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PubMed2002

Immediate effect of a stabilization splint on masticatory muscle activity in temporomandibular disorder patients.

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).

Adult↗

PubMed1989

[The changes of the orofacial muscle activity induced by the lip forces in subjects with normal occlusion].

This study was intended to investigate whether lip exercise affect the activities of the lips, tongue, digastric and masseter muscles and to understand the functional interrelationship between them. As the forces of maximum lip grimace was reduced to slight lip seal gradually, the electromyograph was taken from 9 conscious human adults with normal occlusion in the upper and lower lips, tongue, digastric and masseter muscle using surface electrodes, especially, newly designed subminiature surface electrodes which was attached directly to the tongue. The results were as follows. 1. During induced maximum lip grimace in the mandibular rest position, there're prominent increase of EMG activity in the upper and lower lips, tongue and digastric muscle 1714 mu v, 2787 mu v, 2142 mu v and 623 mu v, respectively, but there was little activity in the masseter muscle, 129 mu v. The force level induced by maximum grimace of the lips was about 110g when the force transducer was positioned between upper and lower lips in the incisor area. 2. As the lip forces were reduced gradually, EMG activities of the lips, tongue and digastric muscles were decreased definitely with certain tendency, but there was no change in the masseteric EMG activity. Above mentioned results suggest that (1) lip exercise can promote the activities of the lips, tongue and digastric muscles but cannot change the activity of the masseter muscle and (2) masseteric muscle activity seems to be independent of the lips and the tongue but digastric muscle activity is related more closely to them through lip exercise in the subjects with normal occlusion.

Adult↗

PubMed1986

The correlation between histophotometrical and biochemical myosin-ATPase measurements in the myocardium and striated muscle of the rat.

To prove the correlation between histophotometrical and biochemical data of myosin-ATPase-activity, the change of enzyme activity during development was measured in the myocardium, masseter muscle, and tensor fasciae latae of rats. Both methods were applied to the same material. To avoid errors due to varying section thickness in each cutting and staining procedure, a reference material (e.g. heart muscle) was used, taken from one and the same animal. The correlation between histophotometrical and biochemical estimations was very good, histophotometrical arbitrary units being used. ATPase-activity in heart muscle during development, slightly decreases in masseter muscle and more in tensor fasciae latae. The ATPase-activity in the latter was higher than in masseter muscle. This is in good agreement with the physiological, biochemical, and histochemical classification.

Adenosine Triphosphatases↗

PubMed1995

Asymmetry of masticatory muscle activity during intercuspal maximal clenching in healthy subjects and subjects with stomatognathic dysfunction syndrome.

The present study investigated the asymmetry of masticatory muscle activity during maximal intercuspal clenching in healthy subjects and subjects with stomatognathic dysfunction syndrome. Stomatognathic dysfunction syndrome, unilateral mastication and the asymmetry of masticatory muscle activity appear to be related to each other. The asymmetry of masseter muscle activity was greater as stomatognathic dysfunction became increasingly severe. Because fatigue and pain are produced more quickly by unilateral clenching than bilateral clenching, clenching under conditions of left and right muscular imbalance can further aggravate stomatognathic dysfunction. It is suggested the asymmetry of masseter muscle activity during maximal clenching correlates with the onset of the stomatognathic dysfunction syndrome. Stomatognathic dysfunction syndrome is closely related to the asymmetry of masseter muscle activity and only slightly related to the asymmetry of temporal muscle activity. The asymmetry of anterior temporal muscle activity appears to have little clinical significance.

Adolescent↗

PubMed2006

Correlation and cluster analysis of sensory, pain, and reflex thresholds to various stimulus modalities in symptom-free subjects.

OBJECTIVE: In order to evaluate the possible relation between the psychophysical response and a motor reflex, sensory and pain thresholds to various stimuli were analyzed in combination with the occurrence threshold of the late masseteric exteroceptive suppression (ES2) period. METHODS: Twenty men and 20 women participated. The tactile detection threshold and the filament-prick pain detection threshold were measured on the cheek skin overlying the left masseter muscles. The pressure pain threshold and pressure pain tolerance threshold were measured at the left masseter muscle. The surface EMG was recorded from the left masseter muscle, while electrical stimuli with 13 fixed intensities were applied to the skin above the left mental nerve. The stimulation intensity at which the ES2 appeared for the first time and the lowest stimulus intensity at which the subjects reported to be painful were defined as the ES2 and pain threshold, respectively. RESULTS: There were significant positive correlations between the tactile detection threshold and the pain thresholds determined using the different stimulus modalities, and the ES2 threshold was also significantly correlated with the pain thresholds (P<0.05). Cluster analysis could significantly discriminate two distinct groups with high versus low tactile, pain and ES2 thresholds (P<0.05). CONCLUSIONS: The present findings suggested that the ES2 reflex response has a relation with the individual sensory and pain sensitivity in symptom-free subjects. SIGNIFICANCE: Combined examination of sensory, pain, and ES2 thresholds might provide complementary information on the pathophysiology underlying orofacial pain.

Adult↗

PubMed2001

[The masseter: an enigmatic muscle].

PURPOSE: To try and explain the frequency of pathologic processes involving the masseter muscle. MATERIALS AND METHODS: Anatomical and histological evaluation of the masseter muscle and its partial continuity with the medial pterygoid muscle. Retrospective evaluation of 21 cases of pathology of the masseter muscle imaged by CT and/or MRI. RESULTS: Two main groups of pathology are identified: benign masseter hypertrophy and hemodynamically inactive vascular malformations. Other etiologies are quite varied. Some are secondary to processes involving the nearby mandible and parotid gland. Others, including tumors, involved the masseter muscle in a non specific fashion. CT and especially MRI were quite valuable with accurate diagnosis in 17/21 cases, two of which with the help of clinical data. CONCLUSION: The main question regarding the preferential involvement of the masseter muscle over nearby muscles remains unanswered.

Adolescent↗

PubMed2002

Acupuncture and sham acupuncture reduce muscle pain in myofascial pain patients.

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 (i.e., needling) may not be specific to the location of the stimulus as predicted by the classical acupuncture literature.

Acupuncture Analgesia↗

PubMed1993

Sternocleidomastoid muscle inhibition induced by trigeminal stimulation.

Among numerous reports of anatomical and functional coupling between the trigeminal and cervical systems is the demonstration that the sternocleidomastoid (SCM) muscles may become activated along with the masseter muscles during forceful abrupt biting maneuvers. Whether the co-activated SCM is also inhibited by stimuli that produce masseter inhibition is not known. This study evaluated the SCM for the presence of inhibition during mechanically-elicited (chin or forehead tap) and electrically-elicited (anterior maxillary gingiva stimulation) inhibition of the masseter muscle in ten healthy men. Surface EMG data were recorded bilaterally from the masseter and SCM muscles. The data for each muscle were converted to ratios of the pre-stimulus maximum voluntary contraction activity for each subject and averaged across subjects. Means of these percentages were determined at several defined pre- and post-stimulus intervals. The results indicate that masseter inhibition was clearly elicited by the electrical and both forms of mechanical stimulation. SCM co-inhibition could be evoked by electrical and chin tap stimulation but not by forehead tap. The responses to these stimuli varied among subjects, from trial to trial, and within subjects depending on the experimental condition. The fact that it was possible for this co-inhibition to be evoked is presented as further indication of the functional coupling of the trigeminal and cervical systems.

Adult↗

PubMed1997

Antagonism of suxamethonium-induced jaw muscle contracture in rats.

Masseter muscle rigidity (MMR) induced during general anaesthesia by suxamethonium is a clinical problem that may interfere with tracheal intubation. We have investigated the relation between twitch tension and contracture response to suxamethonium in rats. Rats were anaesthetized with 1% halothane (1.35 MAC). Jaw muscle temperature was maintained at either 37 or 41 degrees C while rectal temperature was kept at 37 degrees C by radiant heat. Twitch tension was produced by nerve stimulation at 0.2 Hz. Rats were pretreated with either a low dose of vecuronium (0.03 mg kg-1) or dantrolene (0.8 mg kg-1). Thereafter suxamethonium 750 micrograms kg-1 was administrated i.v. Low-dose vecuronium pretreatment significantly (90%) decreased suxamethonium-induced jaw muscle contracture (JMC) with minimal (3%) twitch block during local hyperthermia. Low-dose dantrolene pretreatment also reduced JMC (81% at 37 degrees C and 82% at 41 degrees C) while decreasing twitch by 30% at 37 degrees C and 31% at 41 degrees C. Both vecuronium and dantrolene at doses that minimally depressed the twitch response antagonized suxamethonium-induced JMC. We speculate that pretreatment with low-dose vecuronium decreases suxamethonium-induced MMR clinically.

Animals↗

PubMed2006

The expression of IGF-I and myostatin mRNAs in skeletal muscle of hypophysectomized and underfed rats during postnatal growth.

AIM: To determine the roles of myostatin and insulin-like growth factor-I (IGF-I) during postnatal growth, we examined IGF-I and myostatin mRNA expression in the skeletal muscles of hypophysectomized and underfed rats during postnatal growth. METHODS: Five-week-old rats were divided into four groups: freely fed control, moderately underfed, severely underfed and hypophysectomized. Four weeks later, blood and muscle samples were gathered to determine serum IGF-I, myosin heavy chain (MHC) isoforms, IGF-I Ea, IGF-I Eb and myostatin mRNA. RESULTS: The weights of soleus, plantaris and masseter muscles were decreased in underfed and hypophysectomized rats. Hypophysectomy resulted in significant increases of type I MHC at the expense of type IIx in plantaris muscle and of neonatal MHC at the expense of types IIx and IIb in masseter muscle. Serum IGF-I was decreased by underfeeding and hypophysectomy. Plantaris muscle IGF-I Ea mRNA in underfed and hypophysectomized rats was significantly lower than in normal controls. Plantaris muscle IGF-I Eb mRNA in underfed rats was significantly lower than in normal controls. Masseter muscle IGF-I Eb mRNA in severely underfed rats was significantly lower than in normal control and hypophysectomized rats. Soleus muscle myostatin mRNA in hypophysectomized rats was significantly higher than in normal and significantly underfed rats. No significant differences in plantaris and masseter muscle myostatin mRNA were observed between groups. CONCLUSION: Suppressed muscle growth caused by hypophysectomy and underfeeding may be attributed mainly to reduced circulating IGF-I and partially to reduced IGF-I mRNA, rather than to a change in myostatin.

Animals↗

PubMed1989

Blood-flow and metabolic response in a contracting canine masticatory muscle.

The mechanical and metabolic characteristics of the canine masseter muscle of seven adult dogs, aged 3 years, weighing 45-55 kg, were evaluated by electrically provoked contractions. The masseter muscle was exposed by careful surgery and stimulated by two silver electrodes placed in the anterior and posterior aspects of the muscle. The bite force was measured with a force transducer. Glycogen, glucose-contents together with lactate, pyruvate, creatine phosphate, NADH and NAD were analysed fluorimetrically. Intra-muscular oxygen tension was continuously recorded by a flexible silver electrode. Blood-flow was measured by the 133Xenon clearance technique. Biopsies were taken at rest and after stimulation. The registered bite force revealed an initial peak, representing maximal force production and thereafter a rapid decline in power output. During the following stimulation events the bite force curve showed decrease in amplitude concerning maximal force as well as duration of bite force production. The blood-flow and oxygen tension were significantly reduced at the end of stimulation. However, after recovery these parameters were normalised to initial values. The glycogen and glucose were depleted after stimulation. The lactate concentration increased about three to four times. The observed changes in NAD and NADH indicate a hypoxic situation in the muscle cells. The oxygen deficit in conjunction with the intramuscular blood-flow impairment and the metabolite variations reflect the energy and redox state in the muscle and may contribute to the decline in bite force production.

Animals↗

PubMed2000

Pain and allodynia/hyperalgesia induced by intramuscular injection of serotonin in patients with fibromyalgia and healthy individuals.

The aim of this study was to investigate the effect of injection of serotonin (5-HT) into the masseter muscle on pain and allodynia/hyperalgesia. Twelve female patients with fibromyalgia (FM) and 12 age-matched female healthy individuals (HI) participated in the study. The current pain intensity (CPI) and the pressure pain threshold (PPT) of the superficial masseter muscles were assessed bilaterally. 5-HT in one of three randomized concentrations (10(-3), 10(-5), 10(-7) M) or isotonic saline was then injected into either of the two masseter muscles in a double-blind manner. After the injections the CPI and PPT were recorded ten times during 30 min. The injections were repeated twice with the other concentrations of 5-HT after 1 and 2 weeks, respectively. In the FM-group there was a non-significant increase of CPI after injection that lasted during the entire 30-min period irrespective of whether 5-HT or saline was injected. Neither did the PPT change significantly. In the HI-group pain developed significantly after injection irrespective of whether 5-HT or saline was injected, but significantly more so after 5-HT at 10(-3) M than saline injection. CPI decreased quickly and then remained on a very low level for most of the experiment. 5-HT at both 10(-5) M and 10(-3) M caused a significantly greater decrease of PPT than saline. In conclusion, our results show that 5-HT injected into the masseter muscle of healthy female subjects elicits pain and allodynia/hyperalgesia, while no such responses occur in patients with fibromyalgia.

Adult↗

PubMed1981

Progressive jaw muscle fatigue of experimental tooth clenching in man.

To determine the onset of subjective fatigue and the subjective endurance of fatigue and pains in the masseter muscle, ten adult male subjects exercised maximal voluntary tooth clenching. Concomitantly, the electrical activity in the masseter muscle was recorded by bipolar surface electrodes and integrated. Onset of subjective fatigue occurred on average 21 s after onset of muscle hyperactivity and the isometric endurance time of the masseter muscle, during which period severe muscle pains were present, was on average 82 s. The electrical muscle activity of the threshold and endurance tests showed a curvilinear configuration (y =a + b log x), and it is suggested that progressive physiological, or peripheral, muscle fatigue accompanied the psychological, or central, endurance of tooth clenching.

Adult↗

PubMed1985

Postnatal development of the anulospiral endings of Ia fibers in muscle spindles of mice.

The formation of the anulospiral ending of Ia fibers in muscle spindles was investigated in the masseter muscle of developing mice. Before 15 days after birth, the complete anulospiral ending was not observed in almost all of the muscle spindles examined. With the growth of mice, the Ia fiber began to construct the spiral ending, and by the 40th postnatal day after weaning, almost all of the Ia fibers of the muscle spindles had complete coiled endings, though the formation still continued in some spindles. The continuous formation of anulospiral endings for a long period after weaning indicates that muscle spindle morphogenesis may be affected by muscle tension in the masseter muscle due to the movement activated after weaning.

Animals↗

PubMed1997

Effect of jaw opening on the direction and magnitude of human incisal bite forces.

The maximum bite force (MBF) appears to be different when measured at different jaw openings (e.g., Manns et al., 1979; Mackenna and Turker, 1983; Lindauer et al., 1993). However, the change could be related to a change in the bite direction. We have measured the MBF on incisors and its direction in three dimensions for different jaw openings in ten subjects. Surface electromyography (EMG) of anterior temporalis and masseter muscles on both sides was recorded simultaneously. The results showed that: (1) the average %MBF increased as the jaw was opened, reached a plateau between 14 and 28 mm of incisal separation, and then decreased at wider jaw openings; (2) the initial forward bite direction with respect to the mandibular occlusal plane shifted backwards during jaw opening; and (3) the activity of the masseter muscles declined and that of the temporalis muscles was largely unchanged, resulting in an increase of the ratio between the activity in temporalis and masseter muscles (T/M). There was a significant correlation between bite direction and jaw opening (r = 0.51, p < 0.001) and between T/M ratio and jaw opening (r = 0.56, p < 0.001). Based on comparative data, we have calculated sarcomere lengths while the jaw is opened and hypothesize that the average %MBF reaches its maximum when the sarcomeres in the masseter muscle achieve their optimum length. A plateau continues during further jaw opening, until those of temporalis reach their optimum length while those of masseter lengthen beyond their optimum length. The change in bite direction was attributed to either a change in the relation between upper and lower bite points as the jaw was opened or the gradual decline of masseter activity at larger openings.

Adult↗

PubMed1984

The distribution of afferent neurones in the mesencephalic nucleus of the fifth nerve in the cat.

The objective of this study was to examine anatomically the distribution of afferent neurones in the mesencephalic nucleus of the fifth nerve (Mes V). HRP was applied, in separate experiments, to the inferior alveolar, infraorbital, and masseter nerves, and injected into the masseter muscle and periodontal ligament. Following application of HRP to the masseter muscle and masseter nerve, labelled cells were found in the ipsilateral motor nucleus of the fifth nerve and in the ipsilateral Mes V. Labelled cells in Mes V, identified as belonging to proprioceptor afferents from jaw-closing muscles, were distributed throughout the full extent of the nucleus. Following application of HRP to the inferior alveolar nerve, infraorbital nerve, and periodontal ligament, labelled cells were found in the ipsilateral trigeminal ganglion and Mes V, and the latter identified as belonging to periodontal receptor afferents. In contrast to the distribution of spindle afferent somata, they were restricted to the caudal region of Mes V. The differential distribution of afferent neurones within Mes V demonstrated in this study confirms previous electrophysiological findings, and its significance is considered.

Animals↗

PubMedDate not supplied

Bruxing patterns in children compared to intercuspal clenching and chewing as assessed with dental models, electromyography, and incisor jaw tracing: preliminary study.

The purpose of the present study was to compare bruxing patterns in children with chewing and maximum intercuspal clenching as defined in a clinical and laboratory environment. Six non-bruxing controls and six children who actively bruxed according to parent reports were evaluated. Both control and experimental subjects were assessed by an initial questionnaire, intraoral examination, extraoral examination, dental study models, incisor mandibular tracking, and bilateral surface electromyographic recordings (e.g., EMG). Bruxing was defined as grinding, clenching, or both in combination. The clinical examination consisted of an intraoral examination of the dentition, number of occlusal contacts, and wear facets. Dental study models were used to substantiate the intraoral findings for occlusal contact and wear facets. The mandibular incisors position was tracked during opening, closing, laterotrusion, protrusion, and chewing and compared to the bruxing movements in the experimental subjects. Bilateral surface EMG signals from the temporalis and masseter muscles were recorded in three maximum intercuspal clenches, ten chewing cycles on sugarless gum, and during simulated bruxing. The dental contacts were equal in number bilaterally in both control and bruxing subjects. Both groups demonstrated wear facets, but the bruxing subjects had more facets. The wear facets indicated lateral excursions but not clenching. Only the incisor jaw tracking and bilateral EMG differentiated the bruxing patterns. In those subjects (n = 4) who clenched during bruxing, the EMG pattern was not similar to that of intercuspal clenching and demonstrated its own unique muscle recruitment for the temporalis and masseter muscles. In the subjects who exhibited lateral excursions for bruxing (n = 2), the pattern of muscle recruitment of the two-closing muscles in terms of amplitude was similar for both the bruxing and chewing gum. Our findings support a concept that bruxing may depend upon factors that modify coactivation of muscle recruitment and do not depend upon occlusal contacts.

Analysis of Variance↗

PubMed2003

Muscular adaptation to gradual advancement of the mandible.

Muscular activity of the superficial masseter muscle and anterior portion of the temporal muscle before, during, and after treatment, with gradual advancement of the mandible, was evaluated by assessing the average integrated electromyogram (EMG) with the mandible in retruded position (RP) and incisal edge-to-edge (EE) position on 23 consecutive subjects with skeletal Class II malocclusion. Toward the end of active treatment and follow-up, the RP position and EE position coincided. At any given registration, the EMG activity of the masseter muscle was at least twice (P < .001) that of the anterior portion of the temporal muscle. The EMG activity in RP for the anterior portion of the temporal muscle was not affected significantly, whereas the EMG activity at EE position decreased significantly (P < .05) during the initial treatment, but, thereafter, it increased continuously. The difference in EMG activity between six months of follow-up and pretreatment level reached statistical significance (P < .05). For the masseter muscle, the EMG activity at both RP and EE position was reduced about 20% during the initial treatment but returned to the pretreatment level during active treatment and exceeded pretreatment level by approximately 30% to 50% at two and six months of follow-up, respectively. In conclusion, it seemed that gradual advancement affected the anterior portion of the temporal muscle to a minor extent, whereas the effect on the masseter muscle was significant.

Adaptation, Physiological↗