Postural activity in the muscles of mastication with the subject upright, inclined, and supine

Abstract

With the mandible at rest, electromyographic recordings were obtained from the anterior temporal, lateral pterygoid, and digastric muscles with the subjects (A) sitting upright with the head unsupported, (B) inclining backwards with the back-rest at an angle of 45", and (C) supine. Two minutes after a shift in posture the electrical activity in the anterior temporal muscles was strongest in the upright position, it decreased slightly when the back-rest was at 45", and was least in the supine position. The digastric muscles showed a pattern similar to that of the temporal. The activity in the lateral pterygoid muscles was strongest when the subject was inclined backwards at 45". The influence, therefore, of these muscles on the posterior border position of the mandible varies with posture. In all the muscles studied there was least activity when the subject was in the supine position. This would suggest that the supine position is suitable .for recording the most retruded position of the mandible. In the intermediate position the lateral pterygoid muscles appear to counteract retrusion.Quantitated Plectromyographic recordings from the 'muscles of mastication of subjects seated upright, with the head unsupported, and the mandible at rest have shown slight, but distinct activity (Moller 1966). T'he present study deals with the postural activity in the temporal, lateral pterygoid, and digastric muscles, i. e. muscles determining the vertical and horizontal position of the mandible. With the subjects sitting upright, inclined backwards, and in the supine position, the aim was to locate the posture in which the mandible was least influenced by muscle activity. It was the assumption that in such a posture registration of the most retruded position of the mandible would be facilitated. This question was not considered in the previous electromyographic studies of head posture concerning either the action of the postcervical muscles (Halbert 1958) or the change in the position of the mandible with the head tilted forwards and backwards (Vanoucek 1957, Preiskel 1965).In the supine position the load of the mandible is directed towards the temporomandibular joints. Recordings, therefore, in this position might indicate whether or not retrusion of the mandible is influenced by the action of the lateral pterygoid muscles (Aprile 8 Saizar 1947.

Regulation of Mandibular Postures: Mechanisms and Clinical Implications

“…The activity in the lateral pterygoid muscles is maximal at an angle of 450 to the vertical axis. The temporal and digastric muscles are more active when the subject's head is vertical (Lund et al, 1970). This explains why it has been suggested that the centric relation should be recorded with the patient lying down (Eberle, 1951).…”

“…This explains why it has been suggested that the centric relation should be recorded with the patient lying down (Eberle, 1951). However, in all cases, the differences in the EMG measurements taken while the patient was sitting or lying down are small (Lund et al, 1970), and no difference has been found in centric relation values between the two positions (Tripodakis et al, 1995). In summary, it seems that gravity, and therefore the position of the head relative to the vertical axis, has little relevance to the clinical determination of the centric relation.…”

“…EMG activity varies in response to different conditions, e.g., eye opening, which suddenly increases the activity of the anterior part of the temporal muscle (Kawamura and Fujimoto, 1957), changes in head or body posture (Lund et al, 1970), the state of relaxation of the subject, or even the subject's will. Indeed, it is possible to train an individual to relax to a point of minimal recorded muscle activity (Gross and Ormianer, 1994).…”

The effect of a Lucia jig for 30 minutes on neuromuscular re-programming, in normal subjects

“…17 Lund et al 17 reported that when the mandible remained in the resting position for longer periods of time, a change occurred in the electromyographic activity of the masseter and temporalis muscles. Such results are in agreement with the ones obtained in this study, in which the re-programming device changed the electromyographic activity during the specified time period; however, the data were not statistically significant.…”

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

“…Previous studies reported that surface EMG recordings were influenced by location of the electrodes over the muscle, inter-electrode distance, body posture and psychological factors [25][26][27]. The electrode location has a large influence especially on characteristics of the recorded EMG signal.…”