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Clin Neurophysiol. 2019 Mar;130(3):388-395. doi: 10.1016/j.clinph.2018.12.008. Epub 2019 Jan 19.

Three-dimensional amplitude characteristics of masseter motor units and representativeness of extracted motor unit samples.

Author information

1
Department of Orthodontics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany. Electronic address: bernd.lapatki@uni-ulm.de.
2
Department of Orthodontics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
3
Department of Prosthodontics, University of Würzburg, Josef-Schneider-Strasse 2, 97080 Würzburg, Germany.
4
Faculty of Electrical Engineering and Computer Science, University of Maribor, Smetanova Ulica 17, 2000 Maribor, Slovenia.
5
Department of Orthodontics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany; Department of Clinical Physics, Kempenhaeghe Epilepsy and Sleep Center, Sterkselseweg 65, 5591 VE Heeze, the Netherlands.

Abstract

OBJECTIVE:

This study aimed to characterize amplitude topographies for masseter motor units (MUs) three-dimensionally, and to assess whether high-density surface electromyography (HDsEMG) is able to detect MU samples that represent the masseter's entire MU pool.

METHODS:

Ten healthy adult volunteers participated in the study, which combined three EMG techniques. A HDsEMG grid covering the entire masseter, and intramuscular fine-wire electrodes were used to obtain two independent MU samples for comparison. The MUs' amplitude profiles in the dimension of muscle depth were determined using scanning EMG. All data were recorded simultaneously during a low, constant contraction level controlled by 3D force feedback.

RESULTS:

The median medio-lateral diameter of 4.4 mm (range: 1.2-7.9 mm) for MUs detected by HDsEMG did not differ significantly (Mann-Whitney-U test, p = 0.805) from that of 3.9 mm (0.6-8.6 mm) for MUs detected by fine-wire EMG. For individual subjects, the medio-lateral diameters of all HDsEMG-detected MUs spanned 70.5% (19.2-75.1%) of the masseter's thickness.

CONCLUSIONS:

HDsEMG is able to examine small and large MUs from a great masseter proportion in one single measurement.

SIGNIFICANCE:

Clinical application of HDsEMG might contribute to a better understanding of neuromuscular adaptations in patients with temporomandibular disorders (TMD) and could allow for monitoring treatment effects.

KEYWORDS:

Electromyography; High-density surface EMG; Masseter; Motor unit; Scanning EMG; Temporomandibular disorder

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