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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: BOP, BOP, BOP, BOP, BOP, BOP; 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 _P to BO_P during the supine position, and the strongest signal was found in BO_P, compared to all of the other positions, and GG muscle activity in BO_P 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.

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BackgroundOral 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.MethodsSeven 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.ResultsGG 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.ConclusionGG 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.