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PubMed1992

[Anatomical observations on the attachment of human temporalis and masseter muscles].

It is very important for orthodontics to investigate the bone remodeling pattern in the area of the attachment of the masticatory muscles induced by the changing muscular function. In the present study, the insertion pattern of Sharpey's fibers and the bone structure are comparatively studied on the temporalis and the masseter muscles macroscopically, light microscopically and electron microscopically, respectively. The following results are obtained: 1) The periosteum on the squamous part of the temporal bone is thinner, while the one on the lower ridge of the zygomatic arch is relatively thicker. 2) The fine and loose Sharpey's fibers are found mostly on the squamous part of the temporal bone, while the ones on the lower ridge of the zygomatic arch are relatively coarse and dense. 3) Comparing with the squamous part of the temporal bone, the fibrous bone is thinner and also few reversal lines and resting lines are observed at the lower ridge of the zygomatic arch. These findings seem to prove the fact that the bone remodeling proceeds frequently within the limited narrow area. These differences are directly due to the differences of the anatomical site and the muscular function.

Aged↗
PubMedDate not supplied

[Registration of the silent period in masseter muscles during study of the mandibular reflex].

Under the application of clinical electromyography, nowadays is more widely used reflex investigation, i.e., the investigation of the reflexes to the extension. In stomatognathic system is the most frequently applied the investigation of mandibular reflex. Silent period was registered during the investigation of mandibular reflex. Silent period is the reflex pause or the period of suppressive activity that is subsequent to some sort of stimuli during or following muscle contraction. In current dentistry, silent period, registered by electromyography, represents an important parameter in functional diagnosis. The aim of the study was to establish the duration of silent period in masseter muscles during the investigation of mandibular reflex in edentulous patients with the pair of newly made full dentures and in the subjects with natural healthy intact dentition, respectively. The investigation included 20 subjects of average age 44 years. The results of registered silent period during the investigation of mandibular reflex in edentulous patients had the lower values (18.21 ms) than in the subjects with healthy intact dentition and with a pair of newly made full dentures (20.51 ms), respectively, which have confirmed the physiologic time of the duration of silent period.

Denture, Complete↗
PubMed1983

Influence of central dopaminergic and oral sensory stimulation on the tone of the rat masseter muscle.

Dopamine neurons in the nigrostriatal subgroup of the basal ganglia are involved in the higher control of muscle tone and repetitive movements, possibly also in the masticatory muscles. For this reason, the effect of mechanical oral stimulation in combination with apomorphine-induced stimulation of dopamine receptors in the brain was experimentally studied in the rat. The masseter muscle tone during and after anesthesia was registered. A tachograph preamplifier and a bipolar electrode were used for the recording of summated potentials from the muscle. Dopaminergic stimulation increased the muscle tone. Oral sensory stimulation alone showed a tendency to increase the masseter tone, although the increase was not statistically significant. The increase of the tone with dopaminergic stimulation is presumably due to the fact that the dopaminergic system in the basal ganglia also controls the motor function of the masticatory muscles. Several pathological conditions of the mouth region, where a dopaminergic mechanism in the facilitation and inhibition of centrally coordinated jaw reflexes is obvious or possible, are discussed. Individual variation in neuronal dopamine synthesis, uptake, or receptor sensitivity may be one of the factors determining predisposition to masticatory disturbances both in experimental and clinical conditions.

Anesthesia, Dental↗
PubMed1993

Contribution of periodontal receptors and food qualities to masseter muscle inhibition in man.

Previous studies of human muscle inhibition during chewing have shown that many factors contribute to the incidence and intensity of this reflex but few studies have been in a physiological context. During the first crushing cycle of brittle foods ipsilateral masseter muscle EMG, mandibular movement and vibration were recorded simultaneously in four healthy dentate subjects. Experiments were repeated before and during anaesthesia of the cheek teeth on the chewing side. The results suggest that vibration seems to be the most important factor in muscle inhibition during food crushing; conversely periodontal sensation, mandibular closing movement and the preload by the muscle at the onset of food fracture play a minor role.

Adult↗
PubMed2005

Association between masseter muscle activity levels recorded during sleep and signs and symptoms of temporomandibular disorders in healthy young adults.

AIMS: To examine whether any signs and symptoms of temporomandibular disorders were significantly associated with masseter muscle activity levels during sleep. METHODS: One hundred three healthy adult subjects (age range, 22 to 32 years) participated in the study. They were asked to fill out questionnaires, undergo a calibrated clinical examination of their jaws and teeth, and perform 6 consecutive nightly masseter electromyographic (EMG) recordings with a portable EMG recording system in their home. The EMG data were considered dependent variables, while the questionnaire and examination data were considered independent variables. Multiple stepwise linear regression analysis was utilized to assess possible associations between these variables. RESULTS: Both gender and joint sound scores were significantly related to the duration of EMG activity. None of the other independent variables were found to be related to any of the muscle activity variables. CONCLUSION: The results suggest that both gender and clicking are significantly related to duration of masseter EMG activity during sleep.

Adult↗
PubMedDate not supplied

Single-wire recording of regional activity in the human masseter muscle.

A new approach is presented for recording regional muscle responses by means of a single intramuscular wire electrode. The technique exploits differences in impedance due to the locations of the recording and indifferent electrodes and also relies upon bandpass filtering. The method is demonstrated by recording the activity of the right masseter muscle at three different sites during voluntary tooth clenching. The results indicate that satisfactory separation of regional muscle activity can be obtained and that the recorded signals can be sampled digitally for quantitative purposes. As this method for recording jaw muscle activity avoids the problem of variable interelectrode distances commonly associated with conventional bipolar wire electrodes, it is advantageous when recording from human muscles in the facial and intraoral regions.

Electromyography↗
PubMed1989

Distribution and central projections of primary afferent neurons that innervate the masseter muscle and mandibular periodontium: a double-label study.

A double-label strategy was used to determine the distribution and central projections of primary afferent neurons that innervate the periodontium and muscles of mastication in cats. Central injections of either Fast Blue (FB) or a mixture of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) and HRP were made into one of three cytoarchitectonically distinct regions of the spinal trigeminal nucleus. These regions included the subnucleus oralis (Vo), the subnucleus interpolaris (Vi), and the medullary dorsal horn (MDH). In each case, injections were also made into the periodontium of the ipsilateral mandibular teeth or into the ipsilateral masseter muscle. FB injections preceded the peroxidase injections by at least 48 hours and total survival time ranged from 72 to 96 hours. Animals were perfused with phosphate-buffered paraformaldehyde (4%; pH 7.2). Serial frozen sections were made through the brainstem and trigeminal ganglion. Tetramethylbenzidine was used as a chromagen to demonstrate HRP and sections were viewed with brightfield and epifluorescent illumination. Cells containing peripherally injected tracer were observed in the lateral portion of the ganglion and in the mesencephalic nucleus (Vmes). Double-labeled ganglion cells were observed in most cats that received periodontal injections in combination with central injections in the dorsal part of spinal trigeminal nucleus regardless of the rostrocaudal level of the central injection. In the animals that received intramuscular injections, double-labeled ganglion cells were observed only in the animals that received central injections caudal to the Vo. Double-labeled Vmes perikarya were observed in cats that received either intramuscular or periodontal injections in combination with central injections into the MDH and Vo but not in animals that received injections into the Vi. These results demonstrate that ganglion cell periodontal afferents project to the three major rostrocaudal subdivisions of the spinal trigeminal nucleus while ganglion cell muscle afferents have more limited central projections to caudal regions of the nucleus. Masseter and periodontal Vmes afferents also project ot the spinal trigeminal nucleus--specifically, to the Vo and MDH. These findings are consistent with physiological observations regarding the role of periodontal and masseteric afferents in oral and facial reflexes and somesthetic mechanisms.

Afferent Pathways↗
PubMed1984

Flexibility in motor-unit firing pattern in the human temporal and masseter muscles related to type of activation and location.

Morphological studies have shown that each human jaw muscle and its sub-portions have a characteristic fibre-type pattern, suggesting special functional tasks. The firing pattern of 68 low-threshold motor units in different portions of the temporal and masseter muscles in 5 healthy subjects were determined by single-fibre EMG during voluntary isometric muscle contraction. The findings showed that each unit may have different activity patterns for different types of activation, which is not so for limb muscles. Thus, a given motor unit discharged with a different regularity in firing rate during retraction of the mandible than during clenching of the jaws in the intercuspal position, probably related to a changed central and peripheral influence on the motoneurone pool. No activity of single units was detected in the mandibular rest position. The results underline the complexity of the human stomatognathic system and the importance of combined morphological and physiological studies.

Adolescent↗
PubMed1993

Influence of mastication on saliva, plaque pH and masseter muscle activity in man.

An earlier study showed that frequent gum chewing may enhance parotid gland function and reduce the acidogenicity of dental plaque. The aim now was to determine whether these effects would be observed after a 2-week period of diet altered to increase masticatory effort, and secondarily to assess the effects of chewing gum on masseter muscle activity. Ten subjects took part in the first experiment. Saliva was collected before and after the diet change and the plaque pH response to a sucrose challenge was measured. Subjects completed 3-day diet histories and wore electromyographic (EMG) devices to record masseter activity. In the second experiment, 10 subjects wore EMG devices for 3 days to record masseter activity on three daily regimens: baseline (no gum chewing), hourly gum chewing (sugar-free gum chewed for 10 min every hour) and chewing five sticks of gum each for 20 min during the day. Data were analysed by paired t test or repeated-measures analysis of variance. For the first experiment, EMG data indicated significant increases in chewing activity (p < 0.05), although there were no changes in salivary flow rates or the plaque pH response to sucrose. The second experiment showed that total EMG activity increased significantly on both gum-chewing regimens (p < 0.01), the magnitude of the increase being greater for hourly chewing. Overall, masseter EMG activity was increased 41% by diet alteration, compared to increases of 96 and 152% on the five-stick and hourly gum-chewing regimens, respectively.

Adult↗
PubMed2001

Oral commissure reconstruction with split masseter muscle transposition and cheek skin flap.

Satisfactory reconstruction of the cheek involving the oral commissure is always challenging. A 64-year-old male patient underwent full-thickness repair of a cheek defect involving the oral commissure following excision of squamous cell carcinoma. Reconstruction was performed with a cheek skin flap combined with split masseter muscle transposition. This method was found to be useful for reconstructing the oral commissure with good functional and aesthetic results.

Carcinoma, Squamous Cell↗
PubMed1992

Arterial supply of the masseter muscle in the lion (Panthera leo).

There are few reports on the vascular system of the lion or Panthera leo except for that on the facial artery investigated by Lin and Takemura (1990). Morphological analysis of the masseter muscle of the lion according to the muscle-tendon theory has been performed only by Takemura et al. (1991). The present authors attempted to elucidate the blood supply of the masseter, using 3 lion heads injected with acryl plastic into the carotid system by the plastic vascular injection method. This description is based on examination of the detailed laminar formation of the masseter. The findings are discussed in comparison with those of the felid family in carnivorae. Masseteric branches of the superficial temporal, buccal and facial arteries were distributed to the primary sublayer of the superficial layer, those of the above arteries and the masseteric artery to its secondary sublayer, the intermediate layer and the anterior and posterior portions of the deep layer, and those of the superficial temporal and masseteric arteries to the primary sublayer of the posterior portion of the deep layer. The maxillomandibularis muscle was supplied by the buccal and masseteric arteries and the zygomaticomandibularis by the superficial temporal and posterior auricular arteries as well. No gross differences between the lion and cat were observed in arterial supply of the masseter proper and improper, although the superficial temporal artery was distributed only to the superficial and intermediate layers in the cat but to all the deep layers in the lion.

Animals↗
PubMedDate not supplied

An electromyographic study of masseter muscle activity amongst overdenture and complete denture patients.

In recent years the dental profession has extended preventive Dentistry Concept in Prosthodontics by using overdenture. An Overdenture has a number of advantages over ordinary full dentures, including an improved neuromuscular performance. This study was carried out on two groups of patients wearing complete overdenture and conventional complete dentures to find out the masseter muscle activity in different oral condition and how muscle activity of patients with overdentures differ from that of patients with conventional complete denture.

Aged↗
PubMed1977

Regeneration of masseter muscle following lidocaine-induced degeneration. A histochemical study.

The histoenzymatic characteristics of regenerating myofibers of rat masseter muscle following injection of 1% lidocaine, as well as morphometric and histochemical characteristics of the typical myofibers, were investigated. Myoblasts appeared initially by day 1 among numerous macrophages within the confines of degenerating myofibers. Myotubes predominated by the 3rd day. Complete regeneration of the muscle occurred by at least 45 days. Phosphorylase activity was absent at day 1 and reappeared by the 5th day when the regenerating myofibers showed slight activity. By the 15th day the myofiber types had partly differentiated; red myofibers were smaller and stained less intensely than the white myofibers. Myotubes stained uniformly for succinic dehydrogenase activity from 3 until 5 days. After 5 days this staining increased gradually. Myofiber types began differentiation by 15 days and were fully differentiated by 45 days. ATPase activity was barely evident by 1-3 days. This activity appeared uniformly low up to 5 days and increased to an intensity comparable with that of the typical myofiber by 15 days. Slight leucine aminopeptidase activity occurred in macrophages 1 day following injection. By 3 days this activity appeared in the remaining myoblasts and in the myotubes. Some activity was found in the fibroblasts. This staining intensity at 5 days was equal to that of earlier lesions. A trace of this activity was found at 7 days, and none at 15 days. Glucose-6-phosphate dehydrogenase activity was present in the macrophages by day 1. It increased by 3 days and occurred mainly in myoblasts and myotubes. This activity decreased by 5 days, and none was found by 7 days.

Adenosine Triphosphatases↗
PubMed1978

Pharmacological properties of curare-sensitive receptors mediating post-tetanic potentiation in rat masseter muscle.

Post-tetanic potentiation (PTP) of single muscle twitches after "tetanic" stimulation at 1 to 20 Hz in rat masseter muscle has been studied. PTP was inhibited by d-tubocurarine (2--6 microgram/kg), hexamethonium (1.75--2.25 mg/kg), succinylcholine (5--7 microgram/kg), prostigmin (1.0--1.5 microgram/kg), lidocain (3--4 mg/kg) and ouabain (215--240 microgram/kg). The doses did not affect the control twitches. Prostigmin could not reverse the blocking effect on the PTP caused by these drugs. Atropin was without any effect on the PTP. The nicotinic receptors mediating PTP differ from both end-plate and ganglionic receptors since drugs blocking both types of receptors are effective. The sensitivity to the blocking agents is higher or the same (in the case of hexamethonium) as for the two other types of nicotinic receptors. Thus the PTP is dependent on activity of a "nicotinic" receptor active during physiological conditions, suggesting the presence of an additional mechanism for neuromuscular transmission in rat twitch fibres.

Animals↗
PubMed1994

Evocation of either excitatory or inhibitory reflex responses in human masseter muscle by electrical stimulation of the lip at varying intensities.

Electrical stimuli at 1 Hz with pulse widths of 0.05, 0.1 and 1 ms with intensities from two to six times sensory threshold (2-6 T) were delivered to the lower lip. The reflex responses were monitored by surface electromyography of the ipsilateral masseter muscle. An excitatory response that was not preceded or followed by an inhibition could be evoked in seven out of ten subjects at intensities below 5 T at all pulse widths. A higher stimulus intensities, the excitation disappeared and/or was preceded by as short-latency inhibition (SLI) or a long-latency inhibition (LLI). The electrical threshold for the excitatory response was statistically lower than the SLI and LLI, especially when longer pulse widths wee used. Three subjects demonstrated a primarily excitatory response, whereas four had a more pronounced inhibitory response. It was concluded that separate populations of myelinated fibres may be responsible for the responses: the lowest-threshold fibres may elicit excitatory responses and fibres with higher thresholds may evoke inhibitory responses. Another possible explanation is that central spatial summation could be responsible for the opening of the inhibitory and excitatory central pathways. The excitatory response may be the result of a reflex pathway similar to that evoked by activation of periodontal mechanoreceptors, and could be responsible for the load compensation mechanisms during chewing and/or positioning of food. The inhibitory responses are well known, and are considered to be a protective reflex.

Adolescent↗
PubMed2000

EMG power spectrum and motor unit characteristics in the masseter muscle of the rabbit.

Masticatory muscles contain a large variety of motor units with different physiological and morphological properties. In this study, we tested the hypothesis that a relationship exists between the mechanical and myo-electric properties of single motor units in the masseter muscle of the rabbit. It was expected that faster-contracting motor units, which usually have a relatively large number of fibers with large diameters, should have faster action potentials with larger amplitudes than slower motor units. Single motor units were stimulated. A two-dimensional force transducer registered mechanical parameters of the units. EMG electrodes were used to determine amplitude and frequency parameters of the action potentials of the same units. The results showed that faster-contracting motor units indeed produced action potentials with higher conduction velocities. However, faster motor units had no significant larger amplitude of the action potential. Small but significant positive correlations were found between the tetanic peak force and the amplitude of the action potentials. Little difference was found among the various frequency and amplitude parameters, respectively, making them equally suitable to describe the action potential. Surprisingly, a negative correlation between the amplitude and frequency parameters of the action potential was found, which may result from variability in arrival times of action potentials at the electrode site. Regional differences in the frequency parameters were found between the anterior and posterior parts of the superficial masseter.

Action Potentials↗