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Background Oral appliances (OAs) are generally designed to displace the mandible anteriorly and downward, to increase the airway patency. The present study aimed to examine the relationship between genioglossus (GG) muscle activity and mandibular position, considering both anterior and vertical displacements during sleep. Methods Seven healthy male adults aged 29.4 ± 1.99 years were evaluated. Maxillary and mandibular OAs were fabricated from 2-mm-thick resin plates with pressure-welding. The activity of the left GG was recorded using two silver ball electrodes attached to the lingual edge of the mandibular OA. Respiratory status and right masseter muscle activity were measured by an airflow sensor and surface electrodes, respectively. Electroencephalography was used to determine the sleep status. Stage 2 (the second stage of sleep) was defined as the state of sleeping. Four test conditions with different mandibular positions (0 and 50% anterior protrusion) and bite openings (4 mm and 12 mm) were examined. Results GG activity in SL4A (4 mm bite opening, 50% protrusion during sleep) and SL12 (12 mm bite opening, 0% protrusion during sleep) were significantly higher than that in SL4 (4 mm bite opening, 0% protrusion during sleep). Respiratory volume did not significantly differ between all test conditions. Conclusion GG activity is influenced not only by anterior protrusion of the mandible but also by vertical displacement during sleep. Thus, when determining the effectiveness of intraoral appliances in the treatment of obstructive sleep apnea, both protrusion and the size of the mandibular opening should be evaluated and taken into account.

Oral appliance (OA) can effectively treat obstructive sleep apnea; however, numerous types of oral appliances and designs are variable and the precise mechanisms behind differences in treatment outcomes are uncertain. The objective of this study was to evaluate the effects of different degrees of mandibular position [4° of bite openings (BO): 2, 4, 8 and 12 mm; and protrusion (P): 0, 50%, MAX], for both the upright and supine positions: BO2 mm_P0%, BO4 mm_P0%, BO4 mm_P50%, BO4 mm_PMAX, BO8 mm_P0%, BO12 mm_P0%; with an OA on the: (1) activity of the genioglossus (GG) muscle by electromyogram, (2) inspiration by airflow sensor, and (3) recording mandibular movements (incisor and mandibular condyle point) in each position. Nine healthy male adults (age 27.5 ± 1.30 years) were recruited. The results show that GG muscle activity increased significantly from BO 4 mm_P0% to BO12 mm_P0% during the supine position, and the strongest signal was found in BO4 mm_PMAX, compared to all of the other positions, and GG muscle activity in BO4 mm_P0% tended to be lower. From supine to upright position the inspiration increased significantly but GG muscle activity did not. These results might be a stimulus to augment a compensatory mechanism of GG muscle induced by OA, however, mainly in protrusion position. The increase of BO (2–12 mm) and even maximum protrusion might not negatively affect the temporomandibular joint.

Summary This clinical report introduces and evaluates the use of a mandibular advancement oral appliance (OA) attached to a denture base for the treatment of obstructive sleep apnoea syndrome (OSAS) in a patient presenting severe dental problems and multiple missing teeth. It concerned a 58-year-old man with moderate OSAS (apnoea index (AI): 15·9 h−1; apnoea hypopnea index (AHI): 21·7 h−1), presenting ten remaining teeth (maxilla: 5, mandible: 5) and important dental and periodontal problems. A treatment OA comprising both maxillary and mandibular parts was fabricated with an acrylic resin base, simulating the structure of a conventional removable partial denture (RPD). The polysomnography examination performed after the use of the OA showed the treatment induced a significant decrease in OSAS symptoms (AI: 0·7 h−1, AHI: 8·2 h−1). All the necessary dental and periodontal treatments were performed to assure the reestablishment of oral health. The treatment OA was modified after each treatment to adapt it to each new oral condition. After 18 months, once the oral health was reestablished with seven remaining teeth (maxilla: 5, mandible: 2), final RPDs and final OA were fabricated. Polysomnography with final OA showed a similar positive result with respect to OSAS symptoms. No side effects related to the OA treatment were detected during the 3-year follow-up. To keep a sound oral condition, periodical dental care was performed by specialists in both periodontal and prosthodontic clinics. This clinical report shows the feasibility of treating OSAS patients with OA even in the presence of severe oral conditions and multiple missing teeth.

Oral appliances are generally designed to displace one’s mandible forward and downward, thus increasing the airway patency of the patient. Although it has been reported that the activity of the muscle genioglossus (GG) is increased by displacing the mandible protrusively, there is no study evaluating the relation between GG activity and the vertical displacement of mandible.