Explore the vast range of titles available.

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.

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 .

This study compared the degree of secondary hyperalgesia and somatosensory threshold changes induced by topical capsaicin between spinal and trigeminal innervation. This crossover clinical trial included 40 healthy individuals in which 0.25 g of 1% capsaicin cream was randomly applied for 45 minutes to a circular area of 2 cm 2 to the skin covering the masseter muscle and forearm in 2 different sessions, separated by at least 24 hours and no more than 72 hours (washout period). The main outcome variables were the area of allodynia and pinprick hyperalgesia, as well as electrical and mechanical pain thresholds within the area of pinprick hyperalgesia. Mixed ANOVA models and McNemar tests were applied to the data ( p  = 0.050). The occurrence of allodynia and pinprick hyperalgesia was higher in the forearm than in the masseter ( p  < 0.050). Additionally, the areas of pinprick hyperalgesia and allodynia were larger in the forearm compared to the masseter ( p  < 0.050). The electrical and mechanical pain thresholds demonstrated a loss of somatosensory function following capsaicin application to the masseter ( p  < 0.050). However, no significant somatosensory threshold changes were observed at the forearm after capsaicin ( p  > 0.050). In conclusion, these findings indicate potential differences compatible with central sensitization related to secondary hyperalgesia between trigeminal and spinal innervation.

Botulinum toxin (BTX) is commonly used in masseter injections to enhance facial contour. However, the injection may harm the surrounding structure due to insufficient research on the anatomical structure of the masseter region. This study is aimed at providing anatomical evidence for facial injections in clinical practice by dissecting the superficial masseter structure and analyzing it by classifying the masseteric nerve and structure. Select 24 adult gross specimens with intact facial characteristics and dissect the masseter regions to expose the surface structure of the masseter muscle. After that, draw a heatmap according to the frequency of occurrence of the above structures. Then, dissect and document the structure relationship of the masseteric nerves and each layer of the masseter. The masseter region has a safe triangular zone (△LMF). The course probability of the facial nerve, parotid gland, parotid duct, facial artery, and facial vein is the lowest in this region. The masseteric structure is classified into three types: overlapped type, juxtaposed type, and parallel type, of which the juxtaposed type is the most common. In the safe triangular zone, the small branches of the masseteric nerve are mainly distributed in the connection range of line LM. The three-point injection approach is presented after a comprehensive analysis incorporating the masseter injection's safe triangular zone and the masseter's internal structure. It provides a more accurate treatment strategy for the masseter microplastic injection.

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.

Study Objectives: To investigate the effects of botulinum toxin type A (BoNT-A) injection on jaw motor episodes during sleep in patients with or without orofacial pain who did not respond to oral splint treatment. Methods: Twenty subjects with a clinical diagnosis of SB completed this study. Ten subjects received bilateral BoNT-A injections (25 U per muscle) into the masseter muscles only (group A), and the other 10 received the injections into both the masseter and temporalis muscles (group B). Video-polysomnographic (vPSG) recordings were made before and at 4 weeks after injection. Rhythmic masticatory muscle activity (RMMA) and orofacial activity (OFA) were scored and analyzed for several parameters (e.g., frequency of episodes, bursts per episode, episode duration). The peak amplitude of electromyographic (EMG) activity in the two muscles was also measured. Results: BoNT-A injection did not reduce the frequency, number of bursts, or duration for RMMA episodes in the two groups. The injection decreased the peak amplitude of EMG burst of RMMA episodes in the injected muscles (p < 0.001, repeated measure ANOVA) in both groups. At 4 weeks after injection, 9 subjects self-reported reduction of tooth grinding and 18 subjects self-reported reduction of morning jaw stiffness. Conclusions: A single BoNT-A injection is an effective strategy for controlling SB for at least a month. It reduces the intensity rather than the generation of the contraction in jaw-closing muscles. Future investigations on the efficacy and safety in larger samples over a longer follow-up period are needed before establishing management strategies for SB with BoNT–A. Citation: Shim YJ; Lee MK; Kato T; Park HU; Heo K; Kim ST. Effects of botulinum toxin on jaw motor events during sleep in sleep bruxism patients: a polysomnographic evaluation. J Clin Sleep Med 2014;10(3):291–298.

Masticatory muscle hypertrophy (MMH) is a rare clinical phenomenon of uncertain etiology, characterized by a soft swelling near the angle of the jaw. This abnormal enlargement of the masseter muscle can alter the facial profile, leading to aesthetic concerns. Moreover, MMH may also have significant functional repercussions, including pain in the masseter region, often associated with temporomandibular disorders, fatigue, and discomfort during mastication. Non-conservative approaches offer an effective and minimally invasive solution by inducing localized muscle relaxation and reducing hypertrophy. Botulinum neurotoxin type A (BoNT/A) represents a therapeutic option for managing MMH, considering that injections can effectively reduce the masseter muscle volume, improving both facial aesthetics and related symptoms. Currently, the standard non-surgical management of MMH is BoNT/A injections, although consensus on the average dosage has not been definitely reached; on the other hand, there are data available in the literature about the injection technique of BoNT/A for lower face contouring. Therefore, the present comprehensive review aimed at exploring in detail the role of BoNT/A in the treatment of masseter muscle hypertrophy, describing its mechanism of action, the administration protocols, the clinical effects, and any side effects.

The purpose of this study is to evaluate the effects of botulinum toxin type A (BoNT-A) for managing sleep bruxism (SB) in a randomized, placebo-controlled trial. Thirty SB subjects were randomly assigned into two groups evenly. The placebo group received saline injections into each masseter muscle, and the treatment group received BoNT-A injections into each masseter muscle. Audio–video–polysomnographic recordings in the sleep laboratory were made before, at four weeks after, and at 12 weeks after injection. Sleep and SB parameters were scored according to the diagnostic and coding manual of American Academy of Sleep Medicine. The change of sleep and SB parameters were investigated using repeated measures analysis of variance (RM-ANOVA). Twenty-three subjects completed the study (placebo group 10, treatment group 13). None of the SB episode variables showed a significant time and group interaction (p > 0.05) except for electromyography (EMG) variables. The peak amplitude of EMG bursts during SB showed a significant time and group interaction (p = 0.001). The injection decreased the peak amplitude of EMG bursts during SB only in the treatment group for 12 weeks (p < 0.0001). A single BoNT-A injection cannot reduce the genesis of SB. However, it can be an effective management option for SB by reducing the intensity of the masseter muscle.

(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.

Purpose Trigeminal neuralgia (TN), a debilitating condition, is commonly treated with microvascular decompression (MVD). However, effective intraoperative neurophysiological monitoring remains challenging. This study introduces a novel electrophysiological technique using sensory-masseter response (SMR) to monitor trigeminal nerve compression during MVD. Methods A total of 34 patients with TN underwent MVD. A concentric neurostimulator was employed to systematically deliver microcurrent stimulation to various intracranial segments of the trigeminal sensory root. We specifically probed the segment distal to the suspected neurovascular conflict (NVC) site, the actual compression point itself, and the segment central to the NVC site. Stimulation was performed at equivalent anatomical levels on both the compressed and non-compressed sides for comparison. Simultaneously, compound muscle action potentials (CMAPs) were recorded from the masseter muscle. These recorded potentials were defined as the SMR. The spatial correlation between SMR positivity and NVC was analyzed to assess its clinical utility. Results SMR was successfully recorded in 28 out of 34 patients (82.4%). Among these 28 SMR-positive cases, NVC was identified at the stimulation site in 24 cases, with 19 showing visible vascular indentation. The mean SMR latency was 3.30 ± 0.36 ms. The stimulation threshold required to elicit SMR was significantly lower at the NVC site (median 0.3 mA, IQR 0.2–0.4 mA) compared to the distal segment of the NVC side ( p  < 0.001), the non-compressed side ( p  < 0.001), and the central segment of the NVC side ( p  = 0.012). A strong association was observed between NVC and SMR positivity ( p  < 0.001). These findings suggest that SMR positivity correlates with NVC sites. Conclusion This study introduces a novel electrophysiological technique SMR for localizing NVC during microvascular decompression for trigeminal neuralgia. SMR is likely mediated by focal demyelination and sensory-motor anastomoses. Although SMR demonstrates potential in assisting intraoperative localization during MVD, its clinical value requires further validation.