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Nocturnal electromyographic evaluation of myofascial pain dysfunction in patients undergoing occlusal splint therapy
The level o f nocturnal muscle activity in 25 patients with m yofascial pain dysfunction was monitored before, during, and after therapy with occlusal splints. Correlations were m ade betw een the severity o f symptoms before treatment and the effectiveness o f the splint in reducing nocturnal activity o f muscles.
N octurnal electrom yographic evaluation of m yofascial p ain dysfunction in patients undergoing occlusal splint th erap y G len n T. C lark, DDS, MS P h y llis L. B eem sterboer, RDH, MS W illia m K. S olb erg, DDS, MSD John D. R ugh, PhD
I t is generally believed that occlusal splints are helpful in the treatment of symptoms of myofascial pain that are associated with the m asticatory system. This assumption has been based primarily on clini cal evaluations of symptoms before and after treat ment with splints. Greene and Laskin1 reported on the effect of various types of occlusal splints in the treatment of patients with myofascial pain. They re ported that the symptoms of myofascial pain of 65% of 40 patients significantly improved with use of full m axillary occlusal splints. They also found com plete or major improvement for 25% of 71 patients with a nonoccluding or placebo splint and im provement for 28% of 60 patients who wore an an terior splint for two weeks. Another study by Block and others2 reported on the use of a soft rubber splint for p atien ts w ith m yofascial pain d ysfu n ction (MPD). This study showed that the symptoms of
myofascial pain of 74% of 19 patients improved with use of this splint. Neither previously mentioned study discussed the effect of occlusal splints on changes in muscle activity. This is important be cause most theories concerning myofascial pain in the masticatory system specify that increased activ ity of the jaw muscle at night is a cause of MPD. Several studies have tried to evaluate changes in muscle activity after treatment with occlusal splints. Jarabak3 showed that resting electrom yographic (EMC) activity of the temporal m uscle was reduced immediately after insertion of the occlusal splint. This activity returned to pretreatment levels five minutes after removal of the splint; continued use of the splint resulted in reduced muscle activity for a longer time. Jarabak’s study did not evaluate the ef fect of splints on nocturnal activity of muscles or the long-term effects of use of a splint for several weeks JADA, Vol. 99, October 1979 ■ 607
or m on th s. It d id , h o w ev er, in d ica te that sp lin ts re d u ce a ctiv ity o f m u sc le s an d that a ctiv ity m ay n ot rem ain lo w after c e ssa tio n o f treatm ent. B eem sterboer and others4 reported on th e duration o f th e s i le n t p eriod before, d u ring, an d after te n p atien ts w ith tem porom and ib u lar join t (TMJ) d y sfu n ctio n w ere treated w ith o c c lu sa l sp lin ts. T he d uration o f the s ile n t p eriod w a s red u ced im m ed ia tely after in sertion o f th e o c c lu sa l sp lin t and rem ain ed lo w after c e ssa tio n o f treatm ent. T here w a s, h o w e v e r, n o fo llo w -u p ex a m in a tio n to ev a lu a te lon g-term ef fects, and n o ev a lu a tio n w a s m ade o f noctu rn al ac tiv ity o f m u scles. Solberg an d others5 m easu red noctu rn al a ctivity o f th e m a ss e te r m u s c le in e ig h t p a tie n ts w ith b ru xism an d fo u n d that, after in sertio n o f a fu ll arch o c c lu sa l sp lin t, m u sc le a ctiv ity w a s red u ced . W hen o c clu sa l sp lin ts w ere rem oved , pretreatm ent EMG le v e ls returned. T h ey c o n c lu d e d that short-term sp lin t therap y (ten days) d id n ot p erm an en tly re d u ce EMG le v e ls. N octurnal a ctiv ity o f th e m astica tory m u s c le s h a s b e e n e x a m in e d b y F u c h s.6 B y stu d y in g a group o f patien ts, h e con firm ed that u se o f a b itep la te red u ces a ctiv ity le v e l o f m asticatory m u sc le s to th e le v e l fo u n d in th e con trol group. F u ch s d id n o t p resen t any data on EMG a ctiv ity after rem oval o f th e sp lin t. B eem sterboer and oth ers7 p u b lish e d an abstract about th e effect o f sp lin t therapy o n sym p tom s an d nocturn al EMG le v e ls in te n pa tien ts w ith m y o fa scia l p ain . In th is stu d y , e ffe c tiv e n ess o f a sp lin t w a s reported to d ep en d on th e in itial severity o f th e sy m p to m s an d th e degree to w h ic h sp lin ts su p p ress th e noctu rnal a ctiv ity o f th e m u s cles. P atien ts w ith few er sy m p to m s o f m y o fascial p ain w ere m ore lik e ly to h a v e a decrease in EMG le v e ls w h e n an o c c lu sa l sp lin t w a s u sed . T h o se pa tien ts w h o h ad a decrease in n octurnal EMG le v e ls w ere reported m ore lik e ly to im p rove in con d ition ; n o fo llo w -u p ev a lu a tio n w a s d o n e to verify lo n g term effects. T he object of th is stu d y w a s to evalu ate ch a n ges in nocturn al a ctiv ity o f m u sc le s in p atien ts u n d erg o in g o c clu sa l sp lin t therapy. E ffectiv en ess o f a sp lin t in red u cin g nocturnal EMG le v e ls w a s a lso evalu ated in regard to severity o f in itia l sy m p to m s o f m yofas cia l p ain . R ecords o f n octu rnal a ctiv ity o f m u sc le s w ere m ade n ig h tly in th e p a tien t’s h o m e before, dur in g , and after u se o f an o c c lu sa l sp lin t.
Materials and methods S e le c tio n o f p a t ie n ts T w en ty -fiv e p atien ts (18 w o m e n an d 7 m en) w ere se le c te d from th e tem porom an dib ular join t c lin ic at th e U n iv ersity o f C alifornia at Los A n g e le s S c h o o l of D entistry. T he average age w a s 2 6 .8 years; ag es ranged from 22 to 50 years. M ed ical h isto ries w ere 6 0 8 ■ J A D A , V o l. 9 9 , O c to b e r 1 9 7 9
taken and all p erson s w ere c lin ic a lly exam in ed . The fo llo w in g criteria w ere used: th e p atien ts had no rem ovab le dentures; th e y w ere n o t m issin g m ore than a tooth per quadrant (ex clu d in g third molars); th ey had n o current sy ste m ic d iseases; th e y w ere free from den tal in fection s; and th ey w ere n ot taking m ed ication s. W ith u se o f a screen in g q u estion n aire, the pa tie n ts’ “su b jectiv e” jaw d y sfu n c tio n w a s c la ssified as a score o f either 0 = n o sy m p tom s, 1 = m ild sym p tom s, or 2 = severe sy m p tom s. C lin ical ex a m i n ation p rovid ed an in d e x o f “c lin ic a l” jaw d y sfu n c tio n that w a s based o n th e range o f m andibular m ovem en t, degree o f fu n ctio n a l im p airm en t o f the TMJ, a m ou n t o f m u sc le p a in d u rin g p a lp a tio n , am ou n t o f TMJ p a in d u rin g p alp ation , and p resen ce o f p ain during m o v em en ts o f th e border o f th e m an dib le. T he score from th e c lin ic a l ex am in ation o f jaw d y s f u n c t io n w a s th e n ra ted as e ith e r 0 = n o sy m p to m s, 1 = m ild s y m p to m s , 2 = m o d e ra te sym p tom s, or 3 = severe sym p tom s. Criteria and m eth od o f scorin g for b oth in d e x e s w ere id e n tica l to th o se o u tlin ed b y H elk im o .8 B y ad d in g th e score of both in d e x es, a co m b in ed cla ssifica tio n o f jaw d y s fu n c tio n w a s e sta b lish ed : 0 to 1 — little or no sym p tom s o f d ysfu n ction ; 2 to 3 — m ild to m oderate s y m p to m s o f d y s fu n c tio n ; or 4 to 5 — se v e r e sym p tom s o f d y sfu n ction .
E le c tr o m y o g r a p h y A portable EMG recording u n it w a s u se d w ith each patient.. T he com pact, portable EMG u n it d irectly m easured nocturnal activ ity o f th e m asseter m u scle. It has b een d escrib ed b y R ugh and S olb erg9 and R u g h .10 Each patient w a s in stru cted on u se o f the EMG u n it and a p p lica tio n o f the electrod e. To en sure that recorders w er e properly u sed , th e patients dem onstrated th e u se to th e experim enter. T he pa tien ts a p p lied th e surface electrod e assem b ly over the m asseter m u sc le w ith u se o f su rgical tape. T he EMG u n it p ro v id ed cu m u la tiv e totals o f e le c trical a ctivity o f the m asseter m u sc le above 20 /xV. T he criterion o f 20 /u.V w a s se le c te d to p revent rec ord in g o f m in or con traction s o f th e m asseter m u sc le that c o u ld n o t be d e fin ed as c le n c h in g or grinding. T he recording u n its w ere calibrated so that a 100 /jlV, 300 Hz sig n a l m a in ta in ed for a se co n d p rovid ed a readout o f 1 “EMG u n it.” R ep eated prelim in ary m easures in d ica ted that 1 EMG u n it w a s eq u ivalen t to a strong m u scu lar con traction o f ap p roxim ately 1 - s e c o n d d u r a t io n . S im ila r ly , f i v e r h y t h m ic c le n c h e s o f th e teeth p rod u ced a readout o f approx im ately fiv e EMG u n its. A ll person s w ere tested to en su re that th e recording w as w ith in th e accep tab le range. T he EMG u n it w a s activated at n ig h t after th e pa tien ts h ad retired and it recorded unilateral a ctivity
of the masseter m uscle during the hours of sleep. In the morning, the total activity of the masseter m us cle (above threshold) and amount of time slept were recorded by the patients. The patients were given the recording units and a supply of electrode paste, surgical tape, instruction sheets, and data cards. They returned after two weeks. Ten nights of re cordings were required before treatm ent with occlu sal splints. At the second appointment, full arch maxillary stabilization splints were fitted and adjusted accord ing to criteria determined by Ramfjord and A sh .11 A week after insertion, any necessary adjustments to the splint were done. The splint used for this part of the study was a full arch m axillary occlusal splint with a vertical opening of approxim ately 2 mm in the region of the molar. The patients were instructed to wear the splints all night and as m uch of the day as possible for at least 14 days. Nocturnal EMG levels were recorded for a minimum of ten days, both during and after the treatm ent with splints. EMG data were subjected to a t-test; differences be fore, during, and after treatment were evaluated.
Fig 2 ■ L evels o f a c tiv ity o f m a s s e te r m u scles a t n ig h t b efo re, d u rin g , a n d a fte r o c c lu sa l s p lin t th e ra p y for one p a tie n t. F ig u re re p re s e n ts p a tie n t w h o h a d n o c h a n g e in n o c tu rn a l EM G le v e ls d u rin g th e ra p y .
Results Of all patients, 17 had moderate symptoms and eight showed severe symptoms, according to the com bined index of jaw dysfunction. Usually, the most frequent subjective com plaint was a dull aching pain around the region of the TMJ. The most com mon (15 of 25 patients) clinical finding was that muscles of mastication were tender when examined. No one reported a history of dislocation of the TMJ, locking in a closed position, or severe symptoms of impaired function of the joints. Use of an occlusal splint had varied effects on nocturnal activity of the masseter m uscle (Fig 1-3). Results are summarized in Figure 4. Nocturnal EMG levels were significantly reduced during use of splints in 13 (52%) of the 25 patients. Seven of the
Fig 3 ■ L evels o f a ctiv ity o f m a s s e te r m u scles a t n ig h t b efo re, d u r in g , a n d a fte r o c clu sa l s p lin t th e ra p y fo r o n e p a tie n t. F ig u re re p re s e n ts p a tie n t w h o h a d s ig n ific a n t in c re a s e in n o c tu rn a l EM G le v e ls d u rin g th e ra p y .
F ig 4 ■ Effect o f o c clu sa l s p lin t th e ra p y o n a c tiv ity o f m a ss e te r m u scles a t n ig h t. E ach g ro u p re p re s e n ts p e rc e n ta g e o f to ta l p a tie n ts w h o sh o w e d e ith e r s ig n ific a n t d e crea se, in c re a se , o r n o c h a n g e in EM G lev els d u rin g th e ra p y .
Fig 1 ■ L evels o f n o c tu rn a l a c tiv ity o f m a ss e te r m u s c le s b efo re, d u rin g , a n d a fte r o c c lu sa l s p lin t th e ra p y fo r o n e p a tie n t. F ig u re re p re s e n ts p a tie n t w h o h a d s ig n ific a n t re d u c tio n in n o c tu rn a l EM G lev els d u rin g th e ra p y .
patients (28%) had no change and five (20%) had a significant increase in nocturnal EMG levels. Of the 13 who had a significant decrease in EMG levels during the use of splints, 12 returned to pretreat ment levels when the splint was rem oved. Dif ferences in mean EMG levels before, during, and after use of splints are shown in the Table. Effects of the splint on nocturnal EMG levels are Clark-others : EVALUATION OF MYOFASCIAL PAIN DYSFUNCTION ■ 609
T able ■ D ifferences in mean n o cturn a l E M G levels* (before-during) and (duringafte r) treatm ent w ith occlusal sp lin t. Patient
Before-during
During-aftcr
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
56.4f 24.3t 47.3f 43.7t 30.4f 44.lt 48.2f 23.lt 7.3f 19.9t 17.4t 36.0t 13.8t 10.4 8.2 5.6 14.0 - 8.2 -18.6 -22.0 -14.0t -17.8t - 9.9t —23.2t —33.5t
—97.5t —10.2f —32.5t —28.8t —21.3t - 1 6 .l t - 2 9 .l t —11.4t - 8.1t —31.8t - 2.0 —45.0t - 3 1 .lt - 0.1 - 1 8 .l t -1 5 .5 t - 8.5t - 2.2 - 6.2 - 4.6 -1 9 .8 t 43.5t 7.9$ 10.7$ 16.5t
‘Masseter activity per hour of sleep. tSignificantly different at the .05 level. Note: A negative EMG value indicates the relative differ ence was increased either during or after treatment.
symptom group
symptom group
F ig 5 ■ Effect o f o c c lu sa l s p lin t o n EM G le v e ls a t n ig h t fo r p a tie n ts w ith e ith e r m o d e ra te o r s e v e re sy m p to m s. E a c h p e rc e n ta g e s h o w n is p e rc e n t a g e o f p a tie n ts in e a c h g ro u p in w h o m EM G le v e ls s ig n ific a n tly d e c re a s e d d u rin g tre a tm e n t.
compared according to severity of symptoms before treatm ent (Fig 5). Those with moderate symptoms were more likely to have a reduction in nocturnal EMG levels. Of the group with moderate symptoms, 64% had a significant decrease in nocturnal EMG lev e l, w h ereas 25% of the group w ith severe symptoms showed a similar reduction.
Discussion This study confirms earlier research and shows that full arch m axillary occlusal splints can affect the nocturnal activity of muscles. The effects observed here, however, are not consistent; they were not al 610 ■ JADA, Vol. 99, October 1979
ways in a positive direction. In this study, 52% of the p a tie n ts s h o w e d th e e x p e c te d r e d u c tio n in nocturnal EMG levels during use of splints. Of con cern is the finding that 24% showed no change and that 20% had an increase in nocturnal m uscle activ ity during use of splints. In an earlier study on effec tiveness of splints for a sample of eight persons with bruxism, Solberg and others5 reported significant reductions in nocturnal activity of masseter muscles in all patients. Results of this study on patients with MPD are not as encouraging; only half had signifi cant reductions in muscle activity. Several factors may account for the differential ef fectiveness of the splint. Effectiveness may differ because of characteristics of the splint, of the pa tients, or because of a combination of characteristics of splints and patients. With respect to characteris tic s of the p a tie n ts , th ese data and th o se of Beemsterboer and others7 suggest that splints are less apt to reduce nocturnal activity of m uscle in pa tients with more severe symptoms of MPD. A l though the rationale for such differential effects is unclear, the results are consistent. Differential effects of the splint on nighttime ac tivity of muscles may also depend on factors such as the causes of the original symptoms, or occlusal fac tors, or characteristics of the splint. Drago and others12 have shown recently that the vertical thick ness of the splint dramatically influences its effec tiveness in reducing nocturnal activity of muscles. When measured in the anterior region, a thin (2 mm) splint was ideal for some patients, whereas others were best treated with relatively thick (6 mm) splints. Several interacting variables that will influ ence the splint’s effectiveness on m uscle activity may be found. These variables will require careful experimental evaluation before recommendations can be made for clinical treatment. Results of this study on patients with MPD are consistent with earlier studies3'5,9 which found the effects of the splint on nocturnal activity of muscles to be of short-term duration. Of the 13 patients in this study in whom activity of muscle decreased with use of a splint, 12 returned to pretreatment levels when use was stopped. Inspection of the nightly recordings shows that the return to pre treatment EMG levels was usually immediate, that is, on the first night that treatment was stopped (Fig 1). The results support clinical observations that therapeutic use of a splint usually requires extended use. Premature termination of use may account for the recurrence of symptoms in some patients. Although activity of muscles returned to pretreatment levels when the splint was removed, acute myofascial pain did not return to most patients. A direct relationship between nocturnal activity of the masseter m uscle and symptoms of MPD is not estab lished. Long-term evaluations are needed that
m on itor m u sc le a c tiv ity and th e sy m p to m s o f jaw d y sfu n ctio n before, d urin g, an d after therap y w ith o c c lu sa l sp lin ts . A rela tio n sh ip b e tw e e n m u sc le h y p er a c tiv ity a n d m y o fa sc ia l p a in h a s b e e n a s su m ed in m a n y ca u sa l th eo ries but h a s n o t b e e n em p irica lly d o cu m en ted . A red u ctio n in noctu rn al a ctiv ity o f m u sc le s is probably n o t a n ecessa ry c o n d itio n for im p ro v em en t o f sy m p to m s w ith u se o f sp lin ts. A lth o u g h n o s y s tem atic records w e r e kept, it w a s o b served that a m ajority o f th e p a tie n ts s h o w e d su b je c tiv e im p rovem en t in sy m p to m s, so m e e v e n w ith an in crease in n octu rn a l EMG le v e ls. T he e ffe c tiv en ess o f the sp lin t w a s o b v io u sly a c h ie v e d th rou gh an alter n ative effect. A lternate ex p la n a tio n s for im p ro v e m en t o f sy m p to m s in clu d e: red istrib u tio n o f oral f o r c e s , or r e d u c in g h y p e r a c t iv it y o f m u s c le s (parafunctional a ctivity) during w a k in g h ours. A s d isc u sse d b y G reene a n d L askin,1 m an y other factors m ay acco u n t for th e reported su c c e ss o f sp lin ts. It is d ifficu lt to d istin g u ish th e p la ceb o effect o f v isitin g a “TMJ s p e c ia lis t.” A lso , th e d ecreased v a lid ity o f u sin g su b jectiv e reports b y p atien ts o f im p ro v em en t in their c o n d itio n s m u st be co n sid ered . S p lin ts u se d in th is stu d y w ere carefu lly d e sig n e d w ith atten tio n to th e o c c lu sa l pattern. It is u n clear w h eth er a particular o c c lu sa l pattern is n ecessa ry for th e o b tain ed effect. W h en th e variety o f sp lin ts u se d in c lin ic a l practice are co n sid ered , it se e m s u n lik e ly that a sp e c ific o c c lu sa l d e sig n o f th e sp lin t is n ecessary for its effect. H ow ever, th e u se o f a p o o rly fittin g or p o o r ly a d ju ste d s p lin t is n o t r e c o m m en d ed . O n th e b a sis o f c lin ic a l ex p erien ce, th is ty p e o f o c c lu s a l s p lin t m a y c a u se u n p r e d ic te d m o v em en t o f teeth or m ay aggravate th e sy m p to m s o f jaw d y sfu n ctio n .
Conclusion T w en ty -fiv e p a tien ts w ith sy m p to m s o f m y o fa scial p a in and abnorm al jaw fu n c tio n w ere treated w ith u se of a fu ll arch m axilla ry o c c lu sa l sp lin t. T he le v e l o f nocturnal a ctiv ity o f the m asseter m u sc le w as m on itored as w e r e sy m p to m s before, d urin g, and
after o c c lu sa l sp lin t therapy. A d ecreased nocturnal EMG le v e l d uring treatm ent w a s n o ted for 52% o f the patien ts. A return to pretreatm ent EMG le v e ls after rem oval o f the sp lin t w a s n o tice d in 92% o f the patients; in 28% n o ch an ge w a s sh o w n and in 20%, an in crease w a s sh o w n in nocturnal EMG le v e ls. T he sp lin t w a s m ost lik e ly to red u ce nocturnal EMG le v e ls in p atien ts w ith least severe sym p tom s. T h e in fo rm e d c o n se n t of a ll su b jec ts w h o p a rtic ip a te d in th e e x p e ri m e n ta l in v e stig a tio n re p o rte d in th is m a n u s c rip t w a s o b ta in e d a fte r th e n a tu re of th e p ro c e d u re s a n d p o s sib le d isco m fo rts a n d ris k s h a d b e e n fu lly e x p la in e d . Dr. C la rk is a ss is ta n t p ro fesso r, s e c tio n o f g n a th o lo g y a n d o c c lu sio n , a n d is re s e a rc h d ire c to r, U CLA T e m p o ro m a n d ib u la r J o in t a n d F a c ia l P a in C lin ic , U n iv e rsity o f C alifornia, Los A n g eles, S ch o o l o f D en tistry . M s. B ee m ste rb o e r is re s e a rc h a s s is ta n t a n d D r. S o lb erg is p ro fesso r, s e c tio n o f g n a th o lo g y a n d o c c lu sio n , U CLA. Dr. R u g h is a s s is ta n t p ro fesso r, d e p a rt m e n t o f o c c lu sio n , U n iv e rsity o f T exas, S a n A n to n io . A d d re ss re q u e sts for re p rin ts to Dr. C lark, S e c tio n o f G n a th o lo g y a n d O c c lu sio n , S c h o o l o f D en tis try , U n iv e rs ity o f C alifo rn ia , T h e C e n te r fo r H e a lth S c ie n c e s, Los A n g eles, 90024. 1. G reen e, C .S., a n d L askin, D.M . S p lin t th e ra p y for th e m y o fascial p a i n - d y s f u n c t i o n (M PD ) s y n d r o m e : a c o m p a r a tiv e s tu d y . JA D A 8 4 (3 ):6 2 4 -6 2 8 ,1972. 2. B lock, S.L.; A p fe l, M .; a n d L ask in , D .M . T h e u s e o f a re s ilie n t ru b b e r b ite a p p lia n c e in th e tre a tm e n t o f M PD sy n d ro m e . J D en t R es 5 7 :A 7 1 ,1978. 3. Jarab a k , J.R. E le c tro m y o g ra p h ic a n a ly s is o f m u s c u la r a n d te m p o ro m a n d ib u la r jo in t d is tu rb a n c e s d u e to im b a la n c e s in o c c lu sio n . A n g le O rth o d o n t 26 :1 7 0 -1 9 0 ,1 9 5 6 . 4. B eem sterb o er, P.L., a n d o th e rs. T h e effect o f th e b ite p la n e s p lin t o n th e e le c tro m y o g ra p h ic s ile n t p e rio d d u ra tio n . J O ral R e h a b il 3{4):349-352, 1976. 5. S o lb e rg , W .K .; C la rk , G .T .; a n d R u g h , J.D. N o c tu rn a l e le c tr o m y o g ra p h ic e v a lu a tio n o f b ru x is m p a tie n ts u n d e rg o in g s h o rt te rm s p lin t th e ra p y . J O ra l R eh a b il 2 (3 ):2 1 5 -2 2 3 ,1975. 6. F u c h s , P. T h e m u s c u la r a c tiv ity o f th e c h e w in g a p p a ra tu s d u rin g n ig h t slee p . A n e x a m in a tio n o f h e a lth y su b jec ts a n d p a tie n ts w ith fu n c tio n a l d is tu rb a n c e s . ) O ra l R eh a b il 2 (l) :3 5 -4 8 ,1975. 7. B eem sterb o er, P.L.; S o lb erg , W .K.; a n d R ugh, J.D. O c c lu sa l th e ra p y : n o c tu rn a l e le c tro m y o g ra p h ic re s p o n se a n d sy m p to m im p ro v e m e n t. J D ent R es 5 5 :B 1 5 9 ,1976. 8. H e lk im o , M . E p id e m io lo g ic a l su rv e y o f d y s fu n c tio n of th e m a stica to ry sy ste m . O ra l S c i R ev 7 :5 4 -6 9 ,1 9 7 6 . 9. R u g h , J.D., a n d Solberg, W .K. E lec tro m y o g rap h ic s tu d ie s o f b ru x is t b e h a v io r b efo re a n d d u rin g tre a tm e n t. C alif D e n t A ssoc J 3 (9 ):5 6 -5 9 ,1975. 10. R u g h , J.D. E lec tro m y o g rap h ic a n a ly sis o f b ru x is m in th e n a tu ra l e n v iro n m e n t. A d v a n ce s in b e h a v io ra l re s e a rc h in d e n tistry . S e a ttle , U n iv e r s ity o f W ash in g to n , 1978, p p 67-83. 11. R am fjord, S.P., a n d A sh , M .M ., Jr. (eds.). O c clu sio n . P h ila d e lp h ia , W . B. S a u n d e rs Co., 1971, p 427. 12. D rago, C.J.; R ugh, J.D.; a n d B arghi, M . N ig h tg u a rd v e rtic a l th ic k n e ss effects o n n o c tu rn a l b ru x ism . J D e n t R es 5 8 :A 9 0 1 ,1979.
Clark-others : EVALUATION OF MYOFASCIAL PAIN DYSFUNCTION ■ 611
N octurnal electrom yographic evaluation of m yofascial p ain dysfunction in patients undergoing occlusal splint th erap y G len n T. C lark, DDS, MS P h y llis L. B eem sterboer, RDH, MS W illia m K. S olb erg, DDS, MSD John D. R ugh, PhD
I t is generally believed that occlusal splints are helpful in the treatment of symptoms of myofascial pain that are associated with the m asticatory system. This assumption has been based primarily on clini cal evaluations of symptoms before and after treat ment with splints. Greene and Laskin1 reported on the effect of various types of occlusal splints in the treatment of patients with myofascial pain. They re ported that the symptoms of myofascial pain of 65% of 40 patients significantly improved with use of full m axillary occlusal splints. They also found com plete or major improvement for 25% of 71 patients with a nonoccluding or placebo splint and im provement for 28% of 60 patients who wore an an terior splint for two weeks. Another study by Block and others2 reported on the use of a soft rubber splint for p atien ts w ith m yofascial pain d ysfu n ction (MPD). This study showed that the symptoms of
myofascial pain of 74% of 19 patients improved with use of this splint. Neither previously mentioned study discussed the effect of occlusal splints on changes in muscle activity. This is important be cause most theories concerning myofascial pain in the masticatory system specify that increased activ ity of the jaw muscle at night is a cause of MPD. Several studies have tried to evaluate changes in muscle activity after treatment with occlusal splints. Jarabak3 showed that resting electrom yographic (EMC) activity of the temporal m uscle was reduced immediately after insertion of the occlusal splint. This activity returned to pretreatment levels five minutes after removal of the splint; continued use of the splint resulted in reduced muscle activity for a longer time. Jarabak’s study did not evaluate the ef fect of splints on nocturnal activity of muscles or the long-term effects of use of a splint for several weeks JADA, Vol. 99, October 1979 ■ 607
or m on th s. It d id , h o w ev er, in d ica te that sp lin ts re d u ce a ctiv ity o f m u sc le s an d that a ctiv ity m ay n ot rem ain lo w after c e ssa tio n o f treatm ent. B eem sterboer and others4 reported on th e duration o f th e s i le n t p eriod before, d u ring, an d after te n p atien ts w ith tem porom and ib u lar join t (TMJ) d y sfu n ctio n w ere treated w ith o c c lu sa l sp lin ts. T he d uration o f the s ile n t p eriod w a s red u ced im m ed ia tely after in sertion o f th e o c c lu sa l sp lin t and rem ain ed lo w after c e ssa tio n o f treatm ent. T here w a s, h o w e v e r, n o fo llo w -u p ex a m in a tio n to ev a lu a te lon g-term ef fects, and n o ev a lu a tio n w a s m ade o f noctu rn al ac tiv ity o f m u scles. Solberg an d others5 m easu red noctu rn al a ctivity o f th e m a ss e te r m u s c le in e ig h t p a tie n ts w ith b ru xism an d fo u n d that, after in sertio n o f a fu ll arch o c c lu sa l sp lin t, m u sc le a ctiv ity w a s red u ced . W hen o c clu sa l sp lin ts w ere rem oved , pretreatm ent EMG le v e ls returned. T h ey c o n c lu d e d that short-term sp lin t therap y (ten days) d id n ot p erm an en tly re d u ce EMG le v e ls. N octurnal a ctiv ity o f th e m astica tory m u s c le s h a s b e e n e x a m in e d b y F u c h s.6 B y stu d y in g a group o f patien ts, h e con firm ed that u se o f a b itep la te red u ces a ctiv ity le v e l o f m asticatory m u sc le s to th e le v e l fo u n d in th e con trol group. F u ch s d id n o t p resen t any data on EMG a ctiv ity after rem oval o f th e sp lin t. B eem sterboer and oth ers7 p u b lish e d an abstract about th e effect o f sp lin t therapy o n sym p tom s an d nocturn al EMG le v e ls in te n pa tien ts w ith m y o fa scia l p ain . In th is stu d y , e ffe c tiv e n ess o f a sp lin t w a s reported to d ep en d on th e in itial severity o f th e sy m p to m s an d th e degree to w h ic h sp lin ts su p p ress th e noctu rnal a ctiv ity o f th e m u s cles. P atien ts w ith few er sy m p to m s o f m y o fascial p ain w ere m ore lik e ly to h a v e a decrease in EMG le v e ls w h e n an o c c lu sa l sp lin t w a s u sed . T h o se pa tien ts w h o h ad a decrease in n octurnal EMG le v e ls w ere reported m ore lik e ly to im p rove in con d ition ; n o fo llo w -u p ev a lu a tio n w a s d o n e to verify lo n g term effects. T he object of th is stu d y w a s to evalu ate ch a n ges in nocturn al a ctiv ity o f m u sc le s in p atien ts u n d erg o in g o c clu sa l sp lin t therapy. E ffectiv en ess o f a sp lin t in red u cin g nocturnal EMG le v e ls w a s a lso evalu ated in regard to severity o f in itia l sy m p to m s o f m yofas cia l p ain . R ecords o f n octu rnal a ctiv ity o f m u sc le s w ere m ade n ig h tly in th e p a tien t’s h o m e before, dur in g , and after u se o f an o c c lu sa l sp lin t.
Materials and methods S e le c tio n o f p a t ie n ts T w en ty -fiv e p atien ts (18 w o m e n an d 7 m en) w ere se le c te d from th e tem porom an dib ular join t c lin ic at th e U n iv ersity o f C alifornia at Los A n g e le s S c h o o l of D entistry. T he average age w a s 2 6 .8 years; ag es ranged from 22 to 50 years. M ed ical h isto ries w ere 6 0 8 ■ J A D A , V o l. 9 9 , O c to b e r 1 9 7 9
taken and all p erson s w ere c lin ic a lly exam in ed . The fo llo w in g criteria w ere used: th e p atien ts had no rem ovab le dentures; th e y w ere n o t m issin g m ore than a tooth per quadrant (ex clu d in g third molars); th ey had n o current sy ste m ic d iseases; th e y w ere free from den tal in fection s; and th ey w ere n ot taking m ed ication s. W ith u se o f a screen in g q u estion n aire, the pa tie n ts’ “su b jectiv e” jaw d y sfu n c tio n w a s c la ssified as a score o f either 0 = n o sy m p tom s, 1 = m ild sym p tom s, or 2 = severe sy m p tom s. C lin ical ex a m i n ation p rovid ed an in d e x o f “c lin ic a l” jaw d y sfu n c tio n that w a s based o n th e range o f m andibular m ovem en t, degree o f fu n ctio n a l im p airm en t o f the TMJ, a m ou n t o f m u sc le p a in d u rin g p a lp a tio n , am ou n t o f TMJ p a in d u rin g p alp ation , and p resen ce o f p ain during m o v em en ts o f th e border o f th e m an dib le. T he score from th e c lin ic a l ex am in ation o f jaw d y s f u n c t io n w a s th e n ra ted as e ith e r 0 = n o sy m p to m s, 1 = m ild s y m p to m s , 2 = m o d e ra te sym p tom s, or 3 = severe sym p tom s. Criteria and m eth od o f scorin g for b oth in d e x e s w ere id e n tica l to th o se o u tlin ed b y H elk im o .8 B y ad d in g th e score of both in d e x es, a co m b in ed cla ssifica tio n o f jaw d y s fu n c tio n w a s e sta b lish ed : 0 to 1 — little or no sym p tom s o f d ysfu n ction ; 2 to 3 — m ild to m oderate s y m p to m s o f d y s fu n c tio n ; or 4 to 5 — se v e r e sym p tom s o f d y sfu n ction .
E le c tr o m y o g r a p h y A portable EMG recording u n it w a s u se d w ith each patient.. T he com pact, portable EMG u n it d irectly m easured nocturnal activ ity o f th e m asseter m u scle. It has b een d escrib ed b y R ugh and S olb erg9 and R u g h .10 Each patient w a s in stru cted on u se o f the EMG u n it and a p p lica tio n o f the electrod e. To en sure that recorders w er e properly u sed , th e patients dem onstrated th e u se to th e experim enter. T he pa tien ts a p p lied th e surface electrod e assem b ly over the m asseter m u sc le w ith u se o f su rgical tape. T he EMG u n it p ro v id ed cu m u la tiv e totals o f e le c trical a ctivity o f the m asseter m u sc le above 20 /xV. T he criterion o f 20 /u.V w a s se le c te d to p revent rec ord in g o f m in or con traction s o f th e m asseter m u sc le that c o u ld n o t be d e fin ed as c le n c h in g or grinding. T he recording u n its w ere calibrated so that a 100 /jlV, 300 Hz sig n a l m a in ta in ed for a se co n d p rovid ed a readout o f 1 “EMG u n it.” R ep eated prelim in ary m easures in d ica ted that 1 EMG u n it w a s eq u ivalen t to a strong m u scu lar con traction o f ap p roxim ately 1 - s e c o n d d u r a t io n . S im ila r ly , f i v e r h y t h m ic c le n c h e s o f th e teeth p rod u ced a readout o f approx im ately fiv e EMG u n its. A ll person s w ere tested to en su re that th e recording w as w ith in th e accep tab le range. T he EMG u n it w a s activated at n ig h t after th e pa tien ts h ad retired and it recorded unilateral a ctivity
of the masseter m uscle during the hours of sleep. In the morning, the total activity of the masseter m us cle (above threshold) and amount of time slept were recorded by the patients. The patients were given the recording units and a supply of electrode paste, surgical tape, instruction sheets, and data cards. They returned after two weeks. Ten nights of re cordings were required before treatm ent with occlu sal splints. At the second appointment, full arch maxillary stabilization splints were fitted and adjusted accord ing to criteria determined by Ramfjord and A sh .11 A week after insertion, any necessary adjustments to the splint were done. The splint used for this part of the study was a full arch m axillary occlusal splint with a vertical opening of approxim ately 2 mm in the region of the molar. The patients were instructed to wear the splints all night and as m uch of the day as possible for at least 14 days. Nocturnal EMG levels were recorded for a minimum of ten days, both during and after the treatm ent with splints. EMG data were subjected to a t-test; differences be fore, during, and after treatment were evaluated.
Fig 2 ■ L evels o f a c tiv ity o f m a s s e te r m u scles a t n ig h t b efo re, d u rin g , a n d a fte r o c c lu sa l s p lin t th e ra p y for one p a tie n t. F ig u re re p re s e n ts p a tie n t w h o h a d n o c h a n g e in n o c tu rn a l EM G le v e ls d u rin g th e ra p y .
Results Of all patients, 17 had moderate symptoms and eight showed severe symptoms, according to the com bined index of jaw dysfunction. Usually, the most frequent subjective com plaint was a dull aching pain around the region of the TMJ. The most com mon (15 of 25 patients) clinical finding was that muscles of mastication were tender when examined. No one reported a history of dislocation of the TMJ, locking in a closed position, or severe symptoms of impaired function of the joints. Use of an occlusal splint had varied effects on nocturnal activity of the masseter m uscle (Fig 1-3). Results are summarized in Figure 4. Nocturnal EMG levels were significantly reduced during use of splints in 13 (52%) of the 25 patients. Seven of the
Fig 3 ■ L evels o f a ctiv ity o f m a s s e te r m u scles a t n ig h t b efo re, d u r in g , a n d a fte r o c clu sa l s p lin t th e ra p y fo r o n e p a tie n t. F ig u re re p re s e n ts p a tie n t w h o h a d s ig n ific a n t in c re a s e in n o c tu rn a l EM G le v e ls d u rin g th e ra p y .
F ig 4 ■ Effect o f o c clu sa l s p lin t th e ra p y o n a c tiv ity o f m a ss e te r m u scles a t n ig h t. E ach g ro u p re p re s e n ts p e rc e n ta g e o f to ta l p a tie n ts w h o sh o w e d e ith e r s ig n ific a n t d e crea se, in c re a se , o r n o c h a n g e in EM G lev els d u rin g th e ra p y .
Fig 1 ■ L evels o f n o c tu rn a l a c tiv ity o f m a ss e te r m u s c le s b efo re, d u rin g , a n d a fte r o c c lu sa l s p lin t th e ra p y fo r o n e p a tie n t. F ig u re re p re s e n ts p a tie n t w h o h a d s ig n ific a n t re d u c tio n in n o c tu rn a l EM G lev els d u rin g th e ra p y .
patients (28%) had no change and five (20%) had a significant increase in nocturnal EMG levels. Of the 13 who had a significant decrease in EMG levels during the use of splints, 12 returned to pretreat ment levels when the splint was rem oved. Dif ferences in mean EMG levels before, during, and after use of splints are shown in the Table. Effects of the splint on nocturnal EMG levels are Clark-others : EVALUATION OF MYOFASCIAL PAIN DYSFUNCTION ■ 609
T able ■ D ifferences in mean n o cturn a l E M G levels* (before-during) and (duringafte r) treatm ent w ith occlusal sp lin t. Patient
Before-during
During-aftcr
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
56.4f 24.3t 47.3f 43.7t 30.4f 44.lt 48.2f 23.lt 7.3f 19.9t 17.4t 36.0t 13.8t 10.4 8.2 5.6 14.0 - 8.2 -18.6 -22.0 -14.0t -17.8t - 9.9t —23.2t —33.5t
—97.5t —10.2f —32.5t —28.8t —21.3t - 1 6 .l t - 2 9 .l t —11.4t - 8.1t —31.8t - 2.0 —45.0t - 3 1 .lt - 0.1 - 1 8 .l t -1 5 .5 t - 8.5t - 2.2 - 6.2 - 4.6 -1 9 .8 t 43.5t 7.9$ 10.7$ 16.5t
‘Masseter activity per hour of sleep. tSignificantly different at the .05 level. Note: A negative EMG value indicates the relative differ ence was increased either during or after treatment.
symptom group
symptom group
F ig 5 ■ Effect o f o c c lu sa l s p lin t o n EM G le v e ls a t n ig h t fo r p a tie n ts w ith e ith e r m o d e ra te o r s e v e re sy m p to m s. E a c h p e rc e n ta g e s h o w n is p e rc e n t a g e o f p a tie n ts in e a c h g ro u p in w h o m EM G le v e ls s ig n ific a n tly d e c re a s e d d u rin g tre a tm e n t.
compared according to severity of symptoms before treatm ent (Fig 5). Those with moderate symptoms were more likely to have a reduction in nocturnal EMG levels. Of the group with moderate symptoms, 64% had a significant decrease in nocturnal EMG lev e l, w h ereas 25% of the group w ith severe symptoms showed a similar reduction.
Discussion This study confirms earlier research and shows that full arch m axillary occlusal splints can affect the nocturnal activity of muscles. The effects observed here, however, are not consistent; they were not al 610 ■ JADA, Vol. 99, October 1979
ways in a positive direction. In this study, 52% of the p a tie n ts s h o w e d th e e x p e c te d r e d u c tio n in nocturnal EMG levels during use of splints. Of con cern is the finding that 24% showed no change and that 20% had an increase in nocturnal m uscle activ ity during use of splints. In an earlier study on effec tiveness of splints for a sample of eight persons with bruxism, Solberg and others5 reported significant reductions in nocturnal activity of masseter muscles in all patients. Results of this study on patients with MPD are not as encouraging; only half had signifi cant reductions in muscle activity. Several factors may account for the differential ef fectiveness of the splint. Effectiveness may differ because of characteristics of the splint, of the pa tients, or because of a combination of characteristics of splints and patients. With respect to characteris tic s of the p a tie n ts , th ese data and th o se of Beemsterboer and others7 suggest that splints are less apt to reduce nocturnal activity of m uscle in pa tients with more severe symptoms of MPD. A l though the rationale for such differential effects is unclear, the results are consistent. Differential effects of the splint on nighttime ac tivity of muscles may also depend on factors such as the causes of the original symptoms, or occlusal fac tors, or characteristics of the splint. Drago and others12 have shown recently that the vertical thick ness of the splint dramatically influences its effec tiveness in reducing nocturnal activity of muscles. When measured in the anterior region, a thin (2 mm) splint was ideal for some patients, whereas others were best treated with relatively thick (6 mm) splints. Several interacting variables that will influ ence the splint’s effectiveness on m uscle activity may be found. These variables will require careful experimental evaluation before recommendations can be made for clinical treatment. Results of this study on patients with MPD are consistent with earlier studies3'5,9 which found the effects of the splint on nocturnal activity of muscles to be of short-term duration. Of the 13 patients in this study in whom activity of muscle decreased with use of a splint, 12 returned to pretreatment levels when use was stopped. Inspection of the nightly recordings shows that the return to pre treatment EMG levels was usually immediate, that is, on the first night that treatment was stopped (Fig 1). The results support clinical observations that therapeutic use of a splint usually requires extended use. Premature termination of use may account for the recurrence of symptoms in some patients. Although activity of muscles returned to pretreatment levels when the splint was removed, acute myofascial pain did not return to most patients. A direct relationship between nocturnal activity of the masseter m uscle and symptoms of MPD is not estab lished. Long-term evaluations are needed that
m on itor m u sc le a c tiv ity and th e sy m p to m s o f jaw d y sfu n ctio n before, d urin g, an d after therap y w ith o c c lu sa l sp lin ts . A rela tio n sh ip b e tw e e n m u sc le h y p er a c tiv ity a n d m y o fa sc ia l p a in h a s b e e n a s su m ed in m a n y ca u sa l th eo ries but h a s n o t b e e n em p irica lly d o cu m en ted . A red u ctio n in noctu rn al a ctiv ity o f m u sc le s is probably n o t a n ecessa ry c o n d itio n for im p ro v em en t o f sy m p to m s w ith u se o f sp lin ts. A lth o u g h n o s y s tem atic records w e r e kept, it w a s o b served that a m ajority o f th e p a tie n ts s h o w e d su b je c tiv e im p rovem en t in sy m p to m s, so m e e v e n w ith an in crease in n octu rn a l EMG le v e ls. T he e ffe c tiv en ess o f the sp lin t w a s o b v io u sly a c h ie v e d th rou gh an alter n ative effect. A lternate ex p la n a tio n s for im p ro v e m en t o f sy m p to m s in clu d e: red istrib u tio n o f oral f o r c e s , or r e d u c in g h y p e r a c t iv it y o f m u s c le s (parafunctional a ctivity) during w a k in g h ours. A s d isc u sse d b y G reene a n d L askin,1 m an y other factors m ay acco u n t for th e reported su c c e ss o f sp lin ts. It is d ifficu lt to d istin g u ish th e p la ceb o effect o f v isitin g a “TMJ s p e c ia lis t.” A lso , th e d ecreased v a lid ity o f u sin g su b jectiv e reports b y p atien ts o f im p ro v em en t in their c o n d itio n s m u st be co n sid ered . S p lin ts u se d in th is stu d y w ere carefu lly d e sig n e d w ith atten tio n to th e o c c lu sa l pattern. It is u n clear w h eth er a particular o c c lu sa l pattern is n ecessa ry for th e o b tain ed effect. W h en th e variety o f sp lin ts u se d in c lin ic a l practice are co n sid ered , it se e m s u n lik e ly that a sp e c ific o c c lu sa l d e sig n o f th e sp lin t is n ecessary for its effect. H ow ever, th e u se o f a p o o rly fittin g or p o o r ly a d ju ste d s p lin t is n o t r e c o m m en d ed . O n th e b a sis o f c lin ic a l ex p erien ce, th is ty p e o f o c c lu s a l s p lin t m a y c a u se u n p r e d ic te d m o v em en t o f teeth or m ay aggravate th e sy m p to m s o f jaw d y sfu n ctio n .
Conclusion T w en ty -fiv e p a tien ts w ith sy m p to m s o f m y o fa scial p a in and abnorm al jaw fu n c tio n w ere treated w ith u se of a fu ll arch m axilla ry o c c lu sa l sp lin t. T he le v e l o f nocturnal a ctiv ity o f the m asseter m u sc le w as m on itored as w e r e sy m p to m s before, d urin g, and
after o c c lu sa l sp lin t therapy. A d ecreased nocturnal EMG le v e l d uring treatm ent w a s n o ted for 52% o f the patien ts. A return to pretreatm ent EMG le v e ls after rem oval o f the sp lin t w a s n o tice d in 92% o f the patients; in 28% n o ch an ge w a s sh o w n and in 20%, an in crease w a s sh o w n in nocturnal EMG le v e ls. T he sp lin t w a s m ost lik e ly to red u ce nocturnal EMG le v e ls in p atien ts w ith least severe sym p tom s. T h e in fo rm e d c o n se n t of a ll su b jec ts w h o p a rtic ip a te d in th e e x p e ri m e n ta l in v e stig a tio n re p o rte d in th is m a n u s c rip t w a s o b ta in e d a fte r th e n a tu re of th e p ro c e d u re s a n d p o s sib le d isco m fo rts a n d ris k s h a d b e e n fu lly e x p la in e d . Dr. C la rk is a ss is ta n t p ro fesso r, s e c tio n o f g n a th o lo g y a n d o c c lu sio n , a n d is re s e a rc h d ire c to r, U CLA T e m p o ro m a n d ib u la r J o in t a n d F a c ia l P a in C lin ic , U n iv e rsity o f C alifornia, Los A n g eles, S ch o o l o f D en tistry . M s. B ee m ste rb o e r is re s e a rc h a s s is ta n t a n d D r. S o lb erg is p ro fesso r, s e c tio n o f g n a th o lo g y a n d o c c lu sio n , U CLA. Dr. R u g h is a s s is ta n t p ro fesso r, d e p a rt m e n t o f o c c lu sio n , U n iv e rsity o f T exas, S a n A n to n io . A d d re ss re q u e sts for re p rin ts to Dr. C lark, S e c tio n o f G n a th o lo g y a n d O c c lu sio n , S c h o o l o f D en tis try , U n iv e rs ity o f C alifo rn ia , T h e C e n te r fo r H e a lth S c ie n c e s, Los A n g eles, 90024. 1. G reen e, C .S., a n d L askin, D.M . S p lin t th e ra p y for th e m y o fascial p a i n - d y s f u n c t i o n (M PD ) s y n d r o m e : a c o m p a r a tiv e s tu d y . JA D A 8 4 (3 ):6 2 4 -6 2 8 ,1972. 2. B lock, S.L.; A p fe l, M .; a n d L ask in , D .M . T h e u s e o f a re s ilie n t ru b b e r b ite a p p lia n c e in th e tre a tm e n t o f M PD sy n d ro m e . J D en t R es 5 7 :A 7 1 ,1978. 3. Jarab a k , J.R. E le c tro m y o g ra p h ic a n a ly s is o f m u s c u la r a n d te m p o ro m a n d ib u la r jo in t d is tu rb a n c e s d u e to im b a la n c e s in o c c lu sio n . A n g le O rth o d o n t 26 :1 7 0 -1 9 0 ,1 9 5 6 . 4. B eem sterb o er, P.L., a n d o th e rs. T h e effect o f th e b ite p la n e s p lin t o n th e e le c tro m y o g ra p h ic s ile n t p e rio d d u ra tio n . J O ral R e h a b il 3{4):349-352, 1976. 5. S o lb e rg , W .K .; C la rk , G .T .; a n d R u g h , J.D. N o c tu rn a l e le c tr o m y o g ra p h ic e v a lu a tio n o f b ru x is m p a tie n ts u n d e rg o in g s h o rt te rm s p lin t th e ra p y . J O ra l R eh a b il 2 (3 ):2 1 5 -2 2 3 ,1975. 6. F u c h s , P. T h e m u s c u la r a c tiv ity o f th e c h e w in g a p p a ra tu s d u rin g n ig h t slee p . A n e x a m in a tio n o f h e a lth y su b jec ts a n d p a tie n ts w ith fu n c tio n a l d is tu rb a n c e s . ) O ra l R eh a b il 2 (l) :3 5 -4 8 ,1975. 7. B eem sterb o er, P.L.; S o lb erg , W .K.; a n d R ugh, J.D. O c c lu sa l th e ra p y : n o c tu rn a l e le c tro m y o g ra p h ic re s p o n se a n d sy m p to m im p ro v e m e n t. J D ent R es 5 5 :B 1 5 9 ,1976. 8. H e lk im o , M . E p id e m io lo g ic a l su rv e y o f d y s fu n c tio n of th e m a stica to ry sy ste m . O ra l S c i R ev 7 :5 4 -6 9 ,1 9 7 6 . 9. R u g h , J.D., a n d Solberg, W .K. E lec tro m y o g rap h ic s tu d ie s o f b ru x is t b e h a v io r b efo re a n d d u rin g tre a tm e n t. C alif D e n t A ssoc J 3 (9 ):5 6 -5 9 ,1975. 10. R u g h , J.D. E lec tro m y o g rap h ic a n a ly sis o f b ru x is m in th e n a tu ra l e n v iro n m e n t. A d v a n ce s in b e h a v io ra l re s e a rc h in d e n tistry . S e a ttle , U n iv e r s ity o f W ash in g to n , 1978, p p 67-83. 11. R am fjord, S.P., a n d A sh , M .M ., Jr. (eds.). O c clu sio n . P h ila d e lp h ia , W . B. S a u n d e rs Co., 1971, p 427. 12. D rago, C.J.; R ugh, J.D.; a n d B arghi, M . N ig h tg u a rd v e rtic a l th ic k n e ss effects o n n o c tu rn a l b ru x ism . J D e n t R es 5 8 :A 9 0 1 ,1979.
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