Immediate Effect of Ultrasound Therapy on Bilateral Masseter Myalgia: Randomized Single Blinded Investigational Trial

Introduction. Temporomandibular disorders (TMD) are a group of conditions that are multifactorial in nature, and it primarily presents with symptoms of pain and decreased functional capacity. Therapeutic ultrasound is a method of physical therapy that has shown clinically to provide immediate relief of pain in patients with different musculoskeletal disorders. In this study, for the purpose of immediate management of painful masticatory muscle and tissues, the investigators attempt to understand the mechanism of therapeutic ultrasound by exploring the physiologic changes peripherally and centrally. In addition, the investigators aim to determine if there is a dose response relationship between two different intensities (0.4 W/cm2 and 0.8 W/cm2) and between two sets of duty cycles (50% and 100%). A third purpose is to determine if therapeutic ultrasound applied to the masseter muscle is capable of eliciting segmental effects in the temporalis muscle. Methods. A total of 28 adult females with bilateral myalgia according to Diagnostic criteria for TMD (DC/TMD) will be recruited for this investigational trial. Each subject will be randomly allocated to one of the four ultrasound intervention groups each of which has different settings. Using Sonicator®740, therapeutic ultrasound intervention will be performed on both masseters for five minutes on each side of the face. A template will be used to confine the borders of the muscle and to determine the sites for the repeated outcome measures. Outcome parameters of: self-reported pain scale, pressure pain threshold, electromyographic muscle amplitudes and intraoral muscle temperatures will be measured for masseter and temporalis muscles on each side of the face, and will be assessed at baseline and after intervention on each side.