Two chronic health conditions are treated with oral appliances during sleep. One condition is temporomandibular disorder (TMD); a musculoskeletal disorder characterized by pain in the masseter muscle and temporomandibular joint. TMD pain is treated with a stabilization splint which operates by limiting abnormal muscle activity. The other condition is obstructive sleep apnea (OSA). Mild to moderate OSA is treated with a mandibular advancement splint (MAS) which holds the mandible in a protruded position to increase the pharyngeal airway space and reduce upper airway collapsibility.

The comorbidity of the two conditions is high. Approximately one in four patients with clinically diagnosed TMD has OSA diagnosed by polysomnogram (PSG). This comorbidity poses a problem for management because neither appliance is considered effective in treating both conditions. In fact, mandible advancement is assumed to worsen TMD pain. However this assumption is not well supported by scientific evidence, with some studies finding that mandibular advancement actually reduces TMD pain, albeit after a transient increase in TMD pain in some patients. Furthermore, anecdotal evidence suggests that mandibular advancement reduces TMD pain. It is believed that by maintaining an open airway with the oral appliance, patients no longer have to clench their teeth in an effort to prevent the airway from collapsing during sleep.

The overall objective of this study is to characterize the temporal nature of TMD pain in adults with comorbid TMD/OSA treated with MAS therapy. It is the first study to monitor adherence to MAS therapy objectively in this study population, using a microsensor embedded in the MAS.

Recruitment and MAS therapy will be conducted at Lane and Associates Family Dentistry; a group of 27 dental practices located throughout the Triangle and Triad region of North Carolina. Advantages of using Lane \& Associates are: large influx of new dental patients every month, fast recruitment, well-established protocols for screening for TMD and OSA and for referral of patients to sleep physicians for evaluation and PSG, standardized protocols for oral appliance therapy, and a Dental Sleep Medicine director who is highly experienced also in the management of TMD. The study coordinator is a dental hygienist in the University of North Carolina (UNC) School of Dentistry Dental Sleep Clinic who works in the School's Dental Sleep Medicine practice. She will travel to the Lane \& Associates offices to assist in clinical and administrative activities and will manage all data collection for the 12 subjects. The Dental Sleep Clinic at the UNC School of Dentistry is not considered adequate to serve as the study site because it currently operates only one day a week and accepts referrals for only patients without TMD pain.

In the pre-enrollment phase, patients at Lane and Associates Family Dentistry will complete a standard TMD screening questionnaire. Those screening positive will be clinically examined against Research Diagnostic Criteria for TMD to confirm Group II: Masticatory Muscle Disorders, 1A: Myalgia. They will also be screened for OSA using the validated STOP-BANG questionnaire. Those at high risk will be referred for evaluation by a sleep physician and a diagnostic PSG, as is the standard of care at Lane and Associates. If the PSG reveals mild to moderate OSA (apnea-hypopnea index (AHI) ≥5 and \<30), the patient is a candidate for oral appliance therapy, pending confirmation of the sleep physician, and thus eligible to enroll in the study.

Subjects will be consented and assessed for demographics, medical history, and medication use. Impressions of the upper and lower dental arches will be recorded, poured in dental stone and sent to the lab. A George Gauge will record a protrusive bite registration with the jaw advanced 60% from the most retruded position. The custom-made MAS will be fitted with a micro-recorder (Braebon DentiTrac Monitor) to assess adherence. The investigators define adherence as use of the splint 4 hours/night for ≥70% of nights as is standard practice for continuous positive airway pressure (CPAP) therapy. Home sleep test (HST): Subjects will complete a series (from 2 to 5) two-night home sleep tests (HSTs) using the portable AccuSom device by NovaSom, which collects sleep parameters of AHI, minimum oxygen saturation, and snoring indices. Novosom arranges shipment of the device and offers 24-hour technical support during the sleep test. Sleep data are uploaded wirelessly from the recorder to an online portal for statistical analysis.

Following a baseline home sleep test (HST), 12 participants will enter the study wearing a MAS during sleep that protrudes the mandible to 60% of its maximal advancement. This approximates the minimum amount of jaw advancement that is expected to be efficacious. A HST will be repeated at the end of Week #4. If that HST shows that the MAS is not efficacious (i.e. has not reduced baseline apnea hypopnea index (AHI) by ≥50% or the AHI is ≥10\*\*), and if TMD pain is not worse, the mandible will be advanced to 70% and the participant will repeat the HST at the end of Week #8. Once efficacy is achieved, there is no need for further HSTs. If efficacy is not achieved at the end of Week #8 and if TMD pain is not worse, the mandible will be advanced to 75% and the participant will repeat the HST at the end of Week #12. If efficacy is not yet achieved and if TMD pain is not worse, the mandibular will be further advanced to 80% and the participant will undergo a final HST at the end of Week #16. Once a HST indicates that the MAS is efficacious in reducing the AHI, the participant will maintain that level of advancement. The minimum number of HSTs for any one participant is 2 (baseline and 4-week follow-up) and the maximum number is 5.