The cone beam computed tomography (CBCT) image provides clear differentiation of
soft tissues from empty spaces. This paper presents a literature review to
evaluate the effects of orthopedic and surgical treatment on the pharyngeal
dimension by CBCT. It was concluded that treatments involving dentofacial
orthopedics and orthognathic surgery have been related with an increase in the
upper airway volume. Standardized capturing of tomographic images and more
controlled and randomized studies are necessary.
Keywords: Cone Beam Computed Tomography; Pharynx; Orthognathic Surgery; Orthodontics.
|Citation: Guimarães TM, Bariani RC, Iafigliola SG, Guimarães CM, Chaves Junior CM, Ferraz O, et al. Cone beam computed tomography in assessment on pharynx effects of orthopedic-surgical treatment - a review of the literature. 12(2):106. doi:10.5935/1984-0063.20190066|
|Financial support: Funding: AFIP, CNPq, and CAPES provided material and financial support.|
|Received: November 08 2018; Accepted: February 05 2019|
The morphology of the human pharynx continues to be the object of different studies that seek to understand its functioning and size in several physiological functions1. The pharynx is a complex structure and has multiple functions that include breathing, speech and swallowing1. It has an intrinsic stiffness, but is quite vulnerable to large variations in its diameter2-4. Some therapeutic approaches seem to influence major changes in pharyngeal configuration2. There are currently investigations to quantify the effects of these approaches, including the impact of orthopedic and maxillomandibular surgical treatment on upper airway size and volume2.
The cone beam computed tomography (CBCT) is an important tool to evaluate the size of the upper airway, and is used to describe the mechanism of action of orthopedic/surgical treatments5. The CBCT presents a well-defined limit between soft tissues and empty spaces, and the airway is easily observed6.
This paper presents a literature review about the use of CBCT in evaluation of dentofacial orthopedics and orthognathic surgical effect on upper airway dimension.
Analysis of upper airway by CBCT
The cone beam computed tomography (CBCT) provided great advances in Dentistry due to its sharpness, practicality, low cost, and low radiation dose7. Shortcomings as distortion, magnification and superimposition of structures were common in bidimensional images, which limited the investigations on the upper airway6. The CBCT was introduced as an alternative to magnetic resonance imaging, due to its lower radiation dose, lower cost, easy access and shorter time required for achievement of images8.
Even though the soft tissue imaging on CBCT is inferior compared to magnetic resonance, the delineation of the upper airway is accurate and easy6. The CBCT presents a clear limit between soft tissues and empty spaces, which is important to evaluate the upper airway6. Conversely, the magnetic resonance imaging differentiates the types of soft tissues as muscles, connective tissue and fat, which is not possible on CBCT6. Based on the current yet limited evidence, evaluation of the pharyngeal airway volume by CBCT presents good intra- and inter-examiner reliability9.
During image acquisition, however, some rules have been discussed to avoid biases that alter the size of the upper airway while achieving the tomographic image. The pharynx is a dynamic flexible tube whose diameter is altered during some functions10. Factors as head posture, breathing cycle and swallowing stages have been discussed as aspects that require guidelines for good reproducibility the image acquisition10.
There is increasing discussion on the importance of standardization and control of head posture during acquisition of CBCT. Gurani et al.7 mention that the dimension and morphology of the upper airway depends on the head posture and cranio-cervical inclination during image acquisition. The authors performed a systematic review to evaluate standardized positioning methods during acquisition, and observed poor standardization of head and tongue posture in CBCT for analysis of the upper airway7. It should be highlighted that this is a significant problem, since the lack of standardization impairs the reproducibility7. Conversely, association of CBCT airway images and health outcomes are a strategy to reinforce the imaging results.
Effect of dentofacial orthopedics on the airway volume
Rapid maxillary expansion
The rapid maxillary expansion is an alternative coadjutant method for the treatment of obstructive sleep apnea (OSA) in children and adolescents. A recent meta-analysis demonstrated the positive effect of rapid maxillary expansion, evidencing a reduction of 6.9 in the apnea/hypopnea index11.
Studies evaluating the increase of the upper airway after rapid maxillary expansion by CBCT in children and adolescents with OSA observed an increase in total pharyngeal volume after treatment12-14. While Caprioglio et al.13, Mordente et al.15 and Kim et al.16 related this increase to the nasopharynx volume, Fastuca et al.12 related this increase to the three pharyngeal thirds.
In children without OSA, the results on the effect of rapid maxillary expansion on the upper airway volume by CBCT are controversial. Two systematics reviews, including studies until 2014 and 2016, concluded that there was no increase in the pharynx after rapid maxillary expansion, highlighting that there are no conclusive evidences on this subject because of small number of studies17,18. However, some studies published after that systematic review observed increase in total pharyngeal volume after rapid maxillary expansion, both of the nasopharynx and oropharynx19, and other studies revealed increase in nasopharynx volume20,21 and reduction of retropalatal area20.
Interestingly, Iwasaki et al.22 suggested improvement of tongue posture after expansion as a factor increasing the airway. In that study, both individuals with and without nasal obstruction were favored by expansion.
Orthopedic mandibular advancement
Few studies have compared orthopedic mandibular advancement to improvement of OSA outcomes. A systematic review including only two studies demonstrated that treatment with orthopedic mandibular advancement improved the apnea/hypopnea index in 5.1 events per hour23. No studies in OSA patients have evaluated this treatment using CBCT.
In individuals without OSA, one study observed increase in the total volume of the pharynx, oropharynx and hypopharynx after treatment with Herbst appliance5. Study analyzing the Forsus appliance followed by the Crossbow evidenced increase in the oropharynx dimension after treatment24, and other study using the Twin block appliance for Class II correction also revealed greater volume of the oropharynx and hypopharynx after treatment25. Erbas and Kocadereli24 reported the increase in oropharynx space to anterior repositioning of the soft palate and hyoid bone, and Li et al.25 observed a more elliptical shape of the oropharynx after treatment.
Orthopedic maxillary protraction
This orthopedic procedure aims at anterior traction of the maxilla in cases where it is retroposited. To our knowledge, there are no studies investigating the impact of maxillary protraction treatment of patients with OSA using CBCT imaging.
Two studies performed rapid maxillary expansion associated with maxillary protraction in Class III individuals without OSA revealed an increase in total pharyngeal volume after treatment26,27. In addition to the total pharyngeal volume, Chen et al.26 also observed increased volume of the nasopharynx and retropalatal area.
As previously mentioned, orthognathic surgery is considered an alternative treatment for OSA in adults, and the increase in upper airway volume as assessed by CBCT has been thoroughly analyzed.
A systematic review conducted in 2016 revealed that maxillomandibular surgery is an effective surgical option for OSA. The apnea/hypopnea index was reduced 48 points in AHI, and there was improvement in oxyhemoglobin saturation and sleepiness. Despite the great decrease in AHI, only 38.5% were cured, because individuals in that sample presented extremely high AHI28. Other systematic review demonstrated that individuals with OSA submitted to maxillomandibular advancement associated with counterclockwise rotation present better outcomes in AHI compared to individuals submitted to maxillomandibular advancement without rotation29.
Some systematic reviews were conducted to assess the changes in upper airway volume using CBCT in individual who did or didn´t OSA. They evidenced a total airway volume increase of 7.42 and 7.86 cm3 after maxillomandibular surgery30,31.
Mandibular retrusion surgery
A systematic review analyzing the mandibular retrusion surgery on the incidence or worsening of OSA did not observe incidence of OSA after surgery. It should be highlighted that this review included studies both addressing only mandibular surgeries and mandibular surgeries with maxillary protraction, thus presenting confounding factors. The authors highlighted the need to consider the potential reduction of the airway dimension during treatment planning32.
A recent systematic review using CBCT reported that maxillary advancement combined with mandibular retrusion reduced the total airway volume in 1.55 cm3, and isolated mandibular retrusion reduces the total airway volume in 1.89 cm3 31.
Dentofacial orthopedics and orthognathic surgery have been related to changes in upper airway volume measured by CBCT. However, the standardized achievement of tomographic images and more controlled and randomized studies are necessary to confirm these findings.
The authors thank the Associação Fundo de Apoio à Pesquisa (AFIP), CNPq and CAPES.