Development and Validation of an MRI-Compatible Jaw Metabolic Stressor Task - Temporomandibular disorders (TMDs) are the most common cause of orofacial pain not related to teeth, affecting 5-12% of the population, and 15% of patients seeking treatment will develop chronic TMD with a greater prevalence in females. Jaw muscle pain (myalgia) is the most common TMD diagnosis, usually mildly present at rest which gets aggravated with function, e.g., chewing, or parafunctional habits, e.g., teeth clenching. Such habits are frequently reported by patients, are strong predictors for TMD incidence and experimentally they can induce jaw pain/fatigue in controls and aggravate symptoms in patients. Putative factors for jaw pain onset and persistence include intrinsic muscle metabolic features related to function. Jaw function tests that evoke symptoms mimicking “real-life” situations are necessary to determine mechanisms of jaw pain and fatigue in chronic TMD. Example models include teeth clenching at maximum force, chewing wax/gum or clenching at pre-defined forces relative to the individual maximum voluntary bite force. Outcome measures include clenching endurance and magnitude of pain/fatigue intensities. Common to most models is a focus on fixed parameters, typically muscle contraction at pre-specified levels. However, little attention has been directed to models whose stimulus-induced outcome is a targeted magnitude of sensation, e.g. moderate pain/fatigue, and the jaw muscle effort required for induction. There is a critical need for new models of jaw function that closely emulate known risk factors for TMD pain. This proposal will address this unmet need by developing and validating a novel jaw metabolic stressor (JMS) task to determine the jaw muscle metabolic stress and brain functional characteristics related to jaw pain perception during function. The JMS task is designed for chairside and magnetic resonance imaging (MRI) uses at high (3T) and ultra-high (7T) field. The following aims are proposed: 1. Develop and validate a JMS task able to evoke targeted intensities of jaw pain and fatigue in pain-free controls; 2. Determine the jaw muscle effort required to evoke moderate jaw pain and fatigue in chronic TMD pain cases and matched controls using a JMS task; 3. Demonstrate feasibility of using a JMS task during functional MRI to evoke brain functional activations secondary to targeted jaw pain and fatigue levels in chronic TMD pain cases and matched controls. In Aim 1, a psychophysics-based JMS task will be validated by contrasting it to traditional models of jaw function by comparing the targeted jaw pain/fatigue intensities and jaw muscle blood oxygenation evoked by each model, and its reliability will be determined from test-retest assessment. Aim 2 will use similar methods as Aim 1 to compare the jaw muscle effort required to achieve a targeted intensity of jaw pain/fatigue for chronic TMD pain cases and matched pain-free controls. Finally, Aim 3 includes feasibility testing for JMS task performance during MRI in both high and ultra-high fields. It is anticipated that a valid and reliable JMS task designed for chairside and MRI uses will render a new method to investigate peripheral and central neural mechanisms of jaw pain/fatigue in chronic TMD.
