1. musculo-aponeurotic architecture of the human masseter muscle
An in vivo study of the
musculo-aponeurotic architecture of the human masseter muscle
Gheorghe TI1, Leekam R3, Lam EWN1,2, Perschbacher SE1,2,
Liebgott B2,3, and AM Agur2,3
Oral and Maxillofacial Radiology Graduate Program1, Graduate Department of Dentistry2, and Division of Anatomy, Department of Surgery3,
University of Toronto, Toronto, Canada

2. MM heads: Superficial (SH) and deep (DH)
Background
Masseter muscle (MM):
Chewing
Swallowing
Speaking
Clenching and grinding
Pathosis:
Masticatory muscle myalgia
Temporomandibular joint disorders (TMDs) DH SH
MM heads: Superficial (SH) and deep (DH)
Agur and Dalley, 2012

3. Background: Laminae of SHZ Z L1 L1 DH DH L1 L3 L3 M L2 L1 M M L2
Fibre bundle: red line
Laminae, L1-L Zygomatic arch, Z
Mandible, M Deep head, DH

4. Gaps in Knowledge
No in vivo ultrasound (US) studies of MM investigating the musculo-aponeurotic architecture volumetrically
Asymptomatic MM architecture needs to be elucidated in vivo to understand pathological changes

5. Objective
Investigate the in vivo musculo-aponeurotic architecture in asymptomatic participants using US in relaxed and maximally contracted states.
Hypothesis
The aponeurotic and fibre bundle components of the laminae differ significantly between the relaxed and maximally contracted states.

6. Methods Inclusion: Exclusion: 24 participants (48 MM); 12M/12F
years old
Asymptomatic
Score of 0 on TMD Pain Screener
Exclusion:
Positive TMD Pain Screener score (Gonzalez et al, 2011)
Disc displacement, degenerative joint disease, or subluxation (Schiffman et al, 2014)
Intramuscular pathosis: preliminary US scan

7. Methods
In vivo US protocol based on “Musculo-Aponeurotic Architecture of the Human Masseter Muscle: a Three-Dimensional Cadaveric Study” L3 L2 L1
Ebrahimi, 2015 MSc Thesis

8. US scanning protocol for each lamina of SH in:
Methods
Equipment: GE Loqiq e (0.1mm axial resolution)
US scanning protocol for each lamina of SH in:
relaxed
maximally contracted (maximum intercuspation)
Electromyography (EMG) used to confirm muscle activation

9. Methods Images acquired from each lamina Axial:
Superior, middle, inferior thirds
Coronal:
Panoramic
Quadrants of SH
Sup 1/3 Q3 Q1
Mid 1/3 Q4 Q2
Inf 1/3

10. Data Analysis Evaluation of SH: Evaluation of each lamina:
Number of laminae
Evaluation of each lamina:
Fibre bundle length (FBL)
Aponeurotic length
Comparison of FBL and aponeurosis length:
Paired t-test
Wilcoxon signed-rank test

11. Results: Panoramic Coronal Relaxed
Three laminae (L1-L3)
Four laminae (L1-L4)
n = 12 MM
n = 8 MM Z Z S S L4 L3 L3 L1 L2 L2 L1 A A
Zygomatic arch, Z; Subcutaneous tissue, S; Angle of mandible, A

12. FBL: length of red line; Aponeurosis: yellow
Results: Coronal Scan Z Z S S R R S S
Relaxed
Contracted
FBL: length of red line; Aponeurosis: yellow
Zygomatic arch, Z; Subcutaneous tissue, S; Ramus, R

13. Results: Panoramic CoronalZ Z S S A A
Relaxed
Contracted
Aponeurosis: yellow
Zygomatic arch, Z; Subcutaneous tissue, S; Angle of mandible, A

14. Results: FBL
SH: 4 laminae (n = 8 MM)
Lamina
(L)
Relaxed
Mean FBL (mm)
Contracted Mean FBL (mm) L1
22.7±8.1
19.6±8.1
L2*
18.0±6.0
14.8±3.7 L3
12.6±2.6
12.3±3.8 L4
15.9±4.4
15.9±5.6
SH: 3 laminae (n = 12 MM)
Lamina
(L)
Relaxed
Mean FBL (mm)
Contracted Mean FBL (mm)
L1*
19.5 ± 5.8
17.9 ± 6.4 L2
13.0 ± 4.1
11.9 ± 3.4 L3
17.0 ± 4.7
16.6 ± 5.1
* Significant difference between relaxed and contracted (p<0.05)

15. Results: Aponeuroses SH: 3 laminae (n = 12 MM) Aponeurosis
Located between
Relaxed mean
length of aponeurosis (mm)
Contracted mean length of aponeurosis (mm) 1
L1-L2
33.8±6.4
36.5±4.9 2
L2-L3
33.6±12.1
32.4±13.1
SH: 4 laminae (n = 8 MM)
Aponeurosis
Located between
Relaxed mean
length of aponeurosis (mm)
Contracted mean length of aponeurosis (mm) 1
L1-L2
30.8±16.2
36.1±12.8 2
L2-L3
35.1±6.5
42.7±10.5 3
L3-L4
30.1±14.4
26.0±14.0

16. Conclusions
First in vivo US study investigating musculo- aponeurotic architecture volumetrically
Successful development of US protocol to study MM based on 3D digitized data
First report of varied changes throughout MM laminae upon maximal contraction

17. eg. protrusion, excursion, retrusion
Future Directions
Movement-based differential contraction in each lamina
eg. protrusion, excursion, retrusion
Musculo-aponeurotic parameters in
pathologic MM

18. Thank you!