Abstract
The purpose of this study was to evaluate changes in the volume and most restricted cross-sectional area of the pharyngeal airway as a result of mandibular advancement surgery with minimal maxillary displacement, and to ascertain the change in height of this restricted area and whether gender and age could influence these results. Cone beam computed tomography scans were obtained from 25 patients (seven male and 18 female, average age 35.5 years). The measurements were done using the InVivoDental software (version 5.0). Comparisons were made between measurements taken prior to treatment (T1) and postsurgery (T2, average 6.3 months after surgery). No variation was detected on the scans with regard to head position, which could influence the pharynx airway. Surgery significantly increased the pharynx airway volume at the total ( P < 0.0001), upper ( P = 0.0001), and lower ( P < 0.0001) levels, with respective enlargements of 54.5%, 37.0%, and 91.3%. Gender and age did not influence this increase. A significant enlargement in the minimum area of the pharynx airway was detected ( P < 0.0001), which changed in shape from a tapering to a rounded shape. Using binomial and multiple logistic regression tests, this constricted site presented an unpredictable change in position as a result of surgery, with no association to gender ( P = 0.0745) or age ( P = 0.5879).
Introduction
Mandibular advancement surgery using bilateral sagittal split osteotomies is indicated for facial esthetics, occlusion, and sleep disordered breathing. Adult subjects with a skeletal Class II malocclusion and moderate to severe retrognathia require improvements in facial esthetics and occlusion. In terms of respiratory problems, the main reason why people undergo mandibular advancement surgery is the prevention or treatment of obstructive sleep apnea (OSA). This disorder is frequently accompanied by dentofacial deformities, which include bimaxillary retrognathia or isolated mandibular retrognathia. El and Palomo recently evaluated 140 patients, ranging in age from 14 to 18 years, divided into three groups, skeletal Class I, II, and III malocclusions, to measure oropharyngeal volume. They concluded that subjects with a Class II malocclusion had a significantly smaller airway because of their retrognathic mandible.
Since the 1980s, changes in the pharyngeal airway space as a result of various orthognathic osteotomies have been reported extensively. Jakobsone et al. showed that maxillary advancement significantly increased the nasopharyngeal airway in skeletal Class III patients. When multiple levels of upper airway space obstruction are present, the first-line surgery recommended is maxillomandibular advancement, because it results in a greater enlargement at different levels of the upper airways when compared to monomaxillary surgery. According to a meta-analysis by Holty and Guilleminault, this procedure is considered the most effective surgical therapy for OSA, with an 86% success rate.
Enlarging the pharyngeal airway volume through orthognathic surgery seems to depend more on mandibular advancement than on maxilla advancement. However, the precise contribution of mandibular advancement surgery to airway enhancement has not as yet been clarified. The pharyngeal airway is the focus of studies related to mandibular positioning. Studies on mandibular advancement using orthopedic devices for the treatment of OSA have shown that, despite a great variety of responses to treatment, there is a decrease in pharynx airway collapsibility through changes in the size and shape of the minimum cross-sectional area and a reduction in airway resistance. On the other hand, the pharyngeal airway has been found to be larger in mandibular prognathism, and postsurgical irreversible narrowing has been mentioned after mandibular setback surgery.
Although the most restricted or minimum cross-sectional area (collapsibility) of the pharynx is the best parameter for predicting changes in upper airway resistance, little is known about changes in this parameter brought about by orthognathic surgery. The majority of obstructions in subjects with OSA occur in the oropharyngeal space, which includes the retropalatal and retroglossal spaces. It is well known that surgical procedures enlarge this narrow space, although changes in the height of the most restricted area of the pharynx brought about by surgery remain unknown.
Most studies on the pharyngeal space have been done on lateral cephalometric radiographs, which are two-dimensional (2D) and provide limited diagnostic information. Recent advances in three-dimensional (3D) visualization of the pharyngeal airway based on cone beam computed tomography (CBCT) scans and automated computer analysis, provide accurate pharyngeal measurements and improved comprehension of their response to orthognathic surgery. CBCT has the technical capacity to show that the pharyngeal airway space enlarges not only in the antero-posterior dimension but also in transverse width, and in addition it provides information on the minimum cross-sectional area and volume dimensions in the pharynx.
The aim of this study was to evaluate (1) changes in pharyngeal airway volume; (2) the size, shape, and location of the airway minimum cross-sectional area; and (3) the influence of gender and age, in order to acquire a better comprehension of the response to surgery, by using CBCT on patients who had undergone mandibular advancement surgery combined with short maxillary displacement.
Materials and methods
The research protocol of this retrospective study was reviewed and approved by the Research Ethics Committee of Charité-Universitätsmedizin (Berlin, Germany #EA1/180/11).
Sample
For this study, CBCT scans of 25 patients were used, selected from a large pool in the files of MESANTIS Berlin, headquarters of the national CBCT network in Germany. Orthodontic treatment with orthognathic surgery according to the ‘surgery first’ protocol (modified from Nagasaka et al. ) had been planned for all patients. Using data obtained from surgical planning records, the selection was based on the criterion of having undergone at least 4 mm of mandibular advancement. Cases of bimaxillary surgery ( n = 25, mandibular advancement combined with short maxillary displacement) were found. The subjects had undergone bilateral sagittal split osteotomies and one- or two-piece Le Fort I osteotomy with rigid fixation.
Patients had not undergone genioplasty or any other such procedures to specifically induce genioglossus muscle advancement, just surgical mandibular advancement. The planned mandibular advancement ranged from 4 to 10 mm, and the maxillary movement could involve, or not, advancement (range 0–3 mm), anterior impaction (range 0–3 mm), posterior impaction (range 0–4 mm), anterior extrusion (only in one case, of 3 mm), anterior segmental expansion (range 0–3 mm), posterior segmental expansion (range 0–5 mm), and contraction (only in one case, of 3 mm). In order to confirm the mean sagittal and vertical minimum movement of the maxilla and to show the mandibular advancement, statistical comparisons with a paired t -test and signed-rank Wilcoxon test were made at the posterior nasal spine (PNS vertical and PNS sagittal) and gnation (Gn) landmarks, respectively, to check displacement based on the anterior cranial base (sella–nasion, S–N) before and after treatment. Maxillary sagittal and vertical displacement were minimal with no statistical difference before and after surgery ( P = 0.6966 and P = 0.8401, respectively), whereas a significant difference was detected for mandibular advancement ( P = 0.0004). The sample was also divided according to gender and age. Using the median age (34.7 years) as a divisor, 12 patients were younger and 12 older, and the patient who represented the average age was omitted ( Table 1 ).
| Characteristic | Number | Age (years) | P -Value a | ||
|---|---|---|---|---|---|
| Mean | Range | SD | |||
| Gender | |||||
| Male | 7 | 33.8 | 17.0–48.9 | 13.4 | 0.602 |
| Female | 18 | 36.7 | 21.4–57.5 | 11.1 | |
| Age | |||||
| Younger, <34.7 years | 12 | 26.8 | 17.0–34.6 | 6.4 | <0.001 |
| Older, >34.7 years | 12 | 45.3 | 34.9–57.5 | 7.0 | |
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