## 1 Introduction  
The dimensions of the upper airway can vary significantly among individuals owing to various factors, including skeletal patterns. These patterns can influence the shape and size of the upper airway, potentially affecting respiratory health by causing issues such as obstructive sleep apnea (OSA) and craniofacial anomalies. Understanding the upper airway dimensions and their relationship with craniofacial growth and surrounding structures has been a priority for ear, nose, and throat (ENT) specialists; healthcare professionals; surgeons; and dentits, especially orthodontis.  
Numerous extensive studies have been conducted on craniofacial factors and their influence on upper airway dimensions; however, most of these studies are based on airway landmarks in two-dimensional (2D) images, which not only incorrectly depict complex shapes but also lack precision for evaluating the volume of the airway and most constricted cross-sectional area (CSA) [1]. To overcome the limitations of evaluations using 2D images, new cone-beam computed tomography (CBCT) systems with higher-quality images and accurate measurement software were developed, specifically for the head and neck region. The introduction of three-dimensional (3D) airway models derived from CBCT scans represents a significant advancement in the objective evaluation of the efficacy of surgical treatments for OSA, orthognathic surgeries, and maxillary expansion by assessing their effects on airway dimensions [2]. However, ensuring the accuracy and reliability of the methods used to generate these models is crucial because they serve as a fundamental baseline for treatment planning. Therefore, proper scientific validation of the generation method is necessary to maintain the integrity and effectiveness of evaluation tools [3].  
The orthodontic literature has long discussed the correlation between the pharyngeal airway space and various craniofacial skeletal patterns in patients, encompassing both anteroposterior (skeletal Classes I, II, and III) and vertical (hyperdivergent, normodivergent) dimensions. In 1907, [PERSON] observed that Class II, division 1 malocclusions were characterized by narrow upper pharyngeal airways and a tendency for mouth breathing, resulting in dentofacial changes such as a narrow upper arch, protruded upper incisors, and abnormal lip function. This early insight highlights the connection between airway characteristics and dental alignment [4]. This discussion highlights the close relationship and intimate association between these factors. Several studies have shown that different skeletal patterns affect the upper airway size (UAS); however, these results are controversial. These conflicting results could be attributed to various factors, such as patient age, sex, ethnicity, head position during radiography, method of measurement, and area of measurement [5].  
Studies examining ethnic differences in the UAS have been conducted in various populations, such as Korean, Lebanese, Chinese, and Brazilian populations [6; 7; 8]. However, there is a lack of specific reports focusing on upper airway dimensions in the Vietnamese population, which originates from a homogeneous ethnic background in Southeast Asia; consequently, the upper airway dimensions in this group remain poorly understood. We hypothesize that vertical growth patterns significantly impact upper airway dimensions, particularly in hyperdivergent individuals, and that these patterns are associated with an increased risk of airway obstruction.  
Therefore, given the evolution of 3D diagnosis, the aim of our cross-sectional study was to determine the dimensions of the upper airway and most constricted CSA and to compare these values among various craniofacial skeletal patterns in healthy Vietnamese adults using CBCT.