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ORIGINAL ARTICLE Table of Contents   
Year : 2006  |  Volume : 9  |  Issue : 1  |  Page : 14-20
EMG pattern of masticatory muscles in altered dentition - Part I

1 Dr. R. Ahmed Dental College & Hospital, Kolkata, India
2 Principal, Santosh Dental College, Gaziabad, UP, India
3 Dept. of Physiology, IMS, BHU, Varanasi, India
4 Santosh Dental College, Gaziabad, UP, India

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The aim of this study is to reveal how any alteration in occlusion results in functional disturbances in masticatory muscles, which may in turn develop TMJ pain dysfunction syndrome in the long ran.
Electromyography (EMG) of masseter and temporalis muscles (if ten adult individuals with normal occlusion and either 36 or 46 carious, was recorded in rest position and during chewing activity of mandible. After cavity preparation, inlay with high point (or occlusal interference) was fabricated, which seas fitted in the tooth and EMG recordings were repeated. Again the same recordings were done after stablishing the occlusal equilibrium.
Atypical pattern of muscle activity was observed only in presence of occlusal interference and obolished after removal of the same. This activity resembled the spasm in skeletal muscle. Spasm in masticatory muscles may initiate the symptoms of TMJ pain dysfunction syndrome.

How to cite this article:
Adhikari H D, Kapoor A K, Prakash U, Srivastava A B. EMG pattern of masticatory muscles in altered dentition - Part I. J Conserv Dent 2006;9:14-20

How to cite this URL:
Adhikari H D, Kapoor A K, Prakash U, Srivastava A B. EMG pattern of masticatory muscles in altered dentition - Part I. J Conserv Dent [serial online] 2006 [cited 2021 May 7];9:14-20. Available from:

   Introduction Top

Occlusal interference is one of the major causes of TMJ dysfunction - functional disorder of stomatognathic system (Landa J.S. '51; Jarabak, J.R.'56; Ramfjord, S.P. '61; Schwartz, 'L, '66. Kloprogge M.J.G.M. '76). It is characterized by pain in muscles, joints, limitation of jaw opening, clicking etc. Occlusal interference may be a result of faulty restorative dental procedure or orthodontic treatment. This study was designed to investigate the effects of intentionally produced occlusal interference or functional malocclusion in the muscles of the system with the help of Electromyography (EMG) in the subjects with normal occlusion.

   Materials and Methods Top

Ten medical volunteers (average age 20 yrs) with complete permanent dentition (3rd molar excluded) and normal occlusion (as per criteria stated by Gravers) with one lower 1st molar carious, were included.

Subject with history of myofacial pain dysfunction syndrome and orthodontic treatment, lip incompetence, tenderness in any muscle of mastication and previous restoration in tooth were excluded.

Five subjects in the study were having 36 carious and remaining five were having 46 carious. The carious molars were subjected to operative procedure and restored with high point inlay to produce occlusal interference [Figure 1] which was later reduced to occlusal equilibrium. Thus in the experimental observation the subjects were divided in two groups

- Left side interference (E-L)

- Right side interference (E-R)

Electromyography (electrical activity) of temporalis and masseter muscles of both the sides were picked up and recorded with the help of "Polyrite"-a 2 channel EMG recorder with integrator and pen writing system [Figure 2] and bipolar surface electrodes.

Electrodes were positioned as shown in [Figure 3] after the method of Moss J.P.'67, Ahlgren J'73, and Kawazoe Y.79.

The calibration of the EMG machine [Figure 4] - 50 uv = 10mm - was fixed for the whole experimental procedure, meaning 10mm of pen deflection was resulted from 50 µv of electrical energy and the paper speed was fixed at 25mm per second of time.

EMG Recording was done in both rest position of mandible and while chewing.

The chewing event commenced with chewing the 'chewing gum' unilaterally. A specific brand of chewing gum was used.

The volunteer was asked to chew it once only (constituting one chewing cycle) and to take rest for a while and to start again when commanded. Consecutive three cycles constituted one session and the same procedure was repeated on other side.

All the volunteers were trained in performing similar chewing events before actual EMG recording was done. During recording, position of the head was kept vertical and no movement was allowed as jaw muscle respond to change in head position.

During chewing the chewing gum EMG recording was done thrice in each individual - (1) pre-operatively before inlay cavity preparation was done (2) post operatively after inlay with occlusal interference was fitted in the tooth and (3) again post operatively after removal of the interference from the inlay was done.

   Observation Top

Analysis of Electromygraphy revealed absence of EMG activity in rest position of mandible [Figure 5]

When the subjects were asked to chew pre­operatively, no EMG activity was also found at rest condition of the jaw in between consecutive chewing cycles and at and of chewing cycles [Figure 6] & [Figure 7].

But post operatively in presence of occlusal EMG activity was observed at the rest condition of mandible in between consecutive chewing cycles and at the end of the cycles [Figure 8], [Figure 9], [Figure 10] & [Figure 11]. This type of activity was abolised after the removal of the occlusal interference. And the EMG pattern returned back, similar to that recorded pre operatively.

This EMG activity at rest condition of mandible was resembling spasm in skeletal muscles (Jarabak J.R.'56) and was having following characteristics [Table 1]:

1. Amplitude (mean activity) - Low voltage discharges varying from 10-20 mv in contrast to that in chewing cycle which ranged from 30-53 uv.

2. Frequency : Low frequency of 15-20 cycle per second in comparision with the frequency of the EMG activity in chewing cycle which varied from 25-35 c.p.s.

3. Duration : The spasm like activity was observed in an unexpected time i.e. during rest period between consecutive chewing cycles and or at the end of last chewing cycle when the muscles were supposed to be exhibiting no EMG activity. Its duration varied from 200-600 msec. It was inharmonious and not properly timed.

In all the muscles in all the cases this activity was not observed. No relationship could be established between the side of chewing (left or right), side of presence of occlusal interference (E-L or E-R) and the muscles exhibiting spasm like activity. However as a whole the incidence of this activity was seen more in the masseter than temporalis

   Discussion Top

Electromyography is the study of electrical activity associated with contracting skeletal muscles and this electrical activity serves as a reliable index for the pattern of muscle contraction and contribute to a more precise diagnosis of functional disorders of the masticatory apparatus (Moller, E. 1969).

It is amply reported (Jarapak, J.R. 1956, Funakashi, M. et al 1976, Ingerval, B. et al 1983) that an alteration in the occlusal pattern of teeth may bring about a change in functional pattern of masticatory muscles. Occlusion is a dynamic phenomenon. Occlusion and occlusal contacts change throughout the day (Jankelson, B. 1979; Berry, D.C. et al 1983). So during restoring a tooth, the pattern of pre-existing occlusal contacts or the functional pattern of dentition cannot be reduplicated exactly. The system within certain limit may adapt with this change. Beyond this limit, it clinically produces deleterious effects on the organs of the stomatognathic system including masticatory muscles.

For functional analysis of masticatory muscles EMG was taken at rest position of jaw (a very comfortable position) and during chewing. The pattern of EMG varies with chewing different types of food. So a particular variety of chewing substance - the chewing gum was supplied to all the volunteers. Consistency of the gum remains more or less same even after repeated chewing.

The abnormal type of muscle activity found during chewing in presence of occlusal interference, was described as state of "Hyper activity" by Jarabak J.R. '56 and "partial contraction of Muscle" by Kloprogge M.J.G.M. '76. Any relationship between this activity and any preferred muscle or side of interference or side of chewing, was not much observed in this study. Whereas, Rosenthal R.L.'75 reported that elevators on the side of interference over work and become tender due to spasm.

Since the inlay with occlusal interference was placed for short period of time so definite pattern of altered muscle activity was not detected.

It is has been seen in the literature (Perry H.T. et al. '60; Jarabak J.R. '56; Graf H. '64; Schaerar al. '67; Koprogge M.J.G.M. '76) that co-ordinated muscle activity for the multidirectional Jaw movement is influenced by the stimulation of periodontal ligament receptors. The stimulation pattern of periodontal ligament receptors is scheduled by the pattern of occlusal contacts. Due to the presence of occlusal interference this pattern was altered which possibly developed a pattern of activity - a "Spontaneous hyper activity or spasmodic activity" to steer the mandible around the point of occlusal interference (Jarabak J.R. '56; Schwartz. P.66, Kloprogge M.J.G.M. '76). Fanakoshi M. et al. '76 described that "occlusal interference may always cause an excess excitation of mechano receptors of periodontal ligaments and afferent impulses from the receptors continuously stimulate the motoneurone which may cause an increase in "Jaw muscle tones".

Therefore, the non-specific pattern of muscle activity found in the study was believed to be due to the neuromuscular stimulation, the pattern of which may vary depending on which jaw relationship the tooth contact was taking place.

In the state of sustained contraction or spasm of muscle, excretory products accumulate more than they are eliminated. This result in painful stimuli. This pain may be referred to other neighbouring muscles and joints and cause further spasm reflexly and may thus produce TMJ pain dysfunction syndrome.

It has also been observed that most of the patients with TMJ dysfunction are associated with occlusal interference (Jarabak J.R. 1956, Ramfjord, S.P. 1961; Schwartz.L. 1966; Kloprogge, M.J.G.M. 1976). The symptoms of these patients are abolished or atleast improved by occlusal therapy (Jarabak J.R. 1956, John .M. 1971; Funa Koshi M. et al 1976). Therefore, it may said that occlusal interference is one of the causes of TMJ dysfunction.

   Conclusion Top

The task of occlusal rehabilitation is a very common job in day to day clinical practice. Therefore the clinician has to be careful to follow properly the procedure of reproducing occlusal pattern of the tooth such that the functional pattern of masticatory muscles remains unaltered otherwise symptoms of TMJ pain dysfunction syndrome may precipitate in the long run.[18]

   References Top

1.Ahlgren, J.: Ingerval, B.F. and Thilander, B.D.: Muscle activity in normal and post normal occlusion. Am. Jour. Ortho. Vol. 64, No.5, 1973.  Back to cited text no. 1    
2.Berry DC and Singh, B.P. : Daily variations in occlusal contacts. Jour. of Pros. Dent. Vol. 50: No.3,1983.  Back to cited text no. 2    
3.Funakoshi, M.: Fujita, N. and Takehana, S.: Relation between occlusal interference and jaw muscle activities in response to changes in head position. Jour. Dent. Res. Vol. 55; No.4,1976.  Back to cited text no. 3    
4.Graf, H.: OccIusal tooth contact pattern in relation to electromyographic activity during function. Am. Jour. Ortho., 50;701, 1964.  Back to cited text no. 4    
5.Ingerval. B & Caisson, G.E. : Masticatory muscle activity before and after elimination of balancing side occlusal interference - Report series No. 28; 1980. Deptt. of Stomatognathic physiology. University of Gothenburg, Sweden; quoted from "Tooth contact pattern and contractile activity of elevator jaw muscles during mastication of two different types of food - by Mohamed, S.E. et al. Jour. of oral rehab. Vol. 10; 87-95,1983.  Back to cited text no. 5    
6.Jarabak, J.R.: An electromyographic analysis of muscular and temporomandibular joint disturbances due to imbalance in occlusion. Angle Ortho. 26:170, 1956.  Back to cited text no. 6    
7.John M: Duration of masseteric silent period in patients with TMJ syndrome. Jour. Appl. Physio. V ol. 30; p. 864,1971.  Back to cited text no. 7    
8.Jankelson.B : Neuro muscular aspect of occlusion Dent. Clinic of North America. 23;2,157;1979.  Back to cited text no. 8    
9.Kloprogge, M.J.G.M : Disturbance in the contraction and Co-ordination pattern of the masticatory muscles due to dental restoration Jour. Oral. Rehabil. Vol.3; pp 207-217,1976.  Back to cited text no. 9    
10.Kawazoe, Y.: Kotani, H.:Hamada. T.:Relation between integrated electromyographic activity and biting force during voluntary isometeric contraction in human masticatory muscles. Jour. Dent. Res. 58 (5); 1440-1449,1979.  Back to cited text no. 10    
11.Landa J.S.: study of the temporomandibular joint viewed from the stand point of prosthetic occlusion. J.P.D.1:601.1951.  Back to cited text no. 11    
12.Moller, E : Clinical Electromyography in dentistry. Int. Dent. Jour. 19; 250-268, 1969.  Back to cited text no. 12    
13.Moss. J.P. : Function-fact or fiction? Am. Jour. of Ortho. Vol.67, No. 6, 1975.  Back to cited text no. 13    
14.Perry, H.T. and Lammse, G.A.: Occlusion in a stress situation. Jour, Am. Dent. Asso. Vol.60; May, 1960.  Back to cited text no. 14    
15.Ramfjord, S.P.: Dysfunctional temporo­mandibular joint and muscle pain. Jour of Pros. Dent. 11;353,1961  Back to cited text no. 15    
16.Rosenthal, R.L.: A simple test to determine the need for occlusal treatment. Jour. Pros. Vol.34; No.5, 1975  Back to cited text no. 16    
17.Schwartz, L.: Disorders of Temporomandibular Joint. Philadelphia, W.B. Saunder Co.P.21-24, 1966.  Back to cited text no. 17    
18.Schaerer, P.: Stallard, R. and Zander H.A.: Occlusal interference and mastication; An Electromyographic study, Jour. Pros. Vol. 17; No.5.438-449,1967.  Back to cited text no. 18    

Correspondence Address:
H D Adhikari
Dr. R. Ahmed Dental College & Hospital, Kolkata
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-0707.41304

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]

  [Table 1]


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