Fifteen young pigs were used in this study. The animals were divided into three groups; 1. Group for removal of the temporal muscle, 2. Group for removal of the masseter muscle, 3. Group for removal of masseter and internal pterygoid muscles. The animals were anesthetized with 3.5% chloral hydrate intraperitoneaily. In the right side the head was shaved. The masticatory muscle was removed. The animals were sacrificed four .months later. The head was separated from trunk and cleaned by boiling in a solution of potassiumm hydroxide. The results were as follows; 1. In the group for removal of the temporal muscle, the Coronoid process of the mandible was resorbed. 2. In the group for removal of the masseter muscle, there was produced asymmetrical growth of the mandible, attrition of the molar teeth in the control side, and resorption of the mandibular angle. 3. In the group for removahof the Masseter and Internal muscles, the changes were more severe than that of the group for removal of the masseter muscle. The mandibular angle was completely absent. 4. The growth of the bone seems definitely related to the presence of the muscular tissue actively pulling upon it.
Animals ; Chloral Hydrate ; Guinea Pigs* ; Guinea* ; Head ; Mandible* ; Masseter Muscle ; Masticatory Muscles* ; Molar ; Muscles ; Pterygoid Muscles ; Swine ; Temporal Muscle ; Tooth

OBJECTIVETo study the effects of repeated + Gz forces on masticatory muscles.

METHODS48 male Wistar rats were randomly divided into 4 groups. Group A was normally fed. Group B was only fixed with rat-kept devices for 5 minutes. Group C was borne + 1 Gz for 5 minutes. Group D was repeatedly exposed + 10 Gz (each for 30 s, onset rate about 0.5 G/s, 5 times/d with + 1 Gz 1 minute intervals, 4 d/wk, 3 weeks in total). The histological changes of the masseter, temporal and lateral pterygoid muscles were observed.

RESULTSNo abnormal changes were observed in Group A, B and C. But pathological changes could be found in group D. The wrench and deformation of muscular fibers, the dissolution of partial myofibril, the swelling of mitochondria, the reduce of hepatin from the masseter and lateral pterygoid muscles could be found.

CONCLUSIONSRepeated + Gz stresses could induce the damage of masticatory muscles in different degrees.

Animals ; Hypergravity ; Male ; Masseter Muscle ; pathology ; ultrastructure ; Masticatory Muscles ; pathology ; ultrastructure ; Microscopy, Electron ; Pterygoid Muscles ; pathology ; ultrastructure ; Rats ; Rats, Wistar ; Temporal Muscle ; pathology ; ultrastructure ; Time Factors

PURPOSE: The purpose of our study was to evaluate the volume of pre- and post operative masseter muscle and bite force in mandibular prognathic patients treated with SSRO with the use of the 3D CT imaging technique and occlusal force meter. MATERIALS AND METHODS: The study group consisted of 12 patients with mandibular prognathism (5 males and 7 females) who underwent mandibular setback surgery (BSSRO) in the Department of Oral and Maxillofacial Surgery, Samsung medical center. Bite force was measured at pre op, post op 3, 6 and 12 months by occlusal force meter(GM10, Nagano Keiki, Japan) The preoperative CT examination of subjects was performed between one month prior to operation and one year after to operation. And muscle volume was measured. RESULT: As compared to preoperative measurements at 1 year postoperatively the masseter and internal pterygoid muscle volume were diminished (p<0.05) The bite force steadily recovered, so at postoperatively 6 months reached the preoperative level. And at 1 year after operation, the maximum bite force was significantly greater than preoperative levels. No significant correlation was presented between masseter muscle and bite force (p>0.05), internal pterygoid muscle and bite force (p>0.05). CONCLUSION: In this study, the results showed that volume and bite force of the masticatory muscles decresed significantly immediate after orthognathic surgery for mandibular set-back. However, reduction of maximum bite force disappears within 6 months after surgery.
Bite Force ; Bites and Stings ; Humans ; Male ; Masseter Muscle ; Masticatory Muscles ; Muscles ; Orthognathic Surgery ; Prognathism ; Pterygoid Muscles ; Surgery, Oral

OBJECTIVETo find out the characteristic topographic distribution of the muscle spindles in human masseter and temporal muscle, and to clarify the neurobiology roles of masticatory muscles during chew and adjusting mandibular position.

METHODSThe muscle spindles of masseter and temporal muscle on both sides of 5 human corpses fixed in formalin for more than 1 year were observed and quantitatively analyzed by picture analysis equipment.

RESULTSThe muscle spindles were maldistributed and spindles were commonly clustered in some individual portions, and the muscle spindle figures were diversiform, which were predominantly composed of the spindle simple and spindle complexes. The masseter spindles of the deep portion were obviously more than that of the superficial. Spindles of temporal muscle were concentrated in the anterior approach to the coracoid.

CONCLUSIONThe distribution of muscle spindles in the masseter and temporal muscle is heterogeneous, spindle density in the deep portion of masseter and the anterior of temporolis muscle is greater than others. The deep of masseter and the anterior of temporal muscle play an important part in maintaining mandibular position and balance.

Cytoskeleton ; Humans ; Mandible ; Masseter Muscle ; Masticatory Muscles ; Muscle Spindles ; Temporal Muscle

OBJECTIVETo evaluate the effects of bruxism on masticatory muscle electromyographic (EMG) activity.

METHODSTwenty-four bruxers and sixteen asymptomatic control subjects were included through questionnaire and clinical examination. EMG activity was recorded by placing surface electrodes on bilateral anterior temporalis (TA), masseters (MM), anterior digastrics (DA) and sternocleidomastoid (SCM) muscles. EMG activities at rest, during maximal voluntary clenching in intercuspal position and swallowing were recorded by means of Bio PAK system.

RESULTSEMG activities of TA and MM at rest were significantly higher in bruxism group than in control group (P<0.05). When subjects clenched their teeth in intercuspal position, the activities of TA and MM were much lower in bruxism group than in control one (P<0.05). EMG activity during swallowing was no significant difference between the two groups. The asymmetry index of bilateral TA and MM in bruxism group was a little higher than the control group, but there was no significant difference between the two groups (P>0.05).

CONCLUSIONMasticatory muscle dysfunction of bruxers is mainly represented as higher potential in postural position and lower potential during maximal voluntary clenching in intercuspal position of anterior temporalis and masseters.

Adult ; Bruxism ; Electromyography ; Female ; Humans ; Male ; Masseter Muscle ; Masticatory Muscles ; Muscle Contraction ; Temporal Muscle

To elucidate the effects of food texture such as hardness, cohesiveness, adhesiveness on mastication procedure, the electromyographic activity (EMG) of the masticatory muscles and the chewing movements were analyzed in eighteen young subjects during ordinary chewing. Seven different foods were selected by sensory texture profiling and mechanical test with texturometer; egg white, sausage, pizza cheese, yang-geng, biscuit, peanut and almond. The indexes of jaw movements used were the chewing number, chewing time, maximum opening, average opening, closing velocity and opening velocity. The EMG indexes analyzed were maximum and average integrated amplitude of the anterior temporal and masseter muscles. The results obtained were as follows. 1. The chewing time and chewing number, mandibular displacement and mandibular movement velocity were not changed by the hardness, cohesiveness and adhesiveness of the food (p>0.05). 2. The harder food materials showed a higher amplitude of the anterior temporal muscle integrated EMGs than the softer ones (p<0.05). 3. The maximum and average integrated EMGs of the masseter muscle increased with the increase of hardness of the food (p<0.05). 4. The integrated EMGs of preferred side and non-preferred side masticatory muscles increased with the increase of hardness of the food (p<0.05). 5. The adhesiveness and cohesiveness of the food were not the determining factor to the integrated EMGs of masticatory muscles (p<0.05).
Adhesiveness ; Cheese ; Egg White ; Hardness ; Jaw ; Masseter Muscle ; Mastication* ; Masticatory Muscles* ; Prunus dulcis ; Temporal Muscle

OBJECTIVETo study the regularity of the passive tensile of the masticatory muscles and ligaments by Twin-Block appliance under various bite reconstruction, and to provide some biomechanical references for the clinical use and improvement of Twin-Block appliance.

METHODS"Temporomandibular joint, mandible and Twin-Block appliance" model was set up by the three dimensional finite element method, and the related masticatory muscles and ligaments were added on it. Seven experimental groups were designed according to the clinical and research, the occlusal inclined plate's angles of Twin-Block appliance were 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees and 70 degrees. The passive tensile in the masticatory muscles and ligaments were analyzed by the computer.

RESULTSUnder various experimental groups, the passive tensile in the anterior deep masseter (AM), the posterior deep masseter (PM), the anterior temporalis (AT), the posterior temporalis (PT), the stylomandibular ligament and sphenomandibular ligament improved with the increased slant angles of occlusal guide. The maximum value of the passive tensile was 82.57 N, the minimum value was 0.07 N.

CONCLUSION1) In various experimental groups, AT, AM, PM, PT, stylomandibular ligament and sphenomandibular ligament are subject to passive tension force in the process of Twin-Block appliance guiding the mandibular forward and play the important role on the remodeling of the mandible. 2)All groups of occlusal inclined plate's angle are in physiologically tolerable range and can be used in clinic.

Dental Occlusion ; Humans ; Ligaments ; Mandible ; Masseter Muscle ; Masticatory Muscles ; Reconstructive Surgical Procedures ; Temporal Muscle ; Temporomandibular Joint

There are several variations in normal mastication. In them, unilateral mastication is chewing, predominantly on a preferred side of the dentition and hardly on the non-preferred side. Continual unilateral mastication may alter the coordination of masticatory muscles. Although they studied about these EMG of masticatory muscles, there were no information about characteristics of masticatory muscle activity in unilateral mastication. Therefore, In this study, we investigated the activity of the masseter and anterior temporal muscles during rest, clenching in maximum intercuspation and gum chewing in habitually unilateral mastication group com-pared with normal group and tried to know effects of continual unilateral mastication on activity of masticatory muscles. The results of this study were as follows 1. In electromyographic activity during rest, in bilateral mastication group pattern of muscle activity of right and left side was symmetrical. But, in unilateral mastication group, records of anterior part of temporal muscle was higher than that of bilateral mastication group (p<.01) and patterns of muscle activity of right and left side in both muscle were asymmetrical.(p<.05). 2. In electromyographic activity during clenching in maximum intercuspation, records of superficial part of masseter muscle were higher than anterior part of temporal muscle in both group. Muscle activity of temporal muscle in unilateral mastication group was a little higher than bilateral mastication group and asymmetry of activity pattern in temporal and masseter muscle was shown but these differences were not statistically significant. (p< .05). 3. In electromyographic activity during gum chewing, temporal muscle was activated earlier than masseter muscle and .aximum bite force is derived from masseter muscle in both group. In unilateral mastication group, electromyographic activity of masseter and temporal muscle of preferred chewing side, regardless of right or left side chewing, was higher than that of bilateral mastication group and especially, difference in masseter muscle was statistically significant. (p< .01) Based on the above results, our study suggested that recording of masticatory muscle activity will be helpful in the effective diagnosis and treatment of some types of the parafunctional habits.
Bite Force ; Dentition ; Diagnosis ; Gingiva ; Masseter Muscle ; Mastication ; Masticatory Muscles* ; Temporal Muscle

This study was performed to investigate the influence of lateral guidance pattern and chewing pattern on masticatory muscle activity and occlusal contact pattern. Twenty-five patients with temporomandibular disorders and thirty students without temporomandibular disorders were selected for this study. Electromyographic examination and occlusal contact examination were performed simultaneously with Bio-Pak System(Bioresearch Inc.,U.S.A.) and T-Scan System(Tekscan Co., USA). The obtained results were as follows : 1. The EMG activity of masseter and anterior temporal muscle in patient group with canine guidance was higher than with non-canine guidance, but there was no significant difference(p>0.05). 2. The EMG activity of anterior temporal muscle in normal group with non-canine guidance was higher at preferred chewing side than at opposite side(p<0.05). 3. The EMG activity of masseter muscle was higher in normal group than in patient group (p<0.05). 4. The number of occlusal contact in patient group with canine guidance was higher than with non-canine guidance, but there was no significant difference(p>0.05). 5. The occlusal contact force at preferred chewing side was higher in patient group than in normal group(p<0.05).
Dental Occlusion ; Humans ; Masseter Muscle ; Mastication* ; Masticatory Muscles* ; Temporal Muscle ; Temporomandibular Joint Disorders

This study was undertaken to compare the activity of masticatory muscle between normal occlusion and anterior openbite. 33 subjects without the experience of orthodontic treatment, missing teeth and the symptom of T. M. disorders were selected for this study: 25 subjects were normal occlusion and 8 subjects were anterior openbite. The ten items were measured from the cephalometric headplates, and EMG recordings of the anterior temporal and masseter muscle were taken at rest position and during maximum clenching at centric occlusion. All data were analyzed and processed with the computer statistical method. The following results were obtained: 1. At rest position, the muscle activities of both temporal and masseter muscle were higher in anterior openbite than in normal occlusion. 2. During maximum clenching, the muscle activities of both temporal and masseter muscle were prominently lower in anterior openbite than in normal occlusion. 3. At rest position, the temporal muscle of anterior openbite showed the highest muscle activity, but showed the lowest muscle activity during maximum clenching. 4. Anterior openbite showed closer interrelationship between facial morphology and the muscle activity, and the muscle activity was more influenced by the form of mandible than that of maxilla.
Mandible ; Masseter Muscle ; Masticatory Muscles ; Maxilla ; Open Bite* ; Temporal Muscle ; Tooth