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Background: This study aimed to prospectively investigate the reference values for masseter muscle thickness and hardness using ultrasonography and shear wave elastography, respectively, in patients with hemifacial microsomia (HFM)., Methods: We enrolled 51 patients, aged 5-20 years, with HFM including 31 males and 20 females. The upper-lower, left-right, and anterior-posterior diameters of 102 masseter muscles and stiffness of 98 masseter muscles were determined by examining the unaffected and affected sides of each participant's face., Results: The upper-lower, left-right, and anterior-posterior diameters of the masseter muscle were significantly smaller at rest (4.26 ± 0.83, 2.94 ± 0.75, and- 0.80 ± 0.25 cm, respectively) and during contraction (3.95 ± 0.78, 2.71 ± 0.78, and 0.87 ± 0.29 cm, respectively) in the affected side than those in the healthy side (5.45 ± 0.66, 3.87 ± 0.49, and 0.97 ± 0.20 cm, respectively, at rest and 4.99 ± 0.45, 3.49 ± 0.53, and 1.07 ± 0.23 cm, respectively, during contraction, p < 0.05). In the resting state, the hardness of the masseter muscle on the affected side (0.77 ± 0.66 m/s) was significantly greater than that on the healthy side (0.42 ± 0.41 m/s; p < 0.05). The magnitude of changes in the upper-lower, left-right, and anterior-posterior diameters of the biting muscle in the occlusal state were significantly smaller on the affected side (-0.30 ± 0.27, -0.23 ± 0.17, and 0.08 ± 0.08 cm, respectively) than those in the healthy side (-0.47 ± 0.38, -0.37 ± 0.25, and 0.10 ± 0.12 cm, respectively, p < 0.05)., Conclusions: The knowledge of these values allows for better understanding of the disease characteristics of HFM, which may be used for its diagnosis, treatment, and prognosis. Patients experiencing different severity levels exhibited significant differences in the morphology and function of the masseter muscle on the affected-side (p < 0.05)., Evidence Level: Level III., Competing Interests: Conflicts of interest None declared., (Copyright © 2024 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.)

Introduction: This study aimed to determine a measurement plane that could represent the maximum cross-sectional area (MCSA) of masseter muscle using an artificial intelligence model for patients with skeletal Class III malocclusion., Methods: The study included 197 patients, divided into subgroups according to sex, mandibular symmetry, and mandibular plane angle. The volume, MCSA, and the cross-sectional area (CSA) at different levels were calculated automatically. The vertical distance between MCSA and mandibular foramen, along with the ratio of the masseter CSA at different levels to the MCSA (R), were also calculated., Results: The MCSA and volume showed a strong correlation in the total sample and each subgroup (P <0.001). The correlation between the CSA at each level and MCSA was statistically significant (P <0.001). The peak of the r and the correlation coefficient between the CSA at different levels and MCSA were mostly present 5-10 mm above the mandibular foramen for the total sample and the subgroups. The mean of R A5 to R A10 was >0.93, whereas the corresponding correlation coefficient was >0.96, both for the entire sample and for the subgroups., Conclusions: MCSA could be used as an indicator for masseter muscle size. For patients with skeletal Class III malocclusion, the CSA 5-10 mm above the mandibular foramen, parallel to the Frankfort plane, could be used to estimate the masseter muscle MCSA., (Copyright © 2024 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.)

Introduction: This study evaluated the masseter muscle changes after surgical-orthodontic treatment in patients with a skeletal Class III malocclusion using automatic segmentation., Methods: Images of 120 patients with skeletal Class III malocclusion were obtained and reconstructed at T0 (pretreatment), T1 (presurgery), and T2 (6-12-month postsurgery). The patients were divided into symmetrical and asymmetrical groups. The volume, major axis length, maximum cross-sectional area, horizontal cross-sectional area 5 mm above the mandibular foramen (CSAF), and orientation were calculated automatically., Results: In the asymmetrical group, the volume and major axis length on the deviated side were lower than on the nondeviated side at T0, T1, and T2 (P <0.05). There were no significant differences in maximum cross-sectional area and CSAF bilaterally. The orientation was coronally more vertical and sagittally more forward on the deviated side (both P <0.001). In the symmetrical group, there were no significant bilateral differences at T0, T1, and T2. The volume, major axis length, and CSAF decreased, and the coronal orientation was more vertical on the nondeviated side at T2 than at T0 in both groups (P <0.05). The coronal plane orientation was more inclined on the deviated side at T2 than at T0 in the asymmetrical group (P <0.05)., Conclusions: The smaller volume on the deviated side at T2 indicates the need for myofunctional training after surgery. The masseter muscle volume and the cross-sectional area did not recover to the preorthodontic levels. Studies with longer follow-up durations are needed to confirm these findings., (Copyright © 2024 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.)

Objective: The present study evaluated the in vivo musculoaponeurotic architecture of the superficial head (SH) of the masseter muscle (MM) of asymptomatic participants in excursive mandibular movements compared to the relaxed state as examined with ultrasonography. It was hypothesized that the mean fiber bundle length (FBL) and mean height of the aponeurosis (HA) of the laminae of the SH would differ significantly between the relaxed state and protrusion, ipsilateral excursion, and contralateral excursion., Study Design: The MM was studied volumetrically in 12 female and 12 male asymptomatic participants bilaterally by using ultrasound imaging. Mean FBL and HA in protrusion and ipsilateral and contralateral excursion were compared to these values in the relaxed state using paired t tests (P < .05). The intraclass correlation coefficient was used to assess intraexaminer reliability., Results: The SH exhibited multiple laminae. Fiber bundles were found to attach to bone and the superior and inferior aponeuroses. Mean FBL was significantly shorter and mean HA significantly longer in protrusion and the excursions than in the relaxed state although the pattern of altered laminae and aponeuroses differed among the mandibular movements. Intraexaminer reliability was excellent., Conclusion: Specific changes in mean FBL and mean HA suggest differential contraction of the SH of the MM based on laminar morphology. These findings provide a baseline to investigate musculoaponeurotic changes in patients with myogenic masseter muscle pain., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Objective: We examined changes in the mandibular angle, ramus, and condylar neck of patients with bruxism after botulinum toxin-A (BTX-A) injection into the masseter muscle as calculated with fractal analysis (FA) on panoramic radiographs (PRs)., Methods: We examined the PRs of 3 groups of 22 patients each (n = 66) obtained upon presentation and 6 months later. One group included healthy controls without bruxism, one group included patients with untreated bruxism, and one group included patients with bruxism who had undergone BTX-A injection into the masseter muscle. We performed FA of the bilateral angle, ramus, and condylar neck of the PRs to calculate fractal dimension (FD)., Results: The FD values of the angle on the second PRs of the untreated bruxism group were significantly higher than those of the other groups (P = .026), specifically when compared to the BTX-A injection group (P = .017). The FD values in the angle and ramus of the bruxism group were significantly higher on the second PRs (P ≤..005)) Conversely, the FD values in the angle of the BTX-A injection group were significantly lower on the second PR (P = .039)., Conclusions: Masseter muscle hyperactivity due to bruxism increases bone density in masseter muscle attachment regions. BTX-A injection restricts muscle activity, thereby chnging bone structure and decreasing FD., Competing Interests: Declaration of interest None, (Copyright © 2023 Elsevier Inc. All rights reserved.)

This study aims to confirm the effectiveness and safety of a prabotulinumtoxin type A (praBTX-A) injection in patients with bruxism and masseter hypertrophy. The study included patients who ground or clenched their teeth while sleeping and had computed tomography (CT) scans that showed a maximum thickness of the masseter muscle of 15 mm or more. The praBTX-A was administered bilaterally into the masseter muscles; 15 U/side for group 1, 25 U/side for group 2, and 35 U/side for group 3. CT scans and bruxism questionnaires were conducted before and eight weeks after the injection. Thirty-seven patients were enrolled, but three dropped out due to loss of follow-up. After injection, masseter thickness decreased to 15.1 ± 2.0 mm for group 1, 14.3 ± 2.9 mm for group 2, and 13.4 ± 1.8 mm for group 3 (p = 0.043). Group 3 showed a statistically significant lower masseter thickness compared to group 1 (p = 0.039). Both subjective and objective frequencies of bruxism decreased for all groups, but there were no significant differences in either subjective (p = 0.396) or objective frequencies (p = 0.87) between the groups after the injection. The results of this study suggest that praBTX-A injection is a safe and effective treatment for bruxism and masseter hypertrophy. A dosage of 35 IU/side can effectively decrease masseter thickness and relieve bruxism symptoms. Even the minimum dosage of 15 IU/side can contribute to improvements in bruxism symptoms. This investigation provides valuable information for managing bruxism that is associated with hypertrophic masseter muscles., (Copyright © 2023 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.)

Objective: To compare the masseter muscle thickness (MMT) of patients with probable sleep/awake bruxism and controls without bruxism in mixed dentition as measured with ultrasonography (USG), and to calculate the correlation of MMT with body mass index (BMI)., Study Design: The diagnosis of probable bruxism was established based on the parents' reports of the children's behavior, habits, and discomfort, and the presence of clinical signs and symptoms such as attrition-type wear on the teeth and the presence of discomfort, fatigue, and/or pain in the jaw muscles on palpation during clinical examination. The bruxist study group and the control group each included 28 children. MMT was measured separately in relaxed and contracted positions in both groups using USG. The height and weight of the patients were recorded in order to calculate BMI. Statistical analysis was performed with significance established at P < .05., Results: MMT was found to be significantly larger in the study patients than in controls on the right and left sides in the relaxed and contracted positions (P < .001). No statistically significant correlation was found between MMT and BMI (P ≥ .134)., Conclusions: MMT as measured with USG can be a beneficial approach in diagnosing bruxism in children. The lack of correlation between MMT and BMI indicates that BMI would not be helpful in diagnosing bruxism., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Background: Elderly patients with glioblastoma (GBM) have a worse prognosis than do younger patients. The present study aimed to identify the patient, treatment, and imaging features, including measures of sarcopenia, associated with worse survival and 90-day postoperative mortality for elderly patients with GBM., Methods: A single-center retrospective study was conducted of patients aged ≥79 years at surgery who had undergone biopsy or resection of a World Health Organization grade IV GBM at the initial diagnosis. Imaging features of sarcopenia were collected, including the masseter and temporalis muscle diameters. Multivariate analyses were performed to identify factors associated with survival and 30-day complications., Results: The cohort included 110 patients with a mean age of 82.8 years at surgery and a median preoperative Karnofsky performance scale score of 80. The majority of patients underwent a surgical resection (66.4%) while a minority underwent biopsy (33.6%). Adjuvant chemo- and/or radiation therapy were used in 72.5% of the cohort. On multivariate analysis, age (hazard ratio [HR], 7.97; 95% confidence interval [CI], 1.63-36.3), adjuvant therapy (RT or TMZ vs. none: HR, 0.12; 95% CI, 0.05-0.3; RT plus TMZ vs. none: HR, 0.05; 95% CI, 0.02-0.14), surgical resection (HR, 0.46; 95% CI, 0.24-0.9), multifocality (HR, 2.7; 95% CI, 1.14-6.4), and masseter diameter (HR, 0.12; 95% CI, 0.02-0.78) were associated with survival. Masseter diameter was the only factor associated with 90-day mortality after surgical resection (P = 0.044)., Conclusions: GBM patients over the age of 79 have acceptable outcomes after resection, followed by adjuvant chemotherapy and RT. In addition to the treatment factors that predicted for survival, a decreased masseter diameter on preoperative imaging, a marker of sarcopenia, was associated with shorter overall survival and 90-day mortality after surgical resection., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

This retrospective case-series study aimed to elucidate the three-dimensional attachment morphometric features and to quantify the volumetric changes of the masticatory muscles following free fibular flap reconstruction of the mandibular condyle. Navigation software (iPlan, version 3.0; Brainlab) was used to perform delineation and volumetric measurement of the masticatory muscles using DICOM data. In total, 30 patients were included in this retrospective case series. In 25 cases (83.33%), the lateral pterygoid muscle achieved reattachment within 6 months postoperatively. The medial pterygoid muscles on the affected side achieved ectopic attachment in all cases. However, masseter reattachment on the affected side was achieved in only three cases. On the normal side, the volumes of lateral pterygoid muscle, medial pterygoid muscle, and masseter had recovered to almost preoperative levels at 1 year postoperatively. On the affected side, the volume of medial pterygoid muscle had decreased significantly (p = 2.4e-04) at 3 months postoperatively. The volumes of lateral pterygoid muscle and masseter showed mild decreases at 3 months postoperatively, but these were not significant (p = 0.52 and p = 0.05 for the pterygoid muscle and masseter, respectively). At 6 months after surgery, with the exception of the volume of the lateral pterygoid muscle (p = 0.06), the total volume of the masticatory muscles decreased significantly on the affected side. The volumes of lateral pterygoid muscle, medial pterygoid muscle, and masseter showed significant decreases at 1 year postoperatively (p = 0.03, p = 4.7e-08, and p = 1.1e-05, respectively) on the affected side. The postoperative volumes of the masseter, medial pterygoid, and lateral pterygoid muscles showed significant decreases due to the loss of reattachment. The results of this study may not help to ascertain whether reattachment of masticatory muscles will lead to better function. As a consequence, clinical trials of higher quality are needed., Competing Interests: Declaration of competing interest None., (Copyright © 2021 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.)

Objective: In the present study, we sought to investigate the in vivo musculoaponeurotic architecture of the masseter muscle (MM) volumetrically with ultrasound in asymptomatic participants. It was hypothesized that the mean fiber bundle length (FBL) and mean aponeurotic height of laminae of the MM differ significantly between the relaxed state and maximally contracted state upon elevation of the mandible., Study Design: The MM was investigated volumetrically in 12 male and 12 female asymptomatic participants (mean age, 25.8 ± 4.1 years) using ultrasound. The mean FBL and mean height of aponeuroses in the relaxed and maximally contracted states were compared using paired t tests, with significance established at P ≤ .05. Intrarater reliability was assessed using the intraclass correlation coefficient (ICC)., Results: The MM consisted of the superficial head (SH) and deep head, each arranged in multiple laminae. Fiber bundles extended between superior and inferior aponeuroses and/or bone. Statistically significant differences (P ≤ .05) were observed in mean FBL and in mean height of aponeuroses between the relaxed and contracted states only in superficial laminae of the SH., Conclusions: These results suggest there is differential contraction of the laminae of the MM in the transition from relaxed to contracted states. Future comparison with pathologic patients can be made on the basis of an established normative database., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The aim of this study was to assess any change between the preoperative and postoperative sizes of temporal and masseter muscles with magnetic resonance imaging (MRI) in patients undergoing unilateral temporomandibular joint surgery. This study was designed and implemented retrospectively. For clinical evaluation, a visual analog scale (VAS) and maximum mouth opening (MMO) were used. In order to make a preoperative diagnosis and perform a 6-month control, muscle size was measured in millimeters (mm) on T1 axial sections in MRI. Statistical analyses were performed using the SPSS 23.0 software package. Numeric variables were compared between two dependent groups using the Wilcoxon signed rank test. Statistical significance was set at p < 0.05. Twelve patients who underwent unilateral discectomy plus dermis-fat grafting, with classical preauricular inverse L incision, were included in the study, and data for eleven female patients were evaluated. The difference in size between the operated and non-operated sides was found to be statistically insignificant at the preoperative stage for both masseter muscle (operated side m M : 13.264 ± 1.822 mm; non-operated side m M : 13.264 ± 2.315 mm; p M  = 0.929) and temporal muscle (operated side m T : 20.345 ± 2.609 mm; non-operated side m T : 20.582 ± 2.366 mm; p T  = 0.594). There was a significant size reduction in the masseter muscle on the operated side in the postoperative period (preop m M : 13.264 ± 1.822 mm; postop m M : 12.036 ± 1.728 mm; p M  = 0.018). Although there was also a size reduction in the operated side of the temporal muscle in the postoperative period, that difference did not reach statistical significance (preop m T : 20.345 ± 2.609 mm; postop m T : 19.445 ± 1.603 mm; p T  = 0.182). On the non-operated side, there were no significant postoperative changes in the sizes of either the masseter muscle (preop m M : 13.264 ± 2.315 mm; postop m M : 12.682 ± 2.059 mm; p M  = 0.248) or the temporal muscle (preop m T : 20.582 ± 2.366; postop m T : 19.891 ± 3.487 mm; p T  = 0.625). Considering the study findings as a whole, a size reduction was observed in the operated side of the masseter muscle after TMJ surgery. The etiology of this change may be surgical trauma to the temporal and masseter muscles, skeletal alteration resulting from condylar change secondary to discectomy, and patients restraining themselves from application of maximum bite force as a result of a self-protection mechanism due to postoperative pain., Competing Interests: Declaration of competing interest There are no conflicts of interest between this research and any of the authors herein listed., (Copyright © 2021. Published by Elsevier Ltd.)

Objectives: To evaluate whether the effects on the mandibular condylar cartilage (MCC) and subchondral bone are transient of botulinum neurotoxin (Botox) injection into the masseter muscle., Methods: Botox (0.3 U) was injected into the right masseter of 6-week-old female mice (C57BL/6; n = 16). In addition, 16 mice were used as control and received no injections. Experimental and matching control mice were killed 4 or 8 weeks after the single Botox injection. Mandibles and mandibular condyles were analyzed by means of microscopic computed tomography (microCT) and histology. Sagittal sections of condyles were stained for tartrate-resistant acid phosphatase (TRAP), toluidine blue, 5-ethynyl-2'-deoxyuridine (EdU), and terminal deoxynucleotide transferase-mediated dUTP nick-end labeling., Results: Bone volume fraction was significantly decreased on the subchondral bone of the Botox-injected side, compared with the control side and control mice, 4 and 8 weeks after injection. Furthermore, histologic analysis revealed decrease in mineralization, cartilage thickness, TRAP activity, and EdU-positive cells in the MCC of the Botox-injected side 4 and 8 weeks after injection., Conclusions: The effects on the MCC and subchondral bone of Botox injection into the masseter muscle persisted for 8 weeks after injection and were not considered to be transient., (Copyright © 2019 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.)

Background and Purpose: Gunshot injuries have been considered a contraindication for MRI because of the risk of secondary dislodgement of retained metallic foreign bodies. The objective of our study was to provide a systematic overview of the behaviour of projectiles and fragments in order to aid decision-making regarding the use of MRI in clinical practice., Materials and Methods: Ferromagnetic (n = 2) and non-ferromagnetic (n = 5) projectiles and fragments that were lodged in soft tissue (porcine masseter muscles) were examined using standard protocols at 1, 1.5 and 3 T, to simulate clinical situations as realistically as possible. CT was performed before and after every MRI to assess rotation and movement. Artefacts and image quality were analysed using Likert-type scales., Results: Ferromagnetic projectiles were of poorer quality and showed larger artefacts and did not provide benefit for clinical practice compared to images of non-ferromagnetic material. Image quality of non-ferromagnetic projectiles varied widely (from very good to moderate) depending on the composition of the projectiles. Field strength (1 T to 3 T) had no relevant influence on image quality., Conclusions: Non-ferromagnetic projectiles are not a contraindication for MR imaging since there is no potential risk of secondary dislodgement. Image quality and the extent of artefacts, however, strongly depend on the type of ammunition used. The presence of ferromagnetic projectiles in or near vital anatomic structures is a contraindication for MRI because these objects may exhibit movement in response to magnetic fields. Knowledge of the type of projectile used appears to be important in order to guide patient management before an examination is performed. So, the production and use of projectiles suitable for MRI should be favored in the future, knowing that this will be hard to fulfil., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Objective: Myofascial pain in temporomandibular joint disorders (TMDs) is evoked by various factors, including edematous change. We investigated whether the pain pattern is related to edematous change by using T2 mapping generated by magnetic resonance imaging to detect water content in the tissue., Study Design: One hundred and five patients diagnosed with TMDs, with or without unilateral masseter muscle pain, were divided into 6 groups according to their pain experience: pain on compression (23 cases), pain on movement (13 cases), spontaneous pain (4 cases), pain on compression and movement (14 cases), pain on compression and spontaneous pain (2 cases), and no pain (49 cases). Differences in the mean T2 values of the masseter muscle between the group with pain on only one side (5 unilateral pain groups) or pain-free on both the right and left sides (pain-free group) were compared with paired t tests. Significant differences were assumed at P < .05., Results: Significant differences in mean T2 values were found between the painful and pain-free sides in the group with pain on compression., Conclusions: The findings of edematous change in the masseter muscle of patients with pain on compression may affect treatment planning and lead to investigation of treatment options for myofascial pain in TMDs., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: The masseter muscle plays a key structural and functional role in the stomatognathic system. Researchers' cumulative evidence has suggested that the variation in the size of a person's masseter muscle may be a critical factor related to individual differences in oral functions. However, researchers have not yet investigated systematically the effect of a person's age and sex on masseter muscle size and the association of masseter muscle size with other clinical metrics, including masticatory performance (MP) and salivary flow rate (SFR). Using T1-weighted magnetic resonance imaging (MRI) data provides a noninvasive method for assessing masseter muscle volume (MMV)., Methods: Using T1-weighted MRI data, the authors developed a voxel-based method to assess MMV and investigated the associations among MMV, MP, and SFR., Results: The authors acquired T1-weighted MRI data from scans of the heads of 62 healthy adults and assessed MMV by means of using a voxel-based approach. The authors' assessment results had acceptable rates of inter-rater and intrarater reliability. MMV was significantly lower in the older subgroup and in the female subgroup. In addition, the correlation for MMV was significantly positive with MP and stimulated SFR., Conclusions: The study results revealed evidence that the authors' voxel-based approach, which they designed on the basis of T1-weighted MRI data, would be a reliable method for quantifying MMV., Practical Implications: The findings suggest that the variation in masseter muscle size may be a critical factor to assess individual differences in oral functions., (Copyright © 2017 American Dental Association. Published by Elsevier Inc. All rights reserved.)

Introduction: The aim of this prospective study was to evaluate the effects of posterior bite-blocks on masseter muscles and on facial growth in prepubertal dolichofacial subjects., Methods: The treatment group comprised 21 consecutive prepubertal dolichofacial patients treated with rapid maxillary expansion followed by mandibular removable bite-blocks. Lateral cephalograms and ultrasonographic scans of the masseter muscles were made before (T1) and after (T2) treatment with bite-blocks. The treatment group was compared with a control group of 21 subjects matched for sex, age, and skeletal vertical pattern. An independent samples t test was used to compare the T1 to T2 changes in ultrasonographic scan measurements between the treatment group and the control group, and the T1 to T2 cephalometric changes in the treatment group. Regression analysis was performed to investigate associations between masseter muscle thickness and cephalometric treatment outcomes., Results: Masseter muscle thickness showed a statistically significant decrease (-0.7 mm) in the treatment group compared with an increase (+0.6 mm) in the control group. A significant anterior rotation of the mandibular plane was observed in the treatment group as well as significant increases in overbite (1.8 mm) and total posterior facial height (1.5 mm). No significant associations were found between masseter muscle thickness and treatment outcomes apart from a tendency for overbite to increase more in subjects with thicker muscles., Conclusions: Treatment with removable bite-blocks produced a decrease in masseter muscle thickness and a reduction in vertical facial dimensions due to upward and forward rotation of the mandible. No significant correlation was found between the pretreatment masseter muscle thickness and the T1 to T2 cephalometric changes in the treatment group., (Copyright © 2017 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.)

Intramuscular nodules can be the clinical presentation of several groups of lesions, such as reactive disorders and benign and malignant tumors. Here, we present three cases with similar clinical features and image aspects on Doppler ultrasonography. Two of the lesions were diagnosed as intramasseteric hemangioma and the third as intramasseteric metastasis from high-grade pleomorphic sarcoma of the thigh. The diagnosis of intramasseteric nodules is challenging, and various differential diagnoses must be considered. Clinical features, evolution time, and information from complementary examinations, such as Doppler ultrasonography and fine-needle aspiration cytology, are useful in making a precise diagnosis and providing appropriate treatment., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Skeletal muscle models are used to investigate motion and force generation in both biological and bioengineering research. Yet, they often lack a realistic representation of the muscle's internal architecture which is primarily composed of muscle fibre bundles, known as fascicles. Recently, it has been shown that fascicles can be resolved with micro-computed tomography (µCT) following staining of the muscle tissue with iodine potassium iodide (I2KI). Here, we present the reconstruction of the fascicular spatial arrangement and geometry of the superficial masseter muscle of a dog based on a combination of pattern recognition and streamline computation. A cadaveric head of a dog was incubated in I2KI and µCT-scanned. Following segmentation of the masseter muscle a statistical pattern recognition algorithm was applied to create a vector field of fascicle directions. Streamlines were then used to transform the vector field into a realistic muscle fascicle representation. The lengths of the reconstructed fascicles and the pennation angles in two planes (frontal and sagittal) were extracted and compared against a tracked fascicle field obtained through cadaver dissection. Both fascicle lengths and angles were found to vary substantially within the muscle confirming the complex and heterogeneous nature of skeletal muscle described by previous studies. While there were significant differences in the pennation angle between the experimentally derived and µCT-reconstructed data, there was congruence in the fascicle lengths. We conclude that the presented approach allows for embedding realistic fascicle information into finite element models of skeletal muscles to better understand the functioning of the musculoskeletal system., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Objectives: To investigate the intramuscular changes on sonographic elastography (SE) after low-level static contraction of the masseter muscle, and to clarify the relationship with the total hardness and edematous change., Study Design: Ten healthy volunteers performed sustained bilateral biting at 20% of maximal voluntary contraction for 10 min. The SE and magnetic resonance (MR) scans of the masseter muscles were performed before, immediately after, and 10 min after exercise. The masseter muscle elasticity index (MEI) ratio, muscle thickness, and intramuscular soft and hard areas distribution were evaluated on SE images. The signal to noise ratio (SNR), indicating the water content, was measured on MR images., Results: The soft area ratio showed significant correlations with the water content expressed as SNR. The hard area ratio showed significant correlations with the total muscle hardness expressed as the MEI ratio., Conclusion: Intramuscular soft and hard areas could be used both clinically and experimentally., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Objectives: To detect whether stabilization splint (SS) treatment of painful myofascial type temporomandibular diseases (TMD) changes the masseter muscle morphology using ultrasound (US)., Study Design: Thirty-five patients with painful myofascial TMD receiving SS treatment were studied. Masseter thickness, length, internal echo-fibrillary structure and vascularization were evaluated using gray-scale and power Doppler US just before and 3 months after the SS application. Visual analog scale (VAS) and mouth opening measurements were used to measure the outcome of treatment., Results: A significant shortening in the masseter muscle length (R: -3.67 mm, P: .010; L: -3.97 mm, P: .005) and thickness (R: -0.93 mm, P: .005; L: -0.90 mm, P: .016) was noted. No change in the internal echo-fibrillary structure or vascularization was detected. A significant decrease in VAS scores (Median: 5-0.5 P < .05) and mouth opening (42.77 ± 7.86 mm to 38.69 ± 6.21, P < .05) was also detected., Conclusion: SSs modify and reduce the dimensions of masseter muscle., (Copyright © 2013 Elsevier Inc. All rights reserved.)

A 2-year-old boy presented with a giant mass in the masticatory space. The mass exhibited a lobulating ossification, with no attachment to the adjacent normal bone. An enucleation was performed under the tentative diagnosis of extra-articular synovial chondromatosis, benign ossifying neoplasm, non-neoplastic heterotopic ossification, or low-grade malignancy. Upon microscopic examination, the excised mass was composed of multiple osteocartilaginous areas. We hereby present detailed clinicopathological findings., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The aim of this article is to compare the soft-tissue changes in the midfacial areas of patients who had undergone mandibular setback sagittal split ramus osteotomy (SSRO) with that of mandibular setback SSRO with paranasal augmentation. The subjects included 15 patients (group I), SSRO with paranasal augmentation and 20 patients (group II), SSRO alone. To evaluate the difference of the midfacial soft-tissue changes between groups, cone-beam computed tomography superimposition was utilized and the soft-tissue changes were measured both preoperatively and postoperatively by a 10 × 27 grid. In group I, the soft tissues were changed at the areas bounded superiorly by the infraorbital foramen, zygomatic eminence, posteriorly by the masseteric muscle and medially by the lateral aspect of the nose and following the nasolabial fold. In group II, the midfacial soft-tissue measurements were unchanged. This study may help clinicians to predict improvement in the midfacial region from mandibular setback SSRO with or without a paranasal augmentation procedure in class III deformities., (Copyright © 2012 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.)

Background: Treacher Collins syndrome (TCS) is a facial dysostosis, the hallmark being bilateral malar hypoplasia. The purpose of this study is to morphologically classify the TCS malar deformity and to volumetrically characterise both the TCS zygoma and masseter muscle, including for left-right symmetry, compared to controls. We hypothesise that the TCS zygoma will be smaller than controls and zygomatic deficiency will portend masseteric hypoplasia., Methods: Demographic and computed tomography (CT) data were recorded. The CT scans were converted into three-dimensional facial renderings, and the zygomatic morphology was grossly evaluated. A classification was reported based on malar structure and presence/absence of normal zygomaticomaxillary complex articulations. The zygoma and masseter muscles were then digitally isolated using 3-D planning software (Materialise, Leuven, Belgium). Volumes and sidedness ratios were calculated and compared using two-sided t-tests., Results: 58 sides were identified (24 TCS: 34 controls), mean age of 60.0 months and normally distributed. The phenotypic dysmorphology was graded as mild, moderate or severe (I, II and III, respectively). TCS malar and masseteric volumes were significantly smaller than controls (p < 0.0001 in both cases). The TCS zygomatic side-side symmetry ratio was 0.66 ± 0.28, compared to 0.97 ± 0.02 for controls (p = 0.002). The TCS masseteric side-side ratio was 0.74 ± 0.20, compared to 0.92 ± 0.09 for controls (p = 0.001)., Conclusions: A range of zygomatic hypoplasia exists in TCS (mild-severe). The decrease in malar volume occurs in concert with masseteric hypoplasia, and the left and right sides are not equally affected., (Copyright © 2012 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.)

Objective: The purpose of this study was to evaluate the influence of the masticatory system in patients with missing teeth., Study Design: The influence of tooth loss on the masticatory system was analyzed with the use of bone scintigraphy ((99m)Tc-MDP) and histochemistry. Eight white rabbits (New Zealand, 12 weeks old) were used. The rabbits were divided into 2 groups: 6 weeks and 12 weeks. Teeth were extracted unilaterally in each rabbit under general anesthesia. Six and 12 weeks after extraction, scintigraphy was conducted, and the rabbits were killed and their masseter muscles removed for histochemical analysis., Results: The results of bone metabolism (relative ratio) measured by bone scintigraphy were 48.27% at extraction sites and 51.73% at nonextraction sites at 6 weeks and 39.96% at extraction sites and 60.04% at nonextraction sites at 12 weeks. There was a significant difference at 12 weeks (P < .05). Tissue calcium contents and osteoclast counts showed different results between the extraction and nonextraction sites, but these differences did not reach statistical significance., Conclusions: The bone metabolism of temporomandibular joints and histochemical aspects of masticatory muscles may be associated with occlusal alterations following tooth loss., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Keratocystic odontogenic tumor (KCOT) is a benign intraosseous neoplasm of odontogenic origin with high recurrence rates and tendency to invade adjacent tissue. Most recurrences occur in the first 5 years after surgery and are usually located at the site of the primary tumor in the jaws. We report a rare case of KCOT which recurred in the masseter muscle 14 years after segmental mandibulectomy and autogenous frozen lesional mandible reimplantation. The patient had undergone enucleation of KCOT in the right mandible 20 years before segmental mandibulectomy. This case could further demonstrate the aggressive behavior of KCOT., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Objective: The aim of this study was to clarify the sonographic features of the masseter muscle as indices for judging the efficacy of massage treatment., Study Design: Fifteen patients with temporomandibular disorder (10 with unilateral and 5 with bilateral muscle pain) underwent massage treatment alternately on the bilateral masseter and temporal muscles with an oral rehabilitation robot. Sonography was performed before and after treatment, and the masseter thickness and existence of anechoic areas were evaluated., Results: The thickness on the symptomatic side in the unilateral group significantly decreased after treatment. Anechoic areas were shown in 20 muscles (66.7%) before treatment, and disappeared or were reduced in size in 17 muscles (85.0%) after treatment. The pretreatment thickness was significantly related to visual analog scale (VAS) scores regarding posttreatment muscle pain and massage impression. The existence of anechoic areas was relevant to VAS scores regarding muscle pain., Conclusion: Masseter thickness and existence of anechoic areas might be related to the therapeutic efficacy regarding muscle pain., (Copyright © 2010 Mosby, Inc. All rights reserved.)

Objective: The aim of this study was to clarify the changes, using magnetic resonance (MR) images, in the masseter muscles caused by low-level static contraction., Study Design: Ten healthy male volunteers were enrolled in the study. The MR scans were performed before, immediately after, and 10 minutes after low-level static contraction. Two imaging sequences were acquired: a diffusion-weighted image and an iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) image. The apparent diffusion coefficient (ADC), the signal-to-noise ratio (SNR), and the thicknesses of the right and left masseter muscles were examined., Results: The ADC and SNR immediately after exercise were significantly higher than those before exercise and 10 minutes after exercise. The muscles were significantly thicker immediately after exercise than before exercise and 10 minutes after exercise., Conclusion: We confirmed the presence of edema in the masseter muscles caused by low-level static contraction using MR images., (Copyright 2010 Mosby, Inc. All rights reserved.)

Purpose: The purpose of this study was to examine the relationship between the morphologies of the masseter muscle and the ramus and occlusal force before and after sagittal split ramus osteotomy (SSRO) in patients with mandibular prognathism., Patients and Methods: The study group consisted of 26 patients with mandibular prognathism. All patients underwent bilateral SSRO as well as 3-dimensional computed tomography on which the masseter muscle, ramus, and condyle were measured preoperatively and at 1 year postoperation. Occlusal force and contact area were also recorded with pressure-sensitive sheets., Results: In the cross-sectional area of the masseter muscle, there were no significant differences between the pre- and postoperative status. However, postoperative ramus width and area were significantly larger than preoperative values (P < .0001). Postoperative right condylar area was significantly larger than the preoperative value (P = .0120). Occlusal force and contact area 1 year after surgery were significantly larger than the preoperative values (P = .0016, P = .0190)., Conclusion: This study suggested that the masseter muscle area did not significantly differ from preoperative status 1 year after SSRO, although occlusal force, contact area, and ramus area and width increased significantly 1 year after SSRO.

Purpose: As the management of prominent mandibular angle and masseter muscle hypertrophy becomes increasingly popular, proper understanding of the volumetric component of the related structures becomes important but is currently lacking., Materials and Methods: Three-dimensional computed tomographic (CT) scans of 18 female and eight male adult patients with square-face appearance were used for volumetric measurement of the osseous hemi-mandible, masseter, medial and lateral pterygoid muscles. CT scans of 28 female and 17 male adult patients without square-face appearance were selected from the imaging laboratory archive to serve as controls., Results: Compared with the sex-matched controls, the square-faced patients had significantly higher volume of the osseous hemi-mandible as well as the masseter and medial pterygoid muscles. There was no significant difference in the volume of the lateral pterygoid muscle between the two groups. This study confirms a significantly greater volume in the osseous mandible and masseter muscle in patients complaining of square-face appearance. The implication of this information on treatment is discussed.

Intramuscular vascular malformations are unusual tumors in the head and neck region. Less than 1% of vasoformative tumors throughout the body occur in skeletal muscle; 15% of them arise in head and neck musculature. Masseter muscle is the most frequent site for such vascular malformations; it accounts for approximately 5% of all intramuscular vascular malformations in the head and neck region. A case of unusual intramuscular vascular malformation of masseter muscle is described and the diagnosis and management of these tumors is discussed.

Cleidocranial dysplasia (CCD) is a rare autosomal dominant skeletal dysplasia. In order to define the morphologic characteristics of the masseter muscle incidental to bone abnormalities, we present 3 cases of CCD with the masseter muscle thickness and maxillofacial bone abnormalities, using computed tomography (CT) and panoramic radiographs. In CCD patients (a) the masseter muscles were less thick than in age- and sex-matched control subjects, (b) the zygomatic arch was discontinuous with the hypoplastic zygomatic bone, (c) the ascending ramus of the mandible had parallel-sided borders, and (d) the coronoid process pointed upwards and/or posteriorly. We have concluded the masseter muscles are less thick than normal, alongside the maxillofacial bone abnormalities in CCD patients.

Objective: To reveal computed tomography (CT) features of patients with coronoid process hyperplasia without interference between the process and the zygomatic bone., Study Design: A case-control study was designed. Thirteen cases without interference (2 male and 11 female, 28-56 years old) and 65 controls were sampled from a patient database. Differences in CT features were analyzed between the 2 groups regarding the following 7 points of 5 regions: configuration of the coronoid process, vertical level of the coronoid process, the distance between the bilateral zygomatic arches, thickness of the temporal muscle, anteroposterior width of the temporal muscle, thickness of the temporal muscle tendon, and thickness of the masseter muscle. Cluster analysis was applied to differentiate between individuals., Results: All cases had bilateral hyperplastic change of the coronoid process. Differences were found between the cases and controls in 6 of 7 CT features with the exception of temporal muscle thickness. All incidences of significant difference showed larger values in the cases. All cases were clustered into the same group and were differentiated from the controls., Conclusion: CT features appeared to be effective for diagnosis of this condition, and these patients should be put into the same category under the diagnosis of coronoid process hyperplasia.

Objectives: The aims of the present study were to clarify the anatomy of impacted mandibular third molars in relation to surrounding structures and to investigate the pathway of infection originating from pericoronitis of this tooth., Study Design: Computed tomography (CT) images were evaluated in 87 patients with uninfected mandibular third molar impaction and in 12 patients with infection originating from an impacted mandibular third molar. In uninfected patients, bony features around the impacted crown were investigated together with the relationship between the crown and surrounding muscles. In infected patients, involvements of bony and soft tissue structures were evaluated according to the disappearance of cortices and lateral asymmetry of density and shape in the spaces and muscles., Results: In uninfected patients, the disappearance of the lingual cortical plate was observed in 48 (35.3%) impacted molars, while only in 11 (8.1%) teeth for buccal cortices. The cortical thickness was thinner on the lingual side than the buccal side. Sixty-five percent of the masseter muscle horizontally overlapped the crown, while almost all of the medial pterygoid muscle was posteriorly situated apart from the crown. The mylohyoid muscle horizontally overlapped the crown at below or intermediate vertical positions. In infected patients, the involvement of lingual structures was more frequently observed than that of buccal structures. The mylohyoid muscle was involved in 10 (83.3%) of 12 patients. Among them, 8 showed submandibular space involvement., Conclusion: CT findings supported the clinical observations of infection spread in patients with pericoronitis of the impacted mandibular third molar. CT appeared to be an effective tool for investigating the pathway of infection originating from the pericoronitis of impacted mandibular third molars.

Objective: The purpose of the present study was to examine ultrasonographic appearances in female patients with temporomandibular disorder (TMD) associated with myofascial pain in comparison with healthy volunteers., Study Design: The thickness of the masseter muscle in 25 female patients with TMD was measured at rest and at maximum contraction using ultrasonography. The visibility and width of the internal echogenic bands of the masseter muscle were also assessed and the muscle appearance was classified as 1 of 3 types: type I, characterized by the clear visibility of the fine bands; type II, thickening and weakened echo-intensity of the bands; type III, disappearance or reduction in number of the bands., Results: There were significant differences in the thickness at rest and the increase ratio by contraction between the patient and control groups. The distribution of muscle types showed a significant difference between the 2 groups., Conclusion: The ultrasonographic features of the masseter muscle in TMD patients with myofascial pain were clarified and they might be related to muscle edema.

Objectives: We sought to evaluate the diagnostic efficacy of computed tomography (CT) images in the differentiation between intraosseous malignant tumors and osteomyelitis spreading into the masticator space., Study Design: A retrospective evaluation was carried out by using CT images from 12 patients with intraosseous malignant tumors and 9 patients with osteomyelitis involving the masticator space and accompanying mandibular bone destruction. The following CT observations are discussed: (1) bone destruction pattern subdivided into spotty, gross, or permeative; (2) cortical bone expansion; (3) diffuse osteosclerotic changes; (4) periosteal reaction; (5) masticator muscle involvement; (6) enlargement of the facial muscle; and (7) attenuation in the subcutaneous adipose tissue., Results: The pattern of permeative bone destruction, cortical bone expansion, and the enlargement of both the masseter and medial pterygoid muscles were all observed in patients with malignant tumors. In contrast, diffuse sclerotic change and a periosteal reaction were significant observations in patients with osteomyelitis., Conclusion: The efficacy of CT in establishing a differential diagnosis of malignant tumors or osteomyelitis is supported by this study.

In this report we present a patient with unilateral masseteric hypertrophy who used anabolic steroids and was chewing entirely unilaterally for 1 month. Computed tomography and histologic examination were used to confirm the diagnosis. The combined action of unilateral mastication and anabolic steroid use is probably responsible for the rapid development of unilateral masseteric hypertrophy.

We evaluated the effect of botulinum toxin A on masseteric muscle hypertrophy by using ultrasound and electromyography. Five patients (four with bilateral and one with unilateral masseteric muscle hypertrophy) were studied prospectively. In each patient, ultrasound-guided percutaneous intramuscular injection of botulinum toxin A was carried out. The change in muscle bulk was evaluated using serial ultrasonography and the electrical activity was assessed with electromyography. All five patients (nine hypertrophic muscles) showed a good response, with the maximal effect of a 31% reduction in muscle bulk seen 3 months after treatment. The effect remained stable one year after injection for six of the hypertrophic muscles, whereas three muscles needed a second injection to maintain the atrophy. This preliminary prospective study suggests that botulinum toxin A is a safe alternative method of treating masseteric muscle hypertrophy. However, the effect may be temporary and further intramuscular injection may be required to maintain atrophy., (Copyright 2001 The British Association of Plastic Surgeons.)

Objective: The purpose of this study was to clarify the normal findings of arteries in and around the masseter muscle and to present their pathologic changes with the use of color Doppler sonography., Study Design: The vascular appearances were examined for the 4 main arteries feeding the masseter muscle in healthy volunteers (n = 38) and patients with inflammation (n = 5) and intramuscular hemangioma (n = 3). The features of these arteries were investigated together with the flow diameter, flow velocities, and arterial resistances. The symmetry indices were also calculated to assess the pathologic changes., Results: The detection rates of the branch from the transverse facial artery, the masseter artery, and the branch from the maxillary or external carotid artery were 98.7%, 21.1%, and 84.2% in healthy volunteers, respectively. The facial artery that feeds the muscle from the inferior part represented 2 patterns according to anatomic variant: the masseteric branch (22.4%) and the main trunk itself (77.6%). The means of the flow diameter, maximum and minimum velocities, resistive index, and pulsatility index in healthy subjects were 1.8 mm, 24.6 cm/s, 5.1 cm/s, 0.80, and 2.51, respectively. In most of the patients with symptoms, the symmetry indices of all measurement values increased in comparison with those of healthy volunteers., Conclusion: Color Doppler sonography is useful in describing the arteries in and around the masseter muscle and has the potential of being used to depict the pathologic changes.

The effects of chronic pressure on the mandible during skin expansion procedures have been investigated. In 19 Göttingen miniature pigs with an average age of 3 months, tissue expanders were placed s.c. in close proximity to the growing ascending ramus of the mandible on the surface of the masseter muscle. After complete filling of the expanders (100 cc) after 6 weeks, a significant transverse discrepancy could be observed compared with the contralateral side. Additionally, severe medial dislocation of the molars were noticed. Ten weeks after the removal of the implant, the occlusal disturbance still existed, deviation of the transverse mandibular diameter still reached up to -13.6 +/- 2.1%. Because only four animals were measured based on a CT investigation, further statistical analysis was not possible. Histological examination showed osteoclastic activity of the expander with consequent bone resorption and remodelling. Strict indications should be agreed for tissue expansion in the vicinity of growing bone, as, for example, when tissue expansion is applied in children.

Objective: The purpose of this study was to review and illustrate the appearances on diagnostic images of pathologic conditions of the buccomasseteric region., Study Design: Computed tomographic, sonographic, and magnetic resonance images of the buccomasseteric masses were reviewed retrospectively., Results: In our series of 66 cases, there were 60 benign lesions; of these, 21 were benign masses, 11 were inflammations, and 28 were myopathies. The most common pathologic condition of the buccomasseteric region was masseteric hypertrophy (n = 22). The most common lesion manifesting as a benign mass in this series was hemangioma (n = 10), which was followed by lipoma (n = 6). Six of the 66 patients had malignant tumors., Conclusions: Computed tomography and magnetic resonance imaging were useful in demonstrating the location and extent of the buccomasseteric masses. Sonography provided clear images of internal architectures of the mass in this region.

Myositis ossificans traumatica of the masseter muscle is uncommon. The condition is benign and results in reactive heterotopic bone formation, usually producing limitation of opening of the jaws. Radiographic and microscopic examination can confirm the diagnosis. Treatment of myositis ossificans traumatica of the masseter muscle is surgical, with other modalities used when occurring in other muscles of the body.

A case of unilateral masseteric hypertrophy in a 30-year-old man is described. Preoperative evaluation was performed by magnetic resonance imaging (MRI), computed tomography (CT) and ultrasonography (USG). MRI could delineate not only the border between medial and lateral layers of the masseter but also delineate the hypertrophic portion. MRI also provided more information in respect of the masseter muscle as well as the other masticatory muscles and the surrounding tissues than CT. USG was useful because of its real-time processing, especially in this case where facial asymmetry was emphasized during mastication. We resected the medial lower-half of the masseter intraorally based on these imagings and obtained a successful result.

Synchronized electromyography and videofluorography (lateral projection) were used to investigate the influence of altered head posture on hyo-mandibular movements, suprahyoid muscle length, suprahyoid working angle, and timing of suprahyoid and masseter muscle activity. Twelve adult male subjects with normal dentofacial morphology were investigated during the open-close-clench cycle. Using upright head position (Frankfort horizontal) as reference, several statistically significant observations were made during forward flexion and backward extension of the head. The results indicate that head posture is a significant factor in studies of mandibular and hyoid bone movements, and masseter and suprahyoid muscle function.