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Aims: (1) To determine the dose-response relationship of therapeutic ultrasound for TMD-related pain in the masseter muscle among four doses comprised of two intensities (0.4 W/cm2 and 0.8 W/cm2) and two duty cycles (50% and 100%); and (2) to determine if therapeutic ultrasound applied to the masseter muscle would elicit a segmental effect on the ipsilateral temporalis muscle. Methods: A total of 28 adult women with bilateral myalgia were randomly allocated to one of the four intervention doses. Therapeutic ultrasound was applied on each side of the masseter sequentially for 5 minutes. The following outcomes were measured before and immediately after each intervention: self-reported pain score, pressure pain thresholds for the masseter and temporalis muscles, and intraoral temperature adjacent to the treated masseter. Results: Self-reported pain scores showed neither significant main effects nor significant interaction among the intensity or duty cycle doses (all P > .05). The change in the pressure pain threshold of the masseter showed a significant interaction (P = .02) attributed to the 0.4 W/cm2 and 100% duty cycle dose. Intraoral temperature was significantly increased and associated with the duty cycle (P = .01). A significant segmental effect of the pressure pain threshold of the temporalis was found for intensity (P = .01) . Conclusion: There was an increase in the pressure pain threshold of the painful masticatory muscles and an increase in intraoral temperature adjacent to the treated area immediately after the use of ultrasound at 0.4 W/ cm2 with a 100% duty cycle. [ABSTRACT FROM AUTHOR]

Aims: To assess the consistency of intentional behavioral performance as an index of whether individuals understood the meanings of the behavioral terms of the Oral Behaviors Checklist, which is a self-report scale for identifying and quantifying the frequency of jaw overuse behaviors. Methods: Surface electromyography was used to measure bilaterally the activity of the masseter, temporalis, and suprahyoid muscles (for assessment of oral behaviors) and the biceps muscles (reference task of biceps curl) in 27 temporomandibular disorder (TMD) cases and 27 controls. Subjects were asked to perform (1) biceps curls to lift 5 weights, with explanation, and (2) 10 oral behaviors (eg, "clench," "yawn") without explanation. Results: Biceps-curl performance resulted in assignments of excellent or very good for linearity-reliability based on inspection and correlation. Test-retest reliability of the 10 performed oral behaviors generally ranged from 0.6 to 0.98 for all 3 muscle groups, and many tasks had reliability coefficients comparable to those for the biceps curl. Across tasks, elevator muscle reliability of cases was 0.87, compared to 0.75 for controls; group values for opening muscles were similar. Conclusion: Individual subjects performed each task at a high level of consistency. Performance was not appreciably altered by being a TMD case versus a control and was not significantly different from the performance level of a reference task, indicating that each individual understood well the meaning of each oral behavior-related word. [ABSTRACT FROM AUTHOR]

Muscle palpation is an important procedure in screening for TM disorders and assessing results of treatment outcome studies, but interpretation of response may be subjective and vulnerable to examiner bias. Masticatory muscle palpation scoring was evaluated with respect to interrater agreement on 31 myofascial pain-dysfunction patients participating in a medication study. Two clinicians independently palpated the temporomandibular joints, muscles of mastication, and related head and neck musculature on three different occasions over the 6-week period of the study. Standardization of palpation technique and initial protocol for interpretation of subject response were discussed prior to the first examination. Further clarification and reinforcement of examination methodology and scoring were carried out prior to the second examination, 1 week later. Another 5 weeks passed, with no further standardization, before the third and last examination. A behaviorally anchored scoring system (0 to 3) was used to rate response to palpation. Results indicate that two investigators can achieve a fair degree of reliability when carefully standardized, further interrater standardization can result in higher reliability, and reliability can be maintained over at least a 5-week period of time. [ABSTRACT FROM AUTHOR]

Aims: To investigate the local and segmental effects of therapeutic ultrasound at a dose of 0.4 w/cm² with 100% duty cycle for 5 minutes compared to the effect of sham ultrasound on painful masticatory muscles. Methods: A total of 20 adult female subjects with bilateral masseter myalgia diagnosed according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) were included. Each subject was randomized to either an active ultrasound group or a sham ultrasound group. The intervention was applied to each masseter muscle for 5 minutes. Measures included pre- and post-self-reported pain intensity recorded on a verbal rating scale (VRS), pressure pain thresholds for the masseter (PPT-M) and temporalis (PPT-T) muscles, and intraoral temperature for the masseter muscle. Preintervention score was subtracted from the postintervention score for all measures to calculate mean change in pain, and nonparametric Mann-Whitney test was used to compare the groups. Statistical significance was set at P < .05. Results: Changes in VRS did not show a significant difference between groups (P > .05). There were significant increases in PPT-M and intraoral temperature in the ultrasound group compared to the sham group (P < .05). There was no significant difference in PPT-T (P > .05), suggesting no segmental effect. Conclusion: Therapeutic ultrasound produced an immediate increase in PPT-M and intraoral temperature compared to sham ultrasound in female subjects with bilateral masseter myalgia. [ABSTRACT FROM AUTHOR]

Background: This observational study was designed to evaluate the reliability and diagnostic validity of Joint Vibration Analysis (JVA) in subjects with bilateral disc displacement with reduction and in subjects with bilateral normal disc position. Methods: The reliability of selecting the traces was assessed by reading the same traces at an interval of 30 days. The reliability of the vibrations provided by the subjects was assessed by obtaining two tracings from each individual at an interval of 30 min. The validity compared the Joint Vibration Analysis parameters against magnetic resonance imaging as the reference standard. The data were analyzed with exploratory factor analysis. Results: The short- term reliability of the Joint Vibration Analysis outcome variables showed excellent results. Implementing factor analysis and a receiver operating characteristic as analytical methods showed that six items of the Joint Vibration Analysis outcome variables could be scaled and normalized to a composite score which presented acceptable levels of sensitivity and specificity with a receiver operating characteristic of 0.8. Conclusion: This study demonstrated that the composite score generated from the Joint Vibration Analysis variables could discriminate between subjects with bilateral normal versus bilateral displaced discs. [ABSTRACT FROM AUTHOR]

The article presents a study which aims to investigate the function of botulinum toxin on pain and muscle fatigue, both induced by sustained fatiguing contraction, after administering botulinum toxin in human masseter muscle. In the study, botulinum toxin and isotonic saline were injected to the subjects. Pressure pain threshold, electromyographic activity, and the electromyographic power spectrum frequency were measured. Results showed reduced contraction and pressure pain threshold.

Analysis of previous data suggested the hypothesis that temporomandibular joint (TMJ) eminence shapes develop ideally to minimize joint loads. Hence, we tested this hypothesis in nine females and eight males in each of two groups, with and without TMJ disc displacement. Participants provided anatomical data used in a joint load minimization numerical model to predict, and jaw-tracking data used to measure, eminence shapes. Coordinate data (x,y) of shapes were fit to third-order polynomials for two sessions, sides, and methods (predicted, measured) for each participant. Inter-session data were reliable and averaged. Those with, compared with those without, disc displacement had higher measured shape range (5:1) and left-right asymmetry prevalence (4:1). In 29 symmetrical individuals, ANCOVA and Bonferroni tests compared vertical dimensions (y) at 11 posteroanterior points (x), 0.5 mm apart. Model-predicted and measured shapes were significantly different (P ≤ 0.01) near the eminence crest, but joint load minimization was consistent with eminence shape for x < 3.0 mm. [ABSTRACT FROM AUTHOR]

Muscle forces determine joint loads, but the objectives governing the mix of muscle forces involved are unknown. This study tested the hypothesis that masticatory muscle forces exerted during static biting are consistent with objectives of minimization of joint loads (MJL) or muscle effort (MME). To do this, we compared numerical model predictions with data measured from six subjects. Biting tasks which produced moments on molar and incisor teeth were modeled based on MJL or MME. The slope of predicted vs. electromyographic (EMG) data for an individual was compared with a perfect match slope of 1.00. Predictions based on MME matched best with EMG activity for molar biting (slopes, 0.89-1.16). Predictions from either or both models matched EMG results for incisor biting (best-match slopes, 0.95-1.07). Muscle forces during isometric biting appear to be consistent with objectives of MJL or MME, depending on the individual, biting location, and moment. [ABSTRACT FROM AUTHOR]

The sequelae of a sustained clench are incompletely understood. Our experimental questions were to compare the responses of men and women, to compare masseter and anterior temporalis muscles, and to test hypotheses for the reduction of the median frequency of power spectra. We recorded duration, amplitude, number of phases, and area of the motor unit action potential before and after a sustained clench and the median frequency of the electromyographic power spectrum in 41 subjects. After the clench, the median frequency was lower, the action potential duration longer, the number of phases increased, and the area larger, but the amplitude was not different. Males and females failed to differ. Compared with the temporalis, the masseter had a lower median frequency, longer duration, larger number of phases, and increased area. Our results are consistent with a decrease in the conduction velocity of the muscle action potential as an explanation of the spectral shift. [ABSTRACT FROM AUTHOR]

A telephone survey to assess treatment success was conducted 2-3 years after treatment of patients suffering from TMJ syndrome. Pre-treatment silent period durations were compared among groups of patients determined by their response to the telephone survey. The short-term (immediately post-treatment) improvement rate was 81%. Some 35 % of patients were completely cured. There was no statistically significant difference in mean silent period duration among the groups of patients that achieved complete, partial or no relief of symptoms. The long-term (2-3 years after treatment) persistence of improvement rate was 72%. There was also no statistical difference in the mean silent period duration between those patients who had experienced persistence of success and those who reported either no relief or relapse of symptoms. [ABSTRACT FROM AUTHOR]

A numerical model of the mandible, its articulating surfaces, and the forces exerted by the primary masticatory muscles has been developed for the purpose of investigating loading of the temporomandibular joint. Evidence is presented which shows that the temporomandibular joint is a load-bearing joint over the normal functional range of bite-force positions and angles. In this investigation, temporomandibular joint loads were found to vary from a maximum appositional force of 60% of the bite force (when bite forces were applied to the incisors) to a distracting force of about 5% of the bite force (when applied to the distal surfaces of the third molars). TMJ loads tended to reach a minimum as a result of vertically directed bite forces positioned at the second molars. A range of conditions in which bite forces were directed parallel to or within approximately 20° of the mid-sagittal plane was found to be conducive to stability of the temporomandibular joint. This stability included symmetry in the direction and in the magnitude of condylar loads as well as the presence of small forces tending to appose the condyle and articular eminence. TMJ loads tended to reach a maximum in response to mediolaterally directed bite forces. This result is consistent with the fact that no muscle of mastication exhibits a spatial orientation in which the muscle fibers are predominantly mediolateral in direction. [ABSTRACT FROM AUTHOR]

Jaw muscle silent periods were recorded in response to a chin tap during maximal clench in asymptomatic subjects. The insertion of a palatal splint did not change the silent period duration. However, an occlusal splint, or part of it, caused a significant increase in the duration of the silent period. [ABSTRACT FROM AUTHOR]

Jaw muscle silent periods in response to chin taps were recorded from immediate complete denture patients before extraction of a residual anterior dentition, after insertion of the dentures, and three and six months after insertion. After three months' use of the dentures, the mean EMG silent period duration was significantly increased compared to the pre-extraction stage. [ABSTRACT FROM AUTHOR]

The neuromuscular mechanisms of the electromyographic silent period are poorly understood but clinically significant. Our purpose was to isolate the contribution of cutaneous afferents from the chin to the latency and the duration of the EMG silent period. Under the conditions of our experiment, the afferents of the mental nerve have no observable influence on the latency or the duration of the silent period educed by a menton tap. [ABSTRACT FROM AUTHOR]

The hypotheses that latency or duration of the EMG silent period evoked by a tap to the chin during a maximal clench would be more prolonged in more severe TMJ patients were tested. The mean latency did not, and the mean duration did, increase significantly with increased severity of TMJ dysfunction. [ABSTRACT FROM AUTHOR]

The purpose of this research was to compare, in the subjects, the duration of the EMG silent period with jaw motion error. The results indicate that both jaw motion error and silent period duration are large in patients with TMJ-muscle-pain dysfunction, both are small in normal subjects, and both are small in successfully treated patients. There is a statistically significant correlation (r = 0.91; P < 0.01) between the two diagnostic parameters of TMJ-muscle-pain dysfunction. [ABSTRACT FROM AUTHOR]

Due to disparate findings across the published studies, the stress-hyperactivity hypothesis has never been fully accepted as a causal mechanism for chronic muscle pain. Two recent comprehensive reviews of the psycho-physiological studies of chronic pain came to opposite conclusions about the viability of the hypothesis, which stemmed from differing importance placed on the experimental methodology: the adequacy of stress manipulation. The present study tested the hypotheses that the adequacy of stress manipulation is influenced by stress stimuli type, degree of personal relevance, and selection of criterion for verification of stress experience, and that these factors have a measurable impact on the related physiological responses in a manner that is consistent with a theory of stress applicable to clinical stress disorders. The three factors investigated were: task (imagery, reaction time), relevance (high, low), and manipulation criterion (autonomic, self-report). The tasks were presented to 16 chronic pain patients while muscle, electrodermal, and self-report responses were recorded. Reaction-time tasks and high-relevance conditions led to high muscle and electrodermal responses. Only the high-relevance imagery, however, produced high self-reported distress. Consistent with other research, the present overall data demonstrated differing physiological profiles for different stimuli types. More importantly, these data suggest that the manipulation type and the manipulation criterion influence outcomes of experimental tests of stress on physiological systems, which may directly lead to contrasting conclusions about causal relations between stress and chronic pain conditions. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the effects of the location of electrode placement and instrumentation in the electromyographic (EMG) silent period of the masseter muscle. The effects of the placement of surface electrodes upon the amplitude and shape of action potential are noted, mentioning the possibility that it could also affect the duration of the silent period. The methods used for measuring the silent period duration are described, which include a method involving a pair of electrodes connected to a commercial EMG amplifier and a method involving electrodes connected to a commercial analyzer and a polygraph system.