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Introduction: Botulinum neurotoxin (BoNT) injections are widely used for the treatment of masseter muscle hypertrophy in Southeast Asia. However, there remains a lack of consensus regarding the optimal injection technique. This study aimed to compare the efficacy and patient discomfort associated with single-entry point injections versus multiple three-point injections for masseter muscle hypertrophy treatment with BoNT., Materials and Methods: Sixteen participants, comprising both male and female Korean adults aged 22-63, were enrolled in the study. On the left side of the face, single-entry point injections were administered, followed by multidirectional injections, while on the right side, three-point injections were given. Pain intensity during the procedure was assessed using visual analogue scale scores., Result: Our results revealed that participants experienced lower levels of pain with single-entry point injections compared to three-point injections (average visual analogue scores of 3.31 and 5.19, respectively)., Conclusion: These findings highlight the potential benefits of single-entry point injections in reducing patient discomfort during masseter muscle hypertrophy treatment with BoNT. We advocate for further research to validate these findings and encourage practitioners to consider single-entry point injections as a viable option for enhancing treatment outcomes in their clinical practice., (© 2024 The Author(s). Journal of Cosmetic Dermatology published by Wiley Periodicals LLC.)

Background: The popularity of noninvasive botulinum toxin type A (BTX-A) injections for masseter muscle hypertrophy is increasing among Asian individuals with a square-shaped lower face., Aims: This study aimed to analyze the adverse events (AEs) caused by BTX-A injections into the masseter muscle., Patients/methods: This observational study retrospectively evaluated 46 250 patients who underwent BTX-A injections into the masseter muscle in 2022. The inclusion criteria were the diagnosis of an AE by the physician at the return visit and subsequent follow-up of progress (n = 223). The patients who were lost to follow-up (n = 40) were excluded from the study., Results: Among the 223 patients with AEs, the most common AE was paradoxical bulging (88.3%, n = 197/223). The average period from treatment until confirmation of improvement was 159.6 ± 113.6 days (range 13-667 days) for all AEs, all of which were temporary. The period until improvement was 166.1 days in the intervention group (n = 122) and 151.9 days in the observation group (n = 101) (p = 0.24). As the period until improvement of AEs included the period until the patients visited the clinics and the improvements were confirmed by physicians, the actual period was likely to have been shorter., Conclusions: (1) All AEs were temporary. (2) All AEs improved within 22.2 months (within 5.3 ± 3.8 months on average). (3) There was no significant difference between the intervention and observation groups in the period until the improvement of AEs., (© 2024 The Author(s). Journal of Cosmetic Dermatology published by Wiley Periodicals LLC.)

Background: Masseter hypertrophy is a common condition that causes a undesirable square face, and often treated with botulinum toxin type A (BoNTA). Subjective assessments of BoNTA effectiveness vary from physician to patient, necessitating an objective approach for evaluation. This study introduces three-dimensional photography (3DP) for the first time in clinical assessment to evaluate BoNTA treatment for masseter hypertrophy., Methods: Ten patients received 36U of BoNTA at three injection points on each side masseter muscle. 3DP scanner using Artec Eva® was taken at the first, third, and sixth postoperative months for objective evaluation. Patient's self-perceived prominence, patients self-rated satisfaction, and physicians provided 5-grade scores were the subjective indicators., Results: A significant decrease in left masseter volume at the sixth month (P = 0.002, P = 0.004 at rest and clenching, respectively) was observed. Patient's self-perceived prominence decreased at the first (P = 0.021) and third (P = 0.039) months. Physicians' scores significantly decreased at all postoperative months. No significant changes were noted in the right masseter volume and patients self-rated satisfaction. Patient self-rated satisfaction did not consistently correlate with objective measures, except for left masseter with clenching at the sixth month., Conclusion: Three-dimensional photography accurately quantifies facial changes post-BoNTA treatment. Despite objective improvements, patient satisfaction may not align consistently. Reliable assessment tools are crucial in cosmetic surgery to manage expectations and prevent disputes., Level of Evidence Iv: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 ., (© 2024. Springer Science+Business Media, LLC, part of Springer Nature and International Society of Aesthetic Plastic Surgery.)

Background: This study aimed to elucidate the effects of botulinum toxin A (BoNT-A) treatment for patients diagnosed with masseter hypertrophy on the temporalis muscle, with a particular focus on assessing alterations in muscle thickness, electromyographic (EMG) activity, and the development of muscle pain., Methods: The present randomized triple-blinded clinical trial enrolled 26 female participants aged between 25 and 50 years complaining about masseter hypertrophy. Participants received 75U of BoNT-A (abobotulinumtoxinA) in both masseter muscles and after three months were randomized to receive a second treatment session of saline solution (S-BoNT-A) or BoNT-A (M-BoNT-A). Longitudinal assessments included temporalis muscle thickness through ultrasound, EMG activity, subjective pain, and masseter prominence severity after one, three, and six months of the first injection session. Muscle thickness, EMG, and subjective pain were analysed using two-way ANOVA with repeated measures and post hoc Sidak test, and for masseter prominence severity, Friedman and Mann-Whitney tests were used., Results: Regarding inter-group comparisons, a higher muscle thickness (p < 0.02) and a higher EMG activity (p < 0.01) were found in the M-BoNT-A group at the 6-month follow-up. For subjective pain assessments, inter-group comparisons showed a higher prevalence of painful regions in M-BoNT-A group at the 6-month follow-up (p < 0.02). No significant differences were found in masseter prominence severity at the 6 months assessment between groups., Conclusion: BoNT-A treatment for masseter hypertrophy lead to structural and functional changes in the temporalis muscle, presenting higher changes after multiple injections of this treatment., Level of Evidence I: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 ., (© 2024. The Author(s).)

With the increasing use of Botulinum toxin type A (BoNT-A) injections in the masseter muscles for both medical and aesthetic purposes, there is a constant need to continually enhance the efficacy of these treatments and reduce the risk of potential adverse events. This review provides an in-depth analysis of the masseter muscle's anatomical structure and essential landmarks and emphasizes the advantages of ultrasound (US) guidance in improving the precision of BoNT-A injections compared to conventional blind methods. The review is supplemented with comprehensive figures, including graphics, clinical images, and ultrasound visuals, to support the discussion. Potential complications such as paradoxical bulging, inadvertent injections into the risorius muscle or parotid gland, facial paralysis, and the risk of bone resorption are examined. Future research should aim at refining injection techniques and assessing the long-term effects of repeated treatments to ensure optimal patient care and safety.

(1) Background: With the increasing aesthetic pursuit of facial features, the clinical use of Botulinum Toxin Type A (BoNT-A) injections for masseter hypertrophy has been on the rise. However, due to variations in masseter muscle structure and differences in clinicians' injection techniques, blind injections may lack precision, potentially compromising treatment accuracy and increasing the risk of complications. (2) Objectives: The study aims to use ultrasonography to detail the deep inferior tendon (DIT) within the masseter muscle in a young Chinese cohort, refine its classification, analyze muscle belly thickness and variations across groups, and propose a customized ultrasound-guided BoNT-A injection protocol. (3) Methods: Ultrasound imaging was used to observe the bilateral masseter muscles at rest and during clenching. The features of the DIT were classified from these images, and the thickness of the masseter's distinct bellies associated with the DIT types was measured in both states. (4) Results: The study cohort included 103 participants (27 male, 76 female), with 30 muscles in the normal masseter group and 176 muscles in the hypertrophy group. The DIT was categorized as Type A, B (subtypes B1, B2), and C. The distribution of these types was consistent across normal, hypertrophic, and gender groups, all following the same trend (B > A > C). In hypertrophy, Type B1 showed uniform thickness across masseter bellies, B2 presented with a thinner intermediate belly, and Type C had mainly superficial muscle enlargement. Changes in muscle thickness during clenching were noted but not statistically significant among different bellies. (5) Conclusions: The study evidences individual variation in the DIT, highlighting the importance of precise DIT classification for effective BoNT-A injections. A tailored ultrasound-guided BoNT-A injection strategy based on this classification may enhance safety and efficacy of the therapy.

Masseter muscle hypertrophy is a rare condition with no known etiology that has become more prevalent due to growing aesthetic concerns. It is distinguished by either unilaterally or bilaterally enlarged masseter muscles. Its origin is still unknown. This study discusses a clinically confirmed case of unilateral masseter muscle hypertrophy and provides an outline of the condition's etiology, prevalence, diagnosis, and course of treatment., Competing Interests: No competing interests were disclosed., (Copyright: © 2024 Sonar PR and Panchbhai AS.)

The present study aimed to assess the effectiveness and functional adverse effects of a single and multiple injections of botulinum toxin A (BoNT-A) for masseter hypertrophy (MH). Twenty-six women complaining about lower third facial enlargement due to MH, received 75 U of BoNT-A (abobotulinum toxin) in each masseter muscles. After 3 months, patients were randomly assigned to receive a second treatment session of Saline Solution: (G1; n = 11) or BoNT-A: (G2; n = 12). Muscle thickness (ultrasound), electrical activity (electromyography; EMG), masticatory performance, and subjective perception of MH were evaluated. Follow-up was performed at 1, 3 and 6 months. Muscle thickness, EMG activity, and masticatory performance were analyzed using ANOVA two-way and Sidak test as post-hoc. Masticatory performance was analyzed by the Friedman's test and Mann-Whitney test. Regarding inter-groups comparisons, there was a significant decrease in the left masseter muscle thickness in the G2 group at the 6 month follow-up (p < 0.02). For EMG, significant differences were evident at the 6 month assessment, with higher masseter activity for G1 (p < 0.05). For masticatory performance, no significant differences were observed throughout the study (p > 0.05) and a higher improvement in subjective perception of MH was observed in the 1 month follow-up for G2 (p < 0.05). In conclusion, BoNT-A is effective for MH, however multiple injections cause functional adverse effects in masseter muscle., (© 2024. The Author(s).)

Background: Despite the widespread use of botulinum toxin (BTX) injection for the treatment of masseter muscle hypertrophy (MMH), there is no standard treatment option., Objective: We report the efficacy and safety for BTX in MMH over a period of 48 weeks., Methods: In double-blinded, placebo-controlled phase 3 trials, 180 patients (randomized 1:1) received treatment with placebo (normal saline) or prabotulinumtoxinA (48 units). Masseter muscle thickness (at maximal clenching and resting positions), 3D imaging analysis, and masseter muscle hypertrophy scale grades were analyzed at each time point. After the 24-week CORE study, all patients who met the same criteria of the CORE study at week 24 ( n = 114) received only prabotulinumtoxinA, regardless of previous treatment, for an additional 24 weeks (48 weeks in total) for the open-label extension study., Results: The largest differences in mean and percent changes from baseline in masseter muscle thickness were observed at 12 weeks, and there were significant differences between the 2 groups at all time points (all p < .001). The effect was independent of the number of injections. No serious adverse event was observed., Conclusion: PrabotulinumtoxinA could effectively ameliorate MMH without major complications., (Copyright © 2024 by the American Society for Dermatologic Surgery, Inc. Published by Wolters Kluwer Health, Inc. All rights reserved.)

Background: The rapid development of cosmetic injections has led to an increased incidence of nontuberculous mycobacterial (NTM) infection., Patients and Methods: Here, we presented a case of cutaneous Mycobacterium abscessus infection subsequent to botulinum toxin injection for treating masseter hypertrophy, and reviewed the literature on skin and soft tissue infections caused by NTM after cosmetic injections., Results and Conclusions: The patient underwent surgical excision and regular antibiotic therapy and has had nearly 2 months of follow-up without any signs of infection. The diagnosis and treatment of NTM infection have always been challenging, and further research is needed to standardize and guide the treatment., (© 2024 The Authors. Journal of Cosmetic Dermatology published by Wiley Periodicals LLC.)

Background: Benign masseteric hypertrophy (BMH) is a condition in which the thickness of the masseter muscle is increased, resulting in jawline prominence with an undesirable cosmetic appearance. Botulinum toxin type A (BTA) injection is a promising treatment option, but its effective dose remains debated., Methods: Adults older than 19 diagnosed with BMH through visual examination and palpation related to a masseter muscle prominence were selected, and 80 patients were randomly assigned into five groups (placebo group and four groups with different doses of BTA: 24 U, 48 U, 72 U, or 96 U, on both sides of the jaw) and treated with placebo or BTA once at their baseline visit. During each follow-up, the treatment efficacy was evaluated with ultrasound examination of the masseter muscle, three-dimensional facial contour analysis, visual evaluation by the investigator, and patient satisfaction evaluation., Results: The mean age of the 80 patients was 42.7 ± 9.98 years; 68.75% were women. The mean change in masseter muscle thickness during the maximum clenching state after 12 weeks of drug administration compared with baseline in the 24-U, 48-U, 72-U, and 96-U groups were -2.33 ± 0.41 mm, -3.35 ± 0.42 mm, -2.86 ± 0.42 mm, and -3.79 ± 0.42 mm, respectively. All treatment groups showed a statistically significant decrease compared with placebo. Regarding subjective satisfaction, all treatment groups, except the 24-U group at 4 weeks, showed higher satisfaction than the placebo group during all visits. No significant adverse events were noted., Conclusion: BTA administration of at least 48 U for BMH is more cost-effective than high-dose units and has a low risk of side effects., Clinical Question/level of Evidence: Therapeutic, II., (Copyright © 2023 by the American Society of Plastic Surgeons.)

Summary: A particularly prominent mandibular angle or a hypertrophied masseter muscle can result in an excessively wide facial appearance, which some individuals may find less aesthetically pleasing. Although normally a benign condition and strictly an aesthetic concern, a hypertrophied masseter can also cause pain, bruxism, and headaches. Neuromodulator for masseter reduction and treatment of bruxism has become first-line treatment. In this article, the authors present the senior author's (R.J.R.) anatomic approach to neuromodulator injection of the masseter, with a corresponding video of the injection technique., (Copyright © 2023 by the American Society of Plastic Surgeons.)

Background: Masseter muscle hypertrophy (MMH) usually presents with cosmetic concerns as it may lead to widening of the lower face. Apart from the traditional surgical approaches, botulinum toxin type A (BTA) injection is a non-invasive treatment option available. There are no standard guidelines for this procedure., Objectives: To study the efficacy of botulinumtoxin A in MMH for lower face contouring., Methodology: The Cochrane Library, PubMed/MEDLINE, Google-scholar, Science-Direct database, and ResearchGate from inception until September 2021 were searched using the keywords "botulinumtoxin type A," "masseter muscle hypertrophy," "lower face contouring," and "masseter botox." All available retrospective and prospective studies, case-series, case-reports, and expert reviews were included with an emphasis on efficacy of BTA in MMH and units injected into the muscle, points of placement, adverse events, and the duration of its effect. Reference lists of the resultant articles, as well as relevant reviews, were also searched., Result: 40 articles were shortlisted for the review, of which 14 studies with sample-size ≥10 in accordance with the study requirements were summarized in a tabular form for analysis and easy comparison and reference., Conclusion: BTA injection is a non-invasive, safe, and effective treatment for MMH. The optimum number of BTA units could not be ascertained due to wide variability in the studies as well as ethnicity of patients and extent or some measurement of MMH. The points of placement of injection should be well within the boundaries of the masseter muscle. The maximum effect of BTA after a single injection session is usually seen in ~3 months, and the duration may last for 6-12 months. Multiple injection sessions may be required to maintain a long-term effect. Injection technique and total number of injection units of neuromodulator must be individualized for each patient., (© 2022 The Authors. Journal of Cosmetic Dermatology published by Wiley Periodicals LLC.)

Aim: To determine if botulinum injections in masseters could be an option to avoid surgery and prolonged treatment with occlusal splints and/or drugs to care for both painful bruxism and cosmetic improvement in a patient with a square jaw, bruxism, and orofacial pain., Background: Masseter muscle hypertrophy (MMH) is a benign, unilateral, or bilateral, painless enlargement in the lower face. It presents as a symmetrical or asymmetrical increase in the masseter muscle. Masseter muscle hypertrophy (MMH) sometimes can be related to bruxism symptoms like muscle and/or temporomandibular joint (TMJ) pain., Case Description: A 38-year-old woman complained of bilateral pain at palpation in the masseter body. She also complained about esthetics because of the prominent masseter muscle in the face and square face shape. A diagnosis of bruxism-related myalgia was performed, and treatment with botulinum injections into the masseter muscles was opted for. An oral electromyography was performed to detect the electrical muscular activity of masseter muscles over time., Conclusion: After a drastic reduction in the mean electrical activity immediately after the botulinum injections, a progressive increase in strength over time was noted, testifying about the decrease in the effect of botulinum over time. The pain disappeared for 5 months after the injections of botulinum. The reduction of the masseter muscle mass led to a softening of the face shape., Clinical Significance: This case report shows that treatment with botulinum can lead, in the short term, to a reduction in orofacial pain due to a decrease in muscle electrical activity.

Background: Masseter hypertrophy is the main cause of an asymmetrical and squared lower facial contour in the Asian community. Botulinum toxin injection technique is crucial to treat this condition., Objective: To improve injection techniques for masseter hypertrophy by elucidating the distribution of the injections within the masseter., Methods: Thirty masseter muscles were divided into 6 groups of 5 muscles each. Each group received one 0.2- or 0.3-mL injection at Point A, B, or C according to a three-point technique. Muscle dimensions and dye of the primary and secondary dye spreading were measured., Results: The average muscle length, width, and thickness were 69.87, 33.50, and 11.23 mm, respectively. The average primary longitudinal and horizontal spreading was 36.56 and 15.60 mm, respectively. No statistically significant difference was found between 0.2- and 0.3-mL injections at each point., Conclusion: The three-point technique best fits in the safe zone and should be the standard injection technique for masseter hypertrophy. Injection at Points B and C may create secondary spreading that affect the risorius muscle and the parotid gland which are the cause of asymmetrical smiling and xerostomia, respectively. The dosage should be adjusted according to the muscle volume and not only the thickness., (Copyright © 2021 by the American Society for Dermatologic Surgery, Inc. Published by Wolters Kluwer Health, Inc. All rights reserved.)

Masseter hypertrophy (MH) is an uncommon disorder which can cause both aesthetic and functional problems. The most common aetiological factors associated with MH are habit of chewing gum, clenching and/or bruxism. The treatment of MH includes conservative management as well as surgical resection of the enlarged muscle and/or bone. Injection of botulinum toxin type A is a relatively new and minimally invasive method for management of masseter muscle hypertrophy, which offers many advantages over conventional surgical management. This paper reports a case of unilateral MH of unknown origin which was treated with injection of botulinum toxin type A, resulting in satisfactory reduction in the volume of muscle and improvement of facial aesthetics., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.)

There are still concerns about masseteric bulging due to a lack of knowledge about the internal architecture of the masseter muscle. Further investigations are therefore required of the most-effective botulinum neurotoxin (BoNT) injection points and strategies for managing masseteric bulging. The purpose of this study was to identify safer and more effective botulinum neurotoxin injection points and strategies by using ultrasonography to determine the structural patterns of the deep inferior tendon. We also measured the precise depths and locations of the deep inferior tendon of the masseter muscle. Thirty-two healthy volunteers participated in this study, and ultrasonography was used to scan the masseter muscle both longitudinally and transversely. Three structural patterns of the deep inferior tendon were identified: in type A, the deep inferior tendon covered the anterior two-thirds of the masseter muscle (21.8%); in type B, the deep inferior tendon covered the posterior two-thirds of the masseter muscle (9.4%); and in type C, the deep inferior tendon covered most of the inferior part of the masseter muscle (68.8%). Depending on the ultrasonography scanning site, the depth from the skin surface to the mandible in the masseteric region ranged from 15 to 25 mm. The deep inferior tendon was typically located 2 to 5 mm deep from the mandible. Ultrasonography can be used to observe the internal structure of the masseter muscle including the deep inferior tendon in individual patients. This will help to reduce the side effects of masseteric bulging when applying retrograde or dual-plane injection methods depending on the structural pattern of the deep inferior tendon.

Background: A wide lower face and a square jaw are considered esthetic problems, particularly in Asia., Objective: To investigate the optimal dose of a novel botulinum toxin (prabotulinum toxin A) for treating masseteric hypertrophy., Methods: Ninety subjects with masseteric hypertrophy were randomly divided into 5 groups and treated with placebo (A, normal saline) or prabotulinum toxin A (B: 24, C: 48, D: 72, and E: 96 units). Photography, ultrasonography, and 3-dimensional imaging were performed before and after injection at baseline and at 4, 8, 12, and 16 weeks after treatment. The participants also rated their satisfaction., Results: Masseter thickness significantly reduced in all groups at 12 weeks, compared with that in the placebo group. A dose-dependent reduction in masseter thickness was observed at the resting and maximal clenching positions. Sonography and 3-dimensional imaging revealed a gradual reduction in masseter thickness and volume, respectively, during the first 12 weeks. Despite being slightly effective, a dose of 24 units might be insufficient for resolving square face problems. Patients in Group E reported discomfort during jaw movement., Conclusion: Prabotulinum toxin A could effectively improve lower face contour without major complications, with an optimal dose of 48 to 72 units, followed by reinjection after 12 weeks., (Copyright © 2020 by the American Society for Dermatologic Surgery, Inc. Published by Wolters Kluwer Health, Inc. All rights reserved.)

Botulinum toxin type A (BoNTA) is a powerful neurotoxin that inhibits acetylcholine release from presynaptic vesicles. The potency and safety profile of BoNTA grant the toxin vast therapeutic potential. It has been used off-label for a variety of dermatologic conditions. This review aims to analyze published literature regarding the benefits and risks of the off-label use of BoNTA beyond facial lines, including eccrine hidrocystomas, enlarged pores, keloids and hypertrophic scars, hidradenitis suppurativa, hyperhidrosis, masseter muscle hypertrophy, and salivary gland hypertrophy, among others. A MEDLINE search from January 2000 to December 2019 was conducted on the off-label uses of botulinum toxin in dermatology.

Background: With the changing trends, more and more patients are opting for nonsurgical or minimally invasive options for reshaping the face. Noninvasive treatments such as incobotulinumtoxinA (Xeomin Cosmetic ® ; Merz Pharma Canada Ltd., Burlington, ON, Canada) are a preferred modality for reducing the volume of the muscle and therefore reducing the width of masseter., Aims: To evaluate the efficacy of Xeomin treatment in long-term management of bilateral masseter hypertrophy in Asian Indian patients., Patients/methods: A total of 30 patients were enrolled in the study and were injected with 30 U Xeomin on each side of face, at baseline. Fifteen patients received a second session of Xeomin injection at 12th week, and remaining 15 patients received an additional third session, at 12th and 24th weeks post the first injection, respectively. Follow-up was done at 4th-, 12th-, 24th-, and 36th-week and at first- and second-year follow-ups., Results: For the patients who received two injections, the maximum reduction of 26.85% was observed at 24th week, which was maintained as 20.04% reduction until second follow-up year. The patients who received three injections exhibited very high reduction of 43.12% of masseter volume at 36th week, which was maintained at 38.72 % until the second follow-up year. Three sessions of Xeomin injections were proved to be more effective in long-term maintenance of reduced masseter volume than 2 sessions of injections., Conclusions: Xeomin injections were found to be effective in long-term management of bilateral masseter hypertrophy. This is the first of its kind paper, which evaluates the long-term effects of Xeomin injections for the treatment of masseter hypertrophy., (© 2020 Wiley Periodicals, LLC.)

Background: Treating the lower face with neuromodulators and targeting the masseter muscle can reduce masseteric hypertrophy but can also change the facial shape. A novel observation after the treatment of the masseter muscle with incobotulinumtoxin Type A was the increase in temporal volume., Aim: Objectively assess temporal volume increase following treatment of masseteric hypertrophy using incobotulinumtoxin Type A., Methods: Nine female patients with a mean age of 35.11 years ± 9.1 [Asian (11.1%) and Caucasian (88.9%)] were treated with incobotulinumtoxin Type A for masseteric hypertrophy. Masseteric prominence and temporal volume were assessed by two independent raters, and temporal fossa volume was measured via 3-dimensional volumetric imaging., Results: Independent of the neuromodulator injection technique (ie, single-injection versus multi-injection), a reduction in masseteric hypertrophy occurred represented by a decrease in the masseter prominence scale. In addition, the treatment resulted in a significant improvement of the temporal volume scale and an increase in the measured volume of the temporal fossa. None of the presented measurements were statistically significantly different between the two utilized injection techniques., Conclusions: This study supports using a full-face approach when performing aesthetic treatments. Anatomical concepts can help to guide treatments: the compensatory increase in temporalis function after masseter muscle treatment resulted in an increased in temporal fossa volume. The findings presented herein should not be considered as a new concept for treating the temporal fossa but rather as an additional possibility for increasing the temporal volume., (© 2020 The Authors. Journal of Cosmetic Dermatology published by Wiley Periodicals LLC.)

Background: Asian Indians usually have wide lower faces because of masseter hypertrophy. The authors evaluated the efficacy of botulinum toxin type A in long-term management of bilateral masseter hypertrophy in Asian Indian patients., Methods: Fifty patients were enrolled in the study and injected with 30 U of botulinum toxin type A to each side of the face, at baseline. Based on masseter muscle thickness and response to the injections, 25 patients underwent a second injection session at week 12, and the other 25 patients underwent additional third sessions, at week 24 after the first injection, respectively. Standardized photography and ultrasonography were performed to assess facial contour and masseter muscle thickness at baseline and at 1-, 2-, 3-, and 4-year follow-ups. A p value < 0.05 was considered statistically significant., Results: The authors observed 12 percent (p < 0.0001) average masseter muscle size reduction at week 12. The maximum reduction (26.6 percent; p < 0.0001) was observed at week 24 for the patients who received two injections and maintained an average 24.43 percent (p < 0.0001) reduction until follow-up at year 4. Patients who received three injections exhibited very high reduction (42.52 percent; p < 0.0001) of masseter volume at week 36 and maintained an average 40.64 percent (p < 0.0001) reduced volume until year 4., Conclusions: Botulinum toxin type A treatment is effective for long-term management of bilateral masseter hypertrophy. Doses repeated at 12-week intervals accentuate masseter volume reduction and also help maintain reduced masseter volume for 4-year follow-up, with satisfactory facial contour.

Objectives : This review investigated the effects of orthodontic or functional orthopedic therapy on masseter muscle thickness through the use of ultrasonography (US) in growing subjects when compared with untreated subjects. Materials and Methods : This review systematically assessed studies that investigated growing subjects undergoing orthopedic therapy for the correction of malocclusion of vertical, sagittal and transversal plane. Electronic databases (CENTRAL, MEDLINE-PubMed, Scopus and Web of Science) were searched up to February 2019, including available RCTs and CCTs, without language restrictions. The primary outcome was the effect of orthopedic or functional treatment on masseter muscle thickness. The risk of bias of included studies was assessed through the Newcastle-Ottawa quality assessment scale with the aim of defining their methodological quality. A random-effects meta-analysis analyzing mean differences with 95% confidence intervals was used for quantitative analysis. Results : The search retrieved 749 titles, but the studies selection resulted in a final sample of 5 CCTs. The studies retrieved data from 233 children (age range: 5-22 years) and were conducted at university dental clinics. Children were treated for Class II malocclusion, increased vertical dimension or lateral cross-bite variably with rapid or slow maxillary expansion, twin block, bite block, mandibular activators, quad helix, alone or in combination. Risk of bias was assessed as medium for three studies, low for one and high for another. The meta-analysis determined that at the end of orthopedic or functional treatment masseter muscle thickness, measured through the use of US, is significantly reduced (MD -0.79 mm; 95% CI -1.28 to -0.31). The reduction in muscle thickness, therefore, could be considered an indicator for the evaluation of the success of therapy with orthodontic appliances. Conclusions : Although the meta-analysis revealed that US could be considered a less invasive and effective method to evaluate the masseter muscle thickness, single-blinded RCTs, are required to confirm US reliability in this field of application. This review was registered on PROSPERO with the following registration number: CRD42018068402., Competing Interests: The authors declare no conflict of interest.

Background: Cultural ideals for a slimmer face have led to an upsurge in interest in facial contouring among East Asians. Although surgical resection has traditionally been the main treatment option, botulinum toxin injection is becoming a popular, noninvasive alternative., Objective: To describe the use of botulinum toxin injection for masseter reduction in East Asians., Methods: An electronic search of the PubMed database was performed for studies published from 2000 to 2017 that meet the word combination of botulinum toxin, masseter, hypertrophy, and/or lower face contouring. Only the studies conducted in East Asian countries were analyzed in this review, exception of one study from Thailand., Results: A total of 12 publications were identified. Each study was reviewed to extract relevant information on patient selection, injection techniques, efficacy, dosage, frequency, and main side effects of treating masseters with botulinum toxin., Conclusion: Botulinum toxin injection for masseter reduction in East Asians is efficacious and generally considered safe with no significant side effects. Future areas for investigation include defining the criteria for benign masseteric hypertrophy, minimum effective dosage of botulinum toxin, and the potential long-term effects of the injection.

Masseter muscle hypertrophy (MMH) is a benign, unilateral or bilateral, painless enlargement. Treatment protocols include surgical excision or a non-invasive option, using botulinum toxin type A (BTX-A). There is no study in the literature that measures this dimensional change in the masseter muscle (MM). The aim of this case report is to present changes in volume and surface area in MM with three-dimensional closer an gestereophotogrammetry (3DCS). For treatment 30 units of BTX-A was injected into the three points hypertrophic muscle and patient records were taken to compare with 3DCS with a non-metric Canon EOS 550 D camera before and after injection. The changes in the surface area and volume of this muscle were mapped and the objective data were obtained. This technique is useful for predicting the results of BTX-A application, and can be a useful tool for better physicianpatient communication.

Introduction: Botulinum neurotoxin A (BoNT-A) is a minimally invasive and technically straightforward treatment of masseter muscle (MM) volume reduction and facial contouring, but the literature on its long-term effect on MM volume remains unclear., Objective: This study aimed to assess quantitatively for progressive volume changes of lower facial contour after 3 BoNT-A injections in patients with bilateral MM hypertrophy causing square facial morphology using 3-dimensional computed tomographic scans., Materials and Methods: Ten female patients with square facial morphology due to bilateral MM hypertrophy were recruited to, and 6 completed, this clinical study. Each received 24 U of BoNT-A into the inferior portion of each MM on both sides, repeated 6 monthly to complete 3 treatments. Masseter muscle volume changes were assessed using 3-dimensional computed tomography at pretreatment (before injections) and posttreatment (1 year after the third injection)., Results: Mean MM volume significantly reduced from 26.39 ± 4.18 cm before treatment to 23.26 ± 4.31 cm 1 year after treatment (P = 0.002)., Conclusion: Three consecutive 6-monthly BoNT-A injections into the MMs reduced their volume by 12% when assessed 1 year after completion of treatment.

Background: Masseteric hypertrophy is a benign condition characterized by the enlargement of the masseter muscles. A square-shaped jawline due to masseter muscle prominence or hypertrophy is one of the general characteristics of the Asian face, making it a frequent target for esthetic treatment requests. While the application of botulinum toxin on the masseter muscle is an off-label use, it is very popular in Asian countries. However, comprehensive reviews of the complications associated with this procedure remain limited in scope., Objectives: The goal of this study is to help physicians achieve a comprehensive understanding of the complications associated with neuromodulator injection over the masseter muscle via a thorough literature review., Methods: A literature search was performed on the PubMed/MEDLINE, Google Scholar, and Science Direct databases using the search terms botulinum toxin, masseter hypertrophy, masseteric hypertrophy, and/or masseter hyperplasia. Literature from January 1994 to February 2018 was deemed to be allegeable for inclusion and analysis. All available prospective and retrospective studies, case series, case reports, and expert reviews were included, with an emphasis on types of complications, incidence rate, onset time, recovery time, and product used. Articles that do not mention side effects, complications, or adverse events were excluded., Results: Thirty-six articles were found, covering type, incidence rate, and clinical course of the complications. These studies were summarized into tabular form for easy reference and comparison., Conclusion: Botulinum toxin masseter injections are commonly performed procedures with good results and safety profiles. The majority of complications appeared within 2-4 weeks of injection and disappeared within 12 weeks. Despite the temporary nature of these complications, they often decrease patient satisfaction and confidence, so physicians should familiarize themselves with the regional anatomy and injection safety zones., (© 2018 Wiley Periodicals, Inc.)

Background: Botulinum toxin (BoNT) is widely used to treat masseter muscle hypertrophy. Changes in the muscle thickness have been found in many studies, but there has been no report on changes in the thickness from the skin surface to the masseter muscle., Objectives: We aimed to use ultrasonography to measure not only changes in the muscle thickness but also changes in subcutaneous thickness., Methods: This study enrolled 20 volunteer patients: 10 were assigned to an experimental group (injected with each side 25 U of botulinum toxin into both masseter muscles) and 10 to a control group (injected with normal saline). The thicknesses were measured before the injection and at 4, 8, and 12 weeks after the injection both at rest and during maximum muscle contraction., Results: The subcutaneous thickness did not differ significantly over time either at rest (P = 0.063) or during maximal contraction (P = 0.392), or between the experimental and control groups at rest (P = 0.392) or during maximum contraction (P = 0.259). The muscle thickness in the experimental group differed significantly over time., Conclusions: Botulinum toxin injection only changes the muscle thickness and does not affect the subcutaneous thickness from the skin surface to the masseter muscle., (© 2017 The American Society for Aesthetic Plastic Surgery, Inc. Reprints and permission: journals.permissions@oup.com)

Background: Masseter hypertrophy is a common, prominent feature in many Asian patients, and correction procedures are often requested for esthetic reasons. Toxin masseter injections have a high efficacy and safety profile, but the risks of a variety of side effects or complications remain., Objectives: The categorization of various complications was based on etiology, with a presentation of the author's own incidence rates for consideration and comparison., Methods: Six hundred and eighty patients received a total of 2036 sessions of toxin injection for masseter hypertrophy from 2011 to 2016, and complications or complaints were recorded through follow-up on a by-treatment basis. Complications were grouped together based on etiology and discussed., Results: Of 2036 sessions, temporary mastication force decrease was reported after 611 (30%), bruising after 51 (2.5%), headaches after 12 (0.58%), smile limitation after 3 (0.15%), paradoxical bulging after 10 (0.49%), sunken cheeks (subzygomatic volume loss) after 9 (0.44%), and sagging after 4 (0.20%)., Conclusions: Masseter injections remain very safe. To further decrease the incidence rate, injections should only be inside the recommended safety zone, a quadrilateral within the muscle that avoids most important local structures. Keeping injections inside the safe zone, and ideally in 3-4 different locations at least 1 cm from any border, is crucial for the prevention of complications., (© 2017 Wiley Periodicals, Inc.)

Botulinum toxin type A (BTA) (also known as onabotulinum toxin A) injection is widely used in the field of cosmetic dermatology. Although a few adverse events related to intramuscular BTA injection have been reported, no life-threatening adverse reaction has been documented to date. We report a case of anaphylaxis induced by intramuscular BTA injection into the masseter muscles of a 35-year-old woman. She had previously received injections of the identical BTA product into the same muscles without incident. However, during the reported procedure, symptoms suggestive of angio-oedema and anaphylaxis developed about 5 min after BTA injection. Intramuscular epinephrine was used to manage the reaction. Following this, the patient was found to have an elevated total serum IgE level. We could not perform testing with BTA because of the risk of triggering another episode of anaphylaxis; however, intradermal tests using the identical sterile saline and patch test using the topical anaesthetic cream both showed negative results, thus we strongly suspect BTA as being the cause of anaphylaxis in this case., (© 2017 British Association of Dermatologists.)

The aim of this study was to investigate the association between patterns of jaw motor activity during sleep and clinical signs and symptoms of sleep bruxism. A total of 35 university students and staff members participated in this study after providing informed consent. All participants were divided into either a sleep bruxism group (n = 21) or a control group (n = 14), based on the following clinical diagnostic criteria: (1) reports of tooth-grinding sounds for at least two nights a week during the preceding 6 months by their sleep partner; (2) presence of tooth attrition with exposed dentin; (3) reports of morning masticatory muscle fatigue or tenderness; and (4) presence of masseter muscle hypertrophy. Video-polysomnography was performed in the sleep laboratory for two nights. Sleep bruxism episodes were measured using masseter electromyography, visually inspected and then categorized into phasic or tonic episodes. Phasic episodes were categorized further into episodes with or without grinding sounds as evaluated by audio signals. Sleep bruxism subjects with reported grinding sounds had a significantly higher total number of phasic episodes with grinding sounds than subjects without reported grinding sounds or controls (Kruskal-Wallis/Steel-Dwass tests; P < 0.05). Similarly, sleep bruxism subjects with tooth attrition exhibited significantly longer phasic burst durations than those without or controls (Kruskal-Wallis/Steel-Dwass tests; P < 0.05). Furthermore, sleep bruxism subjects with morning masticatory muscle fatigue or tenderness exhibited significantly longer tonic burst durations than those without or controls (Kruskal-Wallis/Steel-Dwass tests; P < 0.05). These results suggest that each clinical sign and symptom of sleep bruxism represents different aspects of jaw motor activity during sleep., (© 2016 European Sleep Research Society.)

Background: Botulinum toxin type A (BTA) is now extensively used to address cosmetic concerns. OnabotulinumtoxinA (ONA, Botox; Allergan Inc., Irvine, CA) received FDA approval for upper face rejuvenation, including glabella frown lines and crow's-feet lines. The other off-label uses for lower face conditions have been utilized for contouring purposes, especially masseter hypertrophy. Recently, a new Daewoong BTA, (NABOTA ® , NBT, Daewoong Pharmaceutical, Seoul, Korea), was recently introduced., Objective: To compare efficacy and safety of ONA and NBT for masseter reduction., Methods: Thirty-five subjects with masseter hypertrophy were randomly injected with 25 units of ONA on one side and 25 units of NBT on the other side into masseter. Standardized photographic documentation was obtained at baseline, 1, 3 and 6 months after treatment. The mean volume of masseter was acquired by using three-dimensional computed tomography (3-D CT) at baseline, 3-, and 6-month follow-up visits. In addition, patients' satisfaction and side effects were also record at every follow-up visits., Results: The mean masseter volume on the sides treated with ONA and NBT at baseline were 21.20 ± 4.23 cm 3 and 21.26 ± 4.58 cm 3 , respectively. There was no statistically significant difference in the mean volume of both sides (p= 0.827). The mean masseter volume at 3- and 6-month follow-up visits reduced significantly on both ONA and NBT sides (p< 0.001 and p< 0.001, respectively). However, there was no statistically significant difference in mean masseter volume when comparing between ONA and NBT sides at 3 and 6 months after treatment (p= 0.769 and p = 0.346, respectively). There was also no statistically significant difference in masseter reduction when compared between ONA and NBT sides evaluated by physicians and patients at each follow-up visit. No side effect on both sides was reported after injection., Conclusions: This study demonstrated that ONA and NBT provided comparable efficacy and safety for masseter reduction.

Masseter muscle hypertrophy is an untypical anomaly with no definite cause and its diagnosis is easily completed through physical examination and imaging examinations. In some cases, patient may report signs and symptoms of well-localizated pain. However, it is generally asymptomatic and patient's chief complaint is about esthetic because of facial asymmetry. In this case, surgery is carefully indicated. The aim of this article is to report a case of a male patient with no painful and functional complaints but an important unease over his facial asymmetry. Patient underwent surgery involving bilateral resection of mandibular angles and unilateral resection of masseter muscle through intraoral approach. Surgical approaches and techniques rely heavily on surgeon. There are few reports in the literature about this anomaly, but those available present several techniques. The surgeon's dexterity and knowledge become extremely important, whereas this procedure is essentiallyesthetic.

Objective and Importance: Hypoplasia of the masseter muscle is a rare condition, described as partial or total, associated with congenital malformations or pathologies. Rare cases are those with no genetic alterations in their familiar picture. The authors present a case of an idiopathic masseter muscle hypoplasia in the absence of other pathologies., Clinical Presentation: The case report involved a patient who presented to the consultant clinic complaining of facial asymmetry. The patient underwent several exams to confirm the diagnosis of masseter muscle hypoplasia, which included an X-ray, magnetic resonance of the temporomandibular articulation, and electromyography., Intervention: The patient was treated with a customized functional appliance and fixed orthodontic treatment with satisfactory functional and esthetic results., Conclusion: The case presented highlights the possibility of finding a hypoplasia of the masseter muscle even in the absence of other pathologies and without specific clinical symptoms, and how to plan an appropriate treatment with functional appliance and fixed orthodontic therapy.

Increased salivary demand can lead to enlarged parotid salivary glands, and increased activity of the masseter muscles can cause masseter hypertrophy. This report describes a most unusual case of simultaneous bilateral hypertrophies of the parotid gland and masseter muscle originating from the very extensive habit of chewing gum. An extensive literature review uncovered many cases of the independent existence of masseteric or parotid hypertrophy, but no example of the simultaneous occurrence of these 2 conditions., (Copyright © 2016 American Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.)

Objective: To evaluate the effect and maintaining period of botulinum toxin A on the masseter muscles through noninvasive monitoring of changes in the structure and function of masseter muscle., Methods: We randomly selected 20 female patients with benign masseter hypertrophy,22-43 years old, who were treated with injection of botulinum toxin A. High-frequency ultrasound was adopted to measure thickness and hardness of muscles.Surface electromyography (sEMG) was used to observe the changes of muscle force. All patients were followed up before and 1,4,12 and 24 weeks after the injection of botulinum toxin type A. Subjective evaluation of the efficacy was performed by questionnaire survey., Results: The thickness and hardness of muscle decreased 1 week after injection which attained the lowest level at 12 weeks. The thickness and hardness reduced by 18％-39％ and 20％-32％ respectively at relaxed state of masseter muscles, the muscle force reduced by 78％ during muscle contraction. The muscle recovered to previous state 24 weeks after injection. The subjective evaluation by doctor and patients was consistent with the results by the high frequency ultrasound and EMG detection results., Conclusions: High frequency ultrasound and surface electromyography are effective and noninvasive means for objective evaluation of masseter muscles after the injection of botulinum toxin type A.

Purpose: To present a patient with an atypical recurrent parotid swelling due to masseter muscle hypertrophy and the diagnostic/therapeutic assessment to treat this condition., Case Report: A patient referring recurrent right facial swelling underwent a complete multidisciplinary assessment of the parotid region that revealed masseter muscle hypertrophy, confirmed by means of clinical (otolaryngological and gnathological evaluation), radiological (utrasonography, dynamic magnetic resonance imaging, and cone beam computed tomography), instrumental (electromyography to evaluate the right masseter muscle function and kinesiography to evaluate maximum right deflection - MaxRDefl and maximum opening - MaxMO) and sialendoscopy assessment where T0 indicates the pre-treatment values. All electromyographic and kinesiographic parameters were evaluated six months after the orthodontic application of a neuromuscular orthosis at T1. At T1, the effectiveness of the orthodontic therapy was demonstrated by the complete resolution of symptoms, and instrumental results documented more efficient muscle activity at rest and during clenching and a better mandibular position. At EMG T1, the resting and post-TENS values were, respectively, 1.2 and 1.8 microV. At kinesiography, MaxRDefl increased from 10.2 (T0) to 10.5 mm (T1); maxMO increased from 41.2 (T0) to 48 mm (T1)., Conclusion: The proposed multidisciplinary assessment based on otolaryngological, gnathological, and radiological evaluation may be useful in the case of recurrent parotid swelling secondary to masseter muscle hypertrophy to plan an appropriate management with a removable neuromuscular orthosis.

Objective: To observe the curative effect of botulinum toxin A on masseter hypertrophy using three-dimensional stereophotogrammetry., Methods: 46 cases with masseter hypertrophy (92 masseters) who received botulinum toxin A injection were enrolled from May 2013 to August 2014.Data were collected before and 3,6 and 9 months after injection., Results: The efficacy of botulinum toxin A in reducing the volume of the lower face has been proven by MAS 3D.3 and 6 months after injection, the volume reduction were measured as 7.23 ％,2.15％ respectively (P ＜ 0.05).The coefficients between middle and lower thirds of the face showed an increase compatible with thinning of the lower face with statistical significance at 3 months follow up. The increase percentage was measured by MAS 3D as 40.21％ between pre-and post-injection (P ＜ 0.05),and the increase percentage was 21.03％ at 6 months follow up (P ＜ 0.05).While 9 months after injection,the value was insignificant comparing to pretreatment at 9 months., Conclusions: Three-dimensional stereophotogrammetry provides a safe effective and direct way to observe masseter hypertrophy.

For correction of this asymmetrical hypertrophy, botulinum toxin type A (BTxA) injection is one of convenient treatment modalities. Unfortunately, physical examination of masseter muscle is not enough to estimate the exact volume of muscle hypertrophy difference. Two Koreans, male and female, of bilateral masseter hypertrophy with asymmetricity were evaluated. BTxA (NABOTA(®), Daewoong, Co. Ltd., Seoul, Korea) was injected at master muscle site with total 50 U (25 U at each side) and volume change was evaluated with three-dimensional (3D) CT image analysis. Maximum reduction of masseter hypertrophy was recognized at 2-month follow-up and reduced muscle size started to restore after 3 months. Mean reduction of masseter muscle volume was 36% compared with baseline. More hypertrophied side of masseter muscle presented 42% of volume reduction at 2-month follow-up but less hypertrophied side of masseter muscle showed 30% of volume shrinkage. In conclusion, 3D CT image analysis might be the exact evaluation tool for correction of asymmetrical masseter hypertrophy by botulinum toxin injection.

Objective: The association of bilateral hypertrophy of temporalis and masseteric muscles is a rare clinical entity. The origin of the condition is unclear, causing cosmetic problems, pain, and functional impairment., Patients and Methods: In this paper we analyzed 15 patients treated at the Department of Maxillo-Facial Surgery of the University of Naples Federico II, from 2000 to 2013, for temporalis and/or masseteric muscle hypertrophy, and in particular, a rare case of a patient with a marked bilateral swelling of the temporalis and masseteric region, in conjunction with a review of the literature., Results: Fourteen patients have not any kind of postoperatively problems. The last patient had been aware of the swelling for many years and complained of recurrent headaches. We adopted a new protocol fort this patients and the patient was very pleased with the treatment results, and reported a reduction in headaches and a continuation of his well-being, in addition to greater self-confidence. The last follow-up was performed three years after the first treatment, and the patient showed a complete resolution of his symptoms, and just a small increase of the swelling., Conclusions: The treatment of temporalis and masseteric hypertrophy with Botulin toxin could be an effective option compared to conservative treatment or surgical intervention, although the review of the literature shows that this is only a temporary treatment. In fact, surgery still remains the best option. The treatment must be repeated every 4/6 months for 2-3 consecutive years before having stable benefits. To overcome this problem, an association with a bite treatment allowed us to achieve more lasting and more stable results over time without a recurrence of symptoms between the treatments. Furthermore, this association has enabled us to obtain a more rapid reduction of the hypertrophy.

Background: Posterior cheek enlargement in human immunodeficiency virus (HIV)+ individuals can lead to significant cosmetic disfigurement. Both parotid gland and masseter muscle overlie the mandibular ramus, contributing to lower facial contour. However, posterior cheek enlargement has not been well characterized anatomically. There are also limited treatment options. Botulinum toxin is a highly efficacious minimally invasive option for improving the shape of the lower face., Objective: A pilot study was undertaken to better characterize posterior cheek enlargement in HIV+ patients and explore treatment with botulinum toxin A., Materials and Methods: Five HIV+ patients with posterior cheek enlargement were treated with botulinum toxin A. Clinical, photographic, and radiological evaluations allowed the precise calculation of any change in volumes resulting from botulinum toxin A., Results: All 5 patients had a good response with a mean decrease of 21.4% and 11.2% in the volumes of the masseter muscle and parotid gland, respectively. The effect was long lasting even at 6 months after injection and well tolerated., Conclusion: Botulinum toxin A may be a less invasive treatment of posterior cheek enlargement in HIV+ patients, with advantages of a good result that is long lasting with good tolerability and minimal risk.

Background: Glucocorticoid has a direct catabolic effect on skeletal muscle, leading to muscle atrophy, but no effective pharmacotherapy is available. We reported that clenbuterol (CB) induced masseter muscle hypertrophy and slow-to-fast myosin heavy chain (MHC) isoform transition through direct muscle β2-adrenergic receptor stimulation. Thus, we hypothesized that CB would antagonize glucocorticoid (dexamethasone; DEX)-induced muscle atrophy and fast-to-slow MHC isoform transition., Methodology: We examined the effect of CB on DEX-induced masseter muscle atrophy by measuring masseter muscle weight, fiber diameter, cross-sectional area, and myosin heavy chain (MHC) composition. To elucidate the mechanisms involved, we used immunoblotting to study the effects of CB on muscle hypertrophic signaling (insulin growth factor 1 (IGF1) expression, Akt/mammalian target of rapamycin (mTOR) pathway, and calcineurin pathway) and atrophic signaling (Akt/Forkhead box-O (FOXO) pathway and myostatin expression) in masseter muscle of rats treated with DEX and/or CB., Results and Conclusion: Masseter muscle weight in the DEX-treated group was significantly lower than that in the Control group, as expected, but co-treatment with CB suppressed the DEX-induced masseter muscle atrophy, concomitantly with inhibition of fast-to-slow MHC isoforms transition. Activation of the Akt/mTOR pathway in masseter muscle of the DEX-treated group was significantly inhibited compared to that of the Control group, and CB suppressed this inhibition. DEX also suppressed expression of IGF1 (positive regulator of muscle growth), and CB attenuated this inhibition. Myostatin protein expression was unchanged. CB had no effect on activation of the Akt/FOXO pathway. These results indicate that CB antagonizes DEX-induced muscle atrophy and fast-to-slow MHC isoform transition via modulation of Akt/mTOR activity and IGF1 expression. CB might be a useful pharmacological agent for treatment of glucocorticoid-induced muscle atrophy.

Background: Botulinum toxin type A (BTX-A) is widely used for the clinical treatment of masseteric hypertrophy. Until now, few reports have discussed how to prolong the duration of its effectiveness., Objective: This study evaluated that purposely adjusting the masticatory movements is possible of postponing the masseter muscle rehypertrophy., Methods: Ninety-eight patients were randomly and equally divided into 2 groups, and 35 U BTX-A per side was injected into the masseters. The thickness and volume of the masticatory muscles were measured by ultrasound and computerized tomography, respectively. Patients in Group 1 were instructed to strengthen their masticatory effort during the denervated atrophic stage of the masseter (the interval was evaluated by real-time ultrasound monitoring), whereas patients in Group 2 were not given this instruction. When the masseter muscle began to recover, patients in both groups were instructed to reduce their chewing., Results: The duration of the masseter muscle rehypertrophy was significantly prolonged in Group 1 patients. The thickness and the volume of the other masticatory muscles were significantly increased in Group 1 but were either slightly decreased or insignificantly different in Group 2., Conclusion: Purposely strengthening masticatory muscle movement during the denervated atrophic stage of the masseter can prolong the duration of masseter rehypertrophy.

Introduction: Botulinum toxin injections are previously reported to be a noninvasive alternative method for treating masseteric hypertrophy. However, there is a debate on finding an ideal place for injection. The aim of this study is to document the anatomical landmarks for defining the motor nerve entry points (MNEPs) of the masseteric nerve in the masseter for effective botulinum toxin injections., Materials and Methods: Twelve sides from six adult fixed cadavers were used for this study. The MNEPs of the masseteric nerve were defined according to standard landmark lines including the orbitomeatal line (OML) and the line (VL), which intersects the mid-distance of the OML to the tip of the angle of the mandible., Results: All MNEPs were located 4.4 cm inferior to the OML. In addition, the average anterior distance of the MNEPs to the VL was 1.4 cm and the average posterior distance was 0.6 cm., Conclusion: The ideal site of Botox injection into the masseter is a rectangular area: 5 cm inferior to the OML, 1 cm anterior and posterior to the VL, and just above the periosteum. Based on the data of our study, injections to the parotid gland and branches of the facial nerve such as the marginal mandibular and buccal can be avoided. The masseteric nerve can easily be found approximately 1.0-1.5 cm inferior to the zygomatic arch, 1 cm medial to the temporomandibular joint capsule, and 1 cm superior to mandibular notch, which makes its use for facial reanimations more efficient., (Copyright © 2014 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.)

Introduction: Mandibular angle resection is rarely used, but is a highly effective means of correcting facial defects. We report a mandibular angle resection technique associated with the removal of a part of hypertrophic masseter muscles and resection of buccal fat pad., Technical Note: Anatomical reminders: the most important entities are the facial artery and vein, crossing the lower margin of the jaw just in front of the anterior boarder of the masseter muscle and the temporomaxillary vein, passing through the temporomaxillary fossa; preoperative aspects: the preoperative examination included a radiological assessment of the shape and size of the mandibular angle; surgical technique: an intra-oral approach was usually used. The most effective and convenient method for the osteotomy was using a reciprocating saw. This technique allowed achieving a smooth contour of masseter muscles during masticatory movements or at rest., Our Experience: Eleven mandibular angle resections were performed from 2001 to 2009. The surgery was supplemented by remodeling the lower margin of the jaw for 5 other patients. No permanent facial palsy was noted. One patient presented a unilateral long-term loss of sensitivity of the lower lip and chin., Discussion: This surgical technique if simple even requires using good technical equipment, and observing a set of rules. Using these principles allows simplifying the surgical technique, and decreasing its morbidity. A part of the masseter muscles and the buccal fat pad can sometimes be resected to improve the morphological results., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)