physiologic processes and to relieve spasm. As a result of this therapy, there should be a return of normal mandibular motion and function and relief from myofascial pain. There are four indications of the patient’s recovery: the absence of pain, the* return of full active vertical opening, the lack of mandibular deviation upon opcsninp. and the disappearance nf clicking and grating within the TMJ. OCCLUSAL

EQUILIBRATION

Correction of the occlusal components may now be considered. Since the go;11 of a good occlusion is to establish a stable cclntric position, it is necessary to defines the centric position. When centric occlusion is identical with centric relation, the patient is said to have his mandible in his true centric position. In many patients, centric relation and centric occlusion do not coincide. This causes the rrtandible to shift into its full intercuspal occlusion. Since the neuromuscular systctlll fioverns mandibular movement from proprioceptive impulses arising within the periodontal membrane, oral mucosa, muscles, tendons, and the TMJ, these movements become trained pathways in the neuromuscular system which are constantly rcillforced bx impulses derived from occlusal contacts. Therefore. nnr must postulate tllnt cent& occlusion is a neuromuscular centric position. This is ;L fully acceptable positiolr until there is a change in neuromuscular function caused by disruptive forces pr+ viously mentioned, which alter the direction in which the lnandibular cusps bypas, the maxillary cusps. The final position of all mandibular Inotion is against the cranial (‘omponent In a normal individual with a normal occlusion, this final position will result ill maximum intercuspation. When the rnandible travels from its resting position ttr full simultaneous intercuspal contact, the neuromuscular mandibular position is said to be harmonious with the intercuspal position. If full intercuspatjon is noi realized at the initial contact, the mandible is deflected to its positioxl of full intercuspal contact. This position is referred to as the “acquired” or, more recently. the “habitual” eccentric position. However, statistics indicate that 90 per cent of the people are capable of retruding their mandibles from this maximum intercuspa{ position4 Beyron has stated that many of these patients will chew in the habitual or acquired centric position but will swallow in the retruded position.5 Since swallowing is an innate function performed on a preconscious level, it becomes essential to permit both functions to occur without introducing neuromuscular disturbances,

PAT”, ‘4”

Fig. Fig. Fig. Fig.

Neuromuscular

disturbances

8. Isometric

exercise.

The thumb

is applying

pressure to left side of mandible.

9. Isometric

exercise.

The thumb

is applying

pressure

to right

side of mandible.

inward

pressure

to tip of chin.

10. Isometric 11. Isometric

exercise.

The thumb

is applying

exercise.

The fingers are applying

forward

393

pressure on the mandible.

to be 1 to 2 mm. It The : distances between both positions have been determined has been referred to as the “long centric” or, facetiously, as the “short protrusiv e.” would be a “short retrusive.” Neuromuscular cent :ric Ar nore accurate description especially when selective grinding or occlu .sal posi tion is of paramount importance, procedures are anticipated. reh; ibilitative or whether by selective grinding The purpose of any occlusal correction, or deflective occlusal c(3nrest1orative measures, should be to eliminate interceptive intercuspation. With the mandibu lar tact s at the precise moment of full mandibular

394

Fig. Fig. Fig. Fig.

Bruno

12. Occlusal 13. A wedge 14. A pencil 15. Note the

indicator wax is covering the teeth of the upper left quadrant. of apple between the teeth of the opposite (riahtl side. marks the perforations. contact markings on the cusp sloprs.

muscles in a more relaxed condition performing normal mandibular movements, it is possible to regain a neuroInuscular centric position devoid of deflective contacts. Any restorative or selective grinding procedure done prior to muscle therapy is doomed to failure. Most restorative failures and most TMJ problems occur because the dentist does not recognize the discrepancies existing within the masticatory system that are due to neuromuscular dysfunction. Occlusal equilibration is a negative procedure and, as such, must be approached with extreme caution lest IVC lose the very structure necessary to maintain proper occlusal harmony. Several approaches to occlusal equilibration are used in practice today. One of these is the so-called “tap tap” method, which is designed to eliminate prematurities (interceptive or deflective contacts) that occur with the mandible held in a retruded position. Articulating paper marks the prematurities which are then reduced, and the process is repeated until there is an even distribution of articulating paper markings. Unfortunately this method often leads to “overequilibration.‘! Another method is to use the casts of the patient’s mouth which have been mounted on an articulator by means of interocclusal and face-bow records. Occlusal interferences are recorded as the casts occlude, and the sequences of their removal is noted until no further interferences are present. This process is repeated in the mouth in the exact sequence of reduction. This method is very inaccurate and

Volume 26 Number 4

Neuromuscular

disturbances

395

scientifically unsound, since the reduction of the first prematurity will result in neuromuscular changes which are impossible to reproduce on the articulator. Several years ago, Messerman6 described a technique for equilibrating the occlusion using wedges of apple and occlusal indicator wax.* The wax is placed on one quadrant of the maxillary teeth while the apple is chewed on the opposite side and swallowed (Figs. 12 and 13). Deflective occlusal contacts cause wax perforations which are marked with an indicator pencil (Fig. 14). After the wax is removed, the marked areas only are reduced, maintaining the original cusp contour. Most of the occlusal correction occurs on the cuspal slopes (Fig. 15). This procedure is repeated in the other quadrant and from one side to the other until no more wax perforations occur. Upon the patient’s return within several days, the occlusal correction is repeated because changes in the neuromuscular system may cause other deflective contacts to occur. If the occlusion is to be restored prosthetically, provisional splints may be inserted free of deflective contacts and in harmony with the neuromuscular system. The final restorations may be inserted only after the patient is certain to be free of any neuromuscular disturbances and myofascial pain. CONCLUSIONS The masticatory mechanism is operated by a very efficient and very precise neuromuscular system. Disturbances from outside forces may be imposed upon the neuromuscular system and, in turn, may disrupt the whole masticatory mechanism. When patients present themselves for treatment, they bring with them multiple problems. Recognition of these problems and ability to determine, on a clinical level, the effect of these problems on the masticatory mechanism determine the difference between success and failure of the subsequent treatment. The most distressed patients and the patients with the most severe unrelenting pain are the patients who are most appreciative of this treatment. There is nothing more gratifying to a patient than to know that his problem was not psychosomatic or imagined but clinically, organically, and biologically real. *Kerr Dental Manufacturing

Company, Detroit, Mich.

References J.: Temporomandibular Joint Pain Referred From Muscles of the Head and Neck, J. PROSTHET. DENT. 10: 745-763, 1960. Perry, H. T., Jr.: Muscular Changes Associated With Temporomandibular Joint Dysfunction, J. Am. Dent. Assoc. 54: 644-653, 1957. Dorrance, G. M.: Oral Surgical Clinics: Trismus, Dent. Cosmos 71: 33-40, 1929. Beyron, H. L.: Occlusal Relations and Mastication in Australian Aborigines, Acta Odontol. Stand. 22: 597, 1964. Beyron, H. L.: Optimal Occlusion, Dent. Clin. North Am. 13: 537-554, 1969. T.: A Concept of Jaw Function With Related Clinical Application, J. Messerman, Prosthet. Dent. 13: 130-140, 1963.

1. Travell, 2. 3. 4. 5. 6.

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SURGERY