Diagnoses and follow up of muscles diseases lack imaging. Severity assessment of masticatory dysfunction and follow up of treatment effectiveness is currently based only on clinical features. Supersonic ShearWave Imaging® is a new, non-invasive, non-irradiating and dynamic imaging technique that uses ultrasound and allows shear wave elastic modulus in a muscle in order to study its viscoelastic properties.

In this study, the investigators study the correlation between changes of shear wave elastography modulus and surface electromyogram features of the masseters between rest and maximal voluntary contraction.

Inclusion Criteria:

• People with social security.
• People aged 20 to 40 years, of both sexes.
• People that gave and signed consent to participate in the study.

Exclusion Criteria:

• Any concomitant muscle disease (myopathy, myositis…)
• Botulinum toxin injections in the masseter in the last 3 months preceding the study.
• Any treatment that induces muscular effect (baclofen, benzodiazepine)
• Bruxism or any masticatory apparatus disease
• Any surgery of the masticatory apparatus