Electrodiagnosis at median occlusal position for human subjects with mandibular joint syndrome.

Neuromuscular inhibitory effects were monitored in the temporalis and masseter muscles for ten patients with mandibular joint (MJ) syndrome, and ten control subjects with normal occlusions. Analysis of the electromyographic (EMG) silent period in the controls showed no significant difference between durations at median occlusal position, following placement of a maxillary acrylic occlusal splint, and during gum chewing. However, for the patients with MJ syndrome, there was an immediate decrease in their mean EMG silent-period duration upon placement of the splint from 19.23 msec to 15.52 msec. This shortened duration was the same with or without a splint after the pain symptoms had subsided. Precise occlusal adjustment of the dentition at the pain-free appointment resulted in a further reduction (10.83 msec) to within the range of the normal control subjects at median occlusal position. Inhibitory pauses during gum chewing showed similar treatment interactions but, during some chewing cycles, no silent periods were evident.     

Influence of auriculotemporal nerve anaesthesia on the masseteric silent period

Silent periods were evoked from the masseter muscles bilaterally in response to chin taps during a clench. Injection of 0.75 ml of 3% Mepivicaine posteromedial to each condyle led to a distribution of skin anaesthesia consistent with the distribution of the auriculotemporal nerve. Silent periods were evoked prior to and during anaesthesia in ten subjects. The silent period latencies (mean +/- standard deviation) prior to anaesthesia were 12.5 +/- 1.8 ms and 11.9 +/- 2.5 ms in the right and left masseters. During anaesthesia the latency decreased by 0.3 +/- 1.3 ms in the right masseter and by 0.3 +/- 2.1 ms on the left masseter. Neither change was statistically significant (P greater than 0.05). The silent period durations prior to anaesthesia were 20.3 +/- 4.0 ms and +/- 22.8 +/- 7.1 ms in the right and left masseters. During anaesthesia, these decreased by 2.74 +/- 5.8 ms on the right and 2.15 +/- 4.4 ms on the left. These decreases were not statistically significant (P greater than 0.05). These results failed to demonstrate an influence of the predominant nerve supply of the TMJ on either the latency or the duration of the masseteric silent period.     

Ultrasonographic thickness and electromyographic activity of masseter muscle of human females

The aims of this study were to assess the thickness of the masseter muscle by means of ultrasonography and to investigate the relationship between masseter electromyographic activity and muscle thickness bilaterally, during maximum voluntary clenches. Participants in the study consisted of 52 young female adults (mean age 23.7 +/- 2.5 years) without craniomandibular disorders and with full natural dentitions. The thickness of the masseter muscle was measured with a real-time ultrasound equipment. Electromyographic activity was recorded with bipolar surface electrodes, during maximum voluntary clenches. The error of the methods was calculated by double recordings in 15 subjects in a 4-week interval. The measurement error for the right muscle was 0.16 mm in thickness and 16.44 microV in electromyographic activity. For the left masseter the corresponding values were 0.19 mm and 18.01 microV. The relationship of masseter muscle thickness to its electromyographic activity was estimated by Pearson's correlation coefficient. The mean masseter thickness under contracted conditions was 13.9 +/- 1.5 mm for the right side and 13.9 +/- 1.4 mm for the left side. The mean maximum electromyographic activity was 379.0 +/- 56.0 microV for the right muscle and 372.3 +/- 73.2 microV for the left. Muscle thickness was strongly correlated to electromyographic maximum activity in the right masseter (r = 0.721, P < or = 0.001) and moderately correlated in the left muscle (r = 0.407, P < or = 0.01). The difference between the two sides is possibly because of the larger method error in the left side. It is apparent that ultrasonography can be used as a useful tool to assess masseter muscle functional capacity during full effort in healthy individuals.     

Muscular activity disorders in relation to intentional occlusal interferences

The electromyographic activity (EMG) of the anterior temporal (AT), masseter (M), trapezius (T) muscles and anterior aspect of the digastric (D) was measured in 50 subjects, during six seconds of maximum contraction, bilaterally with and without unilateral premature contacts and individually for each tooth. Special occlusal interferences were designed to assess muscular activity. Muscular activity was measured simultaneously by placing premature contacts on each tooth, under T-Scan monitoring. Premature contacts reduced EMG activity during maximum contraction of the AT, D and M muscles, the highest disruption is in the AT muscle, at the level of upper right 2nd molar, with a 56% reduction in activity. Conversely, there was an increase of activity of the T muscle in all teeth when placing artificial occlusal premature contacts, with the highest difference in the upper right 1st bicuspid. Therefore, occlusal interferences can cause neuromuscular disruptions, thus inducing important muscular discrepancy. Both the EMG and T-Scan monitoring can be considered suitable methods to use in daily dental practice to identify premature contacts and to measure EMG activity.     

Occlusal adjustment for a physiologically balanced occlusion.

An investigation of the neuromuscular effects of dental contact at the physiologic median occlusal position was conducted before and after occlusal adjustments. Eighteen patients with histories of functional disturbances of the masticatory system, but whose painful symptoms had subsided, were analyzed before and after occlusal adjustments. Nine of the patients with missing teeth received fixed partial dentures and occlusal adjustments. Another group of nine subjects with normal occlusions were used as controls. Electromyographic recordings of the bilateral temporal and masseter muscles enabled quantification of two reflex parameters, the EMG silent period duration, and the mechanical latency of the jaw-opening reflex. Phase-plane traces of jaw-closing velocity as a function of position displayed the repeatability of the median occlusal position. The statistical analysis disclosed that the mean duration of EMG silent periods and latency of the jaw-opening reflex were significantly reduced following the treatment procedures. Within the limits of this study it was concluded that the described occlusal adjustments will reduce the masticatory reflexes evoked at median occlusal position to within the range of normal subjects. Furthermore these changes can be monitored by electrophysical methods.     

Relationship between the number of occlusal contacts and masticatory muscle activity in healthy young adults

The electromyographic (EMG) potentials of left and right masseter and temporalis anterior muscles were recorded in 23 healthy young adults during: 1. a 3-second maximum voluntary clench (MVC) on cotton rolls positioned on the posterior teeth (standardized recording); and 2. a 3-second MVC in intercuspal position. EMG potentials recorded in intercuspal position were standardized as a percentage of the mean potentials of the standardized recording, and the EMG muscle activity was calculated. The number of occlusal contacts in intercuspal position was assessed by using eight microm thick shim stocks. Two groups of subjects with either 1. Less than ten occlusal contacts (11 subjects with "few contacts"); or 2. At least ten occlusal contacts (12 subjects with "many contacts") were selected. The MVC muscle activity in the "few contacts" group was significantly lower than that recorded in the "many contacts" group (p<0.005). In conclusion, the number of occlusal contacts and masticatory muscular function are significantly related, at least in young adults with a sound stomatognathic apparatus.     

正常(牙合)牙尖交错位咬合平衡的定量研究

目的　对正常（牙合）牙尖交错位（ICP）最大（牙合）力咬合进行定量研究，初步探讨ICP咬合平衡的生理范围。方法　应用T－Scan　Ⅱ系统记录123名正常骀者ICP最大（牙合）力的咬合情况，测量并计算力的中心点（COF）、（牙合）力百分比值、胎接触点数目。结果　正常胎者ICP最大（牙合）力时力的中心点相对位置、（牙合）力百分比差值以及不对称系数均服从正态分布，95％参考值范围分别为：－6．60～6．68mm，－15．50％～12．10％，0．65～1．39；98．4％的正常（牙合）者ICP最大（牙合）力咬合时力的中心点分布于后牙区。结论　正常（牙合）者最大（牙合）力时ICP咬合是稳定、平衡的咬合。     

Bite force, endurance and masseter muscle fatigue in healthy edentulous subjects and those with TMD

It is well known that bite force and EMG activity are considerably reduced in edentulous patients, but the susceptibility of their jaw-closing muscles to localized fatigue is less certain. This information is even less clear for edentulous subjects who have TMD. Eleven healthy edentulous subjects and 10 edentulous subjects with TMD participated in this study. Maximum bite force was measured first, with the transducer placed on the canine-first premolar region bilaterally, and then two rapid relaxations were made from a brief voluntary clench to 50% of maximum. A sustained voluntary clench of 50% of maximum was then maintained and endurance time was noted. EMG was recorded from both masseter muscles and the median frequency of the power spectrum of the EMG from 2 s at the beginning of the sustained clench and 2 s at the end was subsequently calculated. Two more rapid relaxations from brief clenches were performed immediately after the sustained clench. The mean maximum bite force in the healthy group was 115 N (SD +/-41) and in the TMD group was 75 N (SD +/-22), this difference being significant (P = 0.0013). The mean endurance time in the healthy group was 86 s (SD +/-51) and in the TMD group was 63 s (SD +/-20). The percentage change in the median frequency in the healthy group as a result of the sustained contraction was 6% (left) and 8.6% (right) and in the TMD group was 13.9% (left) and 12.8% (right). The percentage change in the mean relaxation half time for the healthy group was 28.5% and for the TMD group was 72%, a significant difference (P = 0.0046). It was apparent that the maximum bite force was low in edentulous subjects and was further reduced in edentulous TMD subjects; endurance time was reduced in TMD subjects; fatigue resistance of the masseter muscles was reduced in TMD subjects.     

The silent period in the masseter and anterior temporalis muscles in young adult subjects unaware of mandibular dysfunction symptoms

In fourteen individuals unaware of mandibular dysfunction symptoms, latency and duration of the silent period in the masseter and anterior temporalis muscles at tooth tapping and jaw jerk were reasonably reproducible after 5 weeks and 5 months. Although the subjects felt no discomfort in the stomatognathic system, in some of them mild to moderate muscle tenderness, TMJ sound and occlusal disharmony were found at clinical examination. The relationship between these symptoms and the silent period was analysed. Muscle tenderness was the only factor to affect the silent period. The subjects with muscle soreness had a shorter duration of the silent period than the subjects without such symptoms.     

TMD chronic pain and masseter silent period in psychiatric patients on antidepressive therapy

Summary  The aim of the study was to evaluate the long-term effects of antidepressive therapy on chronic pain and related disability, and masseter silent period in psychiatric depressive patients with temporomandibular disorders (TMD). The study included hospitalized psychiatric depressive patients on antidepressive therapy protocol (tetracyclic antidepressant-maprotiline and anxiolytic-diazepam) ( n  = 30) and non-psychiatric patients seeking prosthodontic treatment (control group, n  = 38). TMD were diagnosed by Research Diagnostic Criteria for temporomandibular disorders proposed by Dworkin and LeResche. The surface electromyography was recorded from left and right masseter muscles and masseter inhibitory reflex (masseter silent period) was recorded after mechanical stimulation. The incidence of TMD appearance was very similar, of aproximately 40% in both group of patients. The results of the study also indicated a higher prevalence of joint related TMD, a lower prevalence of muscular subtype of TMD and a lower grade of chronic pain and related disability in the psychiatric group of patients on antidepressive therapy in comparison with findings in the control group. In the patients on antidepressive therapy with TMD masseter silent period was not prolonged, while in the control group of patients with TMD the prolongation of the silent period was observed. The study provided evidence that long-term, combined therapy (maprotiline and diazepam) in psychiatric depressive patients significantly modulated signs and symptoms of TMD in comparison with the control group.     

Relationship of electromyographic parameters in jaw dysfunction patients classified according to Helkimo's index

Forty-two jaw pain-dysfunction syndrome patients (PDS) were divided into three groups depending on the severity of their condition using the Helkimo clinical dysfunction index. For both the left and right masseter and anterior temporal muscles three parameters of their electromyographic activity were measured, the silent period (SP), the root mean square value (RMS) and the mean power frequency (MPF). During the experiments the patients were instructed to clench as hard as possible in the intercuspal position. No statistically significant differences could be found between the values for any of the muscles measured between the different Helkimo clinical dysfunction groups. However, when the affected side was compared with the unaffected side in this patient material, statistically significant longer silent period durations and greater RMS values were found in the masseter muscles of the affected side group.     

Response patterns of craniomandibular muscles with and without alterations in sensory feedback

1. Surface EMG recordings were made bilaterally from the anterior part of the temporal muscle, superficial masseter muscle, and the suprahyoid complex of muscles while tracking mandibular incisor movement in three planes. This was done in 20 normal subjects with 16 different responses. Some responses involved clenching whereas other responses occurred with actual mandibular movement. 2. Each muscle demonstrated a probability of recruitment dependent on the response that correlated with the intensity of recruitment. The higher the probability of recruitment, the greater the intensity of muscle activity. 3. The anterior temporal muscle demonstrated no statistically significant difference in any of the responses between the left and right muscles. The masseter muscle also demonstrated bilateral symmetry. 4. The anterior part of the temporal muscle was recruited in more than 60% of its trials (60% to 100%) in ipsilateral laterotrusion, retrusion, fast vertical raising, clenching on the ipsilateral or intercuspal position, and mastication. The temporal muscle was recruited in less than 60% of its trials in contralateral and incisor clenching, and less than 30% in contralateral laterotrusion, protrusion, and opening. 5. The superficial masseter muscle was recruited in more than 60% of its trials in protrusion, vertical raising, all clenches, and mastication. The masseter muscle was recruited less than 60% in retrusion, ipsilateral laterotrusion, and opening. 6. The suprahyoid group of muscles was recruited in more than 60% of its trials in protrusion, opening, and mastication. This group of muscles was recruited less than 60% of the time in clenching, lateral movements, and rapid vertical raising of the mandible. 7. Applying a maxillary splint to seven subjects significantly decreased the recruitment of the anterior temporal and masseter muscles during mastication. The splint also modified the use of the masseter muscle during protrusion so that it was less active, but increased its recruitment during contralateral clenching. The suprahyoid muscle group was unaffected by the maxillary splint. 8. These data support the concept that movement of the mandible from the intercuspal or rest position develops a coactivation pattern that will excite or inhibit a given muscle regardless of whether clenching with occlusal contacts or no occlusal contact is involved. 9. The data also demonstrate that the maxillary splint can alter the use of the jaw elevator muscles, predominantly in mastication.     

An electromyographic study of masseter and anterior temporalis muscles in extra-articular myogenous TMJ pain patients compared to an asymptomatic and normal population

The purpose of this study was to evaluate the effectiveness of the therapy with a centric relation stabilization appliance (CRSA) in patients with temporomandibular disorders of myogenous origin by electromyography and compare the results with two asymptomatic control groups. Three groups of 20 patients each were selected for the study. Electromyography (EMG) of masseter and anterior temporalis muscles was performed during mandibular rest position. In the treated group, the occlusal appliance reduced the electrical activity of the analyzed muscles at right and left sides (p<0.0001), and equilibrated muscular activity between right and left sides (p<0.0001), reaching values close to the control groups. Although there was not a statistically significant difference, the normal control group presented lower EMG values than control group II and presented the lowest asymmetry index of all subjects. More than 85% of all subjects, including the controls, demonstrated a statistically significant temporal anterior activity prevalence (p<0.0001). Treatment with the CRSA reduced the activity index, although the prevalence of the temporal muscle over the masseter was maintained. The significant laterodeviating (torque) effect found in the temporomandibular disorder patients was reduced after treatment. No side prevalence was found in the control groups.     

Occlusal contacts in maximum intercuspation in normal dentitions

summary A cross-sectional study of the contacts in maximum intercuspation was undertaken using a method to identify occlusal contacts, which is indicated as satisfactory by modern research. The aims were to describe in subjects with normal dentitions and normally functioning masticatory systems: (a) the general distribution of contacts; (b) the numbers in the various classes and types of occlusal contacts; (c) the numbers of teeth without contact. A randomized sample of 18 women and 20 men was used. Classical theoretical proposals for the numbers, distribution and nature of occlusal contacts were not supported. Wide variability was evident and asymmetry of distribution on the right and left sides of individual subjects was common. Contacts with stabilizing tendencies involved the mandibular supporting cusps in 79% of occurrences. Overall, the difference in the number of contacts with stabilizing effects was not significantly different from the number with unstabilizing tendencies. Contacts with mechanically unstabilizing effects did not produce clinically discernible, unfavourable sequelae in the dentitions. Because of the sparse number of stabilizing contacts, interventions involving the occlusal surfaces should maintain or improve on the number of such contacts in maximum intercuspation.     

Bilateral variation of the masseteric myotatic reflex and the silent period in young humans

Increased bilateral differences in jaw reflexes have been considered as pathological findings. The aim of this study was to investigate the normal variation between sides in the jaw jerk and the silent period and determine the range of its boundaries, using the present experimental set-up. Electromyographic data were simultaneously recorded from the right and left masseter muscles by surface electrodes, using a computerized recording and analysis system. The reflexes were elicited by chin taps during mandibular rest and at moderate intercuspal clenching in 20 healthy dentate adults (10 males and 10 females) with a mean age of 26 years. The reflexes were always elicited bilaterally and no overall significant differences were observed between sides for occurrence, latency, duration and amplitude of the jaw jerk and for the latency and duration of the silent period (P > 0.05). However, in the individual analysis significant bilateral variation was occasionally recorded, particularly for the jaw jerk at rest and mainly in the amplitude measurements. On the other hand, in the silent period duration measurements individual variation was very limited. Bilateral individual latency differences for the jaw jerk did not exceed 1 ms at rest (x = 0.3 +/- 0.3 ms) and 0.7 ms at clench (x = 0.3 +/- 0.2 ms), while latency differences for the silent period did not exceed 0.8 ms for the early type (x = 0.4 +/- 0.2 ms) and 4.8 ms for the late phase of depression (x= 1.9 +/- 1.7 ms). Bilateral differences for the silent period duration did not exceed 7.1 ms (x = 2.2 +/- 2.3 ms) in the early type (simple + early phase of combined types) and 3.3 ms (x = 1.5 +/- 0.9 ms) in the total duration of the combined types.     

A clinical and electromyographic study of the long-term effects of an occlusal splint on the temporal and masseter muscles in patients with functional disorders and nocturnal bruxism

The postural activity of the temporal and masseter muscles in thirty-one patients with signs and symptoms of functional disorders were studied: before, during and after 3-6 months of occlusal splint therapy. The fluctuating signs and symptoms, as well as the postural activity of the temporal and masseter muscles were significantly reduced after treatment. Further, the coefficients of correlation within pairs of postural activity of the right and left muscles increased significantly. After cessation of the splint therapy the signs and symptoms recurred to the pre-treatment level within 1-4 weeks in about 80% of the patients. The results indicate that an occlusal splint can eliminate or diminish signs and symptoms of functional disorders and re-establish symmetric and reduced postural activity in the temporal and masseter muscles, which can facilitate procedures, such as functional analysis and occlusal adjustment.     

The distribution of occlusal contacts in the intercuspal position and temporomandibular disorder

The aim of this study was to describe the distribution of occlusal contacts in subjects with signs or symptoms of temporomandibular disorder (TMD), and to assess whether any difference exists with healthy subjects. Twenty-five university dental students with complete natural dentition who exhibited TMD (13 females and 12 males, age from 19 to 30 years) and 25 age- and sex-matched controls entered the study. Occlusal contacts were evaluated in the intercuspal position and wax registrations were made in all subjects. Occlusal contacts were classified according to location and intensity. No differences were found between TMD and control groups for the overall number and distribution of contacts or for any side and intensity of contact. An intra-subject analysis showed that TMD subjects had significantly greater bilateral asymmetry in the number of contacts than controls. Median absolute difference of the number of contacts on right and left sides was 3 (95% CI, 2-4) in TMD subjects and 2 (95% CI, 1-2) in controls. In TMD subjects with mono-lateral TMD there was a significant concordance (88.9%) between the side of disorder and the side of higher number of contacts. These findings, while confirming that a significant relationship exists between distribution of occlusal contacts and TMD, further suggest that in young adults it may be primarily expressed by asymmetries in occlusal contact patterns. Existence and aetiology of any association of TMD with occlusal contacts should be further investigated.     

Influnece of an occlusal splint on integrated electromyography of the masseter muscles

In order to examine the effect of an occlusal splint on the integrated electromyography (EMG) of the masticatory muscles, EMG of bilateral masseter muscles of 23 patients with temporomandibular joint disturbance syndrome (TMJDS), with and without an occlusal splint, was measured and integrated on line during maximum clenching. It was found that the integrated myoelectrical value of the masseter muscle on the involved and non-involved side was reduced with the occlusal splint. The absolute difference between integrated myoelectrical values in the left and right masseter muscles was reduced with an occlusal splint, but the relative difference remained virtually unchanged. These results indicate that the occlusal splint can decrease masseter muscle activity and thus exert a therapeutic effect.     

Duration of the electromyographic silent period following the jaw-jerk reflex in human subjects.

During voluntary jaw clenching, a sharp tap to the menton of the mandible resulted in a transitory silent period (pause) in the electromyographic activity of the masseter and anterior temporalis muscles. Factors that could influence the duration of the silent period were studied, including direction and magnitude of the stimulus applied by the operator, the amount of muscular effort exerted by the subjects, and varying occlusal vertical dimensions. Decreased isometric muscle force resulted in statistically significant increases in silent period durations.