the effect of different occlusal splints on the electromyographic

The Effect of Different Occlusal Splints on The Electromyographic Activity of Elevator Muscles: A Comparative Study

INTRODUCTION

The Journal of Gnathology Vol. 7, No. 1, 1988

Arturo Manns, D.D.S. • Jose Valdivia, D.D.S.** Rodolfo Miralles, D.D.S. ••• Maria Cecilia Pena * * * * Santiago, Chile

The occlusal splints are intraoral devices whose design, material and fabrication method vary with different authors1 •2 •3 , in ac-cordance with the usage aimed at, but they all have the idea in common to maintain the upper teeth separated from the lower ones. In this way they eliminate premature contacts and/or oc-clusal interferences, thus being a reversible, temporary and inter-ceptive treatment 2 • 4 used with the purpose to obtain a har-monious relationship between occlusion, temporo-mandibular joints and the neuromuscular system.4 • 5

EMG investigations in normal patients6 • 7 • 8 have shown that during maximum voluntary clenching on a total coverage splint an increase of the EMG activity of the masseter muscle was noted with regard to the one noted without the splint.

Regarding the temporal muscle, Freesmeyer and Manns6 , as well as Miralles et al. 7 have demonstrated a similar activity with and without splint in normal patients. Contrary to these findings, Wood and Tobias8 have noted an increased EMG activity in the temporal muscle, with splint.

On the other hand, McDonald and Hannam9 register similar values of EMG activity of the elevator muscles in intercuspal position with acrylic resin occlusal stops, with the following oc-clusal arrangements: bilateral and symmetric contacts of both

Associate Professor and Director, Oral Physiology Laboratory, Department of Physiology and Biophysics.

• • Assistant, Department of Physiology and Biophysics. • • • Assistant Professor, Department of Physiology and Biophysics. • • • • Research Fellow.

61

Manns, Valdivia, Miralles, Pena

MATERIAL AND METHODS

62

canines and second molars; bilateral and symmetric contacts of the second molars only, asymmetric bilateral contacts (canine and second molar having contact on one side and second molar on the other side only).

With regard to frontal or anterior occlusal splints, several au-thors 10, 11 • 12 • 13 have demonstrated a significant decrease of EMG activity while a frontal splint was used.

Dahlstrom et al. 14 report a statistically significant decrease of EMG activity in the postural mandibular position of anterior and posterior temporal muscles when using a total coverage splint as well as a frontal splint on normal patients.

Fuchs 15 , when studying the muscular activity while sleeping of healthy patients and of patients with jaw dysfunction treated with frontal splints, arrived at the conclusion that their use decreases the activity of the chewing muscles to the level of normal pa-tients.

In an EMG investigation comparing a complete coverage splint, a frontal splint and an interceptor splint with contacts only at the level of the lower first premolars over the working surface of the splint, Bollinger 10 reported that lesser EMG activity was registered when using an interceptor under conditions of teeth grinding.

The purpose of the present paper is to determine the magnitude of the variation in the integrated EMG activity that is produced by different types of occlusal splints on the jaw elevator muscles (masseter and anterior temporal).

This investigation was performed on 7 subjects (four female and three male), who ranged in age from 19 to 29 years for an average of 23.1 years, with healthy functional occlusion, bilateral molar support and absence of signs and symptoms of temporo-mandibular dysfunction. Each one was subjected to a clinical and functional exam in accordance with an occlusal diagnostic record that had been prepared specifically for this investigation.

For each subject a full upper stabilization occlusal splint was made of transparent heat-polymerizing acrylic resin with uniform, simultaneous and multiple tooth contacts at centric relation-centric occlusion. After four nights of continuous usage, the splint was cut into three parts: an anterior section with contact of the canines, lateral incisors and central incisors; and two posterior sections with contacts of the premolars and molars ( Fig. 1).

The different sections of the splint made it possible to record the


66

Table 1 Integrated EMG activity (arbitrary units: A.U. and percentage: %) of the masseter muscle during maximum voluntary clenching in centric occlusion for the different experimental series

Series I Series 2 Series 3 Series 4 Series s With complete With onterior With posterior With contact of :

the first lower r Without splint splint section sections premolors

Subjects i t so i t so x t SD i t SD i t so I A.U. 27.00 t I. 73 3 1.00 ! 1.00 21.00 ! 1.00 34. 7 ! 0.58 23. 40 ! 0.58

% 87.00 :t 5.58 100. ! 0. 67 .74 :t 3 .23 11 I. 93 ! 1.88 75 48 :t 1.88 i

2 A.U . 19.40 :t 0 . 58 27 .70 ! 0.58 15.00 :t 1.00 27 . 70 :t 0.58 18 .00 :t 1.00 ! I

% 70 .03 t 2.09 100 . :t 0 54 . 15 ! 3 61 100 . ! 2 . 10 64 .98 ! 3 .61 I

3 A.U. 26.40 :t I . 53 30.4 ! 0 58 I 8 .40 ! 1.20 29. 00 ! 1.00 25 00 t I oo I % 86.84 ! 5.04 100 ! 0 60.52 :t 3.95 95. 39 t 3.29 82.23 :t 3.29 j

4 A.U . 16.40 :t 0.58 25.00 :t 1.00 13.00 ! 1.00 29 00 ! 1.00 15. 70 :t I. 53 1

% 65.60 :t 2 .32 100 :t 0 52 .00 ! 4.00 116.00! 4 .00 l 62 .80 ! 6.12

5 A.U 27.70 :t 0.58 29.40 ! 1.53 15.70 ! 0.58 31. 00 ! 2 .00 126. 70 ! 0.58 % 94.21 :t I .98 100 :t 0 53.40 ! 1.98 105 . 40 ! 6.80 ; 90.80 ! I .98

6 A.U 27.00 :t 0 29.00 :t 1.00 21.00 :t 1.00 28. 70 t 2.08 22.70 :t 2.30 % 93.10 t 0 100 :t 0 72.41 ! 3.45 98. 96 ! 7.1 8 78.27 ! 7.94

7 A.U. 26.00 t I .00 31.00 t 1.00 2200 t 1.00 32.00:t 0 121.00 ! 0 l % 83.87 t 3 23 100 t 0 70.96 :t 3.23 103. 22 :t 0 87.09 :t 0 !

I '

~ ± SO of I

A.U 24.27 t 4.47 29.07 ! 2. 15 18.02 ! 3.50 30. 30 ! 2.43 22.64 ! 4 . 3 : the 7

subjects % 82.95 :t 11.03 100 .00 ! 0 61 .59 ! 8 .74 104.41 ! 7 . 34 i 77 .38 ! 10 .56 :

Table 2 Integrated EMG activity (arbitrary units: A.U. and percentages: %) of the anterior temporal muscle during maximum voluntary clenching in centric occlusion for the different experimental series

Series I Series 2 Series 3 Series 4 Series S

With onterior With posterior With conloct of With complele the first lower

Without splint splint section sections premolars· Subjects i ! so i :t SD i ! so i t so x :t so

I A.U. 21. 70 ! 2.08 18.00 ! 0 14 .00 ! 0 20 .00 ! 1.00 12. 70 ! 2.52 % 120.56 :t 11. 56 100 ! 0 77.76 ! 0 111.12 ! 5.56 70. 56 ! 13.99

2 A.U. 19.4 ! 0.58 19.7 :t 1.53 13.4 !: 0.58 19.00 ! 1.00 13.00 :t 0 % 98.47 t 2.95 100 :t 0 68.02 ! 2.95 96.44 ! 5.08 65.98 ! 0

3 A.U. 28. 70 ! 0.58 28. 70 ! 0.58 22. 70 ! 1.53 30.00 ! 1.00 29.40 ! 0.58 % 100.00 ! 2.03 100 ! 0 79 09 ! 5.34 I 04.52 ! 3.49 102 43 ! 2.03

4 A.U. 13.70 ! 0.58 17.40 ! 1.53 9.00 ! 1.00 20.40 ! 0 . 58 12.40 ! 2.08 % 78 .73 ! 3. 34 100 ! 0 51.72 ! 5 .75 I I 7.24 ! 3.34 71 . 26 ! 11. 96

5 A.U. 32.4 t 0.58 34.4 ! 0.58 23. 70 ! 0.58 3 4.00 ! 1.00 28. 70 ! 2.30 % 94.1 8 :t 1.69 100 :t 0 68.89 ! 1.69 98.83 ! 2.91 83. 43 ! 6.69

6 A.U. 19.70 ! 0.58 16.4 ! 0.58 8.00 ! 1.8 I 7.00 ! 1.0 13.00 ! 2.00 % 120.12 :t 3.54 100 t 0 48. 78 ! 10.98 103.65 ! 6.1 79. 26 ! 12.2

7 A.U. 37. 7 ! I. I 6 32 .7 t I. I 6 20.40 ! 0.58 31.40 ! 0.58 27 .00 ! I. 74 % 115.29 :t 3. 55 100 ! 0 62 . 38 ! I. 78 96 . 02 ! I. 78 82. 56 ! 5. 33

x ± SD of of the A.U. 24.76 ! 8 . 44 23 . 9 ! 7.76 15.89 ! 6.42 24.54 ! 6 .97 19 . 46 ! 8 . 37

7 subjects % 103.90 ! 15.50 100 :t 0 65.23 ! 11.77 103.97 ! 7.89 79.35 ! 12. 12 -

The Effect of Different Occlusal Splints on The Electromyographic Actinity of Elevator Muscles

Fig. 5. Bar graph shows the comparison between the five experi-mental series of the integrated EMG activity of each muscle tested, using the group mean value of all subjects (n=7) for each series. E

M G

125 MASSETER TEMPORAL

RESULTS


A c T I v I T y

(%)

1 (1(1

"".'C'

,· ·-·

5(1

.-.c-L · .. •

t 8 ::::::: c::· : ...... -: :::::~ ::::::: :::::::::

!! f !l k ::::::: ::::::: \J LJ f::::

.: .• : .• : •• ::_:_.:1:.: ):,:_ •• :(:••_ •. :: •• : :::::~ H:::1 (: .. (~J LJ L:. :::J F:: ::A L:J t::: ::::J L::: ::::J L:J : .. :::: ··1···' }··1·· ..... } '···1···' '······ ·····f·· ·· " .. !.~ .. " ·· "Y'L..!. .... !..!.,f.. .. f

I 2 345 I 2 345 ·:;EF.'. IE·:;

during maximum voluntary clenching in intercuspal position with the complete splint (series 2) was defined as 100%. The remaining mean values of the other series were expressed in percentage points of the earlier defined 100%. The comparison of all series for each muscle was performed with the non parametric Friedman Test. On the other hand, for paired comparison between different series the Wilcoxon Rank Test was employed.

Tables 1 and 2 show the mean values with their corresponding standard deviation for each subject and for each recording series of the integrated EMG activity expressed in arbitrary units as well as percent for the masseter and the anterior temporal muscles, re-spectively. Also shown is the group mean of the seven subjects with its standard deviation for each one of the five recorded series.

These tables show that the EMG activity of the masseter during maximum voluntary clenching when the full coverage splint is placed in the mouth (Series 2), is greater than without the splint (Series 1 ). On the other hand, the EMG activity with the splint as compared with the EMG activity without splint, is variable for the anterior part of the temporal; whereas it increases in some patients, in others it decreases. Nevertheless, the mean activity of the seven subjects showed to be similar with or without splint.

Furthermore, one can appreciate that for both muscles and for the different subjects a manifest reduction of the EMG activity occurs for Series 3 (anterior splint) as well as for Series 5 (interceptor splint) in relation to the other series, exception made for the

67


68

Table 3 Analysis of the integrated EMG activity of the masseter and anterior temporal muscles between all investigated series (non parametric Friedman Test)

Condition :\lasseter Temporal X2 , r X 2

• r

Between all series 26.03* * * 17. 97* * • • p < 0.01; • • • p < 0.001

Table 4 Analysis of integrated EMG activity of the masseter and anterior temporal muscles between the different paired series (Wilcoxon Rank Test)

Condition ~lasseter

T \·alue

Series 1 ,·Is Series 2 ** Series 1 \'Is Series 3 ** Series 1 \'Is Series 4 ** Series 1 \'Is Series 5 * Series 2 v Is Series 3 ** Series 2 vis Series 4 :'-!.S.

Series 2 v Is Series 5 ** Series 3 v Is Series 4 ** Series 3 \'Is Series 5 ** Series 4 vis Series 5 **

Temporal

T value

x.s. ** x.s. *

** x.s. *

**

* **

• p < 0.05; • • p < 0.01; N.S. non significative

temporal muscle of patient number 3 in Series 5.

Fig. 5 was drawn using the group mean of the seven subjects and for each series of records of the EMG activity of the masseter and anterior temporal muscles, expressed as a percentage value that was obtained from Tables I and 11. In this figure, one can gra-phically see the behavior of both muscles that was already de-scribed in the different series of recordings.

Table 3 shows a comparison of the integrated EMG activity for both elevator muscles between al I investigated series. For the masseter as well as for the temporal, significant differences of their EMG activity were found to exist (non parametric Friedman Test).

Table 4 shows the comparison between paired series in both muscles (Wilcoxon Rank Test).

In the masseter muscle the activity that is recorded without the splint (Series 1) is significantly less as compared with that re-


DISCUSSION


corded with the splint (Series 2). On the other hand, for the temporal muscle no significant differences are observed. In addi-tion, the EMG activity without the splint (Series 1) is significantly greater than the one observed with the frontal splint (Series 3) and with the interceptor splint (Series 5), in both muscles. However, the activity without the splint (Series 1) is significantly less than with the posterior splint (Series 4) in the masseter muscle, while the temporal shows a similar activity in both series.

The EMG activity in both muscles with the full coverage splint (Series 2) is significantly greater than the one obtained with the frontal splint (Series 3) and with the interceptor splint (Series 5). Furthermore, when comparing the EMG activity while inserting the full coverage splint (Series 2) with that obtained while wearing the rear splint (Series 4), no significant change can be appreciated in the activity of the two muscles.

The EMG activity observed in both muscles with the frontal splint (Series 3) is significantly less than that recorded with the posterior splint (Series 4) and with the interceptor splint (Series 5).

On the other hand, in both muscles the EMG activity with the posterior splint (Series 4) is significantly greater than that re-corded with the interceptor splint (Series 5).

The present investigation has shown a different behavior of the EMG activity of the masseter and anterior temporal muscles dur-ing the recording with splint vs. without splint. Whereas the ac-tivity of the masseter significantly increased with the splint, the activity of the anterior temporal was similar under both condi-tions.

The greater activity of the masseter that was observed with the splint placed in the mouth, coincide with the findings of Wood and Tobias 8 , Freesmeyer and Manns6 and Miralles et al.7 This increase of the masseter EMG activity during maximum voluntary clenching with the splint, is probably due to the fact that this muscle provides an effective occlusal stability of the jaw in its centric position through bilateral, simultaneous and symmetrically distributed contacts of equal intensity, of the lower pieces on the functional surface of the splint. This permits the masseter muscle to respond efficiently to the splint effect that is produced by the total stabilization plane, in this way being able to develop its greatest muscular power and act primarily as a muscle that gen-erates interocclusal forces. 19

The similar behavior of the EMG activity of the anterior temporal muscle with and without splint is in accordance with the findings

69


70

by Freesmeyer and Manns6 and Miralles et al. 7 , but is in dis-agreement with those of Wood and Tobias 8 , who observed an increase of the EMG activity with the splint. This similar activity of the anterior temporal under both conditions is probably due to the fact that this muscle preferably functions more as a postural stabi I izer of the jaw than as a generator of forces. 1 9

The highly significant decrease of the EMG activity of the masseter as well as of the anterior temporal muscles during maximum voluntary clenching with the frontal splint (Series 3) in relation with that obtained with the full coverage splint (Series 2), may be explained through the following biomechanical and neurophysio-logical considerations: - The biomechanics of the stomatognathic system is composed in

such a manner that it produces a greater generation of inter-occlusal forces in the posterior area of the dental arch; on the other hand, the anterior teeth being more distant from the point of application of the force and the condylar fulcrum (temporo-mandibular joints), receive smaller interocclusal forces because the stomatognathic system behaves like a third order lever.9 • 20

- Neurophysiologically speaking, the feedback of the periodontal mechanoreceptors can also be involved, given that there is a greater density of mechanoreceptors with lower mechanosensi-tive thresholds that are located more in front of the dental arch.21 • 22 Because the mechanoreceptors are involved in the inhibitory feedback mechanisms on the jaw elevator muscles23 ,

it is only logical to expect greater inhibition and, consequently, lesser muscular activity on the anterior contact points during maximum voluntary clenching.

Furthermore, according to Wood 8 , the decrease of the muscular activity during maximum voluntary clenching on a frontal splint would indicate that pressure areas are created on the level of both temporo-mandibular joints, because the posterior occlusal support is lacking, reason for which the inhibitory reflex effect also origi-nates partially from the proprioceptors of the temporo-mandibular joints. 20

These findings obtained for both muscles with the frontal splint are in accordance with the investigations of Cox et al.11 , Moini et al.13 and Bollinger. 10 These investigators found an important reduction of the EMG activity upon placing a frontal splint in the mouth where onl_y the canines and the lower incisors made contact.

In the present investigation, the EMG activity of both muscles during maximum voluntary clenching with the posterior splint was similar to the activity obtained with the full coverage splint. This coincides with the observations of Miralles et al.7 , who also used


The Journal of Gnathology Vol. 7, No. 1. 1988

both posterior sections of the splint, similarly to the present investigation. In addition, it is in accordance with observations made by MacDonald and Hannam9 during the voluntary clenching in centric position on occlusal stops built in acrylic with a very small increment in the vertical dimension, when these stops were placed at the level of the two first molars, or when they were placed on the level of a canine and a second molar on one side, with molar contact on the opposite side, as well as when building bilateral symmetrically distributed stops. These findings seem to show that, to allow for the development of greater occlusal forces during maximum voluntary clenching in centric position, it is important to establish bilateral and symmetrical contacts on the posterior level, whereas the number of these is less important than their location 9 , which should aim to obtain an adequate occlusal stabilization of the lower against the upper jaw. 5 • 24

In Series 5, where a full coverage splint was used with bilateral contacts that were concentrated on the level of the lower pre-molars only, simulating an interceptor or Schulte splint, the EMG jaw elevator activity during maximum voluntary clenching was significantly reduced, when comparing it with the splint of full coverage as well as with the Gelb splint. This real reduction of the EMG activity could be explained based on the following argu-mentation:

The sole and bilateral contacts of the buccal cu~ps of the first lower premolars on the functional surface of the splint and their immediate distal localization with regard to the canine would allow to explain the reduction of the recorded jaw elevator ac-tivity, based on the already mentioned biomechanical considera-tions. The contacts of the first premolars are certainly more dis-tant from the point of application of the force and the condylar fulcrum, than the contacts at the molar level.

On the other hand, the occlusal pattern in centric position with the interceptor splint implies that the jaw elevator force is only concentrated on the two teeth in contact with the splint, which means that this force, spread over a small periodontal area, stimu-lates its periodontal mechanoreceptors faster and, in the presence of a much smaller magnitude of forces, triggers an inhibitory reflex effect of the jaw elevator muscles.

Nevertheless, it is important to note that the electromyographic decrease of the elevator force that is caused by the interceptor splint, was of lesser magnitude than the one obtained with the frontal splint. This electromyographic evidence again may be partially explained by the previously discussed biomechanical and neurophysiological considerations.

The findings of the present investigation suggest certain clinical

71

Manns, Valdivia, Miralles, Peiia

SUMMARY

REFERENCES

72

implications in the sense that each occlusal splint that is used in the treatment of dysfunctions of the stomatognathic system, possesses its exact indication in accordance with the therapeutical goal.

Th is paper is a comparative study of the effects that are produced by four different occlusal splints on the electromyographic (EMG) jaw elevator activity.

For this purpose, full coverage maxillary occlusal splints were made for seven subjects with a normal function of the stom-atognathic system. These splints were divided into three sections (one anterior and two posterior ones), thus permitting to record the EMG effects that were produced by the different types of occlusal splints on one and the same subject and with equal varia-tion in the vertical dimension. The integrated EMG activity was recorded from the masseter and the anterior temporal muscles during maximum voluntary clenching.

The findings showed a greater masseter activity during the clench-ing on the splint with its three sections or with only the two posterior sections than with natural dentition, while the activity of the :Jnterior temporal was similar. In addition, a significant reduc-tion of the EMG activity of both muscles was observed during the clenching on the anterior section of the splint, as well as while maintaining contact only at the level of the first lower premolars. In this condition the reduction obtained was greater with the anterior splint.

These findings suggest that each type of occlusal splint affects the elevating jaw muscles in a different way and, consequently, have an exact indication depending on the therapeutical approach.

Note: This research was supported by the Departamento de Desarrollo de la lnvestigaci6n y Bibliotecas, Universidad de Chile, GRANT No. B 2362-8613.

1. Ash, M. and Ramfjord, S.: An introduction to functional occlusion. Saunders Co .• U.S.A.. W.B .• 240 pages, 1982.

2. Kawazoe, Y. et al.: Effect of occlusal splints on the electromyographic activities of masseter muscles during maximum clenching in patients with myofascial pain dysfunction syndrome. J. Prosthet. Dent., 43: 578-580, 1980.

3. Timm, T. and Ash, M.: The occlusal bite plane splint. An adjunct to orthodontic treatment. J. Clinical Orthod., 11: 383-390, 1977.

4. Dawson, P.: Evaluaci6n, diagn6stico y tratamiento de problemas oclusales. Ed. Mundi, Bs. As., S.A.I.C. y F .• 459 pages, 1977.



5. Valdivia, J., Manns, A. and Miralles, R. : S{ndrome de disfunci6n dolorosa mio-facial: evaluaci6n clinica comparativa de su terapia en base a tres tipos de pianos; Rev. Chi I. de Ortodoncia, 2: 108-116, 1985.

6. Freesmeyer. W. and Manns, A.: Einfluss experimenteller Okklusionsstorungen auf die elektromyographische Aktivitat der Elevatoren. Deutsche Zahnarztliche Zeitschrift, 40: 875-880; 1985.

7. Miralles, R., Manns, A. and Pasini, Ch.: Influence of different centric functions on the electromyographic activity of elevator muscles. Journal of Craneomandibular Practice, (in press). 1987.

8. Wood, W. and Tobias, A.: Electromyographic response to alteration of tooth contacts on occlusal splints during maximal clenching . J. Prosthet. Dent.: 394-396, 1984.

9. Mc Donald, J. and Hannam, A.: Relationship between occlusal contacts and jaw closing muscle activity during tooth clenching. Part I, J. Prosthet. Dent., 52: 718-729, 1984 .

10. Bollinger, K.: Zur lndikation der Aufbissbehelfe bei der Therapie der Myoarthro-pathien. Dtsch. Zahnarztliche Zeitschrift, 27: 816-821, 1972.

11. Cox, P., Rothwell. P. and Duxbury, A.: The masseteric silent period following experimental bruxism in subjects wearing acrylic anterior bite planes. J. Oral Rehab., 10: 51-55.1983 .

12. Manns, A., Miralles. R. and Cumsille. F.: '. .• ,'luence of vertical dimension on masseter muscle electromyographic activity in patients with mandibular dysfunc-tion. J. Prosthet. Dent., 53: 2~3-247 ; 1985 .

13. Moini, M., Mc Call. W. and Mohl, N.: Jaw muscle silent periods: the effect of acrylic splints. J. Dent. Res., 59: 683-686, 1980.

14. Dahlstrom, L., Haraldson, T. and Janson, T. : Comparative electromyographic study of bite plates and stabilization splints. Scand. J. Dent. Res., 93:. 262-268, 1985.

15. Fuchs, F.: The muscular activity of the chewing apparatus during night sleep. An examination of healthy subjects and patients with functional disturbances. J. Oral Rehab., 2: 35-46. 1975.

16. Schulte, W.: Die exzentrische Okklusion. Quintessenz Verlags GmbH . Berlin, Chicago, Ri'ode Janeiro and Tokyo, 1983 .

17. Manns, A. and Spreng, M. : EMG amplitude and frequency at different muscular elongations under constant masticatory force or EMG activity. Acta Physiol. Latinoam., 27: 259-271. 1977.

18. Manns. A., Miralles. R. and Palazzi. C.: EMG. bite force and elongation of the masseter muscle under isometric voluntary contractions and variations of vertical dimension. J. Prosthet. Dent., 42: 647-682, 1979.

19. Hannam, A. : Der neuromuskulare Apparat und seine Beziehung zur Unter-kieferdysfunktion. Orthod . und Kieferorthop ., 4: 423-432. 1980.

20. Manns, A .• Diaz, G. : Sistema estomatognatico. Ed. Empigraf. Fae. Odontologia, Universidad de Chile, 249 pages, 1983.

21 . Hannam. A .: The innervation of the periodontal ligament. In Beerkovitz, B.K .• Editor: Periodontal ligament in health and disease. Pergamon Press, Oxford, 1981.

22. Miralles, R., Carvajal. E., Manns. A. and Rossi, E.: Estudio comparative de umbrales presorreceptivos en dientes con normofunci6n vs. hiperfunci6n o trauma oclusal. Rev. Dent.de Chile, 11: 3-7.1980.

23. Van Steenberghe, D. and De Vries, J. : The influence of local anaesthesis and occlusal surface area on the forces developed during repetitive maximal clenching efforts. J. Period . Res .• 13: 270-274, 1978 .

24. Manns, A., Chan. 0.: Optimierte Herstellung einer Repositionie -rungsschiene anhand van EMG-Registrierungen . Swiss. Dent ., 5 : 37-41 , 1984.

Dr. Arturo Manns Universidad de Chile, Faculty of Medicine Department of Physiology and Biophysics Casilla 70055, Santiago 7, Chile

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the effect of different occlusal splints on the electromyographic

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