Acoustic myography, electromyography and bite force in the masseter muscle

Acoustic myography (AMG) offers some advantages over electromyography (EMG) in certain circumstances, but the use of AMG on the jaw-closing muscles has not been fully tested. The purpose of this study was to examine the relationship between AMG, EMG and force in the masseter muscles of nine healthy male subjects. The AMG was recorded using a piezoelectric crystal microphone and the EMG was recorded simultaneously with surface electrodes. Force was recorded between the anterior teeth with a strain-gauge transducer. Analysis showed that Pearson's correlation coefficient was 0.913 for force/AMG and 0.973 for force/EMG in all subjects, indicating a linear relationship between force, AMG and EMG at the four different force levels tested (25-75% of maximum). It is apparent that AMG may be used as an accurate monitor of masseter muscle force production, although some care is required in the technique.     

Craniomandibular disorders, edentulousness and the clinically estimated size of the masseter muscle

We report on an aphakic 30 year-old patient who underwent penetrating keratoplasty on his only functioning eye. On the first day after the operation he developed a total choroidal detachment due to suprachoroidal bleeding. The patient had no sense of orientation. Vision decreased to faulty light perception. One week postoperatively a posterior sclerotomy was performed in order to drain the suprachoroidal blood. Via a paracentesis the globe was pressurized with hyaluronic acid. The following day the suprachoroidal blood had almost disappeared. The retina had become reattached. During a follow-up period of 2 years the visual acuity remained 20/30.     

A metabolism study of human masseter muscle by 31P magnetic resonance spectroscopy during long periods of exercise and recovery

The metabolism of the human masseter muscle was investigated using phosphorus (31p) magnetic resonance spectroscopy (MRS) during long periods of exercise and recovery. Eleven subjects aged 19 to 28 yr were examined by 31p MRS during four consecutive periods of 13 min each: rest, exercise, recovery 1 and 2. For each subject, a biting force equal to 20% of maximum voluntary biting force was applied and controlled during the exercise period to produce maximum fatigue. 31p MR spectra were localized from a 24 cm3 volume of interest using an image selected in vivo spectroscopy (ISIS) sequence and a 6 cm diameter surface coil placed on the left masseter. Compared to the resting level, the phosphocreatine (PCr) content decreased by 26% during exercise, while the inorganic phosphate (Pi) concentration increased by 65%. During the two recovery periods, the Pi content remained decreased compared with the resting level by 36% and 30%, respectively. The Pi/PCr ratio was increased from 0.30+/-0.04 at rest to 0.63+/-0.13 during exercise while the adenosine triphosphate (ATP)/Pi ratio was decreased. The pH decreased from 7.02+/-0.03 to 6.93+/-0.04 during exercise and returned to control level (7.09+/-0.08) only during the second recovery period. These results suggest that the masseter muscle is characterized by high ATP turnover and, therefore, high oxidative phosphorylative activity in agreement with its constitution of predominantly fatigue resistant type I fibers.     

Relationship between mandibular position and the coordination of masseter muscle activity during sleep in humans

Although bruxism has been regarded as having a possibly important role in the aetiology of craniomandibular disorders, the activity of masticatory muscles relative to mandibular position during sleep grinding as recorded by electromyography (EMG) has not yet been clarified. Surface EMGs of the bilateral superficial masseter muscles were recorded simultaneously with mandibular position during sleep from 12 volunteers for three consecutive nights. The incidence of two mandibular positions were recorded with magnetic sensors for both left- and right-sided mandibular grinding. One of the mandibular positions was the canine edge-to-edge position, and the other was the midpoint between the intercuspal position and the canine edge-to-edge position. The mode of the working/ balancing activity ratio ranged from 1/10 to 2/10, showing the marked predominance of balancing side masseter muscle activity during sleep grinding. During sleep grinding, EMG bursts of masseter muscle were observed mainly with mediotrusive mandibular movement from the canine edge-to-edge position. From the results of the present study, it is suggested that muscular dynamics during sleep are unique compared to that during voluntary clenching, and exert a greater mechanical load to the balancing side temporomandibular joint.     

Effect of muscle relaxation splint therapy on the electromyographic activities of masseter and anterior temporalis muscles

The purpose of this study was to compare the effectiveness of splint therapy on the electromyographic activity of masticatory muscles (anterior temporalis and masseter) before and after the application of a muscle relaxation splint. Electromyography recordings from the masseter and anterior temporalis muscles were analyzed quantitatively during maximal biting in the intercuspal position both before and after treatment without a splint. Fourteen patients whose chief complaint was masticatory muscle pain were selected for the study. After the initial evaluations muscle relaxation splints were applied, and the patients were instructed to use the splints for 6 weeks. Surface electromyographic recordings were taken from each patient before the beginning of clinical therapy and after 6 weeks of wearing the splints. The data obtained were analyzed through paired sample t tests and Wilcoxon's signed rank tests. The results of the study were as follows: (1) the electromyographic activity of the two muscles during maximal biting was not markedly changed after the muscle relaxation splint was used; and (2) the changes observed in electromyographic activity of the involved and noninvolved sides were insignificant as well.     

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

Recently, several systems of topical antibiotic administration have been investigated. Most systems use sustained release devices to obtain high levels of antibiotics in the deepened periodontal pockets. Metronidazole and tetracycline can be administered without causing systemic side-effects. All systems summarized in this article are to be used after scaling and root planing of the diseased sites to increase the effect of the mechanical treatment.     

The effect of pain from orthodontic arch wire adjustment on masseter muscle electromyographic activity

Pain has been shown to have an effect on muscle activity even when it does not originate in the muscle itself or in the related joint. The effect of pain from arch wire adjustment on jaw muscle activity is unclear. This study systematically evaluated the effects of orthodontic arch wire adjustment pain on masseter electromyographic (EMG) activity and on the swallowing threshold. The EMG recordings were made on 22 subjects (ages 11 to 15) under three conditions: chewing five peanuts (10 seconds), watching TV chewing gum (15 minutes), and watching TV with no gum (15 minutes). An arch wire adjustment or placebo adjustment was then made. Subjects returned after 48 hours, and the EMG measurements were made under the same conditions. After 3 weeks, subjects received arch wire or placebo treatment in a crossover design with identical recording procedures. The EMG levels while chewing peanuts decreased in 18 of 22 subjects after treatment, compared with 9 of 22 subjects after the placebo. While watching TV with gum, the EMG levels of 20 of 22 subjects decreased after treatment, compared with 9 of 22 subjects after the placebo. The number of chewing strokes before swallowing increased significantly after treatment compared with after placebo. The results suggest that orthodontic pain on teeth tend to reduce muscle activity during function.     

The influence of gender on the masseter electromyographic jaw-jerk reflex in young human subjects

The purpose of this study was to investigate the effect of gender on the masseteric jaw-jerk reflex, evoked in a sample of nine male and nine female young subjects. Electromyographic jaw-jerk recordings elicited by chin-taps in the relaxed masseter muscle of the preferred chewing side, were obtained using a computerized recording and analysis system. In both groups, a jaw-jerk reflex was recorded in 95.56% out of the total number of chin-taps. The mean latency was significantly shorter in the females (5.75 ms) than in the males (6.14 ms, P = 0.0045), while the amplitude of the reflex was significantly higher in the females (P = 0.0005). No significant differences were found in the mean duration between males (6.86 ms) and females (6.73 ms). It was concluded that sex variation should be taken into consideration in the interpretation of the jaw-jerk reflex.     

Biomechanical topography of human articular cartilage in the first metatarsophalangeal joint

The objective of this study was to provide a map of cartilage biomechanical properties, thickness, and histomorphometric characteristics in the human, cadaveric first metatarsophangeal joint, to determine if normal articular cartilage was predisposed topographically to biomechanical mismatches in articulating surfaces. Cartilage intrinsic material properties and thickness were obtained from seven pairs of human, freshly frozen, cadaveric, metatarsophalangeal joints using an automated creep indentation apparatus under conditions of biphasic creep. Eight sites were tested: four on the metatarsal head, two on the proximal phalanx base, and one on each sesamoid bone to obtain the aggregate modulus, Poisson's ratio, permeability, shear modulus, and thickness. Cartilage in the lateral phalanx site of the left metatarsal head had the largest aggregate modulus (1.34 MPa), whereas the softest tissue was found in the right medial sesamoid (0.63 MPa). The medial phalanx region of the right joint was the most permeable (4.56 x 10(-15) meter4/Newton-second), whereas the medial sesamoid articulation of the metatarsal head of the left joint was the least permeable (1.26 x 10(-15) meter4/Newton-second). Material properties and thickness are indicative of the tissue's functional environment. The lack of mismatches in cartilage biomechanical properties of the articulating surfaces found in this study may be supportive of clinical observations that early degenerative changes, in the absence of traumatic events, do not occur at the selected test sites in the human first metatarsophalangeal joint.     

Local anaesthetic bupivacaine alters function of sarcoplasmic reticulum and sarcolemmal vesicles from rabbit masseter muscle

The effects of local anaesthetics, bupivacaine and lidocaine, on Ca2+ flux behaviour of sarcoplasmic reticulum and on sarcolemmal functions were studied in the rabbit masseter muscle. The experiments were performed on sarcoplasmic reticulum and sarcolemmal vesicles prepared at 1 to 10 days after injection of local anaesthetics or saline into masseter muscle as well as on sarcoplasmic reticulum vesicles prepared from non-treated rabbits (for assessment of the effect on in vitro incubation with local anaesthetics). Bupivacaine potently reduced the efficiency of active sarcoplasmic reticulum Ca2+ transport as evaluated by coupling ratio (Ca2+ transported/ATP hydrolyzed, in the presence of oxalate) at 3 days after the injection; there was only a slight degree of uncoupling of Ca2+ transport from ATP hydrolysis with lidocaine injection. Bupivacaine but not lidocaine, at 3 days after injection, decreased both the apparent permeability of sarcoplasmic reticulum vesicles to Ca2+, determined by measuring net efflux of Ca2+ after stopping pump-mediated fluxes, and the steady-state Ca2+ load in sarcoplasmic reticulum, but had no effect on overall turnover of the Ca2+ATPase. The effects of bupivacaine on apparent sarcoplasmic reticulum Ca2+ permeability and steady-state Ca2+ load were inhibited by a Ca2+ antagonist verapamil. The reduction of Ca2+ uptake of sarcoplasmic reticulum and the protective effect of verapamil were reproduced in unfractionated homogenates prepared at 3 days after bupivacaine injection. In vitro exposure of sarcoplasmic reticulum vesicles to bupivacaine (0.5 to 50 mM) reduced steady-state Ca2+ load in a dose-dependent manner. The observed effect elicited by bupivacaine (25 mM) was partially protected by procaine, an inhibitor of Ca2(+)-induced Ca2+ release from sarcoplasmic reticulum, or by specific closure of the sarcoplasmic reticulum Ca2+ release channel by ryanodine, suggesting the possibility that in vitro exposure of sarcoplasmic reticulum vesicles to bupivacaine may produce an increase in apparent permeability of sarcoplasmic reticulum to Ca2+. In sarcolemma, bupivacaine reduced Na+,K(+)-ATPase and Na(+)-Ca2+ exchange activities at 3 days after injection; the effects on sarcolemmal vesicles were prevented by verapamil. These results suggest that although the effects elicited by bupivacaine injection and the in vitro exposure to bupivacaine on steady-state Ca2+ load of sarcoplasmic reticulum vesicles were similar, the membrane properties of the vesicles from bupivacaine-treated masseter muscles and those from normal untreated muscles may not be the same, which indicates that pure bupivacaine effect is due partly by an effect on ryanodine- and procaine-sensitive Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)     

Intraoperative localization of functional regions in the sensorimotor cortex by neuronavigation and cortical mapping

Surgery of lesions within the central region requires exact intraoperative anatomical orientation and knowledge of the position of functional cortical regions to minimize the surgical trauma and to avoid postoperative neurological deficits. We combined somatosensory evoked potential (SSEP) phase reversal and/or cortical electrical stimulation with neuronavigation in 26 patients for localization and visualization of functional cortical areas and their anatomical site in relation to the lesion. After location of the central sulcus by means of SSEP phase reversal, the precentral gyrus was electrically stimulated to detect functional motor regions. Electrode position was documented, and the functional regions were related to the site of the lesion using a specially developed neuronavigation system. In 11 of 15 patients the central fissure was located with SSEP phase reversal. Electrical stimulation yielded motor evoked potentials in 23 of the total 26 patients. The anatomical site of these functional regions and their relation to the lesion were evaluated with the neuronavigation system. The precentral gyrus, central sulcus, and postcentral gyrus could be identified in all 23 cases. The combination of intraoperative electrophysiological mapping and neuronavigation provides safe and reliable localization of the sensorimotor cortex. This technique is a promising tool to minimize the risk of surgically caused sensory and motor deficits.     

Functional mapping of the surface residues of human thrombin

Utilizing site-directed mutagenesis, 77 charged and polar residues that are highly exposed on the surface of human thrombin were systematically substituted with alanine. Functional assays using thrombin mutants identified residues that were required for the recognition and cleavage of the procoagulant substrate fibrinogen (Lys21, Trp50, Lys52, Asn53 + Thr55, Lys65, His66, Arg68, Tyr71, Arg73, Lys77, Lys106 + Lys107, Asp193 + Lys196, Glu202, Glu229, Arg233, Asp234) and the anticoagulant substrate protein C (Lys21, Trp50, Lys65, His66, Arg68, Tyr71, Arg73, Lys77, Lys106 + Lys107, Glu229, Arg233), interactions with the cofactor thrombomodulin (Gln24, Arg70) and inhibition by the thrombin aptamer, an oligonucleotide-based thrombin inhibitor (Lys65, His66, Arg70, Tyr71, Arg73). Although there is considerable overlap between the functional epitopes, distinct and specific residues with unique functions were identified. When the functional residues were mapped on the surface of thrombin, they were located on a single hemisphere of thrombin that included both the active site cleft and the highly basic exosite 1. No functional residues were located on the opposite face of thrombin. Residues with procoagulant or anticoagulant functions were not spatially separated but interdigitated with residues of opposite or shared function. Thus thrombin utilizes the same general surface for substrate recognition regardless of substrate function although the critical contact residues may vary.     

Characterisation and mapping of the human SOX14 gene

The effects of nimodipine, a calcium channel blocker, on noise-induced hearing loss were examined in gerbils. Animals were implanted subcutaneously with a timed-release pellet containing either nimodipine (approximately 10 mg/kg/day) or placebo and exposed to either 102 or 107 dBA noise. Serum levels were tested in two subjects and were in the range known to protect humans from cerebral artery vasospasm and ischemia-related neurologic deficits. Nimodipine and control groups had similar amounts of noise-induced (a) permanent threshold shift; (b) reductions in distortion product otoacoustic emissions; (c) reductions in tuning and suppression of the compound action potential; and (d) loss of outer hair cells. The results suggest that nimodipine, at a dose which results in clinically relevant serum levels, does not provide protection from the effects of moderately intense noise exposures.     

Oxidative capacity of rat masseter muscle after implantation of thyrotropin-releasing hormone microspheres in proximity to trigeminal motoneurones

Earlier work has shown that two important consequences of implanting thyrotropin-releasing hormone (TRH) microspheres near motoneurones within the trigeminal motor nucleus of actively growing rats are increased muscle mass and a darkening of the implant-side masticatory muscles. These phenomena have been associated with altered neuromuscular activity patterns and biomechanical forces that directly influence craniofacial growth and development. Now, whether the implantation of TRH microspheres in proximity to trigeminal motoneurones would affect the oxidative capacity of the implant-side masseter muscles was investigated. Cytochrome C oxidase (COX) assays were carried out for both implant- and non-implant-side masseters of TRH (n = 5) and blank microsphere (n = 6) Sprague-Dawley rats after stereotactic surgery at 35 days of age. Analyses of both groups at 14 days post-implantation revealed that the COX activity levels of implant-side masseters in TRH-implanted rats was significantly (P< or =0.05) greater than that of non-implant-side masseters; rats implanted with blank microsphere exhibited no significant difference between implant- and non-implant-side masseter COX activity levels. The stated null hypothesis was therefore rejected. These data suggest that TRH implants in proximity to trigeminal motoneurones effect increased oxidative capacity of the masseter muscle as measured by COX activity.     

Transcranial Doppler and cortical microcirculation at increased intracranial pressure and during the Cushing response: an experimental study on rabbits

The effect of increased intracranial pressure on the flow velocity of the basilar artery was measured with transcranial ultrasonic Doppler in New Zealand White rabbits under alpha-chloralose anesthesia and artificial respiration. Laser Doppler flowmetry served to study changes of the cortical microcirculation. The results confirm a high inverse correlation of the diastolic flow velocity, the pulsatility index, and the resistance index with the cerebral perfusion pressure (CPP). During acute intracranial hypertension, however, these parameters do not show a good correlation with the local cortical blood flow. The absence of a correlation was evident over a wide CPP range down to values of 35 mm Hg. Only at CPP values below this critical threshold is the microcirculation impaired. The threshold is reached at pulsatility index values of more than 2.0 and at resistance index values of more than 0.8. Therefore, transcranial Doppler indices permit the detection of critical reductions of microcirculatory blood flow. The Cushing reaction occurred with a constant time lag of 5.5 +/- 0.7 seconds after the loss of CPP. The Cushing reaction did not establish systolic blood flow, which remained below the functional threshold, as concluded from the temporary loss of somatosensory evoked potentials.     

Fine mapping of human HOX gene clusters

The chromosome localization of human HOX gene clusters has been reinvestigated by fluorescence in situ hybridization (FISH). Three loci were precisely localized in 7p15.3 (HOXA@), 17q21.3 (HOXB@) and 12q13.3 (HOXC@). The localization of HOXD@ was confirmed to 2q31.     

Somatotopical mapping of the human somatosensory cortex with echo-planar MRI

The somatotopical organization of the somatosensory cortex was analyzed. Echo-planar imaging was used to obtain functional images, and magnetic field strength was 1.5T. Natural stimulation at a frequency of 3 Hz (scrubbing or tapping) was applied to one of the three cutaneous areas: toes, fingertips, and tongue tip. The focal bands which show the significant signal increases were located on the contralateral post-central gyrus, and these changes of signal intensity originate from the cortical parenchyma because there were no major veins in the central sulcus. The focal bands which respond to each stimulation sites were anatomically distinct and located medially-to-laterally in the order of toes, fingertips, and tongue tip.