No abstract available.
Masseter Muscle*

A case is reported of neurilemmoma of the right masseteric nerve in the masseter muscle. We experienced a 34-years-old male patient who had neurilemmoma in the masseter muscle caused by chronic irritation. Special stain using S-100 immunoperoxidase was useful in establishing the diagnosis in this case. The most important aspect of this case is the anatomical site of the neurilemmoma; this tumor was originated from the masseteric nerve and is the first case reported in the masseter muscle. The patient underwent surgical excision of the tumor and no recurrence occured.
Diagnosis ; Humans ; Male ; Masseter Muscle* ; Neurilemmoma* ; Recurrence

ABSTRACT The present study aimed to evaluate the surface electromyography (sEMG) activity of the masseter muscles in patients with a history of temporomandibular joint disorder (TMJD) who received orthodontic treatment. In total, 22 participants aged 18–35 years old were included in this study. They were divided into the control group (patients without a history of TMJD [n = 11]) and the test group (those with a history of TMJD [n = 11]). Each participant underwent sEMG of the right and left masseter muscles at 5-s maximum voluntary contraction (MVC). Results showed that the TMJD group had a lower sEMG activity of masseter muscles at MVC than the non-TMJD group. However, the differences were not statistically significant (p > 0.05, t-test). The Spearman’s correlation coefficient test revealed a weak negative correlation between muscle activity on sEMG and history of TMJD (p > 0.05). In conclusion, orthodontically treated patients in TMJD group have reduced masseter muscle activity during MVC, compare to the non-TMJD group.
Masseter Muscle ; Orthodontics ; Electromyography ; Temporomandibular Joint Disorders

Micrognathia is a severe craniofacial deformity affecting appearance and survival. Previous studies revealed that multiple factors involved in the osteogenesis of mandibular bone have contributed to micrognathia, but concerned little on factors other than osteogenesis. In the current study, we found that ectopic activation of Fgf8 by Osr2-cre in the presumptive mesenchyme for masseter tendon in mice led to micrognathia, masseter regression, and the disrupted patterning and differentiation of masseter tendon. Since Myf5-cre;Rosa26R-Fgf8 mice exhibited the normal masseter and mandibular bone, the possibility that the micrognathia and masseter regression resulted directly from the over-expressed Fgf8 was excluded. Further investigation disclosed that a series of chondrogenic markers were ectopically activated in the developing Osr2-cre;Rosa26R-Fgf8 masseter tendon, while the mechanical sensing in the masseter and mandibular bone was obviously reduced. Thus, it suggested that the micrognathia in Osr2-cre;Rosa26R-Fgf8 mice resulted secondarily from the reduced mechanical force transmitted to mandibular bone. Consistently, when tenogenic or myogenic components were deleted from the developing mandibles, both the micrognathia and masseter degeneration took place with the decreased mechanical sensing in mandibular bone, which verified that the loss of mechanical force transmitted by masseter tendon could result in micrognathia. Furthermore, it appeared that the micrognathia resulting from the disrupted tenogenesis was attributed to the impaired osteogenic specification, instead of the differentiation in the periosteal progenitors. Our findings disclose a novel mechanism for mandibular morphogenesis, and shed light on the prevention and treatment for micrognathia.
Mice ; Animals ; Micrognathism ; Masseter Muscle ; Mandible ; Osteogenesis

Hemimasticatory spasm is a rare disorder that often accompanies facial hemiatrophy and is characterized by spasm in one or more of the jaw-closing muslces supplied by the fifth cranial nerve. We report a clinical and electrophysiological observation of a patient of hemimasticatory spasm, who presented involuntary spasm on masseter muscle and hemiatrophy of the face on the right side for 7 years.
Facial Hemiatrophy ; Humans ; Masseter Muscle ; Spasm* ; Trigeminal Nerve

PURPOSE: To determine if ultrasonography is a reliable technique to assess masseter muscle sites within intra- and interobserver and the scanning level and/or the muscle condition affect local cross-sectional dismension (LCSD) measurements of masseter muscle. MATERIALS AND METHODS: 10 subjects without sign and symptom of temporomandibular disorders and missing posterior teeth were examined by ultrasonography. Bilateral ultrasonographic examinations were performed with a linear (B-scan) 7.5 MHz small-part transducer to register LCSDs of the masseter muscle on three different levels. Scans were made on relaxed and clenching condition. Three oral and maxillofacial radiologists measured at two sessions with a time interval of at least 5 minutes. RESULTS: Variables such as 'condition' and 'level' had a significant effect on muscle measurements (p< 0.05). There was no significant difference between 'sessions' (p> 0.05) and 'observers' (p> 0.05). LCSDs on lower scan level were significantly thinner than those on upper and middle level. Those on clenching condition were significantly thicker than those on relaxed condition (p< 0.05). The scanning level with the highest reproducibility was middle with clenching condition (ICC = 0.90, MSE = 0.55%). CONCLUSION: The data suggested that ultrasonography was a reliable method for measuring LSCD of masseter muscle in intra- and interobserver and middle scan level showed the most reliable data.
Masseter Muscle* ; Temporomandibular Joint Disorders ; Tooth ; Transducers ; Ultrasonography

OBJECTIVETo analyze changes of myoelectrical activity of anterior funicle of temporal muscle (TA) and masseter muscle (MM) after raising vertical distance of occlusion by flat bite plate during treatment of deep overbite in order to approach an optimal raised vertical distance.

METHODSA total of 70 persons were selected and divided into two groups: Experiment group (36 patients) with deep overbite and control group (34 persons) with individual normal occlusion. The experiment group was subdivided into three groups that were respectively raised D, D+2 mm and D+4 mm (D means free way space, mm). Electromyologram (EMG) was utilized to measure the average peak potential of TA and MM on quiescent condition before treatment and two weeks after wearing flat bite plate.

RESULTS1) Before treatment, the average peak potential of experiment group was obviously higher than that of the control group (P<0.05). 2) After two weeks the potential of TA and MM of all persons in experiment group was obviously lower than before (P<0.05), the degree between the group D+2 mm and the group D+4 mm was not manifestly different, but both of the two groups were more obvious than the group D.

CONCLUSIONThe raised vertical distance of occlusion by flat bite plate, which exceeded free way space, was favourable to the functional recovery of masticatory muscles.

OBJECTIVETo study the influence of emotion stress on mechanical hyperalgesia of masseter muscles in rats through the equipment of communication box.

METHODS50 Sprague-Dawley rats were randomly divided into 5 groups: Control group, emotion stress (ES) group, drug control group, saline treated control group and footshock (FS) group, 10 rats each group. Footshock group only induced emotion stress and was not concerned with the result of the experiment. The last four groups of the rats were placed in communication box and bred under the same conditions during the experiment time. According to Rens' method, von Frey filaments were used to assess the muscle mechanical threshold, head withdrawal, leg raising and crying were observed as pain action.

RESULTS1) During the adaptive period of 7 days before the emotion stress experiment, mechanical pain values of bilateral masseter muscles were descent and were stabilized in the 5 th to 7 th day. In emotion stress period, hyperalgesia of emotion stress group was induced in bilateral masseter muscles, and the peak time was the 7 th day, then it alleviated in the following days and was stabilized in the 12 th to 14 th day, but its pain threshold was lower than blank control group. 2)During the emotion stress period, the change of drug control group was similar to stress group but its pain threshold was higher.

CONCLUSIONIt is suggested that emotion stress can lead to the hyperalgesia of masseter muscles and antidepressant drug can lower the hyperalgsia resulted of emotion stress.

Since the time of its inception within facial anatomy, wide variability in the terminology as well as the location and extent of retaining ligaments has resulted in confusion over nomenclature. Confusion over nomenclature also arises with regard to the subcutaneous ligamentous attachments, and in the anatomic location and extent described, particularly for zygomatic and masseteric ligaments. Certain historical terms—McGregor's patch, the platysma auricular ligament, parotid cutaneous ligament, platysma auricular fascia, temporoparotid fasica (Lore's fascia), anterior platysma-cutaneous ligament, and platysma cutaneous ligament—delineate retaining ligaments of related anatomic structures that have been conceptualized in various ways. Confusion around the masseteric cutaneous ligaments arises from inconsistencies in their reported locations in the literature because the size and location of the parotid gland varies so much, and this affects the relationship between the parotid gland and the fascia of the masseter muscle. For the zygomatic ligaments, there is disagreement over how far they extend, with descriptions varying over whether they extend medially beyond the zygomaticus minor muscle. Even the ‘main’ zygomatic ligament's denotation may vary depending on which subcutaneous plane is used as a reference for naming it. Recent popularity in procedures using threads or injectables has required not only an accurate understanding of the nomenclature of retaining ligaments, but also of their location and extent. The authors have here summarized each retaining ligament with a survey of the different nomenclature that has been introduced by different authors within the most commonly cited published papers.
Cheek* ; Fascia ; Ligaments* ; Masseter Muscle ; Parotid Gland ; Rejuvenation

PURPOSE: To assess the internal echo intensity and morphological variability of masseter muscles on ultrasonography and to establish diagnostic criterion of estimation. MATERIALS AND METHODS: Participants consisted of 50 young adults (male 25, female 25) without pathologic conditions and with full natural dentitions. Sonographic examinations were done with real time ultrasound equipment as Logiq 500 (GE Medical Systems, Seoul, Korea) at 3 parts according to lines paralleling with ala-tragus line as reference line. The thickness and area of masseter muscles according to reference line in cross-sectional images were measured at rest and at maximum contraction. The visibility and width of the internal echogenic intensity of the masseter muscles were also assessed and the muscle appearance was classified into 4 types. Data were statistically analyzed by paired t-test and chi-square-test. RESULTS: 1. When comparing the thickness and area of masseter muscles concerning with gender, there was few significant difference between right and left sides, however, there were significant differences between males and females except for the greatest thickness of left side. 2. The changes of the greatest thickness and the area between rest and maximum contraction showed that the part of the least thickness manifested more increase at maximum contraction. 3. Each part the manifestations of the internal echogenic intensity of the masseter muscles were different depending on the locations. But there was no statistically significance. CONCLUSION: Changes of muscles thickness with contraction and internal echogenic intensity with locations showed great disparity within the masseter muscles, which will be diagnostic criteria for pathophysiologic and anatomic changes of masseter muscles.
Contracts ; Dentition ; Female ; Humans ; Male ; Masseter Muscle ; Muscles ; Young Adult