Wednesday, December 16, 2009

The effect of four jaw relations on electromyographic activity in human masticatory muscles

Hickman, David, M., Cramer, Richard, Stauber, William T. (1993) The effect of four jaw relations on electromyographic activity in human masticatory muscles. Archs Oral Biol 38:3, pp 261-264.


Significant differences were found in the electromyographic (EMG) activation between the masseter and temporalis muscles for the leaf gauge (LG), manually manipulated (CR) and neuromuscular (NM) bite positions during maximal static clench. The LG position consistently demonstrated the lowest EMG activity, while the NM position displayed the highest degree of muscle activity. Similarly, the ratio of the masseter/temporalis EMG activity during maximal clench was lower for the LG and CR positions and highest for the NM position. These data indicate that the NM position produced the greatest total muscle recruitment, with more masseter involvement during maximal clench, and enabled the subjects to generate greater clenching forces in the NM position as compared to the LG and CR positions.

Analysis of maximal electromyographic activity of the masseter and anterior temporalis muscles in Myocentric and Habitual Centric in Temporomandibular Joint and Musculoskeletal Dysfunction

Jankelson, Robert (1990) Analysis of maximal electromyographic activity of the masseter and anterior temporalis muscles in Myocentric and Habitual Centric in Temporomandibular Joint and Musculoskeletal Dysfunction. Front. Oral Physiol., Karger, Basal, Vol. 7, pp 83-97

A computer review of maximal bite integrated EMG values for 46 consecutive patients referred to a clinical practice for treatment of TMJ/MSD was analyzed for data correlation. The 46 patients included 37 females and 9 males. The average ages of the patients were 42 and 46 years, respectively, for females and males. The patients all displayed 3 or more of the standardized symptoms in the Kinnie-Funt TMJ profile [23]. Only those patients with EMG/CMS profiles indicating a positive rationale for orthosis therapy were selected. This meant that the patients had either an excess of 2.0 mm of freeway space, or had an anterior/posterior discrepancy between neuromuscular and habitual trajectory of closure that precluded selective grinding of the teeth.

(1) Analysis of 46 temporomandibular joint/musculoskeletal dysfunction patients showed masseter EMG activity significantly lower than anterior temporalis EMG activity during maximal bite to habitual occlusion. Since the masseter muscle is the primary force muscle, while the anterior temporalis is the primary posturing muscle, this appears to be a consistent finding in temporomandibular joint/musculoskeletal dysfunction patients with nonoptimal occlusion.
(2) The combined integrated EMG in the symptomatic temporomandibular joint/musculoskeletal dysfunction patient is significantly diminished when the patient maximally occludes in the habitual occlusion as opposed to the myocentric position. Restoration of the occlusion to a neuromuscular myocentric resulted in a 72.2% improvement in motor unit recruitment. The marked increase in motor unit recruitment and the significant reduction in the number of symptoms as reported by the patients in this study, suggests that the myocentric position is a more efficacious functional position for motor muscle recruitment than the existing habitual occlusion in the musculoskeletal dysfunction patient.
(3) The study supports previous studies showing reduced EMG activity during maximal bite in temporomandibular joint and musculoskeletal dysfunction patients. Therefore, integrated EMG of maximal function appears to be a reliable, quantitative modality to identify functional disorders of the masticatory system.
(4) Integrated EMG of maximal bite effort can be used as a quantitative means to monitor patient progress. There appears to be a significant correlation by the increase in maximal EMG activity of the masseter and anterior temporalis, and the reduction in the number of patient-reported symptoms.
(5) Providing a neuromuscular myocentric occlusal position for the temporomandibular joint/musculoskeletal dysfunction patients allowed markedly increased motor unit recruitment during maximal bite. The increase in function correspondingly resulted in concomitant reduction in the patient symptom index.
(6) Treatment to the myocentric position resulted in significantly more symmetrical recruitment of masseter and anterior temporalis motor units. The temporomandibular joint/musculoskeletal dysfunction patient appears to have a greater asymmetry of muscle function during maximal bite to the habitual occlusal position. Restoration of the temporomandibular joint/musculoskeletal patient to a neuromuscular myocentric position resulted in significant improvement of muscle recruitment and symmetry.

To conclude, this study of 46 consecutive clinical dysfunction patients confirmed the findings of Moller, Erikkson, Sheikholeslam, Ruse, Molin, Pruim, Jarabak, Kydd, Bigland, Lous, Prayer-Galletti, and Pantaleo and others in support of maximal bite EMG analysis for diagnosis and temporomandibular joint/musculoskeletal dysfunction.

The restoration of the dysfunctional patient to a neuromuscular myocentric occlusion results in significantly increased function and synergy of the anterior temporalis and masseter muscles.

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