Influence of gum-chewing on the haemodynamics in female masseter muscle.

Blood flow in active skeletal muscles provides energy substrate, oxygen and reduction of excessive heat and metabolic by-products. Although cyclic jaw motions such as those during mastication and speech articulation are the primitive oro-facial functions, possible effects of the cyclic muscle contractions on the intramuscular haemodynamics of the jaw muscles remains scarcely known. We investigated the masseteric haemodynamics during and after gum-chewing. Ten healthy female adults participated in the study. Electromyography, kinetics of masseter muscle oxygenation, electrocardiogram and blood pressure were recorded simultaneously. The subjects were asked to perform gum-chewing and cyclic jaw motion without gum bolus (empty-chewing task). The haemodynamics parameters were compared between the two experimental conditions. During gum-chewing task, deoxygenated haemoglobin and sympathetic nerve activity increased, while tissue blood oxygen saturation decreased. Blood pressure and parasympathetic nerve activity did not change. The overall behaviour of haemodynamic parameters during empty-chewing task was similar to that observed during gum-chewing task. However, the latency periods from the end of chewing until significant changes in the haemodynamic parameters were notably shorter (P < 0.05) in gum-chewing task as compared with those associated with empty-chewing task. The duration of the changes was shorter with empty-chewing than with gum-chewing. Fluctuations in masseter muscle haemodynamics associated with chewing jaw movement differed depending on the level of muscle contraction during movement. The differences became statistically significant immediately after the commencement of chewing and after the cessation movement. During the chewing movement, automatic nerve activities increased in response to the level of muscle contraction during movement.

Mental stress-induced physiological changes in the human masseter muscle.

The effect of a long mental stress on the hemodynamics of masticatory muscles has not been investigated to date. We hypothesized some hemodynamic and electromyographic changes in jaw-closure muscles related to sympathetic nervous system activity. While healthy adult female volunteers performed a two-hour mental stress task, electromyographic activity of the temporal and masseteric muscles was recorded, and hemodynamic changes of the masseter muscle were measured non-invasively. Autonomic function was assessed by heart rate spectral analysis. Integrated electromyographic activity of the temporalis muscle, but not the masseter muscle, showed an increase that coincided with the increase in sympathetic nervous activity. In the masseter muscle, despite little change in integrated electromyographic activity, notable changes were found in hemodynamic parameters. These results suggest that hemodynamics of jaw muscles is susceptible to mental stress, implying a potential role in the etiology of jaw muscle dysfunction associated with mental stress.

Asymmetry in the condylar long axis and first molar rotation.

Asymmetric growth occurs frequently in the mandibulofacial region, but little attention has been given to asymmetry in the temporomandibular joint. The purpose of this study was to clarify the feature of asymmetry in the condylar long axis and its relation to upper first molar rotation. Records of 148 pre-orthodontic patients were used. The angle of the condylar long axis and that of the molar rotation were both larger on the left side than on the right side. Positive correlations were found between the corresponding bilateral measurements of condylar long axes and also between those of molar rotations, whereas no correlation was found between the condylar long axis and molar rotation. These findings were found in most subgroups classified by dental age, skeletal pattern, bite force balance, or gender. These results suggest that consistent left-right differences in the condylar long axis and first molar rotation are common.

Changes in masseteric hemodynamics time-related to mental stress.

Mental stress may cause a dissociation of sympathetic outflow to different regions. However, it remains unclear how the sympathetic outflow to jaw muscles is related to other sympathetic outflow under mental stress. The objective of this study was to clarify the temporal relationship between the finger sweat expulsion elicited by mental stress and the hemodynamic and electromyographic changes in the masseter muscle. Healthy adult female volunteers participated in this study. Masseteric hemodynamic changes were closely time-related to mental stress, showing a decrease in oxygen saturation of muscle blood around the onset of mental stress. In contrast, EMG activity of jaw-closing muscles was not time-related to mental stress. These results suggest that mental stress induces hemodynamic changes that are not associated with EMG activity in the masseter muscle of healthy adult females.

Adjustment of the occlusal vertical dimension in the bite-raised guinea pig.

In humans, the inappropriate occlusal vertical dimension (OVD) causes several orofacial disorders, such as bruxism and pain in the masticatory muscles and temporomandibular joint. However, it is still unclear how strictly the OVD is adjusted. To answer this question, we studied the temporal change of the OVD in bite-raised young guinea pigs. The OVD was raised by fixation of a bite-raising appliance to the lower incisors, and increased by either 3 or 1.5 mm at the first molars. After the space produced between the upper and lower molars was filled within 10 days due to eruption of the molars, the appliance was removed. In the bite-raised animals, the raised OVD was reduced until it attained that observed in the control animals, after which the OVD increased according to cranial growth. These results show that the OVD is developmentally changed and strictly controlled.

Putative feed-forward control of jaw-closing muscle activity during rhythmic jaw movements in the anesthetized rabbit.

When a thin plastic test strip of various hardness is placed between the upper and lower teeth during rhythmical jaw movements induced by electrical stimulation of the cortical masticatory area (CMA) in anesthetized rabbits, electromyographic (EMG) activity of the masseter muscle is facilitated in a hardness-dependent manner. This facilitatory masseteric response (FMR) often occurred prior to contact of the teeth to the strip, and thus preceded the onset of the masticatory force. Since this finding suggests involvement of a feed-forward mechanism in the induction of the FMR, the temporal relationship between the onset of the FMR and that of the masticatory force was analyzed in five sequential masticatory cycles after application of the strip. The FMR was found to precede the onset of masticatory force from the second masticatory cycle after application of the strip, but never did in the first cycle. This finding supports the concept of a feed-forward control mechanism that modulates FMR timing. Furthermore, the FMR preceding the force onset disappeared after making a lesion of the mesencephalic trigeminal nucleus (MesV) where the ganglion cells of the muscle spindle afferents from the jaw-closing muscles are located. In contrast, no such change occurred after blocking periodontal afferents by transection of both the maxillary and the inferior alveolar nerves. The putative feed-forward control of the FMR is therefore dependent mainly on sensory inputs from the muscle spindles, but little on those from the periodontal receptors, if any. We further examined the involvement of the CMA with the putative feed-forward control of the FMR via the transcortical loop. For this purpose, rhythmical jaw movements were induced by stimulation of the pyramidal tract. No significant change in the timing of the FMR occurred after the CMA ablation, which strongly suggests that the CMA is not involved in the putative feed-forward control of the FMR. The FMR was also noted to increase significantly in a hardness-dependent manner even after the MesV lesion, although the rate of increment decreased significantly. Contribution of muscle spindles and periodontal receptors to the hardness-dependent change of the FMR is discussed.

Neuronal activity in the putamen and the globus pallidus of rabbit during mastication.

The pattern of jaw movements is changed during a masticatory sequence from ingestion of food to its deglutition. The masticatory sequence is divided into three distinct stages in the rabbit. However, the neural mechanism involved in the alteration of the masticatory stages is still unknown. This study was designed to determine whether neuronal activity in the putamen and globus pallidus is related to the alteration of the masticatory stages. Fifty-three percent of the recorded neurons showed significant alterations of activity during mastication. Of these neurons, 16% changed their firing frequency throughout the masticatory sequence (sequence-related neurons) and 84% changed their firing frequency with the transition of the masticatory stages (stage-related neurons). The stage-related neurons were classified into two groups based on their neuronal activity patterns observed during mastication, i.e. simple type and complex type. The former are the neurons that were either facilitated or inhibited once during mastication, and the latter are those showing the facilitation or inhibition twice or more during mastication. Complex-type neurons were observed more frequently in the globus pallidus than in the putamen. These results suggest that the basal ganglia is involved in mastication and may related to the transition between the masticatory stages.

Influence of food thickness and hardness on possible feed-forward control of the masseteric muscle activity in the anesthetized rabbit.

The facilitatory masseteric muscle response (FMR) elicited by polyurethane foam strip application between the opposing molars during cortically-induced rhythmic jaw movements (CRJMs) was induced earlier than masticatory force onset. The occurrence of this early response of the FMR (e-FMR) could not be explained by a simple reflex mechanism. One possible mechanism of the e-FMR is the involvement of a feed-forward control mechanism of the masticatory jaw movement. In the present study, experimentally designed polyurethane foam strips with various thickness and hardness were applied during CRJMs and analyzed in terms of how the e-FMR was modulated by the food hardness and thickness. The FMR onset was not related to the strip thickness or the strip hardness. However, the magnitude of the e-FMR increased in a thickness and a hardness-dependent manner. The sensory information of the food properties in the masticatory cycle may make the FMR adequate to chewing of the food in the following cycle, and such modulation may help chewing rhythms remain stable.

Kinematic modeling of jaw-closing movement during food breakage.

It has been demonstrated that the vertical jaw movement trajectories during gum-chewing can be explained by jerk-cost minimization. However, it is uncertain whether the masticatory jaw movement in space can be predicted by the minimum-jerk model. The aims of the present study were to develop minimum-jerk models that would explain 3D masticatory jaw movements with different hardnesses of foods, and to evaluate if the models can predict the movements accurately. The 3D masticatory jaw movement during food breakage was formulated for two types of test foods. The coefficients of determination (R2) between the measured and model-based values ranged from 0.846 to 0.882. Differences were found in the kinematic parameters between the test foods. The results suggest that the models predict the 3D jaw movements during food breakage and are effective in differentiating among the kinematic features of masticatory jaw movements that are peculiar to the mechanical properties of foodstuffs.

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.

Influence of clenching intensity on bite force balance, occlusal contact area, and average bite pressure.

It has been difficult for investigators to simultaneously and reliably evaluate bite force in the intercuspal position with the area and location of occlusal contacts. This study was designed to investigate the variations in these parameters with respect to two factors: three levels of clenching and the preferred chewing side. Human subjects with normal occlusion were examined with a recently developed system (Dental Prescale Occluzer, Fuji Film, Tokyo, Japan). The three levels of clenching intensity were assessed by masseteric EMG activity and included the maximum voluntary contraction, and 30% and 60% of the maximum. The results indicated that the bite force and occlusal contact area on the whole dental arch increased with clenching intensity. In contrast, the average bite pressure, obtained by dividing the bite force by the contact area, remained unchanged regardless of the clenching intensity. As the clenching intensity increased, the medio-lateral position of the bite force balancing point shifted significantly (P<0.01) from the preferred chewing side toward the midline. The antero-posterior position remained stable in a range between the distal third of the first molar and the mesial third of the second molar. The bite force and occlusal contact area, which were mainly on the molars, increased with the clenching intensity, whereas the proportions of these two variables on each upper tooth usually did not change significantly. The exception was the second molar on the non-preferred chewing side. When comparisons were made between pairs of specific upper teeth of same name, usually no significant difference was found in bite force or occlusal contact area, regardless of the clenching level. Again, the exception to this observation was the second molar on the preferred chewing side, which had a larger area at the 30% clenching level. The results in normal subjects suggest that as the clenching intensity increases in the intercuspal position, the bite force adjusts to a position where it is well-balanced. This adjustment may prevent damage and overload to the teeth and temporomandibular joints.

Characteristics of the muscle spindle endings of the masticatory muscles in the rabbit under halothane anesthesia.

To explore the response characteristics of muscle spindle units in the masticatory muscles in the rabbit, the responses of muscle spindle units were recorded from the mesencephalic trigeminal nucleus (MesV) under halothane anesthesia during ramp-and-hold stretches. Three firing patterns, initial burst (IB) at the onset of the dynamic phase, negative adaptation (NA) at the end of the dynamic phase and firing during the release (FDR) phase, were observed during muscle stretch. IB was present at higher stretch velocities, FDR at lower stretch velocities. The velocity at which an IB or FDR was present was different from unit to unit. Because, within the range of the velocities of stretch tested, units with NA always showed NA and units without NA never did, all recorded units were divided into two groups on the basis of the existence of NA (NA(+) or NA(-) units). Response characteristics of the two groups were then compared. NA(+) units showed an IB more frequently and FDR less frequently than NA(-) units. NA(+) units had significantly higher dynamic responsiveness and discharge variability than NA(-) units. The conduction velocity of the afferents of NA(+) units was higher than that of NA(-) units. However, distributions of these measurements were not bimodal. These results suggest that NA is the useful criteria to classify the muscle spindle endings in the masticatory muscles in the rabbit under halothane anesthesia.

Fusimotor influence on jaw muscle spindle activity during swallowing-related movements in the cat.

1. The activity patterns of muscle spindle afferents in jaw-closer muscles were studied during reflex swallowing movements in anaesthetized cats. Simultaneous records were made of the electromyogram (EMG) in masseter and anterior digastric muscles and of the unloaded jaw movements. The underlying patterns of fusimotor activity were deduced by comparing afferent discharges occurring during active swallowing with those occurring when exactly the same movements were imposed passively. The interpretation of spindle behaviour was greatly facilitated by characterizing the afferents according to the evidence for their contact with the various intrafusal muscle fibres, derived from testing with succinylcholine. It was also valuable to have two different types of afferent recorded simultaneously. 2. There was clear evidence of fusimotor activity occurring during active jaw closing so as to oppose the spindle silencing. This effect was most marked in b2c-type afferents (probably secondaries) and was therefore attributed to a modulation of static fusimotor discharge approximately in parallel with alpha-activity. 3. Afferents with evidence of bag1 fibre contacts (primaries) showed much greater sensitivity to muscle lengthening during active movement than when the movement was imposed. This difference was exaggerated when anaesthesia was deepened for the passive movements. This was interpreted as evidence for a higher level of dynamic fusimotor activity maintained during active movements than at rest. 4. The results support the view that for a variety of active jaw movements, static fusimotor neurone firing is modulated roughly in parallel with alpha-activity but leading it so as to counteract spindle unloading. Dynamic fusimotor neurone firing appears to be set at a raised level during active movements. Anaesthesia appears to depress activity in the alpha-motoneurones more than in gamma-motoneurones.

Regulation of masticatory force during cortically induced rhythmic jaw movements in the anesthetized rabbit.

To examine the relationships between masticatory force, electromyogram (EMG) of masticatory muscles, and jaw movement pattern, we quantitatively evaluated the effects of changing hardness of a chewing substance on these three variables. Cortically induced rhythmic jaw movements of a crescent-shaped pattern were induced by electrical stimulation of the cerebral cortical masticatory area in the anesthetized rabbit. The axially directed masticatory force was recorded with a small force-displacement transducer mounted on the ground surface of the lower molars. EMGs were recorded from the masseter and digastric muscles simultaneously with jaw movements. Five test strips of polyurethane foam of different hardness were prepared and inserted between the upper molar and the transducer during the movements. The peak, impulse, and buildup speed of the masticatory force increased with strip hardness, whereas duration of the exerted force did not vary with strip hardness. The integrated activity and duration of the masseteric EMG bursts also increased with strip hardness. The integrated EMG activity of the digastric bursts was weakly related to strip hardness, whereas the duration was not. The minimum gape increased with strip hardness, but the maximum gape did not. The horizontal excursion of the jaw did not vary in a hardness-dependent manner, although it was greater in the cycles with strip application than in the cycles without strip application. Deprivation of periodontal sensation by cutting the nerves to the teeth reduced the buildup speed of the force, maximum gape, net gape, and horizontal jaw movements. The denervation also elongated the force duration and that of masseteric EMG bursts. However, the rate of the hardness-dependent changes in the above parameters did not alter after denervation. The latency of the masseteric EMG response to strip application was evaluated before and after denervation. In both conditions, it was > or = 6 ms in approximately 70% of the cycles and <6 ms in the remaining approximately 30%, which cannot be explained by a simple reflex mechanism. On the basis of the analysis of correlation coefficients, the masseteric integrated EMG seemed to be a good indicator of the peak and impulse of the masticatory force both before and after denervation. We conclude that periodontal afferents would be responsible for a quick buildup of masticatory force and that afferents other than those from periodontal tissue would contribute to the hardness-dependent change of masticatory force during cortically induced rhythmic jaw movements.

Role of calcium conductances on spike afterpotentials in rat trigeminal motoneurons.

Intracellular recordings were obtained from rat trigeminal motoneurons in slice preparations to investigate the role of calcium conductances in the depolarizing and hyperpolarizing spike afterpotential (ADP and mAHP, respectively). The mAHP was suppressed by bath application of 1 microM apamin, 2 mM Mn2+, and 2 mM Co2+, and also by intracellular injection of ethylene glycol-bis(b-aminoethylenether)-N,N,N',N'-tetraacetic acid (EGTA), suggesting that the potassium conductance generating the mAHP is activated by Ca2+ influx. Mn2+ (2 mM) or Cd2+ (500 microM) reduced the ADP, whereas the ADP amplitude was increased by raising extracellular Ca2+ concentration from 2 to 8 mM by bath application of Ba2+ (0.5-5 mM) and by intracellular injection of EGTA. This would suggest that Ca2+ itself is likely to be the charge carrier generating the ADP. Focal application of omega-conotoxin GVIA (10-30 microM) suppressed the mAHP and enhanced the ADP, whereas focal application of omega-agatoxin IVA (10-100 microM) reduced the ADP amplitude without apparent effects on the mAHP. We conclude that Ca2+ influx through omega-agatoxin IVA-sensitive calcium channels is at least in part responsible for the generation of the ADP and that Ca2+ influx through omega-conotoxin GVIA-sensitive calcium channels contributes to the generation of the mAHP. Because of the selective suppression of the ADP and mAHP by omega-agatoxin IVA and omega-conotoxin GVIA, respectively, it is suggested that both calcium channels are separated geometrically in rat trigeminal motoneurons.

Modulation of jaw muscle spindle discharge during mastication in the rabbit.

Discharges of jaw muscle spindles were recorded during chewing carrot from mesencephalic trigeminal nucleus (Mes V) in the awake rabbit to evaluate contribution of the muscle spindles to the development of complete sequences of masticatory movements. The Mes V spindle units were divided into two types according to the maximum firing rates during mastication, with a dividing line at 200 Hz; high-frequency units and low-frequency units. Although both types of units fired maximally during the jaw-opening phase of chewing cycles, their firing rates and pattern varied according to three sequential stages of mastication (stages I, IIa, and IIb). The high-frequency units often increased firing before the start of mastication and built up firing in the first few chewing cycles. Their maximal firing rate was sometimes lower during stage IIa (chewing stage) than during stage I (ingestion stage) and stage IIb (preswallowing stage), although the jaw movements were greater in stage IIa than in other stages. The phase relationship of the firing to a jaw movement cycle in stage IIa was consistent in individual units. The low-frequency units did not build up activity before the onset of movements. They fired mostly during the jaw-opening phase, but the peak of firing did not necessarily coincide with the time of maximal opening. It was concluded that the difference in the firing pattern among masticatory stages may be ascribed to a stage-dependent modulation of both fusimotor activity and jaw movement pattern.

A case of intracystic carcinoma of the breast: the importance of measuring carcinoembryonic antigen in aspirated cystic fluid.

We report a case of intracystic carcinoma of the breast in which a correct preoperative diagnosis was achieved on the basis of an increased level of carcinoembryonic antigen (CEA) in the aspirated cystic fluid. A 62-year-old woman was admitted with a 10 x 10 cm painful mass occupying the right breast. Ultrasonography revealed a cystic lesion with papillary projections arising from the cyst wall. Cytological examinations showed no malignant cells in the hemorrhagic aspirated fluid. However, the CEA level in the fluid was 5.5 times higher than the serum CEA level using a murine anti-CEA monoclonal antibody. The high level of CEA led to the preoperative diagnosis of intracystic carcinoma. Histological examinations confirmed the diagnosis of intracystic carcinoma after a modified radical mastectomy. Immunohistochemical staining by an anti-CEA monoclonal antibody elicited a strong positivity with diffuse intracytoplasmic distribution in the carcinoma cells, although heterogeneity of staining was observed. It is suggested that the measurement of the CEA value by anti-CEA monoclonal antibody in the aspirated fluid is easy, safe, and helpful for the definitive diagnosis of intracystic carcinoma of the breast.

Purification and properties of amylase produced by a moderately halophilic Acinetobacter sp.

A moderately halophilic Acinetobacter sp., capable of producing dextrinogenic amylase, was isolated from sea-sands. Maximum enzyme production was obtained when the bacterium was cultivated aerobically in media containing 1 to 2M NaCl or 1M KCl. Two kinds of amylase, amylases I and II were purified from the culture filtrate to an electrophoretically homogenous state by glycogen-complex formation, DEAE-Sephadex A-50 chromatography, and Sephadex G-200 gel filtration. Both enzymes had maximal activity at pH 7.0 in 0.2 to 0.6 M NaCl or KCl at 50 to 55 degrees C. The activities were lost by dialysis against distilled water. Molecular weights for amylases I and II were estimated to be 55 000 and 65 000 respectively by SDS-gel electrophoresis. The action pattern on amylose, soluble starch, and glycogen showed that the products were maltose and maltotriose.