Masseter Muscle Activity Research Articles

Occlusal function and electromyographic activity of masticatory muscles in skeletal Class III patients with different patterns of mandibular asymmetry.

Although jaw asymmetry is commonly seen in skeletal Class III patients, its correlation with occlusal function and masticatory muscle activity has not been fully elucidated. The purpose of this study was to investigate the occlusal function and masticatory muscle activity in skeletal Class III patients with various patterns of mandibular asymmetry. Forty-two patients and 10 normal participants were examined. The patients were categorised into three groups. Groups 1 and 2 exhibited menton and ramus deviation to the same side. Menton deviation was larger than ramus deviation in Group 1, whereas Group 2 showed the inverse relation. Group 3 patients showed menton and ramus deviation in opposite directions. Occlusal contact area (OCA), relative bite force (RBF), and temporalis anterior (TA) and masseter muscle (MM) activity at maximum clenching were measured using T-Scan Novus system and Bio-EMG-III. Statistical analysis was performed using the t-test, one-way analysis of variance with Bonferroni correction and Spearman correlation (α=.05). Compared with normal participants, the patients had smaller OCA and greater asymmetry in the distribution of masticatory muscle activity. Greater ramus deviation was associated with smaller OCA in Group 1 but with larger OCA in Group 3. In Group 1, greater menton deviation was related to stronger TA activity on the non-deviation side. In Group 2, greater ramus deviation was related to stronger MM activity on the deviation side. Deviation of the menton and ramus was individually related to OCA and masticatory muscle activity, and this relationship varied according to the pattern of mandibular asymmetry.

Electromyographic Analysis of Masticatory and Accessory Muscles in Subjects With Implant-Supported Fixed Prostheses: A Three-Arm Comparative Clinical Study.

Aim This study compares the electromyographic (EMG) activity of the masticatory and accessory muscles in patients with natural teeth and those wearing full-mouth fixed prostheses supported by implants. Method In this study, 30 subjects of 30-69 years performed static and dynamic EMG measurements of masticatory and accessory muscles (masseter, anterior temporalis, SCM, and anterior digastric) and were divided into three groups: Group 1 (G1, Control, Dentate), comprising 10 subjects with 14 or more natural teeth(30-51 years of age); Group 2 (G2, single arch implant-supported fixed prosthesis) composed of 10 patients with unilateral edentulism who were successfully rehabilitated with implant-supported fixed prostheses in the maxilla or mandible, restoring occlusion to 12-14 teeth per arch; (39-61 years of age); and Group 3 (G3, full mouth implant-supported fixed prosthesis) with10 subjects with completely edentulous arches with full mouth implant-supported fixed prosthesis with 12 occluding pairs of teeth (46-69 years of age). The left and right masseter, anterior temporalis, superior sagittal, and anterior digastric muscles were examined at rest, as well as maximum voluntary clenching (MVC), swallowing, and unilateral chewing. On muscle bellies, disposable, pre-gelled silver/silver chloride bipolar surface electrodes were parallel to muscle fibers. BIO-PAKeight® channels recorded electrical muscle activity (Bio-EMG III, BioResearch Associates, Inc. Brown Deer, WI). Results Full mouth embed upheld fixed prostheses patients had higher resting EMG activity than dentate and single curve implants. Full mouth embeds supported fixed prostheses and dentate patients had significantly different temporalis and digastric muscle mean EMG activity. Dentate people used their temporalis and masseter muscles more during the MVC than those with single-curve embedded upheld fixed prostheses limiting natural teeth or full-mouth implants. No event had the crucial item. Neck muscle differences were insignificant. All groups had higher SCM and digastric EMG activity during MVC than at rest. The single curve embed upheld fixed prosthesis group's temporalis and masseter muscles were significantly more active during gulping than the dentate and entire mouth groups. Single curve and entire mouth gulping SCM muscle EMG activity were similar. Digastric muscular EMG activity differed significantly between those with full-arch or partial-arch fixed prostheses and dentures. When instructed to bite one side, the masseter and temporalis front muscle mean EMG activity increased on the unrestricted side. Unilateral biting and temporalis muscle activation were comparable between groups. For the masseter muscle, the mean EMG was also higher on the functioning side, with no truly large differences between the three groups except for right-side biting when comparing the dentate and full mouth embed upheld fixed prosthesis groups and the single curve and full mouth groups. Conclusion The temporalis muscle activity difference was statistically significant in the full mouth implant-supported fixed prosthesis group.The three groups' static (clenching) sEMG analysis showed non-significant temporalis and masseter muscle activity increases. Full mouth swallowing increased digastric muscle activity. All three groups had similar unilateral chewing muscle activity except for the working side masseter muscle.

Evaluation of Masticatory Muscles in Adult Patients with Maxillary Hypoplasia Treated with Surgically Assisted Rapid Maxillary Expansion (SARME): A Retrospective Study.

Aim: The aim of the present study was to investigate modifications in electromyographic activity of temporal and masseter muscles before and after surgically assisted rapid maxillary expansion (SARME) in adult subjects. Materials and Methods: Data from 20 patients with unilateral posterior crossbite were selected retrospectively from the Orthodontics Department of the University of Genoa and the Department of Biomedical Surgical and Dental Sciences of the University of Milan, Fondazione IRCCS Ca’ Granda, Ospedale Maggiore Policlinico Milan. Inclusion criteria were set as skeletal class I; adult patients (age > 18); good general health; patients with a transverse maxillary deficiency with unilateral posterior crossbite and maxillary constriction ≥ 5 mm; Superficial electromyographic (EMG) examinations at T0 and T1. Exclusion criteria were smoking, metabolic bone diseases (e.g., hyperparathyroidism, vitamin C deficiency), chronic use of corticoids before or during treatment, parafunctional habits (e.g., bruxism), and temporomandibular joint dysfunction. The Shapiro−Wilk test was performed to check whether the data were normally distributed. Differences for each variable before and after SARME were analyzed with a paired t-test (p < 0.05). Results: The statistical analysis demonstrated no statistically significant differences between the EMG values taken before and after SARME regarding the standardized electrical activity of the masticatory muscles (masseter and anterior temporalis (p > 0.05)). Conclusions: Considering the specific conditions of this study, it can be concluded that SARME did not alter the EMG activity of the masseter and temporal muscles. The present study has shown that the masticatory musculature evaluated after approximately 8 months of therapy can adapt well to SARME.

A hiperboloide não influencia a atividade eletromiográfica dos músculos mastigatórios durante movimentos mandibulares em indivíduos com disturbiotemporomandibular

Abstract Introduction The hyperboloid is a masticatory device made of silicone with an hourglass (hyperbolic) shape that has been used as an aid to jaw functional orthopedic therapy. Objective To evaluate whether the hyperboloid device affects electromyographic (EMG) activity of the masticatory muscles during jaw movements in individuals with temporomandibular joint disorders (TMD) compared to controls. Methods The study sample consisted of 49 participants divided into two groups: mild, moderate and severe TMD (TMD group; n = 25) and a control group (n = 24). We evaluated EMG activities of temporal and masseter muscles bilaterally during jaw protraction and retraction, and left and right lateralization with and without the use of the hyperboloid device. Statistical analyses were performed using two-way ANOVA with two factors: group (healthy and TMD) and situation (with or without the use of the hyperboloid). Results We found higher EMG activity in the left temporal in the TMD group and no difference in EMG activities with the use of the hyperboloid device. Conclusion The use of the hyperboloid device did not affect EMG activity of the muscles evaluated in the groups studied. We found higher EMG activity of the left temporal muscle in participants with TMD. Long-term randomized studies should be conducted in individuals with TMD to investigate the effects of functional orthopedic therapy using the hyperboloid device with visual and quantitative feedback.

Comparative evaluation of bite pressure and electromyographic activity of temporalis and masseter muscles between osteoporotic and non-osteoporotic patients after prosthetic rehabilitation

Comparative evaluation of bite pressure and electromyographic activity of temporalis and masseter muscles between osteoporotic and non-osteoporotic patients after prosthetic rehabilitation

Response of masticatory muscles to treatment with orthodontic aligners: a preliminary prospective longitudinal study

The emergence of orthodontic aligners has provided an aesthetic and comfortable option for orthodontic treatment. However, the encapsulated design of the aligners can influence the masticatory muscles, and might compromise safe treatment. This preliminary longitudinal study aimed to investigate whether the use of orthodontic aligners affects the biting force and myoelectric activity of the superficial masseter and anterior temporal muscles. Ten subjects participated in the study and underwent treatment during an 8-month follow-up period. The root mean square (RMS), the median power frequency (MPF) of the surface electromyography (sEMG) signals, and the biting force (kgf) were recorded and normalized relative to the pretreatment condition. The data were analyzed by repeated-measure analysis of variance (ANOVA), with the significance level set at 5%. Both the superficial masseter and the anterior temporal muscles presented an increase in sEMG signal activity during the treatment, with a marked increase in the latter compared to the former (p<0.05). Moreover, a significant decrease in bite force was evidenced (p<0.05). This preliminary study observed that the orthodontic aligners affected the muscle recruitment pattern of masticatory muscles, and reduced biting performance during the 8-month follow-up period.

Masseter and digastric muscle activity evaluation using a novel electromyogram that utilizes elastic sheet electrodes.

To evaluate the reproducibility and reliability of a novel electromyogram (EMG) device with a flexible sheet sensor for measuring muscle activity related to mastication and swallowing. We developed a new EMG device made of elastic sheet electrodes to measure the masseter and digastric muscle activities for evaluating mastication and swallowing. To examine the measurement reproducibility of the new EMG device, masseter muscle activity was analyzed using the intraclass correlation coefficient (ICC). Further, we measured the maximum amplitude, duration, integrated value, and signal-to-noise ratio (SNR) using the new EMG device and conventional EMG devices and evaluated the reliability using ICC and Bland-Altman analysis. We confirmed high ICC (1,1) and ICC (2,1) scores (0.92 and 0.88, respectively) while measuring the reproducibility of the new EMG device. When compared to the active electrode EMG device, we found a high correlation for the maximum amplitude (0.90), duration (0.99), integrated values (0.90), and SNR (0.75), with no observation of significant fixed errors. Moreover, the regression coefficient was not significant for any of the evaluation items and no proportional error was observed. Compared with the passive electrode EMG device, the maximum amplitude and duration were highly correlated (0.73 and 0.89). In addition, the SNR exhibited a significant fixed error. In contrast, the regression coefficient was not significant for any of the evaluation items and no proportional error was observed. Our results suggest that the new EMG device can be used to reliably and reproducibly evaluate muscle activity during mastication and swallowing.

The neurophysiology aspect of congenital craniofacial deformities in children

Congenital craniofacial deformities in children are conditions with varying degrees of severity between minor and severe, they can be present at birth, but they can also be detected during the child's development. Material and methods. In the period 2014-2021, 57 children (29 boys and 28 girls), average age 9,1 ± 2,4 months, with craniofacial deformities from different medical centers in the Republic of Moldova were examined polysystemically. In this sense, we evaluated the state of the masseter, temporal and tongue muscles by electromyography with surface electrodes to determine the quality of their muscle activity. Recordings of the bioelectrical activity of muscle activity during exercise were performed using a Nihon Kohden portable electromyograph (Japan). Results. The balance dysfunction of the neuromuscular system in these children, as a neuro-physiological sign of pathological muscular weakness in the sucking reflex activity, is highlighted in 87.7% of cases by a marked asymmetry (p&lt;0.001) of the tongue and masseter muscles activity and, respectively less highlighted (p&lt;0.05) of the anterior temporal. Discussion. Thus, the EMG pattern evaluation highlights a decrease in the average amplitude of the action potentials (mV) mainly for the tongue, mm. masseters and temporalis on the left side, associated with an increase in the potential (ms) average duration from both the affected and the contralateral muscles, thus reflecting the reduction in their contraction capacity and the quality decrease in the act of sucking and mastication, predominantly on the left, in the child with congenital craniofacial deformities and disorders of the sucking reflex in infants. Conclusions. The neurophysiological examination highlights various forms of muscle function abnormalities in children with craniofacial deformities, which require multifunctional and multidisciplinary recovery.

Electromyographic Assessment of Masseter Muscle Activity: A Proposal for a 24 h Recording Device with Preliminary Data

The instrumental measurement of electromyographic (EMG) activity in the natural environment is the best strategy available to collect information on bruxism. The twofold aim of this study was to (1) introduce and discuss a novel EMG device for the assessment of awake (AB) and sleep bruxism (SB) in the home environment over 24 h and (2) present some preliminary data. Fifteen healthy volunteers (eight males and seven females; mean age: 48.2 ± 4.1 years) underwent 24 h EMG recording trials of their masseter muscle activity (MMA) with a miniaturized wireless device. This device allowed us to measure the durations of the different phases of the recordings (total duration, awake time, sleep time, and electrode dislodgement time) as well as the bruxism time index (BTI) and bruxism work index (BWI) for both the waking and sleeping hours. For the healthy volunteers, on average, the bruxism work index (BWI) values were 0.4 ± 0.2 and 0.1 ± 0.1 for awake and sleep, respectively, while the mean bruxism time index (BTI) values were 0.9 ± 0.5 for awake and 0.3 ± 0.1 for sleep. This investigation describes the technical features of a novel EMG recording device that permits the evaluation of masseter muscle activity in the home environment over 24 h. For the first time, a dedicated elaboration of the EMG signal allowed an assessment of muscle work and not just a count of purported SB/EMG events. Based on the multidisciplinary approach in the study of bruxism, such a methodology, thanks to its peculiar features, will allow researchers and clinicians to monitor the epidemiology of MMA and delve deeper into the awake and sleep bruxism correlates for tailored management in clinical settings.

Ecological Momentary Assessment of Masseter Muscle Activity in Patients with Bruxism.

According to the International Bruxism Consensus, bruxism refers to the activity of the masticatory muscles reflecting contraction disorders, regardless of whether it is during sleep (SB) or an awake (AB) state. The objective of the present study was to evaluate the activity of the masseter muscle by surface electromyographic (sEMG) recordings. This study was performed on 20 participants with self-reported "possible bruxism" (study group) and 20 participants with no self-reported bruxism (control group); all participants underwent an evaluation of the masseter muscle activity using the dia-BRUXO device, which provides numerical parameters regarding sEMG (the total duration and the type of bruxism specific events, the effort made by the masticatory muscles during the recording period, and the personal bruxism index of each participant). Participants from the study group presented more clenching events during AB, three times more frequent than the control group (p = 0.002, Mann-Whitney U test); for SB, the frequency of clenching and grinding events was comparable within the study group, being more frequent than for the control group; the mean value of the effort index was higher for AB (1.177%) than SB (0.470%) and the same for the duration index, with a mean value of 2.788% for AB and 1.054% for SB. All participants from the control group presented reduced values for all acquired parameters. Overall, the personal bruxism index in AB was approximately four times higher for the study group (2.251%) compared to the control group (0.585%) (p < 0.005, Mann-Whitney U test). Similar values were obtained for SB. All participants with "possible bruxism" from the study group presented a higher activity of the masseter muscle, which is specific for bruxism, thus being defined as "definite bruxism".

Physico‐chemical, sensory, antioxidant and electromyographic analyses of functional liquid diets (IDDSI levels 0–2) formulated for dysphagia patients

SummaryDysphagia is a symptom that refers to difficulty during the progression of the alimentary bolus from the mouth to the stomach. This may lead to malnutrition and negative effects on quality of life. Doctors and dieticians around the globe are looking for nutritious texture‐modified diets which are easier to chew and swallow thus could reduce the risks associated with choking in dysphagia patients. In this study, different functional liquid diets were formulated under International Dysphagia Diet Standardization Initiative (IDDSI) levels 0–2. The diets were made with incorporation of various fruits and vegetables to enhance their nutritional profile. The formulated liquid diets were analysed for their proximate composition, colour, antioxidant and sensory properties. The formulated liquid diets were high in nutrients and antioxidants. Also, all the formulated products were highly acceptable based on various sensory attributes indicating their potential to be incorporated in the diet plan of dysphagia patients. Electromyography (EMG) study was conducted to acquire myoelectrical activities of both masseter and suprahyoid muscles during oral processing of liquid diets by human subjects. The acquired EMG oral processing parameters significantly (P &lt; 0.05) correlated with ease of swallowing and IDDSI levels. Hence, EMG technique provides in vivo texture evaluation and real‐time swallowing patterns and thus can be an effective approach for the formulation of texture‐modified diets for dysphagia patients.

Emotional modulation of cortical activity during gum chewing: A functional near-infrared spectroscopy study.

Distinct brain regions are known to be associated with various emotional states. Cortical activity may be modulated by emotional states that are triggered by flavors during food intake. We examined cortical activity during chewing with different flavors and assessed the emotional modulation of cortical activity using multichannel near-infrared spectroscopy. Thirty-six right-handed volunteers participated in this crossover trial. The participants experienced positive and negative emotions from chewing flavorful (palatable) or less flavorful (unpalatable) gums, respectively for 5 min. Participants rated the taste, odor, and deliciousness of each gum using a visual analog scale. Bilateral hemodynamic responses in the frontal and parietal lobes, bilateral masseter muscle activation, and heart rate were measured during gum chewing. Changes in all measured data during gum chewing were also evaluated. The ratings of the tastes and odors of each gum significantly differed among the participants (P < 0.001). Hemodynamic response changes were significantly elevated in the bilateral primary sensorimotor cortex during gum-chewing, in comparison to resting. The difference in hemodynamic responses between palatable and unpalatable gum conditions was detected in the left frontopolar/dorsolateral prefrontal cortex. Muscle activation and heart rate were not significantly different between different gum types. Our findings indicate that differential processing in the left prefrontal cortex might be responsible for the emotional states caused by palatable and unpalatable foods.

Electromyographic evaluation of masseter and temporalis muscle activity after periodontal surgery: A prospective clinical trial

ObjectivesFollowing periodontal treatment, tooth supporting structures are restored to functionality and hence improve muscle activity. In this study, we aimed to investigate the influence of periodontal disease on muscle activity by electromyography and the subjective perception of periodontal therapy through the Oral Impact on Daily Performance (OIDP) questionnaire. MethodsSixty subjects with moderate to severe periodontitis were included. Periodontal condition was re-evaluated 4–6 weeks after non-surgical periodontal therapy (NSPT). Subjects with persistent probing pocket depths ≥5 mm were designated for flap surgery. All clinical parameters were recorded at baseline, 3 months and 6 months after surgery. The activities of the masseter and temporalis muscles were measured by electromyography and OIDP scores were recorded at baseline and 3 months. ResultsThe mean plaque index scores, probing pocket depths, and clinical attachment levels were reduced from baseline to 3 months. Mean EMG scores were compared at baseline and 3 months post-surgery. The mean OIDP total score prior to and after periodontal therapy was significantly different. ConclusionThere was a statistically significant correlation between clinical parameters, muscle activity and a patient's subjective perception. Therefore, it can be concluded that successful periodontal flap surgery led to improvements in masticatory efficiency and subjective perception, as determined by the OIDP questionnaire.

Effect of four conservative treatment methods on the muscular activity of masseter and temporalis muscles for subjects with temporomandibular joint disc displacement with reduction

Effect of four conservative treatment methods on the muscular activity of masseter and temporalis muscles for subjects with temporomandibular joint disc displacement with reduction

Muscle Activity in Pre-Treatment and Post-Treatment Oral Submucous Fibrosis Patients: Electromyography Study.

Background Oral submucous fibrosis (OSMF) is a premalignant condition of insidious onset which affects the oral mucosa, pharynx, and esophagus. The muscles of mastication are known to be affected resulting in limited mouth opening. Electromyography (EMG) is a sophisticated method of measuring and evaluating muscle activity. Previously, EMG was primarily utilized in medical sciences, but it is currently being used extensively in both the medical and dentistry fields. Objectives The aim of the study is to evaluate the electromyographic activity of masseter muscle in OSMF patients before and after treatment and to compare with healthy controls. Materials and Methods This prospective case-control clinical study comprised 180 OSMF patients who were divided into four groups and 45 healthy individuals served as the control group. The OSMF individuals were injected with hyaluronidase 1,500 IU mixed in 1.5 ml of dexamethasone and 0.5 ml of lignocaine HCL intralesionally twice a week for one month along with a basic physiotherapy regimen consisting of mouth exercises two times daily. The control subjects were given placebo capsules. The treatment was carried out for a month and the electromyographic masseter muscle activity was evaluated among the OSMF patients and control group before and after treatment. Results The results revealed that the electromyographic activity of master muscles in OSMF patients showed increased activity when compared with healthy controls. Patients with OSMF showed decreased muscle activity after treatment. Conclusion When compared with healthy controls, OSMF patients had higher electromyographic activity of the masseter muscles and the muscle activity was decreased following treatment. In OSMF patients, EMG may help in determining the involvement of the mastication and facial expression muscles. It can also be used as a diagnostic tool to assess the treatment outcome of muscle activity in OSMF patients.

Electromyographic Activity of Masticatory Muscles in Asymptomatic Young Adults

Introduction: The masseter and the anterior part of the temporalis are the muscles mainly responsible for the clenching function. Clenching patterns and the activity of these muscles are not expected to differ between male and females, nor between different occlusal classes. Objective: The aim of this study was to determine whether the activity index of the masseter and temporalis muscles is related to occlusal class and gender. Methods: This study involved 145 eighteen-year-old Caucasian volunteers who underwent surface electromyography. The sEMG was analyzed at the moment of 100% occlusal contact. Occlusal classes were determined used plaster casts. Results: The Class I group contained 34 males and 63 females, while Class II had 11 males and 25 females. Comparison of the AcI data showed an insignificant relation between the genders in the activity indices of Classes I and II. Significant relation between male gender and predominance of the masseter muscles, as well as between female gender and an almost equal balance between the muscles, though with a tendency towards a predominance of the temporalis anterior. Conclusion: The activity of masseter muscles during clenching the teeth is bigger in the male than in the female group. Activity index is related to gender.

The Axial Length of the Eyeball and Bioelectrical Activity of Masticatory and Neck Muscles: A Preliminary Report.

Objective The present study aimed to evaluate the correlation of eye length and bioelectric activity of temporalis, masseter, digastric, and sternocleidomastoid muscles in women with myopia compared to healthy women. Methods Based on the exclusion and inclusion criteria, 42 women aged 24 years (±2 years) were eligible for the study. Two equally sized groups with myopic (n = 21) and emmetropic healthy subjects (n = 21) were formed. An electromyographic study of the examined muscles was performed in four conditions: at rest, during maximal voluntary clenching in the intercuspal position, during maximal voluntary clenching on dental cotton rollers, and during maximal mouth opening using BioEMG III (BioResearch Associates, Inc. Milwaukee, WI, USA). The IOL Master 500 (Carl Zeiss Meditec, Jena, Germany) was used to examine the eyeball length. Statistical analysis showed significant positive correlations during mouth opening in both groups with open and closed eyes. Results A greater number of correlations between the analyzed variables was observed in emmetropic women. In almost all cases, the longer axial eye length was associated with an increase in the bioelectrical activity of the analyzed muscles. Significant correlations were most often observed within the masseter and digastric muscles during the maximum mouth opening and at rest. Conclusion There is a relationship between the bioelectrical activity of the masticatory muscles and the axial length of the eyeball on the same side.

Combined Effects of Botulinum Toxin Injection and Oral Appliance Therapy on Lower Facial Contouring: A Randomized Controlled Trial.

(1) Background: Botulinum toxin (BoNT) injection is an esthetically effective and safe treatment for contouring the lower face. This study aimed to evaluate the combined effects of BoNT and supplementary oral appliance (OA) therapy on lower facial contouring. (2) Methods: We conducted a prospective randomized controlled trial from January 2015 to June 2016 at the Yonsei University Dental Hospital. Volunteers aged 20–45 years with masseter hypertrophy were randomly assigned to one of two groups: the non-OA group and the OA group. The non-OA group received BoNT injections alone, whereas the OA group received an OA in addition to BoNT injections. Changes in the bulkiest height of the lower face were evaluated by three-dimensional laser scanning before and 4, 8, 12, and 24 weeks after injections in both groups. (3) Results: In both groups, the bulkiest height reductions decreased, with a significant interaction between group (p = 0.046) and time (p < 0.001), although the overall reduction was at a similar level at 24 weeks. (4) Conclusions: The pattern of the bulkiest height reduction of the lower face after BoNT injection differed between standalone treatment and OA therapy, implying a normalizing effect of OA on masseter muscle activity.

Chronic Pain–Related Jaw Muscle Motor Load and Sensory Processing

Chronic pain associated with temporomandibular disorders (TMDs) may reflect muscle mechanoreceptor afferent barrage and dysregulated sensory processing. This observational study tested for associations between Characteristic Pain Intensity (CPI), physical symptoms (Patient Health Questionnaire–15 [PHQ-15]), and cumulative jaw muscle motor load (mV*s). In accordance with institutional review board oversight and Strengthening the Reporting of Observational Studies in Epidemiology guidelines, adult subjects gave informed consent and were identified via Diagnostic Criteria for TMD (DC-TMD) examination and research protocols. Subjects were assigned to ±Pain groups using DC-TMD criteria for myalgia. CPI scores characterized pain intensity. PHQ-15 scores were surrogate measures of dysregulated sensory processing. Laboratory tests were performed to quantify masseter and temporalis muscle activities (mV) per bite force (N) for each subject. In their natural environments, subjects recorded day- and nighttime electromyography from which cumulative jaw muscle motor loads (mV*s) were determined for activities consistent with bite forces of >1 to ≤2 and >2 to ≤5 N. Data were assessed using univariate analysis of variance, simple effects tests, K-means cluster classification, and 3-dimensional regression analyses. Of 242 individuals screened, 144 enrolled, and 125 with complete data from study protocols, there were 35 females and 15 males for +Pain and 35 females and 40 males for −Pain. Subjects produced 324 daytime and 341 nighttime recordings of average duration 6.9 ± 1.7 and 7.6 ± 1.7 h, respectively. Overall, +Pain compared to −Pain subjects had significantly higher (all P ≤ 0.002) CPI and PHQ-15 scores. Cumulative jaw muscle motor loads showed significant between-subject effects for time, diagnostic group, and sex (all P < 0.003), where motor loads tended to be higher for daytime versus nighttime, +Pain versus −Pain groups, and males versus females. Two clusters were identified, and regression relations showed associations of low-magnitude daytime masseter motor load, PHQ-15, and CPI scores for cluster 1 (n = 105, R2 = 0.44) and cluster 2 (n = 18, R2 = 0.80). Furthermore, these regression relations showed thresholds of motor load and PHQ-15 scores, above which there were nonlinear increases in reported pain.

Assessment of Electromyographic Changes in a Patient with Masseter Hypertrophy and Muscle Pain after Botulinum Injections: A Case Report and 5 Months Follow-up

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