The masseter muscle represents an area of important functional interest. The present study aims to verify the feasibility of ultrasound imaging for quantifying the muscular deformation pattern in the masseter. Fifteen consecutive subjects were enrolled and underwent masseter ultrasound according to a repeatable protocol. Ultrasound was carried out during teeth clenching in natural conditions and after the insertion of a medical device that alters the distance between the dental arches, and was repeated on 3 different days. Results showed that masseter deformation is not uniform within the muscle. The same strain patterns were repeated in the different ultrasounds of the same patient and were modified after the introduction of a medical device. This was supported by quantitative comparisons in the deep portion of the muscle (standard deviation on the three measures: 3% normal conditions, 2% with medical device) showing a systematic reduction with the prosthesis (30% on average). This study demonstrated that masseter strain analysis is a repeatable and sensitive tool for the study of functional analysis of the masticatory organ. This opens new technical perspectives for the diagnosis and therapy of dysfunctional pathologies of the masticatory organ.