Jaw Muscle Activity Research Articles

The effect of intercuspal clenching on the masseteric jaw-jerk reflex in humans

Although several studies have been conducted regarding the jaw-jerk reflex and its various modifying parameters, the effect of intercuspal clenching still remains poorly understood. Evidence of both excitatory and inhibitory influences of periodontal receptors on jaw muscle activity has been reported. It is also suggested that a level of background activity in the stimulated muscle facilitates the reflex response. It was therefore the purpose of this study to investigate the effect of simultaneously activated periodontal receptors on the various parameters of the masseteric jaw-jerk reflex during moderate masseter muscle activation. Electromyographic recordings were obtained from the masseter muscle of the preferred chewing side at rest and at intercuspal clenching in 10 men, by use of a computerized recording and analysis system. In the clenching trials the level of muscular activity was set at 40% of the maximum value obtained through visual feedback. The results showed that at 40% clenching the occurrence of the reflex was reduced as compared with that obtained at rest. Moreover, when present during clenching, its latency and duration were shorter, whereas its amplitude was higher,. It was suggested that the simultaneous activation of periodontal receptors may occasionally inhibit the masseteric monosynaptic excitation.

An investigation of the coupling between respiration, mastication, and swallowing in the awake rabbit.

1. The interrelationships between respiration, mastication, and swallowing were studied in awake rabbits previously prepared for the chronic recording of jaw movements and the electromyographic activity of jaw and throat muscles. These signals were recorded before, during, and after the mastication of rabbit chow, together with respiratory movements. 2. The onset of activity in the thyrohyoid muscle was used as a marker for swallowing. Measurements were made of cycle duration, and the phase relationship between the masticatory and respiratory rhythms was calculated. Deviations in masticatory and respiratory movements during swallowing were detected; the phases of the masticatory and respiratory cycles in which the deviations occurred were determined, and the intervals between the deviations and the swallowing marker were calculated. 3. Two characteristic swallowing patterns were observed that were called Interposed and Terminal swallows. Interposed swallows occurred within a masticatory sequence, while Terminal swallows ended the sequence. 4. In most rabbits, respiratory rate slowed during mastication. This brought the average frequency of the two movements closer together, and there was a weak but significant correlation between the masticatory and respiratory rates. However, respiration and mastication were not linked on a cycle-by-cycle basis, and the change in respiratory rate was found to be unrelated to masticatory rate. Further, there was no tendency for the masticatory and respiratory rhythms to adopt any particular phase relationship as swallowing was approached. Some weak and transient phase coupling of the two systems occurred after swallowing. 5. During swallowing, respiration was most often inhibited soon after the start of the inspiratory phase. Swallows within a masticatory sequence occurred most frequently during the early opening phase of the masticatory cycle, and swallows after the end of a sequence occurred with the jaw in the resting position. There was a strong tendency for the durations of the masticatory and respiratory cycles containing deviations to be longer than preceding control cycles, and the effect on respiration lasted several cycles. 6. For both Interposed and Terminal swallows, a tight temporal relationship was observed between deviations in respiration and the swallowing marker: most deviations tended to occur before swallowing. In contrast, the time of deviations in mastication relative to the swallowing marker depended on swallow type and was more variable. Finally, there was no link between the start of the pauses in the two rhythms. 7. We conclude that respiratory and masticatory processes are not strongly coupled.(ABSTRACT TRUNCATED AT 400 WORDS)

The recording and analysis of EMG and jaw tracking. II. reproducibility of jaw tracking

In 10 male and 10 female adults jaw movements and muscle activity were monitored during chewing. Subjects had a Class I occlusion and fluent unrestricted jaw movements; non exhibited signs or symptoms of craniomandibular disorders. Recordings were made on two occasions separated by 2 weeks. Within each recording session the subjects carried out a number of tasks under direction, including eating nuts and gum. The jaw movements were monitored with a Sirognathograph which had been interfaced to a computer for data logging and analysis. A computer program identified each chewing stroke and after scrutiny a data base was constructed of measurements from a subset of 4447 suitable strokes. Mean values of 10 parameters selected to describe jaw movements during chewing were entered into an ANOVA. This indicated that the major contribution to variance was due to the subject from whom the data was recorded. This intersubject variability is well known, but can its separation from the other contributions to the variation within the data be assessed? To provide an estimate of the spread of data the variance for each parameter was calculated, transformed and these values entered into an analysis of variance. All subject differed significantly in their chewing movements from one another. But 15 of the 20 subjects showed a greater degree of consistency than the other five: they exhibited good inter- and intra-recording reproducibility. The food being eaten made a major contribution to the variability. The timing of the chewing strokes was also more consistent than the dimensions of the chewing envelope.

Skull mechanics in the pigeon, Columba livia, a three-dimensional kinematic model.

AbstractThe mechanics of the skull of the pigeon are analyzed quantitatively, based on a three‐dimensional kinematic computer model that considers the skull as a mechanism (Goodman, '60). The degrees of freedom at each cranial joint are defined and translated into geometric relations, using the method of Elshoud ('80). The model predicts the positions of cranial elements from three input variables: the positions of the upper and lower bills and the length of the M. protractor quadrati et pterygoidei. Simulations with the model suggest the presence of a locking mechanism for the lower bill, which prevents its depression. High speed films of feeding pigeons confirmed that locking can occur at different upper bill positions. The locking mechanism may permit feeding pigeons to use the elastic energy stored in the hinge of the upper bill during the grasp, producing simultaneous fast closing of the upper and lower bills. Simulation of jaw muscle activity suggests that these jaw muscles should not be divided into “openers” and “closers.” © 1992 Wiley‐Liss, Inc.

Jaw muscle activity, the nucleus accumbens and dopaminergic agonists: A new approach

A method was developed to analyze electromyographic (EMG) signals in terms of power, viz., a measure for overall muscle activity and number of seconds marked by distinct frequency ranges. With the help of this method, the effects of intraaccumbens administration of distilled water, the D 1 receptor agonist SK&F 38393 (SKF; 5 μg), the D 2 receptor agonist LY 171555 (LY; 10 μg) and their combination upon the EMG signals of the masseter and the digastric muscle were analysed in freely moving rats. Only the combined treatment affected the power: The noted increase was limited to the digastric muscle. The time/frequency analysis was limited to frequency ranges 3–4 Hz (class A), 4–5 and 5–6 Hz (class B) and 6–7, 7–8, …, 12–13 and 13–14 Hz (class C). Apart from a small effect of SKF alone and of SKF in combination with LY on class B of the masseter muscle, neither SKF nor LY affected class A or B. SKF and LY increased and decreased, respectively, class C in both muscles. The data suggest that SKF and LY elicited both opposite and synergistic effects. The method is a new tool to analyze EMG signals in freely moving rats.

Jaw movement kinematics and jaw muscle (EMG) activity during drinking in the pigeon (Columba livia)

Movements of the maxilla and mandible were recorded during drinking in the head-fixed pigeon and correlated with electromyographic activity in representative jaw muscle groups. During drinking, each jaw exhibits opening and closing movements along both the dorso-ventral and rostro-caudal axes which may be linked with or independent of each other. All subjects showed small but systematic increases in cycle duration over the course of individual drinking bouts. Cyclic jaw movements during drinking were correlated with nearly synchronous activity in the protractor (levator) of the upper jaw and in several jaw closer muscles, as well as with alternating activity in tongue protractor and retractor muscles. No EMG activity was ever recorded in the lower jaw opener muscle, suggesting that lower jaw opening in this preparation is produced, indirectly, by the contraction of other muscles. The results clarify the contribution of the individual jaws to the generation of gape variations during drinking in this species.

Postural contractile activities of human jaw muscles following use of an occlusal splint

As induced by an occlusal splint over a period of 1 week, this study monitored surface electromyographic changes in the postural contractile activities of jaw elevator and depressor muscles in six healthy adults. The immediate effect of the occlusal splint was to increase the postural contractile activities of the suprahyoid muscles. All postural muscle activities showed wide-ranging biological variation, but the activities induced by the splint tended to stabilize within 1 week, with decreased postural activities in the masseter and anterior temporalis muscles, and increased postural activities in the suprahyoid muscles.

Three-dimensional analyses of human bite-force magnitude and moment

The effect of the three-dimensional orientation of occlusal force on maximal bite-force magnitude was examined in seven human subjects at three different unilateral anteroposterior bite positions (canine, second premolar and second molar). At each position, bite-force magnitude was registered in 17 precisely defined directions using a three-component force transducer and a feedback method. In addition, to assess the efficiency of transfer of muscle to bite force, for bites produced in the sagittal plane, moment-arm length was determined and the produced bite-force moment calculated. The results showed that the largest possible bite force was not always produced in a direction perpendicular to the occlusal plane. Generally, maximal bite force in medial and posterior directions was larger than that in, respectively, corresponding lateral and anterior directions. In each direction the produced force was larger at the posterior bite point than at the anterior bite point. The combined moment produced by the jaw muscles was largest for vertical bites, smallest for posteriorly directed bites and intermediate for anteriorly directed bites. In the case of vertically and anteriorly directed bites the produced moment did not vary significantly with the bite position. Hence, for these bite positions the jaw closing moment of the muscles must have kept constant. In the case of posteriorly directed bites the produced moment decreased when bite position changed from the anterior to the posterior side of the dentition. This indicated that jaw muscle activity had declined.

Effect of functional appliances on jaw muscle activity

The electromyographic (EMG) activity of masticatory muscles was monitored longitudinally with chronically implanted EMG electrodes to determine whether functional appliances produce a change in postural EMG activity of the muscles. Preappliance and postappliance EMG levels in four experimentals that had been fitted with functional appliances were compared against the background of EMG levels in controls without appliances. The insertion of two types of functional appliance to induce mandibular protrusion was associated with a decrease in postural EMG activity of the superior and inferior heads of the lateral pterygoid, superficial masseter, and anterior digastric muscles; the decrease in the first three muscles was statistically significant. This decreased postural EMG activity persisted for approximately 6 weeks, with a gradual return toward preappliance levels during a subsequent 6-week period of observation. Progressive mandibular advancement of 1.5 to 2 mm every 10 to 15 days did not prevent the decrease in postural EMG activity.

Jaw Muscle Activity in Relation to the Direction and Point of Application of Bite Force

This study examined the way the masseter and the anterior and posterior temporal muscles of human subjects were activated when a bite force of constant magnitude was exerted at different teeth in different defined directions. Subjects were instructed to produce a bite force of a particular magnitude (250 N) and direction (vertical, anterior, lateral, posterior, or medial) using a three-component force transducer and a feedback method. Simultaneously, the EMG activity of the muscles was registered with use of surface electrodes. Unilateral bite forces were produced at the right canine, second premolar, and second molar. In addition, a bilateral vertical premolar bite was examined for comparison of activity levels of the muscles of both sides. The results showed that, on average, the activities of the right and left side muscles did not differ in a bilateral vertical bite. Moreover, in a unilateral vertical bite, there were no significant right-left differences. For all bite force directions, more muscle activity was required for production of a constant bite force at the anterior side of the dental arch than at the posterior side. An exception to this rule was the activity of the posterior temporal muscle in a posteriorly directed bite. There was a close relationship between the direction of bite force and jaw muscle activity. Variations in activity were small for the anterior temporal muscle and large for the posterior temporal and masseter muscles. All muscles that were studied were always active, even in directions in which they could be expected to act antagonistically.

The relationship between three-dimensional bite force direction and activity of the human jaw muscles

A linear programming model, operating in a three-dimensional coordinate system, was written to study the effect on unilateral maximum bite forces (MBFs) of small changes in the design of human jaws. Under some conditions the MBF was larger on a more anterior tooth than a more posterior tooth for a given bite direction. The MBF was increased (i) as the bite force was tilted forward, (ii) as the jaw was opened if its direction was kept perpendicular to the occlusal plane of the lower jaw, (iii) by placing teeth nearer the midline, (iv) by raising the height of the teeth for forward bite forces, and (v) by tilting forward the articular surface of the condyle (equivalent to creating an articular eminence). Increasing the distance between the condyles spread the load more evenly between the two joints. The articular eminence was the only design feature which seemed to be clearly related to increasing the MBF.

Jaw movements and muscle activity during mastication in growing rabbits.

To investigate the biomechanical effects of juvenile growth changes in the rabbit masticatory apparatus a comparison was made of mastication in just-weaned and adult animals. Mandibular movements in two planes were registered by cineradiography. Masticatory muscle activity was recorded by fine-wire electromyography. The same pattern of unilateral mastication was present in the two ages. The most important changes in the jaw movements are 1) a decrease of jaw opening speed and chewing frequency and an increase in jaw opening time, 2) a decrease in maximum gape in soft food and an unaltered gape in small-particle hard food, and 3) an increase in lateral jaw excursion, mainly due to a more pronounced movement of the jaw to the balancing side (lingual phase). The contraction patterns were basically similar in the two ages. The higher chewing frequency in young animals was attained by a larger degree of overlap between opening and closing muscle activities. Young animals used relatively more EMG activity to chew hay, the hardest food. The changes in opening speed, gape, and chewing frequency are consistent with earlier predictions from the morphological changes, and so is the extra activity needed to chew hard food. The increase in lateral excursion was not predicted. It is suggested to be caused by cheek teeth wear, making possible smooth occlusal guidance of the jaw at the balancing side. Some of the changes in juvenile morphology can be viewed as adaptations to a changing diet.

Single-wire recording of regional activity in the human masseter muscle

A new approach is presented for recording regional muscle responses by means of a single intramuscular wire electrode. The technique exploits differences in impedance due to the locations of the recording and indifferent electrodes and also relies upon bandpass filtering. The method is demonstrated by recording the activity of the right masseter muscle at three different sites during voluntary tooth clenching. The results indicate that satisfactory separation of regional muscle activity can be obtained and that the recorded signals can be sampled digitally for quantitative purposes. As this method for recording jaw muscle activity avoids the problem of variable interelectrode distances commonly associated with conventional bipolar wire electrodes, it is advantageous when recording from human muscles in the facial and intraoral regions.

A 2-year electromyographic study of patients with an immediate complete upper and a partial lower denture.

A longitudinal electromyographic (EMG) investigation was performed on thirty subjects provided with an immediate complete upper and a partial lower denture. Electromyographic recordings in maximal clench, light tapping and postural position were obtained from the anterior temporal and masseter muscles before final extractions and 7 weeks, 6 months, 1 year and 2 years after denture insertion. The maximal clench activity of the jaw closing muscles showed an average tendency to decrease upon insertion of the dentures, but thereafter significant increases in mean voltages were observed during the first year of denture wear. During the second year no significant changes in EMG clenching force were noted. At the 2-year stage most of the muscles showed significantly greater clench activity than at the post-insertion stage, but did not exceed the pre-extraction level. The jaw muscle activity in light tapping showed no significant mean changes during the observation period. The postural activity tended to decrease during the period of denture wear, the decrease being significant for some of the muscles at the 2-year stage.

Effect of lingual surface inclination of maxillary canine on jaw muscle activity

The effect of lingual surface inclination of the maxillary canine on the jaw muscle activity was investigated on five subjects. Several different metal maxillary canine risers were fabricated to change the lingual inclination. The EMG activity of the masseter and posterior temporal muscle was recorded bilaterally by means of bipolar surface electrodes simultaneously with the LED mandibular tracking device. On each subject the lateral gliding movements were carried out while maintaining the occlusal contact on the canine riser. The recorded muscle activity and mandibular gliding movements were analyzed quantitatively. During the lateral gliding, the working-side posterior temporal muscle was more active than the other three muscles. Steeper canine risers caused a reduction of the muscle activity when compared with the more flat guidance. In the gliding movement from maximum intercuspation, the temporal muscle showed more activity than the masseter muscle. However the relative relationships between the individual muscles as well as the working-side muscle and nonworking-side muscle remained unchanged with all canine risers. In the gliding movement into maximum intercuspation, the difference of the canine riser showed no consistent change in the muscle activity. In each subject, it was found that the canine riser with a moderate inclination was more comfortable to move the mandible, but no relationship between the EMG activity and his or her feeling was revealed.

食品の硬さがそしゃく運動に及ぼす影響に関する実験的研究

The purpose of this study is to investigate the relationship of food consistency to patterns of mandibular movement and jaw muscle activity during mastication in adults with normal dentitions. Ten young people who ranged in age from 23 to 26 were studied. Specially made chewing gums of 3 graded consistencies (4.4 x 10(2), 1.4 x 10(4), 1.3 x 10(5) poise), not contain any additive like sugar and flavor, were used as test foods. Mandibular movements were recorded and analyzed using a Mandibular Kinesiograph (Myotronics Research Co.) during chewing of the 3 grades of chewing gums for 40 strokes. Surface EMG signals were also recorded from the bilateral masseteric and anterior temporal muscles. Displacement and velocity of jaw movement, duration of each phase, and amount of EMG activity were then statistically compared among chewing trials of the 3 grades of chewing gums with two way analysis of variance. The results were as followed. With the increase of consistency of chewing gum; 1. Maximal vertical, antero-posterior and lateral displacements were significantly increased (p less than 0.01). 2. Maximal opening and closing velocities were significantly increased (p less than 0.01). 3. Opening phase time was significantly increased while occlusal phase time was significantly decreased (p less than 0.01). Cycle time and closing phase time were about constantly. 4. Burst duration, interval and cycle time were about constantly. 5. Burst activity were significantly increased (p less than 0.01). 6. Burst co-ordination pattern was about constantly.

Rhythmic electromyographic activities of trunk muscles characterize the sexual behavior in the Him� salmon (landlocked sockeye salmon,Oncorhynchus nerka)

In order to describe precisely the fixed action patterns of salmon sexual behavior, we recorded the electromyographic (EMG) activities of trunk and jaw muscles from freely behaving male and female Hime salmon (landlocked sockeye salmon,Oncorhynchus nerka). A series of action patterns (quivering and spawning act in males, digging, covering, prespawning act and spawning act in females, and the swimming and turning movements in both sexes) were characterized by rhythmic activities of the trunk muscles. Each of these activity patterns is quantitatively distinct from the others in such parameters as frequency, bout duration, duty value, intersegmental phase delay, and spatial distribution of rhythmic activities. However, all of these rhythms share a qualitatively homologous pattern with the forward swimming movement: rhythmic activities alternate on both sides of the body (bilateral coupling) and are posteriorly propagated (intersegmental coupling). In addition, a 3∶1 intersegmental phase coupling occurs in the most anterior trunk muscles during the spawning act in some males. Based on these observations, we discussed the biomechanics for these motor patterns (oviposition, ejaculation, body vibration, and mouth opening), and the neural mechanisms for the pattern generation. A possibility was pointed out that the locomotor pattern generator in the spinal cord may be modulated by descending supraspinal signals and recruited to generate such diverse forms of action patterns in sexual behavior.

Prey Processing in Haemulid Fishes: Patterns of Variation in Pharyngeal Jaw Muscle Activity

ABSTRACT This study examines patterns of variation in 15 electromyographic (EMG) variables measured from recordings of pharyngeal jaw muscle activity during prey processing in four species of the perciform fish family Haemulidae. Two questions were of primary interest. (1) Are motor patterns conserved across the four species? (2) Do the fishes alter (modulate) muscle activity patterns when feeding on different prey types? The experimental design used allowed the partitioning of variance in EMG variables among species, among individuals within species, among days within individuals, among feedings within days, and among prey types. Only one variable exhibited a significant species effect, indicating that the four species used virtually the same motor pattern during prey processing. In response to three prey types differing in hardness, all four species demonstrated an ability to modulate several EMG variables that characterized the intensity of electrical activity. However, variables characterizing the relative timing of muscle activities were not influenced by prey type. A significant variance component was found among recording days and, together with the possibility of variation among experimental preparations, this raises questions about the extent of previously reported inter-individual variation in EMGs. These results support a growing data base on aquatic feeding in lower vertebrates which finds that: (1) motor patterns tend to be highly conserved among closely related taxa; (2) the ability to modulate motor patterns in response to different prey types appears to be a general property of teleost fish feeding mechanisms; and (3) variation in experimental EMG data is ubiquitous and, when unaccounted for, confounds comparisons among treatment groups.

Task-specific organization of activity in human jaw muscles.

Coordination of jaw muscle activity for speech production sometimes has been modeled using nonspeech behaviors. This orientation has been especially true in representations of mandibular movement in which the synergy of jaw muscles for speech production has been suggested to be derived from the central pattern generator (CPG) for chewing. The present investigation compared the coordination of EMG activity in mandibular muscles over a range of speech and nonspeech tasks. Results of a cross-correlational analysis between EMG signals demonstrated that the muscle synergies of the mandibular system depend on task demands. Contrary to some of the models discussed, continuous speech production yielded activation patterns that were clearly not related to coordinative patterns generated by the chewing CPG.

Aging and the accuracy of jaw muscle control.

This study was designed to investigate the effect of ageing upon the accuracy with which subjects control jaw muscle activity during voluntary tooth clenching. The experiment involved the subjects clenching on a force transducer to achieve and maintain a predetermined target force displayed using a biofeedback light bar. The subjects were seventeen healthy, dentally fit males, ranging in age from 22 to 77 years, each of whom performed the experiment on one occasion. Target forces of 0.5, 1 and 2 Kg were demanded, and were maintained for two minutes duration with an equivalent rest period between each task. Subject performance was a measure of the difference between the force achieved and the target force, and was obtained electrically using an integrator controlled by a timing device. The results showed that performance deteriorated both at higher force levels and with increasing age, although there was a wide variation in ability between different individuals.