The goal of this free-choice parallel design clinical trial is to examine the potential beneficial effects of using open-label placebo (OLP) in improving chronic pain related outcomes and sleep quality in people with temporomandibular disorders. This study will enroll a cohort of participants with temporomandibular disorders (TMD) which lasts for more than 3 months. The main questions it aims to answer are: 1. Will participants with TMD be more likely to take open-label placebo pills if they are introduced to the effects of placebo (e.g., going through an expectation management session)? 2. Will taking open-label placebo plus expectation management improve chronic pain related outcomes, such as chronic pain intensity, interference, levels of anxiety and depression, in the cohort of TMD? 3. Will open-label placebo plus expectation management improve sleep quality in participants suffering from TMD? To answer the above questions, participants with TMD will be randomly assigned to three groups: 1. Open-label placebo plus expectation management group, where participants will complete a 1-hour discussion session about their expectations toward open-lable placebo intervention, and then take 1 open-labe placebo pill per day for a total of 45 days. 2. Open-label placebo only group where participants will be asked to take open-label placebo pills, one pill per day, for a total of 45 days. 3. standard of care group where participants will maintain their usual care without introducing open-label placebo to them during the 45 days monitoring. Researchers will compare the chronic pain intensity, interference, mood, anxiety, and sleep quality between the open-label placebo group and the wait-list group. Daily chronic pain will be measured using visual analog scale (VAS) ranging from 0=no pain at all to 100=maximum tolerable pain. Chronic pain interference using Patient-Reported Outcomes Measurement Information System (PROMIS) pain interference and pain behavior. Anxiety and depression will be measured using PROMIS-anxiety, and PROMIS-depression scales respectively. Finally, sleep quality will be quantified using the objective measurement Motion Watch during the 45 days intervention and monitoring. In order to have a rigorous measurement of the baseline pain and sleep fluctuation, this study will include a 7-day phenotyping period before the starting of the 45-day intervention and monitoring. During the 7-day phenotyping period, participants will record their daily chronic pain and sleep quality using polysomnography.