We defined silent OSA is first observed 5 ≤ AHI by polysomnography even if patient ESS under 10. The Epworth Sleepiness Scale (ESS) is established as self-reporting questionnaire used by the clinical assessment an individual’s level of daytime sleepiness 15. In clinical practice, ESS scores of 11–24 represent increasing levels of ‘excessive daytime sleepiness’ to recommend for OSA examination. The diagnosis for OSA is defined as follows: normal, AHI < 5; mild sleep apnea, 5 ≤ AHI < 15; moderate sleep apnea, 15 ≤ AHI < 30; severe sleep apnea, AHI ≥ 30 16. In this study, 3 patients of 72 patients (4.1%) were diagnosed mild silent OSA although they had no symptom of OSA before polysomnography evaluation. Posnick et al reported 23%(60 of 262)had silent OSA with dentofacial deformities exceeded that estimated in the general population by PSG confirmed. This prevalence rate of 23 % was remarkable higher than our results of 4.1% although these two studies were performed both dentofacial deformities. Prevalence of OSA was reported in the range of 3 to 7% for adult men and 2 to 5% for adult women 17–20 in Asia, however, in the range of 13–33% in adult men and 6–19% for adult women, in Europe and North America21. LI et al 22 evaluated the possible differences between Asian and White patients with OSA and reported that the Asian patients were less obese and had maxillomandibular protrusion, narrower cranial base angle, larger posterior airway space, and more superiorly positioned hyoid bone compared with the White patients. Mandibular protrusion has a wider airway than that of normal occlusion without dentofacial deformities 9. For that reason, silent OSA in our study targeted Japanese was low rate may be due to difference of ethnicity between Asian and White patients. Ethnicity was one of the risk factors of OSA was reported23.
Further in previous research, male gender, obesity, age, and craniomaxillofacial morphology are considered to be predictable factors for development of OSA too23. Regarding gender, OSA was more prevalent in male than female regardless of ethnicity17–21. These facts supported our result of OSA in male was higher than in female even if participants were Asian in this study. Anatomical differences or sex hormone are cause for OSA differences between male and female was reported. Pharyngeal airway anatomy or tissue characteristics between males and females has fundamental difference and males are more susceptible than females to load-induced hypoventilation because of the increased airway collapse 24. A low testosterone level results in a higher OSA risk 25 and Estrogen protects against OSA by exerting antidepressant and sleep effects26. A reduced estrogen level could affect the level of serotonin, which controls the tongue and palate muscle tone. In women who are pregnant or with menopause, the OSA risk is higher27. Regarding obesity, It was also greater in obese men and women compared with overweight men and women21. According to World Health Organization definitions, BMI ≥ 30 kg/m2 can be defined as obesity, and BMI 25–29.9 kg/m2 can be defined as overweight 28. Two of three patients with silent OSA of BMI in our study were over 30 kg/m2 was convincing results.
. Regarding age, The prevalence of OSA in the elderly population was remarkably high was reported. This was 88% in men and 66% in female aged 65–69 years old 29, 90% in men and 78% in female aged 60–85 years old 21. The reason is why there is no significant relationships with age in our study may be our participants were almost under 50 years old and young. Regarding morphology, another previous study 30 suggested that skeletal conditions such as short mandibular body and mandibular retrusion, size of the tongue, position of the hyoid bone, and shape of the airway are factors that contribute greatly to a further increase in the severity of OSA syndrome in males. On the other hand, mandibular protrusion has a wider airway than that of normal occlusion without dentofacial deformities 9. We speculated before study that large ANB angle and small SN-MP angle will be the factors related to prevalence of silent OSA. However, overbite and mandibular asymmetry were related to prevalence of silent OSA. Although mandibular retrusion was included in our study, patients with symptomatic OSA were excluded was may be the reason different factors had in silent OSA. However, large overbite generally indicate short face pattern and asymmetry was reported as factor related to OSA in previous study. Our results was should be considered to risk factors of silent OSA.
Guillminault et al31and RILEY et al32 reported on female patients who developed OSAS after bilateral mandibular osteotomies for treatment of skeletal Class III malocclusion. Two other patients with relatively high values of 3%ODI (26.0 and 19.9 at T1) were mildly obese (BMIs of 26.2 kg/m2 and 27.3 kg/m2) and their amounts of mandibular setback were comparatively large (10.4 mm and 13.0 mm) 33. A large amount of mandibular setback might inhibit biological adaption and cause sleep-disordered breathing, and it might be better to consider maxillary advance or another technique that does not reduce the airway for patients with skeletal class III malocclusions who have large anteroposterior discrepancy and/or maxillary hypoplasia34. A systematic review suggested that although the development of postsurgical OSA has been reported, there is no clear evidence that confirms a direct cause-and-effect relationship between mandibular setback surgery and OSA development16. On the other hand, maxillomandibular advancement (MMA) is the most effective surgical treatment for OSA, with results that are comparable to the efficacy of therapeutic use of continuous positive airway pressure (CPAP) 35,36. Another results showed a high prevalence of acute sleep disturbance. Patients with acute sleep disruption had low postoperative sleep efficiency and impaired functional ability three months after surgery37. In this way, maxillamandibular morphology is related to risk of OSA and orthognathic surgery caused perioperative acute respiratory complication or postoperative OSA and improvement OSA by MMA. Preoperative diagnosis for silent OSA is very important alike symptomatic OSA in treatment for dentofacial deformities.