The upper airways are formed by the nasal cavities, pharynx, and larynx. The pharynx (portion most susceptible to collapse) is divided into 3 parts: nasopharynx, oropharynx, and hypopharynx [1,2]. The nasopharynx begins in the choanae (posterior opening of the nasal cavities) and ends on the hard palate. The oropharynx ranges from the uvula to the epiglottis. The hypopharynx spans the area from the epiglottis to the vocal cords, where the trachea begins [1,2].

There are several radiographic methods that allow the evaluation of craniofacial structure. Profile teleradiography, cone-beam computed tomography (CBCT), axial computed tomography (CT), and magnetic resonance imaging are some examples of imaging modalities that allow for this evaluation. Among these auxiliary diagnostic means and comparing those that are available to dentists, CBCT has demonstrated usefulness in 3D evaluation of the airways. For example, the time and radiation exposure in CBCT are considerably shorter than those in CT [1-3]. Profile teleradiography provides a quick 2D assessment of the upper airways but can only depict the 2D morphology and has prone of numerous superimpositions [4-6].

Furthermore, CBCT images are not magnified and are recorded on a 1:1 scale, which permits accurate and direct dimensional measurements [4-6]. Although a radiographic examination, CBCT has a far more favorable risk-to-benefit ratio. It helps determine the total volume of the airways and their area in the different anatomical planes (sagittal, coronal, and transverse) and identify the regions with the highest anteroposterior and laterolateral constriction of the airways [1].

Upper airway analysis in CBCT is useful to help diagnose some pathologies such as the obstructive sleep apnea syndrome (OSAS).

The OSAS is defined by repeated episodes, greater than 5 per hour, of partial or total obstruction of the upper airways during sleep, leading to airway obstruction (apnea) or reduced airflow (hypopnea). An apnea event, by definition, should last at least 10 seconds and is usually associated with sleep or microarousal fragmentation. Hypopnea can be defined as a reduction in ventilation (at least 50%) with an oxygen desaturation of ≥4% [4-11].

This pathology has a relevant negative impact on patients' daily lives and its prevalence has increased significantly in recent decades worldwide, justified by increased obesity and average life expectancy. Benjafield et al [12] estimated that around the world, approximately 1 billion adults aged 30-69 years experience OSAS, of whom more than 45% (425 million) of adults present moderate to severe OSAS requiring treatment [8]. There is a wide geographical variation in the prevalence of OSAS, with some countries having a prevalence above 50%. OSAS is highly underrecognized, and it is estimated that 82% of men and 93% of women with OSAS in the United States are not diagnosed [12-14]. The clinical presentation of OSAS includes fatigue, daytime sleepiness, and snoring. If not treated, it can be associated with cardiovascular (coronary artery disease, arrhythmias, hypertension, congestive heart failure, and stroke), respiratory (exacerbation of asthma, respiratory dysfunction in chronic obstructive pulmonary disease, pulmonary embolism, and pulmonary hypertension), and neurological diseases (frustration, distress, neurocognitive dysfunctions, and attention deficit) and diabetes [4-11].

In OSAS, despite respiratory effort, there is a repetitive total or partial collapse of the upper airways. In normal situations, the genioglossal muscle contracts at each inspiration in order to avoid the posterior movement of the tongue aided by the lift and tensor muscles of the palate, geniohyoid, and stylopharyngeus [4-11]. Together, these muscles ensure continuous air passage through the airways. However, in some individuals, the upper airways are compromised and narrowed as a result of the deposition of adipose tissue in the pharyngeal muscles and parapharyngeal pathways or due to anomalies in the craniofacial structure [4-11].

One of the regions relevant to the pathophysiology of OSAS is the oropharynx. Steffy et al [1] related the constriction value of the oropharynx with the risk of developing OSAS. An area of <52 mm² is considered as having a high risk of OSAS; 52-100 mm², intermediate risk; and >100 mm², low risk [1,10]. Obstruction may arise at different levels of the oropharynx, being more frequent in the retropalatal, retroglossal, and epiglottis areas [10,11].

Due to the severity of this syndrome, multidisciplinary intervention is essential. The role of the dentist in OSAS is essentially 2-fold: contributing to early diagnosis and therapy. This clinician has the possibility to make a direct observation of the palate’s soft and oropharyngeal tissues (eg, tonsil region and tongue), can identify breathing difficulties and breathing type (nasal or oral), and has easy access to the cervical region, which helps assess its volume or even measure the cervical perimeter [12]. Furthermore, according to the American Academy of Dental Sleep Medicine, the dentist plays a key role in screening and can help to reduce the number of undiagnosed or untreated patients with OSAS [13].

Currently, CBCT is used in dentistry. Its additional use for upper airway assessment would be an added value for the screening of some abnormalities related to an increased risk of OSAS. Studies on airway measurement methods have revealed that there is no objective and consensual methodology [14,15], which makes it difficult to obtain scientific evidence in this area. There is an urgent need to standardize the protocol and to develop a simple workflow for upper airway measurement, which is the aim of this study.

To establish this protocol, CBCT images of 30 patients were used (56% for males and 44% for females), and, in cases where an area of <52 mm² or 52-100 mm² was detected, the patient was contacted and referred to the hospital for diagnostic confirmation tests.

No differences were found between measurements obtained by the different researchers following the protocol described.

The protocol that the authors suggested for evaluation of the upper airways in CBCT allows for automatic calculation of the total volume of the pharyngeal airspace, its area of greatest narrowing, its location, and the smallest anteroposterior and laterolateral dimensions of the pharynx [15-18]. The measurement is performed automatically by the imaging software whose reliability is proven by the existing literature [16]. Thus, we reduce the possible bias of manual measurement, aiming at data collection.