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

Selected muscle tone and asymmetry of the occlusal plane in case of intracapsular temporomandibular joint disorder

Objective: To discover the extent of the connection between occlusal plane asymmetry and the rest tone of the four muscle groups of the orofacial region with temporomandibular joint pathology.Methods: Eighty-seven subjects were divided into two groups. The following methods were applied: clinical examination, roentgenological examination, and electromyography. Data were evaluated and statistically analyzed.Results: The variability of occlusal plane inclination in relation to the porion plane was 0-4.6º.The tonus of masseter muscle was higher in the experimental group: 1.45 mV more than in the control group: 1.23 mV (p < 0.05).Conclusion: Asymmetry of the occlusal plane inclination was found for nearly all subjects in both groups. It can be compensated for by adaptation mechanisms and does not cause temporomandibular joint disorders. Undertaken research shows the existence of a proven correlation between TMJ disorders and the resting tonus of the masseter muscle.

Effect of teeth clenching on handgrip force in adult men: role of periodontal mechanoreceptors

PURPOSE

Voluntary teeth clenching is shown to increase the strength of muscle reflexes contributing to the improvement of postural stability. However, the interaction between the handgrip strength and teeth clenching is not yet understood. In this study, we aimed to evaluate the change in handgrip force in response to voluntary teeth clenching, and its relation to the peripheral receptors that play a central role in the control of mastication.

METHODS

Thirty-six healthy men were divided into two groups: aged 50-59 years, no dental prosthesis, and 53-62 years with total dental prosthesis. Each individual was given handgrip and teeth clenching instructions for five experiments: only handgrip, teeth clenching followed by handgrip without teeth clenching, teeth clenching followed by handgrip with teeth clenching, and the repetition of the last two instructions while wearing mouth guards.

RESULTS

Our findings showed that maximum handgrip force decreased and the resistance to fatigue increased in complete edentulous individuals using appropriate prostheses. Also, the significantly lower maximum handgrip force and higher resistance to fatigue values of the participants with dental prosthesis using a mouth guard while teeth clenching, revealed the central roles of periodontal mechanoreceptors.

CONCLUSION

Decreases in masticatory sensory information processes influence handgrip force values which is the most important indicator of motor function. The lack of periodontal mechanoreceptors associated with dental prosthesis usage may lead to a loss in muscle strength.

Can the subject reliably reproduce maximum voluntary contraction of temporalis and masseter muscles in surface EMG?

OBJECTIVE

To evaluate the repeatability of the surface EMG variables of myoelectric signals from the masseter and temporalis muscles according to three methods to induce maximum voluntary contraction (MVC) in healthy adults.

METHODS

Thirty healthy young subjects performed the following three MVC tasks three times each in three sessions on the same day without replacing surface electrodes: clenching the teeth (MVCIC) and biting down on two cotton rolls bilaterally with the posterior teeth (MVCBP) or first molars (MVCB6).

RESULTS

The intra-class correlation coefficient (ICC) of the amplitudes during the three MVC tasks ranged from 65 to 79%. The ICCs of the spectral variables ranged from 78 to 86%. The ICCs of the asymmetry index of the masseter ranged from 77 to 86%, and those of the activity index ranged from 68 to 90%.

CONCLUSION

The surface EMG measurements according to the three MVC methods exhibited good to excellent reproducibility.

Effects of rehabilitation with complete dentures on bite force and electromyography of jaw and neck muscles and the correlation with occlusal vertical dimension

OBJECTIVES

The purpose of this study was to assess the effects of oral rehabilitation with complete dentures on bite force and electromyography of the suprahyoid and sternocleidomastoid muscles, and their correlation with occlusal vertical dimension (OVD). The research questions were "What are the effects of rehabilitation with complete dentures on bite force and electromyography of suprahyoid and sternocleidomastoid muscles, and how are they correlated with OVD?"

MATERIALS AND METHODS

Patients who are wearers of unsatisfactory removable complete dentures were attended in three sessions (T0, T1, and T2). At T0, while the patients still wore the old dentures, they were submitted to bite force and surface electromyographic exams of the suprahyoid and sternocleidomastoid muscles. These exams were repeated, and the OVD was measured while the patients wore their old and new prostheses, 30 days after insertion of the new prosthesis (T1). The exams were repeated 100 days after the insertion of the new prosthesis (T2). The data were submitted to the Shapiro-Wilk normality test, analysis of variance (ANOVA), and Pearson correlation and linear regression, all with 5% significance.

RESULTS

Fifteen patients participated in the study. No statistically significant difference was observed for bite force or electromyography in T0, T1, or T2. However, the correlation and regression tests showed important interactions between the OVD and maximum voluntary occlusal bite force, as well as the OVD and electromyography during deglutition for the suprahyoid muscles.

CONCLUSION

Rehabilitation did not impact bite force nor the activity of the assessed muscles (electromyography). On the other hand, OVD was shown to be an important factor for bite force, and deglutition of water after rehabilitation.

CLINICAL RELEVANCE

This study shows what are the influences of rehabilitation on oral functions and reinforces the importance of corrected reestablishment of OVD because it has been found to be an important factor for bite force and electromyography during deglutition.

Co-contraction behaviour of masticatory and neck muscles during tooth grinding

The objective of this study was to analyse the co-contraction behaviour of jaw and neck muscles during force-controlled experimental grinding in the supine position. Twelve symptom-free subjects were enrolled in the experimental study. Electromyographic (EMG) activity of semispinalis capitis, splenius capitis and levator scapulae muscles was recorded bilaterally with intramuscular fine-wire electrodes, whereas that of sternocleidomastoideus, infrahyoidal, suprahyoidal, masseter and anterior temporalis muscles were registered with surface electrodes. EMG and force measurements were performed during tasks simulating tooth grinding on custom-made intraoral metal splints. The mean EMG activity normalised by maximum voluntary contraction (% MVC) of each of the neck muscles studied during grinding was analysed and compared with previous data from jaw clenching at identical force (100 N) and (supine) position. The occurrence of low-level, long-lasting tonic activation (LLTA) of motor units was also documented. The mean three-dimensional force vector of the grinding forces was 106 ± 74 N. In the frontal plane, the incline to the midsagittal plane ranged between 10° and 15°. In the midsagittal plane, the incline to the frontal plane was negligibly small. Posterior neck muscle activity during grinding ranged between 4.5% and 12% MVC and during clenching with 100 N between 1.8% and 9.9% MVC. Masticatory muscle activity during grinding ranged between 17% and 21% MVC for contralateral masseter and ipsilateral temporalis and between 4% and 6.5% for ipsilateral masseter and contralateral temporalis. LLTA had an average duration of 195 ± 10 seconds. The findings from this study do not support pathophysiological muscle chain theories postulating simple biomechanical coupling of neck and jaw muscles. Co-contractions of neck and masticatory muscles may instead occur as a result of complex neurophysiological interactions.

Spectral components in electromyograms from four regions of the human masseter, in natural dentate and edentulous subjects with removable prostheses and implants

OBJECTIVE

To compare the frequency or spectral components between different regions of the superficial masseter in young natural dentate and total edentulous older adults rehabilitated with removable prostheses and fixed-implant support. A secondary objective was to compare these components between the three groups.

DESIGN

21 young natural dentate and 28 edentulous (14 with removable prostheses and 14 with fixed-implant support) were assessed. High-density surface electromyography (sEMG) was recorded in four portions of the superficial masseter during submaximal isometric bites. Spectral components were obtained through a spectral analysis of the sEMG signals. An analysis of mixed models was used to compare the spectral components.

RESULTS

In all groups, the spectral components of the anterior portion were lower than in the posterior region (p < 0.05). Both edentulous groups showed lower spectral components and median frequency slope than the natural dentate group (p < 0.05). The removable prostheses group showed the greatest differences with natural dentate group.

CONCLUSIONS

There were significant differences in the spectral components recorded in the different regions of the superficial masseter. The lower spectral components and fatigability of older adults rehabilitated with prostheses could be a cause of a greater loss of type II fibers, especially in the removable prostheses group.

Analysis of the stomatognathic system of children according orthodontic treatment needs

PURPOSE

The present study evaluated electromyographic activity (EMG), masticatory performance, and tongue strength in children without and with orthodontic treatment needs.

PATIENTS AND METHODS

A total of 90 children were screened and divided into the following groups: Group I (no treatment needed; mean age: 8.00 ± 0.43 years; n = 26), Group II (few malocclusions, treatment needed; mean age: 8.89 ± 0.43 years; n = 28), and Group III (slight-to-borderline treatment needed; mean age: 8.44 ± 0.22 years; n = 36). Orthodontic treatment need was classified on the basis of IOTN-DHC (Index of Orthodontic Treatment Need - Dental Health Component). The electromyographic Trigno EMG Systems was used for muscle analysis and the Iowa Oral Pressure Instrument (IOPI) was used to measure tongue strength. Data were analyzed using normality tests and one-way analysis of variance with a Bonferroni post hoc test (p ≤ 0.05).

RESULTS

EMG in almost all mandibular movements was higher in Group III with statistically significant differences compared to position at rest: right masseter (p = 0.03); protrusion: left temporal (p = 0.02); saliva swallowing: left temporal (p = 0.05) and water swallowing: orbicularis oris mouth, right upper segment (p = 0.05). Lower masticatory performance was found in Group III, but the difference compared to Group I and II was not significant. There were no significant differences between the groups in terms of tongue strength.

CONCLUSIONS

Children with borderline orthodontic treatment needs show functional disorders of the stomatognathic system.

Quantitative sensory response of the SCM muscle on sustained low level activation simulating co-contractions during bruxing

OBJECTIVE

Bruxism is discussed as an etiological factor in the pathogenesis of orofacial and cervical pain. As the sternocleidomastoid muscle (SCM) is co-activated during clenching, our aim was to investigate, whether the muscle loading leads to peripheral or central sensitizations.

DESIGN

In twenty-one healthy female volunteers, somatosensory profiles of the SCM were recorded according to the test battery of the German Research Network on Neuropathic Pain (DFNS) prior to and after an isometric muscle exercise. QST comprised thermal and mechanical stimuli. A submaximal activation of the SCM (15% MVC) was kept for 10min in sitting position. In separate test sessions one month apart, one sham and one verum experiment were conducted in randomized order. During the muscle loading, the parameters cold detection threshold (CDT), mechanical pain sensitivity (MPS) and pressure pain treshold (PPT) were tested and experimental pain recorded by visual analogoue scales (VAS). All test sessions were performed during the follicular phase of the menstrual cycle (day 5), to avoid effects on pain perception. Data were analyzed with Repeated Measures ANOVA (SPSS 22.0) RESULTS: No significant changes were found during or after (sham) loading except for stimulus-response-function (SR, P=0.01) and PPT (P=0.02) in the sham test. No effect was observed in the verum experiment (P=0.12 up to 1.0).

CONCLUSION

Prolonged low level contraction of the SCM does not evoke painful sensitization. In contrast, submaximal muscle activation seems to have a protective effect corresponding to a training effect preventing sensitization.

Does altered mandibular position and dental occlusion influence upper cervical movement: A cross-sectional study in asymptomatic people

OBJECTIVE

Gross mandibular position and masticatory muscle activity have been shown to influence cervical muscles electromyographic activity. The purpose of this study was to investigate the influence of three different mandible positions including conscious occlusion, tongue tip against the anterior hard palate (Palate tongue position) and natural resting position (Rest), on sagittal plane cervical spine range of motion (ROM) as well as the flexion-rotation test (FRT) in asymptomatic subjects.

MATERIALS AND METHODS

An experienced single blinded examiner evaluated ROM using an Iphone in 22 subjects (7 females; mean age of 29.91years, SD 5.44).

RESULTS

Intra-rater reliability for range recorded was good for the FRT with ICC (intraclass correlation) 0.95 (95% CI: 0.88-0.98) and good for sagittal plane cervical ROM with ICC 0.90 (95% CI: 0.77-0.96). A repeated measures ANOVA determined that mean ROM recorded during the FRT differed significantly between assessment points (F(1.99, 41.83) = 19.88, P < 0.001). Bonferroni Post hoc tests revealed that both conscious Occlusion and Palate tongue position elicited a significant large reduction in ROM recorded during the FRT from baseline (p < 0.01). Despite this, one activation strategy did not influence ROM more than the other. An additional repeated measures ANOVA determined that mean sagittal cervical ROM did not significantly vary between assessment points (F(2, 42) = 8.18, P = 0.08).

CONCLUSION

This current study provided further evidence for the influence of the temporomandibular region on upper cervical ROM. Results suggest that clinicians should focus on the natural mandible rest position when evaluating upper cervical mobility.

Influence of craniomandibular and cervical pain on the activity of masticatory muscles in individuals with Temporomandibular Disorder

PURPOSE

This study aimed to establish the prevalence of pain in the craniomandibular and cervical spine region in individuals with Temporomandibular Disorders (TMD) and to analyze the effects of these disorders on the bilateral activation of anterior temporalis (AT) and masseter (MA) muscles during the masticatory cycle.

METHODS

The participants were 55 female volunteers aged 18-30 years. The presence of TMD and craniomandibular and cervical spine pain was evaluated by applying the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) questionnaire and using a combination of tests for the cervical region. The muscle activity of AT and MA during the masticatory cycle was assessed using the symmetry and antero-posterior coefficient indices.

RESULTS

The AT activity during the masticatory cycle is more asymmetric in individuals with TMD. The craniomandibular pain, more prevalent in these individuals, influenced these results.

CONCLUSION

Individuals with TMD showed changes in the pattern activity of AT. The craniomandibular nociceptive inputs can influence the increase in asymmetry of the activation of this muscle.

Co-activation of jaw and neck muscles during submaximum clenching in the supine position

OBJECTIVE

The purpose of this study was to test the hypothesis that jaw clenching induces co-contraction and low-level long-lasting tonic activation (LLTA) of neck muscles in the supine position.

DESIGN

Ten healthy subjects developed various feedback-controlled submaximum bite forces in different bite-force directions in supine position. The electromyographic (EMG) activity of the semispinalis capitis, semispinalis cervicis, multifidi, splenius capitis, levator scapulae, trapezius, sternocleidomastoideus, masseter and infra/supra-hyoidal muscles was recorded. For normalization of EMG data, maximum-effort tasks of the neck muscles were performed.

RESULTS

Co-contractions of the posterior neck muscles varied between 2% and 11% of their maximum voluntary contraction. Different bite forces and bite-force directions resulted in significant (p<.05) activity differences between the co-contraction levels of the neck muscles. In addition, LLTA of specific neck muscles, provoked by the jaw clenching tasks, was observed.

CONCLUSIONS

This study demonstrated for the first time moderate co-contractions of jaw and neck muscles in the supine position under controlled submaximum jaw clenching forces. LLTA of most neck muscles was observed, outlasting clenching episodes and indicating an additional neuromuscular interaction between the two muscle groups.

Surface electromyography in orthodontics - a literature review

Electromyography is the most objective and reliable technique for evaluating muscle function and efficiency by detecting their electrical potentials. It makes it possible to assess the extent and duration of muscle activity. The main aim of surface electromyography is to detect signals from many muscle fibers in the area of the detecting surface electrodes. These signals consist of a weighted summation of the spatial and temporal activity of many motor units. Hence, the analysis of the recordings is restricted to an assessment of general muscle activity, the cooperation of different muscles, and the variability of their activity over time.

This study presents the main assumptions in the assessment of electrical muscle activity through the use of surface electromyography, along with its limitations and possibilities for further use in many areas of orthodontics. The main clinical uses of sEMG include the diagnostics and therapy of temporomandibular joint disorders, an assessment of the extent of stomatognathic system dysfunctions in subjects with malocclusion, and the monitoring of orthodontic therapies.