obstructive sleep apnea syndrome ( osas ) , which is caused by a complete or partial obstruction of the upper airway producing apnea or hypopnea , is a sleep disorder characterized by repetitive cessation of breathing occurring during sleep . according to the american academy of sleep medicine , a diagnosis of osas can be made in the presence of five or more episodes of apnea / hypopnea per hour of sleep , accompanied by clinical symptoms ( such as daytime sleepiness , mood disorder , insomnia , hypertension ) , or at least 15 events per hour without additional symptoms . osas is defined as mild when characterized by 5 - 15 events per hour , moderate in the presence of up to 30 events per hour , and severe when these number more than 30 . the pathogenesis of osas is multifactorial , however two main categories are described in the literature that , in some cases , can occur in combination . the first , and more common , form is due to obstruction of the respiratory lumen , for example at the level of the retropalatal and retroglossal spaces , involving the soft palate and the base of the tongue . this obstruction , which can be partial or total , is linked to tissue factors such as tonsillar hypertrophy , but also to obesity , which can determine fatty infiltration of the pharyngeal wall . the second , less frequent form is central osas , which is due to dysfunction of the cerebral mechanisms that control the pharyngeal muscles that keep the airways open during sleep . in this case , suppression of nerve impulses results in a narrower airspace that is more prone to collapsing on inspiration during sleep . certain skeletal abnormalities , such as reduced sagittal linear dimensions of the cranial base , of the maxilla , and also of the bony naso - oropharynx , can also predispose to osas . retrognathia of both the maxilla and the mandible and increased lower face height frequently show a bold relationship with osas . in addition , in osas subjects the hyoid bone is located more inferiorly , between the fourth and the sixth cervical vertebra , and the intermaxillary space length ( the distance between the posterior pharyngeal wall and the tip of the lower incisor ) is reduced . these alterations decrease the tongue space , causing it to lie in a lower and a more posterior position , where it causes partial or total obstruction of the pharyngeal lumen during sleep . due to repeated apnea / hypopnea episodes , osas patients have disturbed and less restorative sleep , and thus present several characteristic symptoms , such as daytime sleepiness associated with a higher risk of motor vehicle accidents , morning headache , mood disorder , depression and lack of libido . they also have an increased incidence of medical comorbidities ( e.g. hypertension , stroke , death ) . in the initial therapeutic approach , osas patients are encouraged to make lifestyle changes , for instance , to lose weight ( in the case of obese patients ) , but also to stop using alcohol or other agents that can facilitate collapse of the upper airway . however , the main therapeutic options also include continuous positive airway pressure ( c - pap ) therapy , oral appliances and surgical procedures . c - pap therapy is based on the maintenance of constant air pressure , preventing the collapse of the upper airway during sleep , and it is recommended for subjects with an upper airway obstruction . it is currently the gold standard non - invasive treatment for osas , but it is not indicated in patients with nasal obstruction or claustrophobia . the cpap machine is quite voluminous and it must be used every night ; this treatment has a high therapeutic efficacy but it is poorly tolerated and refused by 50% of patients . other therapeutic strategies are the use of oral mandibular repositioning appliances , usually better tolerated by patients , but successful only in the treatment of mild - to - moderate cases of sleep apnea . these appliances cover the upper and lower teeth and hold the mandible in an advanced position , thus widening the upper airway . surgical modifications of the soft tissue of the upper airway - e.g. uvulopalatopharyngoplasty ( uppp ) , partial midline glossectomy and radiofrequency volumetric tissue reduction - were , in the past , commonly used to increase the posterior airway space in severe osas . orthognathic surgical procedures , on the other hand , consist of : anterior inferior mandibular sagittal osteotomy ( genioglossal advancement ) , which , together with hyoid suspension , constitutes phase i surgery , genioplasty , and maxillomandibular advancement osteotomies . maxillomandibular advancement ( mma ) is used for osas patients with dentofacial deformities requiring orthognathic surgery and/or for those with extremely severe obstructive disease , in whom all applicable conservative therapies have failed or proved intolerable . it consists of le fort i osteotomy of the maxilla and a bilateral sagittal split osteotomy of the mandible producing simultaneous advancement of both the maxilla and the mandible , and of the soft tissue overlying these structures . this procedure , by modifying the pharyngeal structures and the tongue space , increases the dimension of the upper airway and thus reduces the risk of pharyngeal collapse during negative pressure inspiration . this method is sometimes associated with anticlockwise rotation of the occlusal plane that advances the soft palate . recently li   reported a success rate of 89% , and prinsell , too , demonstrated that mma is a highly effective treatment with a success rate of between 86.5% and 86.6% . for this reason it can be considered the surgical treatment of choice that is able , especially when performed in young patients , to significantly improve the quality of life of individuals with osas . this study set out to evaluate the effects of mma on osas patients treated with orthognathic surgery ; specifically , its aim was to establish which cephalometric variables can influence changes in respiratory symptoms . this retrospective study analyzed 15 patients ( 11 males and 4 females ) from an initial pool of 27 patients ( 
 table 1 
 , who had clinical and polysomnographic evidence of moderate ( 1 subject ) or severe ( 14 subjects ) osas and were submitted to orthognathic surgery as detailed in 
 table 2 
 . the mean age of the 15 patients who underwent mma was 42.3  9.5 years ( range from 26.3 to 62.5 years ) . on the basis of anb , nine patients were deemed to have presurgical skeletal class ii malocclusion ( anb > 4 ) , five patients class i malocclusion ( anb = 2  2 ) , and only one patient class iii ( anb < 0 ) malocclusion . all the patients had already undergone other non - invasive treatments that had been unsuccessful ( oral appliances ) or had been rejected in the long term ( c - pap ) . all the subjects included in this study were adults referred from the department of maxillofacial surgery of the sant'anna hospital in como , italy . each patient was evaluated with nocturnal polysomnoraphy ( psg ) and lateral cephalometric radiographs preoperatively ( t1 ) and after the surgery ( t2 ) . the variables taken into account were : age , gender , apnea / hypopnea index ( ahi ) , lowest oxygen saturation ( lsat ) level , and cephalometric data . selection and exclusion criteria used to recruit osas patients c - pap = continuous positive airway pressure therapy . psg was performed at the sleep center of the san raffaele hospital in milan and at the department of sleep medicine of the felice villa hospital in mariano comense ( co ) using a somnocheck effort polygraph ( weinmann , hamburg , germany ) . the following variables were measured for each patient : ahi , as measure of therapeutic efficacy , and lsat . these variables were used to determine the presence and severity of osas before surgery and to establish ( on the basis of changes in the psg variables after surgery ) the clinical effectiveness of the therapy . cephalometric analysis 
  pre- and postoperative lateral cephalometric radiographs for each patient were taken with the teeth in occlusion and following a standardized procedure . the cephalometric examination was carried out with a standardization of the magnification factor , and each cephalogram was double hand - traced by two different investigators who were unaware of the clinical results . the following linear and angular variables were analyzed : sna ( angle between the sella , nasion and subspinale point a ) , snb ( angle between the sella , nasion and supramentale point b ) , anb ( angle between the maxilla and the mandible ) , pas ( the narrowest distance between the base of the tongue and the posterior pharyngeal wall  a measurement used to detect pharyngeal obstruction ) , mp - h ( distance from the mandibular plane to the most anterior point of the hyoid bone ) , co - a ( the amount of maxillary advancement ) and co - pog ( the amount of mandibular advancement ) . cephalometric variables measured : 1 = sna ( angle between sella , nasion and subspinale 
 point a ) ; 2 = snb ( angle between sella , nasion and supramentale point b ) ; 3 = anb 
 ( angle between the maxilla and the mandible ) ; 4 = pas ( the narrowest distance between 
 the base of the tongue and the posterior pharyngeal wall ) ; 5 = mp - h ( distance from 
 the mandibular plane to the most anterior point of the hyoid bone ) ; 6 = co - a ( amount 
 of the maxillary advancement ) ; 7 = co - pog ( amount of mandibular advancement ) . the surgical procedure consisted of le fort i advancement and bilateral mandibular sagittal split osteotomies ( 
 figure 2 
 , 
 figure 3a 
 , 
 b 
 ) . rigid fixations were used in all patients to hold the bones in their new position : microplates at the maxilla and miniplates with monocortical screws at the mandible ( synthes cmf , missisauga , ontario , canada ) . it consisted of a clinical follow - up , a radiological evaluation with orthopantomography and lateral cephalometric radiographs , and a psg assessment . mma , whose amount depended on the initial craniofacial characteristics , was evaluated in each patient . statistical analysis 
  descriptive statistical analysis was performed for all demographic variables ( age and gender ) and outcome variables at t1 and t2 . the wilcoxon signed rank test was used to determine the correlation between the psg variables and the cephalometric variables for each outcome measure , and p < 0.05 was considered statistically significant for all analyses . in addition , pre- versus postoperative reduction in the ahi was calculated to establish the treatment effectiveness . application of the paired t - test revealed no significant mean differences between the two series of records . errors were normally less than one unit , ranging from 0.2 to 0.8 mm for linear measurements and from 0.4 to 1 for angular measurements , corresponding of a coefficient of reliability of 96% . effect of mma on osas 
 
 table 2 
 shows preoperative and postoperative ahi and lsat values with corresponding percentage changes . postoperatively , the overall mean ahi dropped from 58.7  16 to 8.1  7.8 events per hour ( p < 0.001 ) . the mean preoperative lsat increased from 71% preoperatively to 90% after surgery ( p < 0.001 ) . pre- and postoperative polysomnographic recordings ahi = apnea / hypopnea index ; lsat = lowest oxygen saturation ; m = male ; f = female . cephalometric analysis 
  lateral cephalometric radiographic evaluation ( 
 table 3 
 ) showed mean preoperative sna and snb values of 79.9  5.8 and 74.3  4.9 respectively ; the mean postoperative values were 85.9  5.8 and 78.5  5.0 , respectively . the mean overall amount of maxillary advancement measured on x - ray was 5.2 mm (  4.5 mm ) , ranging from 0 mm to 14 mm . the mean amount of mandibular advancement measured on x - ray was 9.5 mm (  8.7 mm ) , ranging from - 2 to 29 mm . postoperative cephalometric analysis ( 
 table 4 
 ) showed a statistically significant average variation ( p = 0.01 ) of the sna which correlated with the decrease in the ahi . the mean sna variation was 6 ( falling from 79.9  5.8 to 85.9  5.8 ) . in addition , the increase in lsat was found to show a statistically significant correlation both with the amount of maxillary advancement ( p = 0.03 ) and with the amount of mandibular advancement ( p = 0.029 ) . in particular , the results show that for each mm of co - a and co - pog increase there was a 1% increase in lsat . no statistically significant correlations were found between the psg parameter ahi and the snb ( p = 0.07 ) , anb ( p = 0.33 ) , pas ( p = 0.74 ) and mp - h ( p = 0.16 ) . the position of the hyoid was recorded in relation to the mandible , and the mean distance from the hyoid to the mandible plane was increased by 1.3 mm ( from 28.2 mm to 29.5 mm ) on the post - treatment x - ray . differences between preoperative and postoperative cephalometric values and means of differences sna = angle between sella , nasion and subspinale point a ; snb = angle between sella , nasion and supramentale point b ; anb = angle between the maxilla and the mandible ; pas = the narrowest distance between the base of the tongue and the posterior pharyngeal wall ; mp - h = distance from the mandibular plane to the most anterior point of the hyoid bone ) ; co - a = amount of the maxillary advancement ; co - pog = amount of the mandibular advancement ; sd = standard deviation . correlation between polysomnographic and cephalometric variables p < 0.05 was considered statistically significant for all analyses . wilcoxon signed rank test was used to determine the correlation between the psg variables and the cephalometric variables for each of the outcome measures . ahi = apnea / hypopnea index ; lsat = lowest oxygen saturation ; sna = angle between sella , nasion and subspinale point a ; snb = angle between sella , nasion and supramentale point b ; anb = angle between the maxilla and the mandible ; pas = narrowest distance between the base of the tongue and the posterior pharyngeal wall ; mp - h = distance from the mandibular plane to the most anterior point of the hyoid bone ; co - a = amount of maxillary advancement ; co - pog = amount of mandibular advancement . this study set out to identify what pre- and postoperative cephalometric characteristics might help predict an osas patient 's response to mma and also which outcome variables might predict a higher success rate . as shown in the previous osa surgical literature , success corresponds to an ahi of less than 20 and/or an at least 50% reduction of ahi from the preoperative level . on this basis , the therapy could be deemed successful in all the 15 patients undergoing mma in our study ( 13 had an ahi < 20 after surgery and the other two recorded a 50% reduction ) . comparison of the pre- and postoperative psg results showed a clear improvement in all patients after mma surgery . albeit in a small sample , we therefore recorded a 100% success rate of mma , which is similar to the findings of previous studies which reported success rates ranging from 95% to 98% . in accordance with the findings of a recent meta - analysis led by holty and guilleminaul , the mean overall lsat level increased from 71% to 90% . the results of the present study also showed a statistically significant increase in the sna in all the successfully treated cases ( p = 0.01 ) . this implies that the improvement in a patient 's respiratory symptomatology is affected by the amount of sna increase . as reported in several publications , bimaxillary advancement surgery has been successfully used to correct craniofacial skeletal anomalies in osas patients , inducing a regression of the syndrome . nevertheless , some authors   concluded that mma can be considered a treatment option in osas patients without cephalometrically defined maxillomandibular deficiency ; it has been shown to be a successful therapeutic option for moderate or severe osas patients even in absence of skeletal and\or occlusal anomalies . in this study , nine patients had presurgical skeletal class ii malocclusion ( anb > 4 ) , five patients class i malocclusion ( anb = 2  2 ) , and only one patient class iii ( anb < 0 ) malocclusion . a comparable study of a population of 82 osas patients found that only one - third were diagnosed as skeletal class ii , 60% as class i and 10% as class iii . the surgical correction of our class iii patient resulted in less anterior movement of the mandible than is typical in mma surgery . although the mandibular advancement in this patient was only 3 mm , the ahi decreased from 44 to 7 events per hour , thus confirming that mma surgery is indicated not only in class ii , but also in class i and in class iii malocclusion , as previously demonstrated by others . other recent studies , moreover , have pinpointed characteristics useful for identifying which patients might benefit from mma . one of these characteristics is the presence of pharyngeal narrowing in the basal lingual area with retrognathia , especially when the length of the pas at the level of the mandibular base is less than 11 mm   or less than 9 mm   and the snb is less than 77. hochban and brandenburg   suggest other traits based on cephalometric measurements , such as pharyngeal narrowing in combination with a retrognathic or dolicofacial profile . holty and guilleminault , through a systematic review and a meta - analysis including 627 osas adults , found that no pre- or postoperative cephalometric measurements , with the exception of a wider pas , were predictive of successful mma surgery . the only predictive factors noted were the degree of maxillary advancement , similar to our own findings , in association with a lower preoperative body mass index , young age and female gender . instead , it is the change in sna that determines the improvement in the respiratory symptoms . in our study the mandibular plane to hyoid bone distance did not show a significant change , thus supporting the findings of gale at al . . the width of the pas was measured as the narrowest distance between the base of the tongue and the posterior pharyngeal wall , which is not related to any skeletal structures . this value increased from 5  2.2 mm to 9.5  3.3 mm , replicating the findings of other studies   and thus demonstrating that the dimension of the airway increased after surgery . several published data support bimaxillary advancement as the most effective available surgical option for treating osa patients ; therefore mma may be considered , in certain cases , the first - line approach in these subjects . the patients treated in our study , regardless of their skeletal anomalies , experienced a remarkable regression of their symptoms . our findings suggest that the improvement in the respiratory symptoms is correlated to the increase in the sna after surgery . this factor could help surgeons to plan surgical interventions on osas patients in advance , allowing them to define the amount of maxillary advancement required . further research in a larger sample is needed to increase the predictive precision and significance of the results with a view to clinical application . sandro veronesi ( department of statistics - university of insubria ) for his help in processing the statistical data .
abstractobjectivesthe present retrospective study analyzes sagittal cephalometric changes in patients affected by obstructive sleep apnea syndrome submitted to maxillomandubular advancement.material and methods15 adult sleep apnea syndrome ( osas ) patients diagnosed by polysomnography ( psg ) and treated with maxillomandubular advancement ( mma ) were included in this study . 
 pre- ( t1 ) and postsurgical ( t2 ) psg studies assessing the apnea / hypopnea index ( ahi ) and the lowest oxygen saturation ( lsat ) level were compared . 
 lateral cephalometric radiographs at t1 and t2 measuring sagittal cephalometric variables ( sna , snb , and anb ) were analyzed , as were the amount of maxillary and mandibular advancement ( co - a and co - pog ) , the distance from the mandibular plane to the most anterior point of the hyoid bone ( mp - h ) , and the posterior airway space ( pas).resultspostoperatively , the overall mean ahi dropped from 58.7  16 to 8.1  7.8 events per hour ( p < 0.001 ) . 
 the mean preoperative lsat increased from 71% preoperatively to 90% after surgery ( p < 0.001 ) . 
 all the patients in our study were successfully treated ( ahi < 20 or reduced by 50% ) . 
 cephalometric analysis performed after surgery showed a statistically significant correlation between the mean sna variation and the decrease in the ahi ( p = 0.01 ) . 
 the overall mean sna increase was 6.conclusionsour findings suggest that the improvement observed in the respiratory symptoms , namely the apnea / hypopnea episodes , is correlated with the sna increase after surgery . 
 this finding may help maxillofacial surgeons to establish selective criteria for the surgical approach to sleep apnea syndrome patients .