Obstructive sleep apnea syndrome (OSAS) is a sleep-related breathing disorder characterized by repeated episodes of partial or total obstruction of the upper airway during sleep, thus leading to phenomena defined as hypopnea and apnea. An apnea episode, by definition, is the cessation of breathing for at least 10 s. Hypopnea is defined as a reduction in airflow of at least 50%, associated with a reduction in oxygen saturation of >4%. The apnea-hypopnea index (AHI), i.e., the total number of hypopneas and apneas per 1 h of sleep, is used to indicate the severity of obstructive sleep apnea (OSA). There are different categories of sleep apnea depending on the OSA index: normal sleep has an AHI of fewer than 5 events, mild sleep apnea has an AHI of 5-15 events, moderate sleep apnea has an AHI of 15-30 events, and severe apnea has an AHI of more than 30 events per hour (1-3).The prevalence of OSA is approximately 22% in men and 17% in women with a gender distribution of 2:1 (4). This distribution is perhaps related to different hormonal effects that induce an increase in upper airway muscle collapsibility, body fat distribution, and different anatomy. Hormonal effects have an important role in OSA pathogenesis, particularly in post-menopausal women compared to pre-menopausal women. Unfortunately, the role of hormones in OSA pathogenesis is still unclear (5).Obstructive sleep apnea syndrome is becoming an increasingly studied condition because of its many comorbidities and consequences, although there is a high prevalence of undiagnosed and untreated patients (6). Because of sleep deprivation and daytime sleepiness, patients with OSA have a higher risk of car accidents (7). Cardiovascular disease is correlated with OSA, with sympathetic activation, oxidative stress, and systemic inflammation defined as the main causes of this association. OSA is an independent risk factor for hypertension, coronary artery disease, heart failure, cardiovascular and cerebrovascular diseases (CVDs), and atrial fibrillation (8,9). OSA is related to many metabolic complications such as type 2 diabetes mellitus (T2DM) (10). The prevalence of T2DM in patients with OSA is higher than in the general population (11). Current research suggests that arousals and sleep fragmentation may have effects on systemic inflammation, sympathetic surges, glucose intolerance, β-cell dysfunction, and insulin resistance (12). Narkiewicz et al. (13) suggested an alternative way to explain the relationship between T2DM and OSA. Oxyhemoglobin desaturation and hypercarbia may alter epinephrine, norepinephrine, and cortisol secretion, which leads to increased gluconeogenesis and decreased glucose uptake.Sleep fragmentation in patients with sleep apnea can also lead to neurocognitive and behavioral consequences (14,15). Although there are questionnaires and several risk factors (age >40 years, male sex, obesity, smoking) and symptoms (snoring, nocturia, nocturnal gasping, daytime sleepiness) to identify patients with obstructive sleep apnea, the diagnostic standard to diagnose the condition is nocturnal polysomnography (16,17). OSA is evaluated by many questionnaires that focus on daytime sleepiness and health-related quality of life (HRQoL) (18,19). The Epworth Sleepiness Scale (ESS) and the STOP-Bang and Berlin questionnaires are the main questionnaires used to evaluate daytime sleepiness (20,21) Continuous positive airway pressure (C-PAP) is the first-line treatment for patients with obstructive sleep apnea. It is a noninvasive treatment method used to maintain airway patency by delivering constant airway pressure. Other alternative methods, such as oral appliances, are also used in patients with apnea, especially for those who do not tolerate the C-PAP mask. Surgery is only used in cases with anatomic obstructions that need to be corrected (25). The oral appliances used are tongue retainer devices (TRDs) and mandibular advancement devices (MADs). A TRD is made of a flexible material with a bulb-like receptacle in the anterior portion. It maintains the tongue in a forward position during sleep, reducing stress on the upper airway and against the posterior pharyngeal wall (26). A MAD has been recommended by the American Academy of Sleep Medicine as a treatment for mild to moderate OSA (27). Some studies suggest that it also has an excellent effect on severe apnea. A MAD is a device with important advantages: low cost, simple production, and portability (28). The effect of a MAD is to increase the upper airway space through a forward and vertical movement of the jaw along with a repositioning of the hyoid bone and tongue (29). A MAD is built as two occlusal splints, fully covering the teeth, allowing for an increase in mandibular sagittal movement and free vertical/transversal movement of the jaw (30). The role of the dentist is becoming increasingly important for both the diagnosis and treatment of snoring and obstructive slee