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At least 163 records · Page 9Linked to original sources
PubMed1984

Activity during active sleep of bulbar reticular neurons firing rhythmically during mastication in cats.

Unitary activity was recorded from 17 bulbar reticular neurons, which fired rhythmically during mastication, in unanesthetized, spontaneously respiring cats during sleep and wakefulness. All these neurons showed the highest mean firing rate during food ingestion, and none of them showed any tonic discharge during active sleep. The results are discussed in terms of a functional differentiation of bulbar reticular inhibitory neurons projecting to jaw-closer motoneurons in relation to phasic inhibition during mastication and tonic inhibition during active sleep of jaw-closer motoneurons.

Animals↗
PubMed1986

Computer-based assessment of habitual mastication.

A computer-based system to assess mandibular movements and EMG masseter and temporal muscle activity during habitual mastication was applied to 12 healthy subjects and the chewing performance was tested with a standardized bolus of crisp bread. A Siemens Sirognatograph instrument was used to record mandibular movements while EMG signals were recorded with surface silver-silver electrodes. Software provided data of single chewing cycles in space and versus time, of mean mandibular displacement during opening and closing, mean velocity, and EMG activity. Clockwise and counterclockwise cycles were computed separately. The data obtained allow the following conclusions: Habitual mastication is a rhythmic event with different envelopes of motion that alternate characteristically in each subject. Each chewing cycle accomplishes several tasks but, depending on its envelope, is probably more oriented to a specific performance. A mean chewing cycle can be constructed for each individual. Its pattern depends on the distribution of different envelopes of motion that alternate during the masticatory sequence. During closure, a prevalently isotonic and a prevalently isometric phase of muscle contraction can be distinguished. Mean movement and EMG data for the whole group are not distributed at random, but according to a typical pattern. The system seems to be finalized to a well-balanced function and distribution of loads.

Adolescent↗
PubMed1986

Replicability of electromyographic recordings of the masseter muscle during mastication.

This study evaluates the reliability of a method to duplicate the location of surface electrodes for recording the electromyographic activity of masseter muscles during mastication and quantifying the activity by a microcomputer system. A plastic framework consisting of a bite fork and electrode positioners was used to place the electrodes by relating the positioners to an occlusal index and keeping this relationship constant at subsequent sittings. EMG recordings were repeated on two different days for each of 10 subjects while they performed standardized masticatory performance tests with peanuts and carrots. The muscle activity recorded with hardware integrators was an average of 26.7% of the computerized software integrations but measures derived from the two methods of integration were highly correlated (r = 0.965) and yielded similar results. Significant correlations were found between test sessions for each measure of masticatory performance and integrated EMG activity for ipsilateral and contralateral muscles. For each subject, no significant differences were found between sessions for any masticatory performance or EMG variable. The results indicate that reliable inter session EMG recordings during mastication can be made by using the template for positioning of the electrodes. In addition, the microcomputer data acquisition system provides results comparable to those obtained with conventional hardware integrators, with the added benefit of providing information on each individual stroke and its various components.

Adolescent↗
PubMed1989

Habitual mastication in dysfunction: a computer-based analysis.

To study the different parameters of habitual mastication in stomatognathic dysfunction, mandibular movements and electromyographic activity of the elevator muscles were recorded during three chewing sequences in 86 dysfunctional subjects. The Dysfunction Index system was used to treat two subgroups, patients with severe temporomandibular joint impairment and patients with severe muscle dysfunction. Data on the different parameters of mastication from the single patients, the whole group, and the two subgroups were statistically assessed and compared with those from 12 normal individuals. The following conclusions were drawn. (1) In dysfunctional patients the normal symmetrical and balanced distribution of the chewing cycles is lost and movements are more restricted. (2) The electromyographic data show marked alterations with a tendency to reduce or suppress the isometric phase of contraction during closing in the temporomandibular joint patients. This can be viewed as a defensive mechanism of the impaired system. (3) The data at hand are helpful in explaining some of the mechanisms that lead to muscle pain in dysfunctional patients.

Electromyography↗
PubMed1992

Properties of rhythmically active reticular neurons around the trigeminal motor nucleus during fictive mastication in the rat.

Response properties of the neurons in the reticular formation around the trigeminal motor nucleus (MoV) were examined during cortically-induced fictive mastication (CIFM) in anesthetized and immobilized rats. Forty-three neurons were rhythmically active (RA neurons) during CIFM, most of which were located in the supratrigeminal nucleus and the reticular formation medial to the oral spinal trigeminal nucleus. The firing frequency of 36 of the RA neurons was modulated in the same rhythm as that of masseteric or digastric nerve activities during CIFM. We divided these neurons into four groups according to the phase of activation: sixteen neurons fired mainly in the phase of masseteric activity (type 1), 11 fired in the transition phase from masseteric activity to digastric activity (type 2), 5 fired in the phase of digastric activity (type 3) and 4 fired in the transition phase from digastric activity to masseteric activity (type 4). Thirty-nine (91%) of the 43 RA neurons responded to at least one of the tested peripheral stimuli. The responses were mostly excitatory but inhibitory responses were sometimes obtained, especially for types-1 and 2 neurons. RA neurons in the reticular formation medial to the oral spinal trigeminal nucleus responded to stimulation of inferior alveolar nerve at a shorter latency than RA neurons in the supratrigeminal nucleus. Fifteen (48%) of 31 RA neurons responded to triple-pulse stimulation of the contralateral cortex. In contrast, only 5(26%) of the 19 RA neurons responded to the ipsilateral cortical stimulation. Stimulation of the ipsilateral MoV was performed on 24 RA neurons, of which 9 responded antidromically (A-RA neurons) at latencies of 0.4-1.4 ms. Eight (89%) of the 9 A-RA neurons received peripheral inputs. The spike triggered averaging method was applied to 4 of the 9 A-RA neurons, ad in all cases short latency field potentials were recorded in the MoV. We conclude that trigeminal premotor neurons receive convergence from central and peripheral inputs. This integration can adjust the appropriate level of motoneuronal excitability during mastication.

Animals↗
PubMed1994

Age changes in mastication in the pig.

A comparative study of chewing in miniature pigs at three stages of dental development was carried out using electromyography and movement analysis. The mastication of the youngest pigs was characterized by longer burst durations of jaw muscles, particularly closing muscles, and greater relative jaw opening. Chewing side alternated irregularly and burst durations were variable. Between the intermediate and oldest ages, the parameters remained almost unchanged. Because the amount of dental development that occurred between the second two stages was just as extensive as that between the first two, progressive eruption cannot account for the age changes observed in mastication.

Age Factors↗
PubMed2004

The involvement of brain-derived neurotrophic factor in the pattern generator of mastication.

Brain-derived neurotrophic factor (BDNF) is a family of neurotrophins that plays crucial roles in neural development, survival, maintenance and regeneration both in central and peripheral nervous systems. To examine the effects of BDNF on mastication, jaw movement trajectories and masticatory muscle activities were electrophysiologically investigated in BDNF-deficient mice, compared with those of littermate wild-type mice. BDNF-deficient mice showed less number of chewing strokes and more irregular chewing pattern during mastication than wild-type mice. Masseter muscle activities of BDNF-deficient mice exhibited smaller values than those of wild-type mice. No significant difference in the cycle duration existed between these two types of the mice. These results indicate that the burst pattern is more susceptible to peripheral sensory inputs than the timing and suggest the involvement of BDNF in the control of jaw movement.

Animals↗
PubMed2006

Evaluation of the toxicity of mastic gum with 13 weeks dietary administration to F344 rats.

Dietary toxicity of mastic gum, a natural food additive, was studied in male and female F344 rats fed 0%, 0.22%, 0.67% and 2% levels mixed into powdered basal diet for 13 weeks. No mortality or obvious clinical signs were observed in any of the animals throughout the experimental period. Body weights were significantly reduced in the high dose-treated group from week 2 to the end of the experiment in males, and at weeks 8 and 13 in females. There were increased absolute and relative liver weights in a dose-related manner or limited to the high dose group males or females, along with changes in hematological parameters, including increased WBC and platelet in high dose males. Altered serum biochemistry parameters included increases of total proteins, albumin, and total cholesterol in both sexes, and gamma-GTP in females only. However, macroscopic examination at necropsy revealed no gross lesions, and microscopic examination also revealed no treatment-related findings in any organs examined. As dietary treatment of mastic gum for 13 weeks in the present study caused decreased body weights at the high dose, especially in males, and increased liver weights in a dose-related manner in both genders without any morphological findings, it is concluded that the administration of it has a no observed adverse effect level (NOAEL) of 0.67% in the diet.

Administration, Oral↗
PubMed2005

Finite element analysis of mechanism of cervical lesion formation in simulated molars during mastication and parafunction.

STATEMENT OF PROBLEM: The mechanical theory of cervical lesion formation is popular; however, the mechanism of formation of these lesions is not fully explained. PURPOSE: The aim of this study was calculation of the stresses and Tsai-Wu strength ratio in the cervical area of the mandibular molar during grinding, clenching, and mastication, as well as theoretical investigation of the mechanism of cervical lesion formation in teeth. MATERIAL AND METHODS: A 2-dimensional finite element model of the mandibular first molar and crown of the opposing maxillary molar in the frontal section was developed. Computational simulation of mastication of a bolus with high elastic modulus, including grinding and clenching, was performed. Pairs of contact elements were used between the bolus and occlusal surfaces of the teeth. The analysis was nonlinear. During these simulations, the pressure exerted on the occlusal surface and the state of stresses in the mandibular molar were calculated. To evaluate the strength of anisotropic tooth tissues, the Tsai-Wu failure criterion was applied. This criterion considers the difference in strength of materials due to tensile, compressive, and shear stresses. RESULTS: Significant pressures were exerted on lingual cusps of the mandibular molar model during computer simulations of physiological and pathological load. In enamel elements close to the buccal cemento-enamel junction (CEJ) of the studied tooth, tensile stresses were observed which exceeded the strength of the enamel. In this area, the Tsai-Wu strength ratio reached values higher than 1. According to the Tsai-Wu criterion, these elements were damaged and, thus, were removed from the computer tooth model. During subsequent modeling of the tooth with the initiated cervical lesion, the Tsai-Wu ratio exceeded 1 along the dentino-enamel junction (DEJ), creating an overhang of enamel in the cervical area. Application of minimal horizontal force caused a fracture of this fragile, unsupported enamel fragment. CONCLUSIONS: Overloading of theoretical teeth by computer simulation resulted in enamel damage at the CEJ and led to initiation of a cervical lesion. Subsequent overloading resulted in enamel destruction along the DEJ. The overhanging enamel fragment may easily be chipped. This process was repeated during subsequent tooth overloading and caused enlarging of the lesion.

Anisotropy↗
PubMed2000

The effects of food fragmentation index on mandibular closing angle in human mastication.

Jaw movements were recorded using a three-dimensional magnetic sensing system (Sirognathograph, Siemens) in 10 human volunteers while chewing standardized volumes of 15 food types, ranging from soft cheeses to hard nuts. The maximum horizontal amplitude inside the chewing loop (width of the loop), the height of the loop (vertical amplitude) and the closing angle made by the jaw during the late closing phase of the cycle relative to the vertical were calculated. The most highly significant correlation was between the closing angle and the square root of the ratio of two mechanical properties of the food - the toughness (R) and modulus of elasticity (E)(r = -0.85, p<0.001). The width of the chewing loop was also significantly correlated with the above combination of food properties (r = -0.75, p<0.01) whereas the vertical amplitude was not. Thus, the mechanical properties of foods appear to influence the pattern of mandibular movements in human mastication similarly to their reported effect on food breakdown rates and anterior temporalis activity during mastication.

Adult↗
PubMed1997

Effect of mastication on regional cerebral blood flow in humans examined by positron-emission tomography with ¹⁵O-labelled water and magnetic resonance imaging.

The interaction between mastication and cerebral blood flow was studied in 12 healthy volunteers (five males and seven females) aged 18-40 years. Positron-emission tomography (PET) autoradiography was carried out after bolus injection of 1.5 GBq H₂¹⁵O (¹⁵O-labelled water) with a half life of 2 min. The PET images were superimposed on magnetic resonance images of each participant. The regional cerebral blood flow images were normalized by the global cerebral blood flow value, and subtraction images (those during gum-chewing minus those during resting) were created and recut at the magnetic resonance image slice positions. Gum specially designed for chewing training was used. Mastication increased regional cerebral blood flow in the primary sensorimotor areas by 25-28%, in the supplementary motor areas and insulae by 9-17%, and in the cerebellum and striatum by 8-11%. These increases demonstrate that chewing activates widespread regions of the brain.

Adolescent↗
PubMed1997

Effect of gustatory stimulation on flow rate and protein content of human parotid saliva according to the side of preferential mastication.

Unstimulated and citric acid-stimulated parotid saliva from the left- and right-hand sides of 20 females, was collected separately to compare the corresponding flow rates, total protein and electrophoretic protein profiles. Individuals having the left-hand side as the preferential side of mastication presented significantly greater flow rates for the ipsilateral glands than for the contralateral ones. Although the data suggested that the left-hand side average protein concentrations were greater for the group with the right-hand side of preferential mastication, the results were not statistically significant. Some minor differences in electrophoretic protein profiles were detected by scanning densitometry.

Adolescent↗
PubMed1999

Reduced mastication stimulates impairment of spatial memory and degeneration of hippocampal neurons in aged SAMP8 mice.

The involvement of reduced mastication in senile dementia was evaluated by examining the effect of cutting off the upper molars (molarless) on spatial memory and numbers of hippocampal neurons in aged SAMP8 mice. Molarless mice showed a decrease in both learning ability in a water maze and neuron density in the hippocampal CA1 region compared with control mice. These changes increased the longer the molarless condition persisted. The data suggest a possible link between reduced mastication and hippocampal neuron loss that may be one risk factor for senile impairment of spatial memory.

Aging↗
PubMed2003

NaCl and sugar release, salivation and taste during mastication of salted chewing gum.

Salt perception impacts on food acceptability and nutrition and depends upon salt release from foods that was determined in situ during mastication of chewing gum with up to 10% (1800 mmol/kg) added NaCl. The mechanical action of chewing increased salivation, which was further increased by the presence of salt, particularly above 180 mmol NaCl/kg gum or above 100 mM NaCl in saliva. The average resting salivary flow rate was 1 ml/min, increasing to 4 and 6 ml/min with gums containing low and high salt, respectively. Thus, stimulation of salivation by salt occurred at a concentration well above the taste threshold of 20 mM NaCl. NaCl concentration in nonstimulated saliva was about 10 mM and increased to 500 mM after 30 s chewing of the 10% NaCl gum and returned to near nonstimulated levels after 4 min chewing. Changes in pH of saliva were more gradual, increasing to a maximum at about 2 min and remaining elevated after 4 min. Salty taste was related to the free chloride ion concentration in saliva irrespective of the initial salt concentration in the gum with an indication of adaptation after 3 min chewing. During chewing, salty taste increased ahead of the increase in salivary conductivity and the salt concentration in the sublingual saliva varied in a cyclic fashion about every 20 s. This is consistent with a cyclic swallowing of saliva and replacement with newly secreted saliva of low salt content and mastication releasing further salt from the gum.

Adult↗
PubMed2001

Jaw muscles and the skull in mammals: the biomechanics of mastication.

Among non-mammalian vertebrates, rigid skulls with tight sutural junctions are associated with high levels of cranial loading. The rigid skulls of mammals presumably act to resist the stresses of mastication. The pig, Sus scrofa, is a generalized ungulate with a diet rich in resistant foods. This report synthesizes previous work using strain gages bonded to the bones and sutures of the braincase, zygomatic arch, jaw joint, and mandible with new studies on the maxilla. Strains were recorded during unrestrained mastication and/or in anesthetized pigs during muscle stimulation. Bone strains were 100-1000 micro epsilon, except in the braincase, but sutural strains were higher, regardless of region. Strain regimes were specific to different regions, indicating that theoretical treatment of the skull as a unitary structure is probably incorrect. Muscle contraction, especially the masseter, caused strain patterns by four mechanisms: (1) direct loading of muscle attachment areas; (2) a compressive reaction force at the jaw joint; (3) bite force loading on the snout and mandible; and (4) movement causing new points of contact between mandible and cranium. Some expected patterns of loading were not seen. Most notably, strains did not differ for right and left chewing, perhaps because pigs have bilateral occlusion and masseter activity.

Animals↗
PubMed2003

Simultaneous real-time measurements of mastication, swallowing, nasal airflow, and aroma release.

Mastication, swallowing, breath flow, and aroma release were measured simultaneously in vivo using electromyography, electroglottography, a turbine air flow meter, and the MS-Nose, respectively. Signals were synchronized either electronically or by aligning the nasal airflow data with the breath by breath release of acetone. Chewing affected nasal airflow, with the flow fluctuations following the mastication pattern. Data analysis suggested that air was pumped out of the mouth into the throat with each chew, and the mean volume was 26 mL. Aroma release was associated with the pulses of air pumped from the mouth with each chew. During swallowing, there was no nasal airflow, but after swallowing, aroma release was evident. The volume of the retronasal route was estimated at 48 mL when swallowing and 72 mL when samples were chewed. The combination of techniques shows the effects of physiological processes on aroma release.

Deglutition↗
PubMed2005

Functional unilateral posterior crossbite effects on mastication movements using axiography.

This prospective study investigated the influence of functional unilateral posterior crossbite on mastication movements. The study group included 16 patients (nine girls and seven boys) with functional unilateral posterior crossbite involving three or more posterior teeth. A control group comprised 15 individuals (nine girls and six boys) with normal occlusion and the mean age of both groups was 9.17 years. The mandibular masticatory movements were registered, using computer axiography, for 30 seconds during chewing to determine the preference side of chewing. The patterns of the first, third, and fifth chewing cycles were compared with the preference side to establish whether they would predict the chewing preference side. The extent of the maximal lateral and vertical displacements of the mandible during chewing were compared between study and control groups. This study found that overall the left side was the preferred mastication side in 43.7% of individuals in the study and 46.7% in the control group. There was no relationship between the side of the crossbite and the masticatory preference side (Mc Nemar test, P = .5). No correlation was present between the patterns of chewing movements in the first, third, or fifth cycles. Both study and control groups showed similar maximal lateral and vertical mandible displacement.

Case-Control Studies↗
PubMed2001

Changes in masticatory muscle activity according to food size in experimental human mastication.

The purpose of this study was to investigate the changes in masticatory muscle activity according to food size in human mastication. Sixteen subjects performed deliberate unilateral chewing of similarly cone shaped hard gummy jellies weighing 5 and 10 g. The masseter and anterior temporal muscle activity on both sides was recorded for the first 10 strokes. The normalized muscle activity during the chewing of the 10 g jelly was significantly higher than that of the 5-g jelly, and there was a considerably high significant correlationship between the muscle activity during the chewing of the 10- and 5-g jellies in each muscle on each side. The 10 g/5 g jelly ratio for the masseter muscle activity on the non-chewing side almost coincided with the theoretical energy ratio required to shear, although that of the chewing side was lower than the ratio. The 10 g/5 g jelly ratio for the temporal muscle activity on both sides almost coincided with the food height ratio. The results suggest that anterior temporal and masseter muscle activity changes according to the rate of change in the height of hard coherent food bolus and food resistance required to shear, respectively, during mastication.

Adult↗