Symmetrical activity of the chewing muscles and its relationship with skeletal class and body posture.

Objective: To describe the role of body posture and skeletal class in the symmetrical activity of chewing muscles.

Methods: Descriptive study with association. Skeletal class measured by the Steiner method. Postural analysis through APECS mobile application for forward head posture and shoulder discrepancy, and surface electromyography with Biopac® device.

Results: The skeletal class, forward head posture, and shoulder discrepancy presented statistical association with the symmetrical electromyographic response of digastric muscles and masseter muscles during swallowing.

Discussion: This study exhibited a positive relationship between digastric muscle symmetry and skeletal class during swallowing. The compensation of the hyoid system explains these results, showing that skeletal Class III has better electromyographic balance. In contrast, masseter muscle symmetry during swallowing presented a negative relationship with skeletal class. The stabilization role that this muscle plays during swallowing explains these findings, caused by the different lengths and direction of this muscle in skeletal Class III.