Reliability of electromyographic activity vs. bite-force from human masticatory muscles

Functional adaptation of the infant craniofacial system to mechanical loadings arising from masticatory forces

The morphology and biomechanics of infant crania undergo significant changes between the pre- and post-weaning phases due to increasing loading of the masticatory system. The aims of this study were to characterize the changes in muscle forces, bite forces and the pattern of mechanical strain and stress arising from the aforementioned forces across crania in the first 48 months of life using imaging and finite element methods. A total of 51 head computed tomography scans of normal individuals were collected and analysed from a larger database of 217 individuals. The estimated mean muscle forces of temporalis, masseter and medial pterygoid increase from 30.9 to 87.0 N, 25.6 to 69.6 N and 23.1 to 58.9 N, respectively (0-48 months). Maximum bite force increases from 90.5 to 184.2 N (3-48 months). There is a change in the pattern of strain and stress from the calvaria to the face during postnatal development. Overall, this study highlights the changes in the mechanics of the craniofacial system during normal development. It further raises questions as to how and what level of changes in the mechanical forces during the development can alter the morphology of the craniofacial system.

The challenge of ecological validity in temporomandibular disorders research

OBJECTIVE

To review the ecological validity of outcomes from current research involving temporomandibular disorders (TMDs), with an emphasis on chronic myofascial pain and the precocious development of degenerative disease of the temporomandibular joint (TMJ).

MATERIALS AND METHODS

Current approaches used to study TMDs in terms of neuromechanics, masticatory muscle behaviours, and the dynamics of the autonomic nervous system (ANS) were assessed for ecological validity in this review. In particular, the available literature was scrutinized regarding the effects of sampling, environmental and psychophysiological constraints and averaging data across biological rhythms.

RESULTS

Validated computer-assisted numerical modelling of the neuromechanics used biological objective functions to accurately predict muscle activation patterns for jaw-loading tasks that were individual-specific. With respect to masticatory muscle behaviour, current findings refute the premise that sustained bruxing and clenching at high jaw-loading magnitudes were associated with painful TMDs such as myofascial pain. Concerning the role of the ANS in TMDs, there remains the need for personalized assessments based on biorhythms, and where the detection of dysregulated physiologic oscillators may inform interventions to relieve pain and restore normal function.

CONCLUSIONS

Future human research which focuses on TMD myofascial pain or the precocious development and progression of TMJ degenerative joint disease requires experimental designs with ecological validity that capture objectively measured data which meaningfully reflect circadian and ultradian states.

Development of a test bench for biomechanical simulation-a preliminary study of mandibular forces

Purpose: The aim of this study is to develop a test bench, which integrates different complexity levels and enables in that way a flexible and dynamic testing for mid and long term intervals as well as testing of maximum loads till implant failure of different osteosynthesis systems on the mandible. Material and Methods: For this purpose, an analysis of the state of the art regarding existing test benches was combined with interviews of clinical experts to acquire a list of requirements. Based on these requirements a design for a modular test bench was developed. During the implementation of the test stand, functional tests were continuously carried out and improvements made. Depending on the level of complexity, the test bench can be used either as an incorporated variant or as a standalone solution. In order to verify the performance and the degree of fulfilment of the requirements of these two variants of the test bench, preliminary studies were carried out for all levels of complexity. In these preliminary studies, commercially available osteosynthesis and reconstruction plates were investigated for their biomechanical behaviour and compared with data from the literature. Results: In total, fourteen test runs were performed for the different levels of complexity. Firstly, five test runs were executed to test the simplified load scenario in the incorporated variant of the test bench. High forces could be transmitted without failure of the miniplates. Secondly a quasi-static test scenario was examined using the incorporated variant with simplified load insertion. Five experiments with a number of cycles between 40,896 and 100,000 cycles were carried out. In one case the quasi-static testing resulted in a fracture of the tested reconstruction plate with a failure mode similar to the clinical observations of failure. The last four test runs were carried out using the standalone variant of the test bench simulating complex load patterns via the insertion of forces through imitated muscles. During the test runs joint forces were measured and the amplitude and vector of the resulting joint forces were calculated for both temporomandibular joints. Differences in the force transmission depending on the implant system in comparison to the zero sample could be observed. Conclusion: The presented modular test bench showed to be applicable for examination of the biomechanical behavior of the mandible. It is characterized by the adjustability of the complexity regarding the load patterns and enables the subsequent integration of further sensor technologies. Follow-up studies are necessary to further qualify and optimize the test bench.

Type of correlation between bite force and EMG activity of the temporalis and masseter muscles during maximal and submaximal clenching

INTRODUCTION

Maximal bite force is an important determinant of masticatory function and is essential for the estimation of dental status. Bite force is usually measured by gnathodynamometry.

In situ quantitative assessment of food oral processing parameters: A review of feasible techniques and devices

Oral processing is a combination of various actions, the detailed description of which has always been the subject of relevant research. By means of imaging technology and sensory evaluation, more knowledge of oral processing have been accumulated. Presently, the advances in sensory technology have added quantitative parameters to the qualitative description of oral processing, which also enriched the specifics of each action. Previous studies have shown that oral processing includes lip closure, dental occlusion, masticatory muscles activity, tongue movement, and swallowing, whose processing contains rich information such as the movement of organ and the intensity of organ contacts. "Quantification" was taken in this review as the basic feature of in situ detection information, the relevant parameters and feasible methods for the quantitative description of each activity was recorded in detail. In addition, basic problems and feasible optimization schemes of the existing in situ detection device are also proposed in the hope of promoting the development of in situ detection device thus providing available information for the description of oral processing.

Textural properties and muscle activities during mastication of normal and ultrasonically softened sticky rice aimed for consumers with swallowing disorder: A pilot study

Ultrasonication was used to develop softer sticky rice for elder adults. Textural properties of original sticky rice (oSR) and ultrasonically modified sticky rice (mSR) were determined. In addition, jaw muscle activities during mastication of both oSR and mSR were investigated. Twenty-seven healthy elderly subjects, age 68.9 ± 7.6 years, were asked to masticate both types of sticky rice in random sequence for three times with a 5-min rest between each test. Activities of bilateral masseter and suprahyoid muscles were recorded. Root mean square (RMS) and mastication duration were analyzed. After mastication trials, subjects were asked to rate preference and softness of the samples. mSR exhibited significantly lower hardness than oSR, while cohesiveness and adhesiveness values of the two samples were not significantly different. Interestingly, all the muscle activities were not significantly different between masticating oSR and mSR, whereas the number of chewing cycles while chewing the mSR was larger. However, 92% of the subjects preferred mSR and felt that it was softer. mSR may therefore be regarded as having potential for elder people who have difficulty masticating hard solid foods based on its lower hardness and higher level of preference compared to oSR.

Analysis of maximum bite force and chewing efficiency in unilateral temporomandibular joint ankylosis cases treated with buccal fat pad interpositional arthroplasty

There is limited knowledge about masticatory function after the release of temporomandibular joint (TMJ) ankylosis. In this study, masticatory function was evaluated by measuring maximum voluntary bite force (MVBF) and chewing efficiency in 30 unilateral TMJ ankylosis patients who were treated with buccal fat pad (BFP) interpositional arthroplasty. Eighteen subjects over 12 years of age were included in study Group A and 12 subjects below 12 years of age in study Group B. Patients in the study groups had completed a minimum follow up of one year after surgery. Control groups C (over 12 years of age, n = 18) and D (under 12 years of age, n = 12) consisted of age, sex, and weight-matched normal subjects. The mean MVBF was measured between occluding molar teeth with a strain gauge transducer. Chewing efficiency was measured with two different coloured chewing gum strips. These were chewed for 5, 10, 20, 30, and 50 strokes. Compared with normal subjects, the study groups (A and B) could generate 64.7% (p = 0.004*) and 89.8% (p = 0.121) of MVBF, respectively. Overall chewing efficiency was 88.7% in Group A and 92.9% in Group B (p = 0.014* and p = 0.138, respectively) when compared with normal subjects. The study has shown that BFP interpositional arthroplasty effectively restores masticatory function.

Sexual dimorphisms in three-dimensional masticatory muscle attachment morphometry regulates temporomandibular joint mechanics

Temporomandibular joint (TMJ) disorders disproportionally affect females, with female to male prevalence varying from 3:1 to 8:1. Sexual dimorphisms in masticatory muscle attachment morphometry and association with craniofacial size, critical for understanding sex-differences in TMJ function, have not been reported. The objective of this study was to determine sex-specific differences in three-dimensional (3D) TMJ muscle attachment morphometry and craniofacial sizes and their impact on TMJ mechanics. Human cadaveric TMJ muscle attachment morphometry and craniofacial anthropometry (10Males; 11Females) were determined by previously developed 3D digitization and imaging-based methods. Sex-differences in muscle attachment morphometry and craniofacial anthropometry, and their correlation were determined, respectively using multivariate general linear and linear regression statistical models. Subject-specific musculoskeletal models of the mandible were developed to determine effects of sexual dimorphisms in mandibular size and TMJ muscle attachment morphometry on joint loading during static biting. There were significant sex-differences in craniofacial size (p = 0.024) and TMJ muscle attachment morphometry (p < 0.001). TMJ muscle attachment morphometry was significantly correlated with craniofacial size. TMJ contact forces estimated from biomechanical models were significantly, 23% on average (p < 0.001), greater for females compared to those for males when generating the same bite forces. There were significant linear correlations between TMJ contact force and both 3D mandibular length (R² = 0.48, p < 0.001) and muscle force moment arm ratio (R² = 0.68, p < 0.001). Sexual dimorphisms in masticatory muscle morphology and craniofacial sizes play critical roles in subject-specific TMJ biomechanics. Sex-specific differences in the TMJ mechanical environment should be further investigated concerning mechanical fatigue of TMJ discs associated with TMJ disorders.

Over-the-counter bite splints: A randomized controlled trial of compliance and efficacy

Background

Occlusal splints are often used to curb the impacts of sleep bruxism (SB) on the dentition, and over‐the‐counter (OCT) options are becoming increasingly popular. OTC splints are usually fabricated at home by patients, but not routinely evaluated by dental professionals. It is unclear how OCT splints compare with more traditional splints that receive dental oversight.

Objectives

The present randomized controlled study tested how an OTC splint compared with a gold standard bite splint in terms of patient compliance (primary outcome) and efficacy (secondary outcomes).

Methods

Sixty‐seven subjects were randomly assigned to receive either the OTC (SOVA, N = 35) splint or the gold standard “Michigan” bite splint (MI, N = 32), with 61 completing the study (SOVA, N = 30; MI, N = 31). OTC‐splint subjects were required to fabricate their splints to clinically acceptable standards. Both groups wore the splints nightly for four months. Compliance was measured via daily diary. Efficacy outcomes evaluated stability, retention, periodontal health, night‐time rhythmic masticatory muscle activity (RMMA), and material wear.

Results

OTC‐splint subjects had difficulty fabricating splints to clinically acceptable standards. The number of night‐time RMMA bursts was significantly greater for the OTC splint group. Compliance and all other efficacy measurements were not significantly different between‐groups.

Conclusions

The results support the potential use of OTC splints for curbing the impacts of SB. However, the results strongly suggest that dentists should be actively engaged in overseeing patients' use of self‐fabricated appliances. This clinical trial is registered at ClinicalTrials.gov, Identifier number NCT02340663.

Intra-Day and Inter-Day Reliability of Measurements of the electromyographic signal on masseter and temporal muscles in patients with Down syndrome

The aim of the present study was to evaluate intra-day (test) and inter-day (re-test) reliability of surface electromyography (sEMG) signals of the masseter and temporal muscles in patients with Down syndrome (DS). We determined the reliability of sEMG variables in 33 patients with DS. EMG signals were recorded at rest as well as during maximum voluntary clenching and maximum habitual intercuspation (MHI). The signals were analyzed considering the amplitude in the root mean square (RMS), mean frequency (MNF), median frequency (MDF) and approximate entropy (ApEn). The intraclass correlation (ICC_2,1) for the three trials recorded during MHI in the two sessions (test and retest) revealed excellent intra-session and inter-session reliability (ICC_2,1 = 0.76 to 0.97) for all sEMG variables and muscles. In the rest position, excellent reliability was found for RMS and ApEn (ICC_2,1 = 0.75 to 1.00) and good to excellent reliability was found for MDF and MNF (ICC_2,1 = 0.64 to 0.93). The intra-session (test) and inter-session (re-test) analyses demonstrated the reliability of nonlinear sEMG variables of the masticatory muscles in adults with Down Syndrome.

Evaluation of tissue oxygen saturation of the masseter muscle during standardised teeth clenching

BACKGROUND

Haemodynamics during recovery after teeth clenching is poorly understood.

OBJECTIVE

To clarify factors influencing tissue blood oxygenation recovery after clenching with altered muscle activity and duration, but constant total muscle activity.

METHODS

The following tasks were based on constant maximum voluntary clenching (100% MVC): (a) 50% MVC × 30 seconds; (b) 30% MVC × 50 seconds; and (c) 10% MVC × 150 seconds. Tissue oxygenated (oxy-Hb), deoxygenated (deoxy-Hb) and total haemoglobin (total-Hb) were recorded using near-infrared spectroscopy in the masseter muscle during recovery after each task. Participants rested for 30 seconds before each task; average resting values were set as baseline. Respective ratios to baseline at 20, 60, 120 and 180 seconds after each task were calculated; the tasks were compared at each time point using one-way repeated-measures ANOVA.

RESULTS

Oxy-Hb and total-Hb decreased and deoxy-Hb increased during the tasks and recovered thereafter. For Task 3, not all values recovered to baseline, even after 180 seconds (oxy-Hb: 96.85%, total-Hb: 98.31%, deoxy-Hb: 102.98%). Oxy-Hb (after 180 seconds, Task 1-Task 3: P < .001, Task 2-Task 3: P = .013) and total-Hb (after 180 seconds, Task 1-Task 3: P < .001, Task 2-Task 3: P = .005) were significantly lower, and deoxy-Hb (after 180 seconds, Task 1-Task 3: P < .001, Task 2-Task 3: P = .005) was significantly higher for Task 3 than other tasks, at all times during and after recovery.

CONCLUSION

Despite the same total muscle activity, weak-force, long-duration clenching is more harmful than strong-force, short-duration clenching, suggesting a greater effect of awakening bruxism than sleep bruxism on myalgia.

Bite force and electromyography evaluation after cranioplasty in patients with craniosynostosis

OBJECTIVE

This long-term follow-up investigation aimed to assess masticatory muscle function in 15 patients with craniosynostosis with detachment of the temporal muscle during fronto-orbital advancement 6 years after cranioplasty compared with a non-operative stomatognathic healthy cohort in the same age group (n = 25).

STUDY DESIGN

The follow-up assessment for the operated children occurred on average 5.2 ± 1.7 years after surgery at the age of 7 ± 1.6 years. The maximum bite force was assessed, in addition to the bilateral function of both temporal and masseter muscles, which were analyzed using superficial electromyography.

RESULTS

The maximum bite force was 257 ± 89 N 255 ± 88 N (right/left), respectively, in the group of operated children and 212 ± 61 N and 203 ± 57 N (right/left), respectively, in the control group, without clinical relevant difference between groups. The surface electromyography signal of the temporal muscle correlated positively with the bite force and showed a slightly lower average resting tone activity in the control group, whereas muscle fatigue occurred slightly faster in the operated children in both muscles without statistically significant difference between the 2 groups.

CONCLUSIONS

There was no measurable dysfunction in the temporal muscle after the operative correction of craniosynostosis compared with a healthy population of children.

Blood oxygenation of masseter muscle during sustained elevated muscle activity in healthy participants

Myofascial pain associated with temporomandibular disorders has often been linked to pathological muscle hyperactivity. As a result, localised disturbances of intramuscular blood flow could lead to a lower level of oxygen distribution, hypoxia and microcirculatory changes. To assess haemodynamic changes in the masseter muscle during sustained elevated muscle activity (SEMA). Sixteen healthy participants performed thirty 1-min bouts of SEMA with intervals of 1-min 'rest' periods between the bouts on a bite force transducer device. The participants completed three sessions with different percentage of their maximal voluntary occlusal bite force (MVOBF): 0% (no task), 10% or 40% MVOBF tasks. The order of the sessions was randomised with 1- to 2-week intervals. Haemodynamic characteristics of the masseter muscle were estimated with use of a laser blood oxygenation monitor. Tissue blood oxygen saturation (StO₂ ) during SEMA was lower than during rest (P < 0·001). The relative changes in total haemoglobin (Total-Hb) and StO₂ were influenced by condition (SEMA and rest) and with interactions between condition and session (0%, 10% and 40% MVOBF tasks). These results suggest that SEMA may lead to hypoxia in the masseter muscle and that the haemodynamic characteristics and muscle symptoms depend on the magnitude of muscle contractions. Overall, the present findings may help to provide better insights into relationships between jaw muscle activity, haemodynamic changes and symptom developments with implications for clinical conditions such as bruxism characterised by different levels of tooth-grinding and tooth-clenching muscle activity.

Relationship between electrical activity of the temporal and masseter muscles, bite force, and morphological facial index

PURPOSE

To analyze possible correlations between the electrical activity of masseter and temporal muscles, Bite Force (BF), and Morphological Facial Indices (MFI).

METHODS

The study involved 43 young adults, both genders, 18 to 37 years old. The individuals were submitted to: face measurement to calculate MFI; Masseter and Temporal Surface Electromyography (sEMG) and BF measurements on right and left premolars and incisors. The following electromyographic tests were conducted: at rest position; Maximal Voluntary Isometrical Contraction (MVIC) and usual chewing of raisins. Statistical analysis was conducted using the coefficient of Spearman correlation with significance level of 5%.

RESULTS

The values at rest in the temporal muscles were significantly higher than those in the masseter muscles. A meaningful correlation was found between MFI and sEMG in the MVIC test for the Left Temporal (rs=36, p=0.017). A significant correlation was observed between FMI and sEMG during BF in incisors for temporal muscles and the Right Masseter. During the force tests, it was possible to observe a meaningful correlation between BF in right premolars and the sEMG of the Left Temporal and Masseters.

CONCLUSION

No correlation was found between the sEMG of temporal and masseter muscles, BF, and FMI in adult individuals based on the tests performed. The SEMG of temporal and masseter muscles seems to be associated only with BF. As a datum of habitual postural characteristic, the electrical activity of temporal muscles is higher than the activity of masseters, also regardless of MFI.

Novel Low-Cost Sensor for Human Bite Force Measurement

This paper presents the design and development of a low cost and reliable maximal voluntary bite force sensor which can be manufactured in-house by using an acrylic laser cutting machine. The sensor has been designed for ease of fabrication, assembly, calibration, and safe use. The sensor is capable of use within an hour of commencing production, allowing for rapid prototyping/modifications and practical implementation. The measured data shows a good linear relationship between the applied force and the electrical resistance of the sensor. The output signal has low drift, excellent repeatability, and a large measurable range of 0 to 700 N. A high signal-to-noise response to human bite forces was observed, indicating the high potential of the proposed sensor for human bite force measurement.

Sex differences in jaw muscle duty factors during exercise in two environments: A pilot study

It is unknown if females and males use jaw muscles similarly during exercise. This pilot study assessed jaw elevator muscle duty factors (DFs=time of muscle activity/total recording time) at repeated sessions to test if DFs are reliable and different between sexes during exercises in two environments. Ten female and seven male subjects recruited from university soccer teams provided informed consent. Surface electromyography was recorded from masseter and temporalis muscles during biting and leg-extension laboratory exercises. Average activities to produce 20N bite-forces for each muscle and subject determined thresholds (5-80%·T20N) for subject-specific DF calculations during exercises performed in laboratory and natural environments. Subjects self-recorded via portable electromyography equipment during in-field leg-extension and weight-lifting exercises. Effects of variables on DFs were assessed via ANOVA (α=0.05) and simple effects testing (Bonferroni-adjusted p⩽0.012). All subjects used jaw muscles during exercises in both environments. DFs between laboratory sessions were reliable (R=0.84). During laboratory exercises, male temporalis DFs were significantly higher than female DFs from both muscles (p⩽0.001). During in-field exercises females had higher DFs during weight-lifting while males had higher DFs during leg-extensions. In-field sex differences were significant at most thresholds and showed larger effect sizes for leg-extension compared to weight-lifting exercises.

Contribution of each masticatory muscle to the bite force determined by MRI using a novel metal-free bite force gauge and an index of total muscle activity

PURPOSE

To develop a metal-free bite force gauge that can monitor the bite force in a strong magnetic field and to analyze the correlations between bite-force and total T2 shift of the mastication muscles.

MATERIALS AND METHODS

The gauge used a micro-pressure sensor made of optical fiber. Ten subjects performed a 60-s isometric bite task at 40% of maximum clenching in various occlusal support conditions (intact dentition, right molar loss, or left molar loss). Spin-echo images were taken with a 1.5 Tesla scanner before and immediately after the task to correlate the bite force with the mean voxel count, mean shift in transverse relaxation time (ΔT2), and total T2 shift of each masticatory muscle.

RESULTS

Measurements of total T2 shift identified significant correlations between the bite force and activities of the superficial layer of the bilateral masseter muscle, regardless of the occlusion condition (intact dentition: left, P = 0.007 and right, P < 0.001; right molar loss: left, P = 0.02 and right, P = 0.021; and left molar loss: left, P = 0.022 and right, P = 0.049). In contrast, significant correlations were not detected between the bite force and mean ΔT2 (intact dentition: left, P = 0.102 and right, P = 0.053; right molar loss: left, P = 0.393 and right, P = 0.868; and left molar loss: left, P = 0.531 and right, P = 0.92).

CONCLUSION

Measurement of total T2 shift using a metal-free bite force gauge is a more sensitive index of individual muscle activity than mean ΔT2 during a bite task. J. MAGN. RESON. IMAGING 2016;44:804-813.

Assessment of masticatory muscle activity and occlusion time in patients with advanced tooth wear

OBJECTIVE

Tooth wear is a basic physiological adjustment mechanism in the masticatory system. Unfortunately, it is not clear what the relationship is between the activity of the masticatory muscles and the tooth hard tissue loss (mainly enamel) in patients with advanced tooth wear. The aims of this study were (1) to compare the occlusion times and (2) to compare the EMG activity in maximal voluntary clench of the masseter and anterior temporalis muscles of patients with advanced tooth wear to the same activity of healthy volunteers.

DESIGN

50 (16F, 34M) patients and 30 (12F, 18M) age matched controls were clinically examined to assess the degree of wear (TWI). Each subject underwent electromyographic analysis (bilateral anterior temporalis, superficial masseter, anterior digastric and sternocleidomastoid muscles) and digital occlusal analysis.

RESULTS

Mean values of the electrical potentials of the mandible elevating muscles during clench were higher in the study group compared to the controls. A negative correlation was found between the temporalis and masseter muscle activities during clench and the mean value of TWI (r=-0.383, p=0.009; r=-0.447, p=0.002). Occlusion time was longer in the study group compared to controls (p<0.05).

CONCLUSIONS

Mandibular adductors demonstrated lower muscular activities during clenching in the tooth wear patients; however, the cause of this finding is not certain. Prolongation of occlusion time may exacerbate occlusal surfaces wear or excessive wear may prolong occlusion time.

Impact of lateral occlusion schemes: A systematic review

STATEMENT OF PROBLEM

Although several lateral occlusion philosophies have been proposed in the literature, there is a lack of compelling evidence supporting any scheme.

PURPOSE

The purpose of this systematic review was to investigate the clinical implications of different lateral occlusion schemes.

MATERIAL AND METHODS

A literature search was completed through PubMed (MEDLINE), Google Scholar, and Cochrane Library, up to January 2014. The literature search aimed to retrieve 2 study categories: group 1: comparative studies; group 2: clinical outcome studies. The inclusion criteria were peer-reviewed human clinical studies published in English. The search was further supplemented by manual searching through the reference lists of the selected studies.

RESULTS

The initial search revealed a total of 680 studies; however, after applying the inclusion criteria, 26 studies were found suitable for the analysis (13 for group 1 and 13 for group 2). The most commonly evaluated lateral occlusion schemes were canine-guided occlusion (CGO) and group function occlusion (GFO). Group 1 studies evaluated the impact of lateral occlusion schemes on muscular electromyographic (EMG) activity, condylar displacement, mastication, and mandibular movement. Group 2 studies evaluated the impact of restored occlusion on longevity, patient comfort, and pathologic consequences. CGO was associated with narrower mastication and less EMG activity of the masticatory muscles during clenching. GFO was associated with wider mandibular movement and quicker mastication. During mastication, there was no difference in EMG activity between the 2 lateral occlusion schemes. Furthermore, the long-term studies indicated that there is no difference between the 2 schemes in patient comfort and restoration longevity.

CONCLUSION

Although there are immediate differences between the different lateral occlusion schemes, patients have the capability to successfully adapt to CGO or GFO.

A pilot study of ambulatory masticatory muscle activities in temporomandibular joint disorders diagnostic groups

OBJECTIVE

To determine differences in masticatory muscle usage between temporomandibular joint disorders diagnostic groups.

SETTING AND SAMPLE POPULATION

Seventy-one informed and consented subjects (27 men; 44 women) participated at the University at Buffalo.

MATERIAL AND METHODS

Research diagnostic criteria and imaging data were used to categorize subjects according to the presence/absence +/- of TMJ disc placement (DD) and chronic pain (P) (+DD+P, n=18; +DD-P, n=14; -DD-P, n=39). Electromyographic (EMG)/bite-force calibrations determined subject-specific masseter and temporalis muscle activities per 20 N bite-force (T20N , μV). Over 3 days and nights, subjects collected EMG recordings. Duty factors (DFs, % of recording time) were determined based on threshold intervals (5-9, 10-24, 25-49, 50-79, ≥80% T20N ). anova and Tukey-Kramer post hoc tests identified 1) diagnostic group differences in T20N and 2) the effects of diagnostic group, gender, time and interval on muscle DFs.

RESULTS

Mean (±SE) temporalis T20N in +DD+P subjects was significantly higher (71.4±8.8 μV) than masseter T20N in these subjects (19.6±8.8 μV; p=0.001) and in -DD-P subjects (25.3±6.0 μV, p=0.0007). Masseter DFs at 5-9% T20N were significantly higher in +DD-P women (3.48%) than +DD-P men (0.85%) and women and men in both other diagnostic groups (all p<0.03), and in +DD+P women (2.00%) compared to -DD-P men (0.83%; p=0.029). Night-time DFs at 5-9% T20N in +DD-P women (1.97%) were significantly higher than in -DD-P men (0.47%) and women (0.24%; all p<0.01).

CONCLUSIONS

Between-group differences were found in masticatory muscle activities in both laboratory and natural environmental settings.

Association of Masseter Muscle Activities during Awake and Sleep Periods with Self-Reported Anxiety, Depression, and Somatic Symptoms

AIM AND BACKGROUND

The objective of this study was to determine if duty factors (DF) of low-magnitude MMA during awake and sleep periods were associated with self-reports of anxiety, depression, and somatic symptoms, and if so, whether or not any associations were modified by gender or the presence of pain. Limited information is currently available in the literature regarding the association of low-magnitude masseter muscle activities (MMA) in habitual environmental settings and the presence of psychological symptoms.

MATERIALS AND METHODS

Sixty-eight consenting participants were classified using the Diagnostic Criteria for Temporomandibular Disorders examination and validated self-reporting psychological symptom evaluation questionnaires. Each subject also had masseter electromyography recordings during standardized biting tasks in 2 laboratory sessions to calibrate the in-field MMA collected during 3 awake and 3 sleep periods.

RESULTS

During awake periods, subjects with self-reported depression and somatic symptoms had statistically high odds of having higher DF of low-magnitude MMA (defined by ≥ 75th percentile of sample). The association between high DF of low-magnitude MMA and self-reported depression symptoms was significantly augmented among male participants, whereas, the association between high DF of low-magnitude MMA and self-reported somatic symptoms was significantly increased among female participants without pain.

CONCLUSION

These pilot data support associations of low-magnitude masseter muscle activities with self-reported depression and somatic symptoms during awake periods.

Tempo de ativação muscular em portadoras de disfunção temporomandibular durante a mastigação

Objetivo Comparar, entre portadoras de disfunção temporomandibular (DTM) e controles, o tempo de ativação do músculo masseter e do músculo temporal anterior, em diferentes faixas de amplitude eletromiográfica de superfície, durante a mastigação. Métodos Foram avaliadas 22 voluntárias, com idades entre 18 e 48 anos, divididas em Grupo DTM (n=14) do tipo “Ia”, de acordo com o Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TDM) e Grupo Controle (n=8), assintomáticas. Foram registrados, por meio de eletromiografia de superfície, a amplitude e o tempo de ativação dos músculos masseter e temporal anterior, durante mastigação bilateral de Parafilm M® por dez segundos. Os sinais eletromiográficos foram categorizados em três faixas percentuais, 0-39%, 40-74% e 75-100%, relativas ao valor médio de amplitude de três contrações máximas de apertamento dentário. As porcentagens dos tempos totais de ativação (duty factor), em cada uma das faixas de amplitude, foram comparadas entre os grupos pelo teste t-Student, para dados não pareados. Resultados Não houve diferenças significativas do duty factor na comparação entre os grupos controle e DTM. Conclusão A variável eletromiográfica testada não se mostrou útil como ferramenta diagnóstica na prática clínica, o que será possível apenas quando em conjunto com a história clínica e exame físico do indivíduo.

Effect of mouth breathing on masticatory muscle activity during chewing food

The aim of this study was to examine the effect of mouth breathing on masticatory muscle activity during chewing food. Masseter muscle activity during chewing of a rice ball was recorded in 45 adult volunteers (three women), identified as nose breathers. Surface electrodes were placed on the skin according to the orientation of the masseter muscle to record the activity of this muscle while the subjects chewed the food until swallowing. Each activity was recorded twice, once with nose breathing and once with mouth breathing induced by nasal obstruction. The integrated and mean electromyography values for mouth breathing were significantly lower than the values for nose breathing (P < 0·05). The resting and total duration of chewing were significantly prolonged (P < 0·05) and the active duration significantly shorter (P < 0·05) when breathing through the mouth compared with the nose. Significantly more chewing strokes were counted for mouth breathing compared with nose breathing (P < 0·05). Taken together, the results indicate that mouth breathing decreases chewing activity and reduces the vertical effect upon the posterior teeth.

Stable tooth contacts in intercuspal occlusion makes for utilities of the jaw elevators during maximal voluntary clenching

Data are inconsistent concerning whether the level of the surface electromyographic (SEMG) activity of jaw-closing muscles increases when biting forces elevated during maximal voluntary clenching (MVC). In this study, T-Scan III system and BioEMG III system were used to record bite force, occlusal contacts and SEMG activity of the anterior temporalis (TA) and of the masseter muscles (MM) simultaneously. Recordings were obtained from 16 healthy young adult males during different conditions: (i) a fast MVC from resting position to intercuspal position (ICP); (ii) mandibular movements from ICP to protrusive or lateral edge-to-edge positions with teeth in contact with biting; (iii) a fast MVC in protrusive and lateral edge-to-edge positions. A higher level of SEMG activity was associated with a higher bite force during occluding movements (P < 0.05). However, during fast MVC from rest to ICP, the largest number of occlusal contacts was achieved and distributed more symmetrically, the highest level of biting force was obtained, but the SEMG activity of the jaw elevator muscles was reduced compared with its maximum level (P < 0.05). This phenomenon was not observed during the fast MVC in protrusive or lateral edge-to-edge positions. The present results that a lower SEMG activity was associated with the largest number of occlusal contacts and the highest level of bite force during centric MVC demonstrated a complex integration of jaw-closing muscles when a stable occlusion is present.

Electrical stimulation device as possible treatment for nocturnal bruxism: preliminary results

Nocturnal bruxism (NB) is a temporomandibular disorder characterized by an excessive clenching and involuntary parafunctional grinding of the teeth during sleep. It can cause dental damage and irreversible temporomandibular joint dysfunction. We designed a device that generates electrical stimulation on inhibitory sensory afferents when an EMG signal is measured. This stimulation was applied to the right mental nerve to produce a decrease in the contraction intensity of the mandibular elevation muscles. To measure the intensity of contraction, electromyographic (EMG) signal of the left temporalis anterior (LTa) muscle was used. The results showed that, on average, the percentage decrease in the bruxist group was 30.53% and for the control group was 28.91%. These results indicate that the device implemented generates an important decrease in the muscle contractile activity. Therefore, the device could be useful as a possible treatment to decrease nocturnal bruxism.

Muscle organization in individuals with and without pain and joint dysfunction

Central nervous system organization of masticatory muscles determines the magnitude of joint and muscle forces. Validated computer-assisted models of neuromuscular organization during biting were used to determine organization in individuals with and without temporomandibular disorders (TMD). Ninety-one individuals (47 women, 44 men) were assigned to one of four diagnostic groups based on the presence (+) or absence (-) of pain (P) and bilateral temporomandibular joint disc displacement (DD). Electromyography and bite-forces were measured during right and left incisor and molar biting. Two three-dimensional models employing neuromuscular objectives of minimization of joint loads (MJL) or muscle effort (MME) simulated biting tasks. Evaluations of diagnostic group and gender effects on choice of best-fit model were by analysis of variance (ANOVA) and Tukey-Kramer post hoc tests, evaluations of right-left symmetry were by Chi-square and Fisher's exact statistics, and evaluations of model accuracy were by within-subject linear regressions. MME was the best-fit during left molar biting in +DD individuals and incisor biting in men (all p < 0.03). Incisor biting symmetry in muscle organization was significantly higher (p < 0.03) in healthy individuals compared with those with TMD. Within-subject regressions showed that best-fit model errors were similar among groups: 8 to 15% (0.68 ≤ R(2) ≤ 0.74). These computer-assisted models predicted muscle organization during static biting in humans with and without TMDs.