Ultrasound and analysis of the deformation patterns of the masseter muscle: comparing surgical anatomy, ultrasound and functional anatomy

Abstract

Purpose: We have tried to demonstrate whether the analysis of the muscle strain allows us to identify the three distinct functional areas of the architecture of the masseter, as one would see them by performing or viewing an anatomical dissection of said muscle, and whether these sections have behave differently in terms of origin and coping of the strain they face (quantitative analysis).

Materials and methods: This work has been elaborated by the use of an ultrasound machine (MicrUs ext-1H Telemed Medical Systems Milano) and a linear probe (L12-5l40S-3 5-12 MHz 40 mm) which allowed us to record a 45 frame per second video (DCM). Videos has been elaborated by use of an ultrasound machine (MicrUs ext-1H Telemed Medical Systems Milano) and a linear probe (L12-5l40S-3 5-12 MHz 40 mm) which allowed us to record a 45 frame per second video (DCM). We applied to the resulting video a software (Mudy 1.7.7.2 AMID Sulmona Italy) for the analysis of muscle deformation patters (contraction, dilatation, cross-plane, vertical strain, horizontal strain, vertical shear, horizontal shear, horizontal displacement, vertical displacement). The number of videos of masseter muscles in contraction at maximum exertion due to dental clenching made during this research is around 12,000. Out of these we chose 1,200 videos which examine 200 patients (100 females, 100 males).

Results: The deformation pattern analysis of the skeletal muscle on ultrasound basis seems to be an adequate instrument to use during the investigation of the functional structure of the masseter muscle given its ability to highlight the distinct activity of each separate part of the muscle.

Conclusions: Moreover the strain does not apply to the muscle uniformly; instead it varies according to the observed area.

Keywords: biomechanics; deformation pattern; masseter muscle; masticatory organ; strain; ultrasound.

Figure 1

Masseter: (1) superficial section; (2) middle section; (3) internal section.

Figure 2

Masseter dissection vs ultrasound image: (1) parting of the two layers of the external masseter; (2) intermediate section; (3) blade tendon of the internal masseter; (4) layers of the internal masseter.

Figure 3

Ultrasound of the master during maximum exertion. External section: (1) external layer; (2) internal layer. (3) Intermediate section. Internal section: (4) outward layer; (5) central layer; (6) inward layer.

Figure 4

Deep masseter and temporomandibular joint: (1) deep masseter; (2) mandibular condyle.

Figure 5

(1) Masseter in maximum exertion contraction with grid for the study of patterns; (2) masseter in maximum exertion contraction with grid for the study of patterns divided in three areas; (3) masseter in maximum exertion contraction and cross-plane; (4) curves time/strain of the three parts of the muscle.

Figure 6

The cross-plane id measured on three single cycles of contraction repeated at 30 seconds intervals and an average is calculated based on that data. C1 and C2 represent the compression areas obtained with another pattern that highlight the parting of the muscle in three functional areas.