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PubMedDate not supplied

Coordinated electromyographic activity of the human masseter and temporalis anterior muscles during mastication.

The present report aimed at evaluating the within- and between-subject electromyographic coordination between the masseter (M) and temporalis anterior (T) muscles during the performance of a standardized chewing task. Electromyographic activity of M and T muscles was recorded in 60 young healthy adults (30 men, 30 women) during two 15-s unilateral mastications of gum. Left-right differential potentials (delta M = MR-ML, delta T = TR-TL) were computed and the square root of (delta M2 + delta T2) moduli were calculated. The maximum modulus relative to each masticatory cycle was located, and each modulus and differential potential were expressed as a % of the maximum modulus for each subject and chewing trial. For each subject and chewing side, the masticatory frequency was computed, and statistics of the moduli as %s of the maximum were determined by means of bivariate analysis. Within-subject repeatability of the unilateral chewing patterns was good. Mean population values for the modulus position (bivariate analysis), chewing frequency, and maximum modulus of the differential potentials (univariate statistics) were computed. A significant gender difference was found for the masticatory frequency, with larger values in men than in women. Conversely, no gender or side differences were found for the mean values of the maximum modulus or for the mean position of the percentage moduli. The chewing test applied allowed the evaluation of the neuromuscular coordination during the performance of a standardized physiologic activity. In particular, it quantified the within-subject and chewing side repeatability of the muscular pattern.

Adult↗
PubMed1986

Intracranial stimulation of the trigeminal nerve in man. I. Direct motor responses.

Direct electrical stimulation of the intracranial portion of the trigeminal nerve was performed in 23 subjects undergoing retrogasserian thermocoagulation for the treatment of idiopathic trigeminal neuralgia. In 16 subjects, who were having the operation for the first time, neurological examination was normal, as was neurophysiological testing of trigeminal function. Seven subjects were being operated for the second time, owing to a recurrence of symptoms. In all the subjects being operated for the first time, direct motor responses were obtained from ipsilateral temporalis, masseter and anterior belly of the digastric. The motor conduction velocity was equal for the fibres directed to all three muscles. This was estimated to be 54m/s in the masseteric nerve and 55-68 m/s in the intracranial portion of the trigeminal nerve. Patients who had undergone previous thermocoagulation had a considerably slower conduction velocity. It is supposed that myelin sheaths had been damaged at the first operation.

Electric Stimulation↗
PubMed2004

Influence of age on adaptability of human mastication.

The objective of this work was to study the influence of age on the ability of subjects to adapt mastication to changes in the hardness of foods. The study was carried out on 67 volunteers aged from 25 to 75 yr (29 males, 38 females) who had complete healthy dentitions. Surface electromyograms of the left and right masseter and temporalis muscles were recorded simultaneously with jaw movements using an electromagnetic transducer. Each volunteer was asked to chew and swallow four visco-elastic model foods of different hardness, each presented three times in random order. The number of masticatory cycles, their frequency, and the sum of all electromyographic (EMG) activity in all four muscles were calculated for each masticatory sequence. Multiple linear regression analyses were used to assess the effects of hardness, age, and gender. Hardness was associated to an increase in the mean number of cycles and mean summed EMG activity per sequence. It also increased mean vertical amplitude. Mean vertical amplitude and mean summed EMG activity per sequence were higher in males. These adaptations were present at all ages. Age was associated with an increase of 0.3 cycles per sequence per year of life and with a progressive increase in mean summed EMG activity per sequence. Cycle and opening duration early in the sequence also fell with age. We concluded that although the number of cycles needed to chew a standard piece of food increases progressively with age, the capacity to adapt to changes in the hardness of food is maintained.

Adaptation, Physiological↗
PubMed2000

Jaw-tongue reflex: afferents, central pathways, and synaptic potentials in hypoglossal motoneurons in the cat.

The tongue position is reflexively controlled by the jaw position (the jaw-tongue reflex). The purpose of this study was to clarify the mechanism of this reflex in terms of afferents, central pathways, and synaptic potentials in hypoglossal motoneurons in the cat. Intracellular recordings from hypoglossal motoneurons revealed that electrical stimulation of the temporalis muscle nerve evoked excitatory and inhibitory post-synaptic potentials in hypoglossal motoneurons. The threshold of temporalis muscle nerve stimulation for evoking the synaptic potentials was higher than 2.0 times the nerve threshold. The amplitude of the potentials increased with stimulus intensity up to 5.0 times the nerve threshold. Punctate light pressure applied to the temporalis muscle induced a tonic depolarizing potential in hypoglossal motoneurons on which action potentials as well as depolarizing synaptic activation noise were superimposed. On the other hand, electrical stimulation of the temporalis muscle during jaw-opening could slightly inhibit the electromyographic activities in the genioglossus and styloglossus muscles. Lesions including the Probst's tract at the level caudal to the trigeminal motor nucleus abolished both excitation and inhibition in hypoglossal motoneurons induced by tonic depression of the lower jaw, but exerted no effects on either the tonic stretch reflex or the trigemino-hypoglossal reflex. In contrast, lesions including the trigeminal spinal tract produced no changes in either excitation or inhibition of hypoglossal motoneurons induced by temporalis muscle afferents, whereas the excitation of hypoglossal motoneurons was abolished by the lesions. We conclude that the group II muscle spindle afferents from the temporalis muscle are primarily responsible for evoking the jaw-tongue reflex.

Afferent Pathways↗
PubMed1993

Effect of jaw opening on masticatory muscle EMG-force characteristics.

This study was designed to evaluate the way in which changes in vertical jaw opening affected the relative contributions of various masticatory muscles to bite force production. EMG activity was recorded simultaneously from the masseter, and anterior, middle, and posterior temporalis muscles, during controlled isometric biting at different force levels and vertical jaw openings. EMG-force characteristics were compared between muscles and bite openings. All but the posterior temporalis muscle displayed significant increases in muscle activity with increased bite force production; the masseter muscle demonstrated the largest activity increments. Statistically significant changes in muscle function due to jaw opening were demonstrated only for the masseter muscle, though similar trends were observed for the anterior and middle temporalis muscles. Minimum increases in muscle activity associated with increases in bite force occurred between 9 and 11 mm of opening, measured at the first molar, for all three muscle groups. The results of this study suggest that changes in masticatory muscle length resulting from vertical jaw opening cause alterations in muscle contractile properties, but the relative contributions of various masticatory muscles toward bite force production may also be affected by biomechanical factors and neural control adaptations.

Biomechanical Phenomena↗
PubMed1994

Direction of a bite force determines the pattern of activity in jaw-closing muscles.

Human individuals were hypothesized to use the same pattern of jaw muscle activity to produce the same bite force. To test this hypothesis, we used a 2-mm-thick force transducer to monitor the magnitude and direction of a bite force between a single pair of occluding first molars. Five subjects performed standardized bite force tasks. Six different magnitudes were tested, each in five directions. The surface electromyographic (EMG) activity in the left and right masseter and temporalis muscles was recorded, integrated, and normalized. Ratios of the EMG activity of paired muscles (e.g., the ratio of working temporalis and working masseter) were calculated for each bite force task. Each ratio was roughly constant for each direction of bite force, regardless of its magnitude. In contrast, when the magnitude of bite force was the same but the directions were different, the ratio was not constant. We conclude that the direction of a bite force, not its magnitude, determines the pattern of activity of jaw-closing muscles. The shared patterns of muscle activation may be the result of a subconscious optimization of jaw muscle forces to improve efficiency.

Adult↗
PubMed2002

The influence of various attachment types in mandibular implant-retained overdentures on maximum bite force and EMG.

The type of attachment that is used in oral rehabilitation by means of implant-retained mandibular overdentures may influence the retention and the stability of the denture. In this study, we examined the hypothesis that a better retention and stability of the denture improve the oral function. Eighteen edentulous subjects received 2 permucosal implants, a new denture, and, successively, 3 suprastructure modalities. Maximum bite force and electrical activity of the masseter and temporalis muscles were measured. The maximum bite force nearly doubled after treatment for each of the 3 attachments. However, the average bite force after treatment was still only two-thirds of the value obtained for dentate subjects. No large differences in maximum bite force and muscle activity were found among the 3 attachment types. Temporalis activity was significantly lower than masseter activity when subjects clenched without implant support. There was no difference in activity when subjects clenched with implant support.

Adult↗
PubMed2003

Myosin heavy-chain isoform composition of human single jaw-muscle fibers.

Diversity in muscle contractile properties is based on the variability of contractile properties of single muscle fibers which in turn is related to the presence of different myosin heavy-chain (MyHC) isoforms. Human jaw muscles are featured by many hybrid fibers expressing more than one MyHC isoform. The purpose of this study was to determine the proportion of each isoform within these fibers for evaluation of the fiber's capacity of producing a large diversity in contractile properties. Electrophoretic separation of MyHC isoforms was performed on 218 single fibers of the temporalis and digastric muscles. Of these fibers, 100 were classified as hybrid fibers. Most hybrid fibers co-expressed MyHC-IIA and -IIX (n = 62); a smaller number co-expressed MyHC-I and -IIA (n = 14), MyHC-I and -IIX (n = 12), and MyHC-I, -IIA, and -IIX (n = 12). The proportions of the individual MyHC isoforms in the hybrid fibers varied highly, suggesting a large range of contractile properties among these fibers.

Aged↗
PubMed2006

The use of a bruxchecker in the evaluation of different grinding patterns during sleep bruxism.

A variety of problems involving the masticatory system can be partially attributed to parafunctional habits such as bruxism. These include occlusal trauma, abfractions, tooth migration, as well as temporomandibular dysfunction. Since bruxism is considered a contributing factor to the above-mentioned dental problems, it is essential to consider parafunctional habits in the diagnosis and treatment planning before doing any occlusal reconstruction. However, the problem lies in the lack or absence of a simple device or gauge useful to be able to diagnose and evaluate the occlusal schemes in the patient's grinding pattern. In this study, we have developed a very simple device (BruxChecker) for evaluating the grinding patterns in sleep bruxism. Using the BruxChecker, it was possible to visualize real or actual interferences during sleep bruxism. Therefore, examination of the grinding pattern using this device is necessary and crucial for making the proper treatment plan for each patient.

Adolescent↗
PubMed2002

Trismus in a 6 year old child: a manifestation of leukemia?

Trismus is a firm closing of the jaw due to tonic spasm of the muscles of mastication from disease or the motor branch of the trigeminal nerve. Trismus may be produced by a variety of reasons such as dental abscess, trauma, following mandibular block with local anesthesia, as a result of radiation to the facial muscles, and patients after chemotherapy. A case of a referral of a six-year-old boy to a dentist from an ENT due to severe limitation in jaw opening is presented. Intraoral examination and panoramic radiograph demonstrated no signs of infection and/or other pathology. After a diagnosis of trismus was made, due to his icteric appearance, the general fatigue and loss of appetite in the last few days, palpated and sensitive lymph nodes in the submandibular and cervical regions, the child was referred for a complete blood count and sedimentation rate. The laboratory and clinical findings resulted in the diagnosis of acute lymphoblastic leukemia (ALL). Dental and oral manifestations of ALL are discussed, and the trismus may be explained by an intensive infiltration of leukemic cells into the deep portion of the contracting muscles of the face. This case emphasizes the importance of physical examination and independent judgement made by dentists, even when patients are referred to them by other members of the medical communities.

Blood Cell Count↗
PubMedDate not supplied

The effect of the occlusal splints on the treatment of temporomandibular disorders--a computerized electromyographic study of masseter and anterior temporalis muscles.

The effect of the occlusal splints on the treatment of temporomandibular disorders--a computerized electromyographic study of masseter and anterior temporalis muscles. The comprehension of the determinant factors of temporomandibular disorders is still inconclusive, since that the etiology is associated with multidisciplinary knowledge. The purpose of this study was to evaluate the effectiveness of the therapy with occlusal splints in patients with temporomandibular disorders by the computerized electromyography. It was selected twenty-two patients with signs and symptoms with changes of the stomatognathic system, males and females patients, with ages between 18 and 53 years old. Plane occlusal surface splints were constructed in acrylic resin and placed in each patients. Electromyographic evaluations of masseter and anterior temporalis muscles were performed during the mandibular isometric clenching before inserting and after 90, 120 and 150 days of using the occlusal splints. After 90 and 120 days of using them, they were changed by canine guidance and group function respectively. The results after the polynomial regression analysis showed that there were significant reductions (p < 0.05) in the electromyographic activity along the entire period of treatment during the mandibular isometric clenching for masseter and anterior temporalis muscles. The group function showed a shorter eletromyographic activity for both muscles.

Adolescent↗
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↗
PubMed1989

[Temporalis muscle flaps for coverage of intraoral defects following radical surgery for oral carcinoma].

The use of the temporalis muscle flap for reconstruction of intraoral defects is not a new procedure. In the oral and maxillofacial surgery clinic of Thessaloniki we have been using this muscular flap for the last three years. The results from the application of this method showed that the use of the temporalis muscle flap is preferable in comparison with the forehead skin flap which we were using in the past for the reconstruction of intra-oral defects left behind after excising large malignancies of the mouth and jaws.

Aged↗
PubMed1984

Temporalis pericranial muscle flap for reconstruction of the lateral face and head.

Large ablative surgical tissue defects of the lateral face and head can pose a difficult task for the reconstructive surgeon who must choose from among a large variety of possible reparative techniques. In many situations the temporalis pericranial muscle flap offers the outstanding feature of providing a large amount of soft tissue at no direct expense of donor site skin cover. It is easily obtained and results in negligible functional loss. With care taken to preserve the neurovascular pedicle, this flap may be rotated in multiple directions and even overturned as either surface can receive surface skin closure. The amount of operative time and effort required is much less than for many of the more elaborate reconstructive flaps. Five representative cases are presented.

Adult↗
PubMed1993

Activity of anterior temporalis and masseter muscles during deliberate unilateral mastication.

The reproducibility of electromyographic parameters descriptive of deliberate unilateral chewing (activity, timing, curve symmetry) was investigated in normal asymptomatic volunteers. The best time for the initiation of muscle activity was also examined, with the future aim of staging TMJ internal derangements. The results suggest that activity is the most reliable variable, indicating that it may be helpful in describing muscle incoordination. When time was used in conjunction with another variable, overall reproducibility decreased.

Adult↗