Activity and asymmetry index of masticatory muscles in women with and without dysfunction temporomandibular

Rodrigues-Bigaton D, Berni KC, Almeida AF, Silva MT


PURPOSE: [corrected] Compare the symmetry of the activity and masticatory muscles in individuals with TMD and asymptomatic.

METHODS: The study included 50 women, while 31 had temporomandibular disorders (TMD) and 19 were asymptomatic (control group), aged between 19 and 40 years. The volunteers were subjected to clinical examination of the diagnostic criteria in research with TMD (RDC/TMD) with the aim of diagnosing volunteers with or without TMD, and evaluate the electromyographic activity of the right temporalis muscle (TR) and left (TL), right masseter (MR) and left (ML), in situations of rest, isometric contraction of the muscles of the jaw elevators. We obtained the rates of activity and asymmetry in each situation and for the collection and TMD control groups.

RESULTS: For the index of activity for the rest there was significant difference (p = 0.0008) between the control group and the TMD group, with predominance of temporal muscle, was not observed difference between groups for the index of activity during the isometric contraction (p = 0.1069). For the index of asymmetry no difference between groups during rest, for the masseter muscles (p = 0.4182) and the temporal (p = 0.7614), and also during the isometry for both masseter muscles (p = 0.8691) and for time (p = 0.6643).

CONCLUSIONS: The control group showed prevalence of TMD and temporal muscle during rest, which did not occur in the isometry, and no difference for the index of asymmetry between the groups for the masseter and temporal muscles.

Standardization of the electromyographic signal through the maximum isometric voluntary contraction

Botelho A.L., Gentil F.H., Sforza C., da Silva M.A.


The objective of this study was to analyze the electromyographic (EMG) data, before and after inormalization. One hundred (100) normal subjects (with no signs and symptoms of temporomandibular disorders) participated in this study. A surface EMG of the masticatory muscles was performed. Two different tests were performed: maximum voluntary clench (MVC) on cotton rolls and MVC in intercuspal position. The normalization was done using the mean value of the EMG signal of the first examination. The coefficient of variation CV showed lower values for the standardized data. The standardization was effective in reducing the differences between records from the same subject and in different subjects.

Myoelectric manifestations of jaw elevator muscle fatigue and recovery in healthy and TMD subjects

Castroflorio T., Falla D., Tartaglia G.M., Sforza C., Deregibus A.


The effects of muscle pain and fatigue on the control of jaw elevator muscles are not well known. Furthermore, the myoelectric manifestations of fatigue and recovery from fatigue in the masticatory muscles are not reported in literature. The main aims of this study were (i) to evaluate the possible use of surface electromyography (sEMG) as an objective measure of fatigue of the jaw elevator muscles, (ii) to compare the myoelectric manifestations of fatigue in the temporalis anterior and masseter muscles bilaterally, (iii) to assess recovery of the investigated muscles after an endurance test and (iv) to compare fatigue and recovery of the jaw elevator muscles in healthy subjects and patients with muscle-related temporomandibular disorders (TMD). The study was performed on twenty healthy volunteers and eighteen patients with muscle-related TMD. An intra-oral compressive-force sensor was used to measure the voluntary contraction forces close to the intercuspal position and to provide visual feedback of submaximal forces to the subject. Surface EMG signals were recorded with linear electrode arrays during isometric contractions at 20%, 40%, 60% and 80% of the maximum voluntary contraction force, during an endurance test and during the recovery phase. The results showed that (i) the slope of the mean power spectral frequency (MNF) and the initial average rectified value (ARV) could be used to monitor fatigue of the jaw elevators, (ii) the temporalis anterior and masseter muscle show the same myoelectric manifestations of fatigue and recovery and (iii) the initial values of MNF and ARV were lower in patients with muscle-related TMD. The assessment of myoelectric manifestations of fatigue in the masticatory muscles may assist in the clinical assessment of TMDs.

EMG spectral characteristics of masticatory muscles and upper trapezius during maximum voluntary teeth clenching.

Lodetti G., Mapelli A., Musto F., Rosati R., Sforza C.


To assess the surface electromyographic spectral characteristics of masticatory and neck muscles during the performance of maximum voluntary clench (MVC) tasks, 29 healthy young adults (15 men, 14 women, mean age 22years) were examined. Electromyography of masseter, temporalis and upper trapezius muscles was performed during 5-s MVCs either on cotton rolls or in intercuspal position. Using a fast Fourier transform, the median power frequency (MPF) was obtained for the first and last seconds of clench, and compared between sexes, muscles, sides, tests and time intervals using ANOVAs. On average, the MPFs did not differ between sexes or sides (p>0.05), but significant effects of muscle (MPF temporalis larger than masseter, larger than trapezius muscles), test (larger MPFs when clenching in intercuspal position than when clenching on cotton rolls) and time (larger MPFs in the first than in the fifth second of clench) were found. In conclusion, a set of data to characterize the sEMG spectral characteristics of jaw and neck muscles in young adult subjects performing MVC tasks currently in use within the dental field was obtained. Reference values may assist in the assessment of patients with alterations in the craniocervical-mandibular system.

Commentary to Manfredini et al. J Oral Rehabil.

Tartaglia G.M., De Felicio C.M, Sforza C.


We have read the review article by Manfredini et al. (1) recently published by JOR. The colleagues discussed the role of different diagnostic tools to address the relationship between dental occlusion, body sway and TMD diagnosis. Diagnosis still remains in medicine and dentistry a clinical decision. Each clinician well knows that without consultation, any instrumental evaluation is not helpful or able by itself to automatically express a diagnosis. At first, clinicians on consultation have to express a diagnostic opinion. It has to be confirmed from quantitative or qualitative data obtained from supplementary exams. Medical instruments have to be considered under this point of view, and never as stand-alone diagnostic tools. In the specific case of TMJ disorders, still there is lack of these data for both the RCD/TMD criteria (2) and imaging support analysis (3, 4). Results are controversial for the above-mentioned tools. We agree with the authors of the review that there is still a lack of evidence also about the use of EMG like diagnostic support in TMJ problems but, we believe, mainly because technology is misused. EMG selected parameters and standardised protocols (differences on maximum voluntary clench, masticatory neuromuscular coordination, EMG on standardised force application) have to be adequate for the clinical confirmation we are looking for. sEMG may provide useful information also for the analysis of a risk population (asymptomatic subjects), considering the time, cost and non-invasive intrinsic characteristics of the tool, even if more research is to be conducted in this field. We have to apply the right standardised protocol (5). Generally speaking, literature about EMG is reductive. In accordance with Al-Saleh et al. (6), we strongly recommend the use of EMG normalisation for both cross-sectional and longitudinal assessments. In our laboratory, we have been using normalised/standardised EMG descriptors since 2000 (7). First of all, surface EMG has to be well-approached (8) both from research and clinical points of view, otherwise it is, as De Luca (9) wrote, only ‘a seductive muse’. With an EMG correct approach, researchers could help clinicians to confirm TMD diagnosis or to assess a risk population. Symptoms are often overlapped, and non-invasive and low-cost exams help clinicians in this way. Thanks to the authors to have recognized some points for the future because we are just at the beginning with an appropriate use of EMG instrumentation in dentistry.

Use of electromyographic and electrocardiographic signals to detect sleep bruxism episodes in a natural environment.

Castroflorio T., Mesin L,. Tartaglia G.M., Sforza C., Farina D.


Diagnosis of bruxism is difficult since not all contractions of masticatory muscles during sleeping are bruxism episodes. In this paper, we propose the use of both EMG and ECG signals for the detection of sleep bruxism. Data have been acquired from 21 healthy volunteers and 21 sleep bruxers. The masseter surface EMGs were detected with bipolar concentric electrodes and the ECG with monopolar electrodes located on the clavicular regions. Recordings were made at the subjects' homes during sleeping. Bruxism episodes were automatically detected as characterized by masseter EMG amplitude greater than 10% of the maximum and heart rate increasing by more than 25% with respect to baseline within 1 s before the increase in EMG amplitude above the 10% threshold. Furthermore, the subjects were classified as bruxers and nonbruxers by a neural network. The number of bruxism episodes per night was 24.6 ± 8.4 for bruxers and 4.3 ± 4.5 for controls (P < 0.0001). The classification error between bruxers and nonbruxers was 1% which was substantially lower than when using EMG only for the classification. These results show that the proposed system, based on the joint analysis of EMG and ECG, can provide support for the clinical diagnosis of bruxism.  

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