Bimaxillary orthognathic surgery (BOS) is commonly used in the correction of severe Class III deformities (mandibular prognathism with maxillary retrognathism). The postural response of the pharyngeal airway after mandibular setback and maxillary advancement procedures is clinically crucial for maintaining optimum respiration. Patients might suffer from obstructive sleep apnoea, postoperatively. The aim of this study was to determine the effects of BOS on pharyngeal airway space, respiratory function during sleep and pulmonary functions. 21 male patients were analysed using cephalometry, spirometry for pulmonary function tests, and a 1 night sleep study for full polysomnography before and 17 ± 5 months after BOS. The data show that the hyoid bone repositioned to the inferior, the tongue and soft palate displaced to the posterior, narrowed at the oropharynx and hypopharynx and widened at the nasopharynx and velopharynx levels significantly ( p < 0.05). The alterations indicated decreased airway resistance and better airflow. As a consequence of polysomnography evaluation, the sleep quality and efficiency of the patients improved significantly after BOS. Patients who undergo BOS should be monitored with pulmonary function tests and polysomnography pre- and postoperatively to detect any airway obstruction.
Class III malocclusions usually present with skeletal discrepancies such as a prognathic mandible with or without a retrusive maxilla. A severe Class III skeletal relationship poses aesthetic and functional problems. Its correction involves orthodontic and orthognathic surgical treatments. Bimaxillary orthognathic surgery (BOS) (mandibular setback (MS) and maxillary advancement (MA) procedures) are commonly used to correct this deformity .
Orthognathic surgery (OS) procedures, reposition the orofacial skeletal together with their soft tissue components, such as the soft palate, the tongue and, relatively, the hyoid bone (HB). The tension of these, directly or indirectly, attached soft tissue affects the associated muscles. The dependent functions attempt to compensate for the recently encountered alterations in the oral environment . This results in alterations to the volume of the nasal and oral cavities and subsequently the pharyngeal airway space (PAS) depending on the direction and magnitude of the skeletal repositioning .
Many studies have examined the changes in craniofacial and pharyngeal morphology after MS surgery , and declared that patients treated with MS surgery might suffer from sleep-disordered breathing typified by obstructive sleep apnoea (OSA) in future. Some types of craniofacial surgery may induce a narrower PAS or sleep disturbance as postoperative sequelae by functionally impairing the anatomical dimensions and may, therefore, be a risk factor .
Studies have shown craniofacial differences in patients with OSA; reduced cranial base length, mandibular or bimaxillary deficiency, increased lower face height, elongated soft palate, large tongue and inferior positioning of the HB . Riley et al. declared that PAS <11 mm and a mandibular plane-to-hyoid distance of >15.4 mm were indicative for OSA. Partinen et al. reported that patients with PAS <5 mm (at the base of tongue level) and mandibular plane-to-hyoid distance >24 mm had the highest respiratory disturbance index. Thus, it could be postulated that any alteration of the facial skeleton that replicates these features may provoke some airway disorder .
The postural response to MS is of particular interest and importance, because of its relationship to maintaining physiological respiration . Shortly after MS, the HB goes downward for physiological adaptation to the soft tissue, including the tongue mass and the altered tongue posture in the reduced oral cavity to prevent airway obstruction. Long term observations revealed that HB progressively returns to its original position , while the postoperative decrease in the hypopharyngeal airway space is maintained during the follow-up period . Adaptive increased craniocervical inclination (anticlockwise rotation of the face or chin up movement) was reported after surgical orthognathic procedures including MS . Wenzel et al. found that the anterior–posterior distance of the upper airway was decreased at the 1 year postoperative follow-up and the patients tended to extend their heads. The extension of the head position and/or the clockwise rotation of the chin may be a physiological adaptation late after surgery. It is unclear whether HB repositioning has an effect on this head extension or camouflages the morphological changes around the upper airway in the late follow up period.
The anatomical and aesthetic aspects of OS are crucial, but the importance of the functional consequences might overcome these aspects. Efforts to improve occlusion and facial aesthetics, and consequently the patient’s quality of life, may have the opposite effect . Creating upper airway resistance by surgical procedures could influence the respiration adversely. Although the pharynx is voluntarily dilated when the patient is awake, there may be trouble during sleep. The pulmonary function test (PFT) and 1 night sleep study for full polysomnography (PSG) are useful examinations for evaluating, detecting and quantifying respiratory impairment and can be performed safely in a variety of clinical situations .
In most studies, reduction of the PAS and changes in the surrounding hard and soft tissue after OS were demonstrated using lateral cephalograms, but there have been a few functional assessments. Kitagawara et al. investigated the effects of MS on PAS using cephalograms and on arterial oxygen saturation (SpO 2 ) during sleep (measured by pulse oximetry); and determined that SpO 2 decreased during sleep just after surgery, but had improved 1 month after MS. Foltán et al. examined the impact of OS for Class III malocclusion on ventilation during sleep and determined a significant increase in the index of flow limitations and decrease in oxygen saturation. Turnbull & Battagel investigated PAS in OS patients, which were included in the study irrespective of the type of maxillo-mandibular surgery, using cephalometric radiographs.
In the light of all these facts, a hypothesis has been proposed that OS may alter not only the craniofacial structures but also their relations with head posture, HB and tongue position and/or PAS. The present study assessed the contribution of craniofacial morphology, plus changes in HB position and PAS. Long-term adaptations of soft tissue, including the changes, in pulmonary function and PSG examinations; briefly, the effect of dentomaxillofacial changes accompanying BOS on sleep and respiratory function were examined.
Materials and methods
Twenty-one male Class III subjects (mean age 20.9 ± 0.8 years), diagnosed as having severe Class III skeletal deformity including mandibular prognathism and maxillary retrognathism received orthodontic treatment prior to bimaxillary surgical procedures. After completion of the orthodontic treatment, all subjects underwent double-jaw surgical orthodontic treatment (Le Fort I MA (mean 4.3 ± 1.7 mm) and bilateral sagittal split ramus osteotomy (SSRO) using the Obwegeser–Dal Pont method) to set back the mandible (MS mean 6.5 ± 2.5 mm). Screws were used for rigid bicortical fixation (which offers superior stabilization of the bony segments compared with wire fixation ) for both mandible and maxilla. Postoperative maxillo-mandibular fixation was maintained with elastics for 2 weeks.
All subjects had completed their dentofacial and pharyngeal growth. The body mass indices (weight (kg)/height (m) ) of the subjects were within normal limits (mean 22.3 ± 4.2) before surgical procedures. Subjects were excluded if they had: undergone previous OS; craniofacial anomalies, such as cleft lip, alveolus and palate; undergone tonsillectomy, adenoidectomy or genioplasty operations; OSA (AHI TST > 5); chronic upper airway diseases; or were excessively obese. Only male subjects were included to eliminate the gender differences in pharyngeal airway changes .
Lateral cephalograms were obtained using a standardized method by cephalostat on the same orthopantomograph (Proline 2002 CC, Planmeca, Helsinki, Finland) while the jaws were in centric relation. The subjects were seated in an upright position. The Frankfurt horizontal plane (FH) was parallel to the floor and the teeth were in occlusion. The cephalograms were exposed at the end of expiration after swallowing to standardize the positins of the oropharyngeal structures. Lateral cephalometric images were obtained preoperatively (T1), and >1 year (T2) postoperatively from each subject and traced by the same investigator (Dr. Gokce). The traditional contours and points of dentofacial structures were digitized to enable measurement of the tongue, pharynx, and hyoid positions. Linear and angular measurements were also determined. The horizontal reference plane (HOR) defined by raising a line 7° from Sella-Nasion (S-N) and the perpendicular line drawn from N to HOR was used as the vertical reference plane (VER) . This coordinate system was transferred from initial to second lateral cephalograms for the evaluation of horizontal and vertical changes between T1 and T2 ( Figs. 1 and 2 ).
The PFT was performed at the Department of Pulmonary Medicine and Tuberculosis, Pulmonary Function Laboratory with a spirometer (Quad PFT1, Cosmed, Rome, Italy) before and >1 year after (17 ± 5 months) BOS. Best forced vital capacity (best FVC), forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), peak expiratory flow rate (PEF), ratio of FEV1 to FVC (FEV1/FVC), mean forced mid-expiratory flow rate (FEF 25–75), maximum forced expiratory flow rates at 25, 50 and 75% of expired FVC (MEF 25, MEF 50 and MEF 75) and forced expiratory time (FET) values were measured ( Fig. 3 ). FVC and FEV1/FVC were accepted as the denominator for determining the presence of obstruction . The patients were instructed to wear comfortable clothing so as not to restrict their ability to inhale and exhale maximally and to avoid vigorous exercise or ingestion of a large meal just prior to the test. Subjects were comfortably seated and avoided both hyperextension and flexion of the neck. Age, height and weight, sex and race/ethnicity were recorded for calculating reference values. During the manoeuvre, the subjects occluded the nostrils manually . It was considered repeatably adequate when a difference of ≤0.15 L existed between the largest and next largest FVC and FEV1 . After the manoeuvre, the percent predicted was determined by dividing the lower limit of normal based on normal value distributions to individual test results.
All subjects underwent a 1 night sleep study at the Department of Psychiatry, Sleep Research Centre, before and >1 year after (17 ± 5 months) BOS. None of the patients had a diagnosis of OSA before surgery. Sleep parameters were recorded on a 32-channel polygraph (Somno Star Alpha Series 4, Sensor Media Corporation, Yorba Linda, CA, USA). Standard recording parameters, including the apnoea-hypopnoea index (AHI), sleep onset, sleep efficiency, sleep stage-weakness, sleep stage-1st, 2nd, 3rd, 4th and REM, and arousals were used . Airflow was monitored through oral and nasal thermistors and cannulae were adapted for the purpose. Arterial oxygen saturation (SaO 2 ) was measured continuously by pulse oximetry, using a finger probe. Body position was assessed continuously both with a closed-circuit camera and with a body position sensor. All variables were recorded on a computerized system. All of the PSG measurements were repeated 17 ± 5 months after BOS. The data obtained from the PSG evaluation of the preoperative and postoperative period were compared in terms of the effect of apnoea and snoring on sleep quality. The sleep studies were staged, according to the Rechtschaffen and Kales criteria by two trained sleep technicians who were blind to the clinical characteristics of each patient. The sleep studies were subsequently reviewed by a sleep clinician .
Descriptive statistics included the mean, standard deviation ( SD ), 95% confidence interval for mean and median ( Table 1 ). Statistical analysis was performed using SPSS for Windows Version 15.00 (SPSS Inc., Chicago, IL, USA) program. Shapiro–Wilk analyses were performed for all measured parameters to determine that the parameters have normal distributions. Differences between groups were evaluated by paired sample t -test. Friedman’s test was used to determine whether changes in each parameter have significance in their groups. After the significance of the parameters was proved, Wilcoxon’s signed-rank test was used to evaluate the changes in paired parameters in each group. Differences were considered to be significant at p < 0.05.