Ecological Momentary Assessment of Masseter Muscle Activity in Patients with Bruxism.

According to the International Bruxism Consensus, bruxism refers to the activity of the masticatory muscles reflecting contraction disorders, regardless of whether it is during sleep (SB) or an awake (AB) state. The objective of the present study was to evaluate the activity of the masseter muscle by surface electromyographic (sEMG) recordings. This study was performed on 20 participants with self-reported "possible bruxism" (study group) and 20 participants with no self-reported bruxism (control group); all participants underwent an evaluation of the masseter muscle activity using the dia-BRUXO device, which provides numerical parameters regarding sEMG (the total duration and the type of bruxism specific events, the effort made by the masticatory muscles during the recording period, and the personal bruxism index of each participant). Participants from the study group presented more clenching events during AB, three times more frequent than the control group (p = 0.002, Mann−Whitney U test); for SB, the frequency of clenching and grinding events was comparable within the study group, being more frequent than for the control group; the mean value of the effort index was higher for AB (1.177%) than SB (0.470%) and the same for the duration index, with a mean value of 2.788% for AB and 1.054% for SB. All participants from the control group presented reduced values for all acquired parameters. Overall, the personal bruxism index in AB was approximately four times higher for the study group (2.251%) compared to the control group (0.585%) (p < 0.005, Mann−Whitney U test). Similar values were obtained for SB. All participants with "possible bruxism" from the study group presented a higher activity of the masseter muscle, which is specific for bruxism, thus being defined as "definite bruxism".

Postural stability in subjects with temporomandibular disorders and healthy controls: A comparative assessment.

PURPOSE OF THE STUDY: The influence of the stomatognathic apparatus on body posture is a continuously discussed topic with contrasting results. The aim of this study is to analyze differences in postural stability between subjects with and without myogenous TMD. METHODS: 25 subjects affected by myogenous TMD according with DC/TMD (6 males, 19 females; mean age 31.75±6.68years) and a healthy control group of 19 subjects (4 Males, 15 Females; mean age 27.26±3.85years) were enrolled in the study. Both groups underwent a posturo-stabilometric force platform exam under different mandibular and visual conditions. Sway area and sway velocity of the COP (Center Of foot Pressure) posturo-stabilometric parameters were evaluated and compared applying Mann-U-Whitney statistical test. RESULTS: The sway area and sway velocity parameters resulted statistically significantly higher in the TMD group (sway area p<0.01; sway velocity p<0.05) in mandibular maximum intercuspation and rest positions with eyes open. CONCLUSIONS: This study demonstrates a significant difference in body postural stability between subjects with myogenous TMD and healthy controls. In particular, sway area and sway velocity postural parameters are increased in these subjects.

Standardised surface electromyography allows effective submental muscles assessment.

The aims of this pilot study were to evaluate: (i) the reproducibility and variability of an electromyographical protocol developed for the assessment of submental muscles (SM) (ii) to apply the new protocol to maximal teeth clenching, a simple and largely studied static task in order to quantify the relative contribution of submental muscles. In 20 healthy subjects, aged 19-35years, surface electromyography of SM, masseter (MM) and anterior temporalis (TA) muscles was performed during maximal voluntary clenching (MVC) with and without cotton rolls and the pushing of the tongue against the palate. Clenching on cotton rolls and pushing the tongue against the palate were used to standardise respectively MM and TA, and SM muscular potentials. The exercises were repeated in two appointments (T1-T2); submental muscles standardisation was also repeated twice (A-B) in each session to assess repeatability. Symmetry and activity were calculated for each couple of muscles. A two-way analysis of variance was computed for SM: no Factor 1 (T1 vs T2) or Factor 2 (A vs B) or F1×F2 significant effects were found. SM recruitment was 31% of the maximal activity, with symmetry values larger than 80%. In conclusion, standardised electromyography allows a reliable assessment of Submental muscles activity.

A validation study of a new instrument for low cost bite force measurement.

Quantitative assessment of force in masticatory muscles is not a routine clinical test, probably due to the lack of an "easy-to-use" device. Aim of this study is (1) to present a low cost bite force instrument located in a custom-made housing, designed to guarantee a comfortable and effective bite action, (2) to evaluate its mechanical characteristics, in order to implement it in clinical settings and in experimental setups. Linearity, repeatability and adaptation over time were assessed on a set of four different sensors in bare and housed condition. Application of the housing to the transducer may appreciably alter the transducer's response. Calibration of the housed transducer is thus necessary in order to correctly record real bite force. This solution may represent a low cost and reliable option for biting force measurement and objective assessment of individual force control in the scientific and clinical setting.

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.

Functional jaw muscle assessment in patients with a full fixed prosthesis on a limited number of implants: a review of the literature.

BACKGROUND: Full fixed prosthesis on a limited number of implants (FFP) are a viable treatment option for edentulous patients with a reduced amount of residual bone. Jaw muscular function in FFP patients has been evaluated in several studies, however heterogeneous data emerge from literature. PURPOSE: The aim of this review of the literature was to assess the function of jaw muscles in edentulous patients restored with full fixed prostheses on a limited number (≤ 6) of implants, as compared to dentate subjects and edentulous subjects wearing dentures, implant-supported overdentures or full fixed prostheses supported by more than six implants. MATERIALS AND METHODS: An electronic search of databases up to December 2013 was performed. The articles were selected using specific inclusion criteria, independent of the study design. RESULTS: A total of 1598 records were identified. After removing the duplicates and excluding records based on title and abstract, only 37 eligible records were identified. After full-text review, seventeen studies were selected for analysis according to the inclusion criteria. From the included studies, only one evaluated masseter muscle thickness in a cross sectional study by means of ultrasound, while the 16 remaining papers evaluated muscular function by using electromyography (EMG). Those studies analysed several heterogeneous parameters throughout the execution of five functional tests and were therefore described and pooled according to the following task categories: clenching; swallowing; reflex and fatigue for statics; and chewing for dynamics. CONCLUSIONS: The results of selected studies seem to indicate that, compared to dentate controls, FFP patients display a global satisfactory neuromuscular equilibrium in static activities, but still have some impairment during chewing.

Intravoxel incoherent motion imaging of masticatory muscles: pilot study for the assessment of perfusion and diffusion during clenching.

OBJECTIVE: The purpose of this study was to evaluate intravoxel incoherent motion (IVIM) imaging for assessing perfusion and diffusion of masticatory muscles during clenching. SUBJECTS AND METHODS: A prospective study was performed to assess the perfusion and diffusion of masticatory muscles during clenching. The masseter and medial pterygoid muscles participate in clenching, and the lateral pterygoids do not. IVIM parameters (microvascular volume fraction, f; pure diffusion coefficient, D; and perfusion-related incoherent microcirculation, D*) were determined on both the clenching and the balancing sides in 24 volunteers. The Wilcoxon test was used to compare the IVIM parameters at rest and during clenching. RESULTS: The f and D* values of the masseters significantly increased on the clenching side (f = 0.17 ± 0.10 vs 0.29 ± 0.11, p < 0.001; D* = 21.3 ± 18.5 × 10(-3) mm(2)/s vs 42.1 ± 33.3 × 10(-3) mm(2)/s, p = 0.0008). However, the D values did not change during clenching (1.26 ± 0.23 × 10(-3) mm(2) vs 1.21 ± 0.35 × 10(-3) mm(2)). The f values of the medial pterygoids also increased on the clenching side (0.20 ± 0.09 vs 0.30 ± 0.09, p < 0.001). On the balancing side, the f values of the masseters (0.19 ± 0.12 vs 0.30 ± 0.12, p < 0.001) and medial pterygoids (0.20 ± 0.09 vs 0.29 ± 0.11, p = 0.0007) significantly increased during clenching. In contrast, the IVIM values of the lateral pterygoids did not change. CONCLUSION: IVIM imaging may be useful for assessing perfusion and diffusion of the masticatory muscles.

Electromyographic assessment of jaw muscles in patients with All-on-Four fixed implant-supported prostheses.

This study evaluated the electromyographic (EMG) characteristics of masticatory muscles in patients with fixed implant-supported prostheses according to All-on-Four(®) principles and in control healthy dentate subjects. Twenty-six subjects aged 50-74 years were examined. Eighteen were edentulous and had been successfully rehabilitated with (i) mandibular All-on-Four(®) implant-supported fixed prostheses and maxillary complete dentures (10 patients) and (ii) mandibular and maxillary All-on-Four(®) implant-supported fixed prostheses (eight patients). Eight reference subjects had natural dentition. Surface EMG recordings of the masseter and temporalis muscles were performed during maximum voluntary teeth clenching and during unilateral gum chewing. All values were standardised as percentage of a maximum clenching on cotton rolls. During clenching, a good global neuromuscular equilibrium was found in all participants. During chewing, all groups had similar values of working-side muscle activities and of chewing frequency. No significant differences in the analysed EMG parameters were found between the patients with mandibular and maxillary All-on-Four(®) implant-supported prostheses and the reference subjects. In contrast, standardised pooled muscle activities and standardised muscular activities per cycle were larger in patients with a maxillary removable prosthesis than in control subjects (Kruskal-Wallis test, P < 0·01). Also, patients wearing a complete maxillary denture showed a poor neuromuscular coordination with altered muscular pattern and lower values of the index of masticatory symmetry than dentate control subjects (P < 0·01). EMG outcomes suggest that All-on-Four(®) implant-supported prostheses may be considered a functionally efficient treatment option for the rehabilitation of edentulous patients with reduced residual bone volume.

Enhancing the quality of life in elderly women through a programme to improve the condition of salivary hypofunction.

OBJECTIVE: The purposes of this study were to examine the effects of oral exercise intended to improve the function of the oral cavity in the elderly and their quality of life to pave the way for the development of oral-health promotion programmes geared towards the elderly. METHODS: The subjects were 78 female Koreans who resided in Seoul and were aged 65 years and older. During a 3-month period, an oral function promotion programme was conducted twice a week, between 10.00 am and 12.00 pm, applying oral exercise suggested by a Japanese public health centre. A survey was conducted by interviewing the selected women to determine the state of their subjective dry mouth, quality of life related to oral health and jaw functional limitation. Their opening, unstimulated whole saliva and pronunciation speed were measured before and after the oral function exercise programme. RESULTS: The subjects showed a significant improvement in subjective dry mouth symptoms, relevant behaviour, the level of discomfort caused by dry mouth and subjective jaw functional limitation during mastication and swallowing and emotional expression after receiving the oral exercise. After the oral exercise, there was a significant increase in mouth opening, unstimulated whole saliva and speaking speed ('patakala' pronunciation) after oral exercise. There was also significant progress in their quality of life related to oral health. Overall improvement in subjective dry mouth symptoms and relevant behaviour over time after oral exercise had a positive correlation with the level of improvement in discomfort triggered by dry mouth and mastication. The level of improvement in OHIP-14 had a positive correlation with the level of overall improvement in dry mouth symptoms and behaviour, the level of improvement in discomfort by dry mouth and that in mastication and swallowing. CONCLUSION: This study showed the effects of the oral function promotion programme and correlation of oral condition and oral health-related quality of life. It is suggested that this oral function promotion programme has positive effects on both objective and subjective oral conditions. It is strongly recommended that this programme, along with other oral health promotion programmes, be implemented to improve oral function and oral health-related quality of life for the elderly.

Jaw-opening muscle contracts more economically than jaw-closing muscle in rat.

Mandibular movement is achieved by coordinated actions of the jaw muscles. To understand the assigned functional role (e.g., motor or postural role) of each jaw muscle, we characterised not only their contractile and energy-consumption properties but also their compositions of myosin heavy chain (MHC) isoforms. The Ca(2+)-dependent isometric tension development and ATPase activity were simultaneously measured in chemically skinned fibers harvested from rat jaw-closing (masseter and temporalis) and jaw-opening (digastric) muscles. After the measurements of isometric tension development and ATPase activity, the MHC compositions in each preparation were determined by SDS-gel electrophoresis. The Ca(2+)-sensitivity of isometric tension development and ATPase activity was significantly (P<0.001) higher in the digastric fibers than in the masseter and the temporalis fibers. The tension cost (ATPase activity/tension) was significantly (P<0.0001) lower in the digastric fibers than in the masseter and the temporalis fibers. The MHCs in the digastric fibers consisted of a mixture of slow type I and fast type II isoforms, while mostly fast type II isoforms in the masseter and temporalis fibers. These results suggest that in rat the jaw-opening muscle contracts more efficiently in terms of the energy use (i.e., more efficient ATP consumption for tension generation) than the jaw-closing muscle.

Functional assessment of the stomatognathic system.

Clinically objective assessment of the occlusal function remains largely, even today, in the research laboratory instead of in the clinical setting, as part of the routine assessment along with the morphologic documentation. Functional outcomes of the stomatognathic system can be measured in terms of occlusal contact area, maximal voluntary bite force, maximal voluntary excursions, masticatory force, masticatory cycle pattern and masticatory performance. It should be emphasized, however, that many of these measures remain to be standardized and validated as tools relevant for assessment of patients who have dentofacial skeletal deformities. This remains a promising area of active research.

Masticatory motor patterns in ungulates: a quantitative assessment of jaw-muscle coordination in goats, alpacas and horses.

We investigated patterns of jaw-muscle coordination during rhythmic mastication in three species of ungulates displaying the marked transverse jaw movements typical of many large mammalian herbivores. In order to quantify consistent motor patterns during chewing, electromyograms were recorded from the superficial masseter, deep masseter, posterior temporalis and medial pterygoid muscles of goats, alpacas and horses. Timing differences between muscle pairs were evaluated in the context of an evolutionary model of jaw-muscle function. In this model, the closing and food reduction phases of mastication are primarily controlled by two distinct muscle groups, triplet I (balancing-side superficial masseter and medial pterygoid and working-side posterior temporalis) and triplet II (working-side superficial masseter and medial pterygoid and balancing-side posterior temporalis), and the asynchronous activity of the working- and balancing-side deep masseters. The three species differ in the extent to which the jaw muscles are coordinated as triplet I and triplet II. Alpacas, and to a lesser extent, goats, exhibit the triplet pattern whereas horses do not. In contrast, all three species show marked asynchrony of the working-side and balancing-side deep masseters, with jaw closing initiated by the working-side muscle and the balancing-side muscle firing much later during closing. However, goats differ from alpacas and horses in the timing of the balancing-side deep masseter relative to the triplet II muscles. This study highlights interspecific differences in the coordination of jaw muscles to influence transverse jaw movements and the production of bite force in herbivorous ungulates.

Electromyographic assessment of the activity of the masticatory using the agonist contract-antagonist relax technique (AC) and contract-relax technique (CR).

Proprioceptive neuromuscular facilitation (PNF) techniques are a group of therapeutic procedures that may be used to cause relaxation of muscles. Studies have found controversial results when applying these techniques. The aim of the present study was to evaluate the effectiveness of masticatory muscle relaxation through the use of the contract-relax technique (CR) when compared with the agonist contract-antagonist relax technique (AC). A convenience sample of 30 students was recruited for this study. The CR and the AC techniques were applied to the subjects in order to cause relaxation of the masticatory muscles. Electromyography activity of all muscles was registered. Two way ANOVA with repeated measures analysis demonstrated that both the AC technique and the CR technique did not decrease the EMG activity of masticatory muscles (P>0.05). Instead, both techniques caused an increase in electromyographic activity of the masticatory muscles. Based on the results obtained from this study, both the CR and the AC techniques were not effective in causing relaxation of the masticatory muscles. The purported physiological mechanisms of PNF techniques, which stated that they act through reciprocal inhibition and autogenic inhibition causing muscular relaxation, are not supported by this study.

Further evaluation of an EMG technique for assessment of the deep cervical flexor muscles.

A novel surface electromyographic (EMG) technique was recently described for the detection of deep cervical flexor muscle activity. Further investigation of this technique is warranted to ensure EMG activity from neighbouring muscles is not markedly influencing the signals recorded. This study compared deep cervical flexor (DCF) muscle activity with the activity of surrounding neck and jaw muscles during various anatomical movements of the neck and jaw in 10 volunteer subjects. DCF EMG activity was recorded with custom electrodes inserted via the nose and fixed by suction to the posterior mucosa of the oropharynx. Surface electrodes were placed over the sternocleidomastoid, anterior scalene, masseter and suprahyoid muscles. Positioned in supine, subjects performed isometric cranio-cervical flexion, cervical flexion, right and left cervical rotation, jaw clench and resisted jaw opening. Across all movements examined, EMG amplitude of the DCF muscles was greatest during neck movements that would require activity of the DCF muscles, particularly during cranio-cervical flexion, their primary anatomical action. The actions of jaw clench and resisted jaw opening demonstrated significantly less DCF EMG activity than the cranio-cervical flexion action (p<0.05). Across all other movements, the neighbouring neck and jaw muscles demonstrated greatest EMG amplitude during their respective primary anatomical actions, which occurred in the absence of increased EMG amplitude recorded from the DCF muscles. The finding of substantial EMG activity of the DCF muscles only during neck actions that would require their activity, particularly cranio-cervical flexion, and not during actions involving the jaw, provide further assurance that the majority of myoelectric signals detected from the nasopharyngeal electrode are from the DCF muscles.

Masticatory muscle activity assessment and reliability of a portable electromyographic instrument.

STATEMENT OF PROBLEM: Masticatory muscle hyperactivity is thought to produce muscle pain and tension headaches and can cause excessive wear or breakage of restorative dental materials used in the treatment of prosthodontic patients. The quantification and identification of this type of activity is an important consideration in the preoperative diagnosis and treatment planning phase of prosthodontic care. PURPOSE: This study investigated the quantification process in complete denture/overdenture patients with natural mandibular tooth abutments and explored the reliability of instrumentation used to assess this parafunctional activity. MATERIAL AND METHODS: The nocturnal EMG activity in asymptomatic complete denture/overdenture subjects was assessed with and without prostheses worn during sleep. Because of the large variance within and between subjects, the investigators evaluated the reliability of the 3 instruments used to test nocturnal EMG activity in the sample. RESULTS: Electromyographic activity data of denture/overdenture subjects revealed no differences between prostheses worn versus not worn during sleep but demonstrated a very large variance factor. Further investigation of the instrumentation demonstrated a consistent in vitro as well as in vivo reliability in controlled laboratory studies. CONCLUSION: The portable EMG instrumentation used in this study revealed a large, uncontrollable variance factor within and between subjects that greatly complicated the diagnosis of parafunctional activity in prosthodontic patients.

Electromyographic-force characteristics in the assessment of oral function.

The purpose of this investigation was to examine the utility of EMG-force characteristics as reliable and valid parameters by which to assess oral function. Masseter-muscle activity was recorded during controlled isometric biting exercises performed at various bite openings and force levels on two separate occasions. Measured muscle-activity levels, as well as the EMG-force characteristics of slope and y-intercept, were compared between bite openings and experimental trials. Sensitivity, assessed as the ability to detect statistically significant differences in muscle function due to changes in muscle length, was found to be acceptable for all measurements, except the y-intercept parameter, and during production of minimal forces. Reproducibility, evaluated as the correspondence between values recorded at different experimental sessions, was best for the EMG-force parameter of slope and during production of higher forces. The results from this study support the following conclusions: (1) Substantial variations in muscle function exist between individuals; (2) acceptable reliability and sensitivity of quantitative EMG values can be achieved, especially at higher muscle-activity levels, by rigidly controlling and quantifying functional activities during experimental trials; (3) the slope of an EMG-force curve is a reproducible, quantitative, and functionally sensitive measurement for assessment of muscle function; and (4) the EMG-force y-intercept is not a reliable quantity by which muscle-function characteristics may be studied.

Spectral analysis of the masseter and anterior temporalis: an assessment of reliability for use in the clinical situation.

The electromyogram (EMG) of contracting muscles can be analysed in the frequency domain by spectral analysis. However, there is a need to establish the reproducibility of spectral parameters such as mean power frequency (MPF). This study examined the variation of MPF (masseter and anterior temporalis) between and within recording sessions. The MPF was found to be significantly reliable for both muscles, but considerable within-subject variation was found despite comprehensive measures to standardize recording methods and conditions. It is concluded that MPF may have clinical application in the diagnosis and treatment of patients with facial pain arising from muscle dysfunctions, but caution should be exercised in interpreting small changes in frequency, given the inherent variability of MPF.

Computer-aided modeling in the assessment of the biomechanical determinants of diverse skeletal patterns.

Aberrant functional patterns of the masticatory musculature have been alleged as a factor influencing the morphogenesis of mandibular dysplasias. These include such expressions as the hyperdivergent skeletal open bite and its counterpart, the hypodivergent skeletal deep bite. A lack of anatomic data dealing with the actual musculoskeletal orientations of these types has resulted in speculative reports on divergent anatomy and its purported effects. In this study anatomic dissections of a hyperdivergent and a hypodivergent human cadaver illustrated that skeletally dysmorphic types possess different spatial orientations of the masticatory adductors in relation to dentofacial structures. A two-dimensional analysis of static equilibrium using computer-aided modeling demonstrated that these two types produce biomechanically distinct modes of muscle action. Temporalis activity must be 40% higher in the hyperdivergent model as compared with its counterpart to produce a biting force of 500 N (112 lb). The data suggest a rationale for the weak biting forces previously reported in long-faced persons when compared with horizontally developed subjects. The direction of condylar reaction force was also found to vary from a vertical orientation in the hyperdivergent model to oblique in the hypodivergent model. "Physis-like" behavior of the condyle, which can orient axially toward loading forces, may present an explanation for the reported differences in the direction of condylar growth in dysmorphic persons. A finite element analysis pictured distinct regions of deformation and compression in a novel perspective to help evaluate the currency of accepted hypotheses of stress-induced osteogenesis. The data support previous work reporting a latent geometric interdependency existing between muscle orientation and mandibular morphology.

Computer-based assessment of habitual mastication.

A computer-based system to assess mandibular movements and EMG masseter and temporal muscle activity during habitual mastication was applied to 12 healthy subjects and the chewing performance was tested with a standardized bolus of crisp bread. A Siemens Sirognatograph instrument was used to record mandibular movements while EMG signals were recorded with surface silver-silver electrodes. Software provided data of single chewing cycles in space and versus time, of mean mandibular displacement during opening and closing, mean velocity, and EMG activity. Clockwise and counterclockwise cycles were computed separately. The data obtained allow the following conclusions: Habitual mastication is a rhythmic event with different envelopes of motion that alternate characteristically in each subject. Each chewing cycle accomplishes several tasks but, depending on its envelope, is probably more oriented to a specific performance. A mean chewing cycle can be constructed for each individual. Its pattern depends on the distribution of different envelopes of motion that alternate during the masticatory sequence. During closure, a prevalently isotonic and a prevalently isometric phase of muscle contraction can be distinguished. Mean movement and EMG data for the whole group are not distributed at random, but according to a typical pattern. The system seems to be finalized to a well-balanced function and distribution of loads.