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At least 271 records · Page 15Linked to original sources
PubMed2002

Effects on mastication of reversible bilateral inactivation of the lateral pericentral cortex in the monkey (Macaca fascicularis).

It is known that intracortical microstimulation (ICMS) of the lateral pericentral cortex can evoke masticatory movements and swallowing in awake monkeys. The aim was to determine if the ability of monkeys to carry out mastication is affected by reversible bilateral cold block of the ICMS-defined cortical masticatory area/swallow cortex. A cranial chamber was implanted bilaterally in two monkeys and a warm or cold alcohol-water solution was pumped through thermodes placed bilaterally on the dura overlying the ICMS-defined cortical masticatory area/swallow cortex while monkeys chewed standardised amounts of fruit during pre-cool (thermode temperature, 37 degrees C), cool (0-4 degrees C), and post-cool (37 degrees C) trials. Electromyographic (EMG) activity was recorded from masseter, genioglossus, anterior digastric, geniohyoid and thyrohyoid or perilaryngeal muscles. Vertical and horizontal jaw movements were recorded with a photodiode position transducer, which monitored movements of a light-emitting diode fixed to the mandible. Each masticatory period was divided into a food-preparatory phase, a rhythmic chewing phase and a preswallow phase. Both monkeys could readily accept and ingest the foodstuffs during pre-cool and post-cool trials. In contrast, cold block was associated with masticatory deficits, reflected in both monkeys as impaired food intake or manipulation and difficulty in carrying out a sequence of masticatory cycles, alterations in of the food-preparatory phase, and alterations in masticatory-related EMG patterns of the jaw and tongue muscles. The cold block-induced changes included significant (P<0.05) prolongations of the total masticatory time, the food-preparatory phase duration, and burst durations of the jaw and tongue muscle EMG activities; furthermore, the amplitudes and temporal correlations of the EMG activities of the jaw and tongue muscles were significantly (P<0.05) changed by cold block. These findings provide further evidence that the lateral pericentral cortex has a critical role in the initiation and regulation of masticatory movements in the primate, and that the programming of masticatory muscle activities may be dependent upon corticofugal influences for engaging masticatory motor activities appropriate to the masticatory conditions.

Animals↗
PubMed2003

Chewing behaviour and bolus formation during mastication of meat with different textures.

During chewing, meat is mashed under compression and shear bite forces whilst saliva is incorporated. The resulting mixture is shaped into a cohesive bolus by agglomeration of small particles, and triggers a swallow. This study aimed to investigate the relationship between chewing behaviour and bolus formation of meat with different textures. Twenty-five consenting young adults participated in this study. Electromyographic activity was recorded from surface electrodes on the elevator muscles (masseter and temporalis) during mastication of cold beef. Two different textures (T(1): tough and dry; T(2): tender and juicy) were studied, and subjects were asked to chew the beef and then spit out the bolus either: (1) after a constant chewing period of 7s or (2) when the bolus was ready to be swallowed. Meat samples were weighed before and after chewing to determine weight changes due to saliva incorporation and the release of meat juice. Cutting tests were applied to measure the maximum shear force. The mechanical shear force was maximal for meat before chewing (T(1)=124 N/cm(2); T(2)=83 N/cm(2)) and decreased with increased chewing duration. Texture differences analysed from mechanical measurements remained significant even when the boli were ready for swallowing (T(1)=39 N/cm(2); T(2)=32 N/cm(2)); the toughest meat gave the toughest bolus. Muscular activity adapted to the texture of the meat as soon as chewing began, and remained constant over the observed chewing period. Mean muscular activity was higher during the chewing of tough meat than during the chewing of tender meat. As a consequence, by the time a bolus was ready to be swallowed, more saliva had been incorporated into the tough meat samples (mean weight increase: 36%) than the tender meat samples (mean weight increase: 30%).

Adult↗
PubMed2000

Head movements and neck muscle activities associated with the jaw movement during mastication in the rabbit authors.

Rhythmical head movements and neck muscle activities associated with the masticatory jaw movement were investigated in rabbits. In natural mastication, head movements and neck muscle activities showed a rhythmical feature synchronized with jaw movement. During cortically induced rhythmical jaw movements, some neck muscle showed rhythmical activity induced by biting a wooden stick. Neck muscles may contribute to the rhythmical head movement after loading the tooth with food.

Animals↗
PubMed1998

Feedback control during mastication of solid food textures--a clinical-experimental study.

STATEMENT OF PROBLEM: On the basis of animal experiments, it has been hypothesized that the dynamics of food reduction are controlled by peripheral receptors. Studies on this subject in human beings are rare. PURPOSE: This study investigated the influence of periodontal and joint proprioceptors on mastication in human beings. MATERIAL AND METHODS: Both jaw joints and the chewing-side teeth were consecutively anesthetized in a 6-person panel by chewing wine gum. The effects on the kinematics, chewing force, and electromyographic activity were measured. RESULTS: The results substantiate a positive feedback of periodontal receptors for chewing force control. A substantial influence of joint receptors on movement control could not be found. CONCLUSION: Despite the absence of proprioception in both jaw joints and the periodontal receptors in the chewing side, the characteristics of the measured kinematic and dynamic values remained essentially unchanged.

Adult↗
PubMed1991

Ingestion and mastication of feed by dairy cattle.

For fiber in dairy cattle diets to be effective it must be masticated initially during feeding and again during rumination. Time spent chewing is directly related to saliva secretion, which helps buffer the rumen environment and optimizes fiber digestion. Reduction in feed particle size occurs during chewing, which is a prerequisite for passage of feeds from the forestomach, but the extent of particle breakdown during chewing depends upon the feed. Manipulating the dietary concentration of plant cell walls or the physical form of forage can alter chewing behavior and rumen function of the dairy cow, thereby optimizing productivity.

Animals↗
PubMed1991

Analysis of repeated-measure multicycle unilateral mastication in children.

This study examined systematic and random errors associated with repeated-measure, multiple-cycle unilateral mastication in children during single recording sessions with the Replicator system. Twenty-six recording sessions with 17 children (10 boys, 7 girls) were examined. Nine of these children had a functional-shift unilateral crossbite malocclusion and were recorded before and after crossbite correction. Repeated recordings (trials) of mandibular movement during each session were made of right-side chewing of similar-sized pieces of cheese. The following variables were computed for each chewing cycle (stroke): time closed, maximum closure velocity, maximum opening velocity, chewing rate, vertical opening, and lateral deviation. From the multiple cycles of each trial, two pattern descriptors--the average and standard deviation--were determined for each variable. In addition, the mean and variance of these pattern descriptors were determined from the multiple trials of each recording session and were the dependent variables in a stepwise multiple regression analysis, with treatment status, sex, age, dentition stage, crossbite presence, and right side status the independent variables. The results disclosed bias in repeated measures of human chewing in response to adaptation to the recording session; this was evident in the average response but not in the variability of the measures. Sex and functional status of the subjects were associated with the mean and variance of measures describing the chewing pattern.

Adolescent↗
PubMed2003

Electromyographic responses to prescribed mastication.

The aim was to understand between-volunteer differences in Electromyography (EMG) behaviour during chewing. EMG was used to record the electrical activity of the temporal and masseter muscles of volunteers, who carried out mastication movements by operating calibrated springs held between their incisors. The volunteers coordinated their jaw movements with the signal produced by a metronome, at four rates: 30, 60, 90 and 120 beats per minute (bpm). Raw data were analyzed to examine the distributions of the intervals between chews. For the highest prescribed chew rates, the volunteers' distributions were very similar. The distributions varied most for the 30 bpm data, suggesting that volunteers differed in their ability to carry out and maintain this prescribed chewing pattern. The data were Fourier transformed to give power spectra in the frequency domain. The low frequency (<10 Hz) region contained spectral features related to the prescribed chew rate. Principal component analysis of the power spectra revealed that readings from each volunteer clustered together, and the clusters could be largely separated. Such grouping was found irrespective of whether data from each chew rate were analyzed separately or simultaneously. This indicated that within-volunteer variance, arising from the different chew rates as well as between-session variance, is lower than between-volunteer variance; even when individuals are asked to make jaw movements in the same prescribed manner, they can nevertheless be uniquely distinguished by their muscle activity as recorded by EMG.

Adult↗
PubMed2003

Analysis of the TMJ intraarticular space variation: a non-invasive insight during mastication.

The analysis of the loading of the temporomandibular joint (TMJ) appears important for the study of joint failure. Reconstruction and animation of the TMJ with real anatomic and kinematic data is currently the only method allowing a non invasive, in vivo, three-dimensional, dynamic, real-time quantitative insight into the relationship between the articulating surfaces of a joint. It consists of the software reconstruction of the joint anatomy from tomography data and the application to it of the corresponding real movement data recorded with a tracking device. Because of the physical properties of the TMJ soft tissues, the reduction of the joint space can indicate compressive loads during function. Analyses of the variation of the TMJ space in ten asymptomatic subjects during unilateral mastication showed a TMJ space that was significantly smaller during closing than during opening (p<0.05) and significantly smaller on the balancing than on the working joint (p<0.05). This occurs especially in the medial part of the posterior slope of the articular eminence at the end of the closing phase (p<0.01). Furthermore, the minimum TMJ space at the end of closing increased from the beginning to the end of food comminution (p<0.01).

Adolescent↗
PubMed1998

Claudication on mastication following bilateral external carotid artery ligation for posterior epistaxis.

This case highlights a potentially disabling complication of intermittent claudication in the region of the masseter muscles on mastication, following bilateral external carotid artery ligation for epistaxis. Although there have been few reports of this complication this may be a reflection of the fact that the operation is rarely performed, and not because the complication is rare. Its potentially disabling nature, and its possible common occurrence after this procedure make awareness of it by surgeons who may carry out this procedure important.

Carotid Artery, External↗
PubMed2002

Saliva and gastrointestinal functions of taste, mastication, swallowing and digestion.

Saliva has multiple essential functions in relation to the digestive process taking place in the upper parts of the gastrointestinal (GI) tract. This paper reviews the role of human saliva and its compositional elements in relation to the GI functions of taste, mastication, bolus formation, enzymatic digestion, and swallowing. The indirect function of saliva in the digestive process that includes maintenance of an intact dentition and mucosa is also reviewed. Finally, pathophysiological considerations of salivary dysfunction in relation to some GI functions are considered.

Deglutition↗
PubMed1997

An examination of the degrees of freedom of human jaw motion in speech and mastication.

The kinematics of human jaw movements were assessed in terms of the three orientation angles and three positions that characterize the motion of the jaw as a rigid body. The analysis focused on the identification of the jaw's independent movement dimensions, and was based on an examination of jaw motion paths that were plotted in various combinations of linear and angular coordinate frames. Overall, both behaviors were characterized by independent motion in four degrees of freedom. In general, when jaw movements were plotted to show orientation in the sagittal plane as a function of horizontal position, relatively straight paths were observed. In speech, the slopes and intercepts of these paths varied depending on the phonetic material. The vertical position of the jaw was observed to shift up or down so as to displace the overall form of the sagittal plane motion path of the jaw. Yaw movements were small but independent of pitch, and vertical and horizontal position. In mastication, the slope and intercept of the relationship between pitch and horizontal position were affected by the type of food and its size. However, the range of variation was less than that observed in speech. When vertical jaw position was plotted as a function of horizontal position, the basic form of the path of the jaw was maintained but could be shifted vertically. In general, larger bolus diameters were associated with lower jaw positions throughout the movement. The timing of pitch and yaw motion differed. The most common pattern involved changes in pitch angle during jaw opening followed by a phase predominated by lateral motion (yaw). Thus, in both behaviors there was evidence of independent motion in pitch, yaw, horizontal position, and vertical position. This is consistent with the idea that motions in these degrees of freedom are independently controlled.

Humans↗
PubMed2002

Occlusal loading of EBA and MTA root-end fillings in a computer-controlled masticator: a scanning electron microscopic study.

AIM: The aim of this investigation was to assess the marginal adaptation of Super-EBA (EBA) and Pro Root MTA (MTA) root-end fillings and the occurrence of microcracks in resected root-ends of extracted teeth before and after occlusal loading for a five-year equivalent period in a computer-controlled masticator. METHODOLOGY: Twenty-four molar teeth were root-filled using lateral condensation and their root-ends resected. Root-end cavities were prepared and either EBA or MTA root-end fillings were placed. All surgical procedures were completed in vitro under an operating microscope. Replicas taken of the root-end fillings and resected root-ends were examined using an SEM before and after they were subjected to in vitro chewing cycles in a computer-controlled chewing simulator for the equivalent of 5 years. Marginal adaptation and integrity of the two root-end filling materials were evaluated and the presence of microcracks recorded. RESULTS: Before loading, a continuous margin was observed with 99.4 +/- 2.4% of EBA and 99.2 +/- 1.6% of MTA root-end fillings. After loading, the percentage of continuous margin decreased to 93.1 +/- 6.6% and 98.9 +/- 3.2% for EBA and MTA, respectively. After occlusal loading, 39.5% of the EBA root-end fillings were overfilled, whilst 52.6% of the MTA root-end fillings were underfilled. In total, 12.5% of the resected root-end surfaces showed microcracking before loading and 25% after occlusal loading. CONCLUSIONS: Both EBA and MTA displayed excellent marginal adaptation before masticatory loading. After loading, the amount of continuous margin for both root-end filling materials decreased slightly but was still high.

Aluminum Compounds↗
PubMed1996

Human mastication modulated by experimental trigeminal and extra-trigeminal painful stimuli.

This paper describes the modulation of human deliberately unilateral mastication by trigeminal and extra-trigeminal standardized painful stimuli. Series with 15 s of gum-chewing before induction of pain, during pain and after pain were quantitatively assessed by jaw-closing muscle electromyography (EMG) and kinematics of the lower jaw. Four different painful stimuli were used: cold stimulation of the frontal region, cold stimulation of the dominant hand, capsaicin stimulation of the hard palate, and pressure pain stimulation of the temporomandibular joint (TMJ). Intensity and quality of perceived pain were rated on visual analogue scales (VAS) and McGill's Pain Questionnaires (MPQ). Analysis of the data showed that frontal cold stimulation was the least painful test and was associated with the fewest changes in masticatory function. Cold stimulation of the hand and palatal capsaicin stimulation caused significant increases in peak amplitudes of EMG bursts from all jaw-closing muscles and faster jaw movements whereas TMJ pressure pain produced significantly lower peak EMG amplitudes. The present results suggest that nociceptive input from different tissues and even extra-trigeminal regions may modulate trigeminal motor function in selective ways. Thus, clinical observations of changes in masticatory function may not always be due to pain in the orofacial region and therefore do not necessitate orofacial treatment.

Adult↗
PubMed1999

Mastication, deglutition and speech considerations in prosthodontic rehabilitation of a total glossectomy patient.

Prosthetic rehabilitation of a total glossectomized patient and specifications of the appliance, which differs from those previously reported, are presented. The functional considerations and logic used to design such a device are described. Speech performance of the patient with and without the prosthesis, is compared with a perceptibility test. Improvement of the functions of mastication, swallowing and speech were found acceptable.

Deglutition↗
PubMed1999

Incidence of occlusal contacts with complete dentures during mastication using a 6-channel telemetry system: preliminary measurements.

The purpose of this study was to observe the incidence of occlusal contact with complete dentures during mastication using a 6-channel telemetry system whose accuracy had been improved. The telemetry system consisted of the transmitter unit and the receiver unit. The transmitter unit was embedded in the lower complete denture. This system detects occlusal contacts by the shift of frequency in 100 kHz. The transmitter allowed 6 channels for the occlusal contacts. The data was telemetered by a time division multiplex communication method. A special switch was designed to measure excursive movement on the occlusal surface. After careful occlusal adjustment, the special switches were inserted in the lower first molars. On the basis of preliminary measurements on a 64-year-old edentulous male, it appears that the width of the gliding on the occlusal surface at the lower first molar was mostly 0.2-1.2 mm and the majority of the excursive movements ended at the centric occlusal position.

Dental Occlusion↗
PubMed2002

Photoelastic analysis of bone deformation in the region of the mandibular condyle during mastication.

INTRODUCTION: The purpose of this experimental study was to demonstrate the stress patterns arising in the region of the mandibular condyle during mastication. MATERIAL AND METHOD: Stress analysis was performed using reflection photoelasticity to demonstrate deformation occurring on the surface of the mandible. The rami of three fresh dentate human mandibles were coated with a shell of photoelastic resin. Using a novel loading device, these mandibles were then subjected to external forces (muscular traction, resultant mandibular forces and intra-articular reaction force) reproducing a unilateral biting task between the first right molars. Deformations were measured from the working side. RESULTS: The trace of isostatic lines from the isoclinic fringes revealed major differences in stress distributions between the three mandibles. These differences were attributed to differences in shape between the three mandibles. Conversely, we consistently found compressive stress patterns along the posterior border of the ramus and tensile stress patterns along the anterior border of the ramus and in the zone situated below the siqmoid notch. CONCLUSION: These findings suggest that during this particular task, the mandible is subjected to sagittal forces which tend to straighten the mandibular angle. This implies that new concepts are needed for the positioning of osteosynthesis plates in the condylar region, close to the tensile strain lines, as has been recommended also for other parts of the mandible when applying semi-rigid internal fixation.

Biomechanical Phenomena↗
PubMed2001

Masseteric hypertrophy associated with administration of anabolic steroids and unilateral mastication: a case report.

In this report we present a patient with unilateral masseteric hypertrophy who used anabolic steroids and was chewing entirely unilaterally for 1 month. Computed tomography and histologic examination were used to confirm the diagnosis. The combined action of unilateral mastication and anabolic steroid use is probably responsible for the rapid development of unilateral masseteric hypertrophy.

Adult↗
PubMed2002

Influence of impaired mastication on nutrition.

It has been suggested that people who suffer from impaired masticatory function may adapt food consistency to their oral status (which may lead to deficient nutrient intake) or rely on the digestive system to compensate for the lack of oral preparation of food (which may increase the likelihood of digestive diseases and decrease gut absorption). Masticatory deficiency thus may be detrimental to health. This article reviews evidence of the effects of masticatory deficiency on nutrition. The selection of relevant literature was based on Medline queries using the following key words: mastication, nutrition, digestion, diet, and disease risk. Earlier work not listed in Medline but related to the subject also was reviewed. Only publications available in English were selected for inclusion. It is difficult to draw conclusions from many of the reviewed studies due to issues related to study design, confounding variables, and the subjective nature of the measurements. In particular, data supporting a link between masticatory function and deficient dietary intake often are based on relatively weak correlations and cannot confer a causal relationship.

Animals↗