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Mit Hilfe von Elektromyographie (EMG) lassen sich die speziellen neurophysiologischen Eigenschaften des Musculus (M.) masseter auf Ebene der motorischen Einheiten (MUs) untersuchen. Intramuskuläre EMG-Techniken liefern u.a. detaillierte Informationen über die Lokalisation von MUs. Im Gegensatz dazu kann mit der hochdichten Oberflächen-EMG (HDsEMG) non-invasiv die Verteilung einzelner MUs auf der Hautoberfläche untersucht werden. In der vorliegenden Studie sollten intramuskuläre und HDsEMG-Techniken kombiniert werden um Zusammenhänge beider Amplitudenprofile zu untersuchen. Dazu wurde ein spezielles HDsEMG-Elektrodengitter (256 Elektroden) für den rechten M. masseter entwickelt und bei 10 Probanden je zwei Scanning-EMG-Messungen zur Erfassung der Ausdehnung der MU-Territorien senkrecht zur Hautoberfläche durchgeführt. Zeitgleich wurden HDsEMG-Ableitungen zur Beurteilung der MU-Topographie auf der Hautoberfläche durchgeführt. Die Isolierung von MU-Potenzialen aus den Interferenz-EMG-Signalen erfolgte mittels zwei unterschiedlich tief positionierten bipolaren Feindrahtelektroden. Aus diesen Daten wurden verschiedene MU-Parameter und deren Interrelation statistisch analysiert. Die Territorien der 161 auswertbaren MUs lagen im Median 11,82mm tief und waren im Median 3,94mm lang. Bei einer mittleren Feuerfrequenz von 15,94Hz wurde eine durchschnittliche elektrische Größe von 193,23µVms/0,62mVms (intramuskulär/HDsEMG) gemessen. Dabei zeigte sich eine positive Korrelation zwischen intramuskulär und oberflächlich gemessener elektrischer MU-Größe. Tiefere MUs zeigten eine Tendenz hin zu einer größeren elektrischen Größe mit einer niedrigeren Feuerfrequenz. Die Ergebnisse dieser Studie stellen eine signifikante Erweiterung des physiologischen Grundlagenwissens über den M. masseter dar und sind zudem eine wertvolle Grundlage für die Entwicklung dreidimensionaler biomechanischer und elektrophysiologischer Modelle dieses Muskels.

This case report illustrates a rare complex of symptoms leading to limited mouth opening in a young woman. The 28-year old suffered from a progressively limited mouth opening over several years that finally resulted in restricted alimentation and made dental treatment impossible. Clinical findings suggest a structural alteration, including a hyperplastic mandibular angle and marked hypertrophy of the masseter muscle. Further radiologic investigations reveal a thickened aponeurosis of the masticatory muscles and hyperplastic coronoid processes that are not interfering with the zygomatic bone. Primary therapeutic options for such conditions are mainly surgical, including reduction of the masseter muscles volume and aponeurorectomy as well as bony reductions, such as coronoidectomy and mandibular angle reduction. With this treatment, the outcome and prognosis are good. Long-term results depend on concomitant physical therapy. A uniform nomenclature for this condition is yet lacking and propositions such as “masticatory muscle tendon-aponeurosis hyperplasia” have been made. However, knowledge of this condition and its typical clinical signs can make the diagnosis and treatment straightforward, thus leading to an improved quality of life of affected patients.

This case report illustrates a rare complex of symptoms leading to limited mouth opening in a young woman. The 28-year old suffered from a progressively limited mouth opening over several years that finally resulted in restricted alimentation and made dental treatment impossible. Clinical findings suggest a structural alteration, including a hyperplastic mandibular angle and marked hypertrophy of the masseter muscle. Further radiologic investigations reveal a thickened aponeurosis of the masticatory muscles and hyperplastic coronoid processes that are not interfering with the zygomatic bone. Primary therapeutic options for such conditions are mainly surgical, including reduction of the masseter muscles volume and aponeurorectomy as well as bony reductions, such as coronoidectomy and mandibular angle reduction. With this treatment, the outcome and prognosis are good. Long-term results depend on concomitant physical therapy. A uniform nomenclature for this condition is yet lacking and propositions such as “masticatory muscle tendon-aponeurosis hyperplasia” have been made. However, knowledge of this condition and its typical clinical signs can make the diagnosis and treatment straightforward, thus leading to an improved quality of life of affected patients.

Increased resting electromyographic activity (EMG), reduced EMG during maximum voluntary clenching, and a shift to lower frequencies of the mean/median power frequency (MPF) of the EMG power spectrum have been reported for patients with temporomandibular disorder pain. It is unclear, however, whether these electrophysiological phenomena can be correlated with symptom improvement during the follow-up of myofascial pain patients in treatment. The objective of this study was to monitor the therapeutic effects of two different splint concepts (standard method and a complex splint procedure assisted by transcutaneous electrical nerve stimulation, TENS) for a period of 12 weeks, by use of clinical outcome criteria and EMG recordings. We tested the hypotheses that both measures evaluated will change in parallel during treatment and that the different splint concepts will result in no outcome differences between the variables studied. For two randomly selected groups, each containing 20 non-chronic myofascial pain patients, the clinical course after splint insertion was documented over a period of 12 weeks on the basis of pain and pain on palpation ratings, in parallel with EMG recording. Baseline values were monitored for matched healthy subjects. Although there was no correlation between the course of symptom improvement and significant changes in EMG data, MPF differed significantly (p0.05) between healthy subjects and patients. The therapeutic effects of splints of different clinical complexity differed significantly (p0.05) between the patient groups, in favor of the complex oral appliances, and substantial (p0.001) but temporary pain relief was achieved by additional TENS. For non-chronic myofascial TMD pain patients treated with splints, the course of symptom improvement is not paralleled by significant changes in EMG data. MPF can, however, be used to distinguish between healthy subjects and patients. Splints of different clinical complexity differ in their therapeutic effects in non-chronic myofascial TMD patients, and substantial temporarily limited pain relief can be achieved by additional muscle stimulation by TENS.

The third part of this literature review on the clinical relevance of surface electromyography (EMG) of the masticatory muscles summarizes the results of clinical studies in patients with temporomandibular disorders (TMD), preferably randomized controlled trials, examining the impact of changes to the dynamic occlusion. Clenching in left and right laterotrusive positions results in decrease in EMG activity of masseter and temporalis muscles on both working and non-working side. Masseter muscle exhibits largely uniform bilateral activity in laterotrusive positions, independent of canine guidance or group function with and without non-working side contacts. There is a dominance of temporalis muscle activity on the working side and, in case of posterior contacts and balancing contacts, temporalis muscle activity increases and changes from an unilateral to a symmetrical pattern.

We are currently developing new software for simultaneous visualisation and analysis of computerized recorded masticatory function and masticatory muscle activity. With the software, motion data recorded using the Jaw Motion Analyser and EMG data on masseter muscle activity can be uploaded in order to evaluate chewing activity immediately proximal to the occlusal surfaces. The software successfully differentiated between jaw opening and closing movements and filtered out muscle activity peaks, which were graphically depicted in the respective movement trajectories. This tracking strategy made it possible to visualize the movement sectors where chewing forces were effective and to estimate the strength of these forces. In the future, this software should improve our ability to analyze and assess the development of chewing forces. Therefore, it could provide a tool for optimal planning of implant-supported or CAD/CAM restorations.

Therapy of chronic orofacial pain (OFP) is often a challenge since OFP can be triggered by numerous medical conditions. Pulpitis is frequently related to acute OFP, only in rare cases pulpitis elicits chronic OFP e. g. due to a cracked tooth. Hypertrophy of masticatory muscles can also cause pain. While this pathosis is easily diagnosed, hypertrophy of masticatory muscles is challenging to treat.The presented case demonstrates a combination of a cracked tooth and a symtomatic hypertrophy of the masseteric muscle in a 19-year old patient. The patient suffered from diffuse chronic OFP for more than four month. After diagnosis an interdisciplinary step-by-step treatment plan was realized with re-evaluation and adjustment.After physiotherapy and medicamentous pain control intramuscular injection of Botolinum toxin type-A was performed with remission of the muscle hypertrophy but only partial success regarding pain control. After root canal treatment of a cracked tooth the patient was free of symptoms.The high degree of specialization in dental medicine requires a multidisciplinary approach for OFP not thoroughly responding to therapy. Stepwise diagnostics and treatments are recommended to clarify the pathology and to address multiple causes of disease.

The aim of the study was to retrospectively analyze the functional outcomes of microneurovascular facial reanimation using the masseteric innervation.Seventeen patients with irreparable facial paralyses resulting from benign lesions involving the facial nuclei (n=14) or Möbius syndrome (n=3) were treated with free muscle flaps for oral commissural reanimation using ipsilateral masseteric innervation and using temporalis muscle transfer for eyelid reanimation. The results were analyzed by a commissural excursion (CE) index and a patient self-evaluation score. The presence of synkinesis was documented. Follow-up ranged from 8 to 48 months (mean 26.4 months).Normalization of the CE index could be observed in 8 out of 17 patients (47%), an improvement in 7 out of 17 (41%) and failure in 2 out of 17 (12%). A natural smiling response was observed in 10 out of 17 (59%) patients. Patient self-evaluation scores were a level higher than objective indices.Innervation of free muscle flaps with the masseteric nerve for oral commissure reanimation might play an important role in patients with long-standing facial palsy (as in Möbius syndrome). Synkinesis persists for long periods after surgery. However, most of the patients had learned to express their emotions by overcoming this phenomenon. Despite hypercorrection or inadequate correction, patients evaluate themselves favorably.

One of the most demanding areas in plastic surgery is reconstruction of the smile in the setting of facial palsy. A multitude of surgical techniques and approaches have been proposed with variable success rates. The most frequently applied treatment algorithm is a two-stage approach with placement of a cross-facial nerve graft (CFNG) initially and subsequent free functional muscle transfer. As this approach has several limitations, the authors have performed single-stage reconstructions utilising the motor nerve to the masseter as the donor nerve. Four patients underwent this single-stage reconstruction for facial palsy between July 2007 and May 2008. In all patients free functional transfer of the gracilis muscle was performed using the motor nerve to the masseter as the donor nerve. Outcome measures were functional result as well as patient satisfaction. The intraoperative as well as postoperative course was uneventful in all patients. In only one patient we encountered a small area of delayed wound healing which was amenable to conservative treatment. In all patients voluntary contraction of the gracilis muscle was visible after a mean period of 2.5 months. All patients displayed a high level of satisfaction with the functional result. Utilising the motor nerve to the masseter muscle as a donor nerve allows single-stage microsurgical reconstruction of the smile in the setting of facial palsy with reproducible results.

In about 20% of patients with Chiari II malformation brainstem signs and symptoms occur. Ventilatory dysfunction is the main cause of death in these patients. The indication for craniocervical decompression is based on clinical examination because supporting electrophysiological or radiological methods were lacking.In a prospective study the clinical courses of 106 patients were documented during a 3-year period. In addition brainstem diagnostic procedures using the masseter reflex (MR), blink reflex (BR) and early auditory evoked potentials (EAEP) were done. Based on the model of binary logistic regression the odds ratio (OR) of progression over time was calculated.The combination of MR and late BR components showed the highest correlation with clinical findings (OR: 23). The highest predictive value regarding clinical progression over a 3-year period was shown by the combined evaluation of MR, late BR components and EAEP interpeak latency I-V (OR: 17.6). Signs and symptoms had no predictive value.Combined brainstem reflex recordings (MR and late BR components) support the clinical examination. To evaluate the long-term prognosis brainstem reflexes and EAEP recordings should be used.

Different hypotheses of reasons for common incidence of temporomandibular disorders (TMD) and otalgia have been discussed. The hypothesis of this study was, that the high prevalence of otalgia in patients with TMD may result in part from pain in the M. masseter pars prof. or in the temporomandibular joint (TMJ) which, due to the close anatomic neighborhood, can feel like ear pain.[corrected] We retrospectively analyzed the anamneses of 720 of our TMD-patients with regard to main treatment motivation: how many patients quoted "pain in the ear" as main treatment motivation and how many of them had no objective findings in the ear but muscle tenderness of the M. masseter prof. or objective findings in the TMJ. Using all pairwise multiple comparison procedures (Dunn's Method) we compared the frequency of muscle and joint findings in patients with ear complaints to two controls: Tinnituspatients and patients seeking orthodontic treatment.51 of 720 patients quoted ear pain as main treatment motivation. 25 of them (49 %) had findings in the masseter muscle, 9 (18 %) in the joint and 15 (29 %) had findings in both the joint and the muscle. The frequency of findings in the controls was significantly (p0.001) lower.A significant fraction of patients seeking treatment due to pain in the ear have no findings in the ear, but in the TMJ and in the masseter muscle.

Masseteric hypertrophy is a unilateral or bilateral enlargement of the masseteric muscle of various aetiologies. The therapeutic options range from solely conservative measures, especially in functionally induced abnormalities, up to surgical ablation of the muscle. The presented study evaluates the application of botulinum toxin serotype A for the treatment of masseteric hypertrophy.Between June 2000 and August 2004 seven patients with a unilateral and one patient with a bilateral manifestation of the condition were treated by an injection of botulinum toxin.A significant improvement of facial asymmetry caused by chemodenervation and following reduction of the hypertrophic muscle mass could be achieved in all cases. Complications during the injection, side effects, signs of intoxication, and therapy failure were not observed.The results of this treatment series show in agreement with the reports in the literature that the application of botulinum toxin can be currently considered as the therapy of choice in masseteric hypertrophy.

The individual jaw position is determined by the masticatory muscle among other factors. Before surgical treatment of malocclusions, thorough evaluation of the muscles is required to estimate the relapse risk.By means of computer tomography, lateral radiographs of the skull and denture models, the relationships between morphological parameters of the masticatory muscles and the jaw bone were analyzed. Furthermore, possible causes for the extent of the malocclusion are described.A patient group with deep overbite was found to have significantly higher muscle densities (measured in Hounsfield units [HU]) in the medial pterygoideus muscle (59.89 +/- 3.91 HU to 48.94 +/- 4.14 HU, p0.01), masseter muscle, and genioglossus muscle (p0.05) in comparison to open bite patients. Significant differences of the muscle cross-section were measured in the masseter muscle between patients with retroclined maxillary incisors and with an open bite (5.4 +/- 0.7 cm (2) to 3.8 +/- 0.4 cm (2), p0.05).The results show a correlation between different jaw positions and masticatory muscles. They also suggest that the function of each muscle may be different. Additional examinations of the muscle structures are required for verification of the influence of the masticatory muscles on facial morphology.

Patients with functional disorders of the temporomandibular apparatus often show painful myogelosis, especially of the masseter muscle. The cause is hypertonia of the affected muscle. The aim of the presented single-blinded clinical trial was to analyze the effects of low-energy extracorporeal shock waves on patients with pain sensitivity in this region. Participating in the trial were 50 patients with painful, palpable and sonographically evident myogelosis of the masseter muscle. Half of the patients received a single application of 250 impulses of 0.04 mJ/mm2. The second half received an equivalent placebo treatment with the shock-wave impact being inhibited by a neopren insert. It was shown that in 64% of the patients significant alleviation of pain with palpable and sonographically evident softening of the myogelosis could be achieved. In 40% of the patients the therapeutic result could be conserved over a period of 2 weeks. The difference from the placebo group was statistically highly significant. ESWT is thus an easy-to-use, non-invasive method of initial pain therapy for patients with functional disorders. To preserve the long-term therapeutic result, additional functional therapy is nevertheless necessary.

Usually malignant pleural mesothelioma causes pain and dyspnoea due to local invasion of the chest wall and compression of the lung. Distant metastases rarely cause symptoms. We report on a patient with an epithelial subtype of malignant pleural mesothelioma who presented himself after chemo- and immunotherapy with shortness of breath and loss of weight due to a temporo-mandibular joint and a new nodular shadow in the contralateral lung. The prior diagnosis of an epithelial subtype of pleural mesothelioma was confirmed histologically in a pleural biopsy as well as in the resected orofacial metastases.

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.

The purpose of this study was to investigate the correlations between malocclusions and the electromyographic activity of the orofacial muscles as this activity reveals itself through multi-channel, simultaneous recording of surface potentials from the masseter muscle. Thirty adults with class II or class III malocclusion formed the study's patient base. Surgical correction of the anomaly was planned for all patients. Ten patients served as the control group. In addition to the standard diagnosis, EMG were recorded during various stress situations such as maximal intercuspidations, chewing, swallowing, and mandible protrusion. We obtained a so-called "myomap" by means of the simultaneous multi-channel recording of the surface potential of the right masseter. Comparison of the EMG revealed a higher activity from the masticatory muscles in the class II cases than in the class III cases. The analysis of the masseter excitation pattern brought to light interesting differences. A higher activity on the lower margin of mandible in the area of the superficial part of masseter was found in the class II cases, whereas contrary to this an increase in EMG activity was found above the deep part of masseter in class III cases. The differing distribution of excitation of the 2 parts of the muscle in class II and class III malocclusions confirms the correlation between muscle function and morphology.

The study presented here was conducted for the purpose of investigating the possible relationship of masseter muscle size and activity to facial morphology. The study examined 50 adults, 25 males and 25 females, by means of electromyography, ultrasonography, and facial photography. The following results were obtained. There was considerable variation in masseter muscle activity and size both between the 2 groups and among individuals in each group. Partly there were strong differentiation's between the males and the females. The interrelationships between masseter muscle activity and size and facial morphology in both groups were generally weak, however, the links were more discernible in the women than in the men. Female subjects with thin faces and large mandibular planes had reduced masseter thickness, whereas women with a small anterior facial height index displayed when relaxed less masseter muscle activity and a smaller masseter width.

Changes in growth dimension and growth direction in three to four week old rabbits were studied cephalometrically after surgically repositioning the anterior part of the superficial masseter muscle dorsally to the angle of the mandible (n = 14). Only a sham operation was performed on 13 animals. Twelve months after the procedure the lower jaws were taken out and cleaned by boiling. X-rays were taken of the right and left part of the mandible. All x-rays were measured cephalometrically and the measurements evaluated statistical (alpha = 0.05) with the U-test (Mann/Whiteney). We found a statistically significant shorter mandible and an enlargement of the gonion angle, which indicate a vertical growth direction. The processus condylaris was unchanged. It can be assumed that the growth of the mandible can be altered permanently by muscle reposition, especially in cases with dysmoysis, a term in the literature first proposed by Eschler.

Retrospective analysis of trigeminal nerve evoked potentials in 40 consecutive patients, most of them with traumatic nerve lesions, showed that in 12 cases no trigeminal nerve SEP were obtainable, and 11 of the remaining 28 patients had normal trigeminal nerve SEP. Therefore the jaw-opening reflex was investigated as a potential tool for electrophysiologic analysis of facial sensory disturbances. The jaw-opening reflex was investigated in 60 healthy subjects (31 female, 29 male) aged 23-82 years. It was elicited by electrical 0.1 ms square wave pulses delivered to the lower and upper lips and to the infraorbital region on either side at a rate below 1 per 5s. The EMG responses were recorded from the bilateral masseter and temporalis muscles at a moderate voluntary activation. Under these conditions, the jaw-opening reflex reveals itself as two inhibitory pauses of the ongoing EMG on both sides, the onset latency of the first EMG-suppression being 10-15 ms, and of the second 35-50 ms. Particular attention was paid to the stimulus strength at threshold (TR) to evoke the jaw-opening reflex. We found that the jaw-opening reflex was constantly evoked by weak stimuli applied to the 2nd and 3rd trigeminal branches. Bilateral reflex responses with unilateral stimulation were a regular finding. The reflex responses increase with increasing stimulus strength (Fig. 1). Moderate to forcible activation of the jaw closing muscles is a prerequisite for optimum recordings of the jaw-opening reflex (Fig. 2).(ABSTRACT TRUNCATED AT 250 WORDS)

The masseter and blink reflexes were investigated in 100 patients with internuclear ophthalmoplegia due to multiple sclerosis (58 patients) or lacunar brainstem infarction (42 patients). In unilateral internuclear ophthalmoplegia, 38 of 60 patients (63.3%) had masseter reflex abnormalities, two patients (3.3%) showed changes of the blink reflex R1 component, and 13 patients (21.7%) combined alterations of the masseter reflex and the blink reflex R1 component. 46 (86.8%) of these 53 patients with electrophysiological abnormalities had unilateral changes, which were ipsilateral to the medial longitudinal fasciculus lesion in 42 patients (91.3%). In bilateral internuclear ophthalmoplegia, 24 of 40 patients (60.0%) had abnormalities of the masseter reflex, two (5.0%) showed changes of the blink reflex R1, and nine (22.5%) combined alterations of the masseter reflex and the blink reflex R1 component. 20 (57.1%) of these 35 patients with electrophysiological abnormalities had bilateral changes. Thus, masseter reflex abnormalities indicating midbrain lesions were seen in 63.3% and 60.0%, respectively, of unilateral and bilateral internuclear ophthalmoplegia. Blink reflex R1 component changes with or without impairment of the masseter reflex indicating rostral pontine to midpontine lesions occurred in 25.0% and 27.5%, respectively. These figures correspond to the results of postmortem examinations and to theoretical considerations based on the length of the medial longitudinal fasciculus.

In 20 healthy volunteers 16-channel surface electromyograms were monopolarly recorded from the right and left masseter muscle during defined functional conditions (force-constant bite, right and left hand side, 196, 333, 530 N chewing force, during a compensation of a load directed from a frontal or a lateral position to the mandible (20, 49, 69 N), during rest position of the mandible). The EMG curves were quantified by the calculation of spectral EMG-parameters (FFT). With respect to the muscle a topographic oriented representation of the myoelectrical activity was realised by a mapping of spectral EMG-parameters. The monopolarly recorded EMG activities significantly differed between the 16 electrode positions (topographic EMG distribution pattern). During the several examination conditions of the masseter muscle different topographic distribution pattern of the myoelectrical activity were found. Moreover, the total EMG power between the muscle functions differed too. The level of the load influenced the spectral EMG power as well as, partly, the topographic EMG distribution pattern.

Cysticercus bovis s. inermis, the larvae phase of Taenia saginata is still widely spread. Many reasons are at the origin thereof, e.g. incomplete destruction of the eggs of Taenia saginata during the waste water purification process and differing meat inspection practises. In an area with the same environmental and animal breeding and fattening conditions a yearly average of 6.49% infestation is found in one slaughterhouse, whilst the yearly average in a neighbouring slaughterhouse is 0.93%. The masseter muscles are the main site of infestation. The meat inspection legislation contributes to the infestation with tape-worms in man because of the weakening of the official inspection procedures.

We report on a 29-year-old male patient, who presented at our outpatient clinic with a 6-year history of progressive swelling of the right cheek. Contraction of the masseter muscle increased the swelling. MR-Imaging revealed a tumor measuring 2 x 3 cm, which was located within the masseter muscle. The histological diagnosis was infiltrating lipoma, which to our knowledge has not been described in this area before. This particular type of lipoma is extremely rare in the head and neck. The diagnostic and therapeutic management of infiltrating lipoma is discussed, and guidelines for adequate follow-up suggested. In addition, the authors review other sites of this tumor and describe its histological characteristics and differential diagnosis.

In 20 healthy volunteers, a bilateral masseter silent period (Mass SP) was constantly evoked by stimulating the mental nerve (latency: x = 13.95 +/- 4.3 ms) and cervical plexus (latency: x = 20.2 +/- 3.7 ms). This was also the case with median nerve stimulation (latency: x = 54.4 +/- 13.1 ms) in 19 of the 20 subjects. Utilizing magnetic stimulation of the lumbal roots, the Mass SP was elicited in 3 of 10 subjects and showed marked habituation. No Mass SP was observed with stimulation of the long nerves of the lower limbs. The central loop of the reflex represents a stable connection between the spinal cord cervical region and the trigeminal motor nuclei. The Mass SP may be abolished in circumscribed brainstem lesions and thus may serve for localizing lower brainstem involvement.

Malignant hyperthermia (MH) may occur, when a genetically predisposed individual or pig (MHS) is exposed to triggering agents. The increase in free, ionized sarcoplasmic calcium inducing the vicious circle of MH is believed to result from calcium-induced release with volatile anaesthetics, and from depolarization-induced calcium release with succinylcholine (SCH). The administration of SCH to susceptible humans or pigs frequently produces an increase in masticatory muscle tone. This hitherto ill-defined phenomenon is referred to as "masseter spasm" (MS). We have attempted to elucidate the pathophysiology of MS in a porcine model. METHODS. After the protocol had been approved by the state authorities, 6 MHS pigs were investigated. The pigs were mixed breeds (German Landrace and Dutch Pietrain) and were 9 +/- 1 weeks old with an average body weight of 25.5 kg. Premedication consisted of intramuscular injection of azaperone, 7.5 mg.kg-1. Anaesthesia was induced with piritramide, 1.2 mg.kg-1, administered via a cannulated ear vein. Subsequent to laryngoscopic endotracheal intubation, neuromuscular blockade was achieved with 4 mg pancuronium. Ventilation was set at 12 breaths per minute and adjusted to maintain an end-tidal CO2 concentration of 4.7% by adapting the tidal volume (PhysioFlex). Anaesthesia was maintained with piritramide, 2.25 mg.kg-1.h-1, pancuronium, 0.4 mg.kg-1.h-1, and N2O (60% in O2). Instrumentation included an arterial line, a central venous line, and a fiberoptic pulmonary artery catheter (Oximetrix). Masticatory muscle tone (MMT) was assessed with an intermolar balloon, connected to a pressure transducer and calibrated to zero prior to SCH administration. As a reference variable for effects produced by SCH, intraocular pressure (IOP) was measured manometrically in the anterior chamber. After stabilization of haemodynamic variables, the neuromuscular blockade was allowed to wear off. After recovery of the evoked masseter electromyogram, a paralyzing dose of pancuronium was administered (0.5 mg.kg-1). When paralysis was complete, SCH was administered (1.5 mg.kg-1), followed a few minutes later by dantrolene infusion (5 mg.kg-1 over 10 min). RESULTS. The administration of SCH was followed by clinically unequivocal MH episodes in all pigs, indicated by an increase in oxygen uptake (VO2; PhysioFlex; Fig. 1) and end-tidal CO2 concentration and a decrease in oxygen saturation of mixed venous blood (svO2; Fig. 2). Despite complete neuromuscular blockade (monitored with EMG), SCH produced an increase in MMT in all pigs which was reversed by dantrolene (Fig. 3). The time course of MMT paralleled that of IOP, suggesting a similar underlying mechanism. DISCUSSION. Succinylcholine is a trigger of MH in susceptible individuals; onset of the syndrome may be associated with "masseter spasm". SCH increases extraocular muscle tone, probably by means of stimulating multiply innervated fibers; the resulting IOP increase is not prevented by competitive neuromuscular blockade. The existence of multiple innervated fibers has also been shown in muscle spindles in the deep layers of the masseter, with their stimulation resulting in elevation of the jaw. We speculate that the increases in MMT and IOP observed in this study reflect the same process, i.e. a motor response, initiated by SCH-induced stimulation of the intramyocellular contractile system of multiply innervated muscle fibers, that is independent of neuromuscular transmission. Triggering of MH with SCH despite complete neuromuscular blockage suggests a mechanism other than depolarization-induced calcium increase. And, for the semantics, according to neurological terminology MS should be referred to as contracture not as spasm.

With the aid of bipolar surface electrodes, the electromyographic activity of the anterior temporal and the superficial masseter muscles were recorded bilaterally and evaluated by counting the integrated potentials and mean power frequency using Fourier's analysis. A comparison between 17 patients with myofacial pain dysfunction (average age 21.3 years) and a group of 20 controls (average age 20.5 years) revealed a significantly greater activity in patients with pain syndrome, while no significant inter-group difference in mean power frequency was seen. The differences in the level of activity between the right and left sides in the control group were significantly smaller than in patients with pain dysfunction. An investigation of measures aimed at reducing the right/left asymmetry in a further 14 patients with pain dysfunction revealed the practice of "maximum occlusion with feedback" to be the most effective measure.

A method for the primary reconstruction of the posterior oral cavity following T2 and small T3 tumor surgery is described. The combination of a masseter flap with a cranially pedicled intraoral buccal transposition flap results in a double layer for the repair of defects. Because of its simplicity and hence a shorter operation time, this functionally satisfactory reconstructive procedure should be used particularly for high-risk patients.

The m. masseter crossover flap according to Tiwari combined with a buccal mucosa transposition flap represents an excellent technique for a primary two-layered closure of defects due to surgical removal of T2- and small T3-tumors of the posterior part of the lateral floor of the mouth, the posterior edge of the tongue, the retromolar trigone, the soft palate and the tonsilar region. Especially advantageous are the low postoperative morbidity, the low rate of postoperative complications, and good functional and cosmetic results. The surgical expenditure is little and recommends the use of this technique also in patients with reduced operability.

The present electromyographic investigations, which were carried out by patients with full dentures should show if the activity-situation of the masticatory muscles would change either using a new full denture without equilibration or using new full dentures with equilibration. Other questions were: Is it possible to classify the patients in such, who prefer the masseter muscles or the temporalis muscles during mastication? Exist a correlation between the preferred masticatory side and an increased activity of the same side masticatory muscles?

On the basis of Discrete Hilbert Transformation spectral parameters for dynamic EMG analysis can be introduced. Within analysis intervals which are used in the same manner as in spectral analysis, the momentary power of EMG frequency bands can be computed as time series of the same interval duration. A close connection exists between momentary power and the current phenomenology of power spectral analysis because the momentary power of a defined frequency band can be seen as the exact dynamic equivalent of the corresponding mean power value deduced from the power spectrum. A multichannel EMG recording (greater than or equal to 16 channels) makes the representation of the topographical distribution of the spectral parameter by a coloured map possible. Additionally, the momentary power can be used to calculate map sequences. In this way, changes of EMG activity can be quantified by map sequences of an arbitrary time resolution. By calculation of momentary frequency via DHT an artefact detection scheme for ECG interference can be suggested. A completion of this methodology can be carried out by applications of adaptive filtration procedures. Using this concept of EMG processing, a new and common methodical basis of EMG power spectral analysis can be introduced.

A 5-year-old boy with acute lymphatic leukemia in remission developed signs of malignant hyperthermia (MH) during general anesthesia for removal of a central venous access port. The anesthetic procedure for implantation of the port 17 months before had been uneventful despite use of the same triggering agents, halothane and succinylcholine. Meanwhile, the patient had received chemotherapy (COALL-03-85). The first sign of MH was masseter spasm following succinylcholine; then tachycardia, acidosis, myoglobinuria, and CPK elevation (8953 IU) appeared. There was only moderate temperature elevation to 37.8 degree C. Rapid improvement and complete recovery occurred after dantrolene i.v. The patient's father was found to have undiagnosed muscle pain and an elevated CPK level. An in vitro contracture test with halothane and caffeine revealed susceptibility to MH and supported the patient's diagnosis and genetic predisposition. Referring to several other cases in the literature concerning MH in patients with lymphomas and leukemias, a possible correlation between the two diseases is discussed. As the MH crisis in our patient was most probably genetic in origin, a common acquired cause such as a viral infection seems less probable. We do not believe the chemotherapy our patient received between the two anesthetics was the cause since about one-half of the patients in the literature had not had chemotherapeutic pretreatment at the time of the MH crisis. We believe that a common genetic predisposition is the most likely link between the two diseases. In any case, patients with leukemias and lymphomas should be monitored very carefully for symptoms of MH.(ABSTRACT TRUNCATED AT 250 WORDS)

The coordination of masseter muscle contraction is inseparably wrapped up in the occlusal elements. This study measured bilaterally the masseter muscle activity of 22 subjects without temporomandibular joint disease. The EMG recordings of the left and the right masseter muscles were repeated 20 times to test symmetry, reproducibility and appearance of silent periods. In 6 subjects the beginning of the muscle contraction showed laterality characteristics depending on handedness. The complex processes of recorded mandibular movements showed more biological variations than the recording patterns of occlusal indicator foils may disclose. That indicates the possibility of pseudocontact markings. The occluding surfaces therefore should allow free mandibular movements.

A method for the primary reconstruction of soft palate after radical tumor excision is described. By combination of a cranial pedicled pharynx flaps and a cranial pedicled intraoral buccal transposition flap is it possible to close the resulting defect in a double layer. In additional resection of the combination of the method with a M. masseter-transposition flap is possible. By the method it is possible to have a satisfactory reconstruction of swallowing and speech functions with only small operative troubles.

This study was focussed on the effects of changes in interocclusal clearance on the activity of oral muscles. Two types of occlusal splints were incorporated in 20 subjects without TMJ-syndrome. Their muscle reactions were recorded electromyographically in the masseter muscle. The results show 5 groups of muscle reaction correlated with the mean postural face height. The changed height of the postural position has a significant influence on the control pattern of the masticatory system.

A sonographic method for diagnosis, follow-up and quantification of normal and hypertrophied masseter muscles is presented. This technique lends itself to diagnosis of macroscopic structural alterations of the muscle as well as tumors in the vicinity. Functional or microscopic tissue changes like trigger points in myofacial pain-dysfunction syndrome cannot be detected sonographically.

Muscle biopsies of the mandible adductors of the Wistar rat (Rattus norvegicus Berkenhout) have been analyzed enzyme-histochemically for the investigation of the postnatal development (42.-126. d post partum) of their muscle fibers with special regards to the fiber types. The following methods have been used in this investigation: myofibrillar adenosine triphosphatase (ATP-ase) with different pre-incubations, Sudan black B (triglycerides), periodic acid-Schiff reagent (PAS) (glycogen), Gomori modified Trichrome staining. Quantitative analysis of muscle fibre-type composition and muscle fibre size was done from different regions of muscle sections. Estimation of the fiber size was carried out by measuring the minimum diameter of each type of muscle fibre.