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At least 19 recordsLinked to original sources
PubMed1993

Effects of jaw clenching, jaw movement and static jaw position on facial skin sensitivity to non-painful electrical stimulation in man.

The effects of isometric jaw clenching, static jaw position and jaw movement on electrically evoked perception thresholds of the facial skin of the mental region were studied in healthy human subjects. Exercise consisted of brief (1 s) isometric contractions of jaw-closing muscles against a static load (30% of the maximum force), or continuous jaw movements at two different frequencies (1 and 3 Hz). A visual cue was used to indicate the start and end of the isometric exercise (duration 1 s.). Isometric jaw clenching induced a significant elevation of perception thresholds in the skin of the lower jaw just before and during the early electromyographic response of the jaw-closing muscles. This elevation was attenuated before the end of the exercise. Corresponding thresholds evoked by electrical stimulation applied to the dorsum of the hand were not changed by isometric jaw clenching. Changes in static jaw position did not have any effect on detection thresholds. Continuous 'masticatory-like' jaw movements produced a velocity-dependent reduction of sensitivity in the facial skin. The suppression was significantly stronger than that produced by isometric jaw exercise. An imagined isometric biting exercise, which presumably activated the supplementary motor cortex, did not cause any threshold elevations. The results indicate that isometric jaw clenching as well as cyclical jaw movements produce segmentally a phasic, rapidly attenuating masking of facial skin sensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

A comparison of jaw-opener and jaw-closer muscle activity in humans to overcome an external force counteracting jaw movement.

In contrast to the jaw-closer muscles, no or very few spindles are present in the jaw-opening digastric muscle. Therefore sensory feedback to the digastric muscle may be different from feedback to the jaw-closer muscles, resulting in a different reaction when jaw movement is perturbed. This possible difference was investigated by comparing the reaction of the digastric muscle when jaw opening is perturbed, with the reaction of the masseter muscle when jaw closing is perturbed. Subjects made rhythmic, 1-Hz open-close movements of the jaw under control of a metronome. During jaw opening (digastric muscle) or, in the other experiments, during jaw closing (masseter muscle), an external force counteracting jaw movement could appear. Series of movements without the force were unexpectedly alternated by series with the force. In both muscles sensory induced activity started approximately 25 ms after the onset of the force and consisted of two phases. In the masseter muscle the maximum of the first increase was reached significantly sooner (37 +/- 2 ms SEM) than in the digastric muscle (54 +/- 3 ms). The second increase appeared much sooner in the masseter muscle (73 +/- 4 ms) than in the digastric muscle (159 +/- 10 ms). When the force was expected, in both muscles an increase in preprogrammed muscle activity was observed. Also an increase in reflex activity, generated before 120 ms after the onset of the force, was observed, compared with when the force appeared unexpectedly. The relative increase in reflex activity was approximately 2 times larger than the relative increase in preprogrammed activity. Therefore, the increase in reflex activity when the force was expected may have been caused not only by an increase in recruitment, but also by an increase in the gain of the reflex loops. Reflex activity relative to preprogrammed activity was on average 4 times larger in the masseter muscle than in the digastric muscle. This indicates that the masseter muscle can react more adequately to disturbances of jaw movement than the digastric muscle.

Adult↗
PubMed1991

The relationship between the isotonic mechanical power in jaw-opening and jaw-closing muscles in man.

The relationship between isotonic jaw-opening and jaw-closing muscle function was studied using a newly developed apparatus which enables load and velocity to be detected simultaneously. The following results were obtained from 17 male adults (age range 22-32 years) without any occlusal dysfunction. (i) The force-velocity relationship in jaw-opening and jaw-closing muscles was represented by a hyperbolic curve, which fitted well with Hill's equation. (ii) The theoretical maximum force obtained by extrapolation from regression was 32.55 +/- 4.98 kg for jaw opening and 35.74 +/- 4.52 kg for jaw closing. (iii) The theoretical maximum velocity obtained by extrapolation from regression was 456.70 +/- 183.27 mm s-1 for jaw opening and 372.77 +/- 141.67 mm s-1 for jaw closing. (iv) The maximum mechanical power (Pmax) calculated from the product of the force and velocity was 772.20 +/- 182.65 kg.mm s-1 for jaw opening and 708.68 +/- 128.14 kg.mm s-1 for jaw closing. (v) The Pmax exerted by individual subjects was approximately 12-34% of the maximum possible force (Fmax) calculated from the force and velocity, in both jaw opening and jaw closing. There were no statistically significant differences between jaw opening and jaw closing with regard to any isotonic muscle functions. In other words, the results of this study strongly indicated a substantial balance between isotonic jaw-opening and jaw-closing muscle function in the subjects who were investigated.

Adult↗
PubMed2000

Integrated jaw and neck function in man. Studies of mandibular and head-neck movements during jaw opening-closing tasks.

This investigation was undertaken to test the hypothesis of a functional relationship between the human temporomandibular and craniocervical regions. Mandibular and head-neck movements were simultaneously recorded in healthy young adults using a wireless optoelectronic system for three dimensional movement recording. The subjects were seated in an upright position without head support and were instructed to perform maximal jaw opening-closing movements at fast and slow speed. As a basis, a study was undertaken to develop a method for recording and analysis of mandibular and head-neck movements during natural jaw function. A consistent finding was parallel and coordinated head-neck movements during both fast and slow jaw opening-closing movements. The head in general started to move simultaneously with or before the mandible at the initiation of jaw opening. Most often, the head attained maximum velocity after the mandible. A high degree of spatiotemporal consistency of mandibular and head-neck movement trajectories was found in successive recording sessions. The head movement amplitude and the temporal coordination between mandibular and head-neck movements were speed related but not the movement trajectory patterns. Examination of individuals suffering from temporomandibular disorders and whiplash associated disorders (WAD) showed, compared with healthy subjects, smaller amplitudes, a diverse pattern of temporal coordination but a similar high degree of spatiotemporal consistency for mandibular and head-neck movements. In conclusion, the results suggest the following: A functional linkage exists between the human temporomandibular and craniocervical regions. Head movements are an integral part of natural jaw opening-closing. "Functional jaw movements" comprise concomitant mandibular and head-neck movements which involve the temporomandibular, the atlanto-occipital and the cervical spine joints, caused by jointly activated jaw and neck muscles. Jaw and neck muscle actions are elicited and synchronised by neural commands in common for both the jaw and the neck motor systems. These commands are preprogrammed, particularly at fast speed. In the light of previous observations of concurrent jaw and head movements during foetal yawning, it is suggested that these motor programs are innate. Neural processes underlying integrated jaw and neck function are invariant both in short- and long-term perspectives. Integrated jaw and neck function seems to be crucial for maintaining optimal orientation of the gape in natural jaw function. Injury to the head-neck, leading to WAD may derange integrated jaw-neck motor control and compromise natural jaw function.

Adult↗
PubMed1988

The effect of prior jaw motion on the plot of electromyographic amplitude versus jaw position.

Fabrication of interocclusal splint at a thickness determined by the vertical dimension at which the jaw muscle EMG amplitude is minimum has been recommended. However, the effect of prior jaw motion and the effect of the recording site on the EMG amplitudes and on the vertical dimension of minimum EMG activity have not been documented. IEMG amplitudes at various static jaw positions achieved during opening and during closing were analyzed in nine subjects. Surface IEMGs were recorded over the left anterior temporal muscle, left masseter and left suprahyoids muscles, and by nonspecific EMG recording as described by Rugh and Drago. The jaw position was recorded in 5 mm increments by a kinesiograph. After 30 seconds of relaxation, 10 successive IEMG reading at 4-second integration times were obtained at each recording site. These 10 recordings at each requested jaw position were averaged and analyzed. The IEMG activity changed with different jaw position. As the jaw opened from centric occlusion, the IEMG from jaw closing muscles decreased to a minimum and then increased with further opening. Moreover, the IEMG for a particular jaw position differed depending on the history of the jaw movement, that is, whether the position was achieved after an opening step or after a closing step. Two factors, the amount of jaw opening and the history of jaw movement to reach that position, seemed to influence the IEMG differently in each of the recorded muscles.

Adult↗
PubMed1999

Behavior of jaw muscle spindle afferents during cortically induced rhythmic jaw movements in the anesthetized rabbit.

The regulation by muscle spindles of jaw-closing muscle activity during mastication was evaluated in anesthetized rabbits. Simultaneous records were made of the discharges of muscle spindle units in the mesencephalic trigeminal nucleus, masseter and digastric muscle activity (electromyogram [EMG]), and jaw-movement parameters during cortically induced rhythmic jaw movements. One of three test strips of polyurethane foam, each of a different hardness, was inserted between the opposing molars during the jaw movements. The induced rhythmic jaw movements were crescent shaped and were divided into three phases: jaw-opening, jaw-closing, and power. The firing rate of muscle spindle units during each phase increased after strip application, with a tendency for the spindle discharge to be continuous throughout the entire chewing cycle. However, although the firing rate did not change during the jaw-opening and jaw-closing phases when the strip hardness was altered, the firing rate during the power phase increased in a hardness-dependent manner. In addition, the integrated EMG activity, the duration of the masseteric bursts, and the minimum gape increased with strip hardness. Spindle discharge during the power phase correlated with jaw-closing muscle activity, implying that the change in jaw-closing muscle activity associated with strip hardness was caused by increased spindle discharge produced through insertion of a test strip. The increased firing rate during the other two phases may be involved in a long-latency spindle feedback. This could contribute to matching the spatiotemporal pattern of the central pattern generator to that of the moving jaw.

Afferent Pathways↗
PubMed1992

Synaptic potentials produced in jaw-closer and jaw-opener motoneurons by palatal stimulation.

Excitation and inhibition of temporal and digastric motoneurons (Temp. and Dig. Mns) during transient jaw closing, the so-called jaw-closing reflex, were studied in cats. Application of diffuse pressure stimulation to the posterior palatal surface produced the jaw-closing reflex and it was found that mechanosensory inputs from the posterior palatal mucosa produce depolarizing potentials on the Temp. Mns responsible for jaw closure during the jaw-closing reflex. We have demonstrated that in one-third of 27 explored Temp. Mns the initial bursts of spikes were elicited before the onset of jaw closure, suggesting that these cells contribute to initiate jaw closure during the jaw-closing reflex. The remaining cells probably contributed to maintain the occlusal phase. Furthermore, it was found that mechanosensory inputs from the posterior palatal mucosa produce a hyperpolarization-depolarization sequence in the Dig. Mns responsible for the jaw-closing reflex. In addition, when pressure stimulation was applied to the anterior palatal mucosa, sustained jaw opening was elicited and an increase of firing frequency of Dig. Mns occurred 40 ms before the onset of jaw opening and continued for 80 ms.

Animals↗
PubMed1997

Architecture of the human jaw-closing and jaw-opening muscles.

BACKGROUND: The human jaw-closing and jaw-opening muscles produce forces leading to the development of three-dimensional bite and chewing forces and to three-dimensional movements of the jaw. The length of the sarcomeres is a major determinant for both force and velocity, and the maximal work, force, and shortening range each muscle is capable of producing are proportional to the architectural parameter volume, physiological cross-sectional area, and fiber length, respectively. In addition, the mechanical role the muscles play is strongly related to their three-dimensional position and orientation in the muscle-bone-joint system. The objective of this study was to compare relevant architectural characteristics for the jaw-closing and jaw-opening muscles and to provide a set of data that can be used in biomechanical modeling of the masticatory system. METHODS: In eight cadavers, sarcomere lengths, muscle masses, fiber lengths, pennation angles, and physiological cross-sectional areas were determined for the following muscles: superficial and deep masseter, anterior and posterior temporalis, anterior and posterior medial pterygoid, inferior and superior lateral pterygoid, posterior and anterior digastric, geniohyoid, posterior and anterior mylohyoid, and stylohyoid. To determine the spatial position of their action lines, the three-dimensional coordinates of the attachment sites were registered. RESULTS: Compared with the jaw openers, the jaw closers were characterized by shorter sarcomere lengths at the closed jaw, larger masses of contractile and tendinous tissue, larger physiological cross-sectional areas, larger pennation angles, shorter fiber lengths, shorter moment arms, and lower fiber-length-to-muscle-length ratios. In addition, architectural features differed across the muscles of the same functional group. Sarcomere length did not differ significantly among the regions of the same muscle. In contrast, in some muscles, significant intramuscular differences were found with respect to, e.g., physiological cross-sectional area, fiber length, pennation angle, and moment arm length. CONCLUSIONS: The results suggest that the jaw-closing muscles have architectural features that suit them for force production. Conversely, the jaw-opening muscles are better designed to produce velocity and displacement.

Aged↗
PubMed2003

Modeling the jaw mechanism of Pleuronichthys verticalis: The morphological basis of asymmetrical jaw movements in a flatfish.

Several flatfish species exhibit the unusual feature of bilateral asymmetry in prey capture kinematics. One species, Pleuronichthys verticalis, produces lateral flexion of the jaws during prey capture. This raises two questions: 1) How are asymmetrical movements generated, and 2) How could this unusual jaw mechanism have evolved? In this study, specimens were dissected to determine which cephalic structures might produce asymmetrical jaw movements, hypotheses were formulated about the specific function of these structures, physical models were built to test these hypotheses, and models were compared with prey capture kinematics to assess their accuracy. The results suggest that when the neurocranium rotates dorsally the premaxillae slide off the smooth, rounded surface of the vomer (which is angled toward the blind, or eyeless, side) and are "launched" anteriorly and laterally. The bilaterally asymmetrical trajectory of the upper jaw is determined by the orientation of the "launch pad," the vomer. During lower jaw depression, the mandibles rotate about their articulations with the quadrate bones of the suspensoria. The quadrato-mandibular joint is positioned farther anteriorly on the eye side than on the blind side, and this asymmetry deflects the lower jaw toward the blind side. Asymmetry in the articular surfaces of the lower jaw augments this effect. Thus, it appears that fish with intermediate forms of this asymmetrical movement could have evolved from symmetrical ancestors via a few key morphological changes. In addition, similar morphological modifications have been observed in other fish taxa that also produce jaw flexion during feeding, which suggests that there may be convergence in the basic mechanism of asymmetry.

Animals↗
PubMed1992

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.

Animals↗
PubMed1982

Limitation of jaw movement by antagonist muscle stiffness during unloading of human jaw closing muscles.

The unloading reflex in the jaw closing muscles in man was investigated with a view to correlating the jaw closing movement with the timing of the electrical activity of the agonist and antagonist muscles. When the resistance to the forceful isometric bite was suddenly and unexpectedly withdrawn, the closing movement of the mandible was always arrested before the teeth came together. The rapid arrest of the jaw closing movement was not adequately accounted for by the timing of the inhibition of the jaw closing muscles and reflex excitation of the jaw opening muscles. It was observed that the jaw opening muscles, as well as the jaw closing muscles, were always active during the phase of isometric biting on an object between the teeth. It is therefore concluded that the resulting stiffness of the antagonist muscles is the mechanism which is principally responsible for limiting the jaw closing movement after unloading of the agonist muscles.

Adult↗
PubMed2002

Anticipatory and reflexive neck muscle activities during voluntary rapid jaw opening and passive jaw depression in humans.

The characteristics of head movement during voluntary rapid jaw opening movement and passive jaw depression were investigated using accelerometers and electromyographs (EMG) on eight healthy examinees. Passive depressions were executed by means of load on the lower jaw, initiated either by examinees themselves or an experimenter. In the depression initiated by examinees, a head-extension movement that preceded the load to the lower jaw and anticipatory activities in the nuchal region of the trapezius muscle were observed. In the depression initiated by the experimenter, the anticipatory activities were not observed. In both of these cases, stretch reflexes were induced in the trapezius muscle. During voluntary rapid jaw opening, a head-extension movement nearly synchronized with the opening movement in the lower jaw acceleration, and dorsal-neck muscle activities accompanying the synchronized movement were observed. The peak timing of these neck-muscle activities preceded the latencies of the stretch-reflex activities observed in the jaw-depressed tasks, but no anticipatory activities were observed in the dorsal-neck muscles. We conclude that neither the anticipatory activities nor the reflex activities observed in the passive depressions have effects on the initial part of the dorsal-neck muscle activities, which are related to the head-extension synchronized with the voluntary lower-jaw opening movement.

Adult↗
PubMed2000

Changes in jaw-jerk on different levels of jaw closure and teeth-clenching in humans.

We investigated how the jaw-jerk in the human masseter muscle is modulated in relation to the level of jaw closure (JC) and teeth clenching. Electromyographic (EMG) activity was recorded with surface electrodes. Background EMG activity of the masseter muscle was kept at three low teeth clenching levels with visual feedback. The level of JC was changed in six steps along the habitual path of closure relative to the mean maximal jaw opening during gum chewing by inserting a bite block between the upper and lower molars. The jaw-jerk was evoked by applying mechanical stimulation of about 20 N with a hammer to the bite-fork placed on the lower molars on one side in each condition of combination of a level of JC with a level of teeth-clenching. At the resting condition the excitability of the jaw-jerk increased with JC, while at weak voluntary teeth clenching it then decreased and increased again as the jaw was progressively closed. It is suggested that the excitability of the jaw-jerk would increase toward the occlusal position, which in turn would contribute to smooth masticatory movements. In addition, the mode of modulation of the jaw-jerk was studied in a subject with skeletal malocclusion.

Adult↗
PubMed2002

Electromyographic activity of the jaw-closing muscles during jaw opening in patients with masseter muscle contracture.

Contracture of the jaw-closing muscles is one of the causes of limitation of jaw opening. This study examined whether there is any difference between the EMG activities of jaw-closing muscles during jaw opening in healthy people and in patients with masseter muscle contracture (MMC), who do not have a history of trauma or infection. The patient group consisted of eleven females, 18 to 62 years old with no history of trauma or infections, with limited mouth opening due to MMC. The control group included eleven healthy females, 23 to 50 years old. The EMG activity was recorded bilaterally in the central portion of masseter muscles (Mm), the anterior portion of temporal muscles (Tm), and the anterior belly of digastric muscles (Dm). Nine out of the patient group showed obvious EMG activity in Mm during jaw opening which was different from typical EMG patterns during jaw opening of up to 40 mm in the control group. Among the nine patients, eight showed antagonistic contraction in Tm as well as Mm. The mean integral value of Mm and Tm during jaw opening in the patient group was significantly higher than in the control group (P<0.01). These results suggest that EMG activity during jaw opening in MMC patients with no history of trauma or infections is different from that in healthy people.

Adolescent↗
PubMed2002

Disturbed jaw behavior in whiplash-associated disorders during rhythmic jaw movements.

As shown previously, "functional jaw movements" are the result of coordinated activation of jaw as well as neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital, and cervical spine joints. In this study, the effect of neck trauma on natural jaw function was evaluated in 12 individuals suffering from whiplash-associated disorders (WAD). Spatiotemporal characteristics of mandibular and concomitant head movements were evaluated for three different modes of rhythmic jaw activities: self-paced continuous maximal jaw-opening/-closing movements, paced continuous maximal jaw-opening/-closing movements at 50 cycles/minute, and unilateral chewing. Compared with healthy subjects, the WAD group showed smaller magnitude and altered coordination pattern (a change in temporal relations) of mandibular and head movements. In conclusion, these results show that neck trauma can derange integrated jaw and neck behavior, and underline the functional coupling between the jaw and head-neck motor systems.

Adult↗
PubMed1997

Changes in jaw movement and jaw closing muscle activity after orthodontic correction of incisor crossbite.

The possible influences of the direction of occlusal loading delivered to the incisors in the sagittal direction during chewing on jaw movement and jaw closing muscle activity were investigated. Ten healthy children with crossbite of one or two incisors on the right side were selected. Each subject chewed a piece of chewing gum on the right side, and jaw displacements and electromyographic signals from the posterior temporalis and superficial masseter muscles on the ipsilateral side were sampled simultaneously. After orthodontic correction of the incisor crossbite relationship, identical records were taken. The inclinations of the gliding contacts for each posterior tooth in the lateral jaw excursion position were consistent before and after the treatment. The posttreatment records showed broader jaw movement patterns in the frontal view and faster jaw movement velocity in the lateral direction at a level close to the habitual maximum intercuspation position, when compared with the pretreatment records (P < 0.05). The duration of the muscle activity and the incidence of the silent periods of the masseter muscle during chewing significantly decreased after the treatment (P < 0.05). The current results give a neurophysiologic rationale for explaining the significance of orthodontic treatment in improving lowered masticatory efficiency in the way that the change in direction of the occlusal load achieved by tooth movement influences on the periodontal sensory input, which, in turn, modifies the trigeminal motor output and thus, eventually, jaw muscle activities.

Bite Force↗