- Email: [email protected]
Effects of controlled tooth stimulation on jaw muscle activity in man
Arch
oral
Bid.
Vol. 17, pp. 1597-1607, 1972. Pergamon
Press. Printed in Great Britain
EFFECTS OF CONTROLLED TOOTH STIMULATION ON JAW MUSCLE ACTIVITY IN MAN B. J. SESSLEand ADRIANNESCHMITT Division of Biological Sciences, Faculty of Dentistry, University of Toronto, Toronto 2, Canada
Summary-The electromyographic activity of the right and left masseter muscles was recorded in nine subjects on tooth tapping. During maintained activity of these muscles, the right maxillary central incisor was tapped by an electronically controlled mechanical stimulator capable of delivering very accurate and reproducible stimuli. Axial or labial stimulation of the tooth produced an inhibitory period in the jaw muscle activity, and this inhibition was frequently preceded by an initial excitation. The inhibition in right and left muscles was quantified in terms of its incidence, latency and duration, and compared with the inhibitory period that followed initiation of a jaw jerk reflex. Local anaesthesia of the incisor abolished the inhibition elicited from stimulation of this tooth, but left unaffected the inhibition accompanying the jaw jerk reflex or stimulation of the left maxillary canine. It was concluded that receptors in or around the tooth are responsible for the inhibition of jaw muscle activity produced by tapping the tooth.
INTRODUCTION
SINCEthe demonstration by SHERRINGTON (1917) in the cat that stimulation of the teeth, gingiva or hard palate produces reflex jaw opening, the work of several groups of investigators in man (AHLGREN, 1967; 1969; SHAERER,STALLARDand ZANDER, 1967; BRENMAN,BLACKand COSLET,1968; BEAUDREAU, DAUGHERTYand MASLAND, 1969; GRIFFINand MUNRO, 1969; MUNROand GRIFFIN, 1970; GOLDBERG,1971) has indicated that receptors in the periodontium are concerned in the control of jaw movements. Moreover, it has been proposed (JERGE, 1964; KAWAMURA,1964, 1967) that periodontal receptors, by virtue of central connections resulting in excitation of jaw opening muscles and inhibition of jaw closing muscles, are intimately involved in cyclic jaw movements and mastication. However, the recent results of HANNAM,MATTHEWSand YEMM (1969; 1970) have cast serious doubt on this view. They observed in man that the reflex inhibition of jaw closing muscles that results from tapping a tooth is not abolished by local anaesthetic infiltration around the tooth. This would indicate that periodontal receptors are not involved in the inhibition. In a similar study, GOLDBERG(1971) also was unable to abolish the inhibitory period induced by tooth tap, although there was some reduction in its duration. These, and the previous studies of the inhibition produced by tapping teeth used rather gross and uncontrolled means of tooth stimulation 1597 A.O.B. 17/l 1-s
1598
B. J.
SESSLE
AND
ADRIANNESCHMIT-~
(e.g. a hammer) and it seems possible that periodontal receptors adjacent to the tooth (which was tapped and then anaesthetized) were contributing to the inhibition under these conditions. Thus from all this previous investigation, it is no longer clear to what extent, if any, periodontal receptors contribute to jaw muscle inhibition. For this reason and because of its relevance to our understanding of the neural basis of jaw movements and mastication, we decided to reinvestigate the possible contribution of periodontal receptors using a more quantitative approach and a controlled means of tooth stimulation. METHOD Nine young adults (four males, five females) with intact dentitions were used in this study. Each subject was seated upright and comfortably in a dental chair. The head of the subject was supported behind by a head board which had a strap attached. The strap was placed around the subject’s forehead to prevent movement during the experimental procedure. Unipolar surface electrodes (Beckman Instruments, Calif.) were positioned on the skin overlying the left and right masseter muscles to record the electromyographic activity of these jaw closing muscles. Reference electrodes were placed on the ear lobes. The activity from both muscles was amplified (Grass Preamplifier III D, frequency range l-10,000 c/set) and displayed on two channels of a dual-beam oscilloscope, and all the oscilloscopic recordings were photographed for subsequent analysis. Each subject was asked to maintain continuous activation of both muscles (Fig. 1) either by biting on cotton rolls placed between the premolars and molars or by clenching the mandible in an open position. While this activity was maintained, the right maxillary central incisor was stimulated using an electronically driven and precisely controlled mechanical stimulator (WERNERand MOUNTCASTLE,1965) capable of delivering reproducible and accurate (63 pm) tactile stimuli to the tooth. The stimulator was bolted firmly into a vice (Universal Vise, Atlas, Mich.) mounted on a heavy wooden platform which was at chest level. The vice permitted vertical and horizontal (in two planes) movement of the stimulator so that it could be accurately positioned with respect to the subject’s incisor. The mechanical stimulus was delivered at a rate of l/2 set, and 10 msec after the start of the oscilloscope sweep (Fig. 2). It had a duration of 10 msec, a displacement of 300 pm, and a rising phase of 3 msec. The stimulus was applied so that it contacted the tooth towards the end of its displacement and in all experiments the dynamic and static components of the force delivered to the tooth were 400 g and 200 g respectively. The stimulus was quite innocuous, and no subject complained of pain or discomfort from the tooth stimulus. The mechanical stimulus was first delivered in an axial direction to the incisor. After the muscle responses were recorded and photographed, the sequence was then repeated with the stimulus delivered from a labial direction. In each subject, the stimulus was applied 10 or more times to allow statistical evaluation (utilizing Student’s t-test of significance) of the incidence, latency and duration of the inhibitory periods in muscle activity. In this study, significance denotes a value of p less than 0.05, unless otherwise specified. Latency reflects the time from onset of the mechanical stimulus to the start of depression in electromyographic activity. The jaw jerk was also elicited in four subjects by applying a short, sharp tap to the chin with a reflex hammer. The oscilloscope beam was triggered to sweep at the instant the hammer made contact with the chin. This arrangement was also used to tap the forehead to determine if the inhibitory period produced by the tooth stimulation could be explained by stimulus spread to remote receptors such as muscle stretch, vestibular or temporomandibular receptors. The involvement of receptors in or adjacent to the tooth in the inhibitory effect produced by incisor stimulation was also tested using local anaesthesia. The entire jaw jerk and tooth stimulation procedures outlined above were repeated 10 min after infiltrating local anaesthetic palatally and labially around the root of the incisor. The anaesthetic used was 2 ml of 2 per cent lidocaine hydrochloride with 1 in 100,000 epinephrine (Xylocaine, Astra, Ont.). In six subjects, a labially directed mechanical stimulus was also delivered to the left maxillary canine before and after the local anaesthetic infiltration around the incisor. This was used as a check on the stimulation procedures and the localization of the local anaesthesia.
EFFECTS OF CONTROLLED
TOOTH
STIMULATION
ON JAW
MUSCLE ACTIVITY
1599
RESULTS
When the subject was instructed to tap his teeth together, a period of complete inhibition in this muscle activity occurred. An example of such an interruption in muscle activity can be seen in the lower recordings of Fig. 1. Typical levels of right and left masseter muscle activity generated by maintaining closure on cotton rolls can be seen in the upper part of Fig. 1. These periods of complete or partial inhibition could also be duplicated by applying the mechanical stimulus to the right maxillary central incisor (Fig. 2). The inhibitory effect was particularly noticeable in the situation where the subject was maintaining
Subject Maintaining
Bite
LM RM
Subject Tapping Teeth Together
1. Inhibitory period produced by subject tapping teeth together. The upper records illustrate the typical levels of activity in the left masseter (LM) and right masseter (RM) when the subject maintained closure on cotton rolls placed between the posterior teeth. When the cotton rolls were removed and the subject instructed to close and tap his teeth (lower records), a period of inhibition of approximately 15 msec duration occurred in both muscles. In this and subsequent figures, negative polarity is upward, voltage calibration is 0.2 mV and time calibration is 20 msec. FIG.
muscle activity by closing on the cotton rolls. All the following results apply to inhibitory effects on this maintained activity, since the inhibitory periods were not so obvious when the tooth was stimulated (or the jaw jerk elicited) with the muscles clenched in the jaw open position.
B. J. SESSLEAND ADRIANNESCHMITT
1600
Apart from the inhibitory period produced by tooth stimulation, another interesting finding was the frequent occurrence of an increased muscle activity immediately preceding the inhibition (Fig. 2). The high level of muscle activity that already existed due to the subject biting on cotton rolls precluded any quantitative assessment of this initial excitatory effect. The inhibitory periods were of very frequent occurrence. Table 1 indicates the incidence of this inhibition in both right and left muscles. Inhibition was most prevalent in the right muscle, occurring in approximately 80 per cent of trials with axial stimulation and 70 per cent with labial stimulation. In the left muscle, inhibition occurred in about 60 per cent and 70 per cent of trials with axial and labial stimulations respectively. Whenever an inhibition occurred, it nearly always was found in both right and left muscles. For example, an inhibitory period occurred in the left muscle in 81 per cent of the trials in which an axial stimulus to the incisor produced inhibition in the right muscle. When the tooth was stimulated in a labial direction, the bilateral occurrence was almost 100 per cent.
LM RM
FIG. 2. Effect of mechanical stimulation of the right maxillary central incisor on the left (LM) and right (RM) masseter maintained closing activity. The electronic analogue of the mechanical stimulus is shown in the lower part of the figure. The stimulus produced an initial excitation followed by a period of inhibition in the muscle activity.
In addition to the incidence of the inhibition produced by tooth stimulation, other parameters of the inhibitory effect were quantified. Table 1 shows the latencies and durations of the inhibition produced in right and left muscles by both axial and labial stimulation of the right incisor. Neither the direction of stimulation of the tooth nor the side on which the inhibition was recorded had any significant effect on the duration of the inhibitory period. However, a significant difference occurred between the right and left muscles in the latency of the inhibition. In the right muscle, the mean latency (& standard error) was 12.9 f 0.29 msec with axial stimulation but in the left muscle a longer latency value, 14.2 & 0’29 msec, was found. Similarly, with labial stimulation, the latency in the right muscle, 15 -2 f 0.62 msec, was significantly shorter
EFFECTS
OF CONTROLLED
TOOTH
STIMULATION
Labial
AXid
Latency Duration Incidence Before anaesthesia With anaesthesia
Each
latency
12.9 15.5
and duration
+ 0.29 f 0.39
ON JAW
15.2 15.1
MUSCLE
ACTIVITY
Axial
f 0.62 * 0.42
14.2 15.8
* 0.29 zk 0.29
1601
Labial
16.8 14.8
f 0.66 zk 0.42
62/91 2197
value is expressed
as mean
*
standard
error
(msec).
than the value of 16.8 + O-66 msec in the left muscle. In addition, a highly significant (p < 0.001) difference occurred between the latencies to axial and labial stimulation. For both the right and left muscles, the latency with axial stimulation was shorter than with labial stimulation. These findings of significant differences in latencies but not in durations were also obvious when the results from individual subjects were analyzed. For example, in one subject, axial stimulation resulted in a significantly shorter latency in the right muscle (12 - 5 f 1.1 msec) than in the left muscle (14.2 f 1.0 msec). It is also noteworthy that these individual values were not significantly different from the mean values of all nine subjects. In no subject was there any clear evidence of an inhibitory period produced by forehead stimulation. However, a period of inhibition followed the jaw jerk in almost 60 per cent of the tests (Fig. 3) and in all but one case it occurred bilaterally. There
FIG. 3. Inhibitory period following the jaw jerk in left (LM)) and right (RM) masseters. A typical record of the jaw jerk and inhibition is shown in the upper part of the figure. In the lower part are listed the latency, duration and incidence of this inhibition in both muscles. Each latency and duration value is expressed as mean & standard error (msec).
1602
B. J.
SESSLEAND ADRIANNE SCHMITT
no significant difference between right and left muscles in the latency and duration of the inhibition. Two noteworthy differences were found, however, when the inhibition following the jaw jerk was compared with that elicited by axial or labial stimulation of the incisor. The duration of the inhibition was longer, at a high level of significance (p < O.OOl), in all cases with the jaw jerk than in the cases with tooth stimulation. Moreover, at the same level of significance, the latency of the inhibition was longer when the inhibitory period accompanied the jaw jerk than when it was elicited by tooth stimulation. The implication of receptors in or around the tooth in the initiation of the muscle inhibition was conclusively demonstrated when local anaesthetic was infiltrated labially and palatally around the incisor and the series of stimulations repeated. Ten minutes after administration of the anaesthetic, there was an almost complete abolition of the inhibitory periods elicited by tooth stimulation. Table 1 shows the marked decrease in the incidence of the inhibition as a result of local anaesthesia of the incisor. In the right muscle, for example, the incidence of inhibition produced by axial stimulation of the incisor decreased from a control (pre-anaesthetic) level of approximately 80 per cent to an occurrence of only 8 per cent when the incisor was anaesthetized. With labial stimulation, the incidence dropped from a control level of about 70 per cent to a 2 per cent level after local anaesthesia of the tooth. In all but two subjects, the local anaesthesia totally abolished the occurrence of the inhibition. This effect of local anaesthesia on the incidence of the inhibition is also shown in Fig. 4 which illustrates typical recordings of muscle activity before and after local anaesthetic infiltration of the incisor. In two successive control (before local anaeswas
BeforeLocalAnaesthesia
After LocalAnaesthesia
-I
FIG. 4. Effect of local anaesthesia on the inhibitory period elicited in the left (LM) and right (RM) masseters by mechanical stimulation of the right maxillary central incisor. Before the local anaesthetic infiltration around the tooth, stimulation produced the typical inhibition in both muscles. The upper part of the figure illustrates this inhibitory effect in two successive trials. When the tooth was anaesthetized (lower records), the same mechanical stimulus no longer produced inhibition.
EFFECTS
OF CONTROLLED
TOOTH
STIMULATION
ON JAW
MUSCLE
ACTIVITY
1603
thesia) recordings of right and left muscle activity, mechanical stimulation of the incisor produced inhibitory periods. However, when the tooth was anaesthetized, the same mechanical stimulation no longer produced any inhibition. The lower recordings of Fig. 4 illustrate the uninterrupted activity which occurred in both muscles after local anaesthesia of the incisor. The inhibition of muscle activity following the jaw jerk was still apparent when the incisor was anaesthetized. The effect of mechanical stimulation of the left maxillary canine on right and left muscle activity was also noted before and after local anaesthetic infiltration around the incisor. Inhibitory periods could be produced by canine stimulation, and local anaesthesia of the incisor had no effect on their occurrence. DISCUSSION JERCE(1964) and KAWAMURA(1964; 1967) have postulated that reflex excitation of jaw opening muscles and reflex inhibition of jaw closing muscles elicited by mechanical stimulation of the teeth constitute the underlying neural basis of cyclic jaw movements and mastication. There has been a considerable number of recent studies in man which have shown these excitatory or inhibitory effects (AHLGREN, 1967; 1969; SHAERERet al., 1967; BRENMANet al., 1968; BEAUDREAU et al., 1969; GRIFFIN and MUNRO,1969; MUNROand GRIFFIN,1970). But these studies, with the exception of that of Beaudreau and colleagues, did not use local anaesthesia to implicate definitively periodontal receptors in the jaw closing muscle inhibition that was observed when the teeth were tapped. The values of the latency and duration of the inhibitory period noted by Beaudreau and associates were two to three times the values recorded by other workers, so considerable doubt exists as to the exact nature of the inhibition that Beaudreau and colleagues noted. In a study designed to overcome these deficiencies in methodology and determine the involvement of periodontal receptors, HANNAMet aE. (1969, 1970) noted the effect of tooth stimulation on muscle activity before and after local anaesthesia of the tooth. They concluded, as a result of infiltration of only 0.5 ml of local anaesthetic, that periodontal receptors are not involved in the inhibition produced. They implicated other receptors, in particular, muscle spindles. However, reference to their illustrated results reveals a definite decrease in the duration of the inhibitory period when the stimulated tooth was anaesthetized and this effect has also been noted recently by GOLDBERG(1971). But these and all previous workers stimulated the teeth mechanically either by tapping the teeth as a result of jaw closure by the subject or by a tap applied to a tooth with a hammer, rod or instrument. These obviously uncontrolled and unreproducible means of tooth stimulation probably account for the inability to implicate fully periodontal receptors in the tooth-evoked inhibition of muscle activity. The present study utilized an electronically controlled mechanical stimulator of similar design to that used in quantitative neurophysiological studies of the tactile response properties of single neurones (e.g. WERNER and MOUNTCASTLE,1965; DARIAN-SMITH, ROWEand SESSLE,1968; TALBOTet al., 1968; ROWEand SESSLE,1972). This stimulator could deliver extremely accurate and reproducible mechanical stimuli
1604
B. J. SESSLEAND ADRIANNE SCHMITT
and so, under the experimental conditions, there would have been little change, if any, in the parameters of the stimulus delivered before and after local anaesthesia of the tooth. Our results provide conclusive evidence that mechanical stimulation of the tooth results in an inhibition of the jaw closing muscles that can be completely attributed to activation of receptors in or around the tooth stimulated. Local anaesthesia of the tooth almost completely abolished the inhibition elicited by tooth stimulation and in most of the individual subjects there was total abolition. This then would rule out the involvement of other receptors, such as muscle spindles which HANNAMet al. (1970) have implicated, although it would not preclude their involvement in the longer-latency inhibition that follows the jaw jerk. Hannam and colleagues felt that periodontal receptors are possibly concerned in jaw muscle inhibition to protect the masticatory system from a traumatic overload only when excessive forces are developed between the teeth. However, the present study used stimulus parameters which could not be considered to deliver excessive or possibly traumatic forces to the tooth. Moreover, the fact that local anaesthetic infiltrated around the incisor abolished the inhibitory period to incisor stimulation, but not to canine stimulation, further indicates that the effect was localized to the incisor region. The stimulation of the right incisor produced an inhibition in the right muscle that was significantly shorter in latency than that occurring in the left muscle. This would suggest that the pathway from the incisor to the contralateral motoneurones innervating the left masseter muscle probably involves an additional interneurone. It is noteworthy that KIDOKOROet al. (1968) also noted the bilaterality of the reflex inhibition of jaw closing muscles as a result of inferior dental nerve stimulation in cat. Moreover, the inhibitory postsynaptic potentials produced in the jaw closing motoneurons ipsilateral to the nerve stimulus showed a shorter latency than those occurring in the contralateral motoneurones. The neural pathway of the inhibitory effect may involve the trigeminal mesencephalic nucleus or trigeminal ganglion since cell bodies of afferent fibres innervating the periodontium have been identified in both regions in cat (CORBINand HARRISON, 1940; JERGE, 1963a ; BEAUDREAU and JERGE, 1968 ; ROWE and SESSLE,1972). The central axon would then probably pass to the supratrigeminal nucleus (JERGE, 1963b; KIDOKOROet al., 1968). KIDOKOROet al. (1968) and SUMINO(1971) have implicated this nucleus as the source of interneurones responsible for a disynaptic inhibition of jaw closing motoneurones produced by inferior dental nerve stimulation. The latency of the inhibition produced in the right masseter muscle by tooth stimulation in the present study is not incompatible with their value of the latency of the motoneurone inhibition. The initial excitatory effect that was found, in the present study and that of GOLDBERG(1971), to precede the inhibitory period could involve the electrotonic coupling recently identified between trigeminal mesencephalic neurones (HINRICHSEN, 1970; BAKER and LLINAS, 1971). Both HINRICHSEN(1970) and GOLDBERG(1971) have suggested that tooth stimulation might excite trigeminal motoneurones through an excitatory coupling with muscle afferent neurones in the mesencephalic nucleus.
EFFECTS
OF CONTROLLED
TOOTH
STIMULATION
ON JAW
MUSCLE
ACTIVITY
1605
However, there is no evidence as yet that mesencephalic neurones activated by tooth stimulation are involved in these couplings. Another possible mechanism of the initial excitation in jaw closing muscles is a direct excitatory connection of periodontal nerve fibres with trigeminal motoneurones. SZENTAGOTHAI’S (1948) classical description of the trigeminal monosynaptic reflex was based on mesencephalic nuclear lesions experiments. He traced degenerating nerve fibres peripherally to jaw muscles and centrally to trigeminal motoneurones. Since periodontally-derived primary afferent neurones also occur in this nucleus, a monosynaptic or disynaptic excitatory connection from this source to the trigeminal motor nucleus should also be considered. Alternatively, the excitatory pathway could be via the trigeminal ganglion and brain stem sensory nuclei where neurones responsive to tactile stimulation of teeth have been described in cat (KRUGER and MICHEL, 1962; KAWAMURAand NISHIYAMA,1966; BEAUDREAUand JERGE, 1968; ROWE and SESSLE,1972). The recent study of SUMINO(1971) would suggest that this pathway is involved in a disynaptic activation of trigeminal motoneurones. Acknowledgements-We gratefully acknowledge the technical assistance of Mr. M. KALOVSKY and Mr. D. OMURAand the critical assessment of the manuscript by Dr. A. T. STOREY.The study was supported by grant DG 73 from the Canadian Medical Research Council. Miss SCHMITTwas the recipient of a Summer Undergraduate Dental Research Scholarship from the Medical Research Council.
Rt%um&L’activite electromyographique des masseters droit et gauche est enregistree chez neuf sujets apres percussion dentaire. Pendant la phase d’activite de ces muscles, l’incisive centrale supbieure droite est percutee par un stimulateur mecanique, controle electroniquement et susceptible de provoquer des stimuli precis et reproductibles. Une stimulation axiale ou vestibulaire de la dent provoque une ptriode d’inhibition dans I’activite musculaire et cette inhibition est souvent pr&cCdCepar une excitation initiale. L’inhibition des muscles droit et gauche est mesuree en termes de frequence, latence et dun&. Elle est cornpar& avec la phase d’inhibition qui suit le debut dun reflexe maxillaire de percussion. L’anesthesie locale de l’incisive supprime l’inhibition provoquee par la stimulation de la dent, mais n’affecte pas l’inhibition accompagnant le reflexe maxillaire de percussion ou la stimulation de la canine sup&ieure gauche. Des recepteurs situ& dans et autour de la dent sont responsables de l’inhibition de l’activite musculaire maxillaire provoquee. par percussion de la dent.
Zusammenfassung-Die elektromyographische Aktivitat des rechten und linken Muskels Masseter, wird bei neun Versuchspersonen, im Zusammenhang mit Zahnperkussion registriert. Wahrend der Aktivitgtsphase dieser Muskeln, wird der obere rechte mittlere Schneidezahn, durch einen, priizise und reproduzierbare Stimulis ausliisenden, elektronisch kontrollierten, mechanischen Stimulator perkutiert. Eine axiale oder vestibuliire Stimulation des Zahnes, hat eine Inhibitionsperiode der Muskeltltigkeit zur Folge, der oft ein anftinglicher Anreiz vorausgeht. Eine lokale Antisthesie des Schneidezahnes beseitigt zwar die, durch die Stimulierung des Zahnes, hervorgerufene Inhibition, beeinflusst jedoch keinesfalls die, den maxillliren Perkussionsreflex, oder die Stimulierung des oberen linken Eckzahnes begleitende Funktionshemmung. Rezeptoren die sich innerhalb und ausserhalb des Zahnes betinden, sind fur die von der Zahnperkussion. verursachten Inhibition der maxilltiren Muskeltltigkeit verantwortlich.
1606
B. J.
SESSLEAND ADRIANNE SCHMITT
REFERENCES AHLGREN,J. 1967. Kinesiology of the mandible. Acra. odont. stand. 25, 593-611. AHLGREN,J. 1969. The silent period in the EMG of the jaw muscles during mastication and its relationship to tooth contact. Acta. odont. stand. 27,219-227. BAKER, R. and LLINAS, R. 1971. Electrotonic coupling between neurones in the rat mesencephalic nucleus. J. Physiol. (Lond.) 212,45-63. BEAUDREAU,D. E. and JERGE, C. R. 1968. Somatotopic representation in the Gasserian ganglion of tactile peripheral fields in the cat. Archs oral Biol. 13, 247-256. BEAUDREAU,D. E., DAUGHERTY,W. F. and MASLAND,W. S. 1969. Two types of motor pause in masticatory muscles. Am. J. Physiol. 216, 16-21. BRENMAN,H. S., BLACK, M. A. and COSLET,J. G. 1968. Interrelationship between the electromyographic silent period and dental occlusion. J. dent. Res. 47, 502. CORBIN,K. B. and HARRISON,F. 1940. Function of the mesencephalic root of fifth cranial nerve. J. Neurophysiol. 3, 423-435.
DARIAN-SMITH,I., ROWE, M. J. and SESSLE,B. J. 1968. “Tactile” stimulus intensity: information transmission by relay neurons in different trigeminal nuclei. Science 160, 791-794. GRIFFIN, C. J. and MUNRO, R. R. 1969. Electromyography of the jaw-closing muscfes in the opencloseeclench cycle in man. Archs oral Biof. 14,141-149. GOLDBERG,L. J. 1971. Masseter muscle excitation induced by stimulation of periodontal and gingival receptors in man. Brain Res. 32,369-381. HANNAM,A. G., MATTHEWS,B. and YEMM,R. 1969. Changes in the activity of the masseter muscle following tooth contact in man. Archs oral Biol. 14, 1401-1406. HANNAM, A. G., MATTHEWS,B. and YEMM, R. 1970. Receptors involved in the response of the masseter muscle to tooth contact in man. Archs oral Biol. 15,17-24. HINRICHSEN,C. F. L. 1970. Coupling between cells of the trigeminal mesencephalic nucleus. J. dent. Res. 49,1369-1373. JERGE, C. R. 1963a. The organization and function of the trigeminal mesencephalic nucleus. J. Neurophysiol. 26, 379-392.
JERGE,C. R. 1963b. The function of the nucleus supratrigeminalis. J. Neurophysiol. 26, 393-402. JERGE,C. R. 1964. The neurologic mechanism underlying cyclic jaw movements. J. prosth. Dent. 14, 667-681.
KAWAMURA,Y. 1964. Recent concepts in the physiology of mastication. In: Advances in Oral Biology (edited by STAPLE,P. H.). ,Vol. I. Academic Press, New York. KAWAMURA,Y. 1967. Neurophysiological background of occlusion. Periodontics 5, 175-183. KAWAMURA,Y. and NISHIYAMA,T. 1966. Projection of dental afferent impulses to the trigeminal nuclei of the cat. Jap. J. Physiol. 16, 584-597. KIDOKORO,Y., KUBOTA,K., SHUTO,S. and SUMINO,R. 1968. Possible interneurones responsible for reflex inhibition of motoneurones of jaw-closing muscles from the inferior dental nerve. J. Neurophysiol.
31, 709-716.
KRUGER, L. and MICHEL, F. 1962. A single neurone analysis of buccal cavity representation in the sensory trigeminal complex of the cat. Archs oral Biol. 7,491-503. MUNRO, R. R. and GRIFFIN, C. J. 1970. Analysis of the electromyography of the masseter muscle and the anterior part of the temporalis muscle in the opencloseclench cycle in man. Archs oral Biol. 15,827-844. ROWE, M. J. and SESSLE,B. J. 1972. Responses of trigeminal ganglion and brain stem neurones in the cat to mechanical and thermal stimulation of the face. Brain Res. 42,367-384. SHAERER, P., STALLARD,R. E. and ZANDER, H. A. 1967. Occlusal interferences and mastication: An electromyographic study. J. prosth. Dent. 17,438449. SHERRINGTON, C. S. 1917. Reflexes excitable in the cat from pinna, vibrissae and jaws. J. Physiol. (Land.) 51, 40443 1. SUMINO,R. 1971. Central neural pathways involved in the jaw-opening reflex in the cat. In: OralFacial Sensory and Motor Mechanisms (edited by DUBNER,R. and KAWAMURA,Y.). AppletonCentury-Crofts, New York. SZENTAGOTHAI, J. 1948. Anatomical considerations of monosynaptic reflex arcs. J. NeurophysioL 11, 445-454.
EFFECTSOF CONTROLLED TOOTH STIMULATION ON JAW TALBOT, W. H., DARIAN-SMITH, flutter-vibration:
Comparison
MUSCLE
ACTIVITY
1607
I., KORNHUBER, H. H. and MOUNTCASTLE, V. B. 1968. The sense of of the human capacity with response patterns of mechanoreceptive
afferents from the monkey hand. J. Neurophysiol. 31,301-334. WERNER, G. and MOUNTCASTLE, V. B. 1965. Neural activity in mechanoreceptive cutaneous afferents: Stimulus-response relations, Weber functions, and information transmission. J. Neurophysiol.
28,359-397.
oral
Bid.
Vol. 17, pp. 1597-1607, 1972. Pergamon
Press. Printed in Great Britain
EFFECTS OF CONTROLLED TOOTH STIMULATION ON JAW MUSCLE ACTIVITY IN MAN B. J. SESSLEand ADRIANNESCHMITT Division of Biological Sciences, Faculty of Dentistry, University of Toronto, Toronto 2, Canada
Summary-The electromyographic activity of the right and left masseter muscles was recorded in nine subjects on tooth tapping. During maintained activity of these muscles, the right maxillary central incisor was tapped by an electronically controlled mechanical stimulator capable of delivering very accurate and reproducible stimuli. Axial or labial stimulation of the tooth produced an inhibitory period in the jaw muscle activity, and this inhibition was frequently preceded by an initial excitation. The inhibition in right and left muscles was quantified in terms of its incidence, latency and duration, and compared with the inhibitory period that followed initiation of a jaw jerk reflex. Local anaesthesia of the incisor abolished the inhibition elicited from stimulation of this tooth, but left unaffected the inhibition accompanying the jaw jerk reflex or stimulation of the left maxillary canine. It was concluded that receptors in or around the tooth are responsible for the inhibition of jaw muscle activity produced by tapping the tooth.
INTRODUCTION
SINCEthe demonstration by SHERRINGTON (1917) in the cat that stimulation of the teeth, gingiva or hard palate produces reflex jaw opening, the work of several groups of investigators in man (AHLGREN, 1967; 1969; SHAERER,STALLARDand ZANDER, 1967; BRENMAN,BLACKand COSLET,1968; BEAUDREAU, DAUGHERTYand MASLAND, 1969; GRIFFINand MUNRO, 1969; MUNROand GRIFFIN, 1970; GOLDBERG,1971) has indicated that receptors in the periodontium are concerned in the control of jaw movements. Moreover, it has been proposed (JERGE, 1964; KAWAMURA,1964, 1967) that periodontal receptors, by virtue of central connections resulting in excitation of jaw opening muscles and inhibition of jaw closing muscles, are intimately involved in cyclic jaw movements and mastication. However, the recent results of HANNAM,MATTHEWSand YEMM (1969; 1970) have cast serious doubt on this view. They observed in man that the reflex inhibition of jaw closing muscles that results from tapping a tooth is not abolished by local anaesthetic infiltration around the tooth. This would indicate that periodontal receptors are not involved in the inhibition. In a similar study, GOLDBERG(1971) also was unable to abolish the inhibitory period induced by tooth tap, although there was some reduction in its duration. These, and the previous studies of the inhibition produced by tapping teeth used rather gross and uncontrolled means of tooth stimulation 1597 A.O.B. 17/l 1-s
1598
B. J.
SESSLE
AND
ADRIANNESCHMIT-~
(e.g. a hammer) and it seems possible that periodontal receptors adjacent to the tooth (which was tapped and then anaesthetized) were contributing to the inhibition under these conditions. Thus from all this previous investigation, it is no longer clear to what extent, if any, periodontal receptors contribute to jaw muscle inhibition. For this reason and because of its relevance to our understanding of the neural basis of jaw movements and mastication, we decided to reinvestigate the possible contribution of periodontal receptors using a more quantitative approach and a controlled means of tooth stimulation. METHOD Nine young adults (four males, five females) with intact dentitions were used in this study. Each subject was seated upright and comfortably in a dental chair. The head of the subject was supported behind by a head board which had a strap attached. The strap was placed around the subject’s forehead to prevent movement during the experimental procedure. Unipolar surface electrodes (Beckman Instruments, Calif.) were positioned on the skin overlying the left and right masseter muscles to record the electromyographic activity of these jaw closing muscles. Reference electrodes were placed on the ear lobes. The activity from both muscles was amplified (Grass Preamplifier III D, frequency range l-10,000 c/set) and displayed on two channels of a dual-beam oscilloscope, and all the oscilloscopic recordings were photographed for subsequent analysis. Each subject was asked to maintain continuous activation of both muscles (Fig. 1) either by biting on cotton rolls placed between the premolars and molars or by clenching the mandible in an open position. While this activity was maintained, the right maxillary central incisor was stimulated using an electronically driven and precisely controlled mechanical stimulator (WERNERand MOUNTCASTLE,1965) capable of delivering reproducible and accurate (63 pm) tactile stimuli to the tooth. The stimulator was bolted firmly into a vice (Universal Vise, Atlas, Mich.) mounted on a heavy wooden platform which was at chest level. The vice permitted vertical and horizontal (in two planes) movement of the stimulator so that it could be accurately positioned with respect to the subject’s incisor. The mechanical stimulus was delivered at a rate of l/2 set, and 10 msec after the start of the oscilloscope sweep (Fig. 2). It had a duration of 10 msec, a displacement of 300 pm, and a rising phase of 3 msec. The stimulus was applied so that it contacted the tooth towards the end of its displacement and in all experiments the dynamic and static components of the force delivered to the tooth were 400 g and 200 g respectively. The stimulus was quite innocuous, and no subject complained of pain or discomfort from the tooth stimulus. The mechanical stimulus was first delivered in an axial direction to the incisor. After the muscle responses were recorded and photographed, the sequence was then repeated with the stimulus delivered from a labial direction. In each subject, the stimulus was applied 10 or more times to allow statistical evaluation (utilizing Student’s t-test of significance) of the incidence, latency and duration of the inhibitory periods in muscle activity. In this study, significance denotes a value of p less than 0.05, unless otherwise specified. Latency reflects the time from onset of the mechanical stimulus to the start of depression in electromyographic activity. The jaw jerk was also elicited in four subjects by applying a short, sharp tap to the chin with a reflex hammer. The oscilloscope beam was triggered to sweep at the instant the hammer made contact with the chin. This arrangement was also used to tap the forehead to determine if the inhibitory period produced by the tooth stimulation could be explained by stimulus spread to remote receptors such as muscle stretch, vestibular or temporomandibular receptors. The involvement of receptors in or adjacent to the tooth in the inhibitory effect produced by incisor stimulation was also tested using local anaesthesia. The entire jaw jerk and tooth stimulation procedures outlined above were repeated 10 min after infiltrating local anaesthetic palatally and labially around the root of the incisor. The anaesthetic used was 2 ml of 2 per cent lidocaine hydrochloride with 1 in 100,000 epinephrine (Xylocaine, Astra, Ont.). In six subjects, a labially directed mechanical stimulus was also delivered to the left maxillary canine before and after the local anaesthetic infiltration around the incisor. This was used as a check on the stimulation procedures and the localization of the local anaesthesia.
EFFECTS OF CONTROLLED
TOOTH
STIMULATION
ON JAW
MUSCLE ACTIVITY
1599
RESULTS
When the subject was instructed to tap his teeth together, a period of complete inhibition in this muscle activity occurred. An example of such an interruption in muscle activity can be seen in the lower recordings of Fig. 1. Typical levels of right and left masseter muscle activity generated by maintaining closure on cotton rolls can be seen in the upper part of Fig. 1. These periods of complete or partial inhibition could also be duplicated by applying the mechanical stimulus to the right maxillary central incisor (Fig. 2). The inhibitory effect was particularly noticeable in the situation where the subject was maintaining
Subject Maintaining
Bite
LM RM
Subject Tapping Teeth Together
1. Inhibitory period produced by subject tapping teeth together. The upper records illustrate the typical levels of activity in the left masseter (LM) and right masseter (RM) when the subject maintained closure on cotton rolls placed between the posterior teeth. When the cotton rolls were removed and the subject instructed to close and tap his teeth (lower records), a period of inhibition of approximately 15 msec duration occurred in both muscles. In this and subsequent figures, negative polarity is upward, voltage calibration is 0.2 mV and time calibration is 20 msec. FIG.
muscle activity by closing on the cotton rolls. All the following results apply to inhibitory effects on this maintained activity, since the inhibitory periods were not so obvious when the tooth was stimulated (or the jaw jerk elicited) with the muscles clenched in the jaw open position.
B. J. SESSLEAND ADRIANNESCHMITT
1600
Apart from the inhibitory period produced by tooth stimulation, another interesting finding was the frequent occurrence of an increased muscle activity immediately preceding the inhibition (Fig. 2). The high level of muscle activity that already existed due to the subject biting on cotton rolls precluded any quantitative assessment of this initial excitatory effect. The inhibitory periods were of very frequent occurrence. Table 1 indicates the incidence of this inhibition in both right and left muscles. Inhibition was most prevalent in the right muscle, occurring in approximately 80 per cent of trials with axial stimulation and 70 per cent with labial stimulation. In the left muscle, inhibition occurred in about 60 per cent and 70 per cent of trials with axial and labial stimulations respectively. Whenever an inhibition occurred, it nearly always was found in both right and left muscles. For example, an inhibitory period occurred in the left muscle in 81 per cent of the trials in which an axial stimulus to the incisor produced inhibition in the right muscle. When the tooth was stimulated in a labial direction, the bilateral occurrence was almost 100 per cent.
LM RM
FIG. 2. Effect of mechanical stimulation of the right maxillary central incisor on the left (LM) and right (RM) masseter maintained closing activity. The electronic analogue of the mechanical stimulus is shown in the lower part of the figure. The stimulus produced an initial excitation followed by a period of inhibition in the muscle activity.
In addition to the incidence of the inhibition produced by tooth stimulation, other parameters of the inhibitory effect were quantified. Table 1 shows the latencies and durations of the inhibition produced in right and left muscles by both axial and labial stimulation of the right incisor. Neither the direction of stimulation of the tooth nor the side on which the inhibition was recorded had any significant effect on the duration of the inhibitory period. However, a significant difference occurred between the right and left muscles in the latency of the inhibition. In the right muscle, the mean latency (& standard error) was 12.9 f 0.29 msec with axial stimulation but in the left muscle a longer latency value, 14.2 & 0’29 msec, was found. Similarly, with labial stimulation, the latency in the right muscle, 15 -2 f 0.62 msec, was significantly shorter
EFFECTS
OF CONTROLLED
TOOTH
STIMULATION
Labial
AXid
Latency Duration Incidence Before anaesthesia With anaesthesia
Each
latency
12.9 15.5
and duration
+ 0.29 f 0.39
ON JAW
15.2 15.1
MUSCLE
ACTIVITY
Axial
f 0.62 * 0.42
14.2 15.8
* 0.29 zk 0.29
1601
Labial
16.8 14.8
f 0.66 zk 0.42
62/91 2197
value is expressed
as mean
*
standard
error
(msec).
than the value of 16.8 + O-66 msec in the left muscle. In addition, a highly significant (p < 0.001) difference occurred between the latencies to axial and labial stimulation. For both the right and left muscles, the latency with axial stimulation was shorter than with labial stimulation. These findings of significant differences in latencies but not in durations were also obvious when the results from individual subjects were analyzed. For example, in one subject, axial stimulation resulted in a significantly shorter latency in the right muscle (12 - 5 f 1.1 msec) than in the left muscle (14.2 f 1.0 msec). It is also noteworthy that these individual values were not significantly different from the mean values of all nine subjects. In no subject was there any clear evidence of an inhibitory period produced by forehead stimulation. However, a period of inhibition followed the jaw jerk in almost 60 per cent of the tests (Fig. 3) and in all but one case it occurred bilaterally. There
FIG. 3. Inhibitory period following the jaw jerk in left (LM)) and right (RM) masseters. A typical record of the jaw jerk and inhibition is shown in the upper part of the figure. In the lower part are listed the latency, duration and incidence of this inhibition in both muscles. Each latency and duration value is expressed as mean & standard error (msec).
1602
B. J.
SESSLEAND ADRIANNE SCHMITT
no significant difference between right and left muscles in the latency and duration of the inhibition. Two noteworthy differences were found, however, when the inhibition following the jaw jerk was compared with that elicited by axial or labial stimulation of the incisor. The duration of the inhibition was longer, at a high level of significance (p < O.OOl), in all cases with the jaw jerk than in the cases with tooth stimulation. Moreover, at the same level of significance, the latency of the inhibition was longer when the inhibitory period accompanied the jaw jerk than when it was elicited by tooth stimulation. The implication of receptors in or around the tooth in the initiation of the muscle inhibition was conclusively demonstrated when local anaesthetic was infiltrated labially and palatally around the incisor and the series of stimulations repeated. Ten minutes after administration of the anaesthetic, there was an almost complete abolition of the inhibitory periods elicited by tooth stimulation. Table 1 shows the marked decrease in the incidence of the inhibition as a result of local anaesthesia of the incisor. In the right muscle, for example, the incidence of inhibition produced by axial stimulation of the incisor decreased from a control (pre-anaesthetic) level of approximately 80 per cent to an occurrence of only 8 per cent when the incisor was anaesthetized. With labial stimulation, the incidence dropped from a control level of about 70 per cent to a 2 per cent level after local anaesthesia of the tooth. In all but two subjects, the local anaesthesia totally abolished the occurrence of the inhibition. This effect of local anaesthesia on the incidence of the inhibition is also shown in Fig. 4 which illustrates typical recordings of muscle activity before and after local anaesthetic infiltration of the incisor. In two successive control (before local anaeswas
BeforeLocalAnaesthesia
After LocalAnaesthesia
-I
FIG. 4. Effect of local anaesthesia on the inhibitory period elicited in the left (LM) and right (RM) masseters by mechanical stimulation of the right maxillary central incisor. Before the local anaesthetic infiltration around the tooth, stimulation produced the typical inhibition in both muscles. The upper part of the figure illustrates this inhibitory effect in two successive trials. When the tooth was anaesthetized (lower records), the same mechanical stimulus no longer produced inhibition.
EFFECTS
OF CONTROLLED
TOOTH
STIMULATION
ON JAW
MUSCLE
ACTIVITY
1603
thesia) recordings of right and left muscle activity, mechanical stimulation of the incisor produced inhibitory periods. However, when the tooth was anaesthetized, the same mechanical stimulation no longer produced any inhibition. The lower recordings of Fig. 4 illustrate the uninterrupted activity which occurred in both muscles after local anaesthesia of the incisor. The inhibition of muscle activity following the jaw jerk was still apparent when the incisor was anaesthetized. The effect of mechanical stimulation of the left maxillary canine on right and left muscle activity was also noted before and after local anaesthetic infiltration around the incisor. Inhibitory periods could be produced by canine stimulation, and local anaesthesia of the incisor had no effect on their occurrence. DISCUSSION JERCE(1964) and KAWAMURA(1964; 1967) have postulated that reflex excitation of jaw opening muscles and reflex inhibition of jaw closing muscles elicited by mechanical stimulation of the teeth constitute the underlying neural basis of cyclic jaw movements and mastication. There has been a considerable number of recent studies in man which have shown these excitatory or inhibitory effects (AHLGREN, 1967; 1969; SHAERERet al., 1967; BRENMANet al., 1968; BEAUDREAU et al., 1969; GRIFFIN and MUNRO,1969; MUNROand GRIFFIN,1970). But these studies, with the exception of that of Beaudreau and colleagues, did not use local anaesthesia to implicate definitively periodontal receptors in the jaw closing muscle inhibition that was observed when the teeth were tapped. The values of the latency and duration of the inhibitory period noted by Beaudreau and associates were two to three times the values recorded by other workers, so considerable doubt exists as to the exact nature of the inhibition that Beaudreau and colleagues noted. In a study designed to overcome these deficiencies in methodology and determine the involvement of periodontal receptors, HANNAMet aE. (1969, 1970) noted the effect of tooth stimulation on muscle activity before and after local anaesthesia of the tooth. They concluded, as a result of infiltration of only 0.5 ml of local anaesthetic, that periodontal receptors are not involved in the inhibition produced. They implicated other receptors, in particular, muscle spindles. However, reference to their illustrated results reveals a definite decrease in the duration of the inhibitory period when the stimulated tooth was anaesthetized and this effect has also been noted recently by GOLDBERG(1971). But these and all previous workers stimulated the teeth mechanically either by tapping the teeth as a result of jaw closure by the subject or by a tap applied to a tooth with a hammer, rod or instrument. These obviously uncontrolled and unreproducible means of tooth stimulation probably account for the inability to implicate fully periodontal receptors in the tooth-evoked inhibition of muscle activity. The present study utilized an electronically controlled mechanical stimulator of similar design to that used in quantitative neurophysiological studies of the tactile response properties of single neurones (e.g. WERNER and MOUNTCASTLE,1965; DARIAN-SMITH, ROWEand SESSLE,1968; TALBOTet al., 1968; ROWEand SESSLE,1972). This stimulator could deliver extremely accurate and reproducible mechanical stimuli
1604
B. J. SESSLEAND ADRIANNE SCHMITT
and so, under the experimental conditions, there would have been little change, if any, in the parameters of the stimulus delivered before and after local anaesthesia of the tooth. Our results provide conclusive evidence that mechanical stimulation of the tooth results in an inhibition of the jaw closing muscles that can be completely attributed to activation of receptors in or around the tooth stimulated. Local anaesthesia of the tooth almost completely abolished the inhibition elicited by tooth stimulation and in most of the individual subjects there was total abolition. This then would rule out the involvement of other receptors, such as muscle spindles which HANNAMet al. (1970) have implicated, although it would not preclude their involvement in the longer-latency inhibition that follows the jaw jerk. Hannam and colleagues felt that periodontal receptors are possibly concerned in jaw muscle inhibition to protect the masticatory system from a traumatic overload only when excessive forces are developed between the teeth. However, the present study used stimulus parameters which could not be considered to deliver excessive or possibly traumatic forces to the tooth. Moreover, the fact that local anaesthetic infiltrated around the incisor abolished the inhibitory period to incisor stimulation, but not to canine stimulation, further indicates that the effect was localized to the incisor region. The stimulation of the right incisor produced an inhibition in the right muscle that was significantly shorter in latency than that occurring in the left muscle. This would suggest that the pathway from the incisor to the contralateral motoneurones innervating the left masseter muscle probably involves an additional interneurone. It is noteworthy that KIDOKOROet al. (1968) also noted the bilaterality of the reflex inhibition of jaw closing muscles as a result of inferior dental nerve stimulation in cat. Moreover, the inhibitory postsynaptic potentials produced in the jaw closing motoneurons ipsilateral to the nerve stimulus showed a shorter latency than those occurring in the contralateral motoneurones. The neural pathway of the inhibitory effect may involve the trigeminal mesencephalic nucleus or trigeminal ganglion since cell bodies of afferent fibres innervating the periodontium have been identified in both regions in cat (CORBINand HARRISON, 1940; JERGE, 1963a ; BEAUDREAU and JERGE, 1968 ; ROWE and SESSLE,1972). The central axon would then probably pass to the supratrigeminal nucleus (JERGE, 1963b; KIDOKOROet al., 1968). KIDOKOROet al. (1968) and SUMINO(1971) have implicated this nucleus as the source of interneurones responsible for a disynaptic inhibition of jaw closing motoneurones produced by inferior dental nerve stimulation. The latency of the inhibition produced in the right masseter muscle by tooth stimulation in the present study is not incompatible with their value of the latency of the motoneurone inhibition. The initial excitatory effect that was found, in the present study and that of GOLDBERG(1971), to precede the inhibitory period could involve the electrotonic coupling recently identified between trigeminal mesencephalic neurones (HINRICHSEN, 1970; BAKER and LLINAS, 1971). Both HINRICHSEN(1970) and GOLDBERG(1971) have suggested that tooth stimulation might excite trigeminal motoneurones through an excitatory coupling with muscle afferent neurones in the mesencephalic nucleus.
EFFECTS
OF CONTROLLED
TOOTH
STIMULATION
ON JAW
MUSCLE
ACTIVITY
1605
However, there is no evidence as yet that mesencephalic neurones activated by tooth stimulation are involved in these couplings. Another possible mechanism of the initial excitation in jaw closing muscles is a direct excitatory connection of periodontal nerve fibres with trigeminal motoneurones. SZENTAGOTHAI’S (1948) classical description of the trigeminal monosynaptic reflex was based on mesencephalic nuclear lesions experiments. He traced degenerating nerve fibres peripherally to jaw muscles and centrally to trigeminal motoneurones. Since periodontally-derived primary afferent neurones also occur in this nucleus, a monosynaptic or disynaptic excitatory connection from this source to the trigeminal motor nucleus should also be considered. Alternatively, the excitatory pathway could be via the trigeminal ganglion and brain stem sensory nuclei where neurones responsive to tactile stimulation of teeth have been described in cat (KRUGER and MICHEL, 1962; KAWAMURAand NISHIYAMA,1966; BEAUDREAUand JERGE, 1968; ROWE and SESSLE,1972). The recent study of SUMINO(1971) would suggest that this pathway is involved in a disynaptic activation of trigeminal motoneurones. Acknowledgements-We gratefully acknowledge the technical assistance of Mr. M. KALOVSKY and Mr. D. OMURAand the critical assessment of the manuscript by Dr. A. T. STOREY.The study was supported by grant DG 73 from the Canadian Medical Research Council. Miss SCHMITTwas the recipient of a Summer Undergraduate Dental Research Scholarship from the Medical Research Council.
Rt%um&L’activite electromyographique des masseters droit et gauche est enregistree chez neuf sujets apres percussion dentaire. Pendant la phase d’activite de ces muscles, l’incisive centrale supbieure droite est percutee par un stimulateur mecanique, controle electroniquement et susceptible de provoquer des stimuli precis et reproductibles. Une stimulation axiale ou vestibulaire de la dent provoque une ptriode d’inhibition dans I’activite musculaire et cette inhibition est souvent pr&cCdCepar une excitation initiale. L’inhibition des muscles droit et gauche est mesuree en termes de frequence, latence et dun&. Elle est cornpar& avec la phase d’inhibition qui suit le debut dun reflexe maxillaire de percussion. L’anesthesie locale de l’incisive supprime l’inhibition provoquee par la stimulation de la dent, mais n’affecte pas l’inhibition accompagnant le reflexe maxillaire de percussion ou la stimulation de la canine sup&ieure gauche. Des recepteurs situ& dans et autour de la dent sont responsables de l’inhibition de l’activite musculaire maxillaire provoquee. par percussion de la dent.
Zusammenfassung-Die elektromyographische Aktivitat des rechten und linken Muskels Masseter, wird bei neun Versuchspersonen, im Zusammenhang mit Zahnperkussion registriert. Wahrend der Aktivitgtsphase dieser Muskeln, wird der obere rechte mittlere Schneidezahn, durch einen, priizise und reproduzierbare Stimulis ausliisenden, elektronisch kontrollierten, mechanischen Stimulator perkutiert. Eine axiale oder vestibuliire Stimulation des Zahnes, hat eine Inhibitionsperiode der Muskeltltigkeit zur Folge, der oft ein anftinglicher Anreiz vorausgeht. Eine lokale Antisthesie des Schneidezahnes beseitigt zwar die, durch die Stimulierung des Zahnes, hervorgerufene Inhibition, beeinflusst jedoch keinesfalls die, den maxillliren Perkussionsreflex, oder die Stimulierung des oberen linken Eckzahnes begleitende Funktionshemmung. Rezeptoren die sich innerhalb und ausserhalb des Zahnes betinden, sind fur die von der Zahnperkussion. verursachten Inhibition der maxilltiren Muskeltltigkeit verantwortlich.
1606
B. J.
SESSLEAND ADRIANNE SCHMITT
REFERENCES AHLGREN,J. 1967. Kinesiology of the mandible. Acra. odont. stand. 25, 593-611. AHLGREN,J. 1969. The silent period in the EMG of the jaw muscles during mastication and its relationship to tooth contact. Acta. odont. stand. 27,219-227. BAKER, R. and LLINAS, R. 1971. Electrotonic coupling between neurones in the rat mesencephalic nucleus. J. Physiol. (Lond.) 212,45-63. BEAUDREAU,D. E. and JERGE, C. R. 1968. Somatotopic representation in the Gasserian ganglion of tactile peripheral fields in the cat. Archs oral Biol. 13, 247-256. BEAUDREAU,D. E., DAUGHERTY,W. F. and MASLAND,W. S. 1969. Two types of motor pause in masticatory muscles. Am. J. Physiol. 216, 16-21. BRENMAN,H. S., BLACK, M. A. and COSLET,J. G. 1968. Interrelationship between the electromyographic silent period and dental occlusion. J. dent. Res. 47, 502. CORBIN,K. B. and HARRISON,F. 1940. Function of the mesencephalic root of fifth cranial nerve. J. Neurophysiol. 3, 423-435.
DARIAN-SMITH,I., ROWE, M. J. and SESSLE,B. J. 1968. “Tactile” stimulus intensity: information transmission by relay neurons in different trigeminal nuclei. Science 160, 791-794. GRIFFIN, C. J. and MUNRO, R. R. 1969. Electromyography of the jaw-closing muscfes in the opencloseeclench cycle in man. Archs oral Biof. 14,141-149. GOLDBERG,L. J. 1971. Masseter muscle excitation induced by stimulation of periodontal and gingival receptors in man. Brain Res. 32,369-381. HANNAM,A. G., MATTHEWS,B. and YEMM,R. 1969. Changes in the activity of the masseter muscle following tooth contact in man. Archs oral Biol. 14, 1401-1406. HANNAM, A. G., MATTHEWS,B. and YEMM, R. 1970. Receptors involved in the response of the masseter muscle to tooth contact in man. Archs oral Biol. 15,17-24. HINRICHSEN,C. F. L. 1970. Coupling between cells of the trigeminal mesencephalic nucleus. J. dent. Res. 49,1369-1373. JERGE, C. R. 1963a. The organization and function of the trigeminal mesencephalic nucleus. J. Neurophysiol. 26, 379-392.
JERGE,C. R. 1963b. The function of the nucleus supratrigeminalis. J. Neurophysiol. 26, 393-402. JERGE,C. R. 1964. The neurologic mechanism underlying cyclic jaw movements. J. prosth. Dent. 14, 667-681.
KAWAMURA,Y. 1964. Recent concepts in the physiology of mastication. In: Advances in Oral Biology (edited by STAPLE,P. H.). ,Vol. I. Academic Press, New York. KAWAMURA,Y. 1967. Neurophysiological background of occlusion. Periodontics 5, 175-183. KAWAMURA,Y. and NISHIYAMA,T. 1966. Projection of dental afferent impulses to the trigeminal nuclei of the cat. Jap. J. Physiol. 16, 584-597. KIDOKORO,Y., KUBOTA,K., SHUTO,S. and SUMINO,R. 1968. Possible interneurones responsible for reflex inhibition of motoneurones of jaw-closing muscles from the inferior dental nerve. J. Neurophysiol.
31, 709-716.
KRUGER, L. and MICHEL, F. 1962. A single neurone analysis of buccal cavity representation in the sensory trigeminal complex of the cat. Archs oral Biol. 7,491-503. MUNRO, R. R. and GRIFFIN, C. J. 1970. Analysis of the electromyography of the masseter muscle and the anterior part of the temporalis muscle in the opencloseclench cycle in man. Archs oral Biol. 15,827-844. ROWE, M. J. and SESSLE,B. J. 1972. Responses of trigeminal ganglion and brain stem neurones in the cat to mechanical and thermal stimulation of the face. Brain Res. 42,367-384. SHAERER, P., STALLARD,R. E. and ZANDER, H. A. 1967. Occlusal interferences and mastication: An electromyographic study. J. prosth. Dent. 17,438449. SHERRINGTON, C. S. 1917. Reflexes excitable in the cat from pinna, vibrissae and jaws. J. Physiol. (Land.) 51, 40443 1. SUMINO,R. 1971. Central neural pathways involved in the jaw-opening reflex in the cat. In: OralFacial Sensory and Motor Mechanisms (edited by DUBNER,R. and KAWAMURA,Y.). AppletonCentury-Crofts, New York. SZENTAGOTHAI, J. 1948. Anatomical considerations of monosynaptic reflex arcs. J. NeurophysioL 11, 445-454.
EFFECTSOF CONTROLLED TOOTH STIMULATION ON JAW TALBOT, W. H., DARIAN-SMITH, flutter-vibration:
Comparison
MUSCLE
ACTIVITY
1607
I., KORNHUBER, H. H. and MOUNTCASTLE, V. B. 1968. The sense of of the human capacity with response patterns of mechanoreceptive
afferents from the monkey hand. J. Neurophysiol. 31,301-334. WERNER, G. and MOUNTCASTLE, V. B. 1965. Neural activity in mechanoreceptive cutaneous afferents: Stimulus-response relations, Weber functions, and information transmission. J. Neurophysiol.
28,359-397.