Background: One of the methods used in malocclusion treatment is the use of fixed appliances. Research conducted so far has revealed that changes in bite force occurring over the course of orthodontic treatment are directly related to the functional status of the masticatory muscles. It is therefore advisable to find out how the biomechanical parameters of the masseter muscles change after treatment with the application of fixed appliances. Methods: The study material comprised 74 individuals, divided into the study group (n = 37) treated by means of fixed orthodontic appliances over the average time of 12.27 months and the control group (n = 37) consisting of individuals did not undergo orthodontic treatment. The biomechanical properties of the masseter muscles were examined by means of myotonometry. Results: Upon completion of orthodontic treatment, the values of the parameters of tension, stiffness, and elasticity of masseter muscles located on both sides did not statistically significantly differ between patients from the study group who were treated by means of fixed orthodontic appliances and patients from control group who did not undergo orthodontic treatment. Conclusions: Treatment of malocclusions with the use of fixed appliances does not affect the biomechanical and visco-elastic properties of the masseter muscles (stiffness, tension, and elasticity) assessed by means of myotonometry and it appears safe for masticatory muscles.