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At least 469 records · Page 26Linked to original sources
PubMed1998

Inclination of the occlusal plane and occlusal guidance as contributing factors in mastication.

OBJECTIVES: The purpose of the present study was to compare the inclination of the occlusal plane with occlusal guidance as a contributing factor to masticatory movement. METHODS: Masticatory movements of 41 young adults were measured using a 3-D mandibular movement analysing system. The inclination of the occlusal plane was measured in the sagittal plane using a 3-D digitizer. The contribution of the occlusal guidance and the inclination of the occlusal plane to the direction of the masticatory path of closure was evaluated at various closing levels. RESULTS: The masticatory path of closure outside the intercuspal range was influenced mainly by the inclination of the occlusal plane, and the masticatory path of closure near the intercuspal range was only influenced by occlusal guidance. The so-called gliding type masticatory pattern was observed predominantly in subjects with a posteriorly inclined occlusal plane. In contrast, a chopping type masticatory pattern was observed predominantly in subjects with an anteriorly inclined occlusal plane. CONCLUSIONS: The contribution of the inclination of the occlusal plane to masticatory movement was greater than that of occlusal guidance throughout the closing phase except near the intercuspal range.

Adult↗
PubMed1997

Effects of chemical stimulation of masseter muscle nociceptors on trigeminal motoneuron and interneuron activities during fictive mastication in the rabbit.

An electrophysiological study was carried out in sixteen decerebrate and paralyzed New Zealand rabbits to determine how a bolus injection of a nociceptor stimulant (hypertonic saline, 5%) into the masseter muscle influences the activity of the trigeminal motor circuitry during fictive jaw movements. Hypodermic needles connected to a syringe held in a computer-controlled infusion pump were inserted into the anterior deep layer of either the right or the left masseter. Twenty-three infusions of 50, 70 or 80 microl saline were made in fourteen animals at constant rates over 1 min. Eight control infusions of normal saline (0.9%) were made in a subpopulation of five animals in an identical manner. Fictive jaw movements were evoked before and after the infusions by repetitive electrical stimulation of the corticobulbar tract. Effects were assessed by extracellular microelectrode recordings made from the digastric motoneuron pool and from putative last-order interneurons in the oral subnucleus of the spinal trigeminal tract and adjacent structures. In comparison with pre-infusion control cycles, nociceptor stimulation caused significant slowing of the rhythm and a reduction of the area of the digastric motoneuron bursts in the majority of the animals (12/14). The decrease in cycle frequency was due almost entirely to a lengthening of the time between the digastric bursts. Changes usually began 1-2 min after the infusion and returned to pre-infusion values within 10-15 min. No significant effects were seen when isotonic saline was applied. Recordings were obtained from nine interneurons, eight of which had low threshold mechanosensitive receptive fields. One neuron was, in addition, excited by pinch. Eight were not active in the absence of motor activity and this did not change when hypertonic saline was applied. However, once fictive movements began, all started to fire rhythmic bursts of spikes. In five cases, there was a significant post-infusion increase in spike frequency, and three showed decreases. Seven showed significant post-infusion changes in mean phase and/or concentration of their firing within the movement cycle. Changes in the preferred phase of interneuronal firing were significantly correlated to changes in the phase of offset of the digastric burst. The present results provide evidence that the stimulation of nociceptors in a muscle slows the frequency of rhythmical movements in the absence of sensory feedback. They confirm that infusions into one muscle affect the output of its antagonist. The results also suggest that neurons in the oral subnucleus of the spinal trigeminal tract and adjacent reticular formation appear to participate in programming these changes in motor output.

Animals↗
PubMed2002

Differential discharge patterns of rhythmical activity in trigeminal motoneurons during fictive mastication and respiration in vitro.

Rhythmical activity in trigeminal motoneurons (TMNs) was studied in an in vitro neonatal rat brainstem preparation that retains functionally active circuits for oral-motor behaviors. Whole-cell current-clamp recording from TMNs demonstrated rhythmical activities during both spontaneously generated respiratory activity and neurochemically induced rhythmical oral-motor activity. TMNs showed spontaneous rhythmical (0.08 +/- 0.04 Hz) activities of burst-firing pattern during inspiration synchronized with inspiratory activities recorded in hypoglossal nerves. During rhythmical oral-motor activity induced by bath application of N-methyl-d,l-aspartic acid and the GABA(A) receptor antagonist bicuculline methiodide, TMNs showed only a rhythmical (5.6 +/- 0.8 Hz) pattern of single-spike discharge. TMNs never showed a burst-firing pattern during rhythmical oral-motor activity even when membrane potentials were shifted either to depolarized or hyperpolarized levels. Rhythmical activity in TMNs exhibited different discharge patterns between rhythmical oral-motor activity and respiratory activity generated in vitro.

Action Potentials↗
PubMed1999

Mastication steal: an unusual precipitant of cerebrovascular insufficiency.

An 83-year-old man had episodic dizziness, visual disturbance, and facial and extremity weakness associated with eating. Occlusion of the ipsilateral common carotid artery and stenosis or occlusion of the major collateral sources were demonstrated. We believe this anatomic configuration, combined with increases in demand for external carotid artery blood flow necessitated by the act of chewing, resulted in a vascular steal syndrome. An extended carotid endarterectomy was performed, and there were no additional episodes.

Aged↗
PubMed2002

A new device for measuring mastication force (Gnathodynamometer).

This work presents a new device, developed and constructed for the determination of the masticatory forces. Our new apparatus worked well in measuring maximal bite force and masticatory efficiency of incisor and molar teeth, respectively. The obtained results related to intraoral forces were very similar to the values previously given in the literature.

Adult↗
PubMed2000

Complete denture wearers: electromyography of mastication and texture perception whilst eating meat.

This study was undertaken to evaluate the sensitivity of denture wearers to different food textures and to follow masticatory pattern adaptation with variation in texture using electromyography (EMG) recordings. Nine patients with complete dentures and 9 dentate control patients without any oro-dental pathology were studied. Six different samples of beef were obtained from the same muscle by altering the state of the muscle fibres and by variation of the cooking temperature. The variations in texture were mechanically controlled. Electromyographic activity was recorded during chewing. The patients' subjective appreciation of texture was reported using a 10-cm non-structured analogue scale. The following parameters were analysed: muscle work, number of masticatory cycles, number of rejected samples, initial tenderness, overall tenderness, juiciness, and duration of chewing for each sample in the mouth. Muscle activity was less for the edentulous group, particularly that of the masseter muscles. The masticatory pattern of complete denture wearers was less adapted to each sample texture than was that of the control group. Both groups perceived differences in texture of the samples. It was concluded that although texture perception is little altered, muscular adaptation to the bolus is reduced in patients with complete dentures.

Adaptation, Physiological↗
PubMed1992

Mastication and swallowing: an overview.

The cycles of jaw and tongue movement during feeding produce not only the breakage of food but its intra-oral transport; which activity predominates depends upon the physical characteristics of the food. When hard food is eaten and tooth-food-tooth contact is made during jaw closure, the velocity of closing is suddenly reduced, producing two clearly different phases of closure; during the second phase the activity of the jaw closing muscles is much increased. Conversely, in cycles with a mainly transport function (eating soft food), the antero-posterior movements of the tongue are much greater; this alters the time and rate at which the jaw opens. The pattern of jaw movement during closing and during opening consequently varies with food consistency. The evidence suggests that sensory input controls the form of the cyclical tongue and jaw movements. However the basic plan of movement is produced by the activity of a brainstem pattern generator which receives input from both cerebro-cortical and peripheral sources. The swallow that occurs in normal feeding consists of the equivalent of the classical second stage of swallowing inserted into the occlusal or initial jaw opening phase of an otherwise standard cycle. Although leakage of traces of food or saliva into the vallecula appears to be a peripheral sensory input of major importance in inducing such a swallow, the execution of the swallow is due to a pattern generator in the brainstem.

Bite Force↗
PubMed1994

Francis Balkwill and the physiology of mastication.

The contribution of Francis Balkwill to the understanding of the masticatory system is virtually unknown in this country. In 1866 he presented the results of considerable research on this subject to the Odontological Society of Great Britain, but his observations were ignored and the paper remained 'buried' in the Transactions for nearly 50 years. In 1912 a copy of the paper was to sent to Professor Gysi in Zurich who immediately published a most generous tribute to the value of his work. The observations made in this 1866 paper are reviewed here together with the 'rediscoveries' made by later workers. It is suggested that Balkwill's neglected work was in fact the most far-seeing and comprehensive piece of research on this subject carried out during the 19th Century.

Dental Articulators↗
PubMed2001

Discharge patterns of neurons in the medial pontobulbar reticular formation during fictive mastication in the rabbit.

In this study, we describe functional characteristics of neurons forming networks generating oral ingestive motor behaviours. Neurons in medial reticular nuclei on the right side of the brainstem between the trigeminal and hypoglossal motor nuclei were recorded in anaesthetized and paralysed rabbits during two types of masticatory-like motor patterns induced by electrical stimulation of the left (contralateral) or right (ipsilateral) cortical masticatory areas. Sixty-seven neurons in nucleus reticularis pontis caudalis (nPontc), nucleus reticularis parvocellularis (nParv), and nucleus reticularis gigantocellularis (Rgc) were studied. These were classified as phasic or tonic depending on their firing pattern during the fictive jaw movement cycle. Phasic neurons located in the dorsal part of nPontc were active during the jaw opening phase, whilst those in dorsal nParv tended to fire during the closing phase. In most neurons, burst duration and firing frequency changed between the two motor patterns, but there was little change in phase of firing. Tonic units were mainly recorded in the ventral half of nPontc, and at the junction between Rgc and caudal nParv. Cortical inputs with short latency from the contralateral masticatory area were more frequent in phasic (82%) than tonic (44%) neurons, whilst inputs from the ipsilateral cortex were equal in the two subgroups (57% and 56%). Phasic neurons had significantly shorter mean contralateral than ipsilateral cortical latencies, whilst there was no difference among tonic neurons. Intra- and perioral primary afferent inputs activated both types of neurons at oligo-synaptic latencies. Our results show that subpopulations of neurons in medial reticular nuclei extending from the caudal part of the trigeminal motor nucleus to the rostral third of the hypoglossal motor nucleus are active during the fictive masticatory motor behaviour. Unlike masticatory neurons in the lateral tegmentum, the medial subpopulations are spatially organized according to discharge pattern.

Action Potentials↗
PubMed1999

The influence of crossbite on the coordinated electromyographic activity of human masticatory muscles during mastication.

The analysis of the masticatory muscle activity in subjects with altered occlusal relationships could provide useful data of the functional impact of morphological discrepancies. Thirty subjects aged 16-18 years, with a sound, full permanent dentition, bilateral angle class I, and an overjet and overbite between 2 and 5 mm, were examined. The control group (10 male, 10 female) had no crossbite, while the crossbite group (four male, six female) had a posterior unilateral crossbite (five on the left side, five on the right side). The electromyographic activity of the left and right masseter and temporalis anterior muscles was recorded during 15 s of unilateral (left and right) chewing of gum, and expressed as a percentage of the maximum voluntary clench on cotton rolls. For each subject, the masticatory frequency, the confidence ellipse of the simultaneous differential left-right masseter and temporal activity (Lissajous figure), and an index of muscular symmetry, were computed to assess muscular coordination. In the crossbite subjects, the four analysed muscles appeared to contract with altered and asymmetric patterns. A large variability was found, and the confidence ellipses calculated for the chewing tests performed on the crossed sides were not significant, while the confidence ellipses of the uncrossed side chewing were different from the ellipses computed in the normal occlusion group. The altered occlusal relationship influenced the coordination of the masticatory muscles during chewing on both sides. The functional alteration was more apparent when the side with the altered morphology was directly involved, i.e. when chewing was performed on the crossbite side.

Adolescent↗
PubMed2001

Effects of 28-day mechanical and chewing stress on content of bound and diffusible ions in muscles of mastication.

Type I and type II muscle fibres have different ion concentrations. Muscles adapt to chronic stress by changing of fibre types and remodelling of the myosin heavy chains in the muscle fibres. The present investigation on ionic change during muscular contraction was carried out on 10-week-old pigs (6 treated animals, 6 controls) over a 28-day period. Six pigs received acrylic build-ups to induce mechanical advancement of the lower jaw and chronic chewing stress. Muscle tissue was taken from the masseter (M1, M2, M3), temporal (TP1, TP2), medial pterygoid (PM) and geniohyoid (GH) muscles by a standardized method. Eighty-four muscle samples were used for histological fibre differentiation with mATPase. Energy-dispersive X-ray microanalysis of muscles was carried out in an environmental scanning electron microscope. Endurance stress in the stressed muscles was seen as an increase of type I fibres (P < 0.001). This histological change and ionic alterations were measured in the anterior region of the masseter (M1 and M2) and in the posterior region of the temporal muscle (TP2). Smaller changes were found in the medial pterygoid muscle. We measured in this muscles increases in potassium, sulphur, chloride (P < 0.05) and even larger increases in phosphate (up to 1.5 mmol/g to 2.3 mmol/g, P < 0.001) and sodium (3-fold, P < 0.001). The results reveal the effects of chronic stress on muscle fibres and ion concentration in the muscle. Chronic stress resulted in an increase of type I fibres and increased ion concentration in the same muscle region. These are considered to be indicators of more efficient contraction. The changes in ion concentration are an important factor in muscle contraction.

Animals↗
PubMed1996

Masticatory tooth contact patterns: cuspid and first molar contacts during mastication of three types of food.

In ten healthy subjects, bilateral contacts between opposing cuspid and first molar teeth were recorded during one sequence of unilateral chewing of apple, peanuts, and banana. Unknown magnitudes of mechanophysical (masticatory) forces were inferred to act directly on the chewing-side cuspid teeth in 71% of all masticatory cycles and on the nonchewing-side cuspid teeth in 68% of all masticatory cycles. In addition, unknown magnitudes of mechanophysical forces were inferred to act directly on the chewing-side first molar teeth in 74% of all masticatory cycles and on the nonchewing-side first molar teeth in 86% of all masticatory cycles. During the chewing of peanuts, the total number of chewing-side cuspid contacts exceeded significantly the total number of nonchewing-side cuspid contacts, suggesting more repetitive direct mechanophysical loading of the chewing-side cuspid teeth. During the chewing of apple, the total number of nonchewing-side first molar contacts exceeded significantly the total number of chewing-side first molar contacts, suggesting more repetitive direct mechanophysical loading of the nonchewing-side first molar teeth. The variable contact patterns were, to a large extent, explained by rotational movements of the entire mandible resulting in translational movements of the hemimandible.

Adult↗
PubMed2003

State of mastication affects quality of life in patients with maxillary sinus cancer.

OBJECTIVES/HYPOTHESIS: The quality of life of head and neck cancer patients after treatment is poor compared with a typical population sample. However, little is known about patients with maxillary sinus cancer. The identification of symptoms that are most troublesome for these patients and the development of strategies to minimize these negative sequelae should be matters of high priority. STUDY DESIGN: A restrospective study of patients with maxillary sinus cancer who underwent maxillary bone resection. METHODS: Thirty patients with maxillary sinus squamous cell carcinoma participated in the study. The relationships among the degree of masticatory ability, the extent of the surgically resected area, and quality of life after combined treatment of maxillary cancer were evaluated. RESULTS: Scores of all physical and mental factors as assessed by the Short Form-36 questionnaire decreased as the masticatory ability of patients worsened. In edentulous cases, the masticatory ability was higher in the reduced operation group than in the extensive operation group. CONCLUSION: Maintaining adaptability to a denture is essential to preserve quality of life, particularly in patients with anodontia.

Affect↗