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

OBJECTIVETo determine the classification of masticatory myospasm by analyzing characteristics of clinical appearances.

METHODSThirty-six cases of masticatory myospasm from 2000 to 2010 were included. The clinical data of these patients were analyzed, including patient information, patient history, clinical characteristics, severity and the frequency of myospasmodic movement, electromyogram (EMG), and the efficacy of botulinum toxin injection treatment.

RESULTSThere were 11 males and 25 females, aged from 15 to 71. According to the clinical manifestation and EMG findings, patients could be divided into two groups: 18 cases were classified as jaw closing type which involved masseter and/or temporalis muscles presenting as trismus and acute pain, the other 18 cases were jaw opening type which involved lateral pterygoid muscles complaining difficulty in jaw closing and teeth clenching. The jaw closing type was often seen in patients of 20 to 50 years old, the jaw opening was frequently seen in patients over 50 years old. Jaw closing type was attacked intermittently and unilaterally, but jaw opening was often attacked continually and bilaterally. The rating scale of the severity of spasmodic movement was not different between the two types, but the frequency of spasmodic attack was much higher for jaw opening type (P < 0.05). The EMG of jaw closing type was classified into persistent, rhythmic and irregular type. The EMG of jaw opening type was classified into spontaneous and exercise-induced type. Twelve cases were treated by botulinum toxin injection that could significantly relieve symptoms.

CONCLUSIONSMasticatory myospasm can be classified into jaw closing and jaw opening types. Jaw closing type involves masseter and/or temporalis muscles and jaw opening type involves lateral pterygoid muscles. Botulinum toxin injection was the most effective therapy for the masticatory myospasm.

Adolescent ; Adult ; Aged ; Botulinum Toxins, Type A ; therapeutic use ; Electromyography ; Female ; Humans ; Jaw ; physiopathology ; Male ; Masseter Muscle ; physiopathology ; Masticatory Muscles ; physiopathology ; Middle Aged ; Pterygoid Muscles ; physiopathology ; Spasm ; classification ; drug therapy ; physiopathology ; Temporal Muscle ; physiopathology ; Young Adult

This study was conducted to establish a functional mandibular biomechanical model for use in the follow-up biomechanical study of the integrated and fractured mandible. The integrated and dry human mandible was used, and the corresponding maxilla and cranial base was duplicated by resin and plaster. 2-mm silicon rubber was used for simulation of the temporomandibular joint (TMJ) disc. A simulated TMJ and physiological mandibular model was developed by four pairs of muscular loadings (Masseter= 180 N, Temporalis = 190 N, Medial Pterygoideus = 120 N, Lateral Pterygoideus = 40 N) in each muscular center, and the functional loading corresponding with physiological condition was reflected and simulated more realistically when compared with that of the previously reported mandibular models which were developed by occlusion loading or by only one pair of muscles loading. In summary, we have established a functional mandibular model which can be used to analyze the biomechanical behavior in various functional conditions.
Biomechanical Phenomena ; Humans ; Mandible ; physiology ; Masseter Muscle ; anatomy & histology ; physiology ; Masticatory Muscles ; physiology ; Models, Biological ; Pterygoid Muscles ; anatomy & histology ; physiology ; Stress, Mechanical ; Temporal Muscle ; anatomy & histology ; physiology ; Temporomandibular Joint ; physiology

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

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 investigate the relationship between the existence of occlusal interference and masticatory muscle hyperalgesia by exploring the stimulus-response relationship between the duration of occlusal interference and masticatory muscle mechanical withdrawal threshold.

METHODSOcclusal interference with 0.4 mm-thick crowns on rat molars was removed under anaesthesia at 2, 3, 4, 5, and 6 d after wear, and masticatory muscle mechanical withdrawal threshold was tested at 1, 3, 5, 7, 10, 14, 21 and 28 d.

RESULTSDecreased mechanical withdrawal thresholds were detected in temporal muscles and masseter muscles on both sides following occlusal interference (P < 0.05). After removal of crowns at 2, 3, 4 and 5 d, rats exhibited the similar head withdrawal thresholds as the sham-application control in masticatory muscles on both sides at 10, 14, 14 and 21 d (P > 0.05). No significant differences were detected between the contralateral side with the ipsilateral side (P < 0.05). After removal of crowns at 6 d, rats still exhibited significantly decreased head withdrawal thresholds[right temporal muscle: (1.365±0.018) N; right masseter: (1.437 ± 0.024) N] in masticatory muscles on both sides until the last day of the experiment[the sham-application control: right temporal muscle: (1.554±0.040) N, P < 0.001; right masseter: (1.546±0.019) N, P < 0.001].

CONCLUSIONSThe mechanical hyperalgesia can disappear after removal of the occlusal interference at 5 d, and the existence of the occlusal interference is positively correlated with the duration of the mechanical hyperalgesia.

Animals ; Hyperalgesia ; physiopathology ; Masseter Muscle ; physiopathology ; Masticatory Muscles ; Molar ; Rats ; Temporal Muscle ; physiopathology