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Revista CEFAC

versão On-line ISSN 1982-0216

Rev. CEFAC vol.14 no.4 São Paulo jul./ago. 2012  Epub 29-Maio-2012 

Surface electromyography of the masseter muscle during chewing: a systematic review



Gerlane Karla Bezerra Oliveira NascimentoI; Daniele Andrade da CunhaII; Leilane Maria de LimaIII; Klyvia Juliana Rocha de MoraesIV; Leandro de Araújo PernambucoV; Renata Milena Freire Lima RégisVI; Hilton Justino da SilvaVII

ISpeech therapist of Health Secretary from Paraiba State, João Pessoa, Brazil; Master in Pathology from Federal University of Pernambuco - UFPE
IISpeech therapist; Institutional Researcher of Recife-Estacio Faculty - Estacio FIR; Doctor in Nutrition from Federal University of Pernambuco - UFPE
IIISpeech therapist from Clinic CEFA, Recife, PE, Brazil; Specialist in Orofacial Movement with a focus on Dysphagia - FUNESO
IVPhysical therapist; Preceptor of Cardio-respiratory Physiotherapy from Salgado de Oliveira University - UNIVERSO, Recife, Brazil; Master in Pathology from Federal University of Pernambuco - UFPE
VSpeech therapist; Assistant I Professor of Speech Therapist Course of the Federal University of Rio Grande do Norte - UFRN, Natal, RN, Brazil; Master of Health Sciences from Federal University of Pernambuco - UFPE
VISpeech therapist from Clinic CEFA - Recife, PE - Brazil; Specialist in Orofacial Motricity by Integrated Faculty of Recife - FIR
VIISpeech therapist; Assistant I Professor of the Federal University of Pernambuco - UFPE, Recife, Brazil; Doctor in Nutrition from Federal University of Pernambuco - UFPE

Mailing Address




The chewing, a complex action controlled by the central nervous system, is one of the most important functions of the Stomatognathic System. During this action, the electrical activity of the masticatory muscles may be quantified using a surface electromyography. In order to systematically review the literature, on the methods and foods used in EMGS masseter muscle during mastication, we carried out a search in the databases SciELO, Brazil, Lilacs and Medline / Pubmed, from September to October 2009. We included population-based studies and excluded review studies without clear methodological definition and studies with children, adolescents and elderly. About 657 articles were found at the intersection of the following descriptors and their corresponding in English: chewing and masseter and electromyography, which 12 of them selected. It was found that the methods involved in the execution of surface electromyography of the masseter muscle during mastication, vary according to each author, and there is no standard for a specific food in order to perform the examination.

Keywords: Masseter Muscle; Electromyography; Mastication




Chewing is one of the most important functions of the Stomatognathic System and is therefore studied by several authors. This physiological act, whose purpose is to break the food into smaller particles, preparing them for swallowing and digestion it is a learning function, different from breathing, sucking and swallowing, which are innate and initially controlled reflexively. The learning process of this function is started from the moment that the first primary teeth emerge, the lower incisors and superiores1.

The chewing function depends on an integrated complex of muscles, ligaments, bone and teeth structures, controlled by the central nervous system. The muscles involved in chewing carry out movements and postures that approaching, or away from the teeth, or exacerbate the interoclusal pressure2.

The lower jaw develops range of motion (lifting, lowering, protrusion, retraction, lateralization), influenced by muscles responsible for chewing. The jaw elevation is performed by the masseter muscle, anterior temporal muscle and pterygoid medial muscle3.

The masseter muscle have muscle fibers when suffer contraction, projecting the jaw projecting upward promoting contact between the dental arches. The chewing efficiency is guaranteed by the force exerted on the contraction of this muscle4.

At the end of the XVIII century Luigi Galvani, an electrical engineer, spoke that a skeletal muscle when electrically stimulated suffer contraction, and on the other hand, produces electric current when contracted voluntarily, French dystrophy in the middle of last century was the first to apply electricity in skeletal muscles intacts. However the credit for developing the technique that promotes the uptake of electrical potentials generated in the muscle, the electromyography, corresponds to the English physiologists and North American Adrian and Bronk and D. Denny-Brown5.

The Surface Electromyography (EMGS) is intended for study of bioelectric phenomena that occur in skeletal muscle fibers during rest, stress and maximum contraction6. Electrodes are placed under the skin overlying the muscle to be evaluated, which capture the sum of the electrical activity of all actived muscle fibers. It is characterized by being a noninvasive and easy to perform. The electromyography registration allows you to observe electrophysiological behavior of several muscles in different physiological conditions. The EMGS has been widely used by physicians, speech therapists, physiotherapists and professionals in Physical Education for the study of human motion7.

In speech therapist clinical is common the assessment of muscle activity through physical examination by means of observations, filming and/or palpation. This methodology is required in orofacial rehabilitation process, but these data are not concise, not susceptible to quantification, because they may be influenced by the subjectivity of the professional, limiting an accurate recording.

With technological development, the use of measuring instruments with high precision is increasingly common in clinical practice, among which stands out electromyography as a method available in the market for over 40 years and have greater accuracy and objectivity to register the electrical activity of a muscle or a group of muscle8 may help in diagnosis and therapy of motor orofacial disorders9.

The methods applied in the execution of the electromyographic examination may vary from examiner to examiner. So, this study aimed to review the methods in the literature and food used in EMGS of masseter muscle during mastication.



We performed an electronic search in the databases SciELO-Brazil, Lilacs and Medline/Pubmed from September to October 2009.

The research was conducted by two authors/evaluators that discussed about the intersection of the following descriptors and their counterparts in English and portuguese, and chewing and electromyography and masseter muscle, all included in the Medical Subject Headings (MeSH). Another strategy used was a manual search of reference lists of identified articles and selected. The discrepancies presented by the authors were informed by a third author/reviewer. The research did not have language restrictions. It was not considered a limit to the time of publication, and being the selected articles for inclusion and exclusion criteria.

We excluded review articles and longitudinal design, animal studies, works whose study population were composed of subjects with diseases, research using invasive electromyography, articles involving other assessment tools, studies that simulate non-physiological or pathological conditions; articles that do not evaluate the function of mastication; articles studying the efficacy of drugs; articles studying physiological effects of therapeutic maneuvers or therapies; articles with the population consisting of children, teen agers or the elderly.

As inclusion criteria, the articles that studied the electrical activity of the masseter muscle during chewing of food in young adults were selected. The methodological quality of all studies was evaluated independently by three reviewers and agreement of this analysis resulted in the elaboration of Table 1.

It was found a total of 657 articles at the intersection of chewing and electromyography and masseter muscle descriptors in the SciELO-Brazil, Lilacs and Medline/Pubmed databases.

Following the inclusion and exclusion criteria defined in the method and subtracted from those contained repeated references in more than one database, we selected a total of 12 articles.

The articles were organized as the author, place and year of publication, population studied, methods used in the electromyographic evaluation of the masseter muscle and results findings.


Figure 1



The statistical treatment was not applied to this study due to the heterogeneity found in the selected articles.

The quantitative or references found and selected in the databases for this study shows that 75% of them were contained in Medline/Pubmed, 16.7% in LILACS and 8.3% in Scielo-Brazil.

The publication dates ranged between 1989 and 2009; two publications occurred in 1999; between the years 1992-1996 were not found publications who met the inclusion criteria proposed in this research as well as in the years 2007, 2005, 2001 and 1990. This statement leads to the inference that in the period of 1997 to 2004 there was an increase in publications dealing with the theme of this study. This may be related to the emergence of new equipment that enable the realization of easier electromyography.

During the articles selection through the inclusion and exclusion criteria, it was observed that most of the publications discarded used chewing non-food substances to test masticatory function and more frequent study population consisted of children, elderly or those with diseases or disorders pre-existing groups. These facts can be related to the scientific need to better characterize human development as well as changes inherent to certain diseases. The research of the characteristics of normality for certain functions are still largely unexplored.

With respect to the people who composed the selected studies, there was disparity in the number of individuals. The samples ranged between 10 and 50 subjects studieds10,11 being the average number of individuals equal to 24 per research. The criterion for evaluating the electrical characteristics of a muscle must consider certain peculiarities that vary between individuals. For this reason, comparisons of muscle patterns when coupled with findings in the same individual at different times and activities can better express the reality of electric power muscle. It is believed that this fact has influenced the limited number of members among the samples referenced, since the comparisons are not made between individuals but between pairs of muscles in each subject.

It was also observed a preference for studies with individuals of male gender11-15 in 42% of the studies, while populations consist of both genders were elected by 58% of the authors. No article investigated the events in isolation of their goals in a women group. The fact that they study more the male population may be related to the amount of variables that affect the hormonal in women16 also being extensively explored in the literature that female muscular activity levels are lower when compared to male4.

The location of publication, it was found that 50% of articles were published in periodics Europeus10,12,14,15,17,18. Other publications occurred in American journals (USA - 50%, Brazil - 50%)11,13,19,20. Of the 12 selected articles, 9 were published in international journals, this fact leads us to think that there is a preference for international publications, possibly because there are more such journals that address more specific subjects of this study, as well as achieve more readers.

By analyzing the methods used for electromyographic evaluation, we noted that all references made to capture the electrical signal of the right and left masseter muscle simultaneously. Not reached a consensus of the best food for the study of mastication. Peanut11, meat12, gelatine13, and grape20 were elected for four articles for the evaluation of mastication, other studies have manipulated various food consistencies in their tests10,14,15,17-19,21,22. The isolated study of chewing was reported in 58% of references11,12,14,15.

The mastication associated with chewing jaw movements observation was isolated object of study in 25% of articles17,19,20. The lack of standardization of the food being used in research with electromyography difficult the reproducibility of the methods referenced. Perhaps because it is a food consistency property is not controlled by undergoing numerous variations (temperature, viscosity, etc.), the mentioned studies have sought to categorize the foods according to a "hardness scale"10,14,15,17-19,21,22, when tested more than one food type, or uniformed a consistency to a isolated study11,12,13,20.

Concerning the time of acquisition of muscle electrical potentials during chewing, there was variation according to each researcher. In a guided experiment14 researchers instructed the evaluated subjects chewing a soft meat and then lasts a hard meat for a sustained period of 7s (each consistency) or until the cake is ready to be swallowed. Other researchers9,19,20 electromyographic analysis of the stipulated 15 chewing strokes, as well as the electrical events observed during 15 seconds of the masseter chewing raisins. Other authors evaluated the chewing in free time11-15,17. This variation of the execution time of electromyographic acquisitions contribute to the prevention of comparison between studies. Diversity in times of chewing analyzed may not accurately represent the actual demand of electrical activity, so it is believed that the studies involving analysis of all masticatory process present results closer to the actual demand of muscle electrical activity.

As the main results in the references arranged, all works reported that there are higher levels of electrical activity of masseter muscle during chewing hard food, therefore, the higher the level of hardness greater food massetres the electrical activity of the masticatory process. The chewing time and number of chewing strokes was increased when the hardness level of food increased from11-13,15,20. They also found that a muscle is usually found with greater electrical activity when compared to its partner10,11,20, this implies that there is no balance of electrical activity between the right and left masseter muscles during mastication, so, it is often have a predominant chewing side.

An article20 analyzed the electrical activity of masseter muscle expressed in microvolts. This type of analysis does not show normalization of the electromyograpich signal, since not get a standard that can confirm the estimated demand of electrical activity in a given activity2,3. This fact decreases the reliability of the results and do not allow to estimate potential differences in the execution of different tasks.



The results from this study show that:

1. The methods involved in the execution of surface electromyography of the masseter muscle during mastication, presents vary according to each author, there is no standard for a specific method for carrying out the examination;

2. There is no consensus on the best food to be used for chewing during electromyographic evaluation of masseter muscle.



To CNPq - Edital MCT/CNPq 14/2009 - Universal - Faixa B.



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Mailing Address:
Gerlane Karla Bezerra Oliveira Nascimento
Av. Fagundes Varela, 383 Apt. 302 -Jardim Atlântico
Olinda - PE - Brasil. CEP: 53140-080

Received on: February 7, 2011
Accepted on: September 22, 2011
Conflict of interest: non-existent

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