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PubMed1992

Masticatory muscle fatigue: endurance times and spectral changes in the electromyogram during the production of sustained bite forces.

The purpose of this experiment was to determine if the characteristics of fatigue observed in the limb muscle system are also evident in the muscles of mastication, specifically, the masseter and temporalis. Surface electrodes were placed bilaterally over the masseter and temporalis muscles of 10 adults. Each subject was instructed to maintain maximal and six levels of submaximal incisal bite forces for as long as possible. The power density spectrum of the electromyographic signals for each muscle was calculated at the onset and failure of the task. The decrease in endurance time with an increase in bite force followed a pattern similar to that in limb muscles, and each muscle was characterized by a consistent reduction in the mean power frequency of the power density spectrum and a variable change in r.m.s. power. The variability of changes in r.m.s. power (which is inconsistent with changes found in the limb muscles) was explained in terms of either changes in motor-unit firing rate or the muscle's relative contribution to the generation of bite force. The analyses also demonstrated a curvilinear relationship between bite force and r.m.s. power, but no relationship between bite force and the mean power frequency of the power density spectrum.

Adult↗
PubMed2004

Repair of large orbito-cutaneous defects by combining two classical flaps.

INTRODUCTION: Despite the fact that orbital exenteration is one of the most socially distressing facial operations, it may be necessary, still. The repair of a radically exenterated orbit is a difficult problem for surgeons to resolve. MATERIAL AND PATIENTS: In the Department of Oral and Maxillofacial Surgery, Madrid, nine patients underwent orbital exenteration including simultaneous periorbital tissue resection for invasive orbital and/or periorbital tumours between 1990 and 2000. Primary repair was performed by temporalis myofascial plus facio-cervico-pectoral flaps. RESULTS: This technique resulted in low morbidity, short period of hospitalization and good facial aesthetics.

Aged↗
PubMed2001

Fatigue and pain in human jaw muscles during a sustained, low-intensity clenching task.

Fatigue, pain and changes in the electromyographic (EMG) activity of the jaw-closing muscles are well documented during short, high-intensity tooth-clenching tasks but less so during sustained, low-intensity tasks. In this study, 11 healthy men clenched on a bite-force meter for 60 min at 10% of the maximal voluntary contraction (MVC) and scored the intensity of fatigue and pain on separate 10 cm visual analogue scales (VAS). Surface EMG activity from the masseter and anterior temporalis muscles was recorded in 10 s epochs every 5 min throughout the task. Pressure-pain thresholds (PPTs) in the jaw-closing muscles, unassisted maximum jaw opening and MVC were determined before and after the task. All participants reported an increasing sensation of fatigue in the jaw-closing muscles during the task (mean+/-SD: peak VAS=7.5+/-2.0 cm) but all were able to maintain the required force. Most (7/11) also reported a painful sensation (peak VAS=2.7+/-2.8 cm). The jaw-opening capacity (59.5+/-7.4 vs. 58.3+/-6.5 mm, P=0.031) and the MVC (777+/-73 vs. 652+/-115 N,P=0.002) were slightly, but significantly, decreased immediately after the task whereas the PPTs remained unchanged (ANOVA: P=0.612). The mean frequency of the EMG activity decreased in all muscles during the task (95.7 vs. 46.6 Hz;P<0.001), and the root mean squares increased (53.2 vs. 154 microV, P<0.001). The changes in EMG activity were more strongly correlated with the sensation of fatigue than pain. These findings demonstrate that a sustained, low-intensity clenching task can induce subjective and electrophysiological indications of fatigue.

Adult↗
PubMed1985

Facial nerve injury during surgery of the temporomandibular joint: a comparison of two dissection techniques.

Changing the dissection technique for gaining access to the temporomandibular joint decreased the incidence of facial nerve injury from 25% to 1.7%. This decrease can be attributed to the elimination of both development of a skin flap and dissection of tissue overlying the lateral capsule. Normal anatomic variation in the distribution of facial nerve branches may relate to the incidence of clinically apparent injury.

Dermatologic Surgical Procedures↗
PubMed1996

Immediate postural responses to total nasal obstruction.

Twenty-five nasal breathing adults were radiographically examined before and after their nasal respiratory pattern had been artificially eliminated for a period of 1 hour. Six angular and six linear variables were measured to determine the extent of the postural reflexive behavior of the cranium, mandible, hyoid bone, tongue, and lips. All subjects coped in their own individual way with the environmental impact. The most generalized findings were parting of the lips (p < 0.05), a drop in mandibular position (p < 0.001), and a downward movement of the hyoid bone (p < 0.05). Cranial extension did not reach statistical significance (p = 0.06). The relevance of these findings relative to primate experiments and human clinical research is discussed. If the same postural reactions are maintained over a long-term period, they may be instrumental in influencing the vertical craniofacial growth pattern.

Adaptation, Physiological↗
PubMed1997

Gonial angles and condylar and ramus height of the mandible in complete denture wearers--a panoramic radiograph study.

It has been accepted that the shape of the mandibular base, and especially the gonial angle of the mandible, correlates with the function of the jaw closing muscles. The gonial angles of the mandible and condylar and ramus heights of 30 complete denture wearers (18 women, 12 men, mean age 61 years, range 42-74 years) coming for renewal of their dentures were measured using panoramic radiographs. The mean period of edentulousness was 26 years (range 10-53 years). No statistically significant difference was observed between the sexes in the the sizes of gonial angles and condylar and ramus heights. The right gonial angle was statistically significantly smaller than the left one and correlated negatively with the ramus height in both sides but positively with the increased EMG activity in the right masseter muscle. The size of the gonial angle and the condylar and ramus heights did not correlate with the age of the patients, edentulous period or alveolar ridge resorption.

Adult↗
PubMed2002

Occlusal support and head posture.

In order to examine the relationship between occlusal support and head posture, the electromyographic (EMG) activities of the jaw closing muscles and the sternocleidomastoid muscle during voluntary maximal clenching (VMC) under several conditions of occlusal support in eight healthy dentates were recorded and analysed. The head posture was also recorded simultaneously by the electromagnetic, 6-degree-of-freedom tracking instrument (POLHMUS Co. 3 SPACE-WIN*). In the VMC with lateral imbalance of occlusal support, EMG activity of the jaw closing muscles and the sternocleidomastoid muscle on the occlusal support side was greater than those on the non-occlusal support side, and the neck was bent in the direction of the occlusal support side. Moreover, a positive correlation was found between the asymmetry of muscle activity (asymmetry index) of the sternocleidomastoid muscle and the angle of lateral bending of the neck. From these results, it can be said that lateral imbalance of the occlusal support could promote imbalance in sternocleidomastoid muscle activity, causing lateral bending of the neck. From this study, it is suggested that there is a close relationship between occlusal support and head posture.

Adult↗
PubMed2002

Correlation between elevator muscle activity and direction of sagittal closing pathway during unilateral chewing.

The closing pathway of masticatory movement in the vicinity of the intercuspal position (ICP) is considered as a functional movement in reconstructing the occlusal guidance. The purpose of this study was to examine a correlation between elevator muscle activity and direction of the closing pathway in the vicinity of the ICP during mastication. Fifty subjects (18 male and 32 female subjects aged from 21 to 34 years) were selected randomly from the students of the Kanagawa Dental College. The measurements of jaw movement during mastication were recorded using a Sirognathograph instrument and surface electromyography (EMG) of the anterior temporalis and masseter muscles simultaneously. The muscle activity and the direction of the closing pathway were calculated on the working and non-working sides during unilateral chewing and analysed at the sections of ICP-2 mm and 2-4 mm in sagittal view. The direction of the closing pathway was expressed by the angle to a vertical reference axis. The direction of the closing pathway correlated significantly with the activity of the anterior temporalis muscles on the non-working side and the masseter muscles on the working side at ICP-2 mm. From the results of this study, it was suggested that the elevator muscle activity may be associated with the direction of the closing pathway during mastication.

Adult↗
PubMed1999

Regional differences in fibre type composition in the human temporalis muscle.

Anatomical and electromyographic studies point to regional differences in function in the human temporalis muscle. During chewing and biting the anterior portions of the muscle are in general more intensively activated and they are capable of producing larger forces than the posterior portions. It was hypothetised that this heterogeneity in function is reflected in the fibre type composition of the muscle. The composition and surface area of different fibre types in various anteroposterior portions of the temporalis muscle were investigated in 7 cadavers employing immunohistochemistry with a panel of monoclonal antibodies against different isoforms of myosin heavy chain. Pure slow muscle fibres, type I, differed strongly in number across the muscle. In the most posterior portion of the muscle there were 24% type I fibres, in the intermediate portion 57%, and in the most anterior portion 46%. The mean fibre cross-sectional area (m-fcsa) of type I fibres was 1849 microm2, which did not differ significantly across the muscle. The proportion of pure fast muscle fibres, type IIA and IIX, remained more or less constant throughout the muscle at 13% and 11% respectively; their m-fcsa was 1309 microm2 and 1206 microm2, respectively, which did not differ significantly throughout the muscle. Pure type IIB fibres were not found. The relative proportion of hybrid fibres was 31% and did not differ significantly among the muscle portions. Fibre types I + IIA and cardiac alpha + I + IIA were the most abundant hybrid fibre types. In addition, 5% of the type I fibres had an additional myosin isoform which has only recently been described by means of electrophoresis and was named Ia. In the present study they were denoted as hybrid type I + Ia muscle fibres. It is concluded that intramuscular differences in type I fibre distribution are in accordance with regional differences in muscle function.

Aged↗
PubMed2005

Reconstruction of #7 facial cleft with distraction-assisted in situ osteogenesis (DISO): role of recombinant human bone morphogenetic protein-2 with Helistat-activated collagen implant.

A case involving concomitant presentation of a #7 lateral facial cleft with a complete cleft of the ipsilateral lip, alveolus, and palate is presented. The mandibular defect was Pruzansky III with a foreshortened body, absent ramus and absent masseter. Taking advantage of developmental field theory, reconstruction of the osseous defect was undertaken using the autogenous periosteum as a source of mesenchymal stem cells. Expansion of the periosteum was followed by implantation of Helistat (Integra Life Sciences, Plainsboro, NJ) collagen sponge saturated with recombinant human bone morphogenetic protein-2. Stimulation of this distraction-induced envelope by rhBMP-2 resulted in abundant production of bicortical membranous bone in situ within 12 weeks. The neoramus was subsequently suspended from the cranial base, and a temporalis muscle transfer was used to provide motor control of the jaw. Synthesis of bone in this manner is termed DISO (distraction-assisted in situ osteogenesis). The biologic rationale and clinical implications of DISO are discussed.

Alveolar Process↗
PubMed1997

Electromyographic heterogeneity in the human temporalis and masseter muscles during dynamic tasks guided by visual feedback.

The complex architecture of the human jaw muscles suggests regional differences in function within these muscles. This study examines the way the temporalis and masseter muscle regions are activated when free mandibular movements with various speeds and against various external leads are carried out guided by visual feedback. Electromyographic (EMG) activity was registered in six temporalis and three masseter muscle regions with bipolar fine-wire electrodes. Recordings were made during open/close excursions, protrusion/retrusion movements, and laterodeviations. During open/close excursions and protrusion/retrusion movements, an anterior and posterior temporalis part could be distinguished, whereas during laterodeviations a more complex partitioning of this muscle was observed. During the protrusion/retrusion movements and the laterodeviations, the temporalis muscle demonstrated higher EMG peak activities than the masseter muscle, and within the masseter muscle the deep masseter showed higher EMG peaks than the superficial one. In contrast to this, during the open/close excursions the masseter showed higher peak activities than the temporalis muscle, while the superficial masseter showed higher EMG peak activities than the deep masseter. Within the deep masseter, differences were also found. During open/close excursions, the anterior deep region demonstrated higher EMG peak activities than the posterior region, whereas during protrusion/retrusion and laterodeviations the posterior deep region showed higher peaks. In general, speed had a greater effect on the EMG peak activity than external load. Only during laterodeviations did speed and load equally influence peak activity in both the deep and superficial masseter. During protrusion/retrusion movements, load showed no significant effect on EMG peak activity in the masseter muscle. A general finding was that, according to task, different regions were activated preferentially. This points to a partitioning of the excitatory command of the motoneuron pool.

Adult↗
PubMed2002

Effect of sustained contraction on motor unit action potentials and EMG power spectrum of human masticatory muscles.

The sequelae of a sustained clench are incompletely understood. Our experimental questions were to compare the responses of men and women, to compare masseter and anterior temporalis muscles, and to test hypotheses for the reduction of the median frequency of power spectra. We recorded duration, amplitude, number of phases, and area of the motor unit action potential before and after a sustained clench and the median frequency of the electromyographic power spectrum in 41 subjects. After the clench, the median frequency was lower, the action potential duration longer, the number of phases increased, and the area larger, but the amplitude was not different. Males and females failed to differ. Compared with the temporalis, the masseter had a lower median frequency, longer duration, larger number of phases, and increased area. Our results are consistent with a decrease in the conduction velocity of the muscle action potential as an explanation of the spectral shift.

Action Potentials↗
PubMed1997

Muscle activity and jaw movements as predictors of chewing performance.

Chewing performance can be defined in terms of the reduction in food particle size after 15 chewing strokes. In this study, the relationship between chewing performance and electromyographic activity was investigated to develop optimal values of electromyographic variables, based on their ability to predict chewing performance. Electrognathographic and electromyographic recordings from surface electrodes over the digastric (abductor), masseter, and temporalis (adductors) muscles were made from 24 subjects while they chewed a hard fruit gum. A moderate negative correlation was found between the food particle size and the root mean square calculation for masseter activity (-.48; P < .01). Weaker positive correlations were found between particle size and the asynchrony of ipsilateral and contralateral anterior temporalis muscles (.36; P < .05). A multiple regression model of electromyographic and electrognathographic variables was able to predict chewing performance with an R2 value of .66. If chewing performance is used as an output measure of masticatory function, it may be possible to determine optimal ranges for electromyographic variables and jaw movements.

Adult↗
PubMed2000

Absolute and relative facial pressure-pain thresholds in healthy individuals.

AIMS: To investigate and compare absolute pressure-pain threshold (PPT) levels and ratios between craniofacial test and reference sites during consecutive PPT recordings, as well as over a 6-month period, in healthy individuals. This study also investigated PPT differences between genders and the clinical usefulness of different reference sites in the craniofacial region. METHODS: Twelve female and 12 male healthy individuals participated in the first examination. Six months later, 9 females and all of the males returned for a second examination. An electronic algometer was used to make 5 consecutive recordings of PPTs with a 2-minute interval at 3 reference sites: mental protuberance (PRO), first metacarpal bone (MET), and frontal bone (FRO), as well as at 3 test sites: temporomandibular joint, masseter muscle, and temporalis muscle. RESULTS: Absolute PPTs decreased significantly for all test sites during the 5 recordings, while they increased significantly between the examinations. No ratio with FRO as a reference site changed significantly. The males had significantly higher absolute PPTs than the females at PRO and FRO sites. CONCLUSION: This study shows that absolute PPT levels in healthy individuals change significantly during consecutive PPT recordings, as well as over a 6-month period; this limits the usefulness of such measurements. This study also shows that the use of relative PPTs with the FRO as a reference site is useful, both for comparison between groups and for longitudinal studies.

Adult↗
PubMedDate not supplied

Pseudo-dental pain and sensitivity to percussion.

Two case reports examine a little-known cause of dental pain and sensitivity to percussion. Contrary to the traditional assumption that pain and sensitivity to percussion almost always are diagnostic of pulpal inflammation and/or necrosis, these symptoms actually may be referred to the sensitive tooth from trigger points in the masticatory muscles. Therefore, myofascial pain syndrome must be ruled out in patients who have dental pain and display sensitivity to percussion.

Adult↗
PubMed2003

The effect of unilateral partial edentulism to muscle thickness.

OBJECTIVE: Teeth and muscles play a very important role for occlusal equilibrium and function. When tooth loss begins, it may also affect the function of the muscle tissues. METHODS: The thickness of the masseter and anterior temporalis muscles were measured bilaterally in 30 healthy fully dentate adults and in 30 unilateral edentulous patients by using ultrasonographic imaging. All scans were carried out by the same radiologist to eliminate the inter-observer difference, using a real time scanner (Toshiba SSA- 270 A Japan). A 7.5 MHz linear transducer was used. The transducer was held against the cheek with light pressure. The effect of age, sex, duration of the partial edentulism, unilateral chewing habits of the individuals to the muscle thickness were also evaluated. In all subjects, facial proportion index was also determined. RESULTS: No study has been found in the literature concerning the masticatory muscle thickness in unilateral partial edentulous patients. Therefore, the main purpose of this study was to compare and establish the differences of the muscle thicknesses between dentate and edentulous sides in unilateral partial edentulous patients with ultrasonography and to test whether the variation in the thickness of the muscle is related to the variation in the facial morphology using the facial proportional indices in the study groups. In the present study, ultrasonography revealed a large variation in the thicknesses of the masseter and temporalis muscles in experimental and control groups, during both relaxed and contracted conditions. The thicknesses of the muscles in females during both relaxed and contracted conditions were less than those in males in both control and experimental groups. In experimental group, a high negative correlation was found between the thickness of the masseter muscle and Facial proportion Index (FPI) in females, however, the statistical analysis showed no significant difference in males. Also, a high negative correlation was found in control group, especially in females. There was no statistically significant relationship between thicknesses of the muscles and age of the subjects in both groups. There was no statistically significant relationship between unilateral chewing habits and muscle thickness. In this study, the duration of partial edentulism did not affect the thickness of the muscles. CONCLUSION: Further research is required to study muscular atrophy for comparison with total edentulism.

Adult↗
PubMed2004

Electromyographic evaluation of masticatory function in denture wearers in related to existing occlusal support.

The aim of this study was to clarify the relationship between partially edentulous pattern and the masticatory function in removable partial denture wearers. Eighty eight removable partial denture wearers and 7 subjects with intact dentition volunteered for this study. Using the Eichner's index, all subjects were divided into 6 groups. Electromyographic (EMG) activities of the masticatory muscle were recorded during chewing a piece of raw carrot. The masticatory function was analyzed by using the variation coefficient (VC) of the time parameter of EMG interval recorded during mastication. The association of the VC with group classification based on Eichner's index was analyzed using analysis of covariance with gender and age as the covariates. The result of the analysis revealed that the VC was significantly associated with group classification and the patients in groups without posterior occlusal supports exhibited significantly higher VC values than those in groups with posterior occlusal supports. These findings suggested that the reduced function in patients without the posterior occlusal contacts was difficult to attain improved and satisfactory outcome with removable partial dentures and that there is a significant need for posterior occlusal support for the preservation of masticatory function.

Adult↗
PubMed1990

Submucosal plexus alone integrates motor activity and epithelial transport in rat jejunum.

It has been well established in several mammalian species, including humans, that contractions of jejunal smooth muscle correlate temporally with increases in mucosal ion transport. Furthermore, this correlation is abolished through local application of neurotoxins, suggesting interaction of enteric neurons. The purpose of this study was to determine whether the myenteric plexus is involved in this correlation. In the rat jejunum in vivo, we simultaneously measured phasic changes in intraluminal pressure and transmural potential difference (PD) as indicators of smooth muscle motor activity and epithelial ion transport, respectively. We compared the temporal association of these parameters in control animals with animals in which either the extrinsic nerves only or the extrinsic nerves and the myenteric plexus of a 5-cm jejunal segment had been ablated 30 days previously. A one-to-one coupling between muscle contractions and transmural PD fluctuations was observed in all animals; ablation of the extrinsic and/or myenteric neurons did not eliminate this correlation. We conclude that, in the rat jejunum, the submucosal plexus alone can integrate the reflex that couples ion secretion to muscle contraction.

Animals↗