Relations between the results of complex clinical and neurophysiological examinations in patients with temporomandibular disorders symptoms

Objective: Reinvestigation of clinical importance of surface electromyography recordings (sEMG) from the masticatory, neck and shoulder girdle muscles in patients with various clinically detected temporomandibular disorders (TMDs).

Methods: Fifty women with myalgia diagnosis of Axis I DC/TMD and the same number of healthy female volunteers were studied clinically and neurophysiologically by means of sEMG.

Results: Unilateral more than bilateral complex symptoms of TMDs were related to the non-neurogenic masticatory rather than neck and shoulder girdle muscles dysfunctions at rest. A strong negative correlation between masticatory muscles activity at rest and during maximal contraction was found (r_s = ?0.778), mainly in the masseter muscle.

Conclusion: sEMG is a suitable tool for prosthodontists because it provides objective results on the stomatognathic system muscles function. Pain and other temporomandibular symptoms detected mostly unilaterally significantly increase muscle tension of the masticatory muscles and diminish muscle motor units recruitment during maximal contraction. Effects may spread to the neck and shoulder girdle muscles.     

Reorganization of muscle activity in patients with chronic temporomandibular disorders

ObjectiveTo investigate whether reorganization of muscle activity occurs in patients with chronic temporomandibular disorders (TMD) and, if so, how it is affected by symptomatology severity.MethodsSurface electromyography (sEMG) of masticatory muscles was made in 30 chronic TMD patients, diagnosed with disc displacement with reduction (DDR) and pain. Two 15-patient subgroups, with moderate (TMDmo) and severe (TMDse) signs and symptoms, were compared with a control group of 15 healthy subjects matched by age. The experimental tasks were: a 5 s inter-arch maximum voluntary clench (MVC); right and left 15 s unilateral gum chewing tests. Standardized sEMG indices characterizing masseter and temporalis muscles activity were calculated, and a comprehensive functional index (FI) was introduced to quantitatively summarize subjects’ overall performance. Mastication was also clinically evaluated.ResultsDuring MVC, TMDse patients had a significantly larger asymmetry of temporalis muscles contraction. Both TMD groups showed reduced coordination between masseter and temporalis muscles’ maximal contraction, and their muscular activity distribution shifted significantly from masseter to temporalis muscles. During chewing, TMDse patients recruited the balancing side muscles proportionally more than controls, specifically the masseter muscle. When comparing right and left side chewing, the muscles’ recruitment pattern resulted less symmetric in TMD patients, especially in TMDse. Overall, the functional index of both TMDmo and TMDse patients was significantly lower than that obtained by controls.ConclusionsChronic TMD patients, specifically those with severe symptomatology, showed a reorganized activity, mainly resulting in worse functional performances.     

Headache attributed to masticatory myofascial pain: impact on facial pain and pressure pain threshold

There is no clear evidence on how a headache attributed to temporomandibular disorder (TMD) can hinder the improvement of facial pain and masticatory muscle pain. The aim of this study was to measure the impact of a TMD‐attributed headache on masticatory myofascial (MMF) pain management. The sample was comprised of adults with MMF pain measured according to the revised research diagnostic criteria for temporomandibular disorders (RDC/TMD) and additionally diagnosed with (Group 1, n = 17) or without (Group 2, n = 20) a TMD‐attributed headache. Both groups received instructions on how to implement behavioural changes and use a stabilisation appliance for 5 months. The reported facial pain intensity (visual analogue scale – VAS) and pressure pain threshold (PPT – kgf cm^?2) of the anterior temporalis, masseter and right forearm were measured at three assessment time points. Two‐way anova was applied to the data, considering a 5% significance level. All groups had a reduction in their reported facial pain intensity (P < 0·001). Mean and standard deviation (SD) PPT values, from 1·33 (0·54) to 1·96 (1·06) kgf cm^?2 for the anterior temporalis in Group 1 (P = 0·016), and from 1·27 (0·35) to 1·72 (0·60) kgf cm^?2 for the masseter in Group 2 (P = 0·013), had significant improvement considering baseline versus the 5th‐month assessment. However, no differences between the groups were found (P > 0·100). A TMD‐attributed headache in patients with MMF pain does not negatively impact pain management, but does change the pattern for muscle pain improvement.     

Effects of orthognathic surgery for class III malocclusion on signs and symptoms of temporomandibular disorders and on pressure pain thresholds of the jaw muscles

The aim of this longitudinal study was to determine the effects of orthognathic surgery on signs and symptoms of temporomandibular disorders (TMD) and on pressure pain thresholds (PPTs) of the jaw muscles. Fourteen consecutive class III patients undergoing pre-surgical orthodontic treatment were treated by combined Le Fort I osteotomy and bilateral sagittal ramus osteotomy. The clinical examination included the assessment of signs and symptoms of TMD and the assessment of PPTs of the masseter and temporalis muscles. Anamnestic, clinical and algometric data were collected during five sessions over a 1-year period. Seven out of 14 patients presented with disc displacement with reduction at baseline, whereas four patients (two of them were new cases) did so at the end of follow up (p>0.05). None of the patients were diagnosed with myofascial pain of the jaw muscles at the beginning or end of follow up. PPTs of the masseter and temporalis muscles did not change significantly from baseline values throughout the whole study period. The occurrence of signs and symptoms of TMD fluctuates with an unpredictable pattern after orthognathic surgery for class III malocclusions.     

The diagnostic value of pressure algometry in myofascial pain of the jaw muscles

Recent evidence suggests that evaluation of muscle tenderness in temporomandibular disorders (TMDs) patients might be improved by the use of pressure algometry; nevertheless, the evaluation of the diagnostic value of this tool has received little attention. The aim of this study was to assess the diagnostic value of pressure algometry in myofascial pain of the jaw muscles, by calculation of sensitivity (Se), specificity (Sp) and positive predictive values (PPV). Pressure pain thresholds (PPTs) of masseter and anterior temporalis muscles were assessed in 40 female myogenous TMD patients and 40 age-matched female controls. PPTs were significantly lower ( P <0·001) in TMD patients than in control subjects for both masseter and temporalis muscles, being 40–50% of the control values. Setting a cutoff value 1 s.d. below the mean PPT values of control subject, sensitivity and specificity were 0·67 and 0·85, respectively, for the masseter muscle and 0·77 and 0·87, respectively, for the temporalis muscle. When taking into account the prevalences of myofascial pain in the general population and in TMD clinics, the PPV ranged from 0·5 to 0·7. As a result of the low PPV, pressure algometry has strong limitations when used as a solitary diagnostic tool.     

Assessment of thickness and function of masticatory and cervical muscles in adults with and without temporomandibular disorders

Objective

The aim of this study was to evaluate the maximal bite force (MBF), electromyographic (EMG) activity and thickness of the masseter, anterior part of the temporalis and sternocleidomastoid (SCM) muscles in a group of young adults with and without temporomandibular disorders (TMDs).

Design

Nineteen individuals comprised the TMD group (6 males/13 females, aged 25.4 ± 3.8 years), classified based on the Research Diagnostic Criteria for TMD (RDC/TMD), and 19 comprised the control group (6 males/13 females, aged 24.1 ± 3.6 years). The MBF was determined with a transducer placed between the dental arches at the first molars level (N). The muscles were evaluated bilaterally at rest and during maximal voluntary clenching (MVC) by assessing EMG activity and performing ultrasonography (USG). The mean values of these measures for both sides of the mouth were used. The normality of the distributions was assessed by the Shapiro–Wilks test. Variables between groups and genders were compared using two-way factorial ANOVA test and correlated using the Spearman coefficient (α = 0.05). Unpaired t test was used to compare variables between TMD subgroups. Logistic regression analysis was used to identify the variables associated with the presence of TMD.

Results

MBF, EMG and USG data were similar among clinical groups and among TMD subgroups. The thickness of masseter and SCM muscles in the relaxed and clenching states were significantly higher in males than females. On the other hand, the EMG of the temporalis muscle in the rest state was significantly higher in females than males. Additionally, the MBF was positively correlated with the USG characteristics of masseter and SCM muscles, as well as with the EMG activity of masseter and temporalis muscles in the TMD group. In this group, there was also a positive correlation between the thickness of the masseter muscle and its activity. On the other hand, the thickness of the SCM muscle was negatively correlated with its activity. A lower MBF was independently associated with the presence of TMD.

Conclusions

Subjects with TMD exhibited similar values of MBF, thickness and electrical activity of masticatory and cervical muscles when compared with controls; positive correlations observed between these variables may suggest a muscular alteration in TMD patients and a co-activation of masticatory and cervical muscles during mandibular movement. This fact may also be confirmed by the negative association between bite forces and presence of TMD.     

The effect of supervised exercise on localized TMD pain and TMD pain associated with generalized pain

Objectives: To evaluate the effect of a supervised exercise program in patients with localized/regional temporomandibular disorder (TMD) pain and with TMD associated with generalized pain.

Material and methods: Consecutively referred patients with localized/regional TMD pain (n?=?56; 46 women and 10 men, mean age 44 years) and TMD associated with generalized pain (n?=?21; 21 women, mean age 41 years) participated. Patients underwent a 10-session structured supervised exercise program over 10–20 weeks that included relaxation, and coordination and resistance training of the jaw and neck/shoulders. The outcomes were jaw pain intensity on the Numerical Rating Scale, endurance time for jaw opening and protrusion against resistance and chewing, and effect of pain on daily activities.

Results: After the exercise program, a reduction in jaw pain was reported by the local (p?=?.001) and general (p?=?.011) pain groups. There were no significant differences in jaw pain intensity between the groups, before (p?=?.062) or after treatment (p?=?.121). Endurance time increased for both groups for jaw opening/protrusion (both p?<?.001) and chewing (both p?=?.002). The effect of jaw pain on daily activities decreased after exercise compared to baseline for both the local (p?<?.001) and general (p?=?.008) pain groups.

Conclusions: Supervised exercise can reduce TMD pain and increase capacity in patients with TMD. The results suggest that activation of the jaw motor system with exercise has a positive effect in patients with localized/regional TMD pain and TMD associated with generalized pain.     

Electromyographic power spectrum of jaw muscles during clenching in unilateral temporomandibular joint osteoarthritis patients

The relationship between temporomandibular joints (TMJ) osteoarthritis and masticatory muscle disorders is poorly understood. The data are sparse, the results are conflicting, and electromyographic (EMG) power spectrum analysis has not been used. The aims of this study were to compare the differences in EMG power spectrum during, and pressure pain thresholds (PPTs) before and after, sustained clenching in patients with unilateral TMJ osteoarthritis and healthy control subjects. Nineteen patients with unilateral TMJ osteoarthritis without masticatory muscle pain and 20 control subjects were evaluated. We measured EMG amplitudes at maximum voluntary contraction, median frequency from the EMG power spectrum during sustained clenching at 70% and PPTs before and after the clenching in both temporalis and masseter muscles. There were no significant differences in PPT decrease between muscles or between groups during sustained clenching. There were no significant differences in maximum voluntary contraction EMG activity ratios of affected to unaffected sides between groups, or of masseter to temporalis muscles between affected and unaffected side of patients with TMJ osteoarthritis. Median frequencies decreased from the beginning to the end of the sustained clench, and the interaction between group and clench was significant: the median frequency decrease was larger in the osteoarthritis group. Our results suggested that masticatory muscles of patients with unilateral TMJ osteoarthritis are more easily fatigued during sustained clenching than normal subjects.     

Effects of prolonged gum chewing on pain and fatigue in human jaw muscles

Gum chewing has been accepted as an adjunct to oral hygiene, as salivary stimulant and vehicle for various agents, as well as for jaw muscle training. The aim of this study was to investigate the effects of prolonged gum chewing on pain, fatigue and pressure tenderness of the masticatory muscles. Fifteen women without temporomandibular disorders (TMD) were requested to perform one of the following chewing tasks in three separate sessions: chewing a very hard gum, chewing a soft gum, and empty-chewing with no bolus. Unilateral chewing of gum or empty chewing was performed for 40 min at a constant rate of 80 cycles/min. In each session, perceived muscle pain and masticatory fatigue were rated on visual analog scales (VAS) before, throughout, and after the chewing task. Pressure pain thresholds (PPTs) of masseter and anterior temporalis muscles were assessed before and immediately after the chewing tasks, and again after 24 h. The VAS scores for pain and fatigue significantly increased only during the hard gum chewing, and after 10 min of recovery VAS scores had decreased again, almost to their baseline values. No significant changes were found for PPTs either after hard or soft gum chewing. The findings indicate that the jaw muscles recover quickly from prolonged chewing activity in subjects without TMD.     

Pressure pain threshold in the detection of masticatory myofascial pain: an algometer-based study

AIMS: To compare pressure pain threshold (PPT) values for masticatory muscles in patients with signs and symptoms of myofascial pain and in asymptomatic individuals. METHODS: Fifty women with masticatory myofascial pain comprised the symptomatic group (group 1), while 49 TMD symptom-free women were selected as controls (group 2). The PPT was obtained with the aid of an algometer by applying pressure to the masseter and to the anterior, middle, and posterior temporalis. A 90.8% specificity value was used to determine the appropriate PPT cutoff values for all 4 muscles studied. Receiver operator characteristic (ROC) curve areas and the likelihood ratio (LR) were also evaluated. RESULTS: The 3-way ANCOVA test (group, muscle, and side) revealed a significantly lower PPT for all muscles in the symptomatic group (P < .001). The lowest overall PPT was found for the masseter muscle, followed by the anterior, middle, and posterior temporalis (P < .001). The 90.8% specificity was obtained with PPT values of 1.5 kgf/cm2 for the masseter, 2.47 kgf/cm2 for the anterior temporalis, 2.75 kgf/cm2 for the middle temporalis, and 2.77 kgf/cm2 for the posterior temporalis. The anterior temporalis had the highest LR. ROC curve areas of 0.84, 0.92, 0.90, and 0.90 were obtained for the masseter, anterior, middle, and posterior temporalis, respectively. CONCLUSION: The masseter and temporalis muscles require different pressures for distinguishing masticatory myofascial pain patients from asymptomatic individuals. Because the highest sensitivity (77%) and LR were found for the anterior temporalis, this muscle was considered to have the most suitable discriminative capacity.     

Comparison of algometry and palpation in the recognition of temporomandibular disorder pain complaints

AIMS: To determine the construct validity of algometry and to compare it with that of palpation, and to compare tenderness of masticatory muscle sites and the temporomandibular joint (TMJ) on palpation and on algometry. Methods: Two hundred fifty subjects, 148 with temporomandibular disorder (TMD) pain complaints, underwent a standardized blinded physical examination that included pain-intensity measures on palpation and pressure pain threshold measures on algometry of masseter muscle sites, temporalis muscle sites, and the TMJ. Results: Logistic regression analysis indicated that the recognition of TMD pain complaints based on pressure algometry was comparable to that of palpation (R2 = 0.22 and R2 = 0.21, respectively). The masseter muscles were most tender to palpation and algometry, followed by the TMJs and the temporalis muscles. Conclusion: Construct validity of algometry in the recognition of TMD pain complaints is comparable to that of palpation, and differences in tenderness on palpation and on algometry are found between masticatory muscle sites and the TMJ.     

Widespread mechanical pain hypersensitivity in patients with chronic migraine and temporomandibular disorders: relationship and correlation between psychological and sensorimotor variables

Objective: This study aimed to assess mechanical hyperalgesia in the trigeminal and extra-trigeminal regions in patients with chronic migraine (CM) and temporomandibular disorders (TMD) in comparison to asymptomatic subjects and to determine the association between sensorimotor variables and psychological and disability variables and evaluate the prediction of a sensorimotor variables though psychological and disability variables in patients with CM and TMD.

Material and methods: A total of 52 subjects with concomitant CM and TMD and 30 asymptomatic subjects were included in the study. The pressure pain threshold (PPT), maximal mouth opening (MMO) and a series of self-reported factors were compared.

Results: There were 52?CM and TMD (92.3% women and 7.7% men; age?=?46.2?±?9.5) and 30 asymptomatic subjects (80% women and 20% men; age?=?47.4?±?10). Differences were found between patients with CM and TMD and asymptomatic participants (p?<?.01) when comparing the PPTs in the trigeminal and extra-trigeminal regions. The PPT for the trigeminal region was predicted by depressive symptoms (variance of 18%) as well as disability and craniofacial pain (variance of 20%). The extra-trigeminal region PPT was predicted by depressive symptoms (variance of 10%), and pain-free MMO was predicted by disability and craniofacial pain (variance of 24%).

Conclusions: This study suggests that patients with CM and TMD present with generalized mechanical hyperalgesia. In addition, an association between sensorimotor, psychological and disability variables was observed.     

Impact of sleep bruxism on masseter and temporalis muscles and bite force

Objectives: This study aimed to analyze the impact of sleep bruxism (SB) on electromyography (EMG) activity and the thickness of the masseter and temporal and maximal molar bite force. Method: Ninety individuals, aged between 18 and 45 years, were selected and divided into two groups: Group I (case group, 45 individuals with SB) and Group II (control group, 45 individuals without SB). A diagnosis of SB was made from polysomnography. Results: The data obtained from EMG and the muscle thickness and the maximal molar bite force were tabulated (SPSS 21.0), normalized, and subjected to statistical analysis (p ≤ 0.05). Comparisons between the groups showed significant differences regarding the habitual chewing of hard food for the left temporalis muscle (p = 0.04) and the chewing of soft food for the right masseter muscle (p = 0.04), but no significant differences for the measurements of muscle thickness and maximal molar bite force. Discussion: The present data suggest that SB negatively altered the masticatory muscles’ functions. Based on the results of this research, it can be concluded that individuals with SB showed decreased EMG activity in the masticatory muscles.     

Asymmetric activation of temporalis, masseter, and sternocleidomastoid muscles in temporomandibular disorder patients

The aim of this study was to analyze the symmetry of the electromyographic (EMG) activity of the temporalis, masseter, and sternocleidomastoid (SCM) muscles in volunteers divided into a control group and a temporomandibular disorder (TMD) group. The surface EMG recordings were made during mandibular rest position, maximal intercuspal position, and during the chewing cycle. Normalized EMG waves of paired muscles were compared by computing a percentage overlapping coefficient (POC). The difference between the groups and between the static and dynamic clenching tests was analyzed through repeated measures, ANOVA. Symmetry of the temporalis, masseter, and SCM muscles activity was smaller in the TMD group compared to the control group. The mandibular postures were also significantly different among themselves. The asymmetric activation of jaw and neck muscles was interpreted as a compensatory strategy to achieve stability for the mandibular and cervical systems during masticatory function.     

Two repetitive bouts of intense eccentric‐concentric jaw exercises reduce experimental muscle pain in healthy subjects

High‐intensity eccentric‐concentric contractions of the jaw‐closing muscles induce muscle soreness, fatigue and functional impairment of the jaw, resembling the symptoms of myalgia, according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). However, it is claimed that repetition of similar exercises can minimise these detrimental effects. This study aimed to evaluate the response of jaw‐closing muscles following two series of intense eccentric‐concentric exercises of the masticatory muscles in healthy subjects. Twelve pain‐free participants underwent 2 sessions of intense eccentric‐concentric jaw exercises, with 1‐week interval in between. Each session of jaw exercises comprises 6 sets of 5‐minute‐long bouts of concentric‐eccentric contractions. Self‐reported muscle fatigue and pain, maximum mouth opening without pain (MMO), pain pressure thresholds (PPTs) of temporalis and masseter muscles and maximum voluntary bite force (MVBF) were recorded before, immediately after, 24 and 48 hours after each bout of exercises. ANOVA for repeated measurements was used to analyse the data. During session 2, muscle pain and fatigue were statistically significantly decreased (P < .05) as compared to session 1. Furthermore, statistically significant increases of MVBF (P < .005), MMO (P < .005) and PPTs (P < .005) were found at session 2 as compared to session 1. Within the limitations of the study, is can be concluded that the repetition of eccentric‐concentric jaw‐closing exercises results in signs of muscle training. Future studies can elucidate whether this motor training might be useful for the treatment of myalgia.     

稳定性咬合板治疗颞下颌关节紊乱病的咀嚼肌肌电图研究

目的：通过对颞下颌关节紊乱病（Temporomandibular disorders,TMD）患者进行稳定性咬合板的可逆性咬合治疗,然后利用肌电图仪测量治疗前后患者的咀嚼肌（TA和MM）的肌电情况,分析探讨用稳定性咬合板对颞下颌关节紊乱病患者咀嚼肌肌电图的影响。方法：选取来我院就诊的10例咀嚼肌功能紊乱患者,在稳定性咬合板治疗前和治疗后3个月时,分别用肌电图仪对其咀嚼肌（TA和MM）进行肌电检查,并通过比较治疗前后的咀嚼肌活动不对称指数情况。结果：戴入稳定性咬合板3个月后,颞肌前束与咬肌的MPP和ICP高电位降低（P〈0.05）;最大紧咬时双侧咀嚼肌总体不对称性指数（Astot）、双侧颞肌不对称性指数（ASTA）和双侧咬肌不对称性指数（ASMM）均降低（P〈0.05）。结论：颞下颌关节紊乱病患者通过稳定性咬合板进行咬合治疗后,使患者双侧咀嚼肌的MPP和ICP高电位较治疗前有明显的降低,最大紧咬时双侧咀嚼肌活动不对称性得到明显的改善。     

Mechanism of motor coordination of masseter and temporalis muscles for increased masticatory efficiency in mice

The demand for the use of mice as animal models for elucidating the pathophysiologies and pathogeneses of oral motor disorders has been increasing in recent years, as more and more kinds of genetically modified mice that express functional disorders of the stomatognathic system become available. However, the fundamental characteristics of mouse jaw movements during mastication have yet to be fully elucidated. The purpose of this study was to investigate the roles of the masseter and temporalis muscles, and the mechanisms of motor coordination of these muscles for increasing masticatory efficiency in the closing phase in mice. Twenty‐two male Jcl:ICR mice were divided into control (n = 8), masseter‐hypofunction (n = 7) and temporalis‐hypofunction groups (n = 7). Botulinum neurotoxin type A (BoNT?A) was used to induce muscle hypofunction. The masticatory movement path in the horizontal direction during the occlusal phase became unstable after BoNT?A injection into the masseter muscle. BoNT?A injection into the temporalis muscle decreased antero‐posterior excursion of the late‐closing phase corresponding to the power phase of the chewing cycle. These results suggest that the masseter plays an important role in stabilizing the grinding path, where the food bolus is ground by sliding the posterior teeth from back to front during the occlusal phase. The temporalis plays a major role in retracting the mandible more posteriorly in the early phase of closing, extending the grinding path. Masticatory efficiency is thus increased based on the coordination of activities by the masseter and temporalis muscles.     

Swallowing changes related to chronic temporomandibular disorders

Objectives

To investigate whether chronic temporomandibular disorder (TMD) patients showed any changes in swallowing compared to a control group. Moreover, it was examined whether swallowing variables and a valid clinic measure of orofacial myofunctional status were associated.

Material and methods

Twenty-three patients with chronic TMD, diagnosed with disc displacement with reduction (DDR) and pain, according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD), and 27 healthy volunteers (control group) were compared. Surface electromyography (EMG) of the temporalis, masseter, sternocleidomastoid, and suprahyoid muscles was performed during swallowing tasks of thin liquid (10 and 15 mL) and spontaneous saliva. Data were normalized.

Results

Compared to the control group, TMD patients showed a prolonged duration of swallowing for liquid and saliva and required a longer time to reach the activity peak and half the integral. While the overall mean value of the relative peaks was similar for the groups, the suprahyoid peak was significantly lower in the TMD group during swallowing of liquid. Moreover, TMD patients recruited the jaw elevator muscles proportionally more than controls. The orofacial myofunctional status was moderately correlated with EMG parameters.

Conclusion

Patients with chronic TMD showed temporal prolongation and changes in the relative activity of the muscles during the swallowing tasks.

Clinical relevance

The present results contribute additional evidence regarding the reorganization of muscle activity in patients with chronic TMD.

     

The effect of culture on pain sensitivity

Cross‐cultural differences in pain sensitivity have been identified in pain‐free subjects as well as in chronic pain patients. The aim was to assess the impact of culture on psychophysical measures using mechanical and electrical stimuli in patients with temporomandibular disorder (TMD) pain and pain‐free matched controls in three cultures. This case–control study compared 122 female cases of chronic TMD pain (39 Saudis, 41 Swedes and 42 Italians) with equal numbers of age‐ and gender‐matched TMD‐free controls. Pressure pain threshold (PPT) and tolerance (PPTo) were measured over one hand and two masticatory muscles. Electrical perception threshold and electrical pain threshold (EPT) and tolerance (EPTo) were recorded between the thumb and index fingers. Italian females reported significantly lower PPT in the masseter muscle than other cultures (P < 0·001) and in the temporalis muscle than Saudis (P = 0·003). Swedes reported significantly higher PPT in the thenar muscle than other cultures (P = 0·017). Italians reported significantly lower PPTo in all muscles than Swedes (P ≤ 0·006) and in the masseter muscle than Saudis (P < 0·001). Italians reported significantly lower EPTo than other cultures (P = 0·01). Temporomandibular disorder cases, compared to TMD‐free controls, reported lower PPT and PPTo in all the three muscles (P < 0·001). This study found cultural differences between groups in the PPT, PPTo and EPTo. Overall, Italian females reported the highest sensitivity to both mechanical and electrical stimulation, while Swedes reported the lowest sensitivity. Mechanical pain thresholds differed more across cultures than did electrical pain thresholds. Cultural factors may influence response to type of pain test.     

Electromyographic activity of superficial masseter and anterior temporal muscles during unilateral mastication of artificial test foods with different textures in healthy subjects

Objectives

This study aimed to examine the electromyographic activity of superficial masseter and anterior temporal muscles during chewing gum and gummy jelly mastication in healthy subjects to reveal the difference of neuromuscular control of jaw-closing muscles, according to the food texture.

Materials and methods

Electromyographic activity was recorded in 30 adults with Angle Class I occlusion and unimpaired function from the bilateral superficial masseter and anterior temporal muscles during unilateral mastication of two test foods: standardized gummy jelly and color-changeable chewing gum. Differences in normalized electromyographic activity and asymmetry index values between gummy jelly and chewing gum mastication were analyzed during the early, middle, and late phases of mandibular closure. Furthermore, changes among the three closing phases were compared for each test food.

Results

High electromyographic activity of both muscles tended to occur bilaterally during the middle and late closing phases during gummy jelly mastication, but increased muscle activity in the late closing phase was not observed during chewing gum mastication. The asymmetry index of the superficial masseter muscle increased significantly from early to late closure, regardless of the food texture, but it tended to decrease for the anterior temporal muscle during gummy jelly mastication.

Conclusion

The different aspects of the chewing process between the comminution and mixing test measures are necessary to elicit the different human neuromuscular strategies of chewing for different test foods.

Clinical relevance

These characteristic EMG activities of the superficial masseter and anterior temporalis muscles may be used as supporting diagnostic information during patient assessments and a reference during evaluation of masticatory system disharmony or dysfunction.