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PubMed2006

Experimental skin pain and muscle pain induce distinct changes in human trigeminal motoneuronal excitability.

Seeking information on the physiological properties of the trigeminal motoneuronal pool we investigated changes in the excitability of trigeminal motor system induced by two types of experimental pain (muscle and skin). In one session, we studied the effect of muscle pain induced by hypertonic saline infusion into the masseter muscle on the recovery cycle of the heteronymous H-reflex in the temporalis muscle and the homonymous silent period (SP) in the masseter muscle, both elicited by stimulation of the masseteric nerve in ten-healthy subjects. In another session, we studied the effect of laser stimuli applied to the perioral region, at conditioning intervals from 20 to 160 ms, on the temporalis H-reflex and masseter SP in nine healthy subjects. Whereas laser-induced skin pain significantly inhibited the temporalis H-reflex and facilitated the masseter SP (P < 0.01), muscle pain left the time course of the temporalis H-reflex and masseter SP unchanged (P > 0.05). The timing of temporalis H-reflex suppression and masseter-SP enhancement induced by laser stimuli indicates that facial skin nociceptors inhibit trigeminal motoneurones via multysynaptic reflex pathways. Hypertonic saline, a stimulus that predominantly activates group III and IV afferents, left both variables reflecting trigeminal motoneuron excitability unchanged. Due to the differences between the two experimental models, we cannot conclude that such inhibitory reflex pathway does not exist from muscle nociceptors to trigeminal motoneurones.

Adult↗
PubMed2006

Myosin isoforms and fibre types in jaw-closing muscles of Australian marsupials.

Myosin heavy chains (MyHCs) and fibre types in the masseter muscle of seven species of Australian marsupials (brushtail and ringtail possums, bettong, bandicoot, dunnart, two species of antechinuses) spanning three orders were studied by native myosin electrophoresis, SDS-PAGE, immunoblotting and immunohistochemistry. We found only two fibre types in the masseter muscles of these animals: (1) masticatory fibres expressing masticatory MyHC, and (2) hybrid alpha/beta fibres that co-express alpha-cardiac and beta-cardiac MyHCs. Masticatory fibres predominate in most species, being appropriate for predation or for chewing tough vegetable matter. The relative abundance of alpha/beta fibres decreased from 60% to 0 in the order: ringtail possum > brushtail possum > bettong > bandicoot > dunnart/antechinus. These variations in masseter fibre type are correlated with decreasing amounts of vegetable matter in the diets of these animals. The results are in contrast to earlier work on masseter fibres of macropodids that expressed alpha-cardiac MyHC almost homogeneously. The fact that the bettong (Family: Potoroidae), which belong to the same marsupial superfamily (Macropodoidea) as kangaroos and wallabies (Family: Macropodidae), has not specialized in the exclusive expression of alpha-cardiac MyHC as members of the latter family suggests that this specialization was of recent phylogenetic origin (30 million years before present).

Adaptation, Physiological↗
PubMed1985

Localization and morphometric analysis of masticatory muscle afferent neurons in the nucleus of the mesencephalic root of the trigeminal nerve in the cat.

Injections of horseradish peroxidase (HRP) were made into the ipsilateral temporal muscle and contralateral masseter muscle of 10 cats in order to identify and characterize neurons in the nucleus of the mesencephalic root of the trigeminal nerve that innervate muscle receptors in the orofacial periphery. Neurons labelled by HRP injections and unlabelled cells from 5 control cats were measured with a computer-based image analyzer, and their position was mapped on a stereotaxic graph. Cells that innervate the masseter and temporal muscles were identified throughout the rostrocaudal extent of the nucleus. There was no indication of a somatotopic pattern nor of a specific segregation within the nucleus for cells innervating muscle receptors. The nucleus contained small, rounded unipolar neurons located primarily in the dorsal border of the periaqueductal gray (PAG) matter in the rostral part of the nucleus and larger oval unipolar neurons which were scattered throughout the nucleus, but were predominant in the pontine portion of the nucleus. HRP injections labelled both large and small cells, as well as occasional multipolar cells. The last-mentioned tended to be located in the lateral margins of the PAG. The mean geometric values obtained for the control group were: area 552.7 microns2 perimeter 110.3 microns; maximum diameter 36.0 microns. and diameter of an equivalent circle 26.1 microns. The mean values of the labelled neurons were: area 606.6 microns2; perimeter 100.1 microns; maximum diameter 36.0 microns, and diameter of an equivalent circle 27.2 microns.

Animals↗
PubMed1984

Phasic and rhythmic responses of the oral musculature to mechanical stimulation of the rat palate.

Activity of the anterior and posterior digastric muscles, the intrinsic tongue muscles and the masseter muscles was recorded electromyographically. Muscle-activity patterns depended on the site of stimulation, the strength of the stimulus and its duration. Five types of reflex patterns were distinguished: type A: on-response in the digastric muscles (latency about 7 ms) and in the intrinsic tongue muscles (latency about 15 ms); type B: on-off response in the digastric and intrinsic tongue muscles; type C: on-response followed by long-lasting low-level activity in the digastric and intrinsic tongue muscles; type D: on-off response and long-lasting low-level activity in the digastric and tongue muscles; type E: rhythmic activity in all muscles under investigation preceded by one of the other reflex types. In the type-E response, the frequency of the bursts was about 4.3 Hz; the masseter bursts were not in phase with those of the digastric muscles; the intrinsic tongue muscles showed constant activity with superimposed rhythmic bursts. By increasing the stimulus strength or the stimulus duration, there was a gradual shift from simple, phasic, reflex responses to more complex reflex patterns. This holds for all palatal sites. However, rhythmic activity was most easily elicited in the region of the incisive papilla, less easily in the antemolar region; no rhythmic activity was found in the intermolar region. Thus stimulus duration is a crucial factor in eliciting rhythmic oral activity in the rat.

Animals↗
PubMed2004

Jaw muscles in older overdenture patients.

OBJECTIVE: To determine, using computer tomography (CT), whether the retention of a small number of teeth in the older adult used to support overdentures could affect the cross-sectional area (CSA) and X-ray density of two jaw closing muscles. DESIGN: Cross-sectional study of a group of older patients subdivided into dentate, edentulous and those wearing overdentures supported by two to five teeth. SUBJECTS: The sample consisted of 24 subjects aged 55-68 years. OUTCOME MEASURES: CSA and X-ray density of two jaw closing muscles, masseter and medial pterygoid were measured and evaluated using CT. RESULTS: There were no significant differences between left and right jaw muscles, but the CSA of the masseter muscles were significantly larger than the medial pterygoid muscles. The CSA of the masseter and medial pterygoid muscles was significantly smaller in edentulous subjects compared with dentate subjects but no significant difference was observed between subjects wearing overdentures and those with a natural dentition. No significant differences were observed with the X-ray density between different muscles or dental states. CONCLUSION: The retention of a small number of teeth in the older adult used to support overdentures appears to sustain the CSA of two jaw closing muscles and therefore could enhance these patients' masticatory ability compared with those who were edentulous.

Absorptiometry, Photon↗
PubMed1999

Masseteric inflammation-induced Fos protein expression in the trigeminal interpolaris/caudalis transition zone: contribution of somatosensory-vagal-adrenal integration.

The effects of vagotomy and adrenalectomy on the expression of Fos protein in brainstem neurons following the inflammation of masseter muscle were examined in order to differentiate the Fos activation related to nociceptive processing in contrast to that due to somatoautonomic processing. The inflammation was induced by a unilateral injection of complete Freund's adjuvant (CFA) into the masseter muscle under methohexital anesthesia after a small skin-cut (S-cut). After the CFA injection, Fos positive neurons were identified in bilateral spinal trigeminal nucleus (VSP), nucleus tractus solitarius (NTS), ventrolateral medulla (VLM) and inferior medial olivary nucleus (IOM). At the level of the trigeminal subnucleus interpolaris/caudalis (Vi/Vc) transition zone, there was a selective induction of Fos-like immunoreactivity (LI) in the VSP and NTS, when compared to control rats (anesthesia with or without S-cut). A major portion of the Fos-LI in the VSP at the level of the caudal Vc was apparently activated by S-cut. Bilateral adrenalectomy or a unilateral vagotomy resulted in a selective reduction of inflammation-induced Fos-LI in the VSP at the Vi/Vc transition zone (P<0.05) and NTS (P<0.05), but had less effect on Fos-LI in the caudal Vc. These results suggest that the inflammation of the masseter muscle, an injury of orofacial deep tissue, results in a widespread change in neuronal activity in the VSP and NTS that depends in part on the integrity of the adrenal cortex and vagus. Thus, in addition to somatotopically organized nociceptive responses, orofacial deep tissue injury also is coupled to somatovisceral and somatoautonomic processing that contribute to central neural activation.

Adrenal Glands↗
PubMedDate not supplied

Reduced late component of exteroceptive reflex in patients with Parkinson's disease.

The exteroceptive reflexes in the masseter muscles in patients with Parkinson's disease (PD) were examined. The reflex produced by 3 Hz mental nerve stimulation consisted of four negative peaks and three positive peaks in the unrectified recordings. The latencies of the peaks in patients with PD were the same as those in control subjects, except for the P2 component in the right masseter muscle. The amplitudes of N3-P3 and P3-N4 were smaller in patients with PD than those in control subjects. Interpeak latency of N3-N4 was shorter in PD patients. Exteroceptive suppression in the masseter muscles was also examined. The early component (ES1) of so-called exteroceptive suppression was normal in patients with PD. The duration and degree of the late component (ES2) of exteroceptive suppression decreased in patients with PD. According to the latencies, N1 and N2 speaks seem to be the onset and end of ESI; N3 and N3 peaks the onset and end of ES2, respectively. The early component did not show any significant abnormality. Reduced late component of exteroceptive reflex in patients with PD might be related to the abnormal motor control system of the facial muscles.

Electric Stimulation↗
PubMed1985

Functions of condylar translation in human mandibular movement.

Mandibular movement in many mammals is controlled by a pure hinge joint. Since condylar translation is a structurally complex adaptation and a common source of human clinical dysfunction, there have been many attempts to evaluate the biologic significance of human condylar translation. The three hypotheses concerning condylar translation considered in this study are (1) that it results in a center of rotation of the mandible in the area of the mandibular foramen, minimizing displacement of the inferior alveolar neurovascular bundle during mandibular movement, (2) that it reduces the amount of stretch in the masseter muscle during opening, allowing the muscle to function within an efficient portion of the muscle fiber length-tension curve, and (3) that it prevents compromise of the airway and other cervical structures by the tongue and mandible during opening. Ten subjects with cephalometric radiographs taken both in centric relation and with the mandible wide open are evaluated. The movement of the mandibular foramen, the stretch of the masseter muscle, and the proximity of the tongue and mandible to the airway are compared during actual opening and when mandibular opening is modeled as a pure hinge movement. The results indicate that condylar translation performs all three functions. However, a review of other data leads to the conclusion that airway preservation in human beings may be a more critical problem and a more essential function of condylar translation than either reducing movement of the mandibular foramen or reducing stretch of the masseter muscle.

Airway Obstruction↗
PubMed2005

Effects of botulinum toxin type A on contouring of the lower face.

BACKGROUND: Masseteric muscle hypertrophy is an uncommon dition represented as a swelling of the masseter muscle. Recent reports have demonstrated the successful use of botulinum in the treatment of masseteric hypertrophy. OBJECTIVE: This study was a prospective trial to evaluate the effectiveness of botulinum toxin type A (Botox) in the treatment of masseteric muscle hypertrophy according to doses of 10, 20, and 30 U. MATERIALS AND METHODS: Twenty-two patients were referred to the dermatologic clinic for the management of masseteric muscle hypertrophy. Ultrasonographic measurements of the thickness of the masseter muscle were performed, and clinical photographs were taken before treatment and 1, 2, 3, 4, 6, and 9 months after the treatment. RESULTS. The median values of percentage reduction of muscle mass were 10.3%, 16.5%, 23.7%, 24.7%, 21.6%, 16.5% in the 10 U group; 11.9%, 18.8%, 24.8%, 27.7%, 26.7%, and 21.8% in the 20 U group; and 12.0%, 19.4%, 25.0%, 27.8%, 37.8%, and 24.1% in the 30 U group. CONCLUSION. The adequate dose of botulinum toxin type A for treatment of masseteric muscle hypertrophy should be above 20 U. The effect of botulinum toxin type A is maintained for at least 9 months as the treatment of masseteric muscle hypertrophy.

Adult↗
PubMed1990

[Electromyographic activity (EMG) of masseter and temporal muscles in edentulous patients before and after complete dentures].

Electromyographic records from the temporal and masseter muscles of 19 edentulous patients were made, before and 30 days after wearing complete dentures. The purpose of this study was to determine the electromyographic changes: The amplitude of electromyographic records from de temporal muscles decreased, while those from the masseter muscles increased. These results suggest that the use of complete denture provokes electromyographic changes by increasing the occlusal vertical dimension and, thus, periodical electromyographic records from temporal and masseter muscles could be useful for determining the time for complete denture change.

Denture, Complete↗
PubMed2004

Biomechanical analysis of the rigid fixation of zygoma fractures: an experimental study.

In this experimental study, the goal was to test the sufficiency of actual fixation plates in zygomatic complex fractures and the efficiency of a modified plate at the zygomaticofrontal suture in a suitable model, which was designed for biomechanical study. To address this issue, a zygomatic fracture model produced by using a cadaveric cranium was simulated and the fractures were fixed by the actual and modified fixation materials. The force simulating masseter muscle pull was applied with the Lloyd material testing apparatus, and the rotation of the zygoma was determined using displacement transducers. In this study, there were three different experimental groups. Although miniplates at the zygomaticomaxillary buttress and microplates at the infraorbital rim were used in all three groups, three different plates (miniplate, microplate, and modified plate) were used at the frontozygomatic suture in these groups. Rotational displacement of the zygoma with the effects of simulated masseter muscle force was determined. According to the results obtained, microplates are not effective in stabilizing the frontozygomatic suture when the masseter muscle forces are within physiological range. Although miniplates stabilize zygomatic complex fractures, it was shown that modified microplates, which have no ondulation along the plate border, have a higher resistance to rotation than that of the conventional plates. The rotation angle at the instant of fracture with microplates was 4.59 degrees, and that with miniplates was 1.26 degrees. The maximum rotation angle with modified microplates was 0.32 degrees. Modified microplates designed for the fixation of fractures in the zygomatico-orbital region have been shown to be suitable in a well-designed experimental model and might be appropriate for clinical use.

Biomechanical Phenomena↗
PubMed2001

Effect of jaw muscle pain and soreness evoked by capsaicin before sleep on orofacial motor activity during sleep.

AIMS: Sleep bruxism, which is a form of orofacial motor activity (OMA), and jaw muscle pain and soreness have for a long time been thought to be mutually linked. The aim of this study was to investigate the effect of clinical and experimental jaw muscle pain and soreness on sleep OMA. METHODS: Twelve healthy subjects aged 21 to 31 years old participated in this study. All of them were aware of signs or symptoms of sleep OMA and were subdivided into a group with clinical pain complaints (n = 5) and a group without pain (n = 7). All subjects slept in the laboratory for 3 consecutive nights, including a habituation night, a baseline night, and an experimental night. Electroencephalographic (EEG) activity and electromyographic (EMG) activity from the masseter muscles were recorded during sleep. On the experimental night, before sleep, all subjects received an injection of capsaicin (0.1 mL, 100 micrograms/mL) into the masseter muscle that had demonstrated the most EMG activity during the previous recordings. The OMA events and episodes were quantified and were compared between the baseline night and the experimental night. Every evening and morning during the study period, pain intensity, unpleasantness, and soreness were scored by the subjects on a visual analog scale (VAS), and pain detection thresholds (PDTs) in the masseter muscles and maximal voluntary occlusal force (MVOF) were also measured. RESULTS: Pre-sleep injection of capsaicin did not cause significant differences between groups in peak pain intensity on the VAS. The PDT and MVOF did not show any significant differences between groups, injection and non-injection sides, or baseline and experimental nights and mornings. The number of EMG episodes/hour sleep, the number of bursts/hour sleep, and total area of all bursts and episodes during the baseline night were significantly higher in the subjects without pain than in the subjects with pain. However, the capsaicin injection did not cause any significant changes in these parameters. CONCLUSION: This study suggests that an acute pre-sleep painful stimulus does not have any effect on OMA during sleep, but the study extends previous findings that clinical jaw muscle pain and soreness are associated with less EMG activity in the masticatory muscles.

Adult↗
PubMed2002

[A study of ultrasound images under 3 different functional mandibular positions in young females].

OBJECTIVE: The aim of this study was to establish the average of superfacial masseter muscle of young females with normal occlusion, and further supply a clue for dentists to evaluate the muscle function of patients with malocclusion. METHODS: Totally 31 young females were investigated in this study, whose mean age was 21 years and 4 months old. Ultrasound technique was applied to obtain the ultrasound parameters of images, including area, width, mean thickness, maximal thickness of the cross-section and the length of the vertical-section of the masseter muscle under relaxing, maximal clenching and maximal protruding condition. The data were analyzed using ANOVA analysis. RESULTS: The mean value and standard deviation of every parameter were figured out and it was found that there was a significant difference between relaxing and maximal clenching as well as maximal protruding. CONCLUSION: The result indicates that ultrasonic technique is an effective method for describing superfacial masseter muscle morphology and diagnosing its function.

Adult↗
PubMed1989

Value of EMG analysis of mandibular elevators in open-close-clench cycle to diagnosing TMJ disturbance syndrome.

The EMGs of the temporal and masseter muscle, in sixty patients with temporomandibular joint disturbance syndrome (TMJDS) and thirty normal controls, were recorded during rhythmical open-close-clench cycle movement and before and after occlusal splint therapy. The duration of the muscle contraction before initial tooth contact (DMC), the latent period (LP) and the silent period (SP) of the myoelectrical activity were used as indices for exploring their diagnostic value. In contrast with the controls, DMC, LP and SP lengthened in the patients. The DMC was prolonged in those patients where there were TMJ sounds, the inter-cuspated position did not coincide with the muscular contact position and there was deviated mandibular movement. An increase of the SP was related to tooth contact on the balancing side. After treatment, the DMC and SP in the patients returned to the level of the controls. It was found that the internal correction rate of Fisher's linear discriminate function established for the DMC and SP of the temporal and masseter muscles was 80.9% and 85.1% respectively. The results show that the DMC and SP of the temporal and masseter muscles have some value in diagnosing muscular dysfunction and discriminating therapeutic effectiveness.

Adult↗
PubMed2003

Botulinum toxin type A treatment for contouring of the lower face.

BACKGROUND: Since type A botulinum toxin was first reported for the treatment of masseter muscle hypertrophy in 1994, there have been few reports about cosmetic indications for contouring procedures of the lower face with injection of botulinum toxin type A, and this procedure remains unpredictable. OBJECTIVES: This study attempted a quantitative prospective analysis of reduction of masseter muscle hypertrophy after Botox injection, using ultrasound and computerized tomography (CT) scans to analyze the possible use of botulinum toxin type A as a contouring procedure for the lower face. METHODS: Forty-five patients consented to the study and received a contouring procedure of the lower face from November 2001 to April 2002. Twenty five to 30 U of Botox per side was injected at five to six points into the prominent portions of the mandibular angle. Serial measurements were made of the thickness of the masseter muscle by ultrasound and CT before the injections and at 1 and 3 months thereafter. A quantitative analysis for the masseter thickness changes was performed on just one patient who underwent all ultrasound and CT scans. Statistical analysis of the masseter thickness change was by two-way and multiple comparison analysis. To evaluate clinical long-term effects, the patient's satisfaction with the procedure and any side effects after injections were monitored during 4 to 10 months of follow-up. RESULTS: Among the total of 45 patients, 15 underwent the three ultrasound measurements, and 14 had the three CT measurements. With regard to quantitative analysis of the thickness change to the masseter on both sides of the face according to time points, this was gradually reduced by both the ultrasound and CT measurements during the first 3 months. By ultrasound, the maximum reduction in masseter thickness was seen 1 month after the injections, with a slight increase being observed at 3 months after injection. A continued reduction of masseteric muscle thickness was seen on the CT up to 3 months after injection. In terms of patient satisfaction for up to 10 months of follow-up, the results were as follows: very satisfied, 1; satisfied, 36; slight improvement, 3; no change or dissatisfied, 5. Main local side effects included masticatory difficulties, muscle aching at injection sites, and speech disturbance. However, these side effects were transitory, usually lasting from 1 to 4 weeks after the injections. CONCLUSIONS: Preliminary results from this study suggest that an injection of Botox resulted in relatively satisfactory clinical effects, although there was only a short-term follow-up. It is suggested that the use of botulinum toxin type A for contouring of the lower face can be established as a simple, predictable, alternative facial contouring procedure without a prolonged recovery time.

Adult↗
PubMed1986

EMG feedback in the treatment of myofascial pain dysfunction syndrome.

The effect of electromyographic (EMG) biofeedback on frontalis and masseter muscle activity was compared with control conditions in two groups of patients with a diagnosis of myofascial pain dysfunction (MPD) syndrome. Patients were selected on the basis of clinical symptoms, radiographic evaluation, and a clinical examination. Depressed patients and patients with signs of a pathological condition in the temporomandibular joint were excluded. Both the experimental (EXP) and the control (CON) group went through two base-line screening sessions before treatment of the EXP group was started. Treatment consisted of eight biofeedback sessions, given twice a week for 4 weeks. Feedback was presented visually on a monitor. Treatment did not include any relaxation training. Control evaluations of both groups took place 1 week, 3 months, and 6 months after the end of treatment. The EXP group was able to reduce EMG levels in frontalis and masseter muscles significantly during training sessions. Follow-up data showed significantly reduced frontalis EMG levels in the EXP group after 3 and 6 months but not in the CON group. Both groups improved subjectively, as judged by reports on pain intensity and duration, but this improvement was significantly more pronounced in the EXP group. Objective clinical indices recorded throughout the study were uncorrelated with EMG changes or subjective reports. It is concluded that biofeedback training facilitated muscular relaxation and self-regulation in the EXP group and that visual EMG feedback, consisting of a patterning of frontalis and masseter muscle activity, can be recommended as an integrated part of MPD syndrome treatment.

Adolescent↗
PubMed2006

TMJ inflammation increases Fos expression in the nucleus raphe magnus induced by subsequent formalin injection of the masseter or hindpaw of rats.

The study was designed to examine the effect of persistent temporomandibular joint (TMJ) inflammation on neuronal activation in the descending pain modulatory system in response to noxious stimulus. Formalin was injected into the left masseter muscle or hindpaw of rats 10 days after injection of the left TMJ with saline or complete Freund's adjuvant (CFA). The results showed that 10-day persistent TMJ inflammation (induced by CFA) alone did not induce a significant increase in Fos-like immunoreactive (Fos-LI) neurons in the rostral ventromedial medulla (RVM) or locus coeruleus (LC), but that formalin injection of the masseter muscle or hindpaw induced a significant increase in Fos-LI neurons in the RVM and LC of rats with and without TMJ inflammation (P < 0.05). However, persistent TMJ inflammation significantly increased Fos-LI neurons in the nucleus raphe magnus (NRM) induced by subsequent formalin injection of the masseter muscle and hindpaw (70.2% increase and 53.8% increase, respectively, over the control TMJ-saline-injected rats; P < 0.05). The results suggest that persistent TMJ inflammation increases neuronal activity, in particularly in the NRM, by the plastic change of the descending pain modulatory system after ipsilateral application of a noxious stimulus to either orofacial area or a spatially remote body area.

Animals↗
PubMed1995

Influence of diet composition and malocclusion on masticatory organs in rats.

The present study was undertaken to determine the effects of different dietary consistencies and malocclusion induced by extraction of molar teeth on the masticatory organs of weaning and adult rats, by determining the biochemical properties of masseter muscle, and also Ca and P levels in mandibular bone. Male SD rats, 3 and 20 weeks old, were divided into 3 groups. Group one (G-1) was maintained on a solid diet, and Groups two (G-2) and three (G-3) on a semi-solid diet. Furthermore, the mandibular molar teeth of G-3 rats were extracted. The experimental period was 120 days. The masseter muscle and mandibular bone weights of G-1 in weaning rats were increased significantly in comparison with G-3, but not in adult rats. The CPK activities in weaning and adult rats of G-1 were higher than those in the other two groups. The order of LDH activity in weaning and adult rats was G-3 > G-2 > G-1. G-2 and particularly G-3 showed significantly lower glycogen contents than G-1. The Ca and P contents of the mandibular bone in G-2 and G-3 were lower than those in G-1. These results suggest that a different dietary consistency and malocclusion induced by extraction of mandibular molar teeth have a considerable influence on the development of masticatory organs, mandibular bone and masseter muscle.

Aging↗