Showing papers on "Masseter muscle published in 2002"
TL;DR: In this study, edible and well-controlled model foods were developed in order to describe some of the stimulus-response functions of the food-mastication loop and gelatine-based visco-elastic model foods identical in shape and size but differing in hardness were prepared.
Abstract: When food is chewed, sensory feedback adapts the motor program to the characteristics of the food. However, the relationship between the physical properties of different foods and the motor response is poorly understood. In this study, we developed edible and well-controlled model foods in order to describe some of the stimulus-response functions of the food-mastication loop. Four gelatine-based visco-elastic model foods identical in shape and size but differing in hardness were prepared. They displayed reproducible sensory and physical characteristics and were distributed on a wide hardness scale. Electromyographic activity of masseter and temporalis muscles and jaw movements in the frontal plane were simultaneously recorded during mastication in 15 young men with intact dentition and good oral status. Almost all EMG and jaw movement parameters were clearly affected by increasing hardness of model foods. However, it is possible to summarise the results by reducing the number of parameters to three: the number of chewing cycles, EMG activity of any one of the two temporal or the two masseter muscles and the amplitude of the opening mandibular movements. Indeed, these were the best transcriptors of the hardness range of the model foods used in this study. As inferred from these parameter recordings, the food hardness modifications were strongest during the first five strokes, began as early as the first stroke and lasted for the whole sequence.
268 citations
TL;DR: The results of the present experiments show that intramuscular injection of 1.0 M glutamate excites and sensitizes rat masseter muscle afferent fibers through activation of peripheral excitatory amino acid receptors and that glutamate-evoked afferent fiber activity, but not sensitization, is greater in female than male rats.
137 citations
TL;DR: To verify the static neuromuscular equilibrium of occlusion, EMG activity of left and right temporal and masseter muscles was recorded in all patients and the activity index was computed over a maximum voluntary clench test of 3 s.
Abstract: Surface electromyography (EMG) allows the quantification of the occlusal equilibrium in dysfunctional patients, for instance in those with temporomandibular disorders (TMD). Fourteen patients (ten women, four men) with internal derangement type I were selected among the TMD patients referred to a private practice in Milan. A stabilization splint with posterior contacts was made for each patient. To verify the static neuromuscular equilibrium of occlusion, EMG activity of left and right temporal and masseter muscles was recorded in all patients and the activity (ratio between the activities of the temporal and masseter muscles) index was computed over a maximum voluntary clench test of 3 s. Muscular waveforms were also analysed by computing a percentage overlapping coefficient (POC, an index of the symmetric distribution of the muscular activity determined by the occlusion). The total electrical activity was measured by calculating the area under the entire muscular waveforms. In all patients EMG was performed just before and immediately after the insertion of the splint and data were compared by paired Student's t-tests. Overall, the splint reduced the electrical activity of the analysed muscles (P < 0.005) and made it more equilibrated both between the left and right side (larger symmetry in the masseter muscle POC, P < 0.05) and between the temporal and masseter muscles (activity index, P < 0.01).
136 citations
Journal Article•
TL;DR: The results suggest that pain reduction resulting from a noxious stimulus (i.e., needling) may not be specific to the location of the stimulus as predicted by the classical acupuncture literature.
Abstract: Aims: To compare the effectiveness of dry needling in classically recognized acupuncture points ("acupuncture") with dry needling in skin areas not recognized as acupuncture points ("sham acupuncture") in reducing masseter muscle pain in a group of patients with myofascial pain of the jaw muscles. Methods: Eighteen patients were randomly assigned to 1 of 2 experimental groups: Ten patients received acupuncture and 8 received sham acupuncture. A visual analog scale (VAS) was used to measure changes in masseter muscle pain evoked by mechanical stimulation of the masseter muscle before and after the experiment. Results: Both groups showed a statistically significant reduction in VAS pain scores (P = .001). Seven out of 10 acupuncture subjects had a 10 mm or greater VAS reduction in pain, while 4 out of 8 of the sham acupuncture subjects had that great a pain reduction. There was no significant difference between the 2 groups. Conclusion: Both acupuncture and sham acupuncture reduced pain evoked by mechanical stimulation of the masseter muscles in myofascial pain patients. However, this reduction in pain was not dependent on whether the needling was performed in standard acupuncture points or in other areas of the skin. These results suggest that pain reduction resulting from a noxious stimulus (ie, needling) may not be specific to the location of the stimulus as predicted by the classical acupuncture literature.
119 citations
TL;DR: There are sex-related differences in glutamate-evoked jaw muscle activity that are dependent on female sex hormones, and increased glutamate concentrations sensitize the TMJ to noxious chemical stimuli.
70 citations
TL;DR: The hypothesis that activation of nociceptive muscle afferent fibers would be linked to an increased excitability of the human jaw-stretch reflex and whether this process would be sensitive to length and velocity of the stretch was tested.
Abstract: The pathophysiology of painful temporomandibular disorders is not fully understood, but evidence suggests that muscle pain modulates motor function in characteristic ways. This study tested the hypothesis that activation of nociceptive muscle afferent fibers would be linked to an increased excitability of the human jaw-stretch reflex and whether this process would be sensitive to length and velocity of the stretch. Capsaicin (10 μg) was injected into the masseter muscle to induce pain in 11 healthy volunteers. Short-latency reflex responses were evoked in the masseter and temporalis muscles by a stretch device with different velocities and displacements before, during, and after the pain. The normalized reflex amplitude increased with an increase in velocity at a given displacement, but remained constant with different displacements at a given velocity. The normalized reflex amplitude was significantly higher during pain, but only at faster stretches in the painful muscle. Increased sensitivity of the fus...
63 citations
TL;DR: It is suggested that emotional stress induces brux-like activity in the masseter muscle of rats, which was reduced with anti-anxiety drugs.
Abstract: The aim of this study was to further clarify the relationship between emotional stress and bruxism. In experiment 1, 60 male 9‐week‐old Wistar rats were divided into four groups: the emotionally stressed (ES), the emotionally non‐stressed (NS), the electrically foot‐shocked (FSd), and the non‐foot‐shocked (NSd). ES rats were confined in a communication box for one hour a day to observe the emotional responses of neighbouring FSd rats. On days 0, 1, 4, 8, and 12, the electromyographic activity of the ES and NS rats' left masseter muscles was recorded for one hour, three hours after confinement in the communication box. Brux‐like activity appeared in the masseter muscle of the ES group on days 1, 4, 8, and 12, but not in the NS group.
In experiment 2, 36 male Wistar rats, 9 weeks old, were divided into three groups: emotionally stressed rats treated with an anti‐anxiety drug (DES), emotionally stressed rats treated with saline as a vehicle (VES), and 24 FSd rats. Stress and EMG procedures were the same as those in experiment 1. Brux‐like episodes decreased in DES rats from day 1 and significant differences were found on days 4 ( P < 0.01), 8 ( P < 0.05), and 12 ( P < 0.05), when compared with the VES group. These findings suggest that emotional stress induces brux‐like activity in the masseter muscle of rats, which was reduced with anti‐anxiety drugs.
63 citations
TL;DR: It was concluded that rehabilitation with implant retained mandibular dentures may result in more regular chewing patterns with higher electrical activity of the masseter muscles, thus providing improved chewing function and comfort.
Abstract: The influence of texture of food on the surface electromyographic (EMG) activity of the masseter muscle was investigated in a sample of mandibular implant overdenture wearers. Six experienced denture wearers (mean age 57.8 years) with mandibular overdentures supported by two implants, consented to participate in this study. Fresh raw carrots and peeled apples of similar size and weight were chosen as representing hard and soft food, respectively. The findings were in line with those earlier reported in dentate subjects and complete denture wearers in that harder foods require higher chewing rates, higher EMG activity and higher relative contraction times, accompanied by shorter cycle durations. It was also concluded that rehabilitation with implant retained mandibular dentures may result in more regular chewing patterns with higher electrical activity of the masseter muscles, thus providing improved chewing function and comfort.
59 citations
TL;DR: It was concluded that the effects of the denture adhesive on masticatory functions were observed overall for both groups, and more significant for denture wearers with poor denture-bearing tissues than with good dentures.
Abstract: The purpose of this study was to examine effects of a denture adhesive on masticatory functions for complete denture wearers considering the condition of denture-bearing tissues. Sixteen edentulous subjects wearing well-fitting complete dentures volunteered to participate in this study. According to the condition of denture-bearing tissues, subjects were divided into two groups; “good group” and “poor group”. Maximum biting forces, masticatory performance, and electromyography of the masseter muscle during mastication were recorded with and without a denture adhesive. Durations of chewing burst and cycle, and coefficients of variation for these variables were calculated using electromyography recordings. Data were analyzed by using two-way repeatedmeasured ANOVA and paired t-test in order to assess the effect of the use of a denture adhesive. The use of the denture adhesive increased maximum biting force and provided rhythmic masseter muscle activity during mastication for both groups. Masticatory performance was improved and duration of chewing burst was decreased only for “poor group”. It was concluded that the effects of the denture adhesive on masticatory functions were observed overall for both groups, and more significant for denture wearers with poor denture-bearing tissues than with good denture-bearing tisuues.
57 citations
TL;DR: Experimental tonic pain, either from muscle or from skin, induced bilateral inhibitory effects on the trigeminal laser evoked potentials and brainstem reflex responses and on the subjective ratings of the laser pulses, which could be mediated through the activation of segmental and suprasegmental inhibitory systems that may function interdependently.
Abstract: Cutaneous laser stimulation activates predominantly the A-delta and C mechano-heat nociceptors. Applied to the perioral region, low intensity CO(2)-laser pulses evoke reproducible trigeminal cortical evoked potentials (LEPs). High intensity CO(2)-laser stimuli induce a reflex response in the contracted jaw-closing muscle, the so-called laser silent period (LSP). Both LEPs and LSP provide a useful tool to study the physiology of the trigeminal nociceptive system. In ten healthy subjects we recorded the subjective ratings of the perioral laser stimulation and the trigeminal LEPs and LSP before, during and after homotopic experimental tonic muscle (infusion of hypertonic saline into the masseter muscle) and tonic skin pain (topical application of capsaicin to the cheek). LEPs were recorded from the vertex at two stimulus intensities: low (1.1 x pain threshold, PTh) and high (1.5 x PTh). LSP from masseter and temporalis muscles were recorded bilaterally through surface electromyographic (EMG) electrodes. CO(2)-laser pulses were applied to the perioral region (V2/V3) on the painful and non-painful side. The amplitude of LEPs increased with higher stimulus intensities (P 0.20). The LSP in the masseter and temporalis muscles had similar onset-latency (80+/-5 ms), offset-latency (111+/-5 ms) and duration (31+/-4 ms). Experimental pain had no effect on the onset- and offset-latency (P>0.05). Experimental pain, whether from muscle or from skin, reduced the degree of suppression (P<0.01) and the area under the EMG curve (P< 0.005) of the LSP. The LSP was still suppressed during the post-pain recordings when the skin pain had disappeared (P<0.05). In all experiments experimental tonic pain decreased the subjective ratings of the perioral laser stimulation (P< 0.001). Experimental tonic pain, either from muscle or from skin, induced bilateral inhibitory effects on the trigeminal laser evoked potentials and brainstem reflex responses and on the subjective ratings of the laser pulses. These effects could be mediated through the activation of segmental and suprasegmental inhibitory systems that may function interdependently.
46 citations
TL;DR: A significant correlation between the PPT of the temporalis muscle and the TT of the overlying skin was observed and appeared very reproducible within subjects and did not fluctuate over time.
Abstract: In order to better objectify reported pain and disturbed sensation, psychophysical parameters as pressure pain threshold (PPT) and tactile threshold (TT) have been introduced in pain research. The present study evaluated fluctuations of these parameters, obtained using an algometer (PPT) and von Frey hairs (TT), in relation to fluctuations in female reproductive hormones. Ten students not using oral contraceptives and eight students using oral contraceptives participated in the study. In addition, seven male students served as a control group. During two menstrual cycles, the PPT and TT of the masseter and temporalis muscles, as well as from the hand, were obtained twice per week. At the end of the study the values were evaluated in relation to the different phases of the menstrual cycle, by means of a linear mixed model. The TT appeared very reproducible within subjects and did not fluctuate over time. Scores on the left temporalis muscle appeared significantly higher than that on the right side. In all subjects the PPT tended to be higher on the left side, while in students using oral contraceptives, the PPT values of the temporalis muscle were significantly higher in the menstrual phase, and lower in the follicular phase. A significant correlation between the PPT of the temporalis muscle and the TT of the overlying skin was observed.
TL;DR: The data from the present study and similar observations from clinical and experimental human studies suggest that increased activity from muscle nociceptors is not sufficient to produce a prolonged increase in postural EMG activity, and the development and maintenance of chronic jaw muscle pain does not appear to result from a feedback cycle mechanism.
Abstract: The aim of the present study was to investigate the effects of noxious chemical stimulation of a jaw muscle on postural electromyographic (EMG) activity from several masticatory muscles in lightly anesthetized rats Unilateral injection of a substance known to induce acute muscle pain (5% NaCl) or longer duration of pain with inflammation (mustard oil) was made into the masseter muscle The changes in EMG activity following the injection were recorded from the injected and contralateral masseter muscles and the ipsilateral digastric muscle The algesic chemicals produced a significant but transient increase in EMG activity in all three muscles The data from the present study and similar observations from clinical and experimental human studies suggest that increased activity from muscle nociceptors is not sufficient to produce a prolonged increase in postural EMG activity Therefore, the development and maintenance of chronic jaw muscle pain does not appear to result from a feedback cycle mechanism
TL;DR: The data suggest that ultrasonography is a reproducible method for measuring LSCDs of the masseter muscle.
Abstract: Local cross-sectional dimensions (LCSDs) of masseter muscle sites may now be measured non-invasively using ultrasonography. The purpose of the present study was to determine (i) whether the muscle site may affect LCSD measurements and (ii) whether measurements made at identical sites may be reproducible. The study included 17 patients who had signs and symptoms of temporomandibular disorders (TMD). Bilateral ultrasonographic investigation was performed with a linear (B-scan) 7.5 MHz small-part transducer to visualize the antero-superior, antero-inferior, medio-superior, medio-inferior, postero-superior, and postero-inferior sites of the masseter muscle. Measurements were made in two sessions with a time interval of at least five minutes. Data were analysed for reproducibility by using the intraclass correlation coefficient (ICC) and the method error (ME). Muscle site had no significant effect on muscle measurements (P = 0.090). Measurements from the various side-related sites did not differ significantly (P = 0.425). Measurements recorded at a given site were consistent across the testing sessions (P = 0.605). The muscle site with highest reproducibility was the medio-inferior site (ICC = 0.92; ME = 6.4%). The data suggest that ultrasonography is a reproducible method for measuring LSCDs of the masseter muscle.
TL;DR: The results support the idea that the strategy of differential activation protects the injured muscle while simultaneously maintaining optimal function.
Abstract: The aim of this randomized, controlled, double-blind study was to examine how the activation pattern of the masseter muscle changes during natural function when experimental pain is induced in a discrete anterior area of the muscle. In 20 subjects, three bipolar surface electrodes and three intramuscular fine-wire electrodes (antero-posterior mapping) were simultaneously attached above and in the right masseter muscle to record the electromyographic (EMG) activity during unilateral chewing before and after infusion of a 0.9% isotonic and 5% hypertonic saline bolus in the anterior area of the muscle. The activity of the contralateral masseter muscle was registered by surface electrodes. In addition, the development of pain intensity was quantitatively measured with a numerical rating scale (NRS). While both saline concentrations caused pain, the hypertonic solution evoked stronger pain. The experiments also provided evidence of a significant although differential activity reduction of the ipsilateral masseter muscle in the antero-posterior direction. The activity reduction decreased with increasing distance from the location of the infusion. The results support the idea that the strategy of differential activation protects the injured muscle while simultaneously maintaining optimal function.
TL;DR: This case is the first documented presentation of bilateral MOT involvement of the lateral pterygoid muscles.
TL;DR: Investigation of the differentiation of myosin heavy chain (MHC) isoforms during the postnatal development periods in mouse MS and mouse tibialis anterior (TA) found expressions of MHC‐2b agree with the weaning period.
Abstract: Functional maturation of muscles is related to the constitutional proportion of muscle protein isoforms during development and growth. Although the mouse masseter muscle (MS) is classified as a fast limb muscle, its functions are different from those of a limb muscle. This study investigated the differentiation of myosin heavy chain (MHC) isoforms during the postnatal development periods in mouse MS and mouse tibialis anterior (TA), which is a fast limb muscle. Many anti-MHC slow-type-positive fibres were observed in neonatal MS and TA; these fibres decreased during development. Adult MS was composed of anti-MHC fast-type-positive fibres. MHC isoforms in MS were composed of MHC-2a and MHC-2d soon after birth. MHC-2b was expressed, but MHC-2a was not seen after 21 days. Expression of MHC-2b agreed with the weaning period, that is 2-3 weeks after birth. This fact suggested that the transformation from suckling to mastication changed the MHC isoforms during this period. In this study, the expressions of MHC-2b agree with the weaning period.
TL;DR: A unique myofibrillar protein isoform expression was observed in the human masseter muscle fibers, suggesting significant differences in structural and functional properties between muscle fibers from humanmasseter and limb muscles.
Abstract: Striated craniofacial and limb muscles differ in their embryological origin, regulatory program during myogenesis, and innervation. In an attempt to explore the effects of these differences on the striated muscle phenotype in humans, the expression of myosin and myosin-associated thick filament proteins were studied at the single fiber level both in the human jaw-closing masseter muscle and in two limb muscles (biceps brachii and quadriceps femoris muscles). In the masseter, unique combinations of myosin heavy chain (MyHC) and myosin binding protein C (MyBP-C) isoforms were observed at the single fiber level. Compared to the limb muscles, the MyHC isoform expression was more complex in the masseter while the opposite was observed for MyBP-C. In limb muscles, a coordinated expression of three MyHC and three MyBP-C isoforms were observed, i.e., single fibers contained one or two MyHC isoforms, and up to three MyBP-C isoforms. Also, the relative content of the different MyBP-C isoforms correlated with the MyHC isoform expression. In the masseter, on the other hand, up to five different MyHC isoforms could be observed in the same fiber, but only one MyBP-C isoform was identified irrespective MyHC isoform expression. This MyBP-C isoform had a migration rate similar to the slow MyBP-C isoform in limb muscle fibers. In conclusion, a unique myofibrillar protein isoform expression was observed in the human masseter muscle fibers, suggesting significant differences in structural and functional properties between muscle fibers from human masseter and limb muscles.
TL;DR: The study showed three distinct anatomical portions in the middle of the temporal muscle which correspond to this functional classification and the MRI study confirmed the results of the anatomical study.
Abstract: The authors carried out an anatomical and magnetic resonance imaging study on the architecture of the mandibular elevator muscles of 169 cadavers. The aim of the study was to define the organisational architecture of the human masseter, temporal and pterygoid muscles. Layer by layer dissection and anatomical cuts in different spatial planes showed that the temporal muscle has a different architecture to the other mandibular elevator muscles. Indeed this muscle does not have the pennate structure of the masseter and pterygoid muscles. Through electromyographic study the behavior of this muscle allowed the establishment of its functional segmentation during the masticatory cycle. Our study showed three distinct anatomical portions in the middle of the temporal muscle which correspond to this functional classification. The MRI study confirmed the results of our anatomical study.
TL;DR: Three separate radiological techniques have been described to predict the position of the facial nerve: Conn's arc; a plane extending posteriorly from the outer surface of the mandibular ramus; and soft-tissue structures, including the posterior belly of the digastric muscle, the retromandibular vein and the lateral border of the masseter muscle.
TL;DR: HMS probably is the consequence of an abnormal trigeminal hyperexcitability likely induced by the demyelinating lesion of its peripheral motor pathway and the main neurophysiological abnormalities may persist unmodified over a long course of the disease.
Abstract: Objectives To describe the clinical and neurophysiological findings in a case of hemimasticatory spasm (HMS) followed during 14 years of evolution. Material and methods A woman suffered from very frequent paroxysmal episodes of painful involuntary occlusion of the jaw. Neurophysiological studies were performed at the 3, 12 and 14 years after the onset of symptoms. They included a needle electromyographic (EMG) evaluation of the main jaw closing and opening muscles, the jaw reflex (JR), the masseteric silent period (MSP) and the masseteric inhibitory reflex (MIR). Results Clinical symptoms remained unchanged throughout the period of observation. Conventional EMG never disclosed neurogenic signs. Voluntary closure of the jaw systematically provoked an abnormal activity with muscle cramps characteristics, restricted to the left masseter muscle. Left JR response was normal in the first evaluation and became delayed and of reduced amplitude in the second. The MSP and MIR were abolished on the left side during the spasmodic episodes whereas they were strictly normal out of them. The MIR abnormalities showed the characteristic pattern of an efferent lesional type. Conclusions Hemimasticatory spasm probably is the consequence of an abnormal trigeminal hyperexcitability likely induced by the demyelinating lesion of its peripheral motor pathway. The main neurophysiological abnormalities may persist unmodified over a long course of the disease and allow the differential diagnosis of HMS from oromandibular dystonia and temporomandibular dysfunction (TMD).
TL;DR: Masticatory muscle capacity seems to influence the effect of the posterior bite blocks on both tooth eruption and skeletal adaptation, and the results suggest that the characteristics of the masticatory muscles should be taken into account when predicting the efficiency of a functional appliance.
Abstract: The aim of this study was to analyse the effects of normal and hypofunctional masticatory muscles on dento-skeletal adaptation to posterior bite blocks in growing rats. Fifty-two young male rats were divided into two groups, fed a hard and soft diet, respectively, to develop different functional capacities in the masticatory muscles. Bone markers were inserted in the mandible on day 0. After two weeks, an appliance that raised the bite by 2 mm was inserted in half of each group. Lateral radiographs were taken on day 0, 14, 28, and 42 of the experiment. Images of the mandible were superimposed on the bone markers. Differences in cephalometric measurements were analysed by two-way ANOVA. The reduced muscle capacity resulted in an upward growth of the snout and a shorter mandibular ramus with less bone apposition on its lower border. Bite blocks induced a more upward growth of the snout and a shorter mandibular ramus, and inhibited the eruption of the upper molars and intruded the lower molars. The rats with weaker masticatory muscles had less inhibitory effect of the posterior bite blocks on upper molar eruption and showed different bone apposition in the ramus, especially during the first two weeks. In conclusion, masticatory muscle capacity seems to influence the effect of the posterior bite blocks on both tooth eruption and skeletal adaptation. The results suggest that the characteristics of the masticatory muscles should be taken into account when predicting the efficiency of a functional appliance.
TL;DR: The results suggest that the differences in muscle endurance between sexes may have some association with higher susceptibility of craniomandibular disorders in females than in males.
Abstract: The purpose of this study was to investigate the nature of fatigue and recovery of masticatory and neck muscles and the differences between sexes in normal subjects during experimentally induced loading. Subjects consisted of eight males (mean age: 27.6 years) and eight females (mean age: 24.2 years) selected from the volunteers in the Faculty of Dentistry, Hiroshima University. The inclusion criteria for the subjects were as follows: (1) good general health, (2) normal horizontal and vertical skeletal relationships, (3) no severe malocclusions and (4) no complaints of temporomandibular disorders. Each subject was requested to bite an occlusal-force meter with 98, 196 and 294 N forces on the first molar region per side for 45 s. Activities of the masseter and sternocleidomastoid (SCM) muscles were recorded during these performances. Fatigue and recovery ratios were calculated with mean power frequency of power spectrum using a fast Fourier transform algorithm. Significant differences in the fatigue ratios between both sexes were found for the masseter muscle with 98, 196 and 294 N bite forces. Meanwhile, the SCM presented a significant difference between both sexes only at 98 N biting. Significant differences in the recovery ratios between both sexes were more prominent in the masseter muscle than in the SCM. These results suggest that the differences in muscle endurance between sexes may have some association with higher susceptibility of craniomandibular disorders in females than in males.
TL;DR: Brief exposure to testosterone produces a permanent change in the proportions of masseter muscle fibers of different phenotypes, and the capacity for this change is not restricted to a critical period of postnatal development.
Abstract: The proportions of muscle fibers of different phenotype in the adult rabbit masseter differ greatly in different sexes. These sex differences are not apparent in young adults, but arise under the i...
TL;DR: It is shown that reduction of masseter level of PGE2 after intramuscular glucocorticoid administration is associated with a decrease of resting pain in patients with fibromyalgia and local myalgia.
Abstract: Our aim was to determine whether masseter muscle (M) and plasma (P) levels of prostaglandin E2 (PGE2) or leukotriene B4 (LTB4) are influenced by local glucocorticoid administration and whether such changes would be associated with corresponding changes in local pain or hyperalgesia. Eighteen patients with fibromyalgia and 15 with local masseter myalgia were examined immediately before and 2 weeks after intramuscular administration of glucocorticoid with regard to masseter muscle resting pain and tenderness to palpation, pressure pain threshold, maximum voluntary mouth opening (MVM), and pain on maximum voluntary mouth opening. The primary criteria for inclusion were presence of pain for a period of at least 3 months and tenderness to digital palpation in the masseter muscle region. At both visits microdialysis samples were obtained from the masseter muscle, and venous blood was collected for analysis of PGE2 and LTB4. Dialysate levels of M-PGE2 did not change significantly after glucocorticoid administration, but reduction of masseter resting pain and increase of MVM were associated with decrease of M-PGE2 in the patients with fibromyalgia. Dialysate levels of M-LTB4 increased in both groups. In the patients with local myalgia the plasma level of LTB4 also increased, and this increase was associated with a decrease of pain and masseter tenderness. In conclusion, this study shows that reduction of masseter level of PGE2 after intramuscular glucocorticoid administration is associated with a decrease of resting pain in patients with fibromyalgia. In addition, the masseter muscle level of LTB4 increases in patients with fibromyalgia and local myalgia.
TL;DR: In this paper, surface EMG activity was picked up from the masseter and from the anterior and posterior temporalis muscles of nine adult subjects, at a bite force level as low as 25 N.
Abstract: The masticatory muscles differ in their fiber type composition. It can therefore be expected that their electromyographic (EMG) power spectra will differ during the performance of different bite force tasks. In the present study, surface EMG activity was picked up from the masseter and from the anterior and posterior temporalis muscles of nine adult subjects. At a bite force level as low as 25 N, the mean power frequency (MPF) values of the posterior temporalis were significantly lower than those of the masseter and anterior temporalis. The MPF values of the masseter muscles decreased with an increase of bite force magnitude, whereas the MPF values of the anterior and posterior temporalis did not change significantly. The MPF values were significantly influenced by the direction of bite force. The observed changes of MPF are possibly related to the recruitment of different fiber types, and support the concept that the masticatory muscles behave heterogeneously.
Journal Article•
TL;DR: Evaluating the effectiveness of the therapy with occlusal splints in patients with temporomandibular disorders by the computerized electromyography showed that there were significant reductions in the electromyographic activity along the entire period of treatment during the mandibular isometric clenching for masseter and anterior temporalis muscles.
Abstract: The effect of the occlusal splints on the treatment of temporomandibular disorders--a computerized electromyographic study of masseter and anterior temporalis muscles. The comprehension of the determinant factors of temporomandibular disorders is still inconclusive, since that the etiology is associated with multidisciplinary knowledge. The purpose of this study was to evaluate the effectiveness of the therapy with occlusal splints in patients with temporomandibular disorders by the computerized electromyography. It was selected twenty-two patients with signs and symptoms with changes of the stomatognathic system, males and females patients, with ages between 18 and 53 years old. Plane occlusal surface splints were constructed in acrylic resin and placed in each patients. Electromyographic evaluations of masseter and anterior temporalis muscles were performed during the mandibular isometric clenching before inserting and after 90, 120 and 150 days of using the occlusal splints. After 90 and 120 days of using them, they were changed by canine guidance and group function respectively. The results after the polynomial regression analysis showed that there were significant reductions (p < 0.05) in the electromyographic activity along the entire period of treatment during the mandibular isometric clenching for masseter and anterior temporalis muscles. The group function showed a shorter eletromyographic activity for both muscles.
TL;DR: The buccinator muscle in the cat was identified underneath an orbicularis oris, arising from the lower buccal membrane and from the molar region of the alveolar border of the mandible, which may aid in mastication, including suckling, and in expelling air forcibly, like the buccinators in humans.
Abstract: Published descriptions of the buccinator muscle of the cat (Felis domestica) differ from those for the same muscle in other mammals. Only an oral component of the muscle has been described in cats, not a buccal part. The purpose of this study was to identify the buccinator muscle in the cat and report on its anatomical features in detail. Dissections of the facial muscles were carried out on 12 specimens of adult cats (6 males and 6 females) that had been fixed with 10% formalin. We then observed the facial muscles and traced their innervations, arteries, and veins under a binocular microscope. The buccinator muscle in the cat was identified underneath an orbicularis oris, arising from the lower buccal membrane and from the molar region of the alveolar border of the mandible. It was about 3 mm wide at its origin, 4 mm wide at its insertion, and about 11 mm in length from origin to insertion. This contrasts with humans, in whom the muscle arises not only from the mandible, but also from the maxilla. Apart from this difference, this muscle in cats displays the following similarities to the buccinator muscle of other mammals: 1) it is innervated by the facial nerve; 2) it supports the buccal membrane; 3) it seems to insert into the modiolus; 4) its bundles run antero-posteriorly; 5) the posterior part of the muscle is located medially to the masseter muscle; 6) the parotid duct, facial nerve, artery, and vein run lateral to the muscle; 7) it is located deeper than other facial muscles; and 8) the buccal nerve runs on its surface. These relationships are spatially similar to those of the buccinator muscle in mammals. This muscle may aid in mastication, including suckling, and in expelling air forcibly, like the buccinator in humans.
TL;DR: The results of this study suggest stabilization-type splints to have a site-specific effect in the immediate reduction of local maximal clenching-related muscle asymmetries.
Abstract: Patients with temporomandibular disorders may present with a cluster of joint and muscle disorders characterized primarily by pain, joint sounds and irregular or deviating jaw function. Maxillary stabilization-type splints represent the best standard therapy, so the purpose of this study was to evaluate changes in local maximal clenching-related asymmetry patterns of masseter muscle sites associated with the immediate `application of splint therapy' using the diagnostic approach of high-resolution gray-scale ultrasonography. The study included 24 patients who had signs and symptoms of temporomandibular disorders. Ultrasonographic investigation was performed with a linear (B-scan) 7·5 Mhz small-part transducer to visualize the antero-superior, antero-inferior, medio-superior, medio-inferior, postero-superior, and postero-inferior sites of the masseter muscle. To assess local maximal clenching-related muscle asymmetry patterns and to evaluate the respective effect of occluding splints, the `absolute asymmetry index' was used, with the mean maximum muscle diameter of the respective right and left sides calculated from three consecutive measurements before and after splint insertion. Comparing the values assessed before splint insertion with those after splint insertion revealed a significant decrease in local maximal clenching-related muscle asymmetry values for the antero-inferior masseter muscle site (P < 0·05). The results of this study suggest stabilization-type splints to have a site-specific effect in the immediate reduction of local maximal clenching-related muscle asymmetries. Further studies are warranted to evaluate muscle-site specific effects in patient and non-patient groups and to relate these effects to pre-treatment variables like bite force, preferred chewing side, facial morphology and occlusion.
TL;DR: The results suggest that in the malocclusion-bearing rats, an abnormal reflex regulation of the motor activity of the masticatory muscles may take place and allow us to hypothesize that muscle spindle alterations might be involved in the pathogenesis of human temporomandibular disorders.
Abstract: Human temporomandibular disorders due to disturbed occlusal mechanics are characterized by sensory, motor and autonomic symptoms, possibly related to muscle overwork and fatigue. Our previous study in rats with experimentally-induced malocclusion due to unilateral molar cusp amputation showed that the ipsilateral masseter muscles undergo morphological and biochemical changes consistent with muscle hypercontraction and ischemia. In the present study, the masseter muscle spindles of the same malocclusion-bearing rats were examined by electron microscopy. Sham-operated rats were used as controls. In the treated rats, clear-cut alterations of the muscle spindles were observed 26 days after surgery, when the extrafusal muscle showed the more severe damage. The fusal alterations affected predominantly capsular cells, intrafusal muscle fibers and sensory nerve endings. These results suggest that in the malocclusion-bearing rats, an abnormal reflex regulation of the motor activity of the masticatory muscles may take place. They also allow us to hypothesize that muscle spindle alterations might be involved in the pathogenesis of human temporomandibular disorders.