Rhythmic Jaw Movements Research Articles

A subcortical feeding circuit linking an interoceptive node to jaw movement.

The brain processes an array of stimuli, enabling the selection of appropriate behavioural responses, but the neural pathways linking interoceptive inputs to outputs for feeding are poorly understood1-3. Here we delineate a subcortical circuit in which brain-derived neurotrophic factor (BDNF)-expressing neurons in the ventromedial hypothalamus (VMH) directly connect interoceptive inputs to motor centres, controlling food consumption and jaw movements. VMHBDNF neuron inhibition increases food intake by gating motor sequences of feeding through projections to premotor areas of the jaw. When food is unavailable, VMHBDNF inhibition elicits consummatory behaviours directed at inanimate objects such as wooden blocks, and inhibition of perimesencephalic trigeminal area (pMe5) projections evokes rhythmic jaw movements. The activity of these neurons is decreased during food consumption and increases when food is in proximity but not consumed. Activity is also increased in obese animals and after leptin treatment. VMHBDNF neurons receive monosynaptic inputs from both agouti-related peptide (AgRP) and proopiomelanocortin neurons in the arcuate nucleus (Arc), and constitutive VMHBDNF activation blocks the orexigenic effect of AgRP activation. These data indicate an Arc → VMHBDNF → pMe5 circuit that senses the energy state of an animal and regulates consummatory behaviours in a state-dependent manner.

Effect of Obesity on Masticatory Muscle Activity and Rhythmic Jaw Movements Evoked by Electrical Stimulation of Different Cortical Masticatory Areas.

This study investigates rhythmic jaw movement (RJM) patterns and masticatory muscle activities during electrical stimulation in two cortical masticatory areas in obese male Zucker rats (OZRs), compared to their counterparts-lean male Zucker rats (LZRs) (seven each). At the age of 10 weeks, electromyographic (EMG) activity of the right anterior digastric muscle (RAD) and masseter muscles, and RJMs were recorded during repetitive intracortical micro-stimulation in the left anterior and posterior parts of the cortical masticatory area (A-area and P-area, respectively). Only P-area-elicited RJMs, which showed a more lateral shift and slower jaw-opening pattern than A-area-elicited RJMs, were affected by obesity. During P-area stimulation, the jaw-opening duration was significantly shorter (p < 0.01) in OZRs (24.3 ms) than LZRs (27.9 ms), the jaw-opening speed was significantly faster (p < 0.05) in OZRs (67.5 mm/s) than LZRs (50.8 mm/s), and the RAD EMG duration was significantly shorter (p < 0.01) in OZRs (5.2 ms) than LZR (6.9 ms). The two groups had no significant difference in the EMG peak-to-peak amplitude and EMG frequency parameters. This study shows that obesity affects the coordinated movement of masticatory components during cortical stimulation. While other factors may be involved, functional change in digastric muscle is partly involved in the mechanism.

Motor representation of rhythmic jaw movements in the amygdala of guinea pigs

ObjectiveThe areas of the amygdala contributing to rhythmic jaw movements and the movement patterns induced remain unknown. Therefore, the present study investigated the areas of the amygdala contributing to rhythmic jaw movements using repetitive electrical microstimulation techniques. DesignExperiments were performed on head-restrained guinea pigs under ketamine-xylazine anesthesia. EMG activities in the masseter and digastric muscles and jaw movements were recorded. Short- and long-train electrical microstimulations of the amygdala were performed and the patterns of jaw movements induced were analyzed quantitatively. ResultThe short-train stimulation induced short-latency EMG responses in the masseter and/or digastric muscles. The stimulation sites inducing short-latency EMG responses were distributed within the ventral part of the amygdala, which covered the medial, basal, and cortical nuclei. The long-train stimulation induced tonic jaw opening and two types of rhythmic jaw movements: those with or without lateral jaw shifts, which were characterized by a larger jaw gape and ipsilateral jaw excursion, respectively. Rhythmic jaw movements with lateral jaw shifts were characterized by overlapping masseter and digastric EMG activities. However, rhythmic patterns did not differ between the two types of rhythmic jaw movements. The stimulation sites that induced rhythmic jaw movements were more localized to the cortical nucleus. ConclusionsThe present results suggest that the ventral part of the amygdala is involved in the induction of rhythmic jaw movements in guinea pigs. The putative roles of the limbic system in the genesis of functional (e.g., chewing) and non-functional (e.g., bruxism) rhythmic oromotor movements warrant further study.

Changes in cortical, cardiac, and respiratory activities in relation to spontaneous rhythmic jaw movements in ketamine-anesthetized guinea pigs.

It has been reported that rhythmic jaw movements (RJMs) spontaneously occur in ketamine-anesthetized animals. The present study investigated the physiological processes that occur during the cortical, cardiac, and respiratory events which contribute to the genesis of RJMs in animals after supplemental ketamine injections. Fourteen guinea pigs were prepared to allow electroencephalographic, electrocardiographic, and electromyographic activities to be recorded from the digastric muscle, measurement of jaw movements, and nasal expiratory airflow under ketamine-xylazine anesthesia. Rhythmic jaw movements spontaneously occurred with rhythmic digastric muscle contractions, 23-29minutes after injection of supplemental ketamine (12.5 and 25.0mgkg-1 , intravenously). The cycle length of RJMs did not differ significantly between the two doses of ketamine (mean±SD: 12.5mgkg-1 , 326.5±60.0ms; 25mgkg-1 , 278.5±45.1ms). Following injection of ketamine, digastric muscle activity, heart and respiratory rates, and cortical beta power significantly decreased, while cortical delta and theta power significantly increased. These changes were significantly larger in animals given 25.0mgkg-1 of ketamine than in those given 12.5mgkg-1 . With the onset of RJMs, the levels of these variables returned to pre-injection levels, regardless of the dose of ketamine administered. These results suggest that, following supplemental ketamine injections, spontaneous RJMs occur during a specific period when the pharmacological effects of ketamine wear off, and that these RJMs are characterized by stereotypical changes in cardiac, respiratory, and cortical activities.

Effects of low occlusal loading on the neuromuscular behavioral development of cortically-elicited jaw movements in growing rats

The effect of altered occlusal force on masticatory-related neuromuscular control, which projects from the anterior part of the cortical masticatory area (A-CMA), during growth remains unclear. This study sought to evaluate the effect of occlusal hypofunction on neuromuscular development of jaw muscle activities and cortically-induced rhythmic jaw movements (RJMs) in growing rats. Sixty-four 2-week-old male albino Wistar rats were divided into the control (fed normal diet) and experimental (fed soft diet) groups soon after weaning. Electromyographic activity was recorded at 5, 7, 9, and 11 weeks from the right masseter and anterior digastric along with RJMs. We found a significantly longer onset latency and smaller peak-to-peak amplitude in the experimental group than that in the control group. The RJMs showed an increase in gape size and lateral excursion until up to 9 weeks in both groups. However, both the average gape size and lateral excursion were significantly smaller in the experimental group than that in the control group after 9 weeks. The jaw movement pattern also showed a significant decrease at the maximum opening period in the experimental group. Our findings indicate that inadequate occlusal function during growth alters neuromuscular control of masticatory behaviors and impairs the pattern of RJMs.

Membrane excitabilities in neonatal rat mesencephalic trigeminal neurons under dietary zinc deficiency.

The present study aimed to evaluate the effects of zinc deprivation on the properties of membrane and spike-discharge features of mesencephalic trigeminal neurons (MTNs), which are important sensory neurons for oral-motor reflexes and rhythmical jaw movements. Neonatal Sprague Dawley rats (P10-12) were distributed equally into a normal diet group and a zinc-deficient diet (ZD) group. Whole cell patch-clamp recordings were obtained from MTNs from coronal brain slices. Passive membrane properties showed a modest depolarized membrane potential and decreased cell capacitance in the ZD group. Zinc deprivation decreased the minimal current amplitude, which induced an action potential and increased the amplitude of afterhyperpolarization following the action potential. Negligible changes were observed for other action potential properties. A decreased burst duration was observed, accompanied by hastened spike frequency adaptation in the burst discharge. There was no difference in the resonant properties at both the subthreshold depolarized potential and hyperpolarized membrane potential between the control and ZD groups. These results suggests that neither the persistent sodium conductance nor slow inwardly rectifying conductance were altered; however, there appeared to be an increase in Ca2+-dependent K+ conductance in zincdeficient MTNs.

Suppression of the Swallowing Reflex during Rhythmic Jaw Movements Induced by Repetitive Electrical Stimulation of the Dorsomedial Part of the Central Amygdaloid Nucleus in Rats.

A previous study indicated that the swallowing reflex is inhibited during rhythmic jaw movements induced by electrical stimulation of the anterior cortical masticatory area. Rhythmic jaw movements were induced by electrical stimulation of the central amygdaloid nucleus (CeA). The swallowing central pattern generator is the nucleus of the solitary tract (NTS) and the lateral reticular formation in the medulla. Morphological studies have reported that the CeA projects to the NTS and the lateral reticular formation. It is therefore likely that the CeA is related to the control of the swallowing reflex. The purpose of this study was to determine if rhythmic jaw movements driven by CeA had inhibitory roles in the swallowing reflex induced by electrical stimulation of the superior laryngeal nerve (SLN). Rats were anesthetised with urethane. The SLN was solely stimulated for 10 s, and the swallowing reflex was recorded (SLN stimulation before SLN + CeA stimulation). Next, the SLN and the CeA were electrically stimulated at the same time for 10 s, and the swallowing reflex was recorded during rhythmic jaw movements (SLN + CeA stimulation). Finally, the SLN was solely stimulated (SLN stimulation following SLN + CeA stimulation). The number of swallows was reduced during rhythmic jaw movements. The onset latency of the first swallow was significantly longer in the SLN + CeA stimulation than in the SLN stimulation before SLN + CeA stimulation and SLN stimulation following SLN + CeA stimulation. These results support the idea that the coordination of swallowing reflex with rhythmic jaw movements could be regulated by the CeA.

Functional Analysis of Rhythmic Jaw Movements Evoked by Electrical Stimulation of the Cortical Masticatory Area During Low Occlusal Loading in Growing Rats.

The maturation of rhythmic jaw movements (RJMs) and related neuromuscular control has rarely been studied in animals, though this process is essential for regulating the development of stomatognathic functions. Previous studies have shown that occlusal hypofunction during growth alters masticatory performance. However, little is known about patterns of cortically-induced RJMs under conditions of soft-diet feeding during development. The aim of this study is to clarify the effect of low occlusal loading on the pattern of cortically induced RJMs and related neuromuscular responses in growing rats. Sixty-four 2-week-old male albino Wistar rats were randomly divided into two groups and fed on either a normal diet (control) or soft diet (experimental) soon after weaning. At 5, 7, 9, and 11 weeks of age, electromyographic (EMG) activity was recorded from the right masseter and anterior digastric muscles along with corresponding kinematic images in RJMs during repetitive intracortical microstimulation of the left cortical masticatory area (CMA). Rats in both groups showed an increase in gape size and lateral excursion until 9 weeks of age. The vertical jaw movement speed in both groups showed no significant difference between 5 and 7 weeks of age but increased with age from 9 to 11 weeks. Compared to the control group, the average gape size and vertical speed were significantly lower in the experimental group, and the pattern and rhythm of the jaw movement cycle were similar between both groups at each recording age. EMG recordings showed no age-related significant differences in onset latency, duration, and peak-to-peak amplitude. Moreover, we found significantly longer onset latency, smaller peak-to-peak amplitude, and greater drop-off mean and median frequencies in the experimental group than in the control group, while there was no significant difference in the duration between groups. These findings indicate that a lack of enough occlusal function in infancy impedes the development of patterns of RJMs and delays the neuromuscular response from specific stimulation of the CMA.

Neuropeptide Y modulates membrane excitability in neonatal rat mesencephalic V neurons.

Neuropeptide Y (NPY) is one of a number of neuropeptides with powerful orexigenic effects. Intracerebroventricular administration of NPY induces increases in food intake and alters feeding rate. Besides it role in feeding behavior, NPY also has significant effects on neuronal systems related to other spontaneous behaviors such as rearing and grooming. In the present study, we examined the direct effects of NPY on mesencephalic V neurons (Mes V), which are important sensory neurons involved in oral motor reflexes and rhythmical jaw movements, as well as masticatory proprioception. Coronal brain slices were prepared from neonatal Sprague-Dawley rats (P3-17) and whole-cell patch clamp recordings were obtained from Mes V neurons. Bath application of NPY depolarized the membrane potential and induced inward current in most neurons. Application of NPY shortened the duration of the afterhyperpolarization following an action potential, and increased the mean spike frequency during repetitive discharge. In those neurons which exhibited rhythmical burst discharge in response to maintained current injection, the bursting frequency was also increased. These effects were mediated predominately by both Y1 and Y5 receptors.

A new classification of wind instruments: Orofacial considerations

Background/objectivePlaying a wind instrument implies rhythmic jaw movements where the embouchure applies forces with different directions and intensities towards the orofacial structures. These features are relevant when comparing the differences between a clarinettist and a saxophone player embouchure, independently to the fact that both belong to the single-reed instrument group, making therefore necessary to update the actual classification. MethodsLateral cephalograms were taken to single-reed, double-reed and brass instrumentalists with the purpose of analyzing the relationship of the mouthpiece and the orofacial structures. ResultsThe comparison of the different wind instruments showed substantial differences. Therefore the authors purpose a new classification of wind instruments: Class 1 single-reed mouthpiece, division 1– clarinet, division 2 –saxophone; Class 2 double-reed instruments, division 1– oboe, division 2– bassoon; Class 3 cup-shaped mouthpiece, division 1– trumpet and French horn, division 2- trombone and tuba; Class 4 aperture mouthpieces, division 1– flute, division 2 – transversal flute and piccolo. ConclusionsElements such as dental arches, teeth and lips, assume vital importance at a new nomenclature and classification of woodwind instruments that were in the past mainly classified by the type of mouthpiece and not taking into consideration its relationship with their neighboring structures.

Chewing or not? Intraoral food processing in a salamandrid newt.

Food processing refers to any form of mechanical breakdown of food prior to swallowing. Variations of this behaviour are found within all major gnathostome groups. Chewing is by far the most commonly used intraoral processing mechanism and involves rhythmic mandibular jaw and hyobranchial (tongue) movements. Chewing occurs in chondrichthyans (sharks and rays), actinopterygians (ray-finned fishes), dipnoi (lungfishes) as well as amniotes and involves similarities in the patterns of muscle activity and movement of the feeding apparatus. It has been suggested that amniote chewing, which involves the interaction of movements of the mandibular jaw and the muscular tongue, has evolved as part of the tetrapod land invasion. However, little is known about food-processing mechanisms in lissamphibians, which might have retained many ancestral tetrapod features. Here, we identified a processing mechanism in the salamandrid newt, Triturus carnifex, which after prey capture displays cyclic head bobbing in concert with rhythmic jaw and tongue movements. We used high-speed fluoroscopy, anatomical reconstructions and analyses of stomach contents to show that newts, although not using their mandibular jaws, deploy a derived processing mechanism where prey items are rasped rhythmically against the dentition on the mouth roof, driven by a loop motion of the tongue. We then compared patterns and coordination of jaw and tongue movements across gnathostomes to conclude that food processing in this newt species shares traits with processing mechanisms in fish as well as amniotes. This discovery casts salamanders as promising models for reconstructing the evolution of intraoral processing mechanisms at the fish-tetrapod split.

The Association between Sucking Behavior in Preterm Infants and Neurodevelopmental Outcomes at 2 Years of Age

To evaluate whether a specific period after birth (in weeks postmenstrual age [PMA]) and specific elements of sucking are associated with abnormal neurodevelopmental outcomes at age 2 years using a longitudinal approach. Fifty-two preterm infants participated in this longitudinal cohort study (mean gestational age, 29.5 weeks; mean birth weight, 1197 g). We assessed the infants' sucking patterns at 37-50 weeks PMA using the Neonatal Oral-Motor Assessment Scale. At age 2 years, based on a neurologic examination and the Dutch version of the Bayley Scales of Infant and Toddler Development, Second Edition, we categorized the children as developing normally (n = 39) or abnormally (n = 13). ORs, including 95% CIs, were calculated to ascertain the risk of abnormal neurodevelopmental outcomes. The inability to sustain sucking at 46 weeks PMA (OR, 6.25; 95% CI, 1.29-30.35) and the absence of a mature sucking pattern at 44 weeks PMA (OR, 6.30; 95% CI, 1.40-28.32) significantly increased the odds of abnormal neurodevelopmental outcomes at age 2 years. The ORs of the Neonatal Oral-Motor Assessment Scale items assessing rhythmic jaw movements, rhythmic tongue movements, and coordination among sucking, swallowing, and respiration were high shortly after term, but failed to reach significance. Specific elements of sucking at 4-6 weeks postterm are associated with abnormal neurodevelopmental outcomes in preterm infants at age 2 years. This period might be a sensitive time of infant development in which sucking behavior is an early marker of abnormal developmental outcomes. This finding may offer opportunities for early intervention.

Differential involvement of two cortical masticatory areas in submandibular salivary secretion in rats

To evaluate the role of the masticatory area in the cerebral cortex in the masticatory-salivary reflex, we investigated submandibular salivary secretion, jaw-movement trajectory and electromyographic activity of the jaw-opener (digastric) and jaw-closer (masseter) muscles evoked by repetitive electrical stimulation of the cortical masticatory area in anesthetized rats. Rats have two cortical masticatory areas: the anterior area (A-area) in the orofacial motor cortex, and the posterior area (P-area) in the insular cortex. Our defined P-area extended more caudally than the previous reported one. P-area stimulation induced vigorous salivary secretion (about 20µl/min) and rhythmical jaw movements (3–4Hz) resembling masticatory movements. Salivary flow persisted even after minimizing jaw movements by curarization. A-area stimulation induced small and fast rhythmical jaw movements (6–8Hz) resembling licking of solutions, but not salivary secretion. These findings suggest that P-area controls salivary secretion as well as mastication, and may be involved in the masticatory-salivary reflex.

Jaw-opening reflex and corticobulbar motor excitability changes during quiet sleep in non-human primates.

To test the hypothesis that the reflex and corticobulbar motor excitability of jaw muscles is reduced during sleep. Polysomnographic recordings in the electrophysiological study. University sleep research laboratories. The reflex and corticobulbar motor excitability of jaw muscles was determined during the quiet awake state (QW) and quiet sleep (QS) in monkeys (n = 4). During QS sleep, compared to QW periods, both tongue stimulation-evoked jaw-opening reflex peak and root mean square amplitudes were significantly decreased with stimulations at 2-3.5 × thresholds (P < 0.001). The jaw-opening reflex latency during sleep was also significantly longer than during QW. Intracortical microstimulation (ICMS) within the cortical masticatory area induced rhythmic jaw movements at a stable threshold (≤ 60 μA) during QW; but during QS, ICMS failed to induce any rhythmic jaw movements at the maximum ICMS intensity used, although sustained jaw-opening movements were evoked at significantly increased threshold (P < 0.001) in one of the monkeys. Similarly, during QW, ICMS within face primary motor cortex induced orofacial twitches at a stable threshold (≤ 35 μA), but the ICMS thresholds were elevated during QS. Soon after the animal awoke, rhythmic jaw movements and orofacial twitches could be evoked at thresholds similar to those before QS. The results suggest that the excitability of reflex and corticobulbar-evoked activity in the jaw motor system is depressed during QS.

Coordination of NMDA-induced rhythmic activity in the trigeminal and hypoglossal nerves of neonatal mice in vitro

Suckling is a rhythmic jaw movement that is symmetrical on the left and right side and is highly coordinated with tongue movement. Thus, we investigated the neuronal mechanisms of the left/right and jaw/tongue coordinations during N-methyl-d-aspartate (NMDA)-induced fictive suckling using isolated brainstem–spinal cord preparations obtained from neonatal mice. We observed synchronous low-frequency rhythmic activity in the left/right trigeminal motor nerves, which differed from respiration, and high-frequency rhythmic trigeminal activity, which was side-independent. The low-frequency rhythmic trigeminal activity was also synchronized with the hypoglossal nerve activity. After a complete midline separation of the preparation or a partial midline transection of the brainstem from the anterior inferior cerebellar artery to the junction of the vertebral artery, the low-frequency rhythmic trigeminal activity disappeared, whereas the high-frequency rhythmic trigeminal activity and low-frequency rhythmic hypoglossal activity still remained. These results suggest that the neuronal network that generates low-frequency rhythmic activity likely contributes to the synchronized activity of the left/right jaw muscles and to the jaw/tongue muscles, where it sends its command to the trigeminal motoneurons mainly via the commissural pathway that crosses the transected midline region. Such a neuronal network may underlie the coordinated movements of the jaw and tongue during suckling.

Cortical area inducing chewing-like rhythmical jaw movements and its connections with thalamic nuclei in guinea pigs

Repetitive electrical stimulation to the cortical masticatory areas (CMA) evokes rhythmical jaw movements (RJM), whose patterns vary depending on the stimulation site, in various species. In guinea pigs, although alternating bilateral jaw movements are usually seen during natural chewing, it is still unclear which cortical areas are responsible for chewing-like RJM. To address this issue, we first defined the cortical areas inducing chewing-like RJM by intracortical microstimulation. Stimulation of the most lateral area of the CMA, the granular cortex, induced chewing-like RJM, but from the region medial to this area, simple vertical RJM were induced. Subsequently, to reveal the properties of these two areas in the CMA, the connections between the CMA and the dorsal thalamus were examined by neuronal tract-tracing techniques. The area inducing chewing-like RJM possessed strong reciprocal connections, mainly with the medial part of the ventral posteromedial nucleus, which is the sensory-relay thalamus. On the other hand, the simple vertical RJM-inducing area had reciprocal connections with the motor thalamus. The present study suggests that the CMA inducing chewing-like RJM is different from the CMA inducing simple vertical RJM, and plays a role in cortically induced chewing-like RJM under the influence of the sensory thalamus in guinea pigs.

Differential involvement of two cortical masticatory areas in modulation of the swallowing reflex in rats

To clarify the functional role of cortical descending inputs involved in the swallowing reflex, the effect of electrical stimulation of two cortical masticatory areas (CMAs: A- and P-area) on rhythmic jaw movements (RJMs) and superior laryngeal nerve (SLN)-evoked swallows were studied. RJMs and swallowing reflex were elicited by repetitive electrical stimulation of CMAs and the SLN, respectively. The electromyographic activities of jaw-closer (masseter), jaw-opener (digastric), and laryngeal-elevator (thyrohyoid) muscles were recorded to identify the RJMs and swallowing reflex. The number of evoked swallows was significantly lower, and swallowing interval was significantly longer during A-area stimulation compared with those without stimulation. Conversely, these parameters were not significantly altered during P-area stimulation. The inhibition of swallows by A-area stimulation was not affected by an increase in sensory input by wooden stick application between upper and lower teeth, or A-area stimulation preceding SLN stimulation. The present findings suggest that the swallowing reflex is inhibited by activation of the A-area, but not the P-area. Since no changes in swallows were seen after the increase in intraoral sensory input and prior activation of masticatory central pattern generator (CPG), swallowing inhibition may be mediated by direct inputs from the A-area or inputs via the masticatory CPG into the swallowing CPG.

Neuronal activities of the vestibular nuclear complex during mechanically induced rhythmic jaw movements in rats

We studied the neuronal activities of the vestibular nuclear complex (VN) neurons during rhythmic jaw movements in rats anesthetized with urethane. Rhythmic jaw movements were induced by mechanical stimulation of the palate mucosa. The firing rate of approximately 25% of VN neurons increased significantly, and that of 10% of VN neurons decreased significantly, during these rhythmic jaw movements. There was no correlation between the change in the firing rate and the phase of the rhythmic jaw movements (jaw-opening and jaw-closing phases). The neurons that were affected were intermingled in the VN. These results suggest that the VN neurons are involved in controlling jaw movements.

Influence of periodontal afferent inputs for human cerebral blood oxygenation during jaw movements

Using functional magnetic resonance imaging (fMRI) and near-infrared spectroscopy (NIRS), we examined the role of periodontal afferent inputs on cerebral activation pattern evoked by masticatory muscle activity in twenty-two subjects. Statistical comparisons were used to identify brain regions with significant activation after subtraction of baseline activity from sham teeth-tapping (no periodontal input) and teeth-tapping (periodontal input) activity in an fMRI (N=14) and NIRS study (N=8). Both sham teeth-tapping and teeth-tapping significantly activated bilateral sensorimotor cortex and supplementary motor area in the fMRI study. NIRS revealed that oxygenated hemoglobin concentrations increased in sensorimotor cortex; however, there was no significant difference in degree of oxygenated hemoglobin changes between sham teeth-tapping and teeth-tapping. A control study (N=8) characterized the jaw muscle activity and amplitude of the two motor tasks and demonstrated significantly higher electromyogram (EMG) activity in the jaw closing muscles during teeth contact in the teeth-tapping session. Since the cerebral activation during sham teeth-tapping and teeth-tapping was similar, we suggest that the influence of periodontal afferent inputs and associated jaw muscle activity is relatively minor compared to the rhythmic jaw movements. Although the clinical significance of the present findings remains unknown, they may have implications for the understanding of awake or sleep-related bruxism characterized by subconscious and rhythmic teeth-grinding or teeth-clenching.

Characteristics of Temporomandibular Joint Vibrations in Anterior Disk Displacement With Reduction in Adults

The objective to the present study was to compare temporomandibular joint (TMJ) vibration in anterior disk displacement with reduction (ADDWR) in adults and to explore the diagnostic value of frequency spectrography of TMJ vibrations. Twenty-one patients with ADDWR formed the case group and were further divided into three subgroups according to the degree of disk displacement, and 26 symptomless adults formed the control group. The joint vibration was recorded during rhythmic maximal open-close jaw movement using JVA/JT, BioPAK (Bioresearch, Inc., Brown Deer, WI)). The sensitivity and specificity of the total integral for diagnosis of ADDWR was calculated. All TMJ vibration parameters, including total integral, integral>300Hz, integral<300Hz, >300/<300 ratio, peak amplitude, peak and median frequencies of the case group were significantly higher than that of the control group. Along with the degree of disk displacement, the amplitude and frequency of TMJ vibrations increased, and the total integral significantly increased. The total integral demonstrated high sensitivity and specificity for diagnosis of ADDWR (85.7% and 84.6%, respectively). TMJ vibration was significantly higher in adults with ADDWR than that in the symptomless control group. Different pathological stages of disk displacement have different TMJ vibrations.