Bichectomy Surgery and EMG Masticatory Muscles Function in Adult Women: A Longitudinal Study.

AIM: This longitudinal study aimed to evaluate the electromyographic activity of the masseter and temporal muscles in adult women who underwent buccal fat removal. MATERIALS AND METHODS: The sample consisted of 20 healthy adult women with no temporomandibular dysfunction and normal occlusion, who were assessed before, 30, and 60 days after the surgery. The electromyographic signal of the masseter and temporal muscles was captured through mandibular tasks including rest, protrusion, right and left laterality, and maximum voluntary contraction with and without parafilm. The results obtained were tabulated and the Shapiro-Wilk normality test was performed, which indicated a normal distribution. Statistical analysis was performed using the repeated measures test (p < 0.05). RESULTS: Significant differences were observed between time periods in maximum voluntary contraction for the left masseter muscle (p = 0.006) and in maximum voluntary contraction with parafilm for the right temporal (p = 0.03) and left temporal (p = 0.03) muscles. CONCLUSION: Bichectomy surgery did not modify the electromyographic activity of the masseter and temporal muscles during the rest task but may have influenced variations in the electromyographic signal during different mandibular tasks after 60 days of surgery, suggesting compensatory adaptations and functional recovery. CLINICAL SIGNIFICANCE: Understanding the impact of buccal fat removal surgery on the stomatognathic system function provides insights into postoperative functional recovery and potential compensatory adaptations, guiding clinical management and rehabilitation strategies for patients undergoing such procedures. How to cite this article: Cardoso AHDLS, Palinkas M, Bettiol NB, et al. Bichectomy Surgery and EMG Masticatory Muscles Function in Adult Women: A Longitudinal Study. J Contemp Dent Pract 2024;25(3):207-212.

Ultrasonographic evaluation of changes in the thickness, width, elasticity index and echogenic pattern of the masseter muscle after mandibular set-back surgery.

INTRODUCTION: The masseter muscle is one of the structures that undergoes significant changes following jaw movements in orthognathic surgery. This study aims to investigate the effects of mandibular setback surgery, performed in patients with skeletal class III deformity, on the thickness, width, elasticity index, and echogenic pattern of the masseter muscle. MATERIAL AND METHODS: This prospective case-control study enrolled patients with class III deformity who underwent mandibular setback surgery, while the control group consisted of class I patients. The predictor variable was the time measured at two different points: preoperative (T1) and postoperative 6 months (T2). The primary outcome variable focused on changes in the internal echogenic pattern of the masseter muscle. Secondary, tertiary, and quaternary outcome variables included changes in the thickness, width, and elasticity index of the masseter muscle, respectively. Gender, age, type of operation, and amount of movement were considered as covariates. Ultrasonography was employed to evaluate the outcome variables. RESULTS: The study group comprised 31 patients, including 17 females (mean age 22.24 ± 3.52 years) and 14 males (mean age 23.14 ± 2.65 years). The control group consisted of 16 females (mean age 23.34 ± 1.22 years) and 15 males (mean age 23.12 ± 1.76 years). Masseter muscle thickness increased significantly after mandibular setback surgery (p = 0.015). However, there was no statistically significant difference in masseter muscle width before and after surgery (p = 0.627), nor in the elasticity index (p = 0.588). Furthermore, a statistically significant transformation from Type I to Type II was observed in the internal echogenic pattern of the muscle (p = 0.039). Additionally, there was no statistically significant correlation between the amount of mandibular movement performed and the changes in the masseter muscle. CONCLUSIONS: Mandibular setback surgery leads to changes in both the physical and structural properties of the masseter muscle.

Masseter muscle cross-sectional area and late implant failure: A case-control study.

INTRODUCTION: Occlusal overload is considered to be one of the causes of late implant failure. However, it is unclear whether the magnitude of the patient's occlusal force is a risk factor for late implant failure. PURPOSE: This case-control study aimed to clarify the association between the cross-sectional area (CSA) of the masseter muscle and late implant failure. METHODS: This case-control study was limited to implant-supported fixed prostheses. We compared cases with at least one late implant failure (n = 25 patients) to controls (n = 82 patients) without implant failure. Patients were matched by age, sex, year of surgery, jaw and tooth type, and bone graft. Log-rank and Cox proportional hazard regression analyses were used to identify possible risk factors for late implant failure. RESULTS: The incidence of late implant failure was significantly associated with masseter muscle CSA ≥504.5 mm2 (hazard ratio: 4.43; 95% CI: 1.82-10.79; p < 0.01). CONCLUSION: Higher masseter muscle CSA increases the risk of late implant failure.

EMG-assisted forward dynamics simulation of subject-specific mandible musculoskeletal system.

Assessment of mandibular dynamics is essential for examining stomatognathic functions, and many kinds of stomatognathic diseases, such as temporomandibular joint (TMJ) disorder and jaw tumors, require individual diagnosis and rehabilitation treatments. Musculoskeletal models of the mandible system provide an efficient tool for fulfilling these tasks, but most existing models are generic, without direct correlation to subject-specific data. For this reason, the objective of this study was to establish a subject-specific mandible modeling framework based on clinical measurements, including medical imaging, jaw kinematics, and electromyographic (EMG) acquisition. First, a non-rigid iterative closest point method was performed to register muscle insertion sites. A flexible multibody approach was introduced to describe the large deformation behavior of jaw muscles. The EMG signals of the temporalis and masseter muscles were then utilized to determine their active forces. Meanwhile, a feedback loop for tracking desired mandibular kinematics was presented to calculate the activations of jaw opening and pterygoid muscles. The subject-specific muscle forces and TMJ joint loading during jaw opening-closing movements were then calculated based on forward-inverse coupling dynamics procedure. As a validation of the proposed framework, the mandible trajectories of seven healthy subjects were predicted and compared with experimental data. The results demonstrated unintentional movement of the head-neck complex together with the activation patterns of jaw opening and lateral pterygoid muscles for different people. The proposed framework combines musculoskeletal modeling with dental biomechanical testing, providing an efficient method of predicting and understanding the dynamics of subject-specific mandible systems.

Variação da atividade elétrica entre o repouso e a máxima contração voluntária dos músculos masseteres em homens adultos / Variation of electrical activity between rest and maximum voluntary contraction of masseter muscles in adult men / Variación de la actividad eléctrica entre el descanso y la contracción voluntaria máxima de los músculos maseteros en hombres adultos

Introdução: A eletromiografia de superfície (EMGs) é um exame objetivo, indolor, não invasivo e de fácil aplicação utilizado para avaliar as atividades elétricas de determinado músculo ou grupo muscular durante a máxima contração voluntária, repouso e dinâmica funcional. Objetivo: Comparar a variação do potencial elétrico dos músculos masseteres entre o repouso e máxima contração voluntária em indivíduos com faixas etárias diferentes. Método: A pesquisa foi aprovada em comitê de ética e executada na Clínica Escola do Departamento de Fonoaudiologia da Universidade Federal de Sergipe obedecendo aos rigores éticos e de biossegurança. A amostra foi composta por 26 adultos sem queixas orofaciais, sexo masculino e idade variando entre 26 e 42 anos, divididos em Grupo 1 e Grupo 2, os quais assinaram um termo de consentimento livre e esclarecido concordando com a participação na pesquisa. Os voluntários foram submetidos à avaliação eletromiográfica dos músculos masseteres durante o repouso e máxima contração voluntária. Resultados: Houve uma diminuição da atividade elétrica do masseter quando se comparou o G1 com o G2, porém não foi observada uma linearidade desse declínio ao analisar o universo estudado. Por isso, deve-se levar em consideração que o envelhecimento é um processo fisiológico particular de cada ser, sendo influenciado por múltiplos fatores intrínsecos e extrínsecos ao organismo. Observou-se, também, que no repouso nenhum indivíduo teve absolutamente 0 nos seus registros eletromiográficos, caracterizando um estado basal de atividade elétrica para garantia do tônus. Conclusão: Foi verificado que os voluntários com 30 anos ou mais apresentaram um declínio nos potenciais mioelétricos e, possivelmente, um déficit de força associado.

Introduction: Surface electromyography (EMGs) is an objective, painless, non-invasive and easily applied test used to assess the electrical activities of a particular muscle or muscle group during maximum voluntary contraction, rest and functional dynamics. Objective: Compare the variation in the electrical potential of the masseter muscles between rest and maximum voluntary contraction in individuals with different age groups. Method: The research was approved by the ethics committee and carried out at the Clínica Escola of the department of Speech, Language and Hearing Sciences at the Federal University of Sergipe, obeying ethical and biosafety rigors. The sample consisted of 26 adults without orofacial complaints, male with age from 26 to 42 years old, divided into Group 1 and Group 2, who signed a consent form agreeing to participate in the research. The volunteers underwent electromyographic evaluation of the masseter muscles during rest and maximum voluntary contraction. Results: There was a decrease in the electrical activity of the masseter when comparing G1 to G2; however, there was no linearity of this decline when analyzing the universe studied. Therefore, it must be taken into account that aging is a particular physiological process of each individual, being influenced by multiple factors, intrinsic and extrinsic to the organism. It was also observed at rest, no individual had absolutely 0 in their electromyographic records, characterizing a baseline state of electrical activity to guarantee tone. Conclusion: It was found that volunteers aged 30 years or more showed a decline in myoelectric potentials and possibly an associated strength deficit.

Introducción: Electromiografía de superficie (EMG) es una prueba objetiva, indolora, no invasiva y de fácil aplicación que se utiliza para evaluar actividades eléctricas de un músculo o grupo muscular en particular durante la contracción voluntaria máxima, el reposo y la dinámica funcional. Objetivo: Comparar la variación del potencial eléctrico de los maseteros entre reposo y contracción voluntaria máxima en individuos de diferentes grupos de edad. Método: La investigación fue aprobada por el comité de ética y realizada en la Clínica Escola del departamento de logopedia de la Universidad Federal de Sergipe obedeciendo rigores éticos y de bioseguridad. La muestra estuvo conformada por 26 adultos sin quejas orofaciales, varones y edades comprendidas entre 26 y 42 años dividido en Grupo 1 y Grupo 2, quienes firmaron formulario de consentimiento aceptando participar en la investigación. Los voluntarios se sometieron a evaluación electromiográfica de los músculos maseteros durante reposo y la máxima contracción voluntaria. Resultados: Hubo disminución en la actividad eléctrica del masetero cuando se comparó G1 con G2, sin embargo no hubo linealidad de esta disminución al analizar el universo estudiado. Por tanto, hay que tener en cuenta que el envejecimiento es proceso fisiológico particular de cada ser, siendo influenciado por múltiples factores intrínsecos y extrínsecos al organismo. También se observó que en reposo ningún individuo tenía absolutamente 0 en sus registros electromiográficos, caracterizando estado basal de actividad eléctrica para garantizar el tono. Conclusión: Se encontró que los voluntarios de 30 años o más mostraron una disminución en los potenciales mioeléctricos y posiblemente un déficit de fuerza asociado.

Modelo lineal vs. vectorial: estimación del movimiento mandibular y trabajo mecánico / Linear vs. vector model: estimation of mandible motion and mechanical work

Objetivo: Determinar los momentos de fuerza del haz superficial del masetero (SMH) obtenidos por modelos lineal y vectorial. Métodos: Investigación comparati-va in silico. Se obtuvo la fuerza del SMH con dinamó-metro en 12 pacientes varones adultos jóvenes para calcular el momento de la fuerza y trabajo mecánico a través de simulaciones en JAVA+ con NetBeans8.2. La descomposición de la fuerza fue F.cos α(x,y) y F.cos α(x,y,z) en el modelo lineal y vectorial respectivamen-te. Los momentos de fuerza fueron comparados por ANOVA (p<0,05). Resultados: La fuerza del SMH unila-teral obtenida con dinamómetro (2,5±0,1N) no difirió significativamente del modelo lineal (2,6±0,05N), pero difirió (p<0,001) del vectorial: 1,7, 2,2, 4,2N en x,y,z (general 2,7±0,02N). El momento medio de la fuerza en el modelo vectorial fue -17,9, -15,5, +14,3N.m-2, apuntando a la inclinación mandibular en el eje lateral en dirección caudal anterior, movimiento de inclina-ción en el eje lateral en la dirección cráneo-medial, e inclinación en el eje craneal en la dirección lateral-an-terior. El modelo lineal mostró momento de fuerza de 13,5N.m-2 apuntando un movimiento traslacional en dirección caudal-craneal en el eje anterior-posterior y menor trabajo mecánico del SMH (p=0,012). Con-clusión: Los modelos vectoriales son más eficientes proporcionando datos detallados para estimar los momentos de fuerza y el trabajo mecánico del SMH, y deben incluirse en los algoritmos de cálculo utilizados por dinamómetros (AU)

Objective: to determine the moments of force exerted by the superficial masseter head (SMH) obtained through linear models and vector ones. Methods: comparative in silico research. Data of SMH force obtained with dynamometer in 12 young adult male patients was used to calculate the moment of the force and mechanical work through simulations in JAVA+ performed with NetBeans8.2. Force decomposition was F.cos α(x,y) and F.cos α(x,y,z) in the linear and vector model respectively. The moments of force were compared by ANOVA (p<0.05). Results: Dynamometrical unilateral SMH force (2.5±0.1N) did not differ significantly from the linear model (2.6±0.05N), but differed (p<0.001) from the vector model: 1.7, 2.2, 4.2N on x,y,z (overall 2.7±0.02N). The mean moment of the force in the vector model was -17.9, -15.5, +14.3N.m-2, pointing to mandible's inclination on the lateral axis in anterior-caudal direction, inclination movement on the lateral axis in the cranio-medial direction and inclination on the cranial axis in the lateral-anterior direction. The linear model showed a moment of force of 13.5N.m-2 pointing to translational motion on caudal-cranial direction on the anterior-posterior axis and lower SMH mechanical work (p=0,012). Conclusion: Vector models are more efficient to provide detailed data to estimate the moments of force and mechanical work of SMH and should be included in the calculation algorithms used by dynamometers (AU)

Functional morphology and fiber types of the masseter muscles of two caviomorph rodents with contrasting lifestyles, Ctenomys talarum (Ctenomyidae) and Cavia aperea (Caviidae).

The aim of this work is the analysis of histochemical and morphometric properties of the masseter muscles of Ctenomys talarum and Cavia aperea. The former belongs to a subterranean rodent clade, Ctenomyidae, which has evolved a robust masticatory apparatus adapted to chisel-tooth digging and processing of abrasive grasses; C. aperea belongs to the family Caviidae, with relatively graceful jaws and mandibular musculatures, consistent with less mechanically challenging diets. Adult males were captured, immediately transported to the laboratory, and euthanized in a CO2 chamber. The musculus masseter superficialis and musculus masseter profundus on the left side of the animals were used to analyze the histochemical composition of the fiber types treated with myosin adenosine triphosphatase, succinate dehydrogenase and periodic acid Schiff. The mean fiber diameters, relative areas, and frequencies of each muscle fiber type were calculated. The mm. masseter superficialis and masseter profundus on the right side were used to measure the physiological cross-sectional area (PCSA). Based on this measurement, the internal force (F) was estimated. In the m. masseter profundus of both species and in the m. masseter superficialis of C. aperea intermediate fast oxidative-glycolytic fibers (FOGi) predominated. In the mm. masseter superficialis and masseter profundus of C. talarum the relative area of fast glycolytic (FG) fibers was greater than that of the muscles of C. aperea, whose main muscle fiber component is FOGi fibers. When corrected for body mass differences, PCSA was higher for the mm. masseter superficialis of C. talarum. This and the larger relative area of FG fibers, probably contributes to the exertion of large bite forces in C. talarum, as measured in previous studies.

Functional analysis of the rat soft palate by real-time wireless electromyography.

OBJECTIVE: The aim of this study was to analyze the function of the palatal muscles in vivo by real-time wireless electromyography in rats. The effects of palatal wounding were also analyzed. METHODS: Microelectrodes were implanted six rats; in the masseter muscle (two-rats) for comparison, in the unwounded soft palate (two-rats) and the soft palate that received a surgical wound (two-rats). Two weeks after implantation, a wound was made in the soft palate using a 1 mm biopsy-punch. Electromyographic measurements and video-recordings were taken weekly to monitor train-duration and peak-amplitude during eating, grooming and drinking. RESULTS: The train-duration of the masseter muscle during eating was 0.49 ±â€¯0.11 s (rat-1) and 0.56 ±â€¯0.09 s (rat-2), which was higher than during grooming. In the unwounded soft palate the train-duration during eating was 0.63 ±â€¯0.12 s (rat-1) and 0.69 ±â€¯0.069 s (rat-2), which was higher than during grooming and drinking. The peak-amplitude for eating in the normal soft palate before surgery was 0.31 ±â€¯0.001 mV (rat-1) and 0.33 ±â€¯0.02 mV (rat-2). This decreased to 0.23 ±â€¯0.03 mV and 0.25 ±â€¯0.11 mV respectively, after surgery. For drinking the peak-amplitude was 0.30 ±â€¯0.01 mV (rat-1) and 0.39 ±â€¯0.01 mV (rat-2) before surgery, which decreased to 0.23 ±â€¯0.09 mV and 0.20 ±â€¯0.14 mV respectively, after surgery. CONCLUSION: The reduced peak-amplitude suggests impaired soft palate function after wounding. This is the first study into the in vivo function of the soft palate after surgical wounding. This model will contribute to develop strategies to improve soft palate function in patients.

Potential of Using Shear Wave Elastography in the Clinical Evaluation and Monitoring of Changes in Masseter Muscle Stiffness.

The study aimed to evaluate masseter muscle stiffness in adult healthy volunteers referred to a massage treatment and also to investigate whether shear-wave elastography can be used to monitor the effect of massage on the masseter muscle. The study included 21 healthy volunteers, who were subjected to a 30-minute massage of the masseter muscle. Muscle stiffness was measured by shear-wave elastography before and directly after the massage. Pain during the massage was assessed using the visual analogue scale (VAS). The data of 20 patients (one excluded due to severe pain) with a median age of 34.5 years were analysed. The stiffness values were 11.46 ± 1.55 kPa before and 8.97 ± 0.96 kPa after the massage (p < 0.0001). The mean drop was 2.49 ± 1.09 kPa. The greatest decrease was observed in people with higher elasticity values before the massage (r = 0.79; p < 0.0001). The median intensity of pain was 7.2 (range: 6-9.5). We concluded that shear-wave elastography is a sensitive tool to monitor changes in the stiffness of the masseter muscle.

Relação entre os músculos masseter e esternocleidomastoideo nas situações de flexão e rotação da coluna cervical, em mastigação e máxima intercuspidação habitual, analisados através da atividade eletromiográfica / Relationship between the masseter and sternocleidomastoid muscles in the flexion and rotation functions of the cervical, chewing and maximum habitual intercuspation, analyzed by the electromyographic activity

Na atualidade, com as frequentes inovações tecnológicas agregadas aos telefones celulares favorecendoseu uso excessivo, altos níveis de estresse e o ritmo acelerado da vida, inconscientemente, as pessoas têmadotado novas e diferentes posturas corporais, que direta ou indiretamente interferem na posição da colunavertebral. Um importante músculo postural do pescoço é o esternocleidomastoideo, cuja relevante função éa de estabilizar. Objetivo: analisar a possível relação entre os músculos masseter e esternocleidomastoideo,em diferentes posições da cabeça e da coluna cervical, nas situações de mastigação, repouso e máximaintercuspidação habitual. Metodologia: os dados foram coletados inicialmente com cabeça e coluna eretas,em repouso e em máxima intercuspidação habitual. Em seguida, coletou-se, sempre em mastigação, com acabeça e a coluna eretas, inclinadas para frente, para trás, para direita, para esquerda, giradas para direita epara esquerda. Todos os momentos de coleta de dados ocorreram por 5 segundos em cada posição. Resultados:nota-se um aumento na atividade elétrica do músculo esternocleidomastoideo quando a mastigaçãoacontece com a cabeça e a coluna fora da posição ereta. Em algumas posições da cabeça, esse aumento, emvalores absolutos, não é observado de forma relevante no sexo feminino, sendo notado no masculino. Conclusões:existe uma relação de trabalho entre os músculos masseter e esternocleidomastoideo. Essa relaçãosugere que o segundo músculo trabalha na tentativa de estabilizar a cabeça para otimizar o ato mastigatório,ação essa notadamente encontrada no sexo masculino e de forma menos ativa no sexo feminino.(AU)

Nowadays, with the frequent technological innovations added to cell phones favoring their excessive use, high levels of stress and the fast pace of life, people have unconsciously adopted new and different body postures that directly or indirectly interfere in the position of the spine. An important postural muscle of the neck is the sternocleidomastoid, whose important function is to stabilize it. Objective: to analyze the possible relationship between the masseter and sternocleidomastoid muscles, in different positions of the head and cervical spine, in situations of chewing, resting and maximum habitual intercuspation. Methodology: data were collected initially with head and spine erect, at rest and at maximum habitual intercuspation. Then, it was collected, always chewing, with the head and column erect, tilted forward, backward, right, left, turned to the right and turned to the left. All moments of data collection occurred for 5 seconds in each position. Results: An increase in the electrical activity of the sternocleidomastoid muscle is observed when chewing occurs with the head and spine out of the upright position. In some positions of the head this increase, in absolute values, is not observed in a relevant way in the female sex, being noticed in the male. Conclusions: there is a working relationship between the masseter and sternocleidomastoid muscles. This relationship suggests that the second muscle works in an attempt to stabilize the head to optimize the masticatory act, an action that is notably found in men and less actively in women.(AU)

Sonoelastographic evaluation of the masseter muscle before and after mandibular setback surgery.

AIMS: The purpose of this study is to compare the thickness and elasticity of the masseter muscle before and after orthognathic surgery in patients with class III skeletal deformity and to investigate the relationship between the sonographic changes in the masseter muscle and the amount of mandibular setback. SUBJECTS AND METHODS: The study group consisted of 14 patients with skeletal class III malocclusions who had orthognathic surgery. The control group consisted of 14 patients who had dental and skeletal class I occlusion. Muscle thickness measurements were performed with B-mode and high-frequency linear scanning probe of the ultrasound device. Elastography feature and muscle hardness ratio were obtained by applying compression and decompression on muscles at rest and during maximum contraction in the transverse plane. Patients were categorized into two groups according to the mandibular setback as <5 mm and ≥5 mm. RESULTS: The masseter muscle thickness after surgery was found statistically increased bilaterally in both at rest and during contraction for the study group (P < 0.05). No difference was found between preoperative orthognathic measurements and postoperative measurements for elasticity index ratio measurements (P > 0.05). CONCLUSION: We believe that in the present study important findings have been emphasized for further research aiming to investigate the possible relationship between masticatory alterations and surgical outcomes after orthognathic surgery.

Endoscope-Assisted Avulsion of the Masseter Nerve Attached to the Temporomandibular Joint Disc for the Treatment of Hemimasticatory Spasm: A Report of Two Cases.

OBJECTIVE: Hemimasticatory spasm (HMS) is a rare masticatory muscle disorder. Drug therapy, microvascular decompression, and botulinum toxin have had varying efficacy and adverse effects. We have reported the cases of 2 patients who had undergone a novel therapy for HMS, based on endoscope-assisted nerve avulsion of the masseter nerve attached to the temporomandibular joint (TMJ) disc. METHODS: We performed a retrospective study of 2 patients with HMS who had undergone surgery from June 2014 to June 2017 at the oral surgery department of Shanghai Ninth People's Hospital affiliated to Shanghai JiaoTong University School of Medicine. Both patients had undergone endoscope-assisted avulsion of the masseter nerve attached to the TMJ disc. Both patients were evaluated by electromyography postoperatively and were followed up for 36 months after surgery. RESULTS: Both patients had had all the signs and symptoms of HMS. The HMS had resolved immediately after surgery. At 1 week after surgery, electromyography revealed that the high-frequency group discharge potential in the motor unit accompanying the spasm was no longer present, and the effect was maintained for the 36-month follow-up period. These results indicated a good curative effect. Electromyography also showed strength weakness and mild shape atrophy of the masseter muscle on the affected side. CONCLUSIONS: Endoscope-assisted avulsion of the masseter nerve attached to the TMJ disc showed a good curative effect, little trauma, few complications, and a quick postoperative recovery. It could be used as an alternative treatment of HMS for selected patients.

Correlation between masseter muscle activity and maximum bite force among various facial divergence pattern / Correlación entre la actividad muscular masetera y la fuerza máxima de mordida entre varios patrones de divergencia facial

Objective: To comparatively assess electromyographic (EMG) activity of masseter muscle and maximum bite force among various facial divergence pattern. To compare bilateral variation therefore derive the clinical importance changes in masseter EMG activity. Materials and Methods: The sample size comprised of 90 subjects, age ranging from 16-25 years. They were further classified under three subgroups-normodivergent, hypodivergent and hyperdivergennt based on the cephalometric values. Tekscan Flexiforce B201H sensor along with the associated software was used to record the bite force. The EMG of the superficial masseter muscle was recorded using Biotech Neurocare 2000 surface electromyography machine. The muscle activity was recorded bilaterally from the superficial masseter. The data obtained were statistically analyzed using ROC curve at p<0.05. Results: The bite force of the Hypodivergent group (571.83N±36.65) was more than the Normodivergent (387.26±27.20) and Hyperdivergent groups (373.21N±29.23). The EMG recording of masseter muscle activity in Hypodivergent group was significantly higher than Normodivergent and Hyperdivergent groups. (p-value= <0.01). A significant correlation existed between masseter activity and bite force. Conclusion: The bite force of Hypodivergent jaw base individuals is highest followed by Normodivergent and least in Hyperdivergent individuals.The strong correlation between the muscular activity and the bite force is definitely a contributor to the anchorage value during treatment by fixed Orthodontics.

Objetivo: evaluar comparativamente la actividad electromiográfica (EMG) del músculo masetero y la fuerza de mordida máxima entre varios patrones de divergencia facial. Para comparar la variación bilateral, por lo tanto, derive la importancia clínica de los cambios en la actividad EMG del masetero. Materiales y métodos: El tamaño de la muestra comprende 90 sujetos, con edades comprendidas entre 16 y 25 años. Además, se clasificaron en tres subgrupos: normodivergente, hipodivergente e hiperdivergénico según los valores cefalométricos. Se usó el sensor Tekscan Flexiforce B201H junto con el software asociado para registrar la fuerza de mordida. La EMG del músculo masetero superficial se registró utilizando la máquina de electromiografía de superficie Biotech Neurocare 2000. La actividad muscular se registró bilateralmente a partir del masetero superficial. Los datos obtenidos se analizaron estadísticamente utilizando la curva ROC a p<0,05. Resultados: la fuerza de mordida del grupo hipodivergente (571.83N±36.65) fue mayor que la de los grupos normodivergentes (387.26±27.20) y los hiperdivergentes (373.21N±29.23). El registro EMG de la actividad muscular masetera en el grupo hipodivergente fue significativamente más alto que en los grupos normodivergente e hiperdivergente. (valor de p=<0.01). Existía una correlación significativa entre la actividad del masetero y la fuerza de mordida. Conclusión: la fuerza de mordedura de los individuos hipodivergentes de la mandíbula es más alta seguida por la de Normodivergent y menos en los individuos hiperdivergentes. La fuerte correlación entre la actividad muscular y la fuerza de mordedura definitivamente contribuye al valor de anclaje durante el tratamiento con ortodoncia fija.

Changes in cross-sectional measurements of masseter, medial pterygoid muscles, ramus, condyle and occlusal force after bi-maxillary surgery.

PURPOSE: The purpose of this study was to examine changes in masseter and medial pterygoid muscles, ramus, condyle and occlusal force after bi-maxillary surgery in class II and III patients. SUBJECTS AND METHODS: The subjects were 42 patients (84 sides) who underwent sagittal split ramus osteotomy with Le Fort I osteotomy (21 class II cases: mandibular advancement and 21 class III cases: mandibular setback). The cross-sectional measurements of the masseter and medial pterygoid muscles, ramus and condyle were measured in horizontal plane images by computed tomography (CT), before and 1 year after the operation. Occlusal force and contact area were also recorded before and 1 year after the operation. RESULTS: Preoperatively, class II was significantly larger than class III in masseter width (P = 0.0068), masseter area (P < 0.0001) and medial pterygoid length (P < 0.0001). However, class II was significantly smaller than class III in medial pterygoid width (P < 0.0001). After 1 year, class II was significantly smaller than class III in masseter length (P = 0.0017). Class II was still larger than class III in medial pterygoid area after 1 year (P = 0.0343). Class II was significantly larger than class III in condylar angle pre-operatively (P < 0.0001) and after 1 year (P = 0.0006). After 1 year, class II decreased significantly more than class III in condylar thickness (P = 0.0020), condylar width (P < 0.0001) and condylar area (P < 0.0001). CONCLUSION: This study suggested that changes in the cross-sectional measurements of masseter and medial pterygoid muscles and the condyle differed between class II and class III patients, although occlusal force did not significantly change 1 year after surgery in both groups.

Investigation of the activation of the temporalis and masseter muscles in voluntary and spontaneous smile production.

INTRODUCTION: Masticatory muscles or their nerve supply are options for facial reanimation surgery, but their ability to create spontaneous smile has been questioned. This study assessed the percentage of healthy adults who activate the temporalis and masseter muscles during voluntary and spontaneous smile. METHODS: Healthy volunteer adults underwent electromyography (EMG) studies of the temporalis and masseter muscles during voluntary and spontaneous smile. Responses were repeated three times and recorded as negative, weakly positive, or strongly positive according to the activity observed. The best response was used for analysis. RESULTS: Thirty healthy adults (median age: 34 years, range: 25-69 years) participated. Overall, 92% of the masseter muscles were activated during voluntary smile (22% strong, 70% weak). Seventy-seven percent of the masseter muscles were activated in spontaneous smile (12% strong, 65% weak). The temporalis muscle was activated in 62% of responses in voluntary smile (15% strong, 47% weak) and in 45% of responses in spontaneous smile (13% strong, 32% weak). No significant difference was found for males vs females or closed vs open mouth smiles. There was no significant difference in responses between voluntary and spontaneous smiles for the temporalis and masseter muscles, and their use in voluntary smile did not predict activity in spontaneous smile. CONCLUSIONS: Our study has shown that masseter and temporalis are active in a high proportion of healthy adults during voluntary and spontaneous smiles. Further work is required to determine the relationship between preoperative donor muscle activation and postoperative spontaneous smile, and whether masticatory muscle activity can be upregulated with appropriate training.

Functional and molecular outcomes of the human masticatory muscles.

The masticatory muscles achieve a broad range of different activities such as chewing, sucking, swallowing, and speech. In order to accomplish these duties, masticatory muscles have a unique and heterogeneous structure and fiber composition, enabling them to produce their strength and contraction speed largely dependent on their motor units and myosin proteins that can change in response to genetic and environmental factors. Human masticatory muscles express unique myosin isoforms, including a combination of thick fibers, expressing myosin light chains (MyLC) and myosin class I and II heavy chains (MyHC) -IIA, -IIX, α-cardiac, embryonic and neonatal and thin fibers, respectively. In this review, we discuss the current knowledge regarding the importance of fiber-type diversity in masticatory muscles versus supra- and infrahyoid muscles, and versus limb and trunk muscles. We also highlight new information regarding the adaptive response and specific genetic variations of muscle fibers on the functional significance of the masticatory muscles, which influences craniofacial characteristics, malocclusions, or asymmetry. These findings may offer future possibilities for the prevention of craniofacial growth disturbances.

Masseter and temporalis muscle electromyography findings after lower third molar extraction.

BACKGROUND: The main clinical application of electromyography is to detect abnormalities in muscle function, to assess muscle activity for purposes of recruitment, and in the biomechanics of movement. OBJECTIVES: To analyze electromyography (EMG) findings for masticatory muscles during chewing following surgical extraction of lower third molars, and to determine any correlation between pain, inflammation, trismus, and the EMG data registered. MATERIAL AND METHODS: This prospective study included 31 patients. Surface EMG was used to study masseter and temporalis muscle function before lower third molar extraction and 72 hours and seven days after surgery. Clinical variables, pain, inflammation, and trismus were registered before and after surgery. RESULTS: Studying the area and size of the masticatory muscles, higher values were found for temporalis than masseter muscles, regardless of the surgical side, which points to the greater involvement of the temporalis muscle in mastication. Comparing the side where surgery had been performed with the non-surgical side, a sharp and statistically significant reduction in amplitude and area were noted on the surgical side reflecting major functional affectation. One week after surgery, amplitude and area had almost returned to base-line values, indicating almost complete recovery. While pain decreased progressively after surgery, inflammation peaked at 72 hours, while mouth opening reached a minimum at this time, returning to normality within the week. CONCLUSIONS: Surgical extraction of lower third molars produces changes to electromyography activity that are more evident during the first hours after surgery and closely related to the intensity of pain suffered and the patient's inflammatory responses, although they are not related to mouth opening capacity.