Effect of tongue position on masseter and temporalis electromyographic activity during swallowing and maximal voluntary clenching: a cross‐sectional study

The purpose of this study was to measure and compare the tonic electromyographic (EMG) activity of the temporalis and masseter muscles following placement of the tongue either on the palate or in the floor of the mouth during swallowing and maximal voluntary clenching (MVC). Thirty healthy dental students with natural dentition and bilateral molar support, between the ages of 18 and 22, with no prior history of oro‐facial injury, or current or past pain in the jaw, mouth or tongue participated in the study. Tonic masseter and temporalis EMG activities were recorded using surface electrodes. Subjects were instructed to passively place the tongue either on the anterior hard palate or in the floor of the mouth during swallowing and MVC. At each tongue position, the resulting EMG was recorded. During swallowing, no significant difference in EMG activity was found either for the masseter (P‐value = 0·1592) or the temporalis (P‐value = 0·0546) muscles, regardless of the tongue position. During MVC, there was a statistically significant difference for both the masseter (P‐value = 0·0016) and the temporalis (P‐value = 0·0277) muscles with lower levels recorded with the tongue in the floor of the mouth. This study found that in normal, pain‐free subjects, placing the tongue in the floor of the mouth significantly reduces masticatory muscle activity during MVC. Thus, it may be considered as a possible therapeutic option to decrease masticatory muscle activity; however, further research is needed in patients with oro‐facial pain.     

Internal kinematics of the tongue in relation to muscle activity and jaw movement in the pig

Summary To explore the coordinative characteristics of tongue deformation, muscle activity and jaw movement during feeding, six ultrasonic crystals were implanted into the tongue body of ten 12‐week‐old Yucatan minipigs 1 week before the recording. These crystals formed a wedge‐shaped configuration to allow recording dimensional changes in lengths, anterior and posterior widths and posterior thicknesses of the tongue body during feeding. Wire electromyographic activities (EMG) of superior and inferior longitudinalis, verticalis/transversus, genioglossus, styloglossus, masseter and digastricus and jaw movements were recorded simultaneously. Signals from these three sources were synchronized for real‐time analyses. The results indicate: (i) dimensional changes were stereotypical in relation to each cycle of all three feeding behaviours; (ii) during chewing, expansion of tongue widths mainly occurred in the occlusal phase of jaw movement and was less coupled with the activity of tongue muscles, but the expansions of length and thickness were seen in the opening and closing phases and were better coupled with the activity of tongue muscles (P < 0·05); (iii) ingestion was characterized by the two‐phased jaw opening, early expansion of anterior width prior to the occlusal phase and strong associations between tongue deformation and muscle activity; (iv) during drinking, the duration of the opening and closing phases was significantly prolonged (P < 0·01), the durations of tongue widening and lengthening were significantly shortened (P < 0·05) and anterior widening was predominant in the opening rather than in the closing or occlusal phases as compared with chewing and ingestion; and (v) the intrinsic tongue muscles did not show more or stronger correlations with the tongue deformation than did the extrinsic tongue muscles. These results suggest that (i) regional widening, lengthening and thickening of the tongue body occurs sequentially in relation to jaw movement phases, but the initiation of tongue dimensional expansions does not correspond with the activation of tongue muscles simultaneously; (ii) there is a better coupling between tongue deformations and tongue muscle activations in the sagittal (lengthening and thickening) than the transverse (widening) planes; and (iii) the patterns and ranges of tongue deformation and their relations to muscle activity and jaw movement are task‐specific and the expansion magnitudes of tongue deformation does not have closer correlations with the amount of EMG activity in the intrinsic than the extrinsic tongue or jaw muscles.     

The effect of tongue position and resulting vertical dimension on masticatory muscle activity. A cross‐sectional study

The purpose of this study was to: (a) compare the tonic electromyographic (EMG) activity of the temporalis and masseter muscles between two tongue positions, (b) compare the vertical dimension (VD) resulting from each tongue position and (c) determine the influence of the VD on the tonic EMG activity for each tongue position. Thirty‐three healthy dental students with natural dentition and bilateral molar support, between the ages of 18 and 22 years, with no prior history of oro‐facial injury, or current or past pain in the jaw, mouth, or tongue participated in the study. Tonic masseteric and temporalis EMG activities were recorded using surface electrodes. Subjects were instructed to passively place the tongue either on the anterior hard palate or in the floor of the mouth. At each tongue position, the resulting EMG and VD were recorded. No significant difference in EMG activity was found for either the masseter (P‐value = 0·5376) or temporalis muscle (P‐value = 0·7410), between the two tongue positions. However, there was a significant difference in the VD resulting from the two different tongue positions, being greater with the tongue placed in the floor of the mouth. There was no statistically significant correlation between VD and EMG activity for both tongue positions. In spite of the lack of difference in the effect of both tongue positions on the masseteric and temporalis EMG activity, an increment of the VD was registered for the floor of mouth–tongue position. However, VD was not correlated with EMG activity for both tongue positions.     

Effect of experimental jaw muscle pain on EMG activity and bite force distribution at different level of clenching

Bite force at different levels of clenching and the corresponding electromyographic (EMG) activity in jaw‐closing muscles were recorded in 16 healthy women before, during and after painful stimulation of the left masseter muscle. Experimental pain was induced by infusion of 5·8% hypertonic saline (HS), and 0·9% isotonic saline (IS) was infused as a control. EMG activity was recorded bilaterally from the masseter and temporalis muscles, and static bite force was assessed by pressure‐sensitive films (Dental Pre‐scale) at 5, 50 and 100% of maximal voluntary contraction (MVC) during each session. Visual feedback was applied by showing EMG activity to help the subject perform clenching at 5, 50 and 100% MVC, respectively. EMG activity at 100% MVC in left and right masseter decreased significantly during painful HS infusion (1·7–44·6%; P < 0·05). EMG activity at 5% and 50% MVC was decreased during HS infusion in the painful masseter muscle (4·8–18·6%; P < 0·05); however, EMG activity in the other muscles increased significantly (18·5–128·3%; P < 0·05). There was a significant increase in bite force in the molar regions at 50% MVC during HS infusion and in the post‐infusion condition (P < 0·05). However, there were no significant differences in the distribution of forces at 100% MVC. In conclusion, experimental pain in the masseter muscle has an inhibitory effect on jaw muscle activity at maximal voluntary contraction, and compensatory mechanisms may influence the recruitment pattern at submaximal efforts.     

Relationship between myoelectric activity in masticatory muscles and bite force

Myoelectric activity in the anterior and posterior temporalis and in the masseter muscle was assessed in five subjects biting unilaterally on a bite fork at 50, 100 and 200 N for 60 s. The bite fork was placed between the right first premolars and the first molars. The ipsilateral muscle activity was recorded first, and the contralateral side was evaluated 1 wk later. The relationship between exerted force and EMG-activity was expressed as ratios between EMG-activity and related bite force. EMG-activity increased with increasing force for all muscles tested. Linearity was found for the anterior temporal muscle, but not for the other muscles. Four of the subjects participated in an endurance test, exerting maximum bite force on the right side for as long as possible. The EMG activity of the right masseter muscle was closely related to bite force, in contrast to the other tested muscles. The activity of the left muscles increased at the end of the endurance test.     

Relationship between myoelectric activity in masticatory muscles and bite force

Myoelectric activity in the anterior and posterior temporalis and in the masseter muscle was assessed in five subjects biting unilaterally on a bite fork at 50, 100 and 200 N for 60 s. The bite fork was placed between the right first premolars and the first molars. The ipsilateral muscle activity was recorded first, and the contralateral side was evaluated 1 wk later. The relationship between exerted force and EMG-activity was expressed as ratios between EMG-activity and related bite force. EMG-activity increased with increasing force for all muscles tested. Linearity was found for the anterior temporal muscle, but not for the other muscles. Four of the subjects participated in an endurance test, exerting maximum bite force on the right side for as long as possible. The EMG activity of the right masseter muscle was closely related to bite force, in contrast to the other tested muscles. The activity of the left muscles increased at the end of the endurance test.     

Effect of a repeated tongue‐lift motor task for tongue function

This study investigated the effect of repeated tongue motor tasks on suprahyoid muscle activity and tongue pressure. Fourteen participants performed three series of a standardized tongue‐lift training (TLT) task on each of five consecutive days. Electromyographic (EMG) activity from suprahyoid muscles and tongue pressure were recorded. In the first and third TLT series, participants were instructed only to target different force levels. During the second TLT series, visual feedback of the force level was given. One series consisted of three measurements [at 10%, 20%, and 40% of maximum voluntary contraction (MVC), respectively]. The coefficient of determination of the target force level–EMG curve and the target force level–tongue pressure curve was calculated from all series. There were no statistically significant day‐to‐day differences in EMG‐root mean square (RMS) values and tongue pressure during MVC. The coefficients of determination of tongue pressure in the first series on day 1 were statistically significantly lower than the coefficients of determination in the first series on day 5. These findings suggest that the control of tongue pressure improved, while the maximum force remained constant. These results could have implications for treatment paradigms related to learning for patients with compromised tongue function, such as swallowing disorders or dysphagia.     

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.     

Activity of inferior head of human lateral pterygoid muscle during standardized lateral jaw movements

OBJECTIVE: (a) To describe the changes in electromyographic (EMG) activity from selected jaw muscles during a standardized lateral jaw movement with the teeth together, and (b) to investigate the effects on jaw muscle activity of changes in both the rate of lateral jaw movement and the relative magnitude of jaw-closing force. DESIGN: In 16 healthy volunteers, recordings were made using a jaw-tracking system, of mid-incisor point (MIPT) movements, as well as EMG activity from the contralateral inferior head of the lateral pterygoid muscle (IHLP), and bilateral anterior and posterior temporalis, masseter and submandibular muscles, during lateral jaw movement tasks at two speeds and two closing force levels with the teeth together. RESULTS: The IHLP was the only muscle to show a consistent increase in activity in association with the outgoing phase of the task and a decrease during the return phase. Under high closing force at slow speed, the EMG activities of the IHLP and bilateral anterior temporalis and masseter muscles were significantly (p < 0.05) higher than those under a low closing force, while there was no significant change (p > 0.05) in bilateral posterior temporalis and submandibular muscles. The change from slow to fast lateral movement at low force did not significantly (p > 0.05) alter the mean activity except for the IHLP (increase in activity) and the contralateral anterior temporalis (decrease in activity). CONCLUSIONS: The data suggest that the IHLP is one of the principal jaw muscles involved in a lateral jaw movement with the teeth together while the other jaw muscles may play a contributory or facilitatory role.     

Task-related electromyographic spectral changes in the human masseter and temporalis muscles

The masticatory muscles differ in their fiber type composition. It can therefore be expected that their electromyographic (EMG) power spectra will differ during the performance of different bite force tasks. In the present study, surface EMG activity was picked up from the masseter and from the anterior and posterior temporalis muscles of nine adult subjects. At a bite force level as low as 25 N, the mean power frequency (MPF) values of the posterior temporalis were significantly lower than those of the masseter and anterior temporalis. The MPF values of the masseter muscles decreased with an increase of bite force magnitude, whereas the MPF values of the anterior and posterior temporalis did not change significantly. The MPF values were significantly influenced by the direction of bite force. The observed changes of MPF are possibly related to the recruitment of different fiber types, and support the concept that the masticatory muscles behave heterogeneously.     

Effect of experimental jaw-muscle pain on the spatial distribution of surface EMG activity of the human masseter muscle during tooth clenching

Summary This study tested the hypothesis that painful injections of glutamate into the human masseter muscle differentially affect the distribution of the electromyographic (EMG) activity in the masseter muscle at rest and during tooth clenching. Surface EMG signals were recorded bilaterally from the superficial masseter of nine healthy men with a grid of 32 electrodes, before and after intramuscular injection of glutamate or isotonic saline, during rest and isometric contractions at 20%, 40%, 60% and 80% of the maximal voluntary bite force. Intramuscular injection of glutamate evoked moderate pain (0–10 visual analogue scale: 6·4 ± 1·4), with sensory‐discriminative characteristics of the perceived pain, evaluated with the use of the McGill Pain Questionnaire (MPQ), similar to those previously reported for patients with temporomandibular disorders. There was no effect of the glutamate injection on EMG amplitude during rest, whereas during tooth clenching, the spatial distribution of the masseter EMG activity on both sides was more uniform in the painful condition compared to the control condition. Moreover, the overall EMG amplitude decreased on both sides during the more forceful tooth clenching following glutamate injection. In conclusion, a unilateral painful stimulation was associated with a bilateral inhibition of the masseter muscles during tooth clenching which resulted in a more uniform distribution of EMG activity.     

The relationship between lingual-palatal pressures and submental surface electromyographic signals

Summary  This study investigated the relationship between lingual-palatal pressures and submental surface electromyographic (sEMG) signals. During isometric and isotonic tongue press tasks, lingual-palatal pressures from the anterior, middle and posterior hard palate and submental sEMG signals were recorded. Peak values of both tasks and mean values of the isotonic task were analyzed using Pearson's correlations. The correlations ranged from slightly negative ( r  = −0·103) between the posterior tongue bulb and sEMG peaks in the isotonic condition, to positive ( r  = 0·360) between the posterior tongue bulb and sEMG peaks in the isometric condition. None of the correlations were statistically significant. Overall, the correlations between submental sEMG signals and lingual-palatal pressures were low. These results suggest that sEMG signals obtained from the submental region measure some of muscle activation during tongue press tasks, but are unable to capture discrete variations in lingual-palatal pressure.     

Modulation of masticatory muscle activity by tongue position

The purpose of this study was to test whether the tongue position affects the electromyographic (EMG) activities of masticatory muscles. We recorded the EMG activities of the masseter and anterior temporalis muscles in 10 skeletal Class I adults. Tongue position was monitored by two pressure transducers embedded in the midpalatal region and the lingual flange of a custom-made acrylic monoblock. We instructed subjects to assume three different tongue positions: rest, superior, and anterior. Friedman's test and Sheffe's F-test were used to statistically examine differences in muscle activities induced by changes in tongue position. Significant differences were found in masseter muscle activity between the rest and anterior positions and in anterior temporalis muscle activity between the rest and both the anterior and the superior tongue positions. We concluded that masticatory muscle activity is affected by tongue position.     

单侧后牙缺失对咀嚼肌肌电图的影响

目的:观察单侧后牙缺失对咀嚼肌肌电图的影响,从而探讨单侧后牙缺失在颞下颌关节(temporomandibular joint, TMJ)发病中的作用。方法:对40例单侧上颌后牙缺失患者组成的缺牙组和40例牙列完整的自愿者组成的对照组,进行肌电图检查。结果:缺牙组无论是松弛状态或紧咬时咀嚼肌的电位明显高于对照组(P<0.05),并且缺牙组紧咬时同名肌不对称性活动增加(P<0.05),其中对照组的咬肌肌电活动的对称性明显高于缺牙组(P<0.01),以上变化缺牙侧较非缺牙侧显著(P<0.05)。结论:单侧后牙缺失可以对咀嚼肌肌电图造成影响,可能是颞下颌关节疾病的发病原因之一。     

Effects of interocclusal distance on bite force and masseter EMG in healthy participants

The aim of this study was to investigate effects of interocclusal distance (IOD) on bite force and masseter electromyographic (EMG) activity during different isometric contraction tasks. Thirty‐one healthy participants (14 women and 17 men, 21·2 ± 1·8 years) were recruited. Maximal Voluntary Occlusal Bite Force (MVOBF) between the first molars and masseter EMG activity during all the isometric‐biting tasks were measured. The participants were asked to bite at submaximal levels of 20%, 40%, 60% and 80% MVOBF with the use of visual feedback. The thickness of the force transducer was set at 8, 12, 16 and 20 mm (= IOD), and sides were tested in random sequence. MVOBF was significantly higher at 8 mm compared with all other IODs (P < 0·001). Only in women, IOD always had significant influence on the corresponding root‐mean‐square (RMS) value of EMG (P < 0·011). When biting was performed on the ipsilateral side to the dominant hand, the working side consistently showed higher masseter EMG activity compared with the balancing side (P < 0·020). On the contralateral side, there was no difference between the masseter EMG at any IODs. The results replicated the finding that higher occlusal forces can be generated between the first molars at shorter IODs. The new finding in this study was that an effect of hand dominance could be found on masseter muscle activity during isometric biting. This may suggest that there can be a general dominant side effect on human jaw muscles possibly reflecting differences in motor unit recruitment strategies.     

Implant-supported prosthesis following Brånemark protocol on electromyography of masticatory muscles

Summary This research evaluated the effects of Brånemark protocol on electromyography of the masseter and temporal muscles. The patients were divided into two groups: Group I: patients who wore an implant‐supported prosthesis in the mandibular arch following Brånemark protocol, and maxillary removable complete dentures; Group II: dentate individuals (control). Electromyography was carried out at rest, right (RL) and left (LL) laterality, protrusion and maximum voluntary contraction (MVC). Data were compared by t‐test. At rest, a higher electromyographic (EMG) activity was observed in Group I, and the values were significant in the right masseter and left temporal muscles. In RL, there were statistically significant differences for right masseter (P < 0·01), left masseter and temporal muscles and for the left temporal muscle in LL (P < 0·05). In protrusion, Group I presented a higher EMG activity, and there was a statistically significant difference for the right masseter muscle (RM) (P < 0·05). In MVC, the EMG values were higher in Group II (control), but significant just for the right temporal muscle (P < 0·05). In conclusion, individuals with mandibular fixed dentures supported according to the Brånemark protocol and maxillary removable complete dentures showed a higher activity of masticatory muscles during the mandibular postural clinical conditions examined; however, in the MVC, Group I presented lower values when compared to dentate group. Despite presenting different EMG values in all of the clinical conditions, both groups showed similar EMG patterns of muscle activation which demonstrates that the proposed treatment can be considered as a good option for oral rehabilitation.     

Does long‐term use of unstable dentures weaken jaw muscles?

Summary Although it is well known that conventional denture wearers have lower maximum bite forces than dentate subjects, no previous studies have compared the strength of the jaw muscles between these two groups. This study compared maximum bite forces, electromyographic (EMG) activity and estimated jaw muscle strength among three groups: (i) 17 edentulous subjects using newly acquired implant‐retained overdentures (seven men, 10 women; mean age 60·3 ± 13·0 years); (ii) 10 age‐matched, fully dentate subjects (five men, five women; mean age 57·9 ± 11·0 years); and (iii) 39 young, fully dentate subjects (19 men, 20 women; mean age 24·4 ± 3·5 years). Electromyographic activity was recorded from subjects’ bilateral superficial masseter and anterior temporalis muscles while they generated maximum voluntary bite forces at the right central incisor, right first premolar and right first molar positions. Jaw muscle strength was estimated as the ratio of average EMG activity for all four muscles to the maximum bite force. At all three bite positions, edentulous subjects produced maximum bite forces that were less than half that of dentate subjects. Edentulous subjects also produced significantly less EMG activity and had significantly lower estimated jaw muscle strength. Our results suggest that weakened jaw muscles are one factor contributing to lower maximum bite forces among users of conventional dentures.     

Masticatory features,EMG activity and muscle effort of subjects with different facial patterns

Summary It has been suggested that craniofacial morphology plays an important role in masticatory function, however, there are controversies and unsolved questions that still require elucidation. The aims of this study were to evaluate masticatory performance, mandibular movement, electromyographic (EMG) activity and muscle effort of masseter and anterior temporal muscles during mastication. Seventy‐eight dentate subjects were selected and divided into three groups according to vertical facial pattern: brachyfacial, mesofacial and dolichofacial. Silicon‐based material was used for chewing tests. Masticatory performance was determined by a 10‐sieve method, and masticatory movements during mastication were assessed using a 3D mandibular tracking device. Electromyographic activities of masseter and anterior temporal muscles were evaluated during mastication, and muscle effort was calculated by the percentage of activity required for mastication based on maximum muscle effort. Data were analysed using anova and anova on‐ranks tests. Dolichofacial subjects presented significantly poorer masticatory performance (6·64 ± 2·04; 4·33 ± 0·70 and 3·67 ± 0·63), slower rate of chewing (1·34 ± 0·27, 1·18 ± 0·22 and 1·21 ± 0·20 cycles per second) and larger posterior displacement during mastication (6·22 ± 2·18; 5·18 ± 1·87 and 5·13 ± 1·89) than meso‐ and brachyfacial individuals, respectively. No statistical difference was detected among groups for the other masticatory movement parameters. There was no difference in absolute EMG amplitudes of masseter and anterior temporal muscles during mastication among groups, but the relative effort of both muscles was higher in dolichofacial, followed by meso‐ and brachyfacial subjects (masseter: 39·34 ± 2·25; 36·87 ± 4·05 and 33·33 ± 4·15; anterior temporal: 38·12 ± 1·61; 38·20 ± 8·01 and 35·75 ± 2·48). It was concluded that the vertical facial pattern influences masticatory performance, mandibular movement during mastication and the effort masticatory muscles required for chewing.     

Changes in masseteric hemodynamics time-related to mental stress

Mental stress may cause a dissociation of sympathetic outflow to different regions. However, it remains unclear how the sympathetic outflow to jaw muscles is related to other sympathetic outflow under mental stress. The objective of this study was to clarify the temporal relationship between the finger sweat expulsion elicited by mental stress and the hemodynamic and electromyographic changes in the masseter muscle. Healthy adult female volunteers participated in this study. Masseteric hemodynamic changes were closely time-related to mental stress, showing a decrease in oxygen saturation of muscle blood around the onset of mental stress. In contrast, EMG activity of jaw-closing muscles was not time-related to mental stress. These results suggest that mental stress induces hemodynamic changes that are not associated with EMG activity in the masseter muscle of healthy adult females.     

Differential activity patterns in the masseter muscle under simulated clenching and grinding forces

The aim of this study was to investigate (i) whether the masseter muscle shows differential activation under experimental conditions which simulate force generation during clenching and grinding activities; and (ii) whether there are (a) preferentially active muscle regions or (b) force directions which show enhanced muscle activation. To answer these questions, the electromyographic (EMG) activity of the right masseter muscle was recorded with five intramuscular electrodes placed in two deep muscle areas and in three surface regions. Intraoral force transfer and force measurement were achieved by a central bearing pin device equipped with three strain gauges (SG). The activity distribution in the muscle was recorded in four different mandibular positions (central, left, right, anterior). In each position, maximum voluntary contraction (MVC) was exerted in vertical, posterior, anterior, medial and lateral directions. The investigated muscle regions showed different amount of EMG activity. The relative intensity of the activation, with respect to other regions, changed depending on the task. In other words, the muscle regions demonstrated heterogeneous changes of the EMG pattern for the various motor tasks. The resultant force vectors demonstrated similar amounts in all horizontal bite directions. Protrusive force directions revealed the highest relative activation of the masseter muscle. The posterior deep muscle region seemed to be the most active compartment during the different motor tasks. The results indicate a heterogeneous activation of the masseter muscle under test conditions simulating force generation during clenching and grinding. Protrusively directed bite forces were accompanied by the highest activation in the muscle, with the posterior deep region as the most active area.