Obstructive sleep apnea syndrome (OSAS) is a clinical syndrome characterized by recurrent apnea during sleep, intermittent hypoxia, disturbances in sleep architecture and recurrent microarousals, with or without hypoventilation. OSAS is related to multiple disciplines, among which dentistry is closely related to it. Wang Zhaoling, Department of Dentistry, General Hospital of Jinan Military Region 1. Clinical manifestations and diagnosis 1.1 Clinical manifestations OSAS patients cannot sleep quietly at night, and often have morning headache, lethargy and excessive drowsiness during the day. OSAS is one of the independent factors causing hypertension and can also be complicated by pulmonary hypertension, coronary artery disease, cerebrovascular disease, perceptual dysfunction, sexual dysfunction and other diseases. It has a serious potential risk and is one of the common clinical causes of sudden death.1.2 Diagnosis Sleep polysomnography (PSG) is currently the gold standard for diagnosing OSAS and can guide the selection of treatment protocols and evaluation of efficacy. The diagnosis is made when an adult has more than 30 recurrent episodes of apnea with no airflow through the upper airway for more than 10 seconds or an apnea hypoventilation index (AHI) (i.e., the average number of apnea and hypoventilation per hour of sleep) ≥ 5 during 7 h of nocturnal sleep time in the presence of thoracoabdominal respiratory movements.2. Pathogenetic factors associated with dentistry OSAS has a complex pathogenesis. Among them, obesity is one of the recognized etiologies of OSAS. In addition, nasopharyngeal diseases, oral and maxillofacial diseases, genetic factors, neuroendocrine factors, smoking, alcohol consumption, gender, and age can all contribute to the development of OSAS. The main ones related to the oral and maxillofacial region are: 2.1 Structural abnormalities of the upper airway: The upper airway involved in dentistry includes: ① Oropharynx: it is divided into the posterior soft palate region (from the level of the hard palate to the back of the soft palate) and the posterior tongue region (from the lower edge of the soft palate to the root of the epiglottis). Narrowing of this area is most important in the pathogenesis of OSAS. ② Hypopharynx: the area between the root of the tongue and the larynx, the root of the tongue is the structure that has the greatest impact on OSAS in this region. 2.2 Oral and maxillofacial malformations: recession of the jaws and low change in the position of the hyoid bone can lead to narrowing of the upper airway and cause OSAS, commonly in the presence of mandibular recession deformity or concomitant maxillary recession. Soft tissue deformities such as hypertrophy of the tongue root, hypertrophy of the tongue body, overgrowth of the soft palate and uvula, hypertrophy of the lateral pharyngeal wall, hypertrophy of the tonsils and compression of the upper airway by oral and maxillofacial tumors can also cause OSAS. 2.3 Neuromuscular factors: the muscles that maintain the pharyngeal cavity are highly excitable in the waking state, and the airway is in an open state; during sleep, excitability decreases, the airway collapses, and sleep apnea occurs due to airway obstruction, causing hypoxia 3.1 Clinical examination: Examination of the craniomaxillofacial structures and occlusal relationships can help to determine the plane of obstruction. Upright observation determines the presence of jaw recession; occlusal relationship can simply determine the positional relationship of jaws; large open mouth position can examine the tongue, lateral wall of pharynx, soft palate and uvula, hard palate, tonsils, and evaluate the height and width of oropharyngeal cavity. 3.2 Imaging examination: X-ray cephalometric measurements can be used to evaluate the upper airway in patients with OSAS. It mainly includes: ①SNA angle: the position of the maxilla relative to the skull base; ②SNB angle: the position of the mandible relative to the skull base; ③ANB angle, which indicates the relationship between the position of the maxilla and mandible; ④PNS-P: the length of the soft palate; ⑤PAS: the distance between the root of the tongue and the posterior pharyngeal wall; ⑥MP-H: the distance of the hyoid bone from the mandibular plane, representing the position of the hyoid bone; ⑦SPD: the thickness of the soft palate; ⑧TD: the length of the tongue. In addition, spiral CT and magnetic resonance imaging can be used to measure and analyze and evaluate the upper airway.4. Dentistry-related treatment methods are mainly divided into non-surgical treatment and surgical treatment, and more targeted treatment methods should be selected based on the identification of the cause and clear diagnosis according to the different conditions of patients, such as weight loss, adjustment of sleeping posture, medication, nasal continuous positive pressure ventilation (NCPAP), etc. The main dentistry methods that have been used to treat OSAS with good results are: 4.1 Oral appliance: Oral appliance, partly also called snore stopper, is a more effective non-surgical method to treat OSAS, but it cannot cure sleep apnea, and is generally considered effective for patients with mild and moderate OSAS, but less effective for patients with severe disease. It is simple, non-invasive, inexpensive, effective and easy to accept when worn by patients during sleep, but it also has disadvantages such as poor comfort and difficulty in adaptation. There are more types of oral appliances, which can be divided into adjustable and fixed according to the mode of action, the former has a certain degree of movement and is relatively comfortable to wear. According to the role of the part can be divided into soft palate appliance, tongue appliance and mandibular advancement appliance, etc. Mandibular advancement appliance: the most widely used, and the most types. Wearing oral appliances can eliminate upper airway obstruction by changing the position relationship of tongue, soft palate, mandible and hyoid bone, and upper airway anterior wall muscle tone, thus relieving apnea. 4.2 Oral and maxillofacial surgical treatment: tracheotomy is the most effective method to treat OSAS, but postoperative patient adaptation is poor and care is difficult, and it is often used when other methods are ineffective or emergency. Oral and maxillofacial surgery for OSAS has made great progress recently, mainly: 4.2.1 Tongue and pharynx surgery Partial lingual resection, radiofrequency ablation of tongue root and soft palate are mainly used to expand the linguopharyngeal airway by reducing the volume of tongue and palate. UPPP is the classic procedure for 0SAS, but the long-term effect of UPPP decreases gradually with time after surgery, and the long-term efficiency of UPPP in unselected cases is only about 50% as reported abroad. It is now considered that this procedure is only applicable to patients with posterior soft palate and posterior uvula stenosis, especially those with combined tonsillar II-IIIº hypertrophy. 4.2.2 The classic orthognathic surgical procedures include bimaxillary anterior migration, mandibular anterior migration, chin anterior migration, chin anterior migration and lingual muscle group cutting suspension, hard palate amputation, etc., which refers to the anterior migration of the maxilla, mandible and/or chin, especially the anterior migration of the mandible. By the pulling action of the oromandibular muscles such as the chin-lingual muscle and chin-lingual muscle, the tongue root and/or hyoid bone is moved forward and the caliber of the upper airway at the level of the tongue root is enlarged. To date, bimaxillary anterior migration has the best outcome in surgical treatment, especially in moderate to severe patients. Due to the occlusal relationship involved, it is still mainly undertaken by oral and maxillofacial surgery in China. Orthognathic surgery is highly invasive and complex, and cases should be selected with great care: anatomical abnormalities of the upper airway causing airway narrowing, obstruction at the root of the tongue or at the level of the soft palate, significant small mandibular or mandibular recession deformity, low hyoid bone position, ineffective conservative treatment or patient unwillingness to insist on non-surgical treatment, and facial deformity or dysfunction that cannot be treated non-surgically and for which the patient can tolerate larger surgery must be confirmed. 4.2 .3 Retraction osteogenesis Retraction osteogenesis enlarges the upper airway by lengthening the body and soft tissues of the mandible and moving the hyoid bone and tongue forward through chin muscle retraction. It has been shown to be an important and effective treatment for OSAS, especially for patients with severe mandibular recession such as patients with temporomandibular joint ankylosis with small jaw deformity, while for patients with upper and lower jaw stenosis, arch expansion can be performed simultaneously. OSAS is a serious threat to human health because of its complex etiology and serious complications, involving multiple systemic pathologies. However, there are still many unknown areas regarding its causes, pathogenesis and treatment, and multidisciplinary collaboration is needed to maximize its therapeutic effects. The development of dentistry has provided more tools to elaborate the pathogenesis and treatment of OSAS, and will certainly play a greater role in the future research of OSAS.