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Amyotrophic lateral sclerosis (ALS) progressively impairs motor neurons, leading to muscle weakness and loss of voluntary muscle control. This study compared the effects of SOD1 mutation on masticatory and limb muscles from disease onset to death in ALS model mice. Notably, limb muscles begin to atrophy soon after ALS-like phenotype appear, whereas masticatory muscles maintain their volume and function in later stages. Our analysis showed that, unlike limb muscles, masticatory muscles retain their normal structure and cell makeup throughout most of the disease course. We found an increase in the number of muscle satellite cells (SCs), which are essential for muscle repair, in masticatory muscles. In addition, we observed no reduction in the number of muscle nuclei and no muscle fibre-type switching in masticatory muscles. This indicates that masticatory muscles have a higher resistance to ALS-related damage than limb muscles, likely because of differences in cell composition and repair mechanisms. Understanding why masticatory muscles are less affected by ALS could lead to the development of new treatments. This study highlights the importance of studying different muscle groups in ALS to clarify disease aetiology and mechanisms.

The serotonergic system modulates the neural circuits involved in jaw movement; however, the role of serotonin (5-HT) neurons in masticatory movement remains unclear. Here, we investigated the effect of selective activation of 5-HT neurons in the dorsal raphe nucleus (DRN), or the raphe obscurus nucleus (ROb), on voluntary masticatory movement using transgenic mice expressing the channelrhodopsin-2 (ChR2) mutant (C128S) in central 5-HT neurons. During voluntary mastication, DRN blue light illumination increased masticatory frequency and decreased the root mean square peak amplitude of electromyography (EMG) in the masseter muscles. DRN blue light illumination also decreased EMG burst duration in the masseter and digastric muscles. These changes were blocked by a 5-HT2A receptor antagonist. Conversely, ROb blue light illumination during voluntary mastication did not affect masticatory frequency and EMG bursts in the masseter and digastric muscles. DRN or ROb blue light illumination during the resting state did not induce rhythmic jaw movement such as mastication but induced an increase in EMG activity in masseter and digastric muscles. These results suggest that both DRN and ROb 5-HT neurons may facilitate jaw movement. Furthermore, DRN 5-HT neuron may contribute to changes in masticatory patterns during the masticatory sequence. [ABSTRACT FROM AUTHOR]

The physiological and functional changes from aging affect the systemic and swallowing muscles. While ultrasound is used to examine muscle characteristics, no previous studies have examined the relationship between age and perioral and trunk muscle characteristics, including stiffness. This study aimed to investigate the relationship between age and the characteristics of perioral and trunk muscles, including quality, quantity, and stiffness, using ultrasound. A total of 215 participants were recruited for this cross-sectional study: 98 younger adults (20–64 years) and 117 older adults (≥ 65 years). Muscle characteristics were assessed along with data on age, sex, body mass index, and number of teeth. The correlation between age and muscle characteristics was examined. Multiple linear regression was performed with muscle characteristics as dependent variables and age, body mass index, and number of teeth as explanatory variables. We found that only trunk muscle stiffness was associated with age, with a stronger correlation in quality and quantity than perioral muscles. Masseter muscle quality and quantity showed a higher correlation with age than those of the geniohyoid muscle. In conclusion, characteristics of the trunk and perioral muscles exhibit differences in age-related changes, highlighting the importance of maintaining both trunk and perioral muscle activity in older adults to prevent functional decline. [ABSTRACT FROM AUTHOR]

Background: Motor imagery (MI) has increasingly been used in physiotherapy. Oral rehabilitation may be a potential application area for MI. The aim of this study is to investigate the acute effects of orofacial and tongue muscle strengthening exercises in the form of physical exercise and motor imagery on pain and tongue strength in healthy adults. Thirty asymptomatic adults were included in this trial. MI skills were evaluated using the Movement Imagery Questionnaire-Revised and the mental chronometer. The pain and strength were assessed using an algometer and a tongue pressure device. Following the baseline evaluations, three interventions: physical exercise, kinesthetic motor imagery, and visual motor imagery, were applied randomly on different days. Pain and tongue strength were re-evaluated immediately after the interventions. Results: The physical exercise program did not significantly improve pain and tongue strength (p > 0.05). Following the kinesthetic MI training, a significant increase was detected (p = 0.016, d = 0.51) in the left masseter muscle pain threshold. Visual MI training resulted in improvements in anterior tongue strength (p = 0.002, d = 0.66) and left masseter muscle pain (p = 0.024, d = 0.40). Conclusions: The present study suggests that different motor imagery strategies may have different effects on tongue muscle strength and pain threshold in healthy adults. [ABSTRACT FROM AUTHOR]

The masticatory muscles of the horse are arranged in an asymmetrical pattern. Four individual muscles on the medial side of the mandible are opposed by one muscle (M. masseter) on the lateral side. However, recent studies on various herbivorous mammals indicate that the masseter muscle features a complex stratigraphic structure that might account for a functional diversity resembling an arrangement of several individual muscles. The functional consideration of the multidirectional equine masticatory movements leads to a similar hypothesis. In order to elucidate the detailed anatomy of the equine masseter muscle, eight cadaveric equine heads were dissected. Additional 29 skull specimens were assessed with regard to the masseteric attachment within the Fossa masseterica. A constant arrangement of nine individual muscular layers within the masseteric muscle was determined. The individual layers were clearly separated by tendon plates and their attachment areas at the masseteric fossa of the mandible were arranged in a constant pattern of bony ridges. With similar consistency, the main trunk of the masseteric nerve was found to run from dorsocaudal to ventrorostral: On that course, the nerve penetrated between the muscular layers from medial to lateral at constant positions. The findings of this study serve as a basis for further studies with the aim of developing biomechanical concepts of equine masticatory movement. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This document contains abstracts from the Anatomical Society Winter meeting in Liverpool, UK. The abstracts cover a range of topics related to craniofacial anatomy and development. Some of the studies discussed include the development of an automated craniofacial segmentation tool, postnatal changes in the semicircular canals of mice, the role of the digastric muscle in rabbits during mastication, tissue engineering the human TMJ disc, diet-related morphological changes in the craniofacial skeleton of red squirrels, and the biomechanics of biting in infants. Other studies explore tooth regeneration in mice, the use of anatomical models for remote learning, cranial blunt force trauma, the development of the soft palate in mammals, the morphology of the mandibular symphysis in snakes, and the mechanical behavior of cranial sutures in cases of craniosynostosis. Additionally, there is a study on the presence of bone growths in the external auditory canal of prehistoric human populations and the creation of accurate 3D printed models of juvenile skulls for educational purposes. The integration of ultrasound into the anatomy curriculum and the anatomical covariation between the endocranium and brain are also examined. These studies provide valuable insights into various aspects of craniofacial anatomy and development. [Extracted from the article]

Objective: To investigate the surface electromyography (EMG) activity of the temporalis, masseter, digastric, and infrahyoid muscles during passive jaw opening in healthy adults. Methods: The EMG activity of the masseter, temporalis, digastric anterior belly, and infrahyoid muscles on the right side was recorded during the four jaw-opening tasks: active opening to 20 mm (AO20); active opening to 40 mm (AO40); passive opening to 40 mm with a rubber mouth prop on the right posterior teeth (POR40); and passive opening to 40 mm with a mouth prop on the left posterior teeth (POL40). Results: The EMG amplitude of the digastric anterior belly and infrahyoid muscles in either POL40 or POR40 was significantly less than that in AO20 or AO40, respectively. Conclusion: Passive jaw opening reduces the EMG activity of the digastric and infrahyoid muscles significantly and could help reduce the load on these muscles during prolonged mouth-opening conditions. [ABSTRACT FROM AUTHOR]

Objective: To determine the role of emotional state in the masticatory system function in a group of young adults. Methods: Ninety-six generally healthy randomly selected students aged 18–21 were examined. They were subjected to a questionnaire survey determining their emotional state, clinical examination, and instrumental diagnostics (EMG, Cadiax Compact, JVA). Results: The stress symptoms group revealed a greater intensity of neck and shoulder muscles pain (p < 0.05) and an increase of electrical potential of the masseter muscles in maximal voluntary clench (p < 0.05). They reported more often headache (p < 0.001), tension/contracture of the head, neck and nape (p < 0.05), and pain while opening the mouth wide (p < 0.05). The values of parameters obtained in the instrumental diagnostics did not reveal differences between the groups. Conclusion: Stressful situations increase muscular tension but do not have a direct impact on the temporomandibular joints function. [ABSTRACT FROM AUTHOR]

The analysis of the masticatory cycle plays a fundamental role in studying the functions of the stomatognathic system and evaluating temporomandibular dysfunctions (TMD). The primary objective of this study is to investigate the complex interplay between mandibular kinematics and surface electromyography (sEMG) activity during the masticatory cycle using advanced 4D dentistry technology in 22 healthy subjects (without TMD). By employing electromyography, it becomes feasible to capture the electrical activity of the masticatory muscles throughout the chewing process. The BTS TMJOINT (© 2023 BTS Bioengineering, Garbagnate Milanese, MI, Italy) electromyograph was utilized in this study. Mandibular tracking, on the other hand, allows for recording the movements of the mandible during chewing and condylar slopes. This latest technology (ModJaw®, Tech in motion™, Villeurbanne, France) utilizes motion sensors placed on the jaw to accurately track three-dimensional movements, including jaw opening, closing, and lateral movements. Nowadays, in clinical gnathology, it is common practice to examine masticatory function by analyzing mandibular kinematics and muscle contraction as distinct entities. Similarly, the results obtained from these analyses are typically assessed independently. The investigation of a correlation between electromyography data and mandibular kinematics during the masticatory cycle could provide several advantages for clinicians in diagnosis and lead to a combined analysis of muscle activities and intraarticular dynamics. In conclusion, it can be inferred from the results obtained in the present study that the chewing cycle with a greater vertical movement results in increased masseter muscular activity, and condylar slopes are positively correlated to an increase in temporalis muscle activation. This comprehensive approach can provide valuable insights into the relationship between muscle activity and mandibular movement, enabling clinicians to gain a deeper understanding of the functional dynamics of the stomatognathic system. [ABSTRACT FROM AUTHOR]

Background: Cancer cachexia is prevalent in head and neck cancer patients. The L3 skeletal muscle index (SMI) is often used to assess sarcopenia and cachexia but is infrequently able to be measured in this population. Masseter muscle thickness (MT) may serve as an alternative predictor of cachexia. Methods: SMI and MT were calculated from 20 trauma (CTRL) and 40 cachectic (CA‐CX) and non‐cachectic (CA‐NCX) head and neck cancer patients. Area Under the Curve of the Receiver Operating Characteristics (AUC‐ROC) analysis was performed for SMI and MT. Results: Both SMI and MT were significantly decreased in CA‐CX patients (vs. CA‐NCX mean difference −19.5 cm2/m2 and −2.06 mm, respectively) and significant predictors of CA‐CX (AUC = 0.985 and 0.805, respectively). When analyzed by sex, the same findings were observed for MT in males and trended toward significance in females. Conclusions: Compared with SMI, MT is a good alternative prognostic biomarker to determine CA‐CX status in HNC patients. [ABSTRACT FROM AUTHOR]

Objectives: The Functional Clear Aligner (FCA) is a novel orthodontic appliance designed for the treatment of Class II malocclusion with mandibular retrognathia in adolescents. The aim of this study was to investigate the biomechanical characteristics of the masticatory muscles, jawbone, and temporomandibular joint (TMJ) during mandibular advancement using either FCA or Class II elastics combined with clear aligner (Class II elastics) through finite element analysis. Materials and methods: A 3D finite element model of the 'muscle-jawbone-TMJ-appliance' system was constructed based on CBCT and MRI images of a boy with skeletal Class II malocclusion. Masticatory muscles included masseter, temporal, medial pterygoid, and lateral pterygoid muscles. The TMJ consists of the temporal bone's glenoid fossa, disc, and mandibular condyle. To observe the biomechanical characteristics of the muscles and TMJ during orthodontic appliance wearing and the retention phase, two different protocols were used: Model 1: The mandibular advancement using FCA; Model 2: The mandibular advancement using Class II elastics. Results: The FCA group produced greater and more coordinated masticatory muscle forces compared to the Class II elastics group. Temporal and masseter muscles exhibited the most pronounced variation in muscle strength during mandibular advancement. The FCA group exhibited greater TMJ region stress compared to the Class II elastics group. Interestingly, the stress on the articular discs in both models decreased over time. Tensile stresses were observed in both the condyle and the posterior region of the articular fossa. Conclusion: During skeletal Class II malocclusion treatment, masticatory muscle forces and stress on the TMJ were higher in the FCA group compared to the Class II elastics group. In both models, stress cushioning was provided by the articular disc. [ABSTRACT FROM AUTHOR]

Purpose: To assess the diagnostic potential of the synthetic MRI (SyMRI) for differentiating Warthin's tumors (WT) from pleomorphic adenomas (PA). Materials and methods: Forty-nine individuals with parotid gland tumors (PA, n = 23; WT, n = 26) were recruited. Using two distinct regions of interest (ROI), SyMRI quantitative parameters of lesions were calculated, including mean and standard deviation (T1, T2, PD, T1sd, T2sd, and PDsd). Meanwhile, T1ratio, T2ratio, and PDratio (lesion/masseter muscle) were calculated based on the mean SyMRI quantitative parameters of masseter muscle (T1, T2, PD). Using the independent samples t test, we compared PA and WT parameters, while comparing the areas under the curve (AUC) using the DeLong's test. A multi-parameter SyMRI model was constructed using logistic regression analysis. Results: In PA, the T1, T1sd, T2, PD, T1ratio, T2ratio, and PDratio derived from full and partial lesion ROIs were significantly higher than in WT. According to the receiver operating curve analysis, the AUC of the quantitative parameters derived from full-lesion and partial-lesion ROIs ranged from 0.722 to 0.983 for differentiating PA from WT. T1 values derived from partial-lesion ROI delineation demonstrated the best diagnostic performance among all single parameters, achieving an AUC of 0.983. Using 1322 ms as a cutoff value, the sensitivity, specificity, and accuracy were 88.46%, 100% and 93.88%, respectively. Conclusion: The SyMRI-derived quantitative parameters demonstrated excellent performance for discriminating PA from WT in the parotid gland. [ABSTRACT FROM AUTHOR]

Purpose: Although the apparent diffusion coefficient (ADC) value from diffusion-weighted imaging can provide insights into various pathological processes, no studies have examined the relationship between the pre-concurrent chemoradiotherapy (CCRT) mean ADC (ADCmean) values of the masseter muscles and radiation-induced trismus (RIT) in locally advanced nasopharyngeal carcinoma (LA-NPC) patients. Therefore, the current research aimed to investigate the significance of pre-CCRT masseter muscle ADCmean values for predicting the RIT rates in LA-NPC patients treated with definitive CCRT. Materials and Methods: The pre-CCRT ADCmean values of the masseter muscles and the post-CCRT RIT rates were evaluated. A receiver operating characteristic curve analysis was employed to determine the optimal ADCmean cutoff. The primary objective was to examine the relationship between the pre-CCRT masseter muscle ADCmean values and the post-CCRT RIT rates. Results: Seventy-seven patients were included. The optimal ADCmean cutoff value was 1381.30 × 10−6 mm2/s, which divided the patients into two groups: an ADCmean < 1381.30 × 10−6 mm2/s (n = 49) versus an ADCmean > 1381.30 × 10−6 mm2/s (n = 28). A masseter muscle ADCmean > 1381.30 × 10−6 mm2/s was found to be associated with significantly higher RIT rates than an ADCmean < 1381.30 × 10−6 mm2/s (71.42% vs. 6.12%; p < 0.001). The multivariate analysis results confirmed a pre-CCRT masseter muscle ADCmean > 1381.30 × 10−6 mm2/s as an independent predictor of RIT. Conclusions: Our study presents the first evidence establishing a connection between elevated masseter muscle ADCmean values and higher RIT rates in LA-NPC patients following CCRT. If confirmed with further research, these findings may help to categorize the risk of RIT in these patients. [ABSTRACT FROM AUTHOR]

Objective: The aim of this study was to quantitatively evaluate morphological and volumetric changes in the masseter muscle using 3-dimensional analysis of facial asymmetry patients and to identify factors influencing these changes before and after orthognathic surgery. Methods: [Reviewer1 (2)]A single-center retrospective cohort study was conducted on twenty-two patients with deviation of the chin > 4 mm. Masseter muscle volume and morphology were measured at different periods during long-term follow-up (mean 15 ± 3.2 months). Factors related to changes in masseter muscle cross-sectional area and volume analyzed were also analyzed. Results: [Reviewer1 (2) and (9)]The volume and cross-sectional area of the masseter muscle on the non-deviated side reduced by 13.5% (P < 0.05) and 16.4% (P < 0.05), respectively, after orthognathic surgery. The length of the masseter muscle increased by 13.9% on the deviated side (P <.05) but decreased by 11.7% on the non-deviated side (P < 0.05). The width decreased on the deviated side from T1 to T2 (13.51 ± 2.09 mm vs. 12.04 ± 1.39 mm), but the non-deviated side showed an opposite tendency (10.81 ± 1.31 mm vs. 12.69 ± 2.37 mm). The difference in masseter muscle length and width between the two sides significantly reduced after surgery (P < 0.05). There was a noticeable decrease in the asymmetry in the muscle in proportion to the degree of the occlusal plane angle. Conclusion: Masseter muscle asymmetry exists in patients with facial asymmetry, but it could be improved with maxilla-mandible correction. Atrophy of the masseter muscle after orthognathic surgery was greater in patients with a large inclined occlusal plane angle due to improved dental compensation. 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. [ABSTRACT FROM AUTHOR]

Objective: The purpose of the present study was to explore the effect of plateau duration in eliciting masseter vestibular evoked myogenic potentials (mVEMPs) in healthy individuals with hearing sensitivity ≤ 15dBHL. Method: A within-subjects design was utilized in the study. Therefore, ipsilateral tone burst evoked mVEMPs were obtained from 30 healthy individuals using the zygomatic montage at 500 Hz tone bursts. Self-monitoring biofeedback was given during the procedure to confirm the tension of the masseter muscle. mVEMPs were recorded across three different plateau duration from 0 to 2 ms with rise/fall time of 2 ms at 95dBnHL. Hence the median and interquartile range were calculated for descriptive analysis of the data followed by non-parametric inferential statistics. Results: Tone burst evoked mVEMPs were found to be 100% present across all three plateau durations for both ears at 95 dBnHL. P11 and N21 latencies increased with longer plateau durations in both ears. There were no significant differences in P11-N21 peak-to-peak amplitude or interaural amplitude ratio (IAAR) observed across different plateau durations. IAAR was lowest for a 2 ms plateau duration in the 2–2-2 cycle. No significant variations were found across the three plateau durations. Conclusion: Significant differences in P11 and N21 latencies were observed across the three stimulus cycles, while no significant differences were found for P11N21 amplitude and IAAR. Yet, there was found to have the highest amplitude and lowest IAAR for 2–2-2 cycle than 2–0-2 and 2–1-2, suggesting it to be the optimal stimulus among the three of them. [ABSTRACT FROM AUTHOR]

Masticatory muscle forces influence craniofacial morphology development. The antegonial notch (Notch) is a bony concavity on the inferior border of the mandible. Considering the Notch is located anteriorly to the insertion of the masseter muscle and varies among individuals, we hypothesised that these muscles influence the formation of the Notch. Therefore, this study aimed to investigate the correlation between mandible morphology and Notch formation. Sixty Japanese patients who visited the Department of Orthodontics at our university hospital were retrospectively evaluated. Morphological and morphometric analyses of the Notch and related craniofacial parameters were conducted using lateral cephalograms taken at the patients' initial visits. Standard values for the Notch area and depth were determined, and the morphology of the Notch and mandible was analysed using Spearman's rank correlation coefficient (p < 0.05). The mean Notch area and depth was 78.71 ± 36.54 mm2 and 3.11 ± 1.09 mm, respectively. The Notch area was significantly correlated with ramus inclination (p = 0.044, r = 0.261) and with the Y-axis (p = 0.039, r = 0.267). This study indicated that both the masticatory muscles and mandibular growth could contribute to the Notch formation. [ABSTRACT FROM AUTHOR]

Chorea-acanthocytosis (ChAc) is an extremely rare neurodegenerative disorder characterized by movement disorders and acanthocytosis. Orofacial dyskinesia is a distinct symptom of this disorder that can lead to lip injuries and feeding difficulties. This paper reports the first case of a patient with ChAc presenting with a lip defect, who was managed with surgical and adjuvant onabotulinumtoxinA (BTX-A) therapy. A 43-year-old woman diagnosed with ChAc was referred to our clinic because of a 5× 5 mm lip defect resulting from orofacial dyskinesia. Wedge resection of the scar tissue was carried out, followed by reconstruction by suturing. Postoperatively, BTX-A injections were administered to ameliorate dyskinesia. Thirty units of BTX-A were injected into each masseter muscle, and 40 units were injected into the orbicularis oris muscle. At 1, 2, and 4 weeks after the injections, assessments were performed using the Abnormal Involuntary Movement Scale, and the patient's impression of change was assessed using the Global Rating of Change Scale. Subsequent adjuvant BTX-A treatment yielded subjective and objective improvements in orofacial dyskinesia. In conclusion, lip reconstruction and adjuvant BTX-A injections were effective in treating lip defects associated with orofacial dyskinesia in patients with ChAc, which highlights the need for a multimodal treatment approach. [ABSTRACT FROM AUTHOR]

Introduction: The success of any prosthetic rehabilitation depends on acceptable occlusion and muscle coordination. Occlusal therapy should be an integral part of restorative and prosthetic treatment. A thorough diagnosis of bite force and muscle activity is required to ensure the patient's masticatory function and comfort. The current system of digitisation lacks devices for the simultaneous evaluation of muscle activity and occlusal bite force, representing a significant limitation in understanding and managing restorative and rehabilitation therapy. Aim: To assess the efficacy of an ingeniously designed integrated device that records occlusal bite force and muscle activity. Materials and Methods: An observational study was conducted among 112 healthy volunteers in the Department of Prosthodontics at Sri Ramachandra Dental College and Hospital, Chennai, Tamil Nadu, India, for a period of one month and 45 days, from February 5, 2024 to March 20, 2024. The study aimed to validate the efficacy of a device designed to record bite force and muscle action potential simultaneously. The device consists of two key components: a square Forcesensitive Resistor (FSR) that records changes in resistance in response to applied force and a MyoWare 2.0 muscle sensor with Arduino (Advancer Technologies) for measuring the electrical activity of muscles. Study participants, aged between 21 and 35 years, were seated in an upright position. Muscle activity was recorded with surface electrodes placed on the masseter region, following Surface Electromyography for the Non Invasive Assessment of Muscles (SENIAM) guidelines, while a ground electrode was placed on the neck. Maximum Bite Force (MBF) was measured by placing intraoral pressure sensors, with recordings taken in maximum intercuspation three times, spaced one minute apart for each recording. Both muscle activity and bite force were recorded simultaneously. The Pearson's correlation coefficient was used to evaluate the correlation between bite forces and muscle action potential with standard average values. Results: The results revealed a strong positive correlation between the masseter muscle activity action potential and the bite force values of the right molar (r=0.964, p<0.001), left molar (r=0.980, p<0.001) and incisor (r=0.550, p=0.002). Conclusion: The device synergistically records muscle activation patterns and bite force distribution, displaying the values in an integrated digital interface. The results of the study reveal that this device can serve as a diagnostic tool in prosthodontic treatment planning. [ABSTRACT FROM AUTHOR]

Background: Square faces, which are influenced by genetic factors and structural features, are considered undesirable among the Asian population. Surgical interventions, such as mandibular angle reduction, aim to alter these characteristics, though complications may arise. We aimed to investigate the morphology of the mandibular angle and masseter muscle thickness using computed tomography (CT) and to analyze hard and soft tissue correlations to enhance surgical outcomes for patients with square faces. Methods: This retrospective clinical study included 100 Taiwanese patients aged 18–50 years. CT was used to analyze key clinical parameters, including bilateral mandibular width, mandibular divergence angle, ramus height, distance from the mandibular angle to the inferior alveolar nerve (IAN), and the thickness of the masseter muscle. Results: Significant correlations were noted between the patients' physical height and weight, mandibular width, ramus height, masseter thickness, and distance from the angle to the IAN. Males exhibited a significantly longer and thicker ramus height (66.48 ± 4.28 mm), greater masseter thickness (15.46 ± 2.35 mm), and greater safety range for mandibular angle reduction surgery (18.35 ± 3.19 mm) (p < 0.00008). Significant correlations were observed among all parameters, except between mandibular width and gonial angle and the distance from the angle to the IAN and between mandibular divergence and masseter muscle thickness (p > 0.1). Conclusions: Our study highlighted the complex interplay among factors that contribute to square facial morphology. Careful preoperative assessments and customized surgical planning are essential for addressing this multifaceted clinical challenge. [ABSTRACT FROM AUTHOR]

Buccal fat pads are biconvex adipose tissue bags that are uniquely found on both sides of the human face along the anterior border of the masseter muscles. Buccal fat pads are important determinants of facial appearance, facilitating gliding movements of facial masticatory and mimetic muscles. Buccal fad pad flaps are used for the repair of oral defects and as a rich and easily accessible source of mesenchymal stem cells. Here, we introduce the buccal fat pad anatomy and morphology and report its functions and applications for oral reconstructive surgery and for harvesting mesenchymal stem cells for clinical use. Future frontiers of buccal fat pad research are discussed. It is concluded that many biological and molecular aspects still need to be elucidated for the optimal application of buccal fat pad tissue in regenerative medicine. [ABSTRACT FROM AUTHOR]

Background: Sleep apnea and nocturnal bruxism belong to sleep disorders that can affect the quality of life. The aim of this study was to investigate the effects on patients with moderate sleep apnea and nocturnal bruxism of Botox injection as monotherapy or associated with wearing thermoformed occlusal splints and to determine the patients' satisfaction degree after the applied treatments. Methods: The selected patients for study were divided into two groups: in the first group, the patients (n = 18) treatment consisted of injecting Botox (Allergan) into the masseter muscle as monotherapy; in the second group, the patients (n = 18) benefited from associated therapy, Botox injections in masseter muscle, and the wear of thermoformed occlusal splints. At baseline, at three weeks, at three months, and six months after the effectuation of therapies, the monitoring sessions were realized. Results: The associated therapy presented better results in decreasing the studied symptoms than the monotherapy. Both therapies improved patient satisfaction. Conclusions: The applied therapies for treating the specific symptomatology in moderate sleep apnea and sleep bruxism were efficacious. Patient satisfaction was very good in both groups after the applied treatments, but the associated therapy presented better results than monotherapy. [ABSTRACT FROM AUTHOR]

Objective: This study aims to evaluate the effects on bite force and muscle thickness of the botulinum toxin (BoNT) injection for patients with sleep bruxism (SB) by comparing injections into the masseter muscle only and both the masseter and the anterior belly of the digastric muscle (ABDM) in a clinical trial. Methods: Twelve SB patients received BoNT‐A injections using US‐guided techniques into the masseter muscle only (Group A), while the remaining 12 SB patients received injections into both the masseter and ABDM (Group B). Bite force and muscle thickness were measured before injection, as well as 1 and 2 months after injection. Results: The bite force and masseter muscle thickness decreased in both Group A and Group B before injection, and at 1 and 2 months after injection. However, there was no significant difference (p >.05, repeated measures analysis of variance) between the two groups, and there was also no significant difference in ABDM thickness (p >.05, repeated measures analysis of variance). Conclusion: This study is the first to assess the short‐term effects of BoNT injected into ABDM for SB control. Results show no influence on SB reduction, suggesting the need for further research on BoNT's effectiveness in controlling intense ABDM contractions during sleep and assessing suprahyoid muscle potential impact on rhythmic masticatory muscle activity occurrence. [ABSTRACT FROM AUTHOR]

Background: Oral food processing is an important part of daily food intake. A major part of this process is mastication, which prepares a bolus of food for swallowing by mechanically crushing and grinding ingested food between the teeth using rhythmic movements. Masticatory dysfunction is common in the elderly and in some neurological disorders and can have serious negative health consequences. Objective: This study investigated the effect of restricted mastication, achieved by experimentally reducing the duration of mastication, on masticatory patterns and subsequent swallowing function. Methods: Thirty healthy men (25 ± 3 years old) were instructed to chew gum jelly with a free mastication duration (G100), a half and a quarter duration of G100. Masseter and digastric electromyographic (EMG) activity was recorded to assess mastication and swallowing activity, respectively. In addition, the acceleration of the thyroid cartilage ridge was measured with an accelerometer. The root mean square (RMS) of muscle EMG activity in the masseter and digastric muscles, the number of masseter EMG bursts, time to peak and total duration of each masseter EMG burst, swallowing duration and laryngeal elevation latency were analysed. Results: Restricting masticatory duration reduced the number of mastication cycles (p <.001), prolonged the time to peak (p <.001) and total duration of masseter EMG bursts (p <.001) and resulted in an overall increased RMS score of masseter muscle activity (p =.017). Furthermore, restricted masticatory duration led to a decrease in both swallowing duration (p =.001) and laryngeal elevation latency (p =.012), with a significant increase in the RMS score of digastric muscle activity (p <.001). Conclusions: Under the experimental conditions of restricted mastication, several adaptation features were observed, including changes in masticatory cycle characteristics and swallowing duration. Thus, although the overall masticatory efficiency was reduced, these adaptations allowed healthy individuals to still swallow safely. [ABSTRACT FROM AUTHOR]

Background: Micrognathia can be diagnosed in utero with ultrasound by measuring the jaw index and/or inferior facial angle, though it can be challenging due to fetal positioning. The jaw index can be measured with magnetic resonance imaging (MRI) using the masseter muscle, but indistinct margins can lead to inaccuracy; the easily visualized posterior teeth buds may be a better landmark. Objective: We aimed to evaluate inter-reader variability, agreement with ultrasound, and association with postnatal outcomes using MRI to measure the inferior facial angle, jaw index by masseter muscle, and jaw index by posterior teeth buds. Materials and methods: A single-institution retrospective review was performed of singleton pregnancies with prenatally diagnosed micrognathia by ultrasound or MRI from September 2013-June 2022. Ultrasound measurements were obtained by a maternal–fetal medicine specialist and MRI measurements by two radiologists to evaluate inter-reader variability. Intraclass correlation coefficients (ICC) and Bland–Altman analysis were used to assess agreement between imaging methods and logistic regressions and ROC curves to assess associations with postnatal outcomes. Results: Forty-three fetuses (median gestational age 26 weeks (IQR 22–31); 47% male (20/43)) were included. Ultrasound measurements could not be obtained for jaw index in 15/43 (35%) fetuses and inferior facial angle in 11/43 (26%); MRI measurements were obtained by at least one reader in all cases. Jaw index by teeth buds demonstrated lowest inter-reader variability (ICC = 0.82, P < 0.001) and highest agreement with ultrasound (bias -0.23, 95% CI -2.8–2.2). All MRI measurements, but not ultrasound, predicted need for mandibular distraction (inferior facial angle P = 0.02, jaw index by masseter muscle P = 0.04, jaw index by teeth buds P = 0.01). Conclusion: Fetal MRI measurements, particularly jaw index measured by posterior teeth buds, demonstrate low inter-reader variability and high agreement with ultrasound, and may predict need for mandibular distraction postnatally. [ABSTRACT FROM AUTHOR]

During the dissection of the cervicofacial area in a donated male cadaver, an asymmetrical division of the facial artery (FA) and a premasseteric artery (PA) were identified. Specifically, on the left side, the FA stem is divided into four branches (quadrifurcation) 4.26 mm below the lower border of the mandible. In contrast, it is divided into two branches (bifurcation) on the right side. Whether symmetrical or asymmetrical, these variants can have significant implications for rhinoplastic, maxillofacial, or reconstructive surgery. This finding underscores the crucial role of surgeons in exercising caution and paying close attention during these procedures to avoid potential damage. [ABSTRACT FROM AUTHOR]

To investigate how absorbed doses to mastication structures in modern radiotherapy (RT) technique for head and neck cancer (HNC) compared with earlier RT techniques and with published trismus tolerance doses. To compare the incidence of radiation-induced trismus by earlier and newer RT techniques. This study investigated two HNC patient cohorts treated with RT in 2007–2012 (three-dimensional conformal radiotherapy [3DCRT] and/or intensity-modulated radiotherapy [IMRT]; n =121 [ Cohort 1 ]) and 2017–2020 (volumetric-modulated arc therapy [VMAT]; n =124 [ Cohort 2 ]). All patients underwent RT without mastication structure–sparing intent, had normal mouth-opening ability before RT, and were prospectively assessed. Trismus was defined as the maximal interincisal opening ≤35 mm at any follow-up (3-, 6-, and 12-months post-RT). The temporomandibular joints (TMJs), masseter, and medial/lateral pterygoid muscles were delineated on the planning CT:s. Mean doses were compared between cohorts, and evaluated with respect to published trismus tolerance doses. P values ≤ 0.05 indicated statistical significance. Within 12 months post RT, 74/121 (61%) of patients in Cohort 1 had experienced trismus compared to 11/124 (9%) in Cohort 2. Averaged mean doses (±S.D.) for the masseter muscles were 35.2±8.3 Gy in Cohort 1 and 20.2±8.7 Gy in Cohort 2 (P <0.001). Corresponding numbers were 19.1±16.2 and 4.3±4.3 Gy for the TMJs, 53.7±10.1 and 40.2±16.8 Gy for the medial pterygoid muscles, and 29.2±18.7 and 9.2±8.4 Gy for the lateral pterygoid muscles (all P <0.001). Masseter muscle doses were below tolerance doses in 23% of patients in Cohort 1 compared with 90% in Cohort 2. The corresponding numbers were 52% and 96% for the TMJs, 8% and 36% for the medial pterygoid muscles and 72% and 100% for the lateral pterygoid muscles. Mastication structure mean doses by more recent RT techniques were generally below proposed tolerance doses, with dose reductions of 10–20 Gy compared with earlier techniques. Modern RT without mastication-structure-sparing intent resulted in below 10% of HNC patients experiencing trismus compared with 60% treated with earlier techniques. • Modern radiotherapy can substantially spare organs-at-risk in head and neck cancer. • Mastication-structure mean radiation doses were reduced by 10–20 Gy. • These dose reductions were accompanied by a trismus reduction from 60% to 10%. [ABSTRACT FROM AUTHOR]

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). 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. 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). 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). Level III. [ABSTRACT FROM AUTHOR]

Copyright of Turkish Journal of Trauma & Emergency Surgery / Ulusal Travma ve Acil Cerrahi Dergisi is the property of KARE Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: This in vitro study compared the stability of different fixation method combinations for the zygomatic complex after simulated L-shaped osteotomy reduction malarplasty, a common facial contouring surgery in East Asia with high postoperative complications due to poor fixation methods. Materials and Methods: The study used 108 zygoma replicas with various fixation methods combinations in the zygomatic body (L-shaped plate with short wing on zygoma and on the maxilla, two bicortical screws, one bicortical screw with L-shaped plate, square plate, and rectangular plate) and zygomatic arch (Mortise–Tenon structure, 3-hole plate, and Mortise–Tenon structure plus short screw). The failure force under incremental load was applied through the Instron tensile machine to a well-stabilized model using a rubber band simulating the masseter muscle and recorded the increasing force digitally. ANOVA test was used for comparison between recorded values (P < 0.05). Results: The results showed that the most stable combination was a six-hole rectangular plate and a Mortise–Tenon structure plus one short screw (358.55 ± 51.64 N/mm2). The results also indicated that the placement vector of the fixation methods around the L-shaped osteotomy and the use of the two-bridge fixation method were important factors in enhancing the stability of the zygomatic complex. Conclusion: The study suggested that surgeons should choose appropriate fixation methods based on these factors to reduce postoperative complications and improve surgical outcomes. No Level Assigned: This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. 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. [ABSTRACT FROM AUTHOR]

Background: Low-level laser therapy (LLLT) is one of the recent treatment modalities for myofascial pain dysfunction syndrome with trigger points. The objective of the present study was to examine the impact of varying LLLT sessions on the treatment of masseter muscle trigger points. Methods: 90 patients diagnosed with orofacial pain and trigger points in the masseter muscle for at least 6 months were selected and divided into 3 groups (n = 30) based on the number of LLLT sessions provided to patients. Patients in Group I received one session/per week, group II received two sessions/per week, and Group III received three sessions/per week. The sessions continued for 4 weeks, evaluations of pain levels, maximum mouth opening (MMO), and quality of life were conducted before and after the procedure at 1, 2, 3, 4, and 8 weeks. Results: The pain scores exhibited a highly statistically significant difference among the three groups (p < 0.001) over the 8-week study period. MMO was statistically significantly different between groups at week 4 and week 8. The Oral Health Impact Profile-14 (OHIP-14) score was statistically significant difference between groups at week 8. The time showed a highly significant effect on the study outcomes within each group. Conclusion: Increased the number of LLLT sessions reduced the pain improved the MMO, and subsequently improved the quality of life. ClinicalTrials.gov ID NCT06327204 - retrospectively registered. [ABSTRACT FROM AUTHOR]

This article in Frontiers in Pain Research explores the role of intraganglionic reactive oxygen species (ROS) in inflammatory pain and hyperalgesia in rats. The study suggests that ROS accumulation in the trigeminal ganglia contributes to hyperalgesia through the TRPA1 receptor. The researchers also discuss potential therapeutic approaches to reduce ROS accumulation or downregulate TRPA1 expression. The document further delves into the intraganglionic mechanisms involved in pain modulation, such as neuropeptide release, ion channel regulation, immune cell interaction, glial cell activation, synaptic plasticity, and modulation of sensory neuron excitability. The understanding of these mechanisms is crucial for developing targeted treatments for chronic pain conditions. The document acknowledges the financial support received for the research and declares no conflicts of interest. [Extracted from the article]

Objective: Rare disease Background: Muscle hernias are an uncommon condition typically found in the extremities; masseter muscle hernia is even rarer. However, it is important for clinicians and radiologists to be aware of this possibility. Intramuscular venous malformation (IMVM) is also uncommon and mostly found in the head, neck, and extremities. The simultaneous presence of both conditions is extraordinary uncommon, and, to our knowledge, this has not been reported before in the masseter muscle. Due to their rarity, vague presentation, and inaccurate clinical diagnosis, radiological evaluation is needed to avoid inappropriate surgical planning. Case Report: A 12-year-old boy had a long-standing focal left cheek swelling exacerbated by teeth clenching. Lateral X-ray revealed a round calcification over the left mandibular region. Ultrasonography indicated a bulky left masseter muscle with focal heterogeneous structure and 2 rounded calcified foci. During teeth clenching, ultrasonography detected focal muscular herniation through the left masseter muscle facia that reduced with rest. The patient was diagnosed with left masseteric muscle hernia coexistent with IMVM. Surgical excision of the IMVM was performed, and the hernia defect was repaired. Histopathology confirmed the diagnosis, and the patient was discharged without postoperative complications on short-term follow-up. Conclusions: Despite their rarity, masseter hernias and IMVMs should be considered in the differential diagnosis of any masseter lesion, especially in children. We reported a very rare coexistence of both pathologies. Comprehensive diagnosis can be achieved through a combination of clinical examination, X-ray, and ultrasound assessments. [ABSTRACT FROM AUTHOR]

AbstractObjectiveDesignStudy sampleResultsConclusionThis study aimed to explore the functional integrity of vestibulo-masseteric and sacculo-collic reflex pathways in individuals with Auditory Neuropathy (AN). The study also aimed at finding the correlation between mVEMP and cVEMP response parameters for AN and healthy individuals.Standard group comparison research designIndividuals with AN (n = 20); age-gender matched healthy individuals (n = 20) were recruited. Each participant underwent routine audiological evaluation; mVEMP and cVEMP testing. mVEMP and cVEMP were recorded using 500 Hz tone burst stimulus for all the participants.Most of the AN individuals had no mVEMP (ipsilateral & contralateral − 60%; bilateral − 50%) and cVEMP (60%) responses. There was no significant association (p > 0.05) between the duration of AN with mVEMP and cVEMP findings. However, a significant correlation (p < 0.05) was found for EMG rectified amplitude of mVEMP and cVEMP in AN.The results of this study suggested an impaired function of the vestibulomassteric and sacculocollic reflex pathways in individuals with AN. Vestibular evaluation should be included as a part of the regular test battery for individuals with AN. [ABSTRACT FROM AUTHOR]

Background: Temporomandibular Disorders (TMD) is the dysfunction of group of muscles and bones in the joint area, the main symptoms of TMD are the pain of the chewing muscles and (or) the temporomandibular joints, mandibular movement disorders and joint noise. This study was designed to explore the therapeutic effects following Individual Musculoskeletally Stable (IMS) position stabilization splint therapy for TMD patients using Fricton index, cone beam computed tomography (CBCT) and surface-Electromyogram (sEMG). Methods: In this study, we enrolled 31 TMD patients (ranging from 18 to 26 years old, including 7 males and 24 females), first Fricton index was used to evaluate the clinical curative effect of TMD with the treatment of IMS stabilization splint; then CBCT was used to observe the TMJ condylar position changes of TMD before and after the treatment of IMS stabilization splint; finally sEMG was used to observe the changes of electromyography of anterior temporalis (AT) and masseter muscles (MM) of TMD before and after the treatment of IMS stabilization splint. Results: The course of treatment was 6–8 months, with an average of 7.6 months. After the IMS stabilization splint treatment, TMD symptoms relieved, especially in pain, mandibular movement disorder, but still slightly inferior in the treatment of joint noise. And there was a statistically significant difference in the anterior and inner joint space, the condyle had the tendency of moving forward and outward. AT presented reduction significantly of EMG value at rest position after treatment. Conclusions: IMS stabilization splint is a therapeutic reversible treatment for TMD, especially for pain and mandibular movement disorder; it produces effects of forward and outward condylar movement and elimination of the masticatory muscles antagonism. [ABSTRACT FROM AUTHOR]

Background: The anatomic characteristics of the masticatory muscles differ across craniofacial skeletal patterns. Objective: To identify differences in the anatomic characteristics of masticatory muscles across different sagittal and vertical craniofacial skeletal patterns. Eligibility criteria: Studies measuring the thickness, width, cross-sectional area (CSA), volume and orientation of masticatory muscles in healthy patients of different sagittal (Class I, Class II, and Class III) and/or vertical (normodivergent, hypodivergent, and hyperdivergent) patterns. Information sources: Unrestricted literature searches in 8 electronic databases/registers until December 2023. Risk of bias and synthesis of results: Study selection, data extraction, and risk of bias assessment with a customised tool were performed independently in duplicate. Random-effects meta-analysis and assessment of the certainty of clinical recommendations with the GRADE approach were conducted. Results: 34 studies (37 publications) were selected with a total of 2047 participants and data from 16 studies were pulled in the meta-analysis. Masseter muscle thickness in relaxation was significantly greater by 1.14 mm (95% CI 0.74–1.53 mm) in hypodivergent compared to normodivergent patients while it was significantly decreased in hyperdivergent patients by − 1.14 mm (95% CI − 1.56 to − 0.73 mm) and − 2.28 mm (95% CI − 2.71 to − 1.85 mm) compared to normodivergent and hypodivergent patients respectively. Similar significant differences were seen between these groups in masseter muscle thickness during contraction as well as masseter muscle CSA and volume. Meta-analyses could not be performed for sagittal categorizations due to insufficient number of studies. Conclusions: Considerable differences in masseter muscle thickness, CSA and volume were found across vertical skeletal configurations being significantly reduced in hyperdivergent patients; however, results should be interpreted with caution due to the high risk of bias of the included studies. These variations in the anatomic characteristics of masticatory muscles among different craniofacial patterns could be part of the orthodontic diagnosis and treatment planning process. Registration: PROSPERO CRD42022371187. [ABSTRACT FROM AUTHOR]

(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. [ABSTRACT FROM AUTHOR]

Neck emphysema after tonsillectomy surgery is very rare. We present a case documenting the conservative management of a post-tonsillectomy neck swelling, accompanied by crepitus. Computed tomography revealed a large air density at the region of the right masticator space and the masseter muscle, proximal to other deep neck spaces and muscles. Further investigations of her associated symptoms resulted in an additional diagnosis of systemic lupus erythematosus. We have also explored the signs and symptoms associated with such cases, along with a discussion of the literature published on surgical emphysema post-tonsillectomy. [ABSTRACT FROM AUTHOR]

Frailty is a vulnerable state that marks the transition to long-term care for older people. Early detection and prevention of sarcopenia, the main symptom of frailty, are important to ensure an excellent quality of life for older people. Recently, the relationship between frailty, sarcopenia, and oral function has been attracting attention. This study aimed to clarify the changes in metabolites and metabolic pathways due to aging in the masseter muscle of senescence-accelerated mouse-prone 8 (SAMP8) mice. A capillary electrophoresis-mass spectrometry metabolome analysis was performed on the masseter muscle of 12-week-old, 40-week-old, and 55-week-old mice. The expression of enzymes involved in metabolome pathways considered to be related to aging was confirmed using reverse transcription polymerase chain reaction. Clear metabolic fluctuations were observed between 12, 40-week-old, and 55-week-old SAMP8 mice. The extracted metabolic pathways were the glycolysis, polyamine metabolome, and purine metabolome pathways. Nine fluctuated metabolites were common among the groups. Spermidine and Val were increased, which was regarded as a characteristic change in the masseter muscle due to aging. In conclusion, the age-related metabolic pathways in SAMP8 mice were the glycolysis, polyamine metabolome, and purine metabolome pathways. The increased spermidine and Val levels in the masseter muscle compared with the lower limbs are characteristic changes. [ABSTRACT FROM AUTHOR]

Background: Botulinum toxin type A (BoNT-A) injection is widely used for masseter hypertrophy. Traditional BoNT-A injection methods often incorporate landmark-guided blind injections, which approximate the shape of the masseter muscle inject across various points. Conversely, ultrasound (US)-guided injection techniques offer real-time visualization and dynamic monitoring, enhancing accuracy. Patients and Methods: 50 patients who underwent BoNT-A injections were included in this trial. One on the face side received a landmark-guided injection, and the other side was treated with a US-guided injection. Initial and post-procedure measurements of muscle thickness at the upper, middle, and lower regions were collected using ultrasound. Results: Both methods led to a significant reduction in muscle thickness one month after injection. In the upper area, the absolute difference in muscle thickness between the two methods was observed as a mean ± standard deviation (SD) value of 0.37 ± 0.0314 (p < 0.0001), indicating a superior effect with US-guided injection. Similarly, in the middle area, the mean ± SD difference was 0.41 ± 0.0608 (p < 0.0001) and in the lower area, the mean ± SD difference was 0.24 ± 0.0134 (p = 0.0004). Conclusions: This study demonstrated that the US-guided single-point injection technique is a more effective and accurate method for BoNT-A injection compared to the conventional method. [ABSTRACT FROM AUTHOR]

Objective: This study aimed to evaluate the distribution and trends of masseter muscle tension in patients with temporomandibular joint (TMJ) pain, examining gender-specific differences and the impact of various TMJ disorders. Methods: From January 2020 to June 2024, a total of 734 patients presenting with facial pain radiating to the head and neck, localized around and extending from the TMJ, were referred for ultrasonographic examination. After applying exclusion criteria, 535 patients (72.9%) were included in the study. The patient cohort consisted of 343 females (64.1%) and 192 males (35.9%), with muscle tension measured using the Aixplorer ultrasound system equipped with a shear wave device. Data were collected and analyzed across different age groups and TMJ conditions, including "no changes", "exudate", "arthrosis", and "disc displacement". Results: The study found that males exhibited higher muscle tension across all conditions, particularly in the "no changes" (40.4 kPa vs. 32.1 kPa, 25.9% higher) and "exudate" (38.5 kPa vs. 29.7 kPa, 29.6% higher) categories, indicating increased muscle strain and inflammation during middle age. In females, a trend of decreasing muscle tension with age was observed, with a significant reduction from 36.2 kPa in the 20–30 age group to 24.3 kPa in the 60–70 age group (32.9% reduction), suggesting a reduction in muscle mass or strength due to aging. Both genders showed high muscle tension in the presence of exudate, with females peaking in the 40–50 age group at 37.1 kPa and males peaking earlier in the 20–30 age group at 41.2 kPa (10.9% higher in males), highlighting potential gender differences in inflammatory response. In the arthrosis group, males displayed a consistent increase in muscle tension with age, peaking at 37.5 kPa in the 50–60 age group (50.7% increase from the 20–30 age group), while females showed high tension, particularly in the 40–50 age group at 31.0 kPa (82.4% higher compared to the 20–30 age group), indicating the need for targeted joint health interventions in middle-aged women. Conclusions: This study reveals significant gender-specific differences in masseter muscle tension among patients with TMJ pain. Males were found to be more affected by muscle strain and inflammation during middle age, whereas females showed a significant decrease in muscle tension with age. The presence of exudate significantly impacted muscle tension across all age groups for both genders. These findings underscore the importance of tailored clinical interventions and preventive strategies to manage TMJ disorders effectively. [ABSTRACT FROM AUTHOR]

Purpose: The primary objective of this study was to assess how age influences masseter vestibular evoked myogenic potential (mVEMP) parameters by utilizing 500-Hz tone burst stimuli delivered through air conduction. Method: The study involved 110 participants ranging from 15 to 60 years of age, grouped into five categories, all of whom had no previous issues related to their vestibular system. The participants were exposed to 500-Hz tone burst stimuli at 125 dB SPL through ER-3A inserts. These stimuli were presented to one ear at a time, with alternating polarity. A Tukey's honestly significant difference test was conducted to compare rectified and unrectified amplitude, along with latencies (P11 and N21) and the asymmetric ratio across all age groups. Additionally, a multivariate analysis of variance was performed to assess the impact of sex on the study variables. Results: All 110 participants (220 ears) in the study provided mVEMP responses, encompassing 100% of the subjects. The results revealed a significant reduction in both amplitude and latency extension for the P11 and N21 peaks. Interestingly, P11 latency was also prolonged in the youngest participants (Group 1), suggesting ongoing maturation of the system even beyond the age of 16 years. Moreover, a significant sex difference was observed in the P11 latencies. However, there were no substantial sex differences (p >.05)inN1peaklatency,peak-to- peak amplitude, rectified amplitude, and asymmetric ratio. Conclusions: Changes in structure occur due to degeneration, and the quantity of vestibular sensory hair cells gradually diminishes with age. The rate of decline is faster in semicircular canals compared to end organs, as observed by Merchant et al. (2000). Following a linear degeneration starting at the age of 40 years, a continuous reduction in sensory cells and primary neurons takes place until approximately 40% of vestibular sensory cells are lost by the age of 75 years and insufficient maturation can lead to prolonged peaks and reduced amplitudes compared with those that are considered normal. Therefore, it is crucial to consider the age of the participants when making diagnoses and incorporate relevant correction factors based on age-related reference data. [ABSTRACT FROM AUTHOR]

Background: A quantitative approach to predict expected muscle activity and mandibular movement from non‐invasive hard tissue assessments remains unexplored. Objectives: This study investigated the predictive potential of normalised muscle activity during various jaw movements combined with temporomandibular joint (TMJ) vibration analyses to predict expected maximum lateral deviation during mouth opening. Method: Sixty‐six participants underwent electrognathography (EGN), surface electromyography (EMG) and joint vibration analyses (JVA). They performed maximum mouth opening, lateral excursion and anterior protrusion as jaw movement activities in a single session. Multiple predictive models were trained from synthetic observations generated from the 66 human observations. Muscle function intensity and activity duration were normalised and a decision support system with branching logic was developed to predict lateral deviation. Performance of the models in predicting temporalis, masseter and digastric muscle activity from hard tissue data was evaluated through root mean squared error (RMSE) and mean absolute error. Results: Temporalis muscle intensity ranged from 0.135 ± 0.056, masseter from 0.111 ± 0.053 and digastric from 0.120 ± 0.051. Muscle activity duration varied with temporalis at 112.23 ± 126.81 ms, masseter at 101.02 ± 121.34 ms and digastric at 168.13 ± 222.82 ms. XGBoost predicted muscle intensity and activity duration and scored an RMSE of 0.03–0.05. Jaw deviations were successfully predicted with a MAE of 0.9 mm. Conclusion: Applying deep learning to EGN, EMG and JVA data can establish a quantifiable relationship between muscles and hard tissue movement within the TMJ complex and can predict jaw deviations. [ABSTRACT FROM AUTHOR]

Background: It remains unclear how the salivary flow and the fat content of food affect bolus formation during mastication. Objectives: We aimed to clarify: (1) how hyposalivation affects jaw‐closing and hyoid‐elevating muscle activities in bolus formation, and (2) if the effect of hyposalivation on muscle activity depends on the fat content of food. Methods: Eighteen healthy male volunteers were instructed to freely ingest four test foods: Plain, Fat without seasoning, Fat with seasoning, and Soft rice crackers. Masseter and suprahyoid electromyographic activities were recorded before and 30 min after the administration of atropine sulfate, a muscarinic receptor antagonist that induces hyposalivation. Results: Hyposalivation extended the masticatory duration significantly in all the test foods except Fat with seasoning. Masticatory cycle time was significantly longer with vs without hyposalivation for the Soft (p =.011). Suprahyoid activity/cycle was significantly greater with vs without hyposalivation (p =.013). Masticatory cycle time was significantly longer at the late stage with vs without hyposalivation for the Soft (p <.001). Suprahyoid activity/cycle was significantly greater at the middle (p =.045) and late stages (p =.002) with vs without hyposalivation for the Soft and greater at the late stage with vs without hyposalivation for the Plain (p =.043). Changes in masticatory cycle time and suprahyoid activity/cycle for these foods had significantly positive relationship (p <.001). Conclusion: Hyposalivation‐induced changes in masticatory behaviours resulted from the middle and late stage suprahyoid activity. Fat content and seasoning compensate for salivary flow inhibition. [ABSTRACT FROM AUTHOR]

A patient presented desiring to improve her esthetics and reduce masseter muscle pain prior to her upcoming wedding. Although the patient had a full-mouth rehabilitation with porcelain restorations at age 16, she presented with extensive overjet, unbalanced occlusion, and lack of contact from premolar to premolar. The clinician was faced with the challenge of determining the best course of treatment. After completing thorough record-taking and a detailed analysis following a systematic approach, the clinician developed a facially driven treatment plan that was carried out over eight phases. The patient's existing crowns were replaced at a reduced vertical dimension of occlusion, esthetics were enhanced, muscle pain was relieved, and her goals were achieved. [ABSTRACT FROM AUTHOR]

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Background and Objectives: The aim was to compare the activity of the masseter muscles in children with different types of breathing. Materials and Methods: A cross-sectional study was conducted including patients aged 6–12 years with mixed dentition, who came for oral care at the Master's Degree in Pediatric Dentistry program at the Complutense University of Madrid (UCM), according to inclusion and exclusion criteria. The sample was divided into three groups: nasal breathers without dental alterations (control group), oral breathers with dental malocclusion, and oral breathers with previous orthodontic treatment. An electromyography was performed, and statistic methods were conducted with a 95% confidence to contrast hypothesis. Results: A total of 122 children were analyzed and distributed into three groups. The electrical muscle activity of masseters was significantly different between the study groups (p < 0.001 for all comparisons). Pairwise comparisons revealed a significantly higher electrical muscle activity in the control group (nasal breathers) during chewing compared to both groups of oral breathers (p < 0.001 for both comparisons). Orthodontic treatment decreased electrical muscle activity during isometric contraction in oral breathers compared to nasal breathers (p < 0.001), but did not significantly affect electrical muscle activity during chewing. Higher decompensation values were obtained in oral breathers without previous orthodontic treatment compared the other study groups (p < 0.001 for both comparisons), although electrical muscle activity values were similar in both groups of oral breathers (p > 0.05 for both comparisons). Conclusions: Differences in electrical muscle activity between nasal and oral breathers can be confirmed. Oral breathers with and without orthodontic treatment showed lower electrical muscle activity of masseters during chewing than nasal breathers, while at isometric contraction, only oral breathers with previous orthodontic treatment showed lower electrical activity. Higher decompensation values were found in oral breathers without previous orthodontic treatment, in comparison to the control group and oral breathers with previous orthodontic treatment. [ABSTRACT FROM AUTHOR]

Abstract Objective The purpose of the present study was to explore the effect of plateau duration in eliciting masseter vestibular evoked myogenic potentials (mVEMPs) in healthy individuals with hearing sensitivity ≤ 15dBHL. Method A within-subjects design was utilized in the study. Therefore, ipsilateral tone burst evoked mVEMPs were obtained from 30 healthy individuals using the zygomatic montage at 500 Hz tone bursts. Self-monitoring biofeedback was given during the procedure to confirm the tension of the masseter muscle. mVEMPs were recorded across three different plateau duration from 0 to 2 ms with rise/fall time of 2 ms at 95dBnHL. Hence the median and interquartile range were calculated for descriptive analysis of the data followed by non-parametric inferential statistics. Results Tone burst evoked mVEMPs were found to be 100% present across all three plateau durations for both ears at 95 dBnHL. P11 and N21 latencies increased with longer plateau durations in both ears. There were no significant differences in P11-N21 peak-to-peak amplitude or interaural amplitude ratio (IAAR) observed across different plateau durations. IAAR was lowest for a 2 ms plateau duration in the 2–2-2 cycle. No significant variations were found across the three plateau durations. Conclusion Significant differences in P11 and N21 latencies were observed across the three stimulus cycles, while no significant differences were found for P11N21 amplitude and IAAR. Yet, there was found to have the highest amplitude and lowest IAAR for 2–2-2 cycle than 2–0-2 and 2–1-2, suggesting it to be the optimal stimulus among the three of them.