Bruxism, a clinical and electromyographic study

Bruxism , a clinical and electrom yographic study

Sigurd P. R a m f jo r d * L .D .S ., M .S ., P h .D ., A n n A r b o r , M ich .

T h ir ty -fo u r patien ts w ith sev ere bruxism w ere stu d ied electrom yog ra p h ica lly and clinically, b e fo r e and a fter occlu sa l a d ­ ju stm en t.

The

m ost

com m on

occlu sa l

fa c to r in bruxism is a d iscrep a n cy b e ­ tw een cen tric relation and cen tric o c clu ­ s io n ; invariably, such a d iscrep a n cy is a cco m p a n ied by asynch ron ous c o n tr a c ­ tions o r sustained strain in th e tem p ora l and m asseter m uscles d uring sw allow ing. O cclu sal

adju stm en ts

elim in a ted

the

bruxism in all 34 patients. S tud ies o f o c ­ clusal relationships are in a d eq u a te and in con clu sive unless cen tric relation and sw allow ing

are

included.

The

e le c tr o ­

m yograph is a sensitive, h elp fu l to o l fo r record in g occlu sal in terferen ces.

The term “bruxism” is derived from the French “la bruxomanie,” first used by Marie and Pietkiewicz in 1907.1 Frohman2 in 1931 described “bruxomania” as a purely psychic state and then went on to say that “ bruxism is not necessarily audible.” This seems to be the first time “bruxism” was introduced in the liter­ ature. “ Bruxism” was also mentioned by Miller8 in 1936. Later he suggested using “bruxomania” to denote habitual grind­ ing of the teeth in the daytime and “brux­ ism” for nocturnal grinding. Other terms have been suggested for habitual grind­

ing of the teeth such as “ neuralgia traumatica” (K arolyi),4 “Karolyi-effect” (W esk i)5 and “ occlusal habit neurosis” (T ishler).6 A t the present, “bruxism” is commonly used to indicate a nonfunctional gnash­ ing, grinding or pressing of the teeth day or night. A tendency to gnash and grind the teeth in association with feelings of anger or aggression has been recognized since Biblical times, and it has been observed in animals as well as in humans.7 Even more common is the pressing or clamping of the jaws and teeth in an effort to sup­ press emotional outbursts such as crying or in relation to nonspecific nervous ten­ sion. Gnashing the teeth and pressing them together have a different signifi­ cance both for the teeth and the peri­ odontium. The etiology of these two con­ ditions may also be somewhat different but they are usually both included in the term “bruxism.” For the purpose of clarity, “ bruxism” in this paper will be used to indicate all nonfunctional gnash­ ing and pressing of the teeth. PREVALENCE

Since bruxism is performed on a subcon­ scious reflex-controlled level, the habit is commonly unknown to the patient unless it has been called to his attention. Sur­ veys of the prevalence of bruxism are,

36/22 • THE JO URNAL OF THE A M E R IC A N DENTAL A SSO C IA TIO N

therefore, very unreliable and the few reports in the literature8,9 of such surveys are totally inadequate. However, they in­ dicate that a very high percentage of

disease or from loss of teeth. Bruxism is often considered the most important fac­ tor in the etiology of traumatic occlusion and temporomandibular joint disurb-

patients with periodontal disease have bruxism. It has also been found that the prevalence of bruxism is much higher in

ances.16

population groups with malocclusion than in comparable groups with normal occlu­ sion.10 SIGNIFICANCE

ETIOLOGY

Great emphasis has been placed always on the psychic component in the etiology of bruxism.2,3’ 8,17-19 Tishler6 in 1928 suggested a relationship between occlusal

oral comfort of the patients. O n the other hand, Eschler14 found that periodontal

interference and neurotic conditions in the etiology of bruxism (probably un­ aware of Karolyi’s earlier w ork). H e ob­ served that “ even mild cases of occlusal trauma or minor occlusal defects such as a sharp cusp” would receive undue attention by neurotic individuals and re­ sult in grinding habits. A number of articles have appeared on bruxism, some stressing the psychic component and others maintaining the importance of the

disease increased the tonus contraction of the jaw muscles. From his and other investigations,15 it appears that periodon­ tal disease predisposes the individual to bruxism. T h e significance of bruxism in the etiology of periodontal disease is con­ troversial. It should be emphasized that bruxism does not necessarily lead to peri­ odontal disease, but it is always a poten­ tial source of damaging influence on the teeth, the periodontium, the jaw , the face, neck and tongue muscles, the cheek and tongue mucosa and the temporo­ mandibular joints. Thielemann5 observed that the greatest amount of periodontal injury from bruxism occurred in patients with steep cusps where the lateral stress from bruxism was applied at the tip of the cusps. T h e stress at the tip of the

local occlusal disharmony in the etiology of this condition. Very little scientific evidence has been offered for either view­ point. Occupation has been suggested also as a predisposing factor to brux­ ism.20'22 Jankelson23 produced bruxism experimentally by placing acrylic cement on the occlusal surfaces of teeth in ten human beings. A similar observation was made by the author of this article about ten years ago when high occlusal amal­ gam fillings were placed in lower first molars of ten rhesus monkeys. T h e mon­ keys gnashed their teeth vigorously until a few days later when they had worn the amalgam down. Then their bruxism stopped. The histologic sections of these monkeys showed periodontal injury cor­ responding mainly to the axially directed

cusps has a longer arm of leverage than stress in the central fossa of the teeth, and the stress on the cusps often will be directed outside of the supporting tissues

stress, but there were also zones of injury at the lateral cervical and lateral apical aspects of the roots of the teeth.

A t the beginning of this century, K a ­ rolyi11"13 was the first to postulate that nocturnal contractions o f the masseter muscles might be a main factor in the etiology of “pyorrhea.” H e emphasized also that spastic contractions of the lip and tongue muscles were damaging to the periodontium and disturbing to the

o f the teeth. It is also evident that the periodontal significance of bruxism in­ creases with decrease in periodontal sup­ port resulting from either periodontal

SIGNS AND SYMPTOMS

The following clinical signs and symp­ toms of bruxism have been observed:

RAMFJORD . . . VO LUM E 62, JA N U A RY 1961 • 37/23

1. Facets indicating a nonmasticatory pattern of occlusal wear. 2. Excessive, often uneven occlusal wear with minimal “ cupping” of the ex­ posed dentin. 3. Increased muscle tonus and un­ controlled resistance to manipulation of the mandible. 4. Compensatory hypertrophy of the masticatory muscles, especially the masseter. 5. Increased mobility of the teeth.24 6. Dull percussion sound from the teeth. 7. Tired feeling in the muscles of the jaws when waking in the morning. 8. “ Locking” of the jaw and a tend­ ency to bite the cheeks, lips, or tongue. 9. Tenderness of the masticatory muscles to palpation. 10. Temporomandibular j oint discom­ fort or pain. 11. Soreness of the teeth to biting stress. 12. Pulpal sensitivity to cold. 13. Audible sounds from bruxism. I f any of these signs or symptoms of bruxism are observed by the dentist and called to the attention of the patient, the habit will often be brought up to the conscious level and a positive history of bruxism may be obtained at a subsequent appointment.

do not change the occlusal relations of the teeth. Occlusal adjustment in the treatment of bruxism was introduced by Karolyi11 in 1901. Tishler6 in 1928 stated that cor­ rection of occlusal disharmony would re­ sult in immediate disappearance of the habitual grinding of the teeth since the adjustment would remove the exciting factor. Several authors have since ob­ served cessation of bruxism following oc­ clusal adjustment15,27,31 or oral recon­ struction, with or without bite-raising. Various forms of psychotherapy includ­ ing psychoanalysis2 have been recom­ mended for the treatment of bruxism. Autosuggestion has been a favorite among several authors,8,9’ 17,18,27,32 and more re­ cently hypnosis has been recommended.33 “ Tranquilizers” or similar drugs34 have been found to be helpful aids in occlusal adjustment, but their action is transient and limited. W hen the use of the drug is discontinued, the patient will revert to his habit of bruxism.35 PURPOSE OF PRESENT INVESTIGATION

Karolyi4,11-13 recommended bite-raising gold caps on the molars ( “Aufbisskappen” ) to be used at night for patients with bruxism. H e also recommended vul­ canite splints covering the occlusal sur­

It has been observed over several years of practice and teaching that in most instances bruxism may be eliminated by occlusal adjustment. T h e results have varied from complete and lasting elimi­ nation of all forms of bruxism to. partial or transient elimination of the habit. In several cases, occasional clenching of the teeth, rather than eccentric grinding, has persisted after the adjustment. Some pa­ tients, after the adjustment, have substi­ tuted for bruxism some other related habits such as tongue, lip or cheek biting

faces of all the teeth.4 A number of articles have appeared since that time

or biting on foreign objects. It has also been observed that elimination of centric

on the use of various types of occlusal splints for patients with bruxism.15'17,25"30 Some splints were for the purpose of hindering the grinding movements and others for stabilizing teeth and pre­ venting excessive occlusal wear. I f such

and balancing interferences was of greater importance for halting of bruxism than was removal of working side and pro­ trusive interferences. The requirements for accuracy of the adjustment to elim­ inate the habit varied greatly from one

splints are used, it is important that they

patient to another.

THERAPY

38/24 • THE J O U R N A L O F THE A M E R IC A N DEN TAL A S S O C IA T IO N

MATERIAL

T hirty-four patients with severe bruxism aged 19 to 60 years (m ean age of 31 years; 12 females and 22 males) were studied before and after occlusal adjust­ ment. Several o f these patients had pain in the tem porom andibular joints and the ja w muscles. T he findings related to the tem porom andibular joint problem s will be reported in a separate paper. Only patients with known severe bruxism were included in the study. M ETHOD

Fig. I • Equipm ent used for the electrom yo­ grap h ic part of the study. The Faraday cage is to the left on this picture

Since a definite relationship had been observed between occlusion and bruxism, it was decided to apply the relatively new technic o f electrom yography to a study o f the contraction pattern o f some o f the masticatory muscles in individuals with bruxism. Furthermore, the electromy­ ographic findings could be related to a clinical analysis o f the occlusion. T h e same patients could be studied also after occlusal adjustment. Electrom yographic technic and inter­ pretation have been discussed in several recent papers to w hich reference is m ade.36'41 T h e purpose o f this paper is to report a com bined clinical and elec­ trom yographic study o f the nature o f bruxism and the clinical and electromy­ ographic effect o f occlusal adjustment on some o f the masticatory muscles and the patient’s habit o f bruxism.

T h e electrom yographic recordings were m ade with a 24 position, eight-channel Grass Electroencephalograph, M od el IV A , m odified fo r electromyography (Fig. 1 ). A single-channel and an eight-chan­ nel oscilloscope were also available and cou ld be integrated with the ink writer o f the electromyograph at any time. T he oscilloscope was fou n d to be im practical fo r studies involving occlusal contacts, and it was used only occasionally for study o f rest position. Surface electrodes were placed bilaterally on the temporal and masseter muscles with the ear lobes as reference points as suggested by M o y ­ ers.36 T he anterior and posterior borders o f the tem poral and masseter muscles were determined by palpation during isometric contraction o f the muscles. T h ree electrodes were placed on each tem poral muscle36 (on the anterior, m e­ dial and posterior groups o f fibers) and one electrode on the m iddle o f the bulg­ ing part o f each masseter muscle. T he recording paper was m oved at a speed o f 60 mm. per second (fast speed, the distance between ten vertical lines on the p a p e r), but could be slowed to 30 mm. (m edium speed, five vertical spaces) or 15 mm . (slow speed, two and a half vertical spaces) per second. Calibration o f the gain was recorded carefully. T h e patients were placed within a Faraday cage (Fig. 1) and seated upright, with­

RAMFJORD . . . VO LUM E 62, JAN UARY 1961 • 39/25

out head support, in a dental chair dur­ ing the recording. They were instructed to look at the opposite wall at the level of their eyes and sit with their arms and feet comfortably supported. A casual in­ terview, without detailed history and examination, preceded this initial record­ ing. All of the patients went through the following routine for ographic recording: 1.

the

electromy­

It was ascertained that the patients

were sitting in the desired position. 2. The rest position was determined and recorded; various routine clinical procedures were used to determine the rest position (relax method, swallow method, Mississippi method, and so o n ) . 3. The patient was instructed to tap his teeth lightly together from rest posi­ tion. 4. The patient was instructed to bite from rest position to maximal solid oc­ clusal contact ( “ centric occlusion” ) by common definition).42 5. The patient was given a cup of water to drink. 6. The operator applied mild distal pressure on the patient’s mandible in an attempt to locate “ centric relation” 42 (the most retruded position of the mandible from which opening or lateral movements can be performed), the terminal hinge position. After this position had been lo­ cated, the patient was instructed to tap his teeth lightly together, maintaining the same contact relationship without the operator’s hand on his teeth. 7. The glide from centric relation to centric occlusion ( “ slide in centric” ) was recorded.

10. A combination of right and left excursions moving through centric occlu­ sion (as outlined in no. 8 and 9 ). 11.

Protrusive excursions from centric

occlusion and back again were recorded with the teeth in light contact. 12. Right lateral excursions from rest position and back to rest position without occlusal contact. 13.

T h e same as no. 12 but to the left.

14. Movements of the mandible from right to left and back to right through rest position and without occlusal contact. 15. Protrusive excursions from rest position without the teeth contacting and back to rest position. 16. Mastication of chewing gum on (a) right side, (b) left side and (c) on the anterior teeth. Each step was repeated several times with a session of electromyographic re­ cordings lasting 45 to 60 minutes. A systemic and dental history was then obtained. M ain emphasis was placed o n : 1.

Psychic or physical stress.

2. History of bruxism, temporoman­ dibular joint or muscle pain or discom­ fort. 3.

Loss of teeth and replacements.

The history was followed by a clin­ ical functional analysis and a roentgenographic study. Occlusal interferences in centric relation, lateral and protrusive excursions were located and recorded. The patient’s habitual masticatory pat­ tern was noted also. After the examination, the occlusion was adjusted. This required from one to five half-hour sittings. T h e occlusal re­ lations and the patient’s symptoms were re-evaluated prior to each adjustment.

8. Right lateral excursions from cen­ tric occlusion to end to end occlusion of the cuspids and then back to centric oc­ clusion were recorded, maintaining light occlusal contact during the entire pro­

T h e previously described electromy­ ographic recording session was repeated

cedure.

eral instances that had been overlooked clinically. This necessitated a readjust­

9.

Same as no. 8 but to the left.

when the patient’s occlusion seemed well adjusted. T h e electromyographic record­ ing revealed occlusal interferences in sev­

40/26 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA T IO N

ment and a new electromyographic re­ cording. Tw o to five series of electro­

ous proprioceptors and sensory nerve endings in the masticatory system. These

myographic recordings were made for each patient.

impulses are evaluated and transferred to efferent signals by the nerve center of the reflex system. Masticatory move­ ments are the result of a conditioned,

A n attempt was made always to adjust the occlusion until mandibular stability in centric relation (terminal hinge posi­ tion) was attained. A ll balancing inter­ ferences were removed and the balancing side contacts were made lighter than the working side contacts. T h e patient’s jaw was guided into retrusive lateral move­ ments during adjustment of lateral ex­ cursions. O n the working side the main emphasis was placed on smoothness of the gliding occlusal movements rather than on the number of contacts and steepness of guiding cusps. Only minimal adjustment was done on the maxillary anterior teeth in protrusive excursion. A t the completion of the adjustment, great emphasis was given to elimination of “ catches” that the patient could find in any excursion or combination of ex­ cursions. A t the beginning of the study, zoxazolamine (Flexin) was used as an aid to secure muscle relaxation, but equally good results seemed to be obtained later without any drug. Th e follow-up electromyographic re­ cording was done at various time inter­ vals (one-half hour to several months) after the occlusal adjustment. T h e total time of observation varied from a few months to three years. During the time of observation, the patients were re-ex­ amined and questioned about possible recurrence of their habit. FINDINGS

In order to make the presentation of the findings more meaningful, an outline will be given on the concept of bruxism that emerged from this study. T h e pattern of mandibular movements within the functional range of the teeth is determined from a combination of nervous impulses derived from the vari­

learned, reflex pattern which, under physiologic conditions, will satisfy the basic requirements to optimal function without damage to any part of the mas­ ticatory system. T h e importance of a reflex-controlled combination of syner­ gistic and antagonistic impulses for the establishment of a well-balanced smooth function of the masticatory system has been stressed by several recent investi­ gators.36,43,44 Furthermore, Moyers,36,38 Perry, H ar­ ris43,44 and others43,46 found that in­ dividuals with malocclusion have an asynchronous contraction pattern o f the masticatory muscles. In these cases occlu­ sal movements start as motor units come into action, but the movements are later inhibited through reflex action by disor­ ganized excitation o f proprioceptors in the periodontal membranes or the tem­ poromandibular joints. The reflex center will try then to work out a compromise pattern of occlusal movements which will inflict the minimum of irritation and damage on the involved tissues, but often this process of adaptation is disturbed by a change in excitability thresholds o f the neurons which govern the jaw move­ ments. Such changes can be brought about by impulses, of both peripheral and central origin. T h e state of facilitation associated with an increased rate of im­ pulses may exaggerate the ordinary im­ pact upon the neuron and elicit efferent impulses and peripheral muscle contrac­ tions which are out of normal propor­ tion to the original stimulus. T h e thresh­ old of the neurons may be greatly changed also by influence from the central nervous system/ as associated with general stress and nervous tension. Another related phenomenon to be considered is muscle tonus. A stretch of

RAMFJORD . . . VO LUM E 62, JA N U A RY 1961 • 41/27

constant degree, such as the force o f gravity on the mandible, causes a m ain­ tained state o f muscle contraction utiliz­ ing only a few alternating muscle fibers at any given time. This steady reflex con ­ traction, usually seen in muscles which are concerned with the maintenance o f posture and counteraction of gravity, is called tonus. T h e fundamental basis for tonus is the myotatic reflex center in the spinal cord, but the degree o f tonus may be altered by impulses both o f pe­ ripheral and central nervous system origin. A state o f hypertonus in the mas­ ticatory muscles may be due, therefore, to either local disharmony between the functional parts o f the masticatory sys­ tem or to increased nervous excitability. Usually it is due to a com bination o f both these factors. W hen the limit for adaptation to occlusal disharmony has been surpassed, hypertonic response will be created in the masticatory muscles. This may result in an injury either to the supporting structures o f the teeth or the tem porom andibular joints. Such an injury will convey increased stimuli to the nerve center with subsequent in­ creased efferent signals resulting in a tendency for further injury. Secondarily, this status o f discom fort may affect the central nervous system, which again may influence the irritability threshold o f the reflex center. Overfatigue and subsequent pain from sustained contraction o f the muscles will lower also the irritability threshold o f the neurons in the reflex center and enter this “ feed-back” m ech­ anism. This vicious cycle o f self-perpetuating increase in muscle tension related to dysfunctional disturbances in the teeth, the periodontium , the tem porom andib­ ular joints and the masticatory muscles is the basis for bruxism. T h e hypertonic, sometimes painful, status o f the muscles o f mastication in bruxism is similar to the “ occupational myalgias” in the arm and neck muscles o f typists under mental stress, o r the pos­ tural myalgias manifested as “ backache”

in persons with postural anomalies under psychic tension. Integration between the psychic and local factors in all o f these dysfunctional conditions is so intimate that it is almost impossible to evaluate the significance o f each factor separately, but both local and systemic factors have to be present to elicit bruxism. T h e local or “ trigger” factors in brux­ ism are related to occlusal disharmony, periodontal disease, pathologic conditions in lips, cheeks and tongue or irritation and pain anywhere in the masticatory system. T h e systemic factors o f psychic ten­ sion are often masked and overcom pen­ sated fo r by an outward appearance of utter calmness which readily may deceive the examiner. It is also extremely difficult to locate occlusal interferences in such patients because o f the tenseness and “ splinting action” o f their jaw muscles. Consequently, the cause and effect rela­ tionship between occlusal interference and psychic tension in bruxism is often over­ looked. CLINICAL AND ELECTROMYOGRAPHIC FINDINGS

T he findings will be discussed in the order o f the electrom yographic record­ ing. A rest position with electromyographically norm al muscle tonus could be re­ corded fo r most o f the patients (Fig. 2 ). This electromyographic rest position did not necessarily coincide with the clini­ cally determined rest position. It often re­ quired a slight opening from clinical rest position to achieve a m ild, even tonus contraction o f the tem poral and masseter muscles. This even tonus contraction could be maintained usually for several millimeters o f further opening. A t times it was impossible to obtain a balanced rest position recording in patients with discom fort or pain in the tem porom an­ dibular joints or in the muscles (Fig. 3 ). D iscom fort in sitting position (in one

42/28 ■ THE J O U R N A L O F THE A M E R IC A N DENTAL A S S O C IA T IO N

Fig. 2 • Electrom yogram of normal tonus activity in rest position in spite of severe occlusal dishar­ mony and sym ptom s of discom fort and pain in the recorded muscles on both sides. The main occlusal discrepancy was a 2.5 mm. slide forward and to the right side from centric relation to centric occlusion (fast speed)

patient a toe went to sleep) , eye strain, distracting noise, apprehension and gen­ eral nervous tension were factors which could disturb the tonus o f the muscles. In one patient, the least disturbed record­ ing o f rest position was obtained when she was holding her teeth in light con ­ tact. A fter occlusal adjustment, a wellbalanced tonus o r rest position recording could be obtained in all o f the patients (Fig. 4 ) . This w ou ld indicate that the disturbance in tonus o f the tem poral and masseter muscles was related directly to the rem oved occlusal interferences. M uscle exercises o r simply holding the teeth apart over an extended period o f time tended to eliminate the muscle m em ory o f the occlusal interferences and equalize the contraction pattern o f the muscles. Speaking to the patient in a

soft m onotonous voice or administering zoxazolam ine also would decrease the abnormal muscle contractions in rest position. These observations indicated that the muscle tonus in patients with bruxism is influenced both by local (occlusal) and systemic (central nervous system) stimuli. H ow ever, when the local disturb­ ing stimuli were eliminated, a well-balanced tonus or rest position could always be recorded. T h e initial light tap from rest posi­ tion to occlusal contact often showed a disturbed and changing contraction pat­ tern (Fig. 5 ) w hich after some m ore taps gradually settled dow n to a fairly har­ monious pattern as the patient’s neuro­ muscular mechanism located a com fort­ able relationship o f the teeth. A sustained

bm it Anterior

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Left Mldffle Temporal !

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Left Maseeter

H I

Right M*»aeter

m/hr#.....*n(» '«i(iii'i,«i^»l.ii»«w «is>»K,ii.»i>A«BP»i|«i»«'W»
Right Anterior Temporal

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Fig. 3 • "R e st position." It was not possible to locate a true rest position with balance of tonus activity for this patient. C o m p la in t of muscle fatigue and pain in the left tem porom andibular joint occasionally. O n e and a half millimeter slide forward and to the right from centric relation to centric occlusion (m edium speed)

L elt Anterior Temporal

L eft Middle Temporal

Left P osterior Temporal

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Eight Middle Temporal

Right P osterior Temporal

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Fig. 4 • Recording of rest position from the sam e patient as Figure 3 after occlusal adjustment. N o te fairly go o d balance of tonus activity com pared with Figure 3 (m edium speed)

44/30 • THE JO U R N A L O F THE A M E R IC A N DENTAL A S S O C IA T IO N

Left Anterior T«m£©r*l «fcN4*NW

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Fig. 5 * L igh t occlusal tap from rest position. Sam e patient as Figure 2. C o nsid e rab le im balance in m uscular activity co rresponding to the occlusal disharm ony (medium speed)

strain with lack o f relaxation between each tap was seen in some cases. A fter the adjustment, a definite relaxation b e­ tween the taps was found. Electrom yographic records o f muscle action in centric occlusion should be in­ terpreted with great caution. T h e first few times a patient bites lightly together from rest position to centric occlusion (providing he has had his teeth apart for some time ), the recording m ay in di­ cate im balance o f occlusion, but muscle m em ory and conditioned guidance may soon establish an optim al contact rela­ tionship o f the teeth in biting, and sub­ sequently an even contraction pattern o f the muscles will appear. I f the patient is biting hard together in centric o cclu ­ sion, a large num ber o f muscle fibers will be engaged in all o f the elevator muscles and the difference in contraction

related to uneven occlusal contact will be masked (Fig. 6 ). It is entirely errone­ ous to assume that an electrom yographic recording o f an even and well synchro­ nized contraction pattern o f the masseter and temporal muscles in centric occlusion is a reliable indication o f an ideal centric relation between the jaws and the teeth. Initially, all o f the patients showed some disturbance o f the contraction pat­ tern o f the muscles during swallowing. Various spastic and asynchronous con ­ traction patterns were observed (Fig. 7, 8 ) . Five o f the patients did not bring their teeth together when they swal­ lowed. T h e act o f swallowing was a ccom ­ panied by considerable sustained muscle activity in these individuals (Fig. 9 ) . O n e patient swallowed with her teeth apart and then brought them firmly together in centric occlusion immediately after the

RAMFJORD . . . VO LUM E 62, JAN UARY 1961 • 45/31

Left Middle T einpoxal

.Left M asseter

Right Masaetjcr

Right Middle Tempos

Right Posterior- Temporal

1 0 4
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Fig. 6 • Biting from rest position to centric occlusion. Light occlusal pressure on the left side of the electrom yogram and biting harder on the right side. The uneven contraction pattern of the muscles (corresponding to the occlusal disharm ony) in light occlusion to the left is alm ost "m a sk e d " b y the large num ber of muscle fibers contracting in heavy occlusion to the right. Sam e patient as Figure 3 and 4 (fast speed)

swallow. In other cases the teeth were barely touching during swallowing and no distinct electromyographic pattern of swallowing could be recorded. After oc­ clusal adjustment all of the patients con­ sistently brought their teeth together when they swallowed and a definite re­ laxation could be recorded between each swallow (Fig. 8 ) . The occlusal adjust­ ment was not considered complete until all electromyographic irregularities in swallowing were eliminated. Only one patient had to terminate the treatment before the “ slide in centric” was elimi­ nated completely, and the electromy­ ographic recording showed a slightly disturbed pattern of swallowing. H ow ­ ever, the clinical result in this case was good with at least temporary elimination of the bruxism and the discomfort in the muscles and temporomandibular joints.

His residual “slide in centric” was less than 1 mm . and almost on a horizontal level. W hen the patients were trained to tap their teeth together in centric relation (terminal hinge position), some tension invariably appeared in the posterior fibers of the temporal muscles.47 Strain in some o f the other recorded muscles appeared also in this position as reported by Moyers38 (Fig. 1 0 ). After adjustment, an even bilateral strain was observed in the posterior fibers of the temporal muscles of most of the patients when the patient was told to hold his jaw in centric rela­ tion. However, when the operator pushed the patient’s jaw back with a mild, steady pressure, in most instances the electro­ myographic activity of all o f the muscles was found to be even less than the activ­ ity associated with normal tonus in rest

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Fig. 7 ’ Swallowing. M a rke d by disturbed contraction pattern of the muscles associated with a 2 mm. forward "slid e in ce n tric" and uneven occlusal contacts on go ld inlays (fast speed)

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Fig. 8 • Recording o f swallowing after occlusal adjustment from the sam e patient as Figure 7 (Channel 8 was out of function). N ote harm onious integration of muscle activity. The contraction of the masseter muscles just prior to the occlusal contact activity is normal and associated with b ringin g the teeth apart in the initial phase of the swallowing (m edium speed)

RAMFJORD . .. VO LUM E 62, JA N U A RY 1961 • 47/33

R ig H t A n t e r i o r

l4 > m p c x * l

R ig h t P o # t e r i o r TemfXKral

Fig. 9 • Strained swallowing with the tongue between the teeth. Spastic, uncoordinated muscle action. A slide of 1.5 mm. forw ard and to the left side from centric relation to centric occlusion was the only occlusal discrepancy in this patient. N o te tension in the right posterior temporal muscle fibers as a response to the slide to the left (fast speed)

position (Fig. 1 0 ). In other cases, a co m ­ plete relaxation o f the muscles could not be obtained until the occlusal adjust­ ment had been at least partially com ­ pleted. A slide from centric relation to centric occlusion ( “ slide in centric” ) was o b ­ served in all o f the patients. Spastic muscle contractions were observed o cca ­ sionally during this sliding movement. A bout a third o f the patients were un­ able on com m and to perform lateral ex­ cursions with the teeth in contact. A t­ tempts at lateral excursions in these instances elicited com pletely uncoordi­ nated spastic muscle contractions, often o f an antagonistic nature with simulta­ neous contractions on both sides (Fig. 1 1 ). Occlusal interference on the bal­ ancing side was accom panied definitely with the most severe disturbance o f

muscle function. Ledges on the teeth be­ tween the masticatory pattern o f wear or facets and the bruxism facets occasionally acted as neurom uscular blocking m ech­ anisms on the working side and elicited severe muscle spasms when attempts were m ade to pass the m andibular teeth over these ledges. T h e steepness o f the cusps on the w ork­ ing side and the num ber or placem ent o f the functioning contacts did not seem very im portant fo r the balance o f the muscle function. O n ly tw o patients had their most severe muscle spasms asso­ ciated with heavy working contacts on steep inclines o f maxillary cuspids. Both patients had extremely tense muscles and tem porom andibular joint pain. Clin­ ical and electrom yographic evidence o f smooth gliding contacts and harmonious muscle action in bilateral movements

48/34 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA T IO N

Fig. 10 * Left two thirds of the electrom yogram is a recording of the patient's attem pt to tap his teeth together in centric relation in the presence of severe occlusal disharm ony. O n the right third, the operator is holding his hand on the patient's lower anterior teeth with a light pressure posteriorly. The action potential from the muscles is then even less than the rest position tonus. Recording from sam e patient as Figures 2 and 5 (fast speed)

was established fo r all o f the patients after the occlusal adjustment (Fig. 11-14). O nly m inor occlusal adjustment was done fo r the protrusive excursion. Incisal ledges from bruxism were eliminated, but no attempt was m ade to reduce the over­ bite or flatten the incisal guidance. Disturbance o f the contraction pattern o f the muscles in lateral excursions from rest position was observed mainly in pa­ tients with tem porom andibular joint or muscle pain. H ow ever, the splinting ac­ tion o f the muscles in relation to occlusal interferences carried over in a few cases to prevent even the noncontact m ove­ ments. A few patients with very tense jaw muscles had greater difficulty with lateral and protrusive movements when their teeth were apart than when they

were contacting. T he disturbances in noncontact movements responded very favorably to occlusal adjustment. T h e electrom yographic findings asso­ ciated with chewing o f gum were not very startling and did not contribute m uch toward the understanding o f occlu ­ sal relations and bruxism. M ost patients had worn in a habitual pattern o f mas­ tication with excellent muscle coordina­ tion. H ow ever, when they attempted to chew away from this favorite pattern disturbed contractions o f the muscles ap­ peared (Fig. 13, 1 4 ). T hree patients had an ideal bilateral masticatory pattern, both from a clinical and electrom yo­ graphic standpoint, before any occlusal adjustment was made. O nly in tw o instances could the “ slide in centric” be identified in the electro­

RAMFJORD ... VO LUM E ¿2, JA N U A RY 1961 • 49/35

Fig. I I • Record of an inhibited attem pt to perform lateral excursions. Spastic uncoordinated muscle action. Som e dull pain in the jaw muscles and severe balancing interference on both sides (fast speed)

myographic recordings o f mastication (Fig. 13). Disturbances in the mastica­ tory muscle pattern associated with ba l­ ancing interference was observed in sev­ eral cases (Fig. 15 ). T h e extent o f the lateral excursions in mastication was in ­ dicated by a difference in the timing o f the contraction potential from one side to the other (Fig. 16). In protrusive mas­ tication various deviations from straight protrusive could be observed (Fig. 17). Harm onious bilateral masticating func­ tion was established in all o f the patients after the occlusal adjustment (Fig. 1 8 ). T h e patients were questioned, and, if possible, re-exam ined from several months to three years after com pletion o f the treatment. A ll o f the patients declared that they stopped the habitual grinding o f their teeth after com pletion o f the occlusal adjustment. H ow ever, tw o pa­

tients stated that a few months after the treatment they developed new “ high spots” and occasionally ground their teeth again. A ll o f the patients have ex­ perienced lasting relief from their tem ­ porom andibular joint and muscle dis­ com fort. T hree patients stated that they still clench their teeth firmly together under nervous strain, but have completely abolished the grinding in lateral or p ro­ trusive excursions. T h ey have n o discom ­ fort associated with the clenching o f the teeth. DISCUSSION OF FINDINGS

A disturbed contraction pattern o f the muscles during swallowing was fou n d in all o f the patients with bruxism. A ll o f the patients also had some discrepancy between centric relation and centric oc-

50/36 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA T IO N

377

Left Anterior Temporal

Left Middle Temporal

;

.

.

i

i

!

.

,

•

!

I*: i ! Right M»*»eter i

Right Anterior T«mpor*l ^Vwy*^A-' ,.>-«-r Middle Temporil

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, ftdáhtf Po*t«tior

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f e s * ^ Fig. 12 • R ecord of lateral excursions starting with right lateral excursion on the extreme left hand side of the electrom yogram , m oving over to the left excursion at the m iddle of this recording and to the right excursion ag ain at the right hand side o f the electrom yogram . This well coordinated m ovem ent pattern is from the same patient as Figure I I after occlusal adjustm ent (fast speed)

elusion. W hen this discrepancy or “ slide in centric” was eliminated by occlusal adjustment, a harmonious contraction pattern o f the muscles during swallowing ensued. These observations indicate that o cclu ­ sal disharmony between centric relation and centric occlusion m ay disturb the contraction pattern o f the masticatory muscles in a similar way as the occlusal interferences in the other ranges o f o c ­ clusal contacts which have been studied electrom yographically in several investi­ gations.36’ 40’ 48,44,46,47 H ow ever, the dis­ turbance from “ slide in centric” is asso­ ciated almost exclusively with swallow­ ing. T h e previous electrom yographic studies o f occlusion have failed to con ­ sider the extremely im portant factor o f swallowing and its relation to the old problem o f “ centric.” O f course, Jankel-

son48 and other prosthodontists have been aware o f the distal thrust o f the mandible during swallowing for a long time. T h e electrom yographic observa­ tions reported in this paper are further indications o f the significance o f centric relation fo r com plete occlusal harmony. Infantile (visceral) swallow is based on an unlearned primary reflex pattern in the baby. T h e seventh cranial nerve muscles are mainly utilized for this type o f swallow.49,50 Later w hen the teeth com e into functional occlusion, the swal­ low ing pattern changes to the adult (som atic) swallow where the fifth cra­ nial nerve muscles are dominating. T he influence o f the occlusal relations o f the teeth on the developm ent o f the muscular contraction pattern in the somatic swal­ low is not known. It m ay be assumed that the somatic swallow pattern is m ore

A ¡Left Middle Temporal

Left Foeterior Tempormi

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^flight Anterior Temporal

Middle Tempafal

Fig. 13 • C hew ing on the right side. This patient (same as Figures 2, 5 and 10) had a 2.5 mm. "slid e in centric," and the dual peaks of the electrom yographic "sp ik e s" indicate the effect of this "s lid e " on the m asticatory movements. A lso lack of bilateral muscle coordination (m edium speed)

Left Antario:* Temporal — L#it Middle T*mpor*l —

*

L eit Posterior Temporal

Right Ro«erioar Temporal

ta r ? Fig. 14 • Sam e patient and same movements as Figure 13 (chewing on the right side), after occlu­ sal adjustment. N ote harm onious bilateral muscle action (fast speed)

52/38 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA T IO N

Fig. 15 • C h e w in g gum on the left side in the presence of heavy balancing side contact. The right side muscles dom inate in left side m astication instead o f the normal stress distribution of weaker action, especially of the masseter muscle, on the balancing side (fast speed)

conditioned by environmental stimuli than the visceral pattern, and consequent­ ly somewhat m ore amenable to change. A prim ary or unlearned reflex pattern is m uch m ore deep-seated and difficult to change than the learned, conditioned, reflex pattern o f the masticatory m ove­ ments. A lthough most individuals can learn to avoid occlusal interferences in lateral and protrusive excursions, it seems m uch m ore difficult to learn to avoid occlusal interferences related to the swal­ low ing position o f the ja w since this probably involves changes in a m ore basic reflex pattern. It was interesting to note that five o f the patients had a visceral type o f swallow with the tongue between the teeth and a lack o f rhythmic co n ­

traction o f the fifth cranial nerve muscles during swallowing. Later, when the o c ­ clusion was adjusted, the patients re­ sumed the somatic swallow with the teeth securely together. T h e implications o f these findings on restorative and pros­ thetic dentistry will be discussed in a separate paper. O n e patient w ho com plained o f per­ sistent bruxism after what was considered a com plete occlusal adjustment showed electromyographically a disturbance o f her swallowing muscle pattern in an otherwise ideal occlusion. A clinical re­ examination revealed a very slight an­ terior glide o f the mandible from centric relation when she was biting firmly to ­ gether (Fig. 19). W hen this “ slide” was

t * j t ^WtfCijnr Temporal

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Right Middle, Temporal

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ir-ZIMM

Fig. 16 • C hew ing gum on the right side. Two years after occlusal adjustment. The action in the temporal muscle on the right side precedes the left side considerably. This corresponded to a wide lateral excursion in m asticating (fast speed)

834

i l l : ' ! Left■Anterior Ten » » ral ,, J Loftt M

11« T«mpoTftl -—<*

Left Posterior Temporal

l^eft Ma#j*eier (•yiwWi"

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Right Anterior Temporal *—“• — ’— —w— Right Middle Temporal

Right po»ter,ij>| Tempora!

2-ÖB lfc.fr.. c. Fig. 17 • C hew ing gum on the front teeth after occlusal adjustment. Sam e patient as Figures 3, 4 and 6. N o te changes in action potential of the masseter muscle as the movements shift slightly to ­ ward the right or the left (fast speed)

Fig. 18 • Bilateral chewing of gum after occlusal adjustment. Sam e patient as Figures 3, 4, 6 and 17. The change from right to left mastication is indicated on the m iddle of the electrom yogram . N ote the marked shift in masseter action with shift in side of mastication. In contrast to the patient in Figure 16, this patient chews with very small lateral excursions (fast speed)

L*ft P osterior Temporal |

L e ft M a i ««ter

i

R ig h t M a s s e t e r

Fig. 19 • Sp astic unharm onious muscle contractions in swallowing after inadequate occlusal adjust­ ment. The patient still had a very minor "slid e in centric" on the right side, otherwise excellent occlusal relations (fast speed)

RAMFJORD . .. VO LUM E 62, JA N U A RY 1961 • 55/41

Loft Anterior Temporal

Fig. 20 • Swallow ing after com pleted occlusal adjustment. Sam e patient as Figure monious muscle activity (fast speed)

corrected, her bruxism subsided and a well-balanced electrom yographic record­ ing o f swallowing was obtained (Fig. 2 0 ). Obviously, this does not mean that every patient with “ slide in centric” will de­ velop bruxism, since it is known that most individuals have such a “ slide” without having bruxism ; but it indicates that for patients with bruxism, tem porom andib­ ular join t discom fort or pain, it is ex­ tremely im portant to establish a stable centric relation. H ow ever, bruxism may be eliminated, at least temporarily, with­ out a com plete elimination o f a “ slide in centric” as seen in one o f the patients in this study; but in such patients there is a great tendency for periodic bruxism associated with increased psychic tension and low ering o f the irritability threshold o f the neurons. Centric relation is, by definition, a terminal jaw position. T he fact that it

19. N ote har­

takes some muscle action to bring the ja w into this position is well known from previous investigations.38,47 It was in ­ teresting to note that only in two patients could it be ascertained electromyographically that the “ slide in centric” disturbed masticatory pattern, whereas this slide disturbed the swallowing pattern in all o f the patients. It seems, therefore, that a “ slide in centric” is o f m uch greater significance in swallowing than in masti­ cation. Occlusal Interference in Lateral Excur­ sions • O cclusal interferences which trig­

gered muscle spasms were observed in the various lateral excursions; but by far the most severe disturbances, electrom yographically and clinically, were found associated with interferences on the bal­ ancing side. H ow ever, during the course o f treatment, the bruxism persisted in

56/42 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA TIO N

one person, w ho at that time had clinical and electrom yographic evidence o f per­ fect occlusal relations in centric and bal­ ance. His only occlusal interference was a heavy contact on the working side on a maxillary cuspid. W hen this interfer­ ence was eliminated, and the bicuspids and molars were brought into contact in the lateral excursion, his bruxism stopped. This, o f course, contradicts the current theories on the “ cuspid rise.” 51 In other cases, isolated balancing interference was responsible for continuation o f bruxism during the treatment. It can, therefore, be stated that any type o f occlusal inter­ ference may trigger bruxism, but centric and balancing interferences are m ore apt to be responsible for the bruxism than working side or protrusive interferences. O cclu sa l I n te r fe r e n c e in M a stica tion

•

It was found, as reported several years ago b y Beyron,52 that the habitual mas­ ticatory pattern cou ld be changed from unilateral to bilateral by occlusal adjust­ ment. Several patients volunteered un­ solicited inform ation about noticing sud­ denly that they were chewing on both sides o f their m outh after the adjustment. T h e electrom yographic recordings con ­ firmed the clinical impression o f har­ m onious muscle coordination in bilateral mastication after occlusal adjustment. H ow ever, the masticatory movements were unreliable as an indicator o f occlusal interferences o f significance for the brux­ ism. Several patients had established ex­ cellent functional relations between their teeth in spite o f the occlusal interference that acted as a trigger factor fo r the bruxism. S ig nificance o f R e st P osition and F reew a y S p a c e • Several patients had a perfectly

balanced tonus activity in rest position in spite o f severe occlusal interferences and bruxism. It seems that muscle bal­ ance in rest position has been given far too m uch significance in previous publi­ cations.53'55 Even m ore misleading are

statements about com plete absence o f muscle activity in rest position. Antigrav­ ity tonus and posture can only be m ain­ tained through muscle action. Tonus activity o f the muscles m ay be m anipu­ lated in several ways that have been dis­ cussed previously and the muscle memory o f occlusal interference seems to be short in the absence o f pain. T h e influence of pain on the contraction pattern o f the muscles will not be discussed in this paper. N o attempt was m ade to measure the freeway space in these patients since it has been observed over the years (and confirm ed in this study) that bruxism may be eliminated by occlusal adjustment regardless o f the w idth o f the freeway space. E valu ation o f th e E lectrom yog ra p h ic T e c h n ic ■ T h e electrom yograph is a com ­

plicated tool with m any possibilities, and some definite limitations. Reports on its usefulness in dental research have varied from uncritical enthusiasm to shouldershrugging negative criticism. New devel­ opments in dental electrom yography56'59 that appeared in the literature during the con duct o f this study were considered and used experimentally. H ow ever, they were not adopted for the follow ing rea­ sons: T he oscilloscope with its wide and sensitive range was not practical fo r study o f occlusal contact relations because o f a masking o f the “ spikes” on the screen. T h e question about placem ent o f refer­ ence electrodes did not seem very perti­ nent to this investigation since the main concern was a com parison between iden­ tically recorded findings. Quantitation, either by integration units,58 or measur­ ing and counting o f action potentials60 (o f questionable value after the use o f surface electrodes) was fou n d not to be indicated since the differences in j action potentials o f interest to this study were clear cut and obvious. It should be emphasized that a very close co-ordination was observed between the clinical evidence o f occlusal interfer­

RAMFJORD . . . VOLUME ¿2, JA N U A RY 1961 • 57/43

ence and the electrom yographic record­ ings o f disturbances in the contraction pattern o f the tem poral and masseter muscles. Properly used, the electromy­ ograph was extremely sensitive in detec­ tion o f occlusal disharmonies. SUMMARY

A com bined clinical and electrom yo­ graphic study o f bruxism in 34 adults, before and after occlusal adjustment, has been reported. T h e neuromuscular m ech­ anism o f bruxism has been explained on the basis o f an intimate relationship be­ tween occlusal interference and psychic tension. O cclusal interference in any jaw position cou ld act as a trigger for brux­ ism, if com bined with nervous tension. H ow ever, the most com m on occlusal fa c­ tor in bruxism was fou n d to be a dis­ crepancy between centric relation (the terminal ja w position) and centric occlu ­ sion (m axim al occlusal contact p osition ). T he second significant occlusal trigger factor was heavy balancing side contact. It was demonstrated electromyographically that a discrepancy between centric relation and centric occlusion was ac­ com panied invariably by asynchronous contractions or sustained strain in the tem poral and masseter muscles during swallowing. A normal muscle balance in swallowing could be attained only when the occlusion was adjusted to a stable occlusal contact in centric relation. E lectrom yographic evidence o f muscle harmony in rest position and centric o c ­ clusion was found in several individuals with occlusal interferences and disturbed contraction pattern o f the muscles in other positions. Consistent correlation was observed between the occlusal interferences and the electrom yographic recordings. A ccordin g to all available inform ation, the bruxism in any excursion was elimi­ nated after com plete occlusal adjustment in all o f the patients. H owever, an o cca ­ sional tendency to clench the jaw s in

centric persisted in three patients, and two patients had a slight relapse o f the bruxism when they developed new occlu ­ sal interferences. CONCLUSIONS

1. A ny type o f occlusal interference may, when com bined with nervous ten­ sion, initiate bruxism. 2. Bruxism m ay be eliminated by o c ­ clusal adjustments. 3. T h e occlusion has to be adjusted to centric relation in order to achieve muscle balance in patients with bruxism. 4. A ll studies o f occlusal relationships are inadequate and inconclusive unless centric relation and swallowing are in­ cluded. 5. T h e electrom yograph is a sensitive and helpful tool fo r recording o f occlusal interferences, but electrom yographic rec­ ords o f a balanced muscle pattern in rest position and centric occlusion are not acceptable as evidence o f an ideal, well balanced occlusion.

Presented as part of the Forum on O c clu sio n and Pe riod on tics Session II, A m e ric a n Dental A sso cia tio n C ente nn ial Session, New York, S e p te m b e r 16, 1959. This in vestigation was su p p o rte d b y the Research a n d D e v e lop m e nt D ivision, Office o f the Su rge on General, D e p a rtm e n t of the Arm y, W a sh in g to n , D. C . under C o n ­ tra ct N o . D A -4 9 -0 0 7 -M D -7 2 I. *P ro fe ssor o f periodontics, U nive rsity o f M ic h ig a n Sch oo l of Dentistry. 1. M a r ie and Pietkiewicz. La bruxom anie. Rev. de Stom at. 14:107 M a rch 1907. 2. Frohm an, B. S. The a p p lic a tio n o f psychotherapy to dental p ro b le m s. D. C o sm o s 73:1117 N o v . 1931. 3. M ille r, Sam uel C . O ra l d ia g n o sis a n d treatment pla n ning. Philadelphia, The Blakiston C o., 1936. 4. Karolyi, M . Z u r Therapie d e r Erkrankungen der M u nd schle im h a ut. Viertelischr. Z ah n h k. 22:226, 1906. 5. Thielem ann, Konrad. Biom e ch anik der Paradentose. Le ipzig, H e rm a n n M eusser, 1938. 6. Tishler, B. O c clu sa l h a bit neuroses. D. C o sm o s 70:690 Ju ly 1928. 7. N a d le r, S. C . Bruxism, a classification : critical re­ view. J .A .D .A . 54:615 M a y 1957. 8. Boyens, P. J . Value o f a u t o su g g e st io n in the ther­ ap y o f " b r u x is m " and other b itin g habits. J.A .D .A . 27:1773 N o v. {940. 9. Peterson, L. N., a n d Dunkin, R. T. The incidence o f bruxism in adults. A c a d . Rev. 4:79 Ju ly 1956. 10. Bober, H . G ru n d la g e n d e r T h e ra pie d e r H a u p t­ form en de s (nächtlichen) Zähneknirschens, österr. Zschr. Stom at. 52:449 Sept. 1955. 11. Karolyi, M . Beob achtun ge n ü b e r Pyorrhoe A lve olaris. Vlerteljschr. Zahnhk. 17:279, 1901.

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12. Karolyi, M . B e ob achtun ge n ü b e r Pyorrhoe A lv e o laris a n d C a rie s Dentium . Vlerteljschr. Z ahn hk. 18:520, 1902. 13. Karolyi, M . U eb er A lv e o ia rp y o rrh ö e . Vierteljschr. Zahnhk. 21:85, 1906. 14. Eschler, J. E le k tro p h yslolog isch e und p a th o lo g ­ ische Untersuchungen des Kausystem s. Deut. Zahnärztl. Zschr. 7:1333, 1952. 15. M oore , D. S. Bruxism, d ia g n o sis a n d treatment. J. Periodont. 27:277 O c t. 1956. 16. G ottlie b , B. T rau m a tic occlu sion a n d the rest position o f the m andible . J. Periodont. 18:7 Ja n. 1947. 17. Leof, M . C la m p in g and g r in d in g habits; their re­ lation to p eriod ontal disease. J .A .D .A . 31:184 Feb. 1944. 18. M iller, S. C., a n d Firestone, J. M . Psychosom atic factors in the e tio lo g y o f p e riod onta l disease. A m . J. O rth o d o n t. & O ra l S u rg. (O ra l S u rg. Sect.) 33:675 Sept. 1947. 19. Landa, J. S. Psychosom atics in relation to p e r­ iod ontics. J. Periodont. 27:209 Ju ly 1956. 20. Sorrin, S. H a b it: an e tio lo g ic facto r of p e rio ­ d onta l disease. D. D ige st 41:290 Sept. 1935. 21. Ingle, J. I. O c c u p a tio n a l bruxism a n d its re la ­ tion to p eriod ontal disease. J. Periodont. 23:7 Jan. 1952. 22. G o ld h a b e r, Paul, a n d G o ld b e r g , H . Extreme occlusal w ear in a yo u n g adult. J. Periodont. 25:50 Jan. 1952. 23. Jankelson, B. P h y sio lo g y o f hum an d e n ta l o cc lu ­ sion. J .A .D .A . 50:664 Ju ne 1955. 24. Hirt, H . A ., a nd M ühlem ann, H . R. D ia g n o sis of bruxism b y m easurem ent o f the tooth m ob ility. D. A b s. 1:356 Ju ne 1956. 25. M atthew s, E. A treatm ent fo r the te e th -grin d ing habit. D. Rec. 62:154 June 1942. 26. Ingersoll, W . B., a n d Kerens, E. G . A treatment fo r excessive occlusal traum a or bruxism . J .A .D .A . 44:22 Jan. 1952. 27. Strother, E. W . t and M itch ell, G . E. Bruxism: a review and a case report. J. D. M e d . 9:189 O c t. 1954. 28. Stahl, D. G . A sim plifie d p ro ce du re fo r fa b ric a t­ ing a tem porary re m ova ble a crylic bite plate. J. P erio­ dont. 27:118 A p r il 1956. 29. Perlow, J. Bruxism: treatm ent o f a case. D. D i­ ge st 64:434 O ct. 1958. 30. G rup e , H . E., a n d G ro m e k, J. J. Bruxism splint. Technique using quick cure a crylic. J. Periodont. 30:156 A p r il 1959. 31. Grew cock, R. J. G .; Thom pson, H., an d T h om p­ son, A . R. F. O cclu sa l e q u ilib ra tio n in ge n e ra l practice. D. Pract. & D. Rec. 5:313 M a y 1955. 32. Ross, I. F. The effects of tenslonal cle n ch in g upon the structures of the neck. J . Periodont. 25:46 Jan. 1954. 33. G e lb e rd , M . B. Treatm ent o f bruxism . A case report. J. H yp n o sis & Psychol, in Den. 1:18 Ja n. 1958. 34. C haslns, A . I. M e th o c a rb a m a l (ro ba xln) as an ad ju n ct in the treatm ent o f bruxism . J. D. M e d . 14:166 Ju ly 1959. 35. G oldstein, M . A clinical In ve stiga tio n o f m ephate In dentistry. D. D ig e st 62:454 O c t.; 498 N o v . 1956. 36. M oyers, R. E. T e m p o ro m a n d ib u la r m uscle co n­ tra ction patterns in A n g le class II, d iv isio n i m a locclu ­ sions: an ele c tro m yo gra p h ic analysis. A m . J. O rth od ont. 35:837 N o v. 1949. 37. M oyers, R. E. A n e le c tro m yo g ra p h ic analysts of certain muscles In volve d in te m p o ro m a n d ib u la r m ove­ ment. A m . J. O rth odont. 36:481 Ju ly 1950.

38. M oye rs, R. E. S o m e p h y sio lo g ic con sid e ratio ns of centric and other jaw relations. J. Pros. Den. 6:183 M a rch 1956. 39. M oyers, R. E. S o m e recent e le c tro m yo gra p h ic findin gs In the o ro -fa clal m uscles. Europe an O rth o d o n t. Soc. Tr. 32:225, 1956. 40. Pruzansky, S. The a p p lic a tio n o f e le c tro m yo gra ­ phy to dental research. J . A .D .A . 44:49 Ja n. 1952. 41. Ja ra b a k, J. R. The a d a p t a b ilit y o f the te m poral a n d masseter m uscles; an e le c tro m yo gra p h ic a l study. A n g le O rth o d o n t. 24:193 O c t. 1954. 42. A c a d e m y o f denture prosthetics. N om e n clature com m ittee. G lo ssa ry o f pro sth o d o n tic term s. J . Pros. Den. M a rch 1956. S u pp le m e n t. 43. Perry, H . T., and H a rris, S. C . Role o f the neuro­ m uscular system In fu nctional a ctivity o f the m andible. J .A .D .A . 48:665 Ju n e 1954. 44. Perry, H . T., Jr. Functional e le c tro m yo gra p h y of the te m poral an d m asseter m uscles in class II, div isio n I m alocclusion a n d excellen t occlusion. A n g le O r th o ­ dont. 25:49 Ja n . 1955. 45. Pruzansky, S. E le c tro m yo gra p h ic m easurem ent of the function o f the m uscles o f m astication In man. Proc. Inst. M e d . 19:315, 1953. 46. Ja ra b a k, J. R. A n e le c tro m yo g ra p h ic an alysis of m uscular an d te m p o ro m a n d ib u la r ]oint d isturba n ce s due to Im ba la n ce s In occlusion . A n g le O rth o d o n t. 26:170 Ju ly 1956. 47. G re e n fie ld, B. E., a n d W yke , B. D. Electrom yo­ g ra p h ic studies of som e o f the m uscles o f m astication. Brit. D. J. 100:129 M a rch 6, 1956. 48. Jankelson, B.; H offm an, G . M ., a n d H e ndron, J. A . The p h y sio lo g y of the sto m a to gn a th ic system. J.A .D .A . 46:375 A p r il 1953. 49. Rlx, R. E. D e g lu titio n an d the teeth. D. J. A u s ­ tralia 18:488 Se p t.-O ct. 1946. 50. Tulley, W . J. M u sc le s a n d the teeth. Proc. Roy. Soc. M ed., Sec. O d o n t. 50:313 M a y 1957. 51. D 'A m ic o , A n g e lo . C a n in e teeth— norm al fun c­ tional relation o f the 'natu ra l teeth o f man. J. South. C a lif. D. A . 26:6 Jan.; 49 Feb.; 127 A p r il; 175 M a y; 194 June; 239 Ju ly 1958. 52. Beyron, H . Stu d ie r a v ocklu sa la fo ra n d rin g a r i. de t a d u lta bettet. Sven. T andlak. Tskr. 45:119 M a y 1952. 53. Shpuntoff, H . t a n d Shpuntoff, W . A stu d y of p h y sio lo g ic rest position a n d centric position by e le c­ tro m yo gra ph y. J. Pros. Den. 6:621 Sept. 1956. 54. Perry, H . T., Jr. M u s c u la r ch an ge s a sso ciate d with te m p o ro m a n d ib u la r joint dysfunction. J .A .D .A . 54:644 M a y 1957. 55. Ja ra b a k, F. R. A n e le c tro m yo g ra p h ic analysis of m uscu lar b e h a v io r In m a n d ib u la r m ovem ents from rest position. J. Pros. Den. 7:682 Sept. 1957. 56. # Latif, A . A n e le c tro m y o g ra p h ic stud y o f the tem ­ poralis m uscle in norm al persons d u rin g selected p o si­ tion s and m ovem ents o f the m a n d ib le . A m . J. O r t h o ­ dont. 43:577 A u g . 1957. 57. H ickey, J. C ., a n d others. E le c tro m yo gra p h y in dental research. Part I. G e o m e tric place m e n t o f ref­ erence electrodes. J. Pros. Den. 8:351 M a rch 1958. 58. Pruzansky, S. Q u a n tita tiv e e le c tro m yo gra p h ic analysis o f m astication. A m . J. O rth od on t. 44:307 A p ril 1958. 59. H ickey, J. C ., a n d others. E le c tro m yo gra p h y in dental research. Part II. Frequency response re qu ire ­ ments. J. Pros. Den. 8:1049 N o v .-D e c . 1958. 60. Parks, J. L. A n e le c tro m y o g ra p h ic a n d mechanlcal_ analysis o f selected a b d o m in a l exercises. Thesis. University of M ic h ig a n , 1959.