## 2 Materials and Methods  
The included study group consisted of 129 Caucasian patients (99 females aged 43.78 \(\pm\) 12.89 and 30 males aged 45.37 \(\pm\) 17.41) who reported sleep-related breathing problems to the Dental Prosthetics Outpatient Clinic, Pomeranian Medical University in Szczecin. The exclusion criteria were as follows: 16 years of age or less, pregnancy, unstable cardiovascular diseases, neurological conditions affecting breathing muscles, moderate to severe respiratory disease or inability to provide reliable information consent or information according to questionnaire, e.g., psychiatric or psychological conditions. The BQ was issued at the time of the patient's initial appointment by a trained examiner (B.D.). Patient's family or bed partner were asked to confirm the accuracy of the responses to the questions. Collected data were analyzed and stored at the Department of Dental Prosthetics. Subsequently, their oxygen saturation (SpO2) was measured with a PO40 pulse oximeter (Beurer, Ulm, Germany), and their oropharyngeal space was assessed according to the modified Mallampati classification. The questions in Berlin Questionnaire are divided into three categories: the first five relate to sleep (presence/absence of snoring, its frequency, and intensity, observation of pauses in breathing), the following 4 questions are used to determine the degree of daytime sleepiness, and the last question refers to the presence of concomitant hypertension [20]. The modified Mallampati classification is used to assess oropharyngeal space. The score reflects the position of the tongue relative to the soft palate and uvula [21]. It is assessed by asking the patient to open their mouth as wide as possible and protrude their tongue as much as possible, without making any sounds. Based on the assessment of the visible structures, the patient will fall into one of four categories:  
Class I soft palate and uvula fully visible;  
Class II soft palate and major part of uvula visible;  
Class III soft palate and base of uvula visible;  
Class IV soft palate not visible. In addition, each patient was referred for cone beam computed tomography (CBCT, iCAT, Imaging Sciences, Hatfield, PA, USA, FOV: 16 \(\times\) 13 cm, 0.25 mm voxel, scanning time 26.9 s). All CBCT scans were acquired by the same calibrated examiner to ensure the repeatable conditions, including head and tongue posture [22; 23]. Every patient's data obtained from CBCT scans were then uploaded into the 3D Amira(tm) visualization and analysis computer program (Thermo Fisher Scientific, Berlin, Germany) and set on cephalogram shot to calculate upper airway volume (UAV). Four landmarks were used, such as posterior nasal spike, the tip of the uvula, the top of the epiglottis, and the base of the epiglottis. The program marked the airways from which the upper airway volume was extracted (based on the landmarks). Mapping from 2D to 3D through interpolation was made to receive the volumetric measure automatically. The details, including landmarks used in the measurements and upper airway volume view in Amira are presented in Figures 1 and 2. To check the normality of data distribution, the Shapiro-Wilk test was used. Variables with normal distribution are presented as a \(\pm\) mean with a standard deviation. Variables with non-normal distribution are presented as a median with an interquartile range (Tables 1 and 2). Variables with a normal distribution were compared using ANOVA variance analysis, [PERSON] non-parametric test, and posthoc multiple comparison test with the Tukey post hoc test. The estimated power for comparison of the three groups at effect size = 0.5 was 0.99 (G*Power software, Dusseldorf, Germany) (Figure 3). In order to estimate the correlation between the variables, [PERSON]'s and [PERSON]'s correlation coefficients were used. In order to estimate the correlation between variables, [PERSON]'s correlation coefficient was used. The chi-square test was carried out for the qualitative evaluation of variables.