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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]

Surgery of jawbones has a high potential risk of causing complications associated with temporomandibular joint disorder (TMD). The objective of this study was to investigate the effects of two drive modeling methods on the biomechanical behavior of the temporomandibular joint (TMJ) including articular disc during mandibular movements. A finite element (FE) model from a healthy human computed tomography was used to evaluate TMJ dynamic using two methods, namely, a conventional spatial‐oriented method (displacement‐driven) and a compliant muscle‐initiated method (masticatory muscle‐driven). The same virtual FE model was 3D printed and a custom designed experimental platform was established to validate the accuracy of experimental and theoretical results of the TMJ biomechanics during mandibular movements. The results show that stress distributed to TMJ and articular disc from mandibular movements provided better representation from the muscle‐driving approach than those of the displacement‐driven modeling. The simulation and experimental data exhibited significant strong correlations during opening, protrusion, and laterotrusion (with canonical correlation coefficients of 0.994, 0.993, and 0.932, respectively). The use of muscle‐driven modeling holds promise for more accurate forecasting of stress analysis of TMJ and articular disc during mandibular movements. The compliant approach to analyze TMJ dynamics would potentially contribute to clinic diagnosis and prediction of TMD resulting from occlusal disease and jawbone surgery such as orthognathic surgery or tumor resection. [ABSTRACT FROM AUTHOR]

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 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

The morphology and biomechanics of infant crania undergo significant changes between the pre- and post-weaning phases due to increasing loading of the masticatory system. The aims of this study were to characterize the changes in muscle forces, bite forces and the pattern of mechanical strain and stress arising from the aforementioned forces across crania in the first 48 months of life using imaging and finite element methods. A total of 51 head computed tomography scans of normal individuals were collected and analysed from a larger database of 217 individuals. The estimated mean muscle forces of temporalis, masseter and medial pterygoid increase from 30.9 to 87.0 N, 25.6 to 69.6 N and 23.1 to 58.9 N, respectively (0–48 months). Maximum bite force increases from 90.5 to 184.2 N (3–48 months). There is a change in the pattern of strain and stress from the calvaria to the face during postnatal development. Overall, this study highlights the changes in the mechanics of the craniofacial system during normal development. It further raises questions as to how and what level of changes in the mechanical forces during the development can alter the morphology of the craniofacial system. [ABSTRACT FROM AUTHOR]

Background Objectives Methods Results Conclusion Activation of β2 adrenergic receptors reduces cutaneous mechanical pain thresholds in rats. While β2 adrenergic receptor activation may contribute to mechanisms that underlie temporomandibular joint pain, its effect on masticatory muscle pain sensitivity is uncertain.The current study sought to determine the extent to which β adrenergic receptors are expressed by masticatory muscle afferent fibres, and to assess the effect of local activation of these receptors on the mechanical sensitivity of masticatory muscle afferent fibres in rats.Trigeminal ganglion neurons that innervate the rat (n = 12) masseter muscle and lower lip were identified by tissue injection of fluorescent dyes and were then stained with antibodies against β1 or β2 adrenergic receptors. Extracellular recordings from 60 trigeminal ganglion neurons that innervate the masticatory muscle were undertaken in a second group of anaesthetised rats of both sexes (n = 37) to assess afferent mechanical activation thresholds. Thresholds were assessed before and after injection of the β adrenergic receptor agonists into masticatory muscle.β1 and β2 adrenergic receptor expression was greater in labial skin than in masticatory muscle ganglion neurons (p < .05, one‐way ANOVA, Holm–Sidak test). There was a higher expression of β2 adrenergic receptors in masticatory muscle ganglion neurons in males than in females. The mixed β agonist isoproterenol increased afferent mechanical activation threshold in male but not female rats (p < .05, Mann–Whitney test). In male rats, salbutamol, a β2 selective agonist, also increased afferent mechanical activation threshold but hydralazine, a vasodilator, did not (p < .05, Mann–Whitney test).Activation of β2 adrenergic receptors decreases the mechanical sensitivity of masticatory muscle afferent fibres in a sex‐related manner. [ABSTRACT FROM AUTHOR]

Background: It has been reported that botulinum toxin type A (BoNT-A) produces structural changes in masticatory muscles. However, not all histomorphometric parameters affected by BoNT-A parameters have been assessed. This study investigated the histomorphometric changes in the masseter muscle of rats after a single injection of BoNT-A. Methods: Forty-four adult animals were randomly divided into control group (n = 22) and BoNT-A group (n = 22). Controls received a single dose of 0.14 mL/kg of saline in masseter muscles, and the BoNT-A group received a 7 U/Kg of BoNT-A. The groups received the same volume of injected substances. Animals were sacrificed on 7th (n = 5), 14th (n = 5), 21st (n = 5), 28th (n = 4) and 90th (n = 3) days post-treatment. Histological masseter tissue slides were obtained from hematoxylin–eosin treatment and analyzed in optical microscopy regarding muscle cross-sectional area, amount of connective tissue and quantity and diameter of myocytes. For statistical analysis, generalized linear models were used to compare the data (ANOVA). In all test, the significance level of 5% was set. Results: BoNT-A values of cross-sectional area of the masseter muscle were significantly lower than controls (p < 0.01) throughout the study. Regarding myocytes quantity, BoNT-A subgroups presented higher values than controls (p < 0.0001) since the 14th day until the end of the study; however, the diameter of myocytes was smaller in all BoNT-A subgroups (p < 0.0001) in all assessment points. The amount of connective tissue was higher in BoNT-A subgroups (p < 0.0001) throughout the study. Conclusion: A single injection of BoNT-A altered the structure of masseter muscle of rats, regarding its histomorphometric parameters. No Level Assigned: 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]

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.

Mastication myalgia is the most common cause of non-odontogenic pain in the orofacial region and is often associated with a reduced quality of life. The purpose of this review is to provide an overview of the clinical aspects of myalgia based on available research. The review includes epidemiological, diagnostic, and etiological aspects. In addition, the potential risk factors related to the transition from acute to chronic myalgia are explored and treatment strategies are presented for its management. As a result, this review may increase clinical knowledge about mastication myalgia and clarify strategies regarding prevention, diagnostics, and management to improve prognosis and reduce patient suffering. [ABSTRACT FROM AUTHOR]

Aim: Occlusal splint treatment is commonly used to treat a variety of temporomandibular disorders (TMDs), with efficacy ranging between 70% and 90%. Centric splints are effective in relieving muscular soreness in individuals with TMD. Electromyography (EMG) quantifies muscle activity and can be used as an accessory diagnostic tool to evaluate the efficiency of the splint on the masticatory complex. Electromyography is used for assessing patients with TMD and observing muscle electromyography. TMD patients have altered electromyographic (EMG) masticatory muscle activity because of its change in electrical activity index or because of the compensatory mechanism for the disorder. Therefore, this study serves to evaluate the efficacy of the centric stabilization splint on TMD using EMG. Settings and Design: This cross-sectional study enrolled Ten TMD Patients with TMD, who underwent treatment with centric stabilization splint. Materials and Methods: The study involved ten young adults with TMD aged 18–45 years who were recruited without regard to sex, religion, caste, or socioeconomic background. The participants were randomized to receive a flat-contact upper stabilization splint and pregelled EMG electrodes to assess the immediate impact of centric splints on TMDs. After 3 months of follow-up, muscle activity and muscle symmetrical activity were measured to assess improvement in the symptoms of TMD. Statistical Analysis Used: The Shapiro–Wilk test was used to assess the normality of the variables’ distribution using SPSS 26.0. Symmetrical activity and treatment response were investigated using the Wilcoxon signed-rank test. Results: It showed an improvement in the temporalis, masseter, and sternocleidomastoid muscles’ resting EMG activity. A statistically significant improvement was seen in the EMG activity of the bilateral temporalis, right masseter, right sternocleidomastoid, and left digastric muscles while clenching. The masseter, sternocleidomastoid, and digastric muscles all displayed significantly enhanced symmetrical activity (P < 0.05). Conclusions: This research concludes that a centric stabilizing splint assists in relieving TMD symptoms. There was enhanced masticatory muscle activity both at rest and during function. Furthermore, there was an improvement in symmetrical activity of the masticatory muscles, which improved balance and enhanced the effective functioning of the masticatory complex. [ABSTRACT FROM AUTHOR]

Objective·To assess muscle changes of patients of temporomandibular joint disorder with nonstructural disorder by using the Dixon technique for MRI of masticatory muscle, and evaluate the clinical effect of manipulation on masticatory muscle pain guided by MRI.Methods·A total of 29 patients with TMD masticatory muscle pain (without disc displacement) who were diagnosed for the first time in the Department of Oral Surgery, Shanghai Ninth People′s Hospital, Shanghai Jiao Tong University School of Medicine from June 2021 to September 2022 were included. Among them, 9 cases who were assessed with Dixon technique for MRI of masticatory muscle were collected and treated by manipulation. Before treatment, the DICOM Viewer workstation was used to compare the value of masticatory muscle pain area (Z1), the value of ipsilateral non-pain area (Z2) and the value of contralateral corresponding masticatory muscle area (Z3) in Dixon image. Manipulation therapy was performed according to the area of abnormal threshold. Follow-up was performed for 1-4 weeks after treatment, the active maximum mouth opening (MMO) and Visual Analogue Scale (VAS) before and after treatment were compared, and the value of masticatory muscle pain area in Dixon image after treatment was obtained again to evaluate the clinical efficacy.Results·The mean value of Z2 and Z3 in Dixon was (66.23±32.90) and (66.27±33.87), while Z1 in masticatory muscle pain region was (131.94±83.99), which was significantly higher than Z2 and Z3. Manipulation therapy showed significant improvement in MMO and VAS, and the effective rate was 88.89%.Conclusion·There is a significant correlation between the imaging findings of Dixon technique for MRI and the pain points of the masticatory muscle reported by the clinical complaints. The manipulation therapy guided by Dixon technique for MRI has a significant effect on improving the degree of mouth opening and pain.

Mastication myalgia is the most common cause of non-odontogenic pain in the orofacial region and is often associated with a reduced quality of life. The purpose of this review is to provide an overview of the clinical aspects of myalgia based on available research. The review includes epidemiological, diagnostic, and etiological aspects. In addition, the potential risk factors related to the transition from acute to chronic myalgia are explored and treatment strategies are presented for its management. As a result, this review may increase clinical knowledge about mastication myalgia and clarify strategies regarding prevention, diagnostics, and management to improve prognosis and reduce patient suffering.

Introduction: Ultrasonography is a common tool for assessing muscle morphology. This study aims to investigate the intra-rater reliability of ultrasonography measurements of the masseter and lateral pterygoid muscles (LPM) in subjects with and without temporomandibular disorder (TMD) and to compare the measurements between the two groups. Materials and Methods: A total of 30 individuals (15 subjects with TMD and 15 subjects without TMD) participated in the study. Imaging of the masseter muscle at rest and contraction, in addition to LPM, was performed using sonography in 2 sessions with a 2-day interval and the thickness of these muscles was measured. To assess the reliability, the intraclass correlation coefficient (ICC(3, 3)), standard error of measurement, minimal detectable change, and limits of agreement were used. Additionally, for the between-group comparison of measurements, the independent sample t-test was used. The Cohen d was used to determine the size of the differences. Results: ICC(3, 3) for intra-rater reliability of masseter thickness in rest and clenched positions and LPM were 0.89, 0.80, and 0.86 in the asymptomatic group, and 0.88, 0.80, and 0.90 in the TMD group, respectively. The values of absolute reliability parameters, such as standard error of measurement and minimal detectable change were in a small range. Additionally, compared to the asymptomatic group, the TMD group had thicker masseter muscle in the rest position and the effect size revealed a large difference between the groups. No significant differences were found between the groups for the thickness of the masseter muscle in contraction position and LPM. Conclusion: The results of the intra-reliability study revealed that ultrasonography is a reliable method to measure the thickness of the masticatory muscles in TMD subjects and asymptomatic subjects. Additionally, TMDs can change the thickness of the masticatory muscles. [ABSTRACT FROM AUTHOR]

Wearable devices are worn on or remain in close proximity of the human body. The use of wearable devices specific to the orofacial region is steadily increasing. Orofacial applications of wearable devices include supplementing diagnosis, tracking treatment progress, monitoring patient compliance, and understanding oral parafunctional behaviours. In this short communication, the role of wearable devices in advancing personalized dental medicine are highlighted with a specific focus on masticatory muscle activity monitoring in naturalistic settings. Additionally, challenges, opportunities, as well as future research areas for successful use of wearable devices for precise, personalized care of muscle disorders are discussed. [ABSTRACT FROM AUTHOR]

The treatment of dentofacial deformities generally includes orthognathic surgery in which mandibular condyle changes following surgery are a common cause of relapse. This study investigated the changes in the mandibular condyle and related muscles to identify the factors that affected the changes in the mandibular condyle after orthognathic surgery in skeletal class II patients. This research studied 60 joints in 30 patients with skeletal class II dentofacial deformities who received surgical orthodontic treatment, including bilateral sagittal split ramus osteotomy, and underwent computed tomography before and after orthodontic treatment. The mandibular condyle, masseter, and medial pterygoid muscles were reconstructed and measured in 3D. Condylar positional and morphology changes, masseter and medial pterygoid muscle volume, temporomandibular joint (TMJ) pain, and distal segment movement were analyzed. The study observed that both the masseter and medial pterygoid muscle volumes decreased with statistical significance. The changes in the horizontal direction were positively correlated with the amount of movement. The findings indicated that mandibular condyle changes were significantly affected by the movement of the distal segment, the medial pterygoid muscle volume, and the direction of the distal segment, which influenced the treatment's long-term stability after orthognathic surgery. [ABSTRACT FROM AUTHOR]

The regression lines of the masticatory muscle mass of males and females in Suncus murinus do not parallel their body mass, and also does not meet the assumption that the slope of the regression line is essentially the same in covariance analysis. Here, we constructed a new mathematical model that accurately compares relative masticatory muscle mass between males and females in terms of body mass. The quantitative relation ships between masticatory muscle mass and body mass in both genders were established by regression analysis. The coordinate points of the male sample were scaled in equal proportion along the regression line, so that the average weight of the male after scaling was the same as that of the female, and the regression equation before and after scaling was unchanged. The expression of the difference between the masticatory muscle masses in males and females was deduced after scaling to produce the model. It is verified that the model can correctly predict the relative mass of masticatory muscles between males and females according to their body mass. The model showed that male shrews have relatively greater masticatory muscle mass and attack power. [ABSTRACT FROM AUTHOR]

Although similar to trunk and limb skeletal muscles, masticatory muscles are believed as unique in both developmental origins and myogenesis. Gαi2 has been demonstrated to promote muscle hypertrophy and muscle satellite cell differentiation in limb muscles. However, the effect of Gαi2 on masticatory muscles is still unexplored. This study aimed to identify the role of Gαi2 in the proliferation and differentiation of masticatory muscle satellite cells, further exploring the metabolic mechanism of masticatory muscles. The proliferation rate, myotube size, fusion index of masticatory muscle satellite cells and Pax7, Myf5, MyoD, Tcf21 and Musculin expressions were significantly decreased by Gαi2 knockdown, while in cells infected with AdV4‐Gαi2, the proliferation rate, myotube size, fusion index and Tbx1 expression were significantly increased. Masticatory muscle satellite cells also displayed phenotype transformation as Gαi2 changed. In addition, Gαi2 altered myosin heavy chain (MyHC) isoforms of myotubes with less MyHC‐2A expression in siGαi2 group and more MyHC‐slow expression in AdV4‐Gαi2 group. In conclusion, Gαi2 could positively affect the adult myogenesis of masticatory muscle satellite cells and maintain the superiority of MyHC‐slow. Masticatory muscle satellite cells may have their unique Gαi2‐regulated myogenic transcriptional networks, although they may share some common characteristics with trunk and limb muscles. [ABSTRACT FROM AUTHOR]

Introduction: Ultrasonography is a common tool for assessing muscle morphology. This study aims to investigate the intra-rater reliability of ultrasonography measurements of the masseter and lateral pterygoid muscles (LPM) in subjects with and without temporomandibular disorder (TMD) and to compare the measurements between the two groups. Materials and Methods: A total of 30 individuals (15 subjects with TMD and 15 subjects without TMD) participated in the study. Imaging of the masseter muscle at rest and contraction, in addition to LPM, was performed using sonography in 2 sessions with a 2-day interval and the thickness of these muscles was measured. To assess the reliability, the intraclass correlation coefficient (ICC(3, 3)), standard error of measurement, minimal detectable change, and limits of agreement were used. Additionally, for the between-group comparison of measurements, the independent sample t-test was used. The Cohen d was used to determine the size of the differences. Results: ICC(3, 3) for intra-rater reliability of masseter thickness in rest and clenched positions and LPM were 0.89, 0.80, and 0.86 in the asymptomatic group, and 0.88, 0.80, and 0.90 in the TMD group, respectively. The values of absolute reliability parameters, such as standard error of measurement and minimal detectable change were in a small range. Additionally, compared to the asymptomatic group, the TMD group had thicker masseter muscle in the rest position and the effect size revealed a large difference between the groups. No significant differences were found between the groups for the thickness of the masseter muscle in contraction position and LPM. Conclusion: The results of the intra-reliability study revealed that ultrasonography is a reliable method to measure the thickness of the masticatory muscles in TMD subjects and asymptomatic subjects. Additionally, TMDs can change the thickness of the masticatory muscles.

In the present paper, a method to evaluate the occlusal state and occlusal morphology that can integrate an optimal occlusal force field under clenching is proposed using simplex optimization and principal component analysis (PCA). The objective function of the optimization is taken as a sum of the weighted occlusal forces and reaction on temporomandibular joint (TMJ) to maximize the former and to minimize the latter. The optimized solutions in the region defined by the combination among three kinds of muscle forces were obtained by two-step simplex method, and the subregion with no reaction of TMJ was summarized as a ratio to the whole region, newly defined here as a good balance ratio. As a result of PCA of total 528 samples of the good balance ratios for 13 different muscle force combinations, two principal components (PCs) are enough to represent the optimized masticatory system. The first PC suggests the ideal state of occlusion and the second one implies the characterization of combination among muscles. From the consideration of PCA, with the wider equalizer angle, the easier it is to support the force of the temporalis muscle in an ideal occlusal position, and the more the occlusal contact point is shifted backward, the harder it is to support the force of the temporalis muscle. Comprehensively, the proposed good balance ratio becomes the effective quantity to evaluate the ideal masticatory system with the optimized occlusal force field for the statistically reduced indexes showing the combination of muscles.

There is no consensus on the most appropriate method for normalizing electromyography (EMG) signals from masticatory muscles during isotonic activity. Aim: To analyze the best method for data processing of the EMG signal of the masticatory muscles during isotonic activity (non-habitual chewing), comparing raw data and different types of normalization. Methods: This is a cross-sectional study. Women aged between 18 and 45 years were selected. Anthropometric data were collected (age, height, body mass index -- BMI, masticatory preference) as well as EMG signal (root mean square -- RMS) data for the anterior temporal and masseter bilaterally, and for the suprahyoid muscles, during isotonic (non-habitual chewing) and isometric tasks. EMG data were processed offline using Matlab® Software. The normalization of the EMG signal was carried out using the 2nd masticatory cycle, chosen at random, of the 20 cycles collected, the maximum RMS value, and the maximum voluntary contraction (MVC). To analyze the best method of data processing for the isotonic data, the coefficient of variation (CV) was calculated. Descriptive data analysis was adopted, using the mean and standard deviation. ANOVA with repeated measures was used to detect significant differences between the methods of normalization. Statistical significance was set at 5% (α<0.05). Results: The final sample of this research was composed of 86 women. The volunteers presented an average age of 27.83±7.71 years and a mean BMI of 22.85±1.91 Kg/m². Regarding masticatory preference, 73.25% reported the right side, and 26.75% the left side. Considering the comparison between the methods, the %CV measure of the 2nd cycle showed the lowest variation coefficient during biting for all the muscles from the raw data, RMS Max, and MVC (p=0.001, p=0.003, and p=0.001 respectively). Conclusion: In conclusion, for non-habitual chewing activity, the results of this study recommend data processing using normalization with the second cycle during chewing. [ABSTRACT FROM AUTHOR]

The current state of portable/wearable electromyographic (EMG) devices for assessment of bruxism was reviewed. A search of full-text articles relevant to portable/wearable EMG devices capable of being used at home was performed. The data source used was MEDLINE via PubMed from January 1970 to July 2019. There were nine kinds of wearable EMG devices capable of being used under unrestrained conditions. Ultra-miniaturized wearable EMG devices with a level of performance equivalent to that of conventional stationary EMG devices have been developed and are being used during sleep and in the daytime. The devices have a high level of diagnostic accuracy for sleep bruxism. A definite cut-off value for awake bruxism has not been established. Assessment of sleep bruxism with a high level of accuracy can be performed using a portable/wearable EMG device. However, a definite cut-off value is required for assessment of awake bruxism. [ABSTRACT FROM AUTHOR]

Wearable technology to augment traditional approaches are increasingly being added to the arsenals of treatment providers. Wearable technology generally refers to electronic systems, devices, or sensors that are usually worn on or are in close proximity to the human body. Wearables may be stand-alone or integrated into materials that are worn on the body. What sets medical wearables apart from other systems is their ability to collect, store, and relay information regarding an individual's current body status to other devices operating on compatible networks in naturalistic settings. The last decade has witnessed a steady increase in the use of wearables specific to the orofacial region. Applications range from supplementing diagnosis, tracking treatment progress, monitoring patient compliance, and better understanding the jaw's functional and parafunctional activities. Orofacial wearable devices may be unimodal or incorporate multiple sensing modalities. The objective data collected continuously, in real time, in naturalistic settings using these orofacial wearables provide opportunities to formulate accurate and personalized treatment strategies. In the not-too-distant future, it is anticipated that information about an individual's current oral health status may provide patient-centric personalized care to prevent, diagnose, and treat oral diseases, with wearables playing a key role. In this review, we examine the progress achieved, summarize applications of orthodontic relevance and examine the future potential of orofacial wearables. [ABSTRACT FROM AUTHOR]

Background: Temporomandibular disorders (TMD) are diagnosed based on symptom presentation and, like other functional pain disorders, often lack definitive pathology. There is a strong association between elevated stress levels and the severity of TMD‐related pain, which suggests that alterations in autonomic tone may contribute to this pain condition. Objectives: This narrative review examines the association between altered autonomic function and pain in TMD. Methods: Relevant articles were identified by searching PubMed and through the reference list of those studies. Results: TMD sufferers report an increased incidence of orthostatic hypotension. As in other chronic musculoskeletal pain conditions, TMD is associated with increased sympathetic tone, diminished baroreceptor reflex sensitivity and decreased parasympathetic tone. It remains to be determined whether ongoing pain drives these autonomic changes and/or is exacerbated by them. To examine whether increased sympathetic tone contributes to TMD‐related pain through β2 adrenergic receptor activation, clinical trials with the beta blocker propranolol have been undertaken. Although evidence from small studies suggested propranolol reduced TMD‐related pain, a larger clinical trial did not find a significant effect of propranolol treatment. This is consistent with human experimental pain studies that were unable to demonstrate an effect of β2 adrenergic receptor activation or inhibition on masticatory muscle pain. In preclinical models of temporomandibular joint arthritis, β2 adrenergic receptor activation appears to contribute to inflammation and nociception, whereas in masticatory muscle, α1 adrenergic receptor activation has been found to induce mechanical sensitisation. Some agents used to treat TMD, such as botulinum neurotoxin A, antidepressants and α2 adrenergic receptor agonists, may interact with the autonomic nervous system as part of their analgesic mechanism. Conclusion: Even if dysautonomia turns out to be a consequence rather than a causative factor of painful TMD, the study of its role has opened up a greater understanding of the pathogenesis of this condition. [ABSTRACT FROM AUTHOR]

The aim of this study was to understand the temporal and spatial distribution of canonical endochondral ossification (CEO) and non-canonical endochondral ossification (NCEO) of the normal growing rat condyle, and to evaluate their histomorphological changes following the simultaneous hypotrophy of the unilateral masticatory closing muscles with botulinum toxin (BTX). 46 rats at postnatal 4 weeks were used for the experiment and euthanized at postnatal 4, 8, and 16 weeks. The right masticatory muscles of rats in experimental group were injected with BTX, the left being injected with saline as a control. The samples were evaluated using 3D morphometric, histological, and immunohistochemical analysis with three-dimensional regional mapping of endochondral ossifications. The results showed that condylar endochondral ossification changed from CEO to NCEO at the main articulating surface during the experimental period and that the BTX-treated condyle presented a retroclined smaller condyle with an anteriorly-shifted narrower articulating surface. This articulating region showed a thinner layer of the endochondral cells, and a compact distribution of flattened cells. These were related to the load concentration, decreased cellular proliferation with thin cellular layers, reduced extracellular matrix, increased cellular differentiation toward the osteoblastic bone formation, and accelerated transition of the ossification types from CEO to NCEO. The results suggest that endochondral ossification under loading tended to show more NCEO, and that masticatory muscular hypofunction by BTX had deleterious effects on endochondral bone formation and changed the condylar growth vector, resulting in a retroclined, smaller, asymmetrical, and deformed condyle with thin cartilage. • spatial and temporal patterns of endochondral ossification in growing rat condyle. • normal transition from canonical to non-canonical endochondral ossification under loading over time. • accelerated endochondral transition due to BTX-induced masticatory muscular hypofunction. • retroclined condyle with anteriorly shifted narrower articulating surface following BTX treatment. [ABSTRACT FROM AUTHOR]

Background: Previous clinical observational studies have suggested that orthodontic tooth movement (OTM) is related, at least partly, to the mass and/or capabilities of the masticatory muscles. Objectives: Our study aimed to examine the influence of masticatory muscle mass on the OTM in an animal experimental model in which the masseter muscle was modulated by botulinum neurotoxin type A (BTX) injection. Methods: Eighteen Wistar rats were equally divided into two groups: BTX injection and control. BTX was injected bilaterally into the masseter muscles. Three days after the injection, the maxillary left first molars were orthodontically moved for 14 days. At the end of the experiment, micro‐computed tomography was performed to evaluate the rate of OTM and bone morphometry. The masseter muscles were weighed and prepared for histological analyses. Results: The masseter muscle mass in the BTX group was less than that in the control group, and histological findings showed atrophy of muscle fibres. The rate of OTM was significantly higher in the BTX group than in the control group. Furthermore, a negative correlation was detected between masseter muscle mass and OTM in the BTX group. Bone morphometry showed no difference between the control and BTX groups. Conclusion: Decreased masseter muscle mass was found to be closely related to an increase in the rate of OTM in rats using BTX injection to modify the masseter muscle mass. Masseter muscle mass could be a predictive factor for OTM in rats injected with BTX. [ABSTRACT FROM AUTHOR]

This retrospective case-series study aimed to elucidate the three-dimensional attachment morphometric features and to quantify the volumetric changes of the masticatory muscles following free fibular flap reconstruction of the mandibular condyle. Navigation software (iPlan, version 3.0; Brainlab) was used to perform delineation and volumetric measurement of the masticatory muscles using DICOM data. In total, 30 patients were included in this retrospective case series. In 25 cases (83.33%), the lateral pterygoid muscle achieved reattachment within 6 months postoperatively. The medial pterygoid muscles on the affected side achieved ectopic attachment in all cases. However, masseter reattachment on the affected side was achieved in only three cases. On the normal side, the volumes of lateral pterygoid muscle, medial pterygoid muscle, and masseter had recovered to almost preoperative levels at 1 year postoperatively. On the affected side, the volume of medial pterygoid muscle had decreased significantly (p = 2.4e-04) at 3 months postoperatively. The volumes of lateral pterygoid muscle and masseter showed mild decreases at 3 months postoperatively, but these were not significant (p = 0.52 and p = 0.05 for the pterygoid muscle and masseter, respectively). At 6 months after surgery, with the exception of the volume of the lateral pterygoid muscle (p = 0.06), the total volume of the masticatory muscles decreased significantly on the affected side. The volumes of lateral pterygoid muscle, medial pterygoid muscle, and masseter showed significant decreases at 1 year postoperatively (p = 0.03, p = 4.7e-08, and p = 1.1e-05, respectively) on the affected side. The postoperative volumes of the masseter, medial pterygoid, and lateral pterygoid muscles showed significant decreases due to the loss of reattachment. The results of this study may not help to ascertain whether reattachment of masticatory muscles will lead to better function. As a consequence, clinical trials of higher quality are needed. [ABSTRACT FROM AUTHOR]

Muscle disorders caused by cerebral palsy (CP) can affect oral function. The treatment for masticatory muscle spasticity is important to minimize muscle hyperactivity and preclude oral damages. Objectives: To evaluate the efficacy and safety of non-surgical interventions for the treatment of masticatory muscle spasticity in CP patients. Methods: A comprehensive search was performed in the following databases: MEDLINE, Embase, Cochrane Library, LILACS, BBO, PEDro, Clinicaltrials.gov and WHO/ICTRP, without date and language restrictions. Randomized controlled trials (RCT) evaluating non-surgical interventions were considered. Primary outcomes such as masticatory function and adverse events were planned to be assessed. The risk of bias assessment was performed using the Cochrane risk of bias tool. The certainty of the evidence was assessed using the GRADE approach. Results: Three RCT assessing the effects of botulinum toxin, functional masticatory training and neuromuscular electrostimulation (NMES) were included. Evidence with a very low certainty showed: (i) no difference between botulinum toxin and placebo regarding maximum chewing strength, chewing efficiency and global oral health scale; (ii) improvement in masticatory function in favor of functional masticatory training versus conventional exercises, and (iii) in favor of strengthening exercises plus NMES versus placebo. Conclusions: There was insufficient evidence to support the use of botulinum toxin and masticatory muscle strengthening programs alone and associated with NMES for the treatment of masticatory muscle in patients with PC. The clinical decision must be individualized, and further studies are needed to support or refute the use of different non-surgical interventions for PC. PROSPERO register number CRD42020209761. [ABSTRACT FROM AUTHOR]

BACKGROUND: The maxillary expansion technique can help and improve the coordination of the maxilla and mandible and can change the growth pattern of the tissues around the maxilla. Especially, it plays an important role in the change of the temporomandibular joint and the airway in children, and can help and guide their growth along the normal direction. OBJECTIVE: To review the research progress in the effect of maxillary expansion technique on the temporomandibular joint and airway in children. METHODS: Literature retrieval was conducted in PubMed, CNKI, WanFang, and Medline. The key words were “maxillary expansion, palatal expansion, temporomandibular joint, masticatory muscle, airway” in English and Chinese, respectively. Studies and experiments of low quality and irrelevant to the topic of the article were excluded. Finally, 71 literatures were included for careful reading and analysis. RESULTS AND CONCLUSION: In patients with underdevelopment of the maxillary, the bilateral condyles are often asymmetrical due to the unbalanced bite. When the maxillary extension technique is used to widen the maxilla, it has certain influence on the surrounding tissues. Maxillary expansion can make the condylar position on both sides of the patients with malocclusion more symmetrical and the muscle force distribution more uniform, which is conducive to the growth and development of the temporomandibular joint, but has no significant change in the position and shape of the joint disc. In addition, maxillary expansion can also improve the volume of the nasal cavity, improve the ventilation function of patients, and therefore, reduce the adverse consequences caused by obstructive sleep apnea hypopnea syndrome. [ABSTRACT FROM AUTHOR]

Objectives: To test the hypotheses that (a) the force thresholds at onset of medial pterygoid muscle single motor unit (SMU) activity do not decrease with an increase in the rate of force generation in standardised vertical or horizontal jaw‐force tasks, and (b) there is evidence for functional heterogeneity within the medial pterygoid muscle. Methods: In 14 healthy participants, electromyographic recordings of the right medial pterygoid muscle were performed with intramuscular fine‐wire electrodes during four isometric force tasks: vertical, horizontal contralateral, horizontal protrusion and horizontal ipsilateral, performed at two rates of force development (slow ramp, fast ramp). Computer tomography scans confirmed electrode location within the muscle, which was divided into medial and lateral parts. Force thresholds of onset of discriminated SMUs were compared between rates in each task; significance accepted at p < 0.05. Results: Of 45 SMU force thresholds studied in one or more tasks, there was no significant difference between slow and fast ramp within each force task, except slow ramp thresholds from the lateral part during the vertical force task were significantly higher than fast ramp thresholds. Reversals of recruitment order between tasks provided evidence for functional heterogeneity within the muscle. Force thresholds of the vertical tasks (range: 1–292.6 N) were mostly higher than for the horizontal tasks (range: 0.1–12.5 N). Conclusion: The data are consistent with the proposal that the medial pterygoid muscle stabilises the jaw in the vertical plane during isometric force generation in the jaw closing, as well as horizontal directions. [ABSTRACT FROM AUTHOR]

Wearable technology to augment traditional approaches are increasingly being added to the arsenals of treatment providers. Wearable technology generally refers to electronic systems, devices, or sensors that are usually worn on or are in close proximity to the human body. Wearables may be stand-alone or integrated into materials that are worn on the body. What sets medical wearables apart from other systems is their ability to collect, store, and relay information regarding an individual’s current body status to other devices operating on compatible networks in naturalistic settings. The last decade has witnessed a steady increase in the use of wearables specific to the orofacial region. Applications range from supplementing diagnosis, tracking treatment progress, monitoring patient compliance, and better understanding the jaw’s functional and parafunctional activities. Orofacial wearable devices may be unimodal or incorporate multiple sensing modalities. The objective data collected continuously, in real time, in naturalistic settings using these orofacial wearables provide opportunities to formulate accurate and personalized treatment strategies. In the not-too-distant future, it is anticipated that information about an individual’s current oral health status may provide patient-centric personalized care to prevent, diagnose, and treat oral diseases, with wearables playing a key role. In this review, we examine the progress achieved, summarize applications of orthodontic relevance and examine the future potential of orofacial wearables.

Malocclusion can be caused by dentocraniofacial growth abnormalities. These growth abnormalities can be caused by dental, maxillary and/or mandibular conditions (skeletal), a combination of dental and jaw (dentoskeletal). Many factors can influence this growth, including the result of genetic, congenital and environmental. One example that plays an important role is the role of soft tissue or muscles. Aim: To investigate the association between masticatory muscle tone and dental and malocclusion class I and class III skeletal in Javanese ethnic patients. This study was analytical observational study with cross sectional and total sampling method in Orthodontics Clinic, Faculty of Dental Medicine, Universitas Airlangga Surabaya. In this study, there were 18 patients with class I or malocclusion class III skeletal malocclusion with an age range of 18-21 years in both sexes. Measurement of muscle tone in patients with class I and class III skeletal malocclusion using a surface electromyography on the temporalis, masseter and suprahyoid muscles. The correlation test between masticatory muscle tone and dental and skeletal malocclusions was analyzed using spearman's analysis (p>0.05). It was found that the muscles that significantly affected the malocclusion were the right temporalis muscle, left temporalis muscle, right masseter muscle, left suprahyoid muscle, and right suprahoyid muscle. There was a strong relationship between suprahyoid muscle tone and class III malocclusion (p>0.05). Weak suprahyoid muscle activity affects mandibular growth and can be one of the causes of malocclusion class III skeletal. [ABSTRACT FROM AUTHOR]

• Higher GABA receptor expression by skin than masticatory muscle ganglion neurons. • GABA receptor agonists attenuate sensory transmission through the trigeminal ganglion. • Muscle afferent conduction velocity determines response to GABA receptor agonists. • There is a sex-related difference in sensory gating through the ganglion. While the trigeminal ganglion is often considered a passive conduit of sensory transmission, neurons and satellite glial cells (SGCs) within it can release neurotransmitters and express neuroreceptors. Some trigeminal ganglion neurons contain the neurotransmitter γ-aminobutyric acid (GABA) and express GABA receptors. There is behavioral evidence that increased GABA levels in the trigeminal ganglion decreases nociception, while a loss of GABA receptors results in hyperalgesia, although the neural mechanisms for this remain to be investigated. In this study, the expression of GABA receptors by trigeminal ganglion neurons that innervate rat labial skin and masseter muscle was compared using immunohistochemistry. The effect of intraganglionic administration of GABA receptor agonists was investigated by single unit recording of trigeminal brainstem and ganglion neuron responses to stimulation of the labial skin and/or masseter muscle in anesthetized rats. The mean frequency of expression of GABA A and GABA B receptors by masseter and labial skin ganglion neurons was 62.5% and 92.7%, and 55.4% and 20.3%, respectively. The expression of both GABA receptors was significantly greater in skin ganglion neurons. Masticatory muscle evoked brainstem trigeminal neuron responses were significantly attenuated by intraganglionic injection of muscimol (GABA A) but not baclofen (GABA B). The mechanical sensitivity of slow and fast conducting masticatory muscle afferent fibers was decreased and increased, respectively, by intraganglionic injection of both muscimol and baclofen. Activation of GABA A receptors may exert a gating effect on sensory transmission through the trigeminal ganglion by decreasing putative nociceptive input and enhancing innocuous sensory input. [ABSTRACT FROM AUTHOR]

Purpose: The present study was performed to clarify the relationship between the electromyographic activities of jaw and neck and flexor carpi radialis muscles and the occluding conditions during exertion of grip strength. Methods: Twenty healthy young men, having natural dentition and bilateral molar support, were examined. The electromyographic activities of the temporal muscle (Tp), sternocleidomastoid muscle (SCM) and flexor carpi radialis muscle (FCR) on the habitual chewing side and SCM on opposite side (opp. SCM) were recorded under the following occluding conditions during exertion of grip strength: 1) mandibular rest position (Rp), 2) voluntary maximum clenching at the intercuspal position (Vmc), 3) maximum clenching with included sheet (Mci), and 4) free occlusion (Fo). They were compared with each other, and results were analyzed with Friedman test. Spearman's rank correlation test was used to analyze the relationship among the activities of the muscles. Differences in occlusal force and occlusal contact area between the habitual and opposite chewing sides were compared by Wilcoxon signed-rank sum test. Results: Grip strength increased during Vmc and Fo compared to Rp (p<0.05). In Tp and both sides of SCM, significant differences were observed between Rp and other occluding conditions (p<0.05). Positive correlation was observed between opp.SCM and FCR in Fo (r=0.650, p<0.05). Differences in occlusal force and occlusal contact area between the habitual and opposite chewing sides were not significant. Conclusions: The present study clarified the relationship between various occluding conditions and activities of jaw and neck and flexor carpi radialis muscles including the sternocleidomastoid muscle of the opposite side. [ABSTRACT FROM AUTHOR]

Objectives: Occlusal alterations may result in changes in the functional performance of masticatory muscles. This study was planned to evaluate mandibular elevator muscles of patients with dental attrition by using ultrasonography (USG). Methods: 30 physiologically dental attrition subjects, aged 35–65 years, were clinically examined by tooth wear index (TWI). Patient group (TWI scores of 2–4) and age-matched controls (TWI scores of 0–1) underwent ultrasonographic analysis to assess the thickness of anterior temporalis, superficial masseter muscles, bilaterally, during clench and rest positions. Results: The mean thickness of masseter and temporal muscles for rest and clench positions and the ratio between thickness of clench and rest position (C/R) were evaluated. Muscle thickness had a higher mean value in the tooth wear group. However, the only significant differences were in the C/R ratio for left side of masseter (p=0.04) and temporal muscles (p=0.03). Although, there was a negative correlation between TWI scores and the muscle C/R ratio for the tooth wear group. A significant positive correlation was found between age and TWI in both groups. Conclusion: The contraction capacity of the chewing muscles and the attrition mutually interact. This study showed an associate on between the severity of occlusal tooth wear and the C/R of chewing muscles. Although dental attrition can occur due to increased jaw muscle activation, and it can also cause a reduction in the contraction capacity of mandibular elevator muscles.

Introduction: The aim of this study was to compare the efficiency of soft and hard splints in treating patients with clenching. Materials and Methods: In this clinical study, 26 patients with clenching disorder randomly divided to two equal group of treatment: hard and soft splint. The amount of masticatory muscle pain and maximum mouth opening were measured at the delivery time and 3, 6, 9, and 12 weeks later by a blind examiner. Data were analyzed by independent T and repeated measure ANOVA tests with significance level of p=0.05. Results: Hard and soft splints were resulted in significant reduction of masticatory muscle pain (hard: P

Irregular antero-posterior relationship of the maxilla and mandible causes unstable occlusion and reduced mandibular movements during muscle contraction, which can cause changes in the masticatory muscle function. Aim: The aim of the present study is to determine whether there is a difference in the asymmetry coefficient (ASIM) of the masticatory muscles (m. temporalis anterior and m. masseter) in patients classified as Class I, Class II and Class III according to Angle, by using the method of surface electromyography (EMG). An additional aim is to determine whether there are differences in the ASIM coefficient in female and male subjects. Material and methods: The sample included 180 subjects, males and females. All subjects were divided into 3 groups of 60 subjects (30 males and 30 females) in skeletal classes I, II and III. An examination of muscle function was conducted by a non-invasive method of surface electromyography. Results: The results of this study showed that there is no statistically significant difference in the ASIM index among groups of respondents (p=0,149). Conclusion: The conclusion of the present study is that there is no statistically significant difference in the coefficient of asymmetry of the masticatory muscles (m. temporalis anterior and m. masseter) in patients across Class I, Class II and Class III according to Angle. The difference in the asymmetry coefficient between female and male subjects is also not statistically significant. [ABSTRACT FROM AUTHOR]

Objectives: The pattern of age distribution in East Asian temporomandibular disorder (TMD) patients and age-related differences in DC/TMD diagnostic subtypes/categories were evaluated., Subjects and Methods: TMD patients from two University-based centers in China and South Korea were enrolled. Axis I physical diagnoses were rendered according to DC/TMD. Patients were categorized into six age groups (15-24, 25-34, 35-44, 45-54, 55-64, and 65-84 years; Groups A-F respectively)., Results: Youths/young adults (Groups A-C) formed 74.1% of TMD patients. TMJ disc displacements (74.9%), arthralgia (49.2%), and degenerative joint disease [DJD] (36.8%) were the most common TMD subtypes. The majority had combined (54.0%) and chronic (58.5%) TMDs. Youths/young adults and middle-aged/old adults had substantially lower frequencies of merely pain-related (6.2-14.5%) and intra-articular (13.8-16.8%) TMDs correspondingly. "Being female" increased the prospects of pain-related/combined TMDs by 96%/49%, respectively., Conclusions: East Asian TMD patients comprised mostly of youths/young adults who had an alarmingly high prevalence of TMJ DJD.

Objective: To develop a simple method to estimate masseter muscle mass. Background: The masseter muscle is important for optimal oral function. A decrease in the masseter muscle mass may affect the oral and physical function of the whole body; therefore, it is an important entity to measure. However, to date, no easy measurement method has been developed for the same. Herein, we devised a simple method to estimate masseter muscle mass. In addition, we compared our method with magnetic resonance imaging (MRI) and skeletal muscle mass (SMM) to verify its validity. Materials and methods: We recorded the age, sex, masseter muscle mass (by MRI), number of retained natural teeth, number of functional teeth, length and thickness of masseter muscle, and skeletal muscle mass in 53 community‐dwelling elderly people (21 men and 32 women, average age 72.9 ± 4.5 years). The estimated masseter muscle mass was calculated by multiplying the length, width and thickness of the muscle. Results: The correlation coefficient between masseter muscle mass and estimated masseter muscle mass was r =.903; thus, a strong correlation was recognised. The correlation coefficient between the estimated masseter muscle mass and SMM was r =.279, considering age and sex. Conclusion: We obtained substantial results using our method for estimating the masseter muscle mass and verified its validity by comparing it with masseter muscle mass measured by MRI and SMM. We believe that our proposed technique is simple and useful for estimating masseter muscle mass. [ABSTRACT FROM AUTHOR]

Aim to evaluate the difference of masticatory muscle activity of Malocclusion Class I and Class II malocclusion in Javanese ethnic patient detected by surface electromyography (sEMG). Observational analytic cross-sectional study was done. The sample consisted of 16 patients, 18-21 years-old taken by the total sampling. The classification of malocclusion based on Angle's malocclusion classification then divided into Class I malocclusion (ANB<4°) and Class II Malocclusion group (ANB>4°) based on cephalometric, study models and intra-oral examination (n=8). The cephalometry was traced using the Orthovision™ digital program and then the anatomical points are determined. The measurement of muscle activity was recorded by means of sEMG. Determine the installation of black-red electrodes according to the direction of muscle contraction from origo to insertio. Pairing the electrode pad then parallel to the muscle belly with muscle fibers with a distance of 1 cm between the electrodes and ground plug. Select the feedback mode and sensitivity according to muscle strength. The right and left side of masseter, temporalis, suprahyoid muscles activity was examined. Mann-Whitney analysis (p<0.05) was done based on homogenity and normality data test (p>0.05). Only the right side of temporal muscle activity was significantly different in Class I and Class II malocclusions in Javanese ethnic patient (p=0.0001). Meanwhile, the masseter and suprahyoid muscles right side, have no significant differences were found in Javanese ethnic patient (p=0.99). Therefore, there was no significant different in left side of temporalis (p=0.11), masseter (p=0.99) and suprahyoid (p=0.104) muscle activity between malocclusion class I and II in Javanese ethnic patient. Temporalis, masseter, and suprahyoid muscle activity detected by sEMG have no significant difference in malocclusion Class I and II in Javanese ethnic patients. [ABSTRACT FROM AUTHOR]

Objective : To investigate the effect of occlusal splints on masticatory muscles electromyography of temporomandibular disorders (TMD). Method : Forty patients with temporomandibular disorders admitted to Affiliated Hospital of Shaanxi University of Traditional Chinese Medicine from March 2016 to March 2019 were enrolled in the study. They were divided into two groups according to the different points of wearing the occlusal splints. Patients in the group A (18 cases) were occluded. The splint and the lower anterior teeth were in point-like uniform contact; In the group B (22 cases), the occlusal splint was in point contact with the function of the right dentition, and the bilateral anterior tibiofibular fascia was compared between the two groups before and after wearing temporal anterior (TA), masseter muscle (MM) changes in masticatory muscles electromyography. Result : There was no significant difference in TA and MM between the two groups before the wearing of the occlusal splint (P>0.05). After one month of wearing the splint, the TA and MM indexes of the two groups were significantly decreased, and the TA of the group B was significantly higher than that of the group B, MM was significantly lower than group A (P<0.05). The TA and MM values of the two groups were significantly increased after one month of wearing the splint (P<0.05), and the TA and MM values of the group A were slightly higher than those of the group B, but the comparison was not statistically significant (P>0.05). The VAS scores of the two groups were significantly decreased after wearing the splint, and the score of group A was significantly lower than that of group B (P<0.05). Conclusion : The treatment of TMD with a occlusal splint and a point-like uniform contact between the lower anterior teeth and the lingual side splint can improve the masticatory muscles function and relieve pain symptoms. [ABSTRACT FROM AUTHOR]

We analyzed the correlations between the T2 shift and integrated electromyographic (iEMG) values in the masseter and temporal muscles. Six healthy adults engaged in a clenching task over two durations at various bite forces. We evaluated the mean T2 shift per voxel and assessed their correlations with iEMG using a linear mixed model. The regression coefficients were different for each muscle type, similar for the left and right sides, and decreased upon doubling duration. [ABSTRACT FROM AUTHOR]

Cytokines are proteins secreted by diverse types of immune and non-immune cells and play a role in the communication between the immune and nervous systems. Cytokines include lymphokines, monokines, chemokines, interleukins, interferons, colony stimulating factors, and growth factors. They can be both pro- and anti-inflammatory and have autocrine, paracrine, and endocrine activities. These proteins are involved in initiation and persistence of pain, and the progress of hyperalgesia and allodynia, upon stimulating nociceptive sensory neurons, and inducing central sensitization. The objective of this review is to discuss several types of pro- and anti-inflammatory mediators and their relation with inflammatory pain in masticatory muscles. [ABSTRACT FROM AUTHOR]

Objectives: To determine (a) whether the medial pterygoid muscle is active in an isometric vertical force task and in isometric horizontal force tasks in the contralateral, protrusion and ipsilateral directions; (b) whether the same single motor units (SMUs) could be active across different directions of isometric force generation; and (c) whether different regions of the medial pterygoid muscle exhibit different patterns of SMU activation during the generation of any one direction of isometric force. Methods: Intramuscular electromyographic (EMG) recordings were made from the right medial pterygoid muscle in 15 healthy participants during isometric force tasks: vertical and horizontal contralateral, protrusion and ipsilateral. A computed tomography scan divided the EMG recording site into a medial or lateral part in each participant. Single motor units were discriminated in each task. Results: Medial pterygoid SMU activity was recorded in 100% of participants for the vertical biting tasks, 86% of participants for the horizontal contralateral and horizontal protrusion tasks and 57% of the horizontal ipsilateral tasks. Of the 72 SMUs that were discriminated, 36% were active in all tasks; 18% were active only in the vertical tasks and 17% were active in the vertical, horizontal contralateral and horizontal protrusion tasks. The proportion of SMUs that was active in at least 1 horizontal task in the lateral part (33/39) was significantly higher than the proportion (21/33) in the medial part (Chi‐Square, P < 0.05). Conclusion: The data are consistent with a stabilisation role for the medial pterygoid muscle in isometric jaw forces in the vertical and horizontal planes. [ABSTRACT FROM AUTHOR]

The lower jaw is considered to be fixed during body exercise. However, the mechanism by which the jaw is fixed remains to be elucidated. We investigated activities of the masticatory muscles during weightlifting to elucidate mandibular movement. Subjects were nine healthy dentulous individuals. They were instructed to lift weights (snatch), and activities of the masticatory muscles during continuous movement were measured. Six stages of weightlifting were chosen according to the weight position, and the activity phases of the temporal, masseter, and digastric muscles were measured. Activities of the masticatory muscles during mastication of peanuts were also measured. Activities of the temporal and masseter muscles during maximum voluntary clenching, and activity of the digastric muscle during maximum voluntary resistance against forced mouth opening were measured to assess maximum voluntary muscle activity. The force expressed as a percentage of the maximum voluntary muscle activity of each muscle was calculated, and this force was compared among the six stages of snatch weightlifting and during mastication of peanuts. The activities of the temporal, masseter, and digastric muscles in the" 1st pull" (the phase of snatch weightlifting demonstrating the greatest activity of each of these muscles) were 44.3, 45.4, and 126.1%, respectively. In contrast, activities of the temporal, masseter, and digastric muscles during" catch", the systemic movement, were 25.9, 18.5, and 75.1%, respectively. Activities of the temporal, masseter, and digastric muscles during mastication of peanuts were 35.1, 24.4, and 20.7%, respectively. The results showed that activities of the masticatory muscles during weightlifting (snatch) were equal to the activity during moderate clenching in the temporal and masseter muscles, and were greater than or equal to maximum strength of the digastric muscle. These results suggest that the digastric muscles strongly participate in fixation of the mandible during snatch weightlifting. [ABSTRACT FROM AUTHOR]

Aims: To compare pressure pain threshold (PPT) values for masticatory muscles in patients with signs and symptoms of myofascial pain and in asymptomatic individuals. Methods: Fifty women with masticatory myofascial pain comprised the symptomatic group (group 1), while 49 TMD symptom-free women were selected as controls (group 2). The PPT was obtained with the aid of an algometer by applying pressure to the masseter and to the anterior, middle, and posterior temporalis. A 90.8% specificity value was used to determine the appropriate PPT cutoff values for all 4 muscles studied. Receiver operator characteristic (ROC) curve areas and the likelihood ratio (LR) were also evaluated. Results: The 3-way ANCOVA test (group, muscle, and side) revealed a significantly lower PPT for all muscles in the symptomatic group (P < .001). The lowest overall PPT was found for the masseter muscle, followed by the anterior, middle, and posterior temporalis (P < .001). The 90.8% specificity was obtained with PPT values of 1.5 kgf/cm2 for the masseter, 2.47 kgf/cm2 for the anterior temporalis, 2.75 kgf/cm2 for the middle temporalis, and 2.77 kgf/cm2 for the posterior temporalis. The anterior temporalis had the highest LR. ROC curve areas of 0.84, 0.92, 0.90, and 0.90 were obtained for the masseter, anterior, middle, and posterior temporalis, respectively. Conclusion: The masseter and temporalis muscles require different pressures for distinguishing masticatory myofascial pain patients from asymptomatic individuals. Because the highest sensitivity (77%) and LR were found for the anterior temporalis, this muscle was considered to have the most suitable discriminative capacity. [ABSTRACT FROM AUTHOR]

Aims: To compare jaw-stretch reflex responses in male and female subjects and to determine whether injection of glutamate into the masseter muscle facilitates these responses in both sexes. Methods: Jaw-stretch reflex responses were evoked with a muscle stretcher, and pain intensity was scored by 11 men and 13 women before and after the injection of glutamate (1.0 mol/L, 0.2 ml) into the masseter muscle. The subjects rated glutumate-evoked pain intensity on a visual analog scale. Results: Baseline jaw-stretch reflex responses were larger and glutamate injections into the masseter muscle were significantly more painful in women than in men, however, glutamate significantly facilitated jaw-stretch reflex responses in men but not in women. Conclusion: These results suggest that there is a significant sex-related difference in human jaw-stretch reflex responses and their modulation by painful stimuli. Since one possible function of facilitated jaw-stretch reflex responses during jaw muscle pain may be to reduce jaw mobility and thus protect against further exacerbation of an existing injury, the finding of a sex-related difference in modulation of jaw-stretch reflex responses may prove to be important in clarifying why the prevalence of temporomandibular disorders is greater in women than in men. [ABSTRACT FROM AUTHOR]