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PubMed2003

Relationship between cognitive function and mastication in elderly females.

In Japan, the elderly population suffering from dementia is rapidly increasing. Several animal studies have indicated a relationship between reduced masticatory function in the elderly subject and cognitive impairment. However, epidemiological studies examining this have been scarce. Using an epidemiological approach, the present study investigated this relationship in 44 females with and 44 without dementia, all aged over 65 years. Age and basic activities of daily living, such as walking, eating, excreting, bathing and dressing, were matched in the two groups. Cognitive impairment of the subjects was measured using the revised Hasegawa Dementia Rating Scale. Masticatory function was assessed in terms of the number of teeth present, maximum bite force, occlusal contact area, and mastication score. The number of teeth present in cognitively normal subjects was significantly higher than in cognitively impaired subjects (P < 0.05). In addition, maximum bite force, occlusal contact area, and mastication scores of cognitively normal subjects were significantly higher than those of cognitively impaired subjects (P < 0.01). These results suggest that masticatory function in the elderly person is associated with cognitive status.

Activities of Daily Living↗
PubMed2006

Computational model of the movement of the human muscles of mastication during opening and closing of the jaw.

Muscle fibre bundles comprising the four major muscles of mastication in the human being were studied in cadavers. Markers were placed along each muscle fibre bundle by means of serial dissections. The 3D coordinates of each marker were tabulated and imported to Cinema 4D, a software animation program. Origins and insertions of each fibre bundle were also digitized and imported, as were the coordinates of the surface of the skull, the mandible and temporomandibular joint. It was then possible to visualize the movement of all relevant fibre bundles during the passive motions of the mandible. An animated film depicts the positions of all relevant muscle fibres during passive movement of the mandible. The properties of the masseter muscle were documented as a prototype for the eventual study of all the muscles of mastication. One can now proceed to study the inverse problem, namely the forces within each fibre bundle that actively generate mandibular motion. It is hoped that these studies will aid in the management of conditions affecting the temporomandibular joint.

Aged↗
PubMed1981

Analysis of particles produced at the end of mastication in subjects with normal dentition.

A study was made to establish a norm for the frequency distribution of the size of particles produced by masticating a certain food item to its swallowable composition by normal dentate subjects. Only about 80% of the initial weight of food taken into the mouth could be recovered after mastication for particle size analysis. The particles ranged from 53 micrometers to 4750 micrometers, showing a positively skewed distribution with a mode value between 600 micrometers and 1200 micrometers.

Adult↗
PubMed1983

Variations in the particles produced at the end of mastication in subjects with different types of dentition.

The final composition of the size of particles of food or the swallowable composition (SC) has been investigated in subjects with different types of dentition. A convenient mouthful of hard-baked soya beans was masticated and thereafter the bolus was dried, sieved and weighed. Full denture wearers prepared a SC with a mode value around 4000 microns whereas subjects with mixed dentition prepared a SC with a mode value around 2000 microns. Subjects with partial dentition produced wide variations in the SC. To produce a SC which is usually swallowed by a particular subject the quantity of masticated food should bear an optimum ratio to the area of the healthy oral tissues.

Adolescent↗
PubMed1984

Influence of experimental interfering occlusal contacts on the activity of the anterior temporal and masseter muscles during mastication.

Quantitative electromyography (EMG) was used to study, in eleven volunteers with complete, natural dentitions, the effects of an experimental intercuspal occlusal interference on the pattern of activity of the anterior temporal and masseter muscles during mastication. The results show that a small occlusal interference (about 0.5 mm) in the intercuspal position can change the co-ordination of muscular activity during mastication. In general, there was a prolonged contraction time as well as a reduction of the activity in all the investigated elevators, especially on the side of the interference. Furthermore, after 48 h several subjects preferred to chew unilaterally. After removal of the interference, the pattern of co-ordination of muscular activity returned almost to the pre-experimental pattern within 2 weeks.

Adult↗
PubMed1994

Effect of unilateral bite splint on mastication in the miniature pig.

Unilateral premature occlusal contacts are known to alter masticatory activity levels during clenching, but whether natural chewing is similarly affected is not known. The purpose of this study was to analyse the effects of a unilateral bite splint on mastication. Eleven experiments were carried out using three miniature pigs. Electromyography of the masticatory muscles and movements of the jaw were recorded during natural chewing before and after inserting a bite splint on the second and third deciduous premolars. In contrast to human clenching, the integrated activities of the jaw-closing muscles increased, especially on the contralateral side. The increases were mainly due to the prolongation of the burst durations. Jaw opening activity was increased as well. The frequency of mastication fell slightly and the animal preferred to chew food on the bite splint side. These results demonstrate the importance within the particular experimental conditions of the occlusal condition in regulating chewing behaviour.

Animals↗
PubMed1995

Influence of stress and occlusal interference on the EMG activity of some masticatory muscles during a single mastication cycle.

The aim of the study was to investigate the influence of stress on the open-close activity in mastication, using an animal model. For this, we have compared the single-motor activities of three muscles: anterior digastric (AD), anterior temporalis (AT) and the superficial masseter (MS) in different groups of rats classed according to emotional state and dental occlusion. The EMG graphs have been analysed by the method proposed by the Weijs & Dantuma (1975). The results show that a dominant action of the stress on the AD and a combined action of the stress and the occlusal state on AT and MS occur during a single mastication cycle. A suppression of the reflex myotatic inhibition for AT and MS occurred in the presence of an occlusal interference.

Animals↗
PubMed1992

The postoperative use of wound adhesives. Gum mastic versus benzoin, USP.

Our results, combined with the work of previous authors, show that gum mastic not only offers superior adhesive qualities compared with benzoin, USP but also has a lower incidence of postoperative contact dermatitis and subsequent skin discoloration. In light of the widespread use of surgical adhesives, this study is important in documenting the low incidence of complications and the advantages of gum mastic compared with benzoin, USP.

Adult↗
PubMed1984

Response of elevator activity during mastication to treatment of functional disorders.

The pattern of elevator activity during mastication in temporal and masseter muscles of 37 patients with functional disorders and pain in the masticatory system was studied before and after conventional treatment and compared with a control group of 43 subjects. As compared to controls, patients before treatment chewed with greater relative strength (percent of maximal elevator activity), longer relative contraction times (percent of total duration of chewing cycle) and stronger intermediary activity between strokes. These parameters of muscle coordination are proposed as quantitative estimates of "hyperactivity". Conventional treatment abolished pain, tenderness and other symptoms and signs completely in 18 patients in whom the most significant findings in the muscles under study were reductions in absolute and relative contraction times ascribed to increased stability produced by occlusal adjustment. It is suggested that relatively shorter pauses before treatment impaired blood flow and that their prolongation following treatment improved circulation. During the strong, dynamic contractions of mastication, masseter muscles tended to be more susceptible to hyperactivity than the temporal muscles.

Dental Occlusion↗
PubMed2001

The development of a simple objective test of mastication suitable for older people, using chewing gums.

AIMS: To develop and assess a simple test for evaluating the mastication of visco-elastic foods and prosthodontic success subsequent to treatment of older people. METHOD: The weight lost from chewing gum during mastication tests and the saliva secreted is weighed. The percentage of the original gum weight that is chewed out in a defined number of strokes is termed the Masticatory Effectiveness (ME) MATERIAL: Five edentate and three dentate volunteers were selected to provide a range of dental states and age. Four commercially available chewing gums of different origins and perceived hardness were tested, one without sweetener acted as a control for salivary stimulation. INTERVENTION: Pre-weighed samples of each gum were chewed, each for defined numbers of strokes. The saliva secreted was collected and weighed. The chewed gum was desiccated and the total weight loss of sweeteners chewed out provided an objective measure of chewing performance. RESULTS: Weight loss showed large differences between gums, between subjects and the number of strokes. ME was significantly correlated with salivary secretion rates for two subjects. The interaction between subject and gum was statistically significant, established by an ANOVA model, the value of which is shown for multivariate studies. Differential success between gums of different thickness may provide evaluation of denture stability. CONCLUSIONS: Measuring the weight lost from gums during chewing provides a simple test of masticatory effectiveness of visco-elastic foods. This has particular value both in functional assessment of older people and in physiological research.

Adult↗
PubMed1971

Evidence for central timing of rhythmical mastication.

1. The origin of the co-ordination and rhythm of mastication provoked by electrical stimulation of the putamen and corticobulbar pathways was studied in the rabbit.2. Bursts of activity were recorded from the mandibular and hypoglossal nerves and the hypoglossal nucleus, which were in phase with the observed masticatory movements. Discharges occurred alternately in nerves to jaw-opening and jaw-closing muscles.3. The rate of burst discharges was not altered by paralysis, or by large variations in the stimulation frequency.4. Regularly recurring bursts of activity continued to occur in the hypoglossal nucleus in response to random frequency stimulation after severing branchial nerves, cervical nerves and the spinal cord of paralysed rabbits.5. Mechanical deformation of the brain of vascular or respiratory origin was discounted as the origin of the rhythm.6. It is concluded that mastication is controlled by a brain-stem pattern generator which can be activated by adequate inputs from certain higher centres and, as concluded in other studies, from the oral cavity itself.

Action Potentials↗
PubMed1981

Interactions between the jaw-opening reflex and mastication.

Electrical stimulation of the anterior hard palate or upper lip was used to evoke the jaw-opening reflex in rabbits lightly anesthetized with urethane. The amplitude of each excitatory response recorded in the digastric electromyogram during mastication was compared with the mean amplitude of 10 prior control responses. When weak stimuli were used, the mean amplitude of the reflex dropped markedly during mastication and was smallest when the digastric muscle was inactive (closing and occlusal phases of the masticatory cycle). As the stimulus strength was increased, the size of the response during closing rose progressively until it exceeded values obtained during the control period or the jaw-opening phase. In addition, strong stimuli altered the total cycle length and the duration and amplitude of muscle activity in a phase-dependent manner. Stimuli given during closing were particularly effective in causing inhibition of jaw-closing muscle activity and in reducing the velocity and amplitude of closure. It is concluded that the cyclical gain changes of the reflex response to noxious stimuli are controlled to a large extent by premotoneuronal mechanisms and that the overall effect on the masticatory cycle structure is phase dependent.

Animals↗
PubMed1983

Phase-linked variations in the amplitude of the digastric nerve jaw-opening reflex response during fictive mastication in the rabbit.

The diagastric nerve reflex response to stimulation of the upper lip was studied in urethan-anesthetized rabbits paralysed with pancuronium bromide. Rhythmic bursts of masticatory activity were evoked in the nerve by repetitive electrical stimulation of the motor cortex. The amplitude and latency of the reflex responses during fictive mastication were compared with preceding control values. When stimuli close to threshold were given, the largest and earliest responses occurred during the digastric burst. When intense stimuli were employed, the largest responses were out of phase with the burst, although the latency was still shortest when the motoneurons were rhythmically active. Since the pattern is essentially the same as that seen during normal mastication, we conclude that the cyclical modulation of reflex amplitude and latency is not the result of sensory feedback generated by the movements themselves but is instead governed by the central motor program.

Animals↗
PubMed2006

Emergence of intrinsic bursting in trigeminal sensory neurons parallels the acquisition of mastication in weanling rats.

There is increasing evidence that a subpopulation of neurons in the dorsal principal sensory trigeminal nucleus are not simple sensory relays to the thalamus but may form the core of the central pattern generating circuits responsible for mastication. In this paper, we used whole cell patch recordings in brain stem slices of young rats to show that these neurons have intrinsic bursting abilities that persist in absence of extracellular Ca(2+). Application of different K(+) channel blockers affected duration and firing rate of bursts, but left bursting ability intact. Bursting was voltage dependent and was abolished by low concentrations of Na(+) channel blockers. The proportion of bursting neurons increased dramatically in the second postnatal week, in parallel with profound changes in several electrophysiological properties. This is the period in which masticatory movements appear and mature. Bursting was associated with the development of an afterdepolarization that depend on maturation of a persistent sodium conductance (I(NaP)). An interesting finding was that the occurrence of bursting and the magnitude of I(NaP) were both modulated by the extracellular concentration of Ca(2+). Lowering extracellular [Ca(2+)] increased both I(NaP) and probability of bursting. We suggest that these mechanisms underlie burst generation in mastication and that similar processes may be found in other motor pattern generators.

Action Potentials↗
PubMed2006

Effect of texture of plastic and elastic model foods on the parameters of mastication.

Mastication is continually modified throughout the chewing sequence in response to the texture of the food. The aim of this work was to compare the effects of an increase in hardness of two model food types, presenting either elastic or plastic rheological properties, on mastication. Each model food type consisted of four products of different hardness. Sensory testing experiments conducted with one group of 14 subjects showed significant perceived differences between products in terms of their increasing hardness. Fifteen other volunteers were asked to chew three replicates of each elastic and plastic product during two sessions. EMGs of masseter and temporalis muscles were recorded simultaneously with jaw movement during chewing. Numerous variables were analyzed from these masticatory recordings. Multiple linear regression analyses were used to assess the respective effects of food hardness and rheological properties on variables characterizing either the whole masticatory sequence or different stages of the sequence. Muscle activities were significantly affected by an increase in hardness regardless of the food type, whereas the shape of the cycles depended on the rheological properties. The masticatory frequency was affected by hardness at the initial stage of the sequence but overall frequency adaptation was better explained by a change in rheological behavior, with plastic products being chewed at a slower frequency. A dual hypothesis was proposed, implicating first a cortical-brain stem preprogrammed mechanism to adapt the shape of the jaw movements to the rheological properties of the food, and second, a brain stem mechanism with mainly sensory feedback from the mouth to adapt muscle force to the food hardness.

Adaptation, Physiological↗
PubMed1987

Evidence that periodontal pressoreceptors provide positive feedback to jaw closing muscles during mastication.

1. Mastication was produced by stimulation of the right motor-sensory cortex of urethan-anesthetized rabbits with 15-s trains of shocks (1-ms duration) at 50 Hz. Movements of the lower jaw and jaw muscle electromyograms (EMGs) were recorded on magnetic tape for later computer analysis. 2. The stimulus site was chosen, and stimulus intensity adjusted, so that stereotyped movements were produced that included a wide swing of the mandible to the left side during jaw closure. 3. Control trials were alternated with trials in which a steel ball (2 mm diam) was thrust between the anterior molar teeth on the left side and left in place for several seconds. 4. When the obstruction was first introduced, a jaw opening reflex was sometimes evoked if the ball struck the buccal surface of the advancing mandibular molar teeth. Thereafter, when the ball was crushed between the occlusal surfaces of the teeth, no jaw opening reflex was seen. 5. Instead, the amplitude and duration of all the jaw closing EMGs increased, beginning at least 12 ms after contact with the ball. This caused a prolongation of the slow closing (SC) phase of the cycle that, coupled with a delay in the start of activity in the digastric muscle (jaw opener), prolonged the cycle by more than 60 ms. 6. During the SC phase of the obstructed trials, the medially directed grinding stroke was exaggerated because of an increase in the contraction of the contralateral zygomaticomandibular and anterior temporal muscles. 7. After collecting data, the sensory nerves to the maxillary and mandibular anterior molar teeth were cut to eliminate feedback from the periodontal pressoreceptors. Control and obstructed trials were repeated. 8. Following denervation, the obstructed cycles were of shorter duration. The mandible still moved to the right during SC in some animals, but the increase in closer muscle EMG activity was much reduced. 9. We conclude that periodontal receptors provide positive feedback to the jaw closing muscles during mastication. This is supplemented by input from other receptors, probably muscle spindles. In addition, an increase in periodontal feedback prolongs the SC phase and the early phases of the opening stroke.

Animals↗
PubMed1989

Mastication in the rabbit: a description of movement and muscle activity.

1. Mastication was studied in awake rabbits that had previously been prepared for chronic recording of jaw movement and jaw muscle electromyography (EMG) under general anesthesia. Data were stored on tape and replayed for computer-assisted analysis. Most data was taken from the mastication of rabbit chow, but the basic features described in the paper also apply to eating of other foods. The series of movements was divided into cycles, and the phases that compose them, using peaks in the vertical movement, velocity, and acceleration. 2. The whole series of movements from ingestion to swallowing was termed the masticatory sequence. We found, as have others, that the sequence can be divided into three consecutive periods, based on the form of the movements. These were named the preparatory, reduction, and preswallowing series of cycles. 3. The results of earlier studies suggest that the food is transported back to the molar teeth during the preparatory series, ground up during the reduction series, and that the bolus is formed for swallowing during the preswallowing series. 4. The typical cycle of the preparatory series was called type I; it had two phases: opening (O) and fast closing (FC). The jaw-opening muscles were very active during O, but EMG bursts from the closer muscles were small or undefinable during FC. There was not much movement away from the midline in either phase, and the cycles were the shortest in the sequence. 5. The reduction series was predominantly composed of type II cycles. These were of intermediate duration and had three phases [O, a short FC, and a slow closing phase (SC)], during which the pellets were crushed between the molar teeth. The jaw moved toward the working side during FC. At or soon after the start of SC, the closer muscles became very active and continued to contract as the teeth were drawn toward the midline and slightly backwards. 6. The preswallowing series was made up of five-phase cycles that we called type III. These were the longest of the sequence. Jaw opening now occurred in three stages: O1 was the fall from tooth contact to approximately the postural position, O2 was a pause, and O3 was defined as the final movement to maximum opening. The digastric burst occurred during O3. There were again two closing phases, FC and SC, but closer bursts were smaller than in type II, and SC was shorter.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1981

A mastication device designed for the evaluation of chewing gums.

A mechanical device designed to simulate the human mastication of chewing gum was used to evaluate the enamel polish, dentin abrasion, and reduction in enamel solubility produced by several commercial gums, as well as experimental gums incorporated with various additives. The results demonstrated that this mastication device was suitable for evaluating in vitro the physical and chemical effects of chewing gums on teeth.

Chewing Gum↗