Objectives: Pharyngeal airway dilator muscles are very important for maintaining upper airway patency. The purpose of this study was to improve our understanding of the physical characteristics of patients with obstructive sleep apnea （OSA） by measuring muscle stiffness in the submental region in healthy persons as a first step.
Methods: Eleven normal dentulous persons （6 males, 5 females; mean age 26.9±1.58 years） without stomatognathic dysfunction were enrolled in this study. Muscle stiffness of the submental region was measured at the habitual occlusal position （HOP）, the maximum mandibular protrusive position （MPP）, and the tongue protrusive position （TPP） at random. All study protocols were in full accordance with the Declaration of Helsinki and approved by the ethics committee at Kyushu Dental University （approval number: 18-28）. All subjects provided written, informed consent.
Results: Muscle stiffness of the submental region was significantly higher at the MPP and at the TPP than at the HOP in all subjects and in male subjects. There was a significant difference between the HOP and the MPP in female subjects. There were no significant differences between the genders.
Conclusion: These results suggest that the suprahyoid and genioglossus muscles play a role in maintaining protrusion of both the mandible and tongue.