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PubMed1988

Gross anatomy of the craniomandibular joint and masticatory muscles of the dog.

The craniomandibular joint (CMJ) and masticatory muscles in 15 dogs (Canis familiaris) were dissected. The major structures were fossa, disc and condyle surrounded by a thin fibrous capsule. The horizontally orientated temporal fossa had a pronounced tubercle anteriorly. Posteriorly, a retroarticular process curved backwards. This fossa and process closely surrounded the condyle. The disc was thin. The cylindrically-shaped condyle was elongated in the medio-lateral direction, situated at right angles to the sagittal plane. The lateral pterygoid muscle was poorly developed; the temporalis was by far the largest masticatory muscle. These findings support the assumption that the movements of the canine mandible are mainly hinge-like. Furthermore, the canine CMJ differs in many respects from the corresponding anatomical structures in the domestic pig, as well as in man.

Animals↗
PubMed1995

[Control ability to coordination pattern of masticatory muscle activities during maximal clenching in centric occlusal position].

The control ability which changes the coordination pattern of masticatory muscles in the Maximal voluntary clenching was investigated in the correlativity, using the electromyogram and the Dental-Prescale system on ten normal subjects. Even the insignificant correlative Activity index to the balancing point of occlusal force was shown, though the anteroposterior control index (CA/P) marked slightly correlative to the deviation of balancing point, when the coordination pattern of the masticatory muscles was controlled in conscious. Asymmetry index also marked insignificant correlation to the balancing point of occlusal force, but lateral control index (CLat) was significantly correlated under conscious deviation of balancing point. Conclusions were as follows: 1. The balancing point of occlusal force was located at maxillo first molar anteroposteriorly and near the median line laterally. 2. The coordination pattern consisted of nearly equal electromyographic activities during maximal clenching in the masseter and tempolaris anterior muscles in present subjects without the third molar. 3. The diagnosing in coordination pattern of masticatory muscles only using prescale system is difficult. But this system is reliable to estimate the control ability of the muscle coordination pattern. From these result, one of the suggestion in central mechanism of masticatory muscles were undertaken in program of the central nerve system.

Adult↗
PubMed1991

Histomorphometrical aspects of the postnatal development of masticatory muscle in the muscular dystrophic mouse.

Histomorphological and histomorphometrical observations were used to describe the development of masticatory muscles from normal and muscular dystrophic mice. The masseter and the digastric muscle were described from the birth to 35-40 week of age. It has not been possible by histomorphological criteria to separate dystrophic muscles from normal muscles at birth. From 2 weeks onwards marked differences between the affected and unaffected muscles appeared, as the affected fibres from this age are rounded with marked variations in size. Central nucleation is frequent and there is an increased amount of connective tissue between the fibres. The histomorphometrical observations revealed an increase in mean size of the fibres with age, both in normal and dystrophic masticatory muscles. The fibre size variance which has been shown to be a reliable parameter for description of degree of affection of dystrophic muscles, increased with increasing age in both groups. However, the variance is at all ages greater in the dystrophic muscles than in the normal ones, and is always greater in the masseter muscle than in the digastric muscle. There seems to be some small differences between male and female masticatory muscles, whereas no differences could be revealed between muscles from normal and heterozygous animals. Possible explanations of the obvious differences in degree and progression of the disease between the masseter and digastric muscle are proposed.

Animals↗
PubMed2003

First night effect of an interocclusal appliance on nocturnal masticatory muscle activity.

The purpose of this study was to examine the effect of an interocclusal appliance on nocturnal masticatory muscle activities. Six healthy Japanese males (mean age: 26.8 years) participated in this study. Electromyographic (EMG) activities of the right anterior temporalis and masseter muscles were recorded using a portable EMG recording unit at night both with and without an interocclusal appliance. In both muscles, the maximal EMG activity and the number of bruxing events decreased significantly by wearing the appliance. Moreover, the duration of a higher level of muscle activity was decreased while that of a lower level of muscle activity increased by wearing the appliance in both muscles. These findings suggest that nocturnal masticatory muscle activity is significantly reduced by wearing an interocclusal appliance, and that the use of such an appliance at night could help to relax masticatory muscles.

Adult↗
PubMed1997

Masticatory muscle pain before, during, and after treatment with orthopedic protraction headgear: a pilot study.

Protraction headgear has been used in conjunction with a palatal expansion appliance to correct Class III malocclusion with maxillary deficiency and/or mandibular prognathism. In general, 800 gm of orthopedic force is used to protract the maxilla, and 75% of this force is transmitted to the temporomandibular joint (TMJ) area via the mandible. The effect of this heavy intermittent force on the TMJ has not been reported in the literature. The objectives of this study were to determine the level of masticatory muscle pain and EMG activity in patients treated with maxillary protraction headgear. Ten patients with skeletal Class III malocclusion whose treatment plan called for maxillary protraction headgear treatment participated in this study. Nocturnal masticatory muscle activity was determined using a portable electromyographic (EMG) recording device. Subjects wore the EMG device 14 nights before treatment, 14 nights during treatment, and 14 nights 1 month after active treatment. Masticatory muscle pain level was determined by muscle palpation, scored on a scale of 0 to 3 each period, according to the method of Gross and Gale. The examiner followed a sequence outlined by Burch to examine the masticatory muscles. Results showed no significant differences for masticatory muscle activities before, during, and after treatment. Only a few patients experienced level 1 masticatory pain during treatment. None of the patients experienced masticatory muscle pain 1 month after treatment. These results demonstrate no significant increase in masticatory muscle activity or muscle pain associated with orthopedic treatment using maxillary protraction headgear.

Adolescent↗
PubMed2000

Does the ovarian cycle influence the pressure-pain threshold of the masticatory muscles in symptom-free women?

AIMS: To test the hypothesis that the ovarian cycle influences the pressure-pain threshold of the masticatory muscles. METHODS: Eighteen healthy women with a regular menstrual cycle (28 +/- 2 days), ranging in age from 18 to 35 years, participated in the study. For each subject, pressure-pain thresholds (PPTs) of the masseter and temporalis muscles were assessed at 4 muscular sites by means of an electronic algometer. Measurements were taken at 4 separate sessions across the menstrual cycle corresponding to the following phases: menstrual, follicular, periovulatory, and luteal. Menstrual cycle phases were determined by a pelvic ultrasonographic screening. The study was carried out in a single-blind design, and the initial session was randomly determined for each individual. Data collected were analyzed by repeated-measures analysis of variance. RESULTS: The findings suggest that the PPTs of several masticatory muscles (2 of 4) are influenced by the ovarian cycle, but to a minor extent (P < 0.05), and the influence is of limited clinical relevance. CONCLUSION: In healthy subjects, there is a link between mechanical sensitivity of the masticatory muscles and fluctuation of the ovarian hormones. The relationship between PPTs of the masticatory muscles and the ovarian cycle should be also investigated in patients with temporomandibular disorders and/or orofacial pain conditions.

Adolescent↗
PubMed1999

Masticatory muscle function in patients with spinal muscular atrophy.

The purpose of this study was to determine whether spinal muscular atrophy affects masticatory muscle strength and mandibular range of motion. A sample of 15 subjects with spinal muscular atrophy was compared to a sample of age-matched and sex-matched controls. Maximum bite force, masticatory muscle electromyography activity, mandibular ranges of motion and masticatory muscle endurance were evaluated. Results showed that maximum bite forces were one-half as great for the sample with spinal muscular atrophy than for the controls, even though their EMG activity was not significantly different. Slopes of the relationship between electromyography activity and bite force were two to four times steeper for patients with spinal muscular atrophy than controls. Maximum opening and protrusion were reduced to approximately one-half control values. Fatigue times of patients with spinal muscular atrophy were reduced by 30% (17.9 seconds versus 11.1 seconds). We conclude that the masticatory muscles of patients with spinal muscular atrophy are weakened, that their muscles are less efficient, and that they fatigue more quickly than controls. In addition, mandibular movements of these patients take place over a more limited range than unaffected controls.

Adolescent↗
PubMed2001

Unilateral fibroadipose degeneration of the masticatory muscles.

A unique case of fatty replacement of the masticatory muscles, causing progressive limitation of mouth opening, is presented. Both CT and MRI revealed an almost total substitution of the masticatory muscles with fatty tissue, confirmed by the histopathology at surgery. Myotomy of masseter and internal pterygoid muscles and coronoidotomy improved his symptoms. There is no known cause of fibroadipose replacement of muscle fibres.

Adipose Tissue↗
PubMed1976

[A functional assessment of the masticatory muscles in mammals and humans].

We have amended and added to Fabian's tables giving a functional assessment of individual masticatory muscles. The data in our tables refer only to the temporalis, masseter, pterygoideus medialis, pterygoideus lateralis and digastricus muscles. The weights of these muscles were determined in three fixed human cadavers and the mean values compared with those of apes, carnivores, herbivores and rodents. In humans, the most powerful masticatory muscle is the M. temporalis, followed by the M. massater, as in apes and carnivores. The M. pterygoideus is also one of the most important. This is remarkable, since in the other groups this muscle occupies the last place. This relative strengthening of the M. pterygoideus lateralis is an important characteristic of the human masticatory apparatus. In humans, the difference between the relative weights of the individual masticatory muscles is not nearly so great as in other mammalian groups. The M. pterygoideus lateralis does lie close behind the other two big adductors (Mm temporalis and masseter) but, as regards power and weight, it hardly differs from the M. pterygoideus medialis and the M. digastricus. In humans the strengthening affects not only the M. pterygoideus lateralis but also the M. digastricus. It would seem that these two masticatory muscles could become the key to the understanding of the specific changes in human mastication.

Animals↗
PubMed2001

A quantitative electromyographic analysis of masticatory muscle activity in usual daily life.

OBJECTIVE: This study was designed to investigate whether a quantitative electromyographic (EMG) analysis with a special reference to the EMG amplitude at 98N bite force could reduce the influence of electrode relocation and to examine the reproducibility of masticatory muscle activity in usual daily life within individuals. SUBJECTS AND METHODS: In the first experiment, two sessions of surface EMG recording for masseter and anterior temporal muscles during tapping, and chewing gum and marshmallow were performed for 10 subjects with an interval of at least 1 week with electrode relocation. In the second experiment, two sessions of EMG recording during daytime (142 min, including mealtime) and sleep (142 min) were carried out for 10 subjects with an interval of at least 1 week. The average rectified EMG values were normalised with a special reference to the EMG amplitude induced by a 98N bite force. RESULTS: In the first experiment, high correlation coefficients and no significant differences in the mean normalised values of muscle activity were found between two sessions. Although the average rectified values showed high correlation coefficients, the mean masseter muscle activity while chewing gum was significantly different between two sessions. In addition, the variation in temporal muscle activity between two sessions while chewing gum was significantly smaller in the normalised values than in the average rectified ones. In the second experiment, less intra-individual variation in the normalised values of masticatory muscle activity between two sessions indicated the reproducibility. Normalised masticatory muscle activity showed less variation during mealtimes than during usual daytime and sleep. CONCLUSIONS: This quantitative EMG analysis could estimate the masticatory muscle activity by reducing the influences of electrode relocation, demonstrating an availability of this analysis for the evaluation of masticatory muscle activity in usual daily life.

Activities of Daily Living↗
PubMed1995

Reflex changes in the masticatory muscles with load perturbations during chewing hard and soft food.

Reflex changes in masticatory muscles were investigated in naturally behaving rabbits while chewing soft food (bread) and hard food (raw rice). To study peripheral control mechanisms of mastication, reflex changes in masticatory muscles were correlated with the jaw movement trajectories. When the hard food was tested, the closing muscle was activated isometrically and the antagonist activity was evident during closure. Under such conditions, the so-called masseteric inhibitory periods (MIPs) and digastric short bursts (DSBs) were found in the closing phase, which was not the case with soft food. The reflex changes in the masticatory muscles were similar to those in an unloading reflex or in a reflex after tooth tap. Precise comparison of the EMG and the movement orbit showed that DSB with MIP was preceded by a trough in the closing velocity which bottomed at 8 +/- 1 ms (mean +/- S.D.: n = 9) before the DSB onset. These results suggest that the DSB with MIP may be a reflex change generated by periodontal mechanoreceptor stimulation after the upper and lower teeth come together with hard food, which have a role in regulatory mechanisms of mastication when the teeth are suddenly loaded by hard food.

Animals↗
PubMed2007

[Therapy of masticatory muscle pain: recommendations for clinical management].

Myalgias of the masticatory muscles are the most frequent noninfectious complaints in the orofacial region. After summarizing the current knowledge on the physiology, etiology, pathophysiology, diagnosis, and differential diagnosis of masticatory muscle pain, we specifically focus on management recommendations. Results of an extensive literature search show that for the majority of patients pain reduction or pain relief can be achieved with noninvasive reversible methods. Longitudinal short- and long-term studies have revealed that different therapeutic measures are similarly effective. In patients with chronic masticatory myalgias associated with psychosocial impairment, however, additional involvement of a psychotherapist is crucial.

Analgesics↗
PubMed1989

The silent period duration of the masticatory muscles.

This study was conducted to determine whether the reflex activity of the masticatory muscles is altered in prostheses wearers. The electromyographic silent period was measured on an oscilloscope screen. Thirty subjects were examined. Five subjects had natural dentitions. Twenty-five partially edentulous subjects wore removable prostheses. The silent period duration reached 18 to 21 ms on the masseter muscles and 20 to 22 ms on the temporal muscles. These values were not significantly different for subjects with and without teeth and in the control group. The duration of the silent period was the same for patients wearing prostheses and for subjects with natural teeth. This finding suggests that wearing a prosthesis does not change the normal activity of the masticatory muscles.

Denture, Partial↗
PubMed1988

The effects of muscle fatigue on the silent period of the masticatory muscles.

Thirteen healthy adults performed sustained clenching at 50% maximum clenching level judged electromyographically. Electromyograms were recorded from both anterior temporal and masseter muscles during clenching and the silent period latency and duration were measured. As the result of muscle fatigue, the silent period latency significantly decreased, whilst the duration significantly increased up to 3 min from the beginning of clenching.

Adult↗
PubMed1990

[EMG analysis of masticatory muscle fatigue and recovery rate during gum chewing].

An EMG computer analysis system was developed to analyze the mandibular function. The system enabled measurements of the masticatory muscle's rhythm, activity, and power spectrum for the same EMG burst during mastication. This study revealed that a power spectrum analysis was able to be carried out by a fast Fourier transform algorithm of the isometric contraction components of EMG bursts during mastication. The normal regulatory mechanism of the mandibular function was temporarily disturbed by clenching to inflict fatigue upon the masticatory muscles. EMG analysis of the masticatory muscles during gum chewing were observed before and immediately after clenching, and during their recovery periods. After fatigue induction, all of the masticatory rhythms of the masticatory muscles showed a decrease in EMG burst duration time (duration) and duration per cycle (D/C) that recovered with time. However, only the coefficient variation of the duration and D/C in the working side increased immediately after fatigue induction. The power spectrum shifted to a lower frequency immediately after fatigue induction, and recovered along with time. Furthermore, it was found that EMG activity influenced the power spectrum during gum chewing. In conclusion, this EMG analysis system may be used as a possible future diagnostic aid for mandibular dysfunction syndromes.

Chewing Gum↗
PubMed1986

Traumatic myositis ossificans in masticatory muscles.

3 cases of traumatic myositis ossificans circumscripta, located within the masticatory muscles are presented. Two of the lesions involved the masseter muscle, and exceptionally, 1 involved the temporalis muscle. Three pathognomonic histological zones, permitting the differential diagnosis of myositis ossificans from sarcomatous lesions, are described, and treatment incorporating ideally early surgical intervention with wide excisional biopsy of the lesion is stressed.

Adolescent↗
PubMed1996

Adaptations of masticatory muscles to a hyperpropulsive appliance in the rat.

The plasticity of masticatory muscles was studied by comparing rats that were wearing a protrusive appliance and were kept on a liquid diet with two control groups: (1) pair-fed rats and (2) rats that had free access to ordinary pelleted food. The animals were 45 days old at the beginning of the experiment and were studied for a period of 20 days. Three jaw muscles with different functions were examined: masseter, temporalis, and digastric. Muscle fiber composition was determined (1) by fiber counting after staining with four monoclonal antibodies, which were able to recognize the four major myosin heavy chain (MHC) isoforms and therefore four fiber types (I, IIA, IIX, IIB) and (2) by electrophoresis on 6% polyacrylamide gels. The comparison between free-diet rats and pair-fed rats showed that the change from a hard pelleted diet to a liquid diet caused a shift in fiber type and MHC distribution, characterized by an increase of IIB MHC in temporalis and digastric muscles but not in the masseter muscle. The comparison between pair-fed rats and rats wearing appliances showed on the contrary a decrease in IIB MHC and an increase in IIA and IIX MHC. The results support the conclusions that (1) rat jaw muscles can quickly adapt to functional demand changing their fiber type composition, (2) the changes appear restricted inside the fast fiber population, and (3) fiber-type changes caused by dietary variation are not less than those caused by orthodontic intervention and must be taken into account to assess the effect of the appliance correctly.

Adaptation, Physiological↗