Objectives To investigate the correlation between elastography values, age, and duration of bruxism by quantitatively measuring masseter muscle (MM) stiffness with shear wave elastography (SWE) in adolescents with bruxism. Methods This prospective study evaluated 132 MMs from 66 adolescents: 33 controls and 33 with bruxism. The thickness and stiffness of the MM were measured. The SWE values (metres/second; m/s) and kilopascals (kPa) of the patient and control groups were quantitatively compared. Results The elastic and velocity values of the MM in both closed and open positions were higher in bruxism patients compared to controls (P<.001, for each). No significant difference existed in MM thickness (P=.904). The receiver operating characteristic analysis for different SWE values found a sensitivity and specificity at baseline of 0.81kPa, 0.60m/s and 0.76kPa, 0.67m/s with the mouth closed. The values found with the mouth open were 0.76kPa, 0.64m/s and 0.76kPa, 0.61m/s. Conclusions Adolescents with bruxism had higher MM hardness values in closed and open positions compared to the control group. SWE can be used as an effective imaging method to measure MM hardness. No relationship existed between SWE values and the patient’s age or duration of bruxism.