Effect of orthognathic surgery on pharyngeal airway space: a cephalometric evaluation using Dolphin Imaging software

. Orthognathic surgery is widely used in the treatment of dento-maxillofacial deformities, which changes both the facial appearance and the pharyngeal airway space. The aim of this study was to evaluate cephalometric changes in the pharyngeal airway space before and after orthognathic surgery in patients with Class II and Class III malocclusions. The sample consisted of 38 lateral cephalograms, 17 of patients with Class II who had undergone mandibular advancement, and 21 of patients with Class III who had undergone mandibular setback. Cephalometric analysis of Arnett-Gunson FAB Surgery using Dolphin Imaging 11.5 evaluated point B’ and Pog’. Statistical analysis used Paired t-test at 5% significance level. The increase in the means of point B’ and Pog’ after mandibular advancement was not statistical. Similarly, the means of point B’ and Pog’ did not differ after mandibular setback. Thus, the pharyngeal airway space at the level of B’ and Pog’ kept constant pre and post orthognathic surgery for both


Introduction
Dento-maxillofacial deformities can cause changes in the volume of the pharyngeal airway space (PAS), as well as breathing problems if the PAS is reduced enough to result in blockage of air passage.In turn, this obstruction may result in 'obstructive sleep apnea-hypopnea syndrome' (GOKCE et al., 2012).
Treatment of Class II and III malocclusions involves a multidisciplinary approach and depends on the severity of the deformities.With regard to Dentistry, facial deformities of mild nature could be treated orthodontically, whilst more severe cases, those affected aesthetically and functionally, may require a combination of orthodontics and orthognathic surgery (GOKCE et al., 2012).
Orthognathic surgery has proved effective as treatment for patients with dento-maxillofacial deformities.Class II treated with mandibular advancement can unblock the pharynx, as there is an increase of the PAS (GOODDAY, 2009).On the other hand, mandibular setback as treatment for Class III can reduce the PAS, given that the ligaments and muscles of the tongue are connected to the hyoid bone and the mandible.Thus, when the mandible is posteriorly repositioned, the tongue assumes a more posterior position, narrowing the PAS.(SAITOH, 2004;CHEN et al., 2005;KITAGAWARA et al., 2008;MUTO et al., 2008).This is why one of the challenges in the planning of orthognathic surgery is to balance concerns related to facial esthetics and changes in the PAS (CONLEY; BOYD, 2007) Obstruction of the PAS can be detected through imaging methods such as lateral cephalometric radiographs and computed tomography, though the former is still the most used method (JOHNS et al., 1998).Lateral cephalometry enables analysis of the pharynx, the soft palate, the tongue, and the hyoid bone, with their soft and bony structures (JOHNS et al., 1998;TSELNIK;POGREL, 2000;LIUKKONEN et al., 2002;MARSAN et al., 2008).
The purpose of this study was to evaluate cephalometric changes, using Dolphin Imaging software, in the PAS at the level of soft tissue B point (point B') and soft tissue pogoniun (Pog') in patients who underwent orthognathic surgery to correct Angle Class II and Class III dentofacial deformities.

Material and methods
The study was approved by the Standing Committee on Ethics in Human Research of the State University of Maringá (Protocol 16804).The records of 38 patients were analyzed-19 women and 19 men, mean age of 28.5 years old, average weight and height for their age.They were all diagnosed with skeletal deformities-17 with Class II and 21 with Class III.They were selected from the medical records of the Project "Orthognathic Surgery Clinic of the State University of Maringá", and had undergone orthognathic surgery between 2008 and 2012.
Inclusion criteria were adult patients with skeletal Classes II or III deformities treated surgically, who had pre and postoperative lateral cephalograms.The radiographs should have been taken within the same standards-with patients positioned in the cephalostat, the midsagittal plane perpendicular to the ground, the Frankfurt horizontal plane parallel to the ground, the film perpendicular to the ground, 1.52 m focus-film distance, and the central X-ray beam aligned to the center of the loaded cassette.Exclusion criteria were tonsillectomy, adenoidectomy, genioplasty, other surgeries for chronic diseases of the upper airways, and excessive obesity.
Both pre and postoperative lateral cephalograms were taken with the same equipment and parameters: Orthoralix 9200 GENDEX (Dentsply ® , Des Plainnes, USA), cephalostat regulated at 70 kVp, 10 mA, 1.2 seconds exposure time, Kodak T-Mat G/RA films (18 x 24 cm, Carestream Health ® , New York, USA), with their metallic cassette and intensifying screen (Kodak Lanex Medium Extraoral Imaging Screens X-Omat).The cephalograms were digitized using a scanner and a transparency adaptor (HP Scanjet G4050, Hewlett-Packard Company ® , Washington, USA) at 300 dpi resolution and archived in TIFF format.Adobe Photoshop ® 7.0 (Adobe Systems Incorporated, San Jose, California) was used to improve brightness, contrast and sharpness.The cephalograms were analyzed according to the type of dentofacial deformity: Class II for patients who had undergone mandibular advancement and Class III for patients who had undergone mandibular setback.
Cephalometric analysis of Arnett-Gunson FAB Surgery was performed by a single examiner using Dolphin Imaging 11.5 software (Figure 1A      The means of PAS for Class III (Figure 3) reduced 0.88% for point B' and increased 1.95% for Pog', although, again, there was no significant differences before and after surgery.The relationship between breathing problems and craniofacial morphology, particularly the relationship between the anatomy of the PAS and the effects of orthognathic surgery, have been examined by several studies (CEYLAN; OKTAY, 1995;EGGENSPERGER et al., 2005), mainly due to changes and consequences caused by different treatments.

Results and discussion
According to Gokce et al. (2012), in order to select patients for orthognathic surgery, it is important that the growth of anatomical structures, particularly of the PAS, is complete by the time of the surgery.This would ensure one can evaluate morphological changes caused by the intervention.
In the present study, the patients' mean age was 28.5 years, hence with established growth.
There is an important relationship between lateral cephalometry, as a measure of PAS, and computed tomography, as a measure of volume (MARSAN et al., 2009), mainly because cephalometric analysis is considered an appropriate method to examine changes in the position of the face bones and their consequences on the PAS (CEYLAN; OKTAY, 1995; BATTAGEL; L 'ESTRANGE, 1996;HOCHBAN et al., 1996;JOHNS et al., 1998;GU et al. 2000;TSELNIK;POGREL, 2000;JOHAL;CONAGHAN, 2004;LAM et al., 2004;SAITOH, 2004;CHEN et al., 2005).It was due to this relationship that the present study used cephalometric analysis, which showed no statistical differences in the PAS for both classes.
Although the means of the PAS at the level of point B' and Pog' increased after surgery for Class II, the differences were not statistical, unlike previous studies that found significant increase in the PAS after surgery (PEREIRA-FILHO et al., 2011;PRADO et al., 2012).
The amount of jaw advancement also changes the airway space.Little change in the retropalatal and retrolingual dimensions might happen due to small mandibular advancement (MEHRA et al., 2001).Conversely, major mandibular advancement may lead to significant increase in the PAS.Such variations may explain the differences between the results of previous studies and those of the present one.
However, as Prado et al. ( 2012) assert, it is important to bear in mind that changes in the PAS are not necessarily permanent, as research on the matter is debatable and controversial.Whereas some longitudinal studies show an increase in the PAS after maxillomandibular advancement (TURNBULL;BATTAGEL, 2000;MEHRA et al., 2001), others show reduction in the dimensions after surgery (FROST;2000).
Similar to previous research (KITAGAWARA et al., 2008, PEREIRA-FILHO et al., 2011), mandibular setback for Class III did not affect the PAS in the present study.However, some studies show that major mandibular setback can cause narrowing of the upper airway space (HOCHBAN et al., 1996;GU et al., 2000;TSELNIK, POGREL, 2000;LIUKKONEN et al., 2002;SAITOH, 2004;EGGENSPERGER et al., 2005;MUTO et al., 2008;MARSAN et al., 2008) due to changes in the position of the hyoid bone (GU et al., 2000) and of the tongue (HOCHBAN et al., 1996), and increase in the length and the slope of the soft palate (GOKCE et al., 2012).
In this study, cephalometric analysis of Arnett-Gunson FAB Surgery used Dolphin Imaging 11.5, considered an accurate program by some authors (GOSSETT et al., 2005;PEREIRA-FILHO et al., 2011).However, errors were found with the use of Dolphin Imaging 8.0, errors that could result in clinically significant miscalculations (POWER et al., 2005).
A limitation of the present study is that, within the orthognathic surgery for each malocclusion, the type of surgery were not specified and taken into account.According to Aydemir et al. (2012), different surgical procedures have different impact on the PAS, which may explain the difference between the present study and previous research.In addition, the reduced number of specimens in both samples of the present study may also explain the divergent results compared to previous research.
Despite the growing body of research on the subject, it is difficult to compare studies due to the diversity of methods.Thus, the impact of orthognathic surgery on the PAS needs further investigation, perhaps using different types of imaging methods.In the present study threedimensional structures were evaluated using lateral cephalograms, a two dimensional imaging method.However, with the increasing popularity of cone beam computed tomography, due to its low radiation exposure and continuous development, perhaps it becomes a routine method for evaluating the PAS in near future, providing researchers more information on the structures.

Conclusion
Cephalometric analyses of the PAS using Dolphin Imaging 11.5 in patients who underwent orthognathic surgery to correct Class II and Class III dentofacial deformities found no statistical difference at the level of point B' and Pog' before and after surgery, for both classes.
and 1B) assessing point B' and Pog'.Statistical analysis between pre and postoperative cephalograms consisted of Paired t-test at 5% significance level, using IBM SPSS 21.0 (Armonk, NY: IBM Corp.).

Figure 2 .
Figure 2. Pre and postoperative values of pharyngeal airway space at the level of point B' and Pog' for the 17 cases of Class II.

Figure 3 .
Figure 3. Pre and postoperative values of pharyngeal airway space at the level of point B' and Pog' for the 21 cases of Class III.

Table 1
displays pre and postoperative means and standard deviations, in mm, of point B' and Pog' of the 17 cases of Class II and the 21 cases of Class III.

Table 1 .
Pre and postoperative means and standard deviations (M ± SD) of the pharyngeal airway space (PAS) at the level of point B' and Pog' for Class II and Class III.