[Masticatory performance and assessment of life quality of children with ectodermal dysplasia after prosthetic rehabilitation]

OBJECTIVE

To evaluate masticatory performance and life quality of children with ectodermal dysplasia (ED) after prosthetic rehabilitation.

METHODS

Six children with ED received denture restoration and 18 healthy children were involved in this study. The surface electromyography (EMG) of masseter (MM) and anterior temporalis (TA) during clenching and chewing movement were recorded. The EMG amplitude, area, asymmetry index of total and activity index of MM/TA were compared at each stage. The masticatory efficiency was measured with spectrophotometer. The life quality was assessed using visual analogue scale questionnaire.

RESULTS

The EMG amplitude of MM and TA during chewing in ED Group were 41.7% and 45.6% of the control group respectively, the area were 35.9% and 36.0% respectively. Significant difference in asymmetry index of total during clenching was observed between the two groups (P < 0.05) but not during chewing (P > 0.05). The differences of activity index of MM/TA during clenching and chewing between the two groups were not detected (P > 0.05). The masticatory efficiency of ED group was 67.2% of the control group. The score of chewing function in children with ED after prosthetic rehabilitation was three times higher than before, and no difference was present between the two groups (P > 0.05).

CONCLUSIONS

Early prosthetic rehabilitation can significantly improve the masticatory performance and life quality of children with ED.

Effect of natural mediotrusive contact on electromyographic activity of jaw and cervical muscles during chewing

OBJECTIVE

This study evaluated the effect of a natural mediotrusive contact on the electromyographic (EMG) activity of the anterior temporalis and sternocleidomastoid muscles during chewing in healthy subjects.

MATERIALS AND METHODS

The study sample included two groups of 15 subjects each (Group 1: with natural mediotrusive contact; Group 2: without natural mediotrusive contact). Bilateral surface EMG activity was recorded on anterior temporalis and sternocleidomastoid muscles during unilateral chewing of a half cookie and unilateral chewing of a piece of apple. Anterior temporalis and sternocleidomastoid muscle activity was normalized against activity recorded during maximal voluntary clenching in intercuspal position and maximal intentional isometric head-neck rotation to each side, respectively. The partial and total asymmetry indexes were also calculated. Data were analyzed using Mann-Whitney, Wilcoxon and unpaired t-test.

RESULTS

EMG activity of anterior temporalis and sternocleidomastoid muscles showed no significant difference between the groups. EMG activity of anterior temporalis was similar between working and non-working sides during chewing in both groups. EMG activity of sternocleidomastoid muscle was higher in the working side than in the non-working side in Group 2 subjects. Asymmetry indexes were not significantly different between groups.

CONCLUSIONS

The similar EMG pattern and asymmetry indexes observed suggest the predominance of central nervous control over peripheral inputs on anterior temporalis and sternocleidomastoid motor neuron pools.

Electromyographic evaluation of masticatory muscles in dentate patients versus conventional and implant-supported fixed and removable denture wearers- a preliminary report comparing model foods

PURPOSE

To evaluate differences in masticatory muscle function during chewing of model foods designed to differ in fracture strength between dentate subjects (n = 5, ages 59 to 68 years) versus patients treated with a maxillary conventional complete denture opposing natural dentition or one of the following types of mandibular complete dentures: conventional, implant-supported overdenture, implant-supported fixed denture (n = 20, ages 45 to 83 years). The authors hypothesized that denture wearers would differ in duration of chewing, frequency of chewing, and masticatory muscle activity while preparing a bolus for swallowing.

MATERIALS AND METHODS

Surface electromyography was recorded bilaterally from the masseter, anterior temporalis, and anterior digastric. Masticatory muscle activity was evaluated using scaled values of the area under the electromyographic curve, while subjects chewed agar-based model foods with different fracture strengths. Chewing duration and frequency also were calculated from electromyographic recordings. Mixed model analysis of variance with "subject" as a random factor was used during statistical analysis. Logarithmic transformation was required to achieve normalization of residuals for the duration of chewing and the relative masticatory muscles activity, but not for the chewing frequency.

RESULTS

Relative masticatory muscle activity was 2.57 times higher for the denture wearers than for the dentate subjects during chewing of model foods (P < .0001). The reduction in masticatory muscle activity from the 1st to the 10th chewing cycle was proportionally less in magnitude and occurred more gradually for denture wearers compared to dentate subjects. While chewing sequence duration increased with food fracture strength, it did not differ significantly in treatment versus dentate groups. Chewing cycle frequency did not differ between groups or with food fracture strength.

CONCLUSIONS

The observed increases in relative masticatory muscle activity for denture wearers compared to the dentate subjects during oral food processing likely reflect supplemental mechanical efforts to accommodate the use of dentures for preparing a bolus for swallowing.

Thirty-year follow-up of a TMD case treated based on the neuromuscular concept

AIM

Occlusal therapy is employed to alleviate the symptoms of a temporomandibular disorder (TMD) at times. However, the long-term effect of occlusal therapy in the masticatory system is not well understood. This case study aims to present a 30-year follow-up of a TMD case.

METHODOLOGY

The patient developed TMD with intermittent closed lock of the left temporomandibular joint (TMJ). Chief complaints included trismus, pain, and noise of the left TMJ during function. The patient's occlusal disharmony was assessed with use of electronic instruments and corrected based on the neuromuscular concept. A minimum-invasive and reversible approach using adhesive occlusal restorations was used.

RESULTS

The jaw movement and masticatory muscle activity assessed at the 7- and 23-year follow-ups revealed that the established occlusion was well adapted, and re-established the patient's functional occlusion system. The patient has been free from TMD symptoms with the corrected occlusion for 30 years.

CONCLUSIONS

Occlusal reconstruction based on the neuromuscular concept can be stably integrated into the patient's functional occlusion system.

The Orthodontic Treatment of TMD Patients: EMG Effects of a Functional Appliance

The aim of this work was to test the effects of the Function Generator Bite (FGB) on the masticatory muscles of temporomandibular joint dysfunction (TMD) subjects. Two groups were selected for the study. A group of 20 TMD patients (group F) requiring orthodontic treatment and treated with FGB and a group of 10 healthy subjects (group H) were considered. Both groups were evaluated before the therapy began (TO) and then after 18 months of therapy (T1). An electromyographic analysis of the masseter and temporalis anterior muscles and a clinical evaluation according to the Research Diagnostic Criteria for TMD (RDC/TMD) were performed. A statistical difference between the two groups was observed at TO with respect to the activity index. TMD subjects showed a lower value of the index. Further studies are necessary to fully understand the utility of this EMG index as a diagnostic indicator.

Fatigue in the Masseter and Temporalis Muscles at Constant Load

Fatigue is usually defined as the point at which a particular level of force can be no longer maintained. In the present study, surface EMG of the masseter and temporalis anterior muscles was measured in ten healthy young adults performing a unilateral molar (right side) clench. The subjects clenched on a bite force transducer at a fixed force level of 13 kg (127 N) as long as they could (endurance). The test ended when the subjects could no longer produce the required bite force. From the EMG recordings, the median power frequency was calculated at the beginning of the task (T0), after one minute of clenching (T1), and at the end of the task (T2, endurance time). For each subject and muscle, percentage decrements in the median power frequency were also computed at T1 and T2. Endurance time ranged between 79 and 470 s. Significant modifications in the median power frequency in both masseter muscles (right side, p=0.003; left side, p=0.02, analysis of variance) were found, with a significant difference for the median frequency at T2 (p<0.02 at post hoc test). The modifications in the temporalis muscles were not significant (p>0.05). Additionally, at T1, significant percentage decrements in the median power frequency were found for both right side muscles (p<0.05, paired Student's ). The left side muscles modifications (p>0.05) were not significant. A significant effect of side was found (p=0.007, analysis of variance), without effects of muscle and no muscle x side interaction. At T2, both masseter muscles and the right side temporalis had a significant modification in their median power frequency. Overall, the modifications were larger in the masseter than in the temporalis muscles (p=0.022, analysis of variance), without effects of side and no muscle x side interaction. In conclusion, a fixed submaximal muscular contraction provoked fatigue modifications in the EMG power spectra that were well comparable to those obtained in previous investigations using forces computed as percentages of individually assessed maximum bite forces The present protocol (endurance clenching at a fixed force level) could be used as both a research and a clinical tool that would allow an easier and less troublesome assessment of both healthy persons and patients.

The Immediate Effect of Changing Mandibular Position on the EMG Activity of the Masseter, Temporalis, Sternocleidomastoid, and Trapezius Muscles

This study investigated the immediate effect of changing mandibular position on the electromyographic (EMG) activity of the masseter (MS), temporalis (TM), sternocleidomastoid (SCM) and trapezius (TR) muscles. Thirty-three (33) asymptomatic subjects (16 males and 17 females), ages 23 to 52 were selected. Surface EMG recordings were obtained for all muscles bilaterally with the mandible in a relaxed open position (relaxed) and during maximal voluntary clenching (fullbite) for the following: a non-repositioning appliance (NONREPOS) and repositioning appliance (REPOS). REPOS significantly reduced EMG activity of all muscles bilaterally during fullbite. During relaxation, reduction in EMG activity was only found for TR bilaterally. NONREPOS decreased the EMG activity bilaterally for TM and TR and unilaterally (left) for MS and SCM during fullbite. During relaxation, NONREPOS decreased muscle activity bilaterally for TR and SCM. A unilateral reduction was found for TM (right). These findings suggest that immediate alterations in mandibular position affect the cranio-cervical system. Both mandibular positions tested lowered the EMG activity of masticatory and cervical muscles in the relaxed and fullbite positions. The trapezius muscle was the most responsive to alterations in mandibular position.

Aging of masticatory efficiency in healthy subjects: electromyographic analysis--Part 2

The masticatory process identifies the level of the individual's masticatory ability and provides important information for an adequate diagnosis of the masticatory function. The purpose of this cross-sectional study was to evaluate the influence of age on habitual and non-habitual mastication by means of the values of the ensemble average of masticatory cycles. All volunteers were Brazilian, Caucasian, fully dentate (except for Group I--mixed dentition), aged 7-80 years and divided into five groups: I (7-12 years), II (13-20 years), III (21- 40 years), IV (41-60 years) and V (61-80 years). Except for Group V, which comprised nine women and eight men, all groups were equally divided with respect to gender (20 M/20 F). All subjects were nasal breathers, had normal occlusion and no parafunctional habits or symptoms of temporomandibular dysfunction (RDC/TMD). The masticatory process was analyzed during habitual mastication of peanuts and raisins, and non-habitual mastication of ParafilmM, for 10 seconds each. The resulting electromyographic data were evaluated using SPSS 19.0 software for Windows. ANOVA (analysis of variance) followed by the Duncan test were used to compare the efficiency of the masticatory cycle between age groups. Multivariate analysis (General Linear Models) was used to analyze the effect of age groups and gender on the efficiency of themasticatory cycle, to compare groups (p < 0.05). The results showed that age is directly associated with the changes in masticatory process in healthy subjects.

Influence of different upper cervical positions on electromyography activity of the masticatory muscles

OBJECTIVE

The aim of this study was to determine the activity of the masseter and anterior temporalis muscles in relation to different positions of the upper cervical spine during maximal voluntary isometric clenching by surface electromyography (EMG).

METHODS

This was a cross-sectional study with a repeated-measures design performed using 25 asymptomatic subjects (13 female and 12 male; mean age, 31 years; SD, 8.51). The EMG activity of the masseter and anterior temporalis muscles was recorded bilaterally during maximal clenching at neutral position and during extension, flexion, ipsilateral lateral flexion, contralateral lateral flexion, and ipsilateral and contralateral rotations in maximal flexion. In addition, the upper cervical range of motion and mandibular excursions were assessed. The EMG activity data were analyzed using a 3-way analysis of variance in which the factors considered were upper cervical position, sex (male and female), and side (right and left), and the hypothesis of importance was the interaction side x position.

RESULTS

The 3-way analysis of variance detected statistically significant differences between the several upper cervical positions (F = 13.724; P < .001) but found no significant differences for sex (F = 0.202; P = .658) or side (F = 0.86; P = .53) regarding EMG activity of the masseter muscle. Significant differences were likewise observed for interaction side x position for the masseter muscle (F = 12.726; P < .001). The analysis of the EMG activity of anterior temporalis muscle did not produce statistically significant differences (P > .05).

CONCLUSION

This preliminary study suggests that the upper cervical movements influence the surface EMG activity of the masseter muscle. These findings support a model in which there are interaction between the craniocervical and the craniomandibular system.

Site-to-site variation of muscle activity and sensitivity in the human anterior temporalis muscle: implications for contingent stimulation

OBJECTIVE

To evaluate variation of electromyographic (EMG) activity and sensitivity between different sites of anterior temporalis (AT) muscle.

MATERIALS AND METHODS

Sixteen healthy subjects (eight men: 28.8 ± 5.2 year old and eight women: 29.1 ± 3.9) participated in one experimental session. EMG activity during masticatory muscle contraction was recorded from nine sites at the AT muscle in a 3 × 3 grid with 1 cm between. The subjects maintained steady 30% of maximal voluntary contraction (MVC) using visual feedback. The surface EMG electrode was moved sequentially between these nine test sites and the contractions were repeated. One site was tested four times to assess test-re-test variability. The sensory threshold to electrical stimulation and impedance was also measured at the same sites as the placement of EMG electrodes.

RESULTS

The 30% MVC force values did not differ between sites (p = 0.863) or within the same site (p = 0.995) due to the feedback. The EMG activity during 30% MVC was highest at the anterior-superior site (p < 0.05) with a marginal difference within the same site (p = 0.044). Impedance was higher at the posterior-superior, posterior-middle and posterior-inferior sites (p < 0.05). The sensory threshold was highest at the posterior-superior site (p < 0.05).

CONCLUSION

These findings showed that electrodes close to the hairline have higher impedance and sensory thresholds and should be avoided. The anterior-superior site produces the highest EMG activity and lower sensory thresholds and can be recommended as the optimal site to place the electrode for contingent stimulation.

Is headache in Behçet's disease related to silent neurologic involvement?

OBJECTIVES

Headache is an interesting issue in Behçet's disease (BD). This study aimed to investigate if headache or a special type of headache was correlated with silent neurologic involvement in BD patients without any neurologic sign.

METHODS

The study was performed on 120 BD patients (30 without headache, 30 with non-structural headache of BD and 30 with migraine headache, 30 with tension type headache) and 30 healthy control subjects. Some neurophysiologic tests of brain stem; temporalis muscle exteroceptive suppression periods (ESP) and brain stem auditory evoked potentials (BAEP) were performed in the patients, when they were not in an attack period of the disease, and control subjects to investigate the presence of silent neurologic involvement and the relation between headache and silent neurologic involvement.

RESULTS

Some electrophysiological abnormalities, as right BAEP 1-5 interpeak latency prolongation (p=0.01) and left ESP2 duration shortening (p<0.005), were seen in BD patients compared to healthy control subjects. Furthermore, the patients with non-structural headache of BD were found to have shorter ESP1 and 2 durations (p<0.001) and longer ESP1 latencies (p<0.05), with respect to the other patient subgroups with different types of headache and healthy control group, showing brain stem pathology. Additionally, they had longer right BAEP 3-5 interpeak latency as compared to the patient subgroup without headache (p=0.001).

CONCLUSIONS

There is a silent neurologic involvement in BD and this involvement may be in relation with a particular type of vascular headache, named as non-structural headache of BD. So, in clinical evaluation of BD patients, this type of headache may be considered as a warning message for neurological involvement.

Effect on anterior temporalis surface EMG of eyes open-closed condition

BACKGROUND

The use of rest surface EMG of jaw elevator muscles is still debated. The low voltage recorded in anterior temporalis muscle by electromyography (EMG) in rest position could be affected by electronic noise or by activity coming from other muscles. Our goal was to evaluate the physiological behaviour of the anterior temporalis by surface EMG at rest mandible position during open or closed eyes condition in healthy young subjects without both malocclusion and visual defect.

MATERIALS AND METHODS

Surface EMG of anterior temporalis, masseter, digastric, sternomastoid muscle and mandible kinesiographic movement were recorded in 20 young, healthy individuals without both malocclusion and visual defect during open-closed eyes condition.

RESULTS

No significant difference was found in surface EMG of anterior temporalis comparing eyes closed to eyes open condition.

CONCLUSION

Physiology of open-closed eyes in healthy, young subjects without malocclusion or visual defect does not imply a change in surface EMG of anterior temporalis muscle.

Age and gender influence on maximal bite force and masticatory muscles thickness

The present study aimed investigate the age and gender influence on maximal molar bite force and at outlining the criteria for normal masticatory muscle development in a sample of 177 Brazilian Caucasian dentate individuals aged 7-80 years divided into five age groups: I (7-12 years), II (13-20 years), III (21-40 years), IV (41-60 years), and V (61-80 years). Except for Group V, which comprised nine women and eight men, all groups were equally divided in respect to gender (20 M/20 F). Bite force was recorded with a mouth-adapted 1000N dynamometer and the highest out of three records was regarded as the maximal bite force. The data were submitted to multivariate statistical analysis (SPSS 17.0 p<0.05). Effects of group and gender were found, but no interactions between them. The ANOVA showed significant differences between groups bilaterally. Bonferroni's test showed that group I had significantly lower bite force means at both sides as compared to all groups, except group V. No differences were found between the left and right sides. In all the groups, gender was found to be a significant factor associated with maximal bite force. A global comparison including all the subjects and measures showed that the means of men were approximately 30% higher than those of women. Within-group comparisons yielded similar results in all groups. Muscle thickness was measured with a SonoSite Titan ultrasound tool using a high-resolution real-time 56mm/10MHz linear-array transducer. Three ultrasound images were obtained from the bilateral masseter and temporal muscles at rest and at maximal voluntary contraction. The means of the three measures in each clinical condition were analyzed with multivariate statistical analysis (SPSS 17.0 p<0.05). A gradual increase in thickness of the masseter and temporal muscles was found both at rest and maximal voluntary contraction for groups I to IV, whereas a decrease in muscle thickness was observed in group V. Multivariate analysis showed that in both conditions there was an effect of group and gender. The study of the development of the stomatognathic system in relation to age and gender can provide useful data for the identification of normal and impaired functioning patterns. The results of this study indicate that age and gender are associated with structural and functional alterations in the muscles of the stomatognathic system.

[Phase space reconstruction of mastication muscles surface electromyography signal based on nonlinear dynamics]

OBJECTIVE

To calculate the delay times and embedding dimensions of surface electromyogragh (sEMG) signal of the masseter and temporal muscle during clenching at intercuspal position (ICP), and to reconstruct the space phase of sEMG signal with method of nonlinear dynamics.

METHODS

Ten male and 10 female young volunteers with normal masticatory system were included in the study, the signals of surface sEMG of bilateral masseter and temporal muscles in the position of ICP were collected, and the delay times and embedding dimensions of the sEMG signals were calculated using C-C method, the space phase of the sEMG signals was reconstructed.

RESULTS

A program of nonlinear dynamic analysis of mastication muscles sEMG signals was developed base on the platform of Matlab. The signals of the sEMG of the masseters and temporals were analyzed with nonlinear dynamic methods, the delay times and embedding dimensions of each muscles sEMG signals were obtained, and the space phase of each sEMG signals were reconstructed. The graphs of the space phase indicated the typical characteristic of chaotic attractor.

CONCLUSIONS

The signals of the masseter and temporal muscles of surface sEMG during clenching at ICP of normal masticatory system show the typical characters of chaos, the methods of nonlinear dynamics are effective to analyze the sEMG signals of mastication system.

Electromyographic and cephalometric correlation with the predominant masticatory movement

OBJECTIVE

This study aimed to evaluate the chewing muscular dynamics and correlate the side of the masticatory movement that is more vertical and/or more horizontal established by the photomeasurement Masticatory Functional Angle (MFA) to the muscular activity behavior, showed in the surface electromyography and in the radiographic images.

MATERIAL AND METHOD

Seventeen people were selected of both genders, with the average age of 25 years, without signs or apparent symptoms of masticatory muscular disorders. The teleradiographies were done in lateral norm and surface electromyography of the masseter muscles, anterior portion of temporal and supra-hyoids in rest position and maximal bite. The bite force measured with a metallic transducer that was connected to a force sensor (Strain Gauge) to measure the deformation of the material model SF4 (EMG SYSTEM DO BRASIL). A mandibular goniometer of the EMG System of Brazil was used to measure the opening size.

RESULTS

The comparison and correlation were established between the groups with MFA>5 degrees and MFA<5 degrees by the test "t" of Student or test of Mann-Whitney conform the distribution was normal or not, respectively. The results showed significant differences between groups, although without sexual dimorphism, to masseter muscle in maximal bite.

CONCLUSION

In conclusion, the anatomic-physiological aspects of temporomandibular disorders are related to the asymmetrical mandible function.

Changes in soft tissue profile and electromyographic activity after activator treatment

BACKGROUND

To date, few studies have correlated the changes in muscle activity and specific soft tissue variables in adolescents with malocclusions.

OBJECTIVE

To determine associations between the soft tissue profile and electromyographic activities in temporalis, masseter and orbicularis oris muscles in children with Class II division 1 malocclusions treated with activators.

METHODS

For this prospective study, 25 subjects with Class II division 1 malocclusions were randomly assigned to either a Treatment group (N=15) or a Control group (N=10). The mean skeletal ages of the subjects in the Treatment and Control groups were 11.3 +/- 1.1 and 11.0 +/- 1.3 years, respectively. The subjects in the Treatment group were treated with activators and the subjects in the Control group were untreated. Lateral cephalometric radiographs and EMG recordings of the anterior temporalis and masseter muscles during clenching, chewing and swallowing and the orbicularis oris muscle during whistling were obtained at the start of the study and 12 months later. Changes in the soft tissue profile were correlated with changes in the EMG activities in anterior temporalis, superficial masseter and orbicularis oris muscles.

RESULTS

The upper lip to E line distance (UL-E) decreased more in the Treatment group than the Control group (p < 0.05) and the H angle decreased in the Treatment group, but increased in the Control group (p < 0.01). The EMG activities of temporalis and masseter muscles increased significantly in both groups. All between-group EMG differences were statistically significant with the exception of the activities in the temporalis and masseter muscles during swallowing. In the Treatment group, a significant positive correlation (r = .57) was found between the changes in UL-E and anterior temporalis activity during swallowing, and significant negative correlations were observed between the EMG activity of masseter muscle during swallowing and changes in LL-E (r = -.54), OLp-UL (r = -.55) and OLp-LL (r = -.67).

CONCLUSIONS

Activator therapy is accompanied by changes in the lips and temporalis and masseter activities during swallowing.

Do the physical properties of occlusal-indicating media affect muscle activity [EMG) during use?

Four occlusal marking media (Parkell film, articulating silk, articulating paper and T-Scan foil) were tested to assess whether they affected neuromuscular function during occlusal marking events. Muscle activity of the anterior temporalis (TA) and superficial masseter (MS) muscles were obtained from surface EMG measurements during a slow closure to occlusion followed immediately by a forceful bite and a maximum clench onto each of the various occlusal indicating media. Muscle activity during the whole period of activation and immediately following onset were investigated. Significant differences in neuromuscular function between the occlusal marking media were observed, particularly between the Parkell film and articulating silk as opposed to the articulating paper and the T-Scan foil. The Parkell film and articulating silk gave neuromuscular function very similar to that of natural dentition occlusal contact, while the articulating paper and T-Scan foil showed similarities to occluding onto cotton rolls as previously reported (1). These results suggest that both the thickness and plasticity of the indicating media affect neuromuscular function during occlusion.

The use of ultrasound in the investigation of the muscles of mastication

The aim of this article was to review the literature concerning ultrasonography imaging (US) of the muscles of mastication and to discuss its use, advantages and disadvantages and the findings of the authors. A web search was performed using the terms "ultrasound" and "muscles". US has been shown to be a reliable method of great utility in the field of diagnosis of alterations in the muscles of mastication and for the study of changes during growth and aging. It should be preferred in comparison to computerized axial tomography (CT) and magnetic resonance imaging (MRI) because of its safety and cost advantages since it is as reliable and precise as these other techniques. Although various techniques have been used in ultrasonographic scanning, this article discusses those techniques most commonly adopted by the authors.

Influence of playing wind instruments on activity of masticatory muscles

The aim of this study was to elucidate the influence of change in sound tone of playing wind instruments on activity of jaw-closing muscles and the effect of sustained playing for a long time on fatigue of jaw-closing muscles. Electromyograms (EMG) of 19 brass instrument players and 14 woodwind instrument players were measured while playing instruments in tuning tone and high tone and under other conditions. Nine brass instrument players and nine woodwind instrument players played instruments for 90 min. Before and after the exercise, power spectral analyses of EMG from masseter muscles at 50% of maximum voluntary clenching level were performed and mean power frequency (MPF) were calculated. Root mean square (RMS) of EMG in masseter and temporal muscles while playing were slightly larger than those at rest but extremely small in comparison with those during maximum clenching. Root mean square in orbicularis oris and digastric muscles were relatively large when playing instruments. In the brass instrument group, RMS in high tone was significantly higher than that in tuning tone in all muscles examined. In the woodwind instrument group, RMS in high tone was not significantly higher than that in tuning tone in those muscles. Mean power frequency was not decreased after sustained playing in both instrument groups. These findings indicate that contractive load to jaw-closing muscles when playing a wind instrument in both medium and high tone is very small and playing an instrument for a long time does not obviously induce fatigue of jaw-closing muscles.

Comparison of the main occluding area between adults and adolescents

It has become clear that foods crushing is performed in the circumscribed region between functional cusps, that is, at "the main occluding area". However, it is not established to evaluate this area objectively. The purpose of this study was to establish the positional evaluation of the main occluding area quantitatively and evaluate the positional change depending on the age with this method. The subjects were fifteen adults and ten adolescents who had no stomatognathic disorder. Temporary Stopping was used as test material in this study. In order to analyze the position of the main occluding area, the projected centroid coordinate of the test material was calculated and projected onto the reference axis. It was possible to quantitatively evaluate positional changes of the main occluding area depending on growth process. As a result, the main occluding areas of the adults were significantly posterior to those of the adolescents and tended to be more stable. There was a significant difference in the occlusal contant area between two groups. The occlusal contact area had great influence on the stability of the main occluding area. However, besides occlusal contact area, there might be other factors which stabilized the main occluding area.

[Functional aspects of lower jaw dynamics--EMG study]

The paper presents a study of muscular forces using EMG records for temporal and masseter muscles on different occlusion situations. Each muscle activity was investigated related to different occlusion situation in order to be able to determine correlations with possible diagnostic and treatment of dental system malfunctions. The results regarding the practical determination of symmetrical indexes and muscle activity indexes were compared with specific references.

Influence of altered occlusal guidance on masticatory muscle activity during clenching

This study investigated the influence of experimentally altered occlusal guidance on masticatory muscle activity. Twenty healthy human subjects (15 males and five females with an average age of 26.5 years) volunteered to participate in this study. Metallic occlusal overlays were fabricated for the lower working side canine and overlaid on the second molar and the non-working side second molar to simulate a canine-protected occlusion, group function occlusion and bilateral balanced occlusion. Electromyography (EMG) activities in the bilateral masseter, anterior and posterior temporalis were recorded during maximal clenching. The experimental occlusal pattern revealed to have statistically significant effects on EMG activity. As the most characteristic change, EMG activity in the anterior temporalis significantly increased in the simulated group function occlusion and the simulated bilateral balanced occlusion compared with the simulated cuspid protected occlusion. The increased teeth contacts to the posterior region altered the unilateral pattern of the anterior temporalis activity to the bilateral pattern, while that of masseter activity remained unchanged.

Electromyographic evaluation of the masseter and temporal muscles activity in volunteers submitted to acupuncture

AIM

To assess the effect of acupuncture on the temporal and masseter muscles activity employing surface electromyography.

METHODS

Thirty volunteers were evaluated according to three groups of acupuncture application: selected local points, selected points at distance and association of local and distant points. Bipolar surface electrodes were positioned bilaterally on the anterior portion of temporal muscle, as well as in the median region of masseter muscle. An electromyograph connected to a computer and a specific software registered the muscular activity before and after acupuncture, in the following experimental conditions: 1- Rest Position (RP); 2- Maximum Intercuspation Clenching (MIC); 3- Bilateral Molar Clenching with Cotton Rolls (BMCCR). The mean values obtained for the activities of the studied muscles were submitted to Analysis of Variance and Tukey complementary test.

RESULTS

The electromyographic activity of the studied muscles was lower after the application of the methods of acupuncture in the Rest, and higher after the application of the acupuncture in the Maximum Intercuspation Clenching; the electromyographic activity of the temporal muscle was higher than the masseter muscle in the Rest and lower in the Bilateral molar clenching with cotton rolls; the electromyographic activity showed to be modified after the three used methods of acupuncture in the Maximum Intercuspation Clenching. In this clinical condition, the method of long-distance acupuncture was higher than the application of local needles and the associated method.

CONCLUSION

Acupuncture provided alterations in the activity of the studied muscles, favoring conditions of rest and muscular tightness.