Immediate Effect of Ultrasound Therapy on Bilateral Masseter Myalgia

This study will compare ultrasound 0.4 W/cm\^2 and 100% duty cycle versus no ultrasound (placebo) for bilateral masseter myalgia in up to 38 adult women. The dose will be applied for 5 minutes on each side. Both the dose and the starting side will be randomized. Both the subject and ultrasound operator will be blind to the dose. The outcome measures will be pressure pain threshold on both masseter muscles and both temporalis muscles, self reported pain scale (0, no pain to 10, worst pain ever), thermographic temperature of the muscles, and intraoral temperature. These outcome measures will be taken before and after each dose, so three times per subject.