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PubMed1995

[A study of the relationship between electromyographic activity of the masticatory muscles and the variations of the occlusal vertical dimension for edentulous subjects]

The study was performed in fifteen edentulous subjects with the EMG activity were recorded at the varying occlusal vertical dimension maintaining constant bite force value of 4kg.The results showed that maintaining constant bite force the amplitudes of EMG activity of the anterior temporal and masseter muscles are decreased with increasing the occlusal vertical dimension and correlation relation between them,that there is a stable region about 1.0mm for the anterior temporal muscle and about 1.5mm for the masseter muscle during the changes in electrical activity.It is represent that there is a physiological region of the occlusal vertical dimension for edentulous patient.

Journal Article↗
PubMed1998

Relationship between masticatory muscle activity and vertical craniofacial morphology.

The purpose of this study was to investigate the relationship between masticatory muscle activity during the day and vertical craniofacial morphology. The sample comprised 30 subjects (20 males and 10 females, age range 15 to 28 years, mean 24 +/- 3.2 years) who had normal anteroposterior skeletal relationships and complete or nearly complete dentition without serious malocclusion or temporomandibular dysfunction. Using a portable electromyographic recording system, activities of the masseter, temporal, and digastric muscles were recorded for 3 hours during the day, excluding time spent eating, sleeping and exercising. A lateral cephalogram was taken of each subject with the teeth in occlusion. Activities of the masseter, temporal, and digastric muscles consisted mainly of low-amplitude bursts. The duration of digastric muscle activity was greater than that of either the masseter or temporal muscles. Masseter and digastric muscle activity was positively correlated. The activities of the masseter, temporal, and digastric muscles during the day consist of low-amplitude bursts and may be related to vertical craniofacial morphology.

Adolescent↗
PubMed2001

Histochemical studies of the masseter, the temporal and small zygomaticomandibular, and the temporomandibular masticatory muscles from aged male and female humans. Fiber types and myosin isoforms.

The purpose of this study was to investigate the histology of two small masticatory muscles from females and males of more than 70 years of age. By using immuno- and enzyme histochemistry the muscles were characterized by their fiber types and myosin heavy chain pattern. The observations were compared with similar studies of the masseter and temporalis muscles. Previously the two small muscles have been described based solely upon their gross anatomy. One muscle originates from the anterior, deep surface of the temporal fascia and inserts in the temporal tendon: the temporo-mandibular muscle (TM). The other muscle originates from the upper part of the temporal surface of the frontal process of the zygomatic bone and the adjacent part of the frontal bone and inserts in the temporal tendon: the zygomaticomandibular muscle (ZM). In the masseter, TM, and ZM, most of the autopsy samples contained an abundant number of fibers containing neonatal myosin heavy chains while in the temporal muscle specimens, such fibers were sparse and scattered. Electrophoresis followed by immuno-staining of Western blots supported the histochemical findings. There was no obvious correspondence between fiber typing based upon ATPase activity and the neonatal myosin heavy chain content in the muscle fibers. Neither did the fibers show accordance in their content of adult slow and fast myosin heavy chains and in their content of neonatal myosin heavy chain.

Aged↗
PubMed1987

Dental stability and maximal masticatory muscle activity.

The electromyographical (EMG) activity of masticatory muscles during full clenching in the retruded contact position (RCP) and intercuspal position (IP) with and without a posterior stabilizing splint was studied. The linear envelope EMG signal from three bilateral muscles was recorded (masseter, anterior temporal and posterior temporal). Thirty-seven subjects were evaluated. Clenching in the RCP without the splint and with the presence of an unstable occlusal contact inhibited the masseter muscle activity and reduced anterior temporal and posterior temporal muscle activity. The masticatory muscle activity returned to normal when clenching in the RCP with a splint that permitted stability in the dentition. EMG activity was the same in the IP with and without the splint. The results indicate that the determinant of maximal masseter isometric muscle contraction is the amount of stability in the dentition rather than the jaw position. If the dentition takes the major role of stabilizing the mandible, i.e., there is good intercuspation, the masseter muscle can exert maximal isometric contraction. If the stability is not provided by the dentition, i.e., there is a premature contact, the jaw muscles must contribute to the stabilization and reduce the magnitude of the maximal contraction to avoid damage to the structures involved in the compensatory stabilization.

Dental Occlusion↗
PubMed1995

[Muscle relaxation by transcutaneous electric nerve stimulation (TENS) in bruxism. An electromyographic study].

In recent years transcutaneous electrical neuromuscular stimulation (TENS) has become increasingly more common in the treatment of functional diseases of the masticatory muscles and currently the practitioner can choose among a variety of stimulators. In an electromyographic study of 17 adults suffering from nocturnal bruxism and of a control group consisting of 18 adults without any functional disturbances of the masticatory muscles, the effect of this kind of neuromuscular stimulation on the temporal and masseter muscle was examined. The myoelectric signals were registered before and after TENS treatment in 3 different positions of the mandible. Each person was treated 3 times with both the Myo-Monitor (Myo-Tronics, Seattle) and the TNS SM2 MF stimulator (schwa-medico, Giessen). The different effects of continuous low frequency and intermittent high frequency muscular stimulation were studied simultaneously. Muscular activity was determined by computer aided integration of the electromyographically measured raw signals. A fourier analysis of the power spectrum yielded information on the frequency behavior of the studied muscles resulting from the TENS treatment. A statistical analysis of the results led to the following significant conclusions: 1. TENS treatment decreased the values of the registered integrated signals on all test persons, however, the treatment increased the median frequency and the mean power frequency (MPF). Since this effect is contrary to muscle fatigue, these electromyographic results can be interpreted as providing objective proof of a relaxation in the treated muscles. 2. The electromyographic changes after TENS treatment were similar when using either the Myo-Monitor or the TNS SM2 MF stimulator. In addition, the 2 different types of stimulation (high or low frequency) showed the same effects. 3. Compared to the persons in the control group, there was no significant increased muscular activity in patients with nocturnal bruxism. Following TENS treatment both groups showed the same alterations in the electromyograms. The results of the study provide further evidence that TENS treatment is an adequate supportive procedure in the treatment of nocturnal bruxism.

Adult↗
PubMed1984

Muscle transposition for facial reanimation. Indications and results.

The technique of transposing the temporalis and masseter muscles to reanimate the face following long-standing facial paralysis was introduced at the turn of the century. More recently it has been popularized by Rubin and Conley. The indications for performing this technique are outlined, and the results are analyzed.

Adolescent↗
PubMed1992

T1 snapshot FLASH measurement of rat brain glioma: kinetics of the tumor-enhancing contrast agent manganese (III) tetraphenylporphine sulfonate.

The ultrafast inversion recovery snapshot FLASH technique was used to determine the kinetics of the contrast agent manganese (III) tetraphenylporphine sulfonate (MnTPPS) in experimental brain tumors in rats. In the first part of the investigation this technique was validated with the conventional inversion recovery spin-echo method by comparing in vivo T1 data of a normal rat brain. Agreement between T1 values obtained from both techniques was complete, as tested for a large number of pixels in identical coronal slices. In the second part the fast IR snapshot FLASH method was applied to study the effect of the NMR contrast agent MnTPPS on the T1 relaxation time of experimental gliomas in rat brains. T1 of normal brain tissue (1024-1035 ms), tumor (1217 ms), and edema (1199 ms) was determined with the inversion recovery version of the snapshot FLASH imaging technique. After intraperitoneal injection of MnTPPS (0.25 mmol/kg body wt) T1 decreased exponentially to 56% of control in tumor and to 62% in muscle. In normal and edematous brain tissue no significant changes in T1 were observed up to 5 h after injection of the contrast agent. Once the T1 contrast between tumor and peritumoral brain tissue had reached a saturation, the enhancement persisted for several hours to days. Therefore application of this contrast agent resulted in a sharp demarcation between glioma and peri-tumoral edema.

Animals↗
PubMed1986

Melanotic neurofibroma: a case report with ultrastructural study.

The authors report a case of a solitary melanotic neurofibroma involving the temporomalar area in a 17-year-old man. Light-microscopic study reveals a benign neurofibroma including melanin deposits. Electron microscopy shows typical premelanosomes and melanosomes within Schwann cell cytoplasm. The literature is reviewed, and theories of histogenesis for this unusual tumor are discussed.

Adolescent↗
PubMed1988

Myogenic and neurogenic regulation of myosin gene expression in cat jaw-closing muscles regenerating in fast and slow limb muscle beds.

Immunocytochemical techniques were used to study changes in myosin gene expression during the regeneration of the cat posterior temporalis muscle transplanted into the bed of either the fast extensor digitorum longus (EDL) or the slow soleus muscle. Strips of the posterior temporalis, a homogeneously superfast muscle, were treated with Marcaine and then transplanted into limb muscle beds which had been completely cleared of host muscle fibres. The regenerates were examined 6 to 224 days after surgery. Early regenerates in both muscle beds reacted with antibodies against the heavy chain of foetal, slow and superfast myosins, but not with antibodies against fast myosin. In the long-term, regenerates innervated by the EDL nerve expressed only superfast myosin whereas in the regenerates innervated by the soleus nerve most fibres expressed only slow myosin and only a few fibres reacted exclusively with the anti-superfast myosin antibody even after 210 days. In contrast, EDL and soleus muscles regenerating in their own beds expressed foetal, slow and fast myosin, but did not express superfast myosin. The isometric contraction times of the various types of regenerates reflected the types of myosin synthesized. It is concluded that jaw and limb muscle cells exist as two distinct allotypes, each having a distinct repertoire for the expression of adult isomyosins, and that within that repertoire isomyosin gene expression can be modulated by the nerve. Thus, myosin gene expression in skeletal muscle fibres is regulated by both myogenic and neurogenic mechanisms.

Animals↗
PubMed1991

Association between surface electromyography of human jaw-closing muscle and quantified food breakdown.

Simultaneous recordings of the activity of the masseter and anterior temporalis and of jaw movement were made on 10 healthy dentate volunteers while they chewed roasted peanuts in their habitual manner. The quantity of food taken was altered by varying (a) its total weight (mouthful) between 8 and 1 g, but with a fixed initial particle size and (b) by varying its initial particle size between median sizes of 9.2 and 2.4 mm, but keeping the mouthful constant. Significant differences were found in the peak and mean (r.m.s.) estimates of muscle activity (particularly in the masseter), and the dimensions of jaw movements. These differences were associated with the variation in both the size of the mouthful and of the initial particles but were much greater with changes in the mouthful. A dimensional argument treating both the weight of food in the mouth and initial particle size as volumes showed that initial particle volume had been varied by approximately 50 times as much as mouthful volume and therefore that the mouthful was a far more critical factor in masticatory physiology than was the particle size of the food. The reasons for this probably lie in an understanding of mechanisms of food comminution.

Adult↗
PubMed1994

Estimating human incisal bite forces from the electromyogram/bite-force function.

This study used the electromyogram (EMG)/force-function curve as a means of estimating functional bite forces. Surface EMG recordings were made for the masseter and anterior temporalis muscles bilaterally in ten adults while incisal bite forces were measured using a force transducer embedded in custom-made hydroplastic bite blocks. Measurements were made for mouth openings of 15 and 30 mm. Each subject was first instructed to develop a maximum level of bite force, and then to develop bite-force levels that corresponded to decreasing percentages of his or her maximum, from 90 to 10%, in 10% decrements. After the force measurements had been made, each subject was instructed to incise various food substances. The power-density spectrum and r.m.s. power level were calculated for each sample. Maximum bite-force levels varied considerably among the 10 subjects, ranging from a minimum of 2.5 kg to a maximum of 40 kg. For the subjects as a whole, estimated bite forces for the different types of food ranged from 3.0 to 5.5 kg. This range was independent of the subjects' maximum bite-force levels. Thus, bite forces exerted to incise different foods probably depend more on the food than on the individual's bite capabilities. There was variability within this range, although, as expected, bite forces were least for chocolate and greatest for apple and toffee.

Adult↗
PubMed1994

Modulation of temporalis muscle exteroceptive suppression by limb stimuli in normal man.

The effects of noxious and non-noxious limb stimulations on the second exteroceptive suppression of voluntary temporalis muscle activity (ES2) were studied in healthy human volunteers. Duration of temporalis ES2 was measured on averaged rectified responses obtained after stimulating the labial commissure at an intensity of 25 mA. Single peripheral electrical stimuli applied over nerve trunks or over the skin before the labial stimulus decreased ES2 duration. This effect was most pronounced after cutaneous stimuli, especially of the index finger, and it was not observed when the conditioning stimulus was a 10 second, high frequency train. For stimulation at the index finger, temporalis ES2 inhibition progressively increased with intensity from 10 mA to 40 mA; it was maximal for an interstimulus interval between 50 and 140 ms. After naloxone (0.4 mg or 4 mg, i.v.) there was a partial reversal of the index-induced ES2 depression, but this effect was not significant. Immersion of one hand in water heated at 47 degrees C produced a short-lasting ES2 reduction. These results are comparable, though not similar, to the inhibition of the digastric reflex (or jaw opening reflex) observed in animals after limb stimuli and to the depression of the spinal flexion reflex reported in man after heterotopic peripheral stimuli. Although peripheral stimuli were able by themselves to suppress temporalis EMG activity in some subjects, it is likely that they reduce labial-induced ES2 via activation of brainstem structures, such as periaqueductal gray matter or raphe magnus nucleus, which are thought to inhibit the medullary inhibitory interneurons mediating ES2.

Electric Stimulation↗
PubMed1995

Modelling of forces in the human masticatory system with optimization of the angulations of the joint loads.

Numerical models of the human masticatory system were constructed using algorithms which minimized non-linear functions of the muscle forces or the joint loads. However, the predicted solutions for isometric biting were critically dependent upon the modelled angular freedom of the joint loads. The most complete mathematical minimization of any objective function occurs when the joint load angles are predicted. However, the predictions have to be sensible in relation to the actual morphology of the joints. Therefore, the models were tested in terms of the angles of joint load predicted for a dry skull, using muscle vectors reconstructed from the geometry of the skull. The minimizations of muscle force were intrinsically incapable of predicting the angles of joint load. Such models must rely on constrained angles and this produces a restricted minimization and also an indeterminacy. In contrast, the minimizations of joint load predicted angles of joint load which varied appropriately with condylar position. The condylar movement was achieved with a positioning model which adjusted the angulation of the muscle vectors as the jaw was positioned. This model also generated the optimal sagittal shape of the articular eminence. Muscle predictions from the various models were not examined in detail, but the general nature of the predicted muscle force patterns was shown to be reasonable in some of the models and unreasonable in others. The results supported the hypothesis that the temporomandibular joint develops functionally to allow an approximate minimization of the joint loads during isomeric biting. This does not necessarily imply that the neurophysiological control is actually based on a minimization of joint load.

Algorithms↗
PubMed1988

Histochemical characteristics of masseter and temporalis muscles after 5 weeks of maxillomandibular fixation--an investigation in Macaca mulatta.

This study describes the histochemical characteristics and cross-sectional areas of the superficial masseter and temporalis muscles in juvenile rhesus monkeys after 5 weeks of maxillomandibular fixation. Four juvenile male Macaca mulatta underwent mandibular surgery and 5 weeks of maxillomandibular fixation as part of a study of temporomandibular joint (TMJ) adaptations after condylar replacement. Immediately before the time the animals were killed (5 weeks postsurgically), biopsies of the masseter and temporalis muscles were obtained and submitted to histochemical analysis and calculation of muscle-fiber areas. The data were compared to histochemistry from 12 juvenile control Macaca mulatta. Significant decreases in mean cross-sectional area were exhibited in both type I (p less than 0.05) and type II (p less than 0.01) fibers in all muscles when compared to controls (n = 12). The ratio of type I to type II fibers, however, remained constant during maxillomandibular fixation in masseter and temporalis muscle samples, indicating no change in relative types of fibers. We conclude from this experimental investigation that (1) significant atrophy occurs in the temporalis and masseter muscles after 5 weeks of maxillomandibular fixation, and (2) this atrophy occurs in both type I and type II fibers, indicating that overall recruitment of the muscle (and not just of one fiber type of motor unit) was affected during fixation.

Adenosine Triphosphatases↗
PubMed1999

Haemodynamic changes in human masseter and temporalis muscles induced by different levels of isometric contraction.

This study evaluated the influence of low contraction forces on intramuscular haemodynamics in human masseter and temporalis using near-infrared tissue spectroscopy. This method allowed the intramuscular haemoglobin (Hb) to be assessed dynamically before, during and after a 5, 15, 25 and 100% maximum voluntary contraction (MVC). Twenty volunteers, 10 males and 10 females, without pain or dysfunction in the masticatory system were included in this study. Data were recorded for 30 s before, 30 s during and 5 min after the four sustained contraction tasks. The results showed that all four levels of voluntary contraction produced a clear haemodynamic response (during and after contraction) in both muscles. For analytical purposes, the maximum Hb achieved after 100% MVC was set equal to 1.00. In the masseter the mean peak Hb during the 5, 15, 25 and 100% MVC was 0.49, 0.92, 1.30 and 1.73 while after the contractions it was 0.50, 0.65, 0.78 and 1.00, respectively. In the temporalis the peak Hb during the contractions was 0.23, 0.36, 0.48 and 0.66 and after the contractions 0.32, 0.45, 0.56 and 1.00, respectively. Repeated-measures analysis of variance revealed a significant main effect for the different contraction levels both in the masseter (during contraction, p = 0.001; after contraction, p<0.001) and the temporalis (during contraction, p = 0.002; after contraction, p<0.001). These data suggest that low levels of contraction induce a clear haemodynamic response, even at 5% effort. When compared, the masseter and anterior temporalis showed clearly different patterns for the Hb signal during the contraction (p<0.001) as well as after it (p = 0.007). Specifically, the Hb during the contractions in the masseter appeared more stable than in the temporalis, which showed a strong return to baseline. Obviously the contracting masseter had a stronger and more sustained venous occlusion than the contracting temporalis. It is speculated that variation in architecture between the two muscles contributes to these differences in blood flow.

Adult↗
PubMed1997

Muscle activity during mandibular movements in normal and mandibular retrognathic subjects.

PURPOSE: The masticatory muscles function as a unit during precise mandibular positioning movements that occur during such activities as speech, singing, or playing musical instruments. This investigation was designed to assess jaw muscle recruitment patterns during controlled mandibular movement in normal subjects and in patients with mandibular retrognathism. PATIENTS AND METHODS: A computer-integrated electromyography (EMG) and movement monitoring (Selspot) system was used to collect data over 7 seconds of a sagittal border movement (Posselt envelope) of the mandible and 4 seconds each of rest position, light tooth contact, and maximum clench. Fine wire bipolar electrodes were placed into the inferior belly of the lateral pterygoid muscles bilaterally and surface electrodes were placed bilaterally over the anterior belly of the temporalis muscles and the masseter muscles. Ten subjects with Class I occlusion, normal cephalometric values, and an absence of temporomandibular joint (TMJ) dysfunction were compared with 12 patients with mandibular retrognathism, Class II malocclusion, and an absence of clinical signs of TMJ internal derangement before and after a bilateral sagittal split and advancement of the mandible. RESULTS: There was a wide variation in standard deviations of EMG activity for the lateral pterygoid muscles in the retrognathic patients compared with normal controls before surgery (P < .05). In light tooth contact, temporalis muscle activity increased after surgery with respect to both control and the presurgical levels (P < .05, P < .005, respectively). In maximum clench, activity in all muscle groups in the retrognathic patients, both before and after surgery, were below that of control subjects (P < .005). The lateral pterygoid muscles showed late recruitment, with low EMG activity levels during the forward movement phase of the envelope, before surgery compared with controls (P < .001). After surgery, the lateral pterygoid muscle showed early recruitment in the forward movement similar to control levels. CONCLUSION: The masticatory muscles function as a unit during mandibular positioning movements. Patients with mandibular retrognathism have different muscle recruitment patterns from those of normal subjects with the mandible at rest and during mandibular movement. After orthognathic surgery, adaptation occurs in the phasic timing of jaw muscle activity.

Adaptation, Physiological↗