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PubMed1993

Location, morphology, and central projections of mesencephalic trigeminal neurons innervating rat masticatory muscles studied by axonal transport of choleragenoid-horseradish peroxidase.

Retrograde and transganglionic transport of horseradish peroxidase conjugated to the B-fragment of cholera toxin (B-HRP) was used to study the location, morphology, and central projections of mesencephalic trigeminal (Me5) neurons innervating rat masticatory muscles. Labeled Me5 cell bodies were found throughout the Me5 nucleus from a level slightly caudal to the trigeminal motor nucleus to the level of the superior colliculus 5 mm further rostrally. Occasionally, labeled Me5 cells were observed in the anterior medullary velum, in the cerebellum, and in the brainstem contralateral to the B-HRP injection. The vast majority of the labeled Me5 cells were pseudounipolar, but multipolar cells were also found. Extensive central projections from labeled Me5 cells could be seen extending from the nucleus of Darkschewitsch rostrally to the C2 segment caudally. Small but consistent projections from Me5 neurons were observed in nuclear islands among the incoming Me5 root fibers. Trigeminal and hypoglossal motor nuclei received direct projections from Me5 cells, but not the facial motor nucleus. The most prominent Me5 projections appeared in the brainstem reticular formation, including the supratrigeminal nucleus. Smaller projections also extended into the main sensory trigeminal nucleus, trigeminal subnucleus oralis, and the nucleus of the solitary tract.

Animals↗
PubMed1988

Reflex excitation of masticatory muscles induced by algesic chemicals applied to the temporomandibular joint of the cat.

Algesic chemicals (7 per cent NaCl, KCl and histamine) applied to this joint of anaesthetized cats evoked reflexes in the ipsilateral anterior digastric, temporalis and genioglossus muscles. Whereas the application of isotonic saline was only briefly and weakly effective, and only consistently so in the genioglossus, a single application of each chemical could produce a sustained increase in electromyographic activity of all the muscles. The excitatory effects usually lasted 30 s or more, and the onset latency and latency to peak activity were usually less than 10 s and 20 s, respectively. These reflex excitatory effects and their temporal characteristics are consistent with recent findings of the effects of these algesic chemicals on trigeminal brainstem nociceptive neurones, and provide support for concepts of temporomandibular joint pain and dysfunction that are based on reflexly induced increases in masticatory muscle activity.

Animals↗
PubMed1998

Relationship between masticatory muscle activity and vertical craniofacial morphology.

The purpose of this study was to investigate the relationship between masticatory muscle activity during the day and vertical craniofacial morphology. The sample comprised 30 subjects (20 males and 10 females, age range 15 to 28 years, mean 24 +/- 3.2 years) who had normal anteroposterior skeletal relationships and complete or nearly complete dentition without serious malocclusion or temporomandibular dysfunction. Using a portable electromyographic recording system, activities of the masseter, temporal, and digastric muscles were recorded for 3 hours during the day, excluding time spent eating, sleeping and exercising. A lateral cephalogram was taken of each subject with the teeth in occlusion. Activities of the masseter, temporal, and digastric muscles consisted mainly of low-amplitude bursts. The duration of digastric muscle activity was greater than that of either the masseter or temporal muscles. Masseter and digastric muscle activity was positively correlated. The activities of the masseter, temporal, and digastric muscles during the day consist of low-amplitude bursts and may be related to vertical craniofacial morphology.

Adolescent↗
PubMed1989

Balance in masticatory muscle activity during natural chewing and submaximal clenching.

The balance in the electromyographic (EMG) activities of the left and the right masseter and the left and right anterior temporal muscles during chewing and during submaximal clenching at 10% and 50% of the maximum voluntary contraction in the inter-cuspal position was investigated in twenty healthy adults. Muscular asymmetry patterns during chewing and clenching were positively correlated for both pairs of masticatory muscles investigated at the 50% level (P less than 0.01-P less than 0.001) and for the masseter muscles, also at the 10% level (P less than 0.01). Stronger correlations in muscular asymmetry were found for the masseter muscles and at the higher submaximal clenching level. In general, the masseter muscles displayed a greater degree of asymmetric activity than the anterior temporal muscles during both chewing and clenching (0.05 less than P less than 0.1-P less than 0.025). The average EMG amplitudes of both masseter or both anterior temporal muscles within each subject showed no correlation between clenching and chewing. The correlations between muscular asymmetries observed during static (clenching) and dynamic (chewing) conditions suggest that there are common factors influencing these activities.

Adult↗
PubMedDate not supplied

[Numerical simulation (FEM) of the human mandible: validation of the function of the masticatory muscles].

The article describes part of a research project aiming to develop a new modular software tool for the individual dynamic numerical simulation of the human mandible using the finite element method (FEM). Its planned use in the clinical setting makes it very important to validate the results of the simulations. Here, the function of the masticatory muscles is to be tested. On the basis of biomechanical data from the literature, standard movements, such as closing the mouth, forward movement, lateral movement or backward movement, were dynamically simulated. Apart from muscle activity, the movements of the mandible are defined by the temporomandibular joint. At present, translating the condylar dynamics to the simulation still poses problems. For this reason, therefore, simulations of the two extreme cases "fixed" and "force-free" condyles are compared. While in the case of fixed condyles, some of the movements could be reproduced either not at all or only weakly, in the case of force-free condyles, all standard movements were reproduced qualitatively, albeit without the guiding effect of the joint capsule or the articular disc.

Biomechanical Phenomena↗
PubMed1995

Effect of amplitude normalization on surface EMG linear envelopes of masticatory muscles during gum chewing.

Various amplitude normalization procedures for surface electromyographic (EMG) signals have been utilized to reduce the inter- and intrasubject variability of data collected on gait analysis. We examined two normalization methods (normalization to mean of ensemble average: NME, and normalization to peak of ensemble average: NPE) for intersubject variability and reproducibility surface EMG profiles for the masticatory muscles during unilateral gum chewing. The EMG profiles for the anterior temporal (Ta), posterior temporal (Tp), masseter (M) and anterior belly of the digastric (Da) muscles on the chewing side from five normal subjects were made at three different sessions. Coefficients of variation and intraclass correlation coefficients were used to assess variability and reproducibility. Each normalization procedure the intersubject variability of unnormalized EMG profiles for Ta, Tp and M. The NME procedure provided lower intersubject variability for Da. The reproducibility of unnormalized profiles for Ta, Tp and M was significantly improved by both procedures (p < 0.05). NME on Da was more effective in its reproducibility (p < 0.05). We found that the phasic characteristics of muscular activity influenced the outcome of amplitude normalization.

Adult↗
PubMed1996

[An electromyographic study of masticatory muscle changes in patients with mandibular protrusion before and after orthognathic surgery].

27 patients with mandibular prognathism were studied with 40 normal people as controls. All subjects were examined with electromyogram. The result shows that the voltage were lower in patients before surgery, the double-silent period inspect rate were much higher than normal subjects. It was concluded that the electromyo-activity of masticatory muscles had some character in patients after surgery: (1) The voltage of masseter and temporal muscle increased significantly during maximal voluntary clenching. (2) During protrusive border movement the voltage of masseter increased while the changes of voltage in the temporal muscle were small. (3) In lateral border movement, the voltage of masseter and temporal muscle increased in the working side, while the balaning side changed slightly. (4) Electromyo-voltage decreased in rest position. (5) The duration of silent period had a tendency of shortening after surgery. It demonstrated the feasibility and necessity of treating mandible deformity through orthognathic surgery, and it provided theoretical and practical support of evaluating the treatment effect of such kind of patients.

Adult↗
PubMed2001

[The influences upon the passive tensile of the masticatory muscles and ligaments by Herbst appliance under various bite reconstruction--a three dimensional finite element analysis].

OBJECTIVE: This study aimed to provide some biomechanical references for the clinical use and improvement of Herbst appliance. METHODS: The three-dimensional model of the 'Temporomandibular joint mandible Herbst appliance system' was set up by SUPER SAP software (version 9.3). On this model, the passive tensile in the masticatory muscles and ligaments were analyzed under various bit reconstruction designed according to specified advanced displacement and vertical bite opening. RESULTS: When Herbst appliance drove the mandible forward, there was not any tensile in the medial, lateral pterygoid and the collateral ligament, while the temporalis, the deep paret of masseter, the stylomandibular ligament, and the sphenomandibular ligament were passively drawn. Under various bite reconstruction, the passive tensile in the medial temporalis, the posterior temporalis, the stylomandibular ligament and the sphenomandibular ligament increased with the amount of the advancement of the mandible; The passive tensile in the posterior temporalis and the deep part of masseter increased with the amount of vertical bite opening of the mandible. CONCLUSION: The StL, SpL, PT and AT played an important role in functional reconstruction of mandible by Herbst. All five group of bite reconstruction (3-7 mm advancement, 4-2 mm vertical bite opening of the mandible) designed by this study can be selected in clinic according to the patient's capability of adaptation, the extent of malocclusion and the potential and direction of growth.

Finite Element Analysis↗
PubMed2000

Asymmetry of masticatory muscle activity during the closing phase of mastication.

The purpose of this study was to investigate the asymmetry of masticatory muscle activity between working and nonworking sides in the closing phase during mastication. Fifty adult subjects displaying normal oral function and occlusion participated in this study. Electromyographic (EMG) activity of the anterior temporalis and the superficial masseter muscle were recorded during mastication, simultaneously with motion data of the mandible. EMG activities of elevator muscles and their Asymmetry Index (AI) were analyzed depending on the vertical deviation of the lower incisal point with a two mm gap from the intercuspal position (ICP). EMG activities of both the anterior temporalis and the masseter on the working side were significantly greater than those on the nonworking side. Masseter muscles tended to show greater AI than the anterior temporalis muscles. Thus, asymmetry of the elevator muscles during mastication was a common finding in normal subjects. The normal range of variability of EMG activity and AI was confirmed in each section.

Adult↗
PubMed2003

Electromyographic activity of masticatory muscles and mandibular movement during function in marginal mandibulectomy patients.

The purpose of this study is to evaluate the masticatory muscle activity and mandibular movement during function in marginal mandibulectomy patients. Three marginal mandibulectomy patients and three healthy subjects participated in this study. The activities of the temporalis (TA) and masseter muscles (MM) on the normal and resected sides during maximum voluntary clenching (MVC) and gum chewing (Gch), and mandibular movement during Gch were analyzed. Paired t-test, Student's t-test and one-way ANOVA were performed at P < 0.05. For MVC, integrated EMG (iEMG) in patients was lower than in healthy subjects. When iEMG of each muscle activity in patients was compared, TA activity on the resected side was greater than that of MM. There were no differences between the normal and resected sides in TA or MM. For Gch, no differences in iEMG, burst or chewing time were found between patients and healthy subjects. MVC was greater than Gch in healthy subjects, but no difference was found in patients. The range of mandibular movement along the X axis in patients was greater than in healthy subjects. Within the limitations of this study, EMG activity in patients during MVC was remarkably lower than that in healthy subjects, and altered mandibular movement was observed.

Adult↗
PubMed1998

The effect of different condylar positions on masticatory muscle electromyographic activity in humans.

OBJECTIVES: The purpose of this study was to determine a condylar position that permitted the greatest total temporalis and masseter muscle activity in maximum static clench. STUDY DESIGN: Twenty normal adults, 9 women and 11 men, were evaluated to determine masseter and temporalis activity in maximum static clench with mandibular condyles in different therapeutic positions. Bimanually manipulated, leaf gauge, centric occlusion, and neuromuscular condylar positions were studied. RESULTS: When mandibular condyles were placed anteroinferiorly in a neuromuscular position, total masticatory muscle recruitment was the greatest. In a bimanually manipulated or a leaf gauge position, mandibular condyles were positioned superoposteriorly, producing the least amount of muscle recruitment. CONCLUSIONS: The result of any therapeutic position should be an improvement in muscle function. With respect to balance and activation, a neuromuscular condylar position proved to be the position capable of recruiting the greatest motor unit activity when compared with a bimanually manipulated position, a leaf gauge position, and a neuromuscular position.

Adult↗
PubMed1999

Three-dimensional dynamical capabilities of the human masticatory muscles.

Many habitual human jaw movements are non-symmetrical. Generally, it is observed that when the lower incisors move to one side the contralateral condyle moves forwards onto the articular eminence, whereas the ipsilateral condyle stays in the mandibular fossa, moving slightly to the ipsilateral side. These jaw movements are the result of contractions of active masticatory muscles and guided by the temporomandibular joints, their ligaments and passive elastic properties of the muscles. It is not known whether the movements are primarily dependent on passive guidance, active muscle control or both. Therefore, the objective of this study was to analyse the interplay between these factors during non-symmetrical jaw movements. A six-degrees-of-freedom dynamical biomechanical model of the human masticatory system was used. The movements were not restricted to a priori defined joint axes. Jaw movement simulations were performed by unilateral activity of the muscles. The ligaments or the passive elastic properties of the muscles could be removed during these simulations. Laterodeviations conform to naturally observed ones could be generated by unilateral muscle contractions. The movement of the lower incisors was hardly affected by the absence of passive elastic muscle properties or temporomandibular ligaments. The latter, however, influenced the movement of the condyles. The movements could be understood by analysing the combination of forces and torques with respect to the centre of gravity of the lower jaw. In addition, the loading of the condyles appeared to be an important determinant for the movement. This analysis emphasizes that the movements of the jaw are primarily dependent on the orientation of the contributing muscles with respect to this centre of gravity and not on the temporomandibular ligaments or passive elastic muscle properties.

Biomechanical Phenomena↗
PubMed2001

Changes in masticatory muscle activity according to food size in experimental human mastication.

The purpose of this study was to investigate the changes in masticatory muscle activity according to food size in human mastication. Sixteen subjects performed deliberate unilateral chewing of similarly cone shaped hard gummy jellies weighing 5 and 10 g. The masseter and anterior temporal muscle activity on both sides was recorded for the first 10 strokes. The normalized muscle activity during the chewing of the 10 g jelly was significantly higher than that of the 5-g jelly, and there was a considerably high significant correlationship between the muscle activity during the chewing of the 10- and 5-g jellies in each muscle on each side. The 10 g/5 g jelly ratio for the masseter muscle activity on the non-chewing side almost coincided with the theoretical energy ratio required to shear, although that of the chewing side was lower than the ratio. The 10 g/5 g jelly ratio for the temporal muscle activity on both sides almost coincided with the food height ratio. The results suggest that anterior temporal and masseter muscle activity changes according to the rate of change in the height of hard coherent food bolus and food resistance required to shear, respectively, during mastication.

Adult↗
PubMed1991

Short-term effect of the stabilization appliance on masticatory muscle activity in myogenous craniomandibular disorder patients.

The short-term effect (4 to 6 weeks) of a stabilization appliance on masticatory muscle activity was investigated in 26 myogenous craniomandibular disorder patients. The patients were instructed to clench at 10% and 50% of their maximum clenching effort in the intercuspal position and on the appliance. Recordings were made before and immediately after appliance delivery, and 2 and 4 weeks after delivery. The average EMG activity of the masseter muscles remained the same during the period of appliance use, whereas the anterior temporal muscles showed an immediate and long-lasting reduction in activity. The appliance also resulted in an improvement in the balance of left and right masseter muscle activity. There was a minor improvement in temporal muscle symmetry at the 50% clenching level and after 4 weeks of appliance use.

Adolescent↗
PubMedDate not supplied

Masticatory muscle pain: an important indicator of giant cell arteritis.

Giant cell arteritis (GCA) is a polysymptomatic disease which constitutes an ophthalmic emergency because early recognition and management can prevent blindness. There is conflicting information in the literature on the validity, sensitivity, and specificity of various systemic symptoms and signs of GCA. This paper presents a review of our prospective studies on the subject, and our findings are particularly relevant to dentists. We investigated 363 patients in a prospective study. Positive temporal artery biopsy was seen in 106 patients and negative in 257 referred for diagnosis of GCA. Systemic symptoms and signs of GCA and erythrocyte sedimentation rate (Westergren-ESR) and C-reactive protein (CRP) levels were compared in these two groups of patients. The odds of having a positive temporal artery biopsy (i.e., GCA) were 9.1 times greater with jaw claudication (pain in masticatory muscles on eating), 3.4 times with neck pain, 3.2 times with CRP > 2.45 mg/dL, 2.0 times with ESR 47.107 mm/hr, 2.7 times with ESR > 107 mm/hr, and 2.0 times when the patients were aged > or = 75 years. Other signs and symptoms did not show a significant association with a positive biopsy. Our study showed that "normal" ESR values do not rule out GCA but that CRP is a more useful test than ESR. Since jaw claudication is one of the most important symptoms of GCA, dentists should keep this possibility in mind when older patients come complaining of jaw pain while eating.

Aged↗
PubMed1987

Mandibular condylosis and apertognathia as presenting symptoms in progressive systemic sclerosis (scleroderma). Pattern of mandibular bony lesions and atrophy of masticatory muscles in PSS, presumably caused by affected muscular arteries.

Apertognathia (open bite) is usually a developmental deformity of the jaws and the dentoalveolar segments in childhood and adolescence. The sudden insidious appearance of an open anterior bite in adult life is extremely rare and may be due to pathologic condylar fractures (with displacement) or to bilateral condylosis. To the best of our knowledge, only five cases of bilateral mandibular condylosis in progressive systemic sclerosis (PSS) have been reported in the literature, and the present article deals with the sixth known case. In the 22-year-old woman presented in this article the mandibular manifestations were the very early symptoms of PSS, which had a very rapid fatal course. A review of the literature is presented, and attention is called to the serious significance of sudden apertognathia. PSS is a chronic generalized disease of the small arterial vessels and the mesenchyme tissues of unknown origin. The musculoskeletal system is often involved, and the disease may affect the mandible, causing bony erosions, osteolysis, and atrophy of the masticatory muscles. It is believed that these bony lesions are of ischemic origin. The lesions, which are usually bilateral, occur only in the condyles, the coronoid processes, and the gonial angles. The main arterial blood supply to the mandible and to the major part of the ascending ramus originates from the inferior alveolar artery. The blood supply of the condyles, the coronoid processes, and the gonial angles originates in small muscular arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗