# Upper Airway Changes in Diverse Orthodontic Looms: A Systematic Review and Meta-Analysis
## 4 Discussion
[43] in which most of the included studies used lateral cephalogram, the use of twin block induced significant changes in the airway volume at the nasopharynx, and hypopharynx, however, no such improvement was observed with the Herbst. A retrognathic maxilla and mandible can compromise the upper airway volume and are associated with obstructive sleep apnoea [35; 44; 45]. Orthognathic surgery involves the manipulation of the jawbones in which their position is changed from the surrounding craniofacial structures. This may cause morphological alteration of the airway resulting in further respiratory complications such as obstructive sleep apnea. However, there is conflicting evidence on the effects of this surgery on the airway [46; 47]. This review identified six studies, three each for skeletal Class II and Class III malocclusion treated by means of orthognathic surgery. [PERSON] et al. [48] found an overall increase in the upper airway after bimaxillary surgery in Class III which contradicts the findings by [PERSON] et al. [49] who noticed a decrease in the oropharynx volume without any change in the STOP-BANG score. The pooled analysis showed a significant decrease in the upper airway after orthognathic surgery for skeletal Class III malocclusion. All included studies for surgical Class II correction found a significant increase in the airway volume. Similarly, in their systematic reviews, [PERSON] et al. [50] [PERSON] et al. [51] found significant improvement in the airway dimensions after maxillomandibular advancement. This systematic review differs from the past reviews in which two-dimensional cephalography was used to assess 3-D airways. In addition, CBCT measures the transverse dimension and evaluates the volume rather than the area. However, there are also some technical issues with the CBCT with regard to quantifying the airway volume. Most of the included studies captured the CBCT images in an upright position with the Frankfort Horizontal (FH) plane parallel to the ground [13; 21; 22] or the head in the natural head position [4; 12; 22]. Only the study by [PERSON] et al. [23] considered CBCT in a supine position with the FH plane perpendicular to the ground. The dimension of the upper airway is sensitive to the body position [52], and the volume at the supine position is important because obstructive sleep apnoea occurs only during sleep. Although CBCT provides a clear picture of the hard and soft tissues at a single point in time, it does not provide any information on the muscle tone or susceptibility of collapse. Hence, the use of CBCT alone is not valuable for the diagnosis of obstructive sleep apnoea [10]. Most of the studies in this review consisted of adolescent participants. It is well known that the pharyngeal airway continues its growth along with the other craniofacial structures until 18 years of age, and future growth of the airway can compensate for any change resulting from the treatment. Furthermore, a shorter duration of follow-up cannot give a clear picture of the result in the long term which is most important for the patient and clinician. In addition, assessment of the respiratory functions and sleep quality would have more clinical applicability. The inclusion of randomised trials with large samples and a longer duration of follow-up would yield a better quality of evidence.