Major M. Ash

Power spectral analysis of the surface electromyogram of human jaw muscles during fatigue.

Abstract Muscle fatigue in the anterior temporal and masseter muscles of 13 normal subjects was induced by maximum clench in intercuspal position. Frequency analysis using a fast Fourier transform algorithm to obtain the power-spectral density function and the power spectrum of the electromyogram signal indicated that the power spectra obtained during fatigue were statistically significantly shifted to lower frequencies and narrower than those obtained at the beginning of the clench. The shift was due to a significant increase of the power in the low-frequency range and a significant decrease of that in the high-frequency range. The power-spectrum shift to lower frequencies had an exponential time course. The most pronounced shift occurred in the first 25 per cent of the total clenching time. Decrease of the conduction velocity of the action potential along the muscle fibre seems to be the main cause of the shift.

Electromyographic Silent Periods and Jaw Motion Parameters: Quantitative Measures of Temporomandibular Joint Dysfunction

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.

Effect of bite force on the power spectrum of the surface electromyogram of human jaw muscles

Abstract The frequency content of the surface electromyogram (EMG) of the anterior temporal and masseter muscles of 14 normal adults was obtained during maximum clench in intercuspal position, as well as at different bite force levels. Frequency analysis was carried out by computer using a fast Fourier transform algorithm to obtain the power-spectral density function and the power spectrum of the EMG signal. Bite force was monitored by a force transducer placed intra-orally. The power spectra of the anterior temporal muscle during maximum clench in intercuspal position were significantly wider than those of the masseter muscle, indicating that the EMG of the former muscle contained more power at high frequencies than that of the masseter muscle. Increase in bite force produced, in both muscles, a power-spectrum shift to lower frequencies. The shift was probably caused by recruitment of larger motor units and by increase in synchronization between them. Different contents of A, B and C fibres and/or differences in thickness of skin covering the muscles could account for the differences between the temporal and masseter muscle power spectra.

The influence of mechanical input parameters on the duration of the mandibular joint electromyographic silent period in man

Abstract The duration of the electromyographic silent period following a tap to the menton has been reported to be clinically useful in the diagnosis of mandibular joint dysfunction but not the influence of details of the tap. Using a solenoid-driven mechanical tapper, the following were investigated: in patients with joint dysfunction, effect on single muscles and position of the tap in a sequence of taps, in normal subjects, force of the tap, degree of opening of the jaw, angle of tap, and the biting force; all on the duration of the resulting silent period. No significant changes could be ascribed to any of these variables. The introduction between the teeth of wooden shims or a bite-force transducer were the only factors to change the duration. The dysfunction group had significantly longer silent periods than the normal group. It is concluded that, provided nothing is introduced between the teeth, the input parameters investigated do not influence the duration of the silent period.

Changes in jaw relations, hyoid position, and head posture in complete denture wearers

In a group of 18 partially edentulous patients provided with immediate complete dentures, changes in hyoid bone position and craniocervical posture were examined on cephalometric radiographs made during 1 year of denture use. The findings indicated that the changes in hyoid bone position largely followed the pattern of forward-upward rotation of the mandible due to ridge resorption. During this course the hyoid position in relation to the cervical spine showed a mean increase. The hyocervical changes, however, showed less variability than the hyomaxillary and hyomandibular changes. The posture of the head and cervical column showed no definite mean changes during the 1-year period. On the other hand, analysis of individual changes revealed that a pronounced decrease in mandibular inclination due to ridge resorption was associated with retroclination of the cervical column and decreased craniocervical angulation. These postural changes may be regarded as adaptive changes to a marked initial change in mandibular position.

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.

Occlusion: Reflections on science and clinical reality

The last 50 years have seen progress in emphasizing scientific evidence as a basis for dental practice, including occlusal therapy. Although a proper understanding of the contributory role of occlusion to temporomandibular disorders should not be minimized, the importance of occlusion in other areas of dental education and practice should not be overlooked. The primary objective of this article is to discuss the nature of this problem as it relates to the duality of science and clinical reality in the evidence-based paradigm, information transfer, quality of evidence, clinical trials, and clinical aspects of occlusion. Some suggested solutions for the problem and thoughts on past and future perspectives of occlusion are expressed in context of inquiry.

Occlusion, TMDs, and dental education

The paradigmatic shift to evidence-based dentistry (EBD) that relates to occlusal therapy, selective occlusal adjustment (OA) and stabilization splints therapy (SS) for TMDs has had an unfavourable impact on the teaching of many of the important aspects of occlusion needed in dental practice. The teaching of OA systematically in dental schools has been nearly abandoned because of the belief that OA is an irreversible procedure and gives the impression that it is without merit elsewhere in the management of occlusion. However, a particular dose of knowledge and practice of occlusion that is necessary for all aspects of dental care should be taught systematically in dental schools. The uses and misuses of OA and SS and their limitations should be emphasized because of their importance to bring clinical reality into the dental curriculum. Thus, and irrespective of EBD induced contradictions, OA and SS should still have a significant place in systematically teaching of occlusal therapy. However, there are many more aspects of the management of occlusion that should to be considered. Hopefully, because of their importance, other aspects of the management of occlusion will once again become a significant part of the dental curriculum.

Computerized data acquisition and analysis for real-time electromyography in clinical dentistry

The purpose of this research was to design and use a minicomputer-based data acquistion system in a clinical dental environment to digitize and analyze electromyogrohic (EMG) and jaw motion data. The quantitation of EMG in clinical problems requires a significant number of patients, short analysis times, and efficient acquisition and analysis of data. A present extension of this system is to utilize interactive computer graphics for presentation of these data for evaluation by clinical personnel. To facilitate EMG evaluation for clinical diagnostic purposes, a real-time capability was designed to accommodate high-speed simultaneous data collection from a multiplicity of signal sources, viz., 5 EMG channels, biting force, and jaw position. Once digitization and storage begin, data reduction and analysis programs are provided for immediate presentation of results. Application of the system to examine jaw motion has resulted in clinically useful diagnostic information. These results suggest that fuller utilization of the potential of the computer system will provide deeper clinical and physiological insight and, therefore, better dental treatment for a large fraction of the population.

An electromyographic study of jaw opening and closing reflexes in man

The electromyographic activity of the right masseter and digastric muscles was recorded in 10 subjects. A jaw-opening reflex was observed shortly after a mechanical stimulation in subjects performing clenching and active jaw-opening exercises. The latency of this reflex activity was about 28 ms, coinciding with the termination of the silent period of the masseter muscle. The experiments show that this opening reflex can occur without masseter spindle-unloading and may respond to low-threshold afferents.