Effect of bite openings and mandibular protrusion on genioglossus muscle activity in healthy adults with oral appliance

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: BO_{2 mm_}P_0%, BO_{4 mm_}P_0%, BO_{4 mm_}P_50%, BO_{4 mm_}P_MAX, BO_{8 mm_}P_0%, BO_{12 mm_}P_0%; 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_P_0% to BO_12 mm_P_0% during the supine position, and the strongest signal was found in BO_4 mm_P_MAX, compared to all of the other positions, and GG muscle activity in BO_4 mm_P_0% 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.