INTRODUCTION

Malocclusions and craniofacial features were reported with obstructive sleep apnea (OSA), including; constriction of the airway at the level of both nasopharynx and oropharynx, hyoid bone positioned inferiorly, increasing of maxillary protruding, a discrepancy of anterior-posterior relation of maxilla and mandible, Class II malocclusion, increasing in the over-jet, and crowding in the mandibular arch.[1-3]

Posterior airway space (PAS) depends on the development of craniofacial structures, which is considered a key factor in orthodontic treatment. Small posterior airway dimensions established early in childhood may predispose to breathing disordered during sleep. Soft-tissue changes due to age, obesity, or genetic reasons may cause a further reduction in the available dimension of the oropharynx.[4] Moreover, the latter also has a significant role in the development of OSA and snoring.[5,6]

OSA is a serious condition that may result in different sequelae, including hypertension, cardiac arrhythmias, and even mortality.[7] Symptoms associated with OSA may include daytime sleepiness, concentration loss, and disturbances in the psychological state that may affect the continuity of the normal patient’s life unless treated.[8]

The current studies concluded that OSA had a significant correlation with the narrow PAS dimensions.[9] In a cone-beam computerized tomography (CBCT) study, the authors reported that the narrowest areas of the PAS were significantly smaller in OSA subjects.[10] Studies[11,12] reported that cases with recurrent OSA in previously treated adults were accompanied by constriction on the PAS dimension.

Size of the adenoid, soft palate length, tongue dimensions, and hyoid bone position have also been suggested as significant predisposing for OSA.[13] Several studies have investigated the association between craniofacial characteristics and PAS dimensions using lateral cephalograms,[14,15] or CBCT.[16,17] in healthy subjects with no OSA or its associated symptoms.

OSA is multidisciplinary care that involves respiratory/ thoracic physicians, ENT, maxillofacial surgeons, orthodontists, and dentists. Options for management of OSA include behavioral modification (weight loss, stopping smoking and alcohol, altering sleeping position, etc.),[18] surgical intervention (mandibular advancement, surgical repositioning of hyoid bone, pharyngeal surgery, or even tracheostomy),[19] and non-surgical management including (continuous positive airway pressure, CPAP, and mandibular advancement, MA).

CPAP which relies on changing the airflow is considered the gold stander management of OSA. However, it also poses many disadvantages: noise, cumbersome, and efficacy highly reliant on patient compliance. MA which relies on only changing the size of airway volume shows a great improvement in the condition regarding the OSA and Snoring.[20]

The correlation between PAS and skeletal class shows a substantial conflict. While some studies pointed to a significant effect of sagittal skeletal malocclusion on the PAS size,[21,22] other studies have failed in such demonstrations.[23,24] These discrepancies in observation could be due to variations in factors such as the age of the participants, sex,[25] ethnicity,[14] measured area (nasopharynx, oropharynx, or hypopharynx), and/or growth patterns.[26]

Several posterior airway studies used more advanced techniques, such as cone-beam computed tomography (CT), magnetic resonance imaging (MRI), fluoroscopy, acoustic reflection, and pharyngoscopy by fiber-optic.[27,28] However, these techniques consume more time, cost more for routine clinical practice, and usually need high doses of radiation. Some papers found that cephalometric radiography can be accurately used to evaluate the hard and soft craniofacial tissues and structures compared to those which used more sophisticated methods mentioned previously.[29] Moreover, many studies compared conventional lateral cephalograms and those derived from three-dimensional (3D) CBCTs showed a non-significant in most.[30-33] Two-dimensional (2D) cephalometric measurements are also well related to the 3D MRI measurements.[34]

Many studies investigated the relationship between specific malocclusions with the posterior airway dimension. Some studies reported that Class II division 1 malocclusion might cause a significant change in the upper airway dimensions.[35,36] On the other hand, some studies found no significant association between them.[37] We should mention that ethnic and racial differences between cases had not been considered in most of the previously published articles, missing an important factor that can significantly affect malocclusion.[38]

Therefore, in this study, we aim to evaluate the size of PAS and hyoid bone position in Chinese and Egyptian races in both genders using cephalometry.

MATERIAL AND METHODS Samples

This study was revised and approved by the Ethical Committee of the Faculty of Medicine, Fayoum University, Egypt. The Institutional Review Board approved this study under the number R-428.

Some articles on dentofacial and upper airway[39] measured effect sizes with α = 0.05 (two-sided) and an 80% power and calculated the sample size to reach a standardized effect size of 0.96 (7.8/8.1 mm) and 1.19 (3.1/2.6 mm) for dentofacial and upper-airway comparisons, respectively. Sample size calculations showed that 17 individuals from both sexes per group were the minimum number to be included for proper sample size in this study.[40] Therefore, for Chinese individuals, cephalometric radiographs of 96 untreated subjects (Males [n = 30] and Females [n = 66]) were selected from the orthodontic subjects at the Stomatology Hospital, Zhengzhou University age: (17.6 ± 5.3) years.

For Egyptian individuals, cephalometric radiographs of 99 untreated subjects (Males [n = 26] and Females [n = 73]) were selected from the orthodontic subjects at the ElGamal Private Clinic, age: (18.4 ± 4.1) years.

The selection of cases in both groups was according to the following;

Inclusion criteria

The following criteria were included in the study:

Age ranged from 12 to 29 years; the proper age group to have low potential to develop breathing disorders (as the risk of developing OSA rises with age due to the development of chronic illnesses-cardiovascular disease, diabetes mellitus, and hypertension- and obesity)[41]

Complete permanent dentition

Chinese and Egyptian origin only.

Exclusion criteria

The following criteria were excluded from the study:

Medical history of previous sleep breathing disorders

Pathologies or anomalies in the head and neck

Oral fixed or removable appliances

History of orthodontic treatment

Professions blowing

Tongue abnormality

Severe skeletal asymmetry, visible jaw fracture, any systemic diseases affecting bone and general growth, and subjects with cephalograms in which an enlargement of tonsils and adenoids was detected. They were excluded from the study.

According to the ANB angle, the subjects were classified into three types of skeletal malocclusion: class I (1° ≤ ANB ≤ 3°), class II (ANB > 3°), and class III (ANB < 1°).[25]

Cephalometric tracing and data analysis

We followed a standard protocol in all cephalometric X-rays using the same X-ray unit ([Sirona Orthophos; Sirona Dental Systems, Bensheim, Germany] for Chinese and [NewTom®; Verona, Italy] for Egyptian individuals). The same cephalostat was used for patient positioning in maximum intercuspation, and the same settings were used for all examined subjects. During lateral cephalogram recording, subjects were asked to stand in a position where Frankfort’s horizontal plane (FH plane) was parallel to the floor and teeth were in centric occlusion. Subjects were instructed to be stable without any movement of their head or tongue and without swallowing during cephalometric exposure.

All digital lateral cephalometric films were traced using Dolphin imaging version 11.5 Premium software (Dolphin Imaging and Management Solutions, Chatsworth, CA, USA) by the same operator to analyze and calculate the maxillary and mandibular position in relation to the cranial base, posterior airway dimension (Nasopharynx, Oropharynx, Hypopharynx, and Deep pharynx), and the position of the hyoid bone. Various landmarks were identified using (Quas/ Airway and Arnett/Gunson FAB Ortho) Analyzes, which included the required variables for the study [Figure 1 and Table 1].[42]

Figure 1:: Various landmarks, reference planes, and linear and angular parameters (for landmarks definition, Table 1).

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Table 1:: Cephalometric landmarks for this study.

Land mark Definition N Nasion A The most concave point between ANS and alveolar bone overlying the maxillary incisors root B The most concave point between the Pog and alveolar bone overlying the mandibular incisors root Po Porion Or Orbitale Pog Pogonion Go Gonion Me Menton RGn Retrognathia—the most posterior point of the symphysis PNS posterior nasal spine H Hyoid bone V Epiglottic fold U Tip of Uvula Et Epiglottic tip C2 Superior posterior part of the 2nd cervical vertebra C3 Inferior anterior part of the 3rd cervical vertebra TT Tongue Tip FMA Angle formed between Frankfort horizontal plan (FH-plane) and the mandibular plan (Go-Me) SNA Angle formed between Sella, Nasion and A point angle between “S,” “N,” and “A;” it represents the antero-posterior position of the maxilla in relation to the anterior cranial base SNB Angle formed between Sella, Nasion and B point angle between “S,” “N,” and “B;” it represents the antero-posterior position of the mandible in relation to the anterior cranial base ANB Angle formed between A point, Nasion and B point OverB Over bite OverJ Over jet PNS_V distance from PNS point to V PNS_U distance from PNS point to U TGL (TT-V) distance from Tongue Tip to the V T Angle(TT-FH) Tongue angle (epiglottis-tongue Tip-FH) Hy-Me-MP Angle formed between hyoid bone and mandibular plane (Go to Me) Hyoid–MP-Prep distance between hyoid bone and mandibular plane Hy_RGn Distance between hyoid bone and RGn point Hy-C3 Distance between hyoid bone and C3 Hy-S Distance between hyoid bone and S point Hy-Angle Angle formed between hyoid bone to go point and hyoid bone to me point Sp length (PNS-U) Soft palate length measured from PNS to U points NasopharyxatA Nasopharynx length at A point level OropharynxatU1 Oral pharyngeal airway space length at maxillary central incisor tip level HypopharynxatB Hypopharynx airway space length at B point level DeeppharyxatPog Deep pharynx airway length at Pog level Statistical analysis

We analyzed the data with the Statistical Package for the Social Sciences (SPSS for Windows, version 23; SPSS Inc., Chicago, IL, USA). To get the maximum reliability of the measurements, all tracings and measurements were repeated by the same orthodontist, and the mean was used in the analysis. The Cronbach’s alpha test was also used to confirm the reliability of the data (r > 0.76) for Chinese and (r > 0.72) for Egyptians.

The variable’s readings were analyzed for normal distribution using a Shapiro–Wilks test, and most of the variables showed a normal distribution. We first confirmed that the sample was normally distributed, then we used the independent sample t-test for evaluation of the impact of modifying variable (gender), while analysis of variance and post hoc test (Tukey test) was used for multiple comparisons for evaluation of the impact of skeletal class on craniofacial characteristics and PAS. Confident intervals of 95 % were used, and P < 0.05 was considered to represent statistically significant differences (*P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001).

RESULTS

The mean age of the subjects and gender distribution is described in [Table 2] (Part A Egyptian and Part B Chinese). When craniofacial relation and posterior pharyngeal airway variables were compared between males and females [Table 2], Group A “Egyptian” showed statistically significant differences in five parameters. Tongue angle (TT_FH) showed significantly higher results in men (P < 0.001), the distance between hyoid bone and RGn point (Hy_RGn) was greater in females (P < 0.001), the distance between hyoid bone and C3 (Hy_C3) was longer in men (P < 0.05), and deep pharynx airway length at Pog level (DeepPharyxatPog) was longer in women (P < 0.05). Concerning skeletal malocclusion classes, there was a statistically significant difference only between Class I and Class II relative to the distance between Hy_C3, with Class I cases showing higher results than Class II cases (P < 0.05) [Table 3 “Part A”].

Table 2:: Descriptive analysis of the selected craniofacial and posterior airway space variables in the sample population and comparison between genders (Independent t-test).

Part A “Egyptian” Values Males (n=26)
Mean±SD Females (n=73)
Mean±SD P-value Overall (n=99)
Mean±SD Age y 17.8±3.6 18.7±4.2 0.343 18.4±4.1 FMA 23.5±5 25.8±6.4 0.108 25.2±6.1 SNA 82.5±4.1 82±4.4 0.608 82.2±4.3 SNB 79.1±3.3 77.2±4.7 0.070 77.7±4.4 ANB 3.5±3.1 4.6±2.9 0.115 4.3±2.9 OverB 2.5±2 1.4±2.3 0.032* 1.7±2.3 OverJ 4.2±2.9 4.1±2.7 0.972 4.1±2.7 PNS_V m 61.3±9.6 58.3±5.9 0.062 59.1±7.1 PNS_U m 31.2±5 30.9±3.8 0.786 31±4.1 TGL (TT_V) mm 71.9±8.1 72.9±6.9 0.554 72.6±7.2 T Angle (TT_FH)° 30.5±5.4 24.6±5.1 0.000*** 26.1±5.8 Hy_Me_MP 23±11.2 20.3±8.3 0.194 21±9.2 Hyoid_MP-Prep 12.9±5.9 13.3±5.3 0.738 13.2±5.4 Hy_RGn mm 31±5 36.7±6.9 0.000*** 35.2±6.9 Hy_C3 mm 35.2±5.2 33±4.1 0.028* 33.5±4.5 Hy_S mm 99.7±22.8 94.1±8.4 0.076 95.6±13.8 Sp length (PNS_U) mm 31.6±5 31.1±3.8 0.602 31.2±4.1 NasopharyxatA mm 15.3±3.6 15.4±3.6 0.896 15.4±3.6 OropharynxatU1 mm 10.2±3.3 10.6±3.3 0.569 10.5±3.3 HypopharynxatB mm 10.3±3.2 11±3.3 0.373 10.8±3.3 DeepPharyxatPog mm 10.7±3.8 12.8±4 0.022* 12.2±4.1 Part B “Chinese” Values Males (n=30)
Mean±SD Females (n=66)
Mean±SD P-value Overall (n=96)
Mean±SD Age y 16.2±5.1 18.3±5.3 0.072 17.6±5.3 FMA° 27.3±5.5 27.7±5.3 0.742 27.6±5.4 SNA° 81.2±2.5 81.8±2.2 0.277 81.6±2.3 SNB° 77.1±3.4 77.7±3.3 0.425 77.5±3.3 ANB° 4.2±2.5 4.1±2.6 0.962 4.2±2.6 OverB 3.1±2.5 3.2±2 0.797 3.2±2.1 OverJ 5.8±2.9 5±2 0.105 5.2±2.4 PNS_V m 64.7±9.2 59.4±6.1 0.001** 61.1±7.6 PNS_U m 32.2±4.1 31±4.9 0.247 31.3±4.7 TGL (TT_V) mm 70.4±8.5 66.6±5.4 0.011* 67.8±6.7 T Angle(TT_FH)° 27.5±5.6 26.1±5.9 0.236 26.6±5.8 Hy_Me_MP ° 28.4±11.9 21.8±10.7 0.008** 23.9±11.5 Hyoid_MP-Prep ° 15.3±6.4 12.2±5.7 0.019* 13.1±6 Hy_RGn mm 30.9±5.8 30.9±5.3 0.992 30.9±5.5 Hy_C3 mm 33.8±5.3 31.4±3.2 0.006** 32.2±4.1 Hy_S mm 107.7±11.9 100.8±14.3 0.023* 102.9±13.9 Sp length (PNS_U) mm 32±4 30.9±4.8 0.297 31.3±4.6 NasopharyxatA mm 15.5±4.1 15.7±2.9 0.684 15.7±3.3 OropharynxatU1 mm 8.7±2.9 8.7±2.2 0.983 8.7±2.4 HypopharynxatB mm 9.4±2.9 9.5±2.3 0.907 9.5±2.5 DeepPharyxatPog mm 11.2±3.5 12.2±3.4 0.209 11.9±3.4

Table 3:: Descriptive analysis of the selected craniofacial and posterior airway space variables in each of the 3 skeletal groups without gender differences.

Part A “Egyptian” Variables Class I (n=18, M=6 F=12)
Mean±SD Class II (n=65, M=14, F=51)
Mean±SD Class III (n=16, M=6, F=10)
Mean±SD P-value Age y 18.4±3.4 18.1±4.1 19.9±4.7 0.290 FMA° 23.5±5.5 26±6.5 23.8±4.7 0.187 SNA° 81.9±6.3 82.4±3.7 81.4±4.2 0.674 SNB° 78.7±5.1 76.5±3.7 81.5±4.2 0.000*** ANB° 2.3±0.6 5.9±2.1 -0.1±0.8 0.000*** OverB 1.1±2 2±2.5 0.9±1.6 0.099 OverJ 3.5±1.8 5.1±2.3 0.9±2.5 0.000*** PNS_V m 60.8±7.9 57.9±6.9 61.7±6.5 0.087 PNS_U m 30.6±4 31±4.3 31.4±3.5 0.853 TGL (TT_V) mm 74.9±7.3 72±7.4 72.5±6.3 0.333 T Angle (TT_FH)° 27.5±6.8 25.6±5.4 26.9±6 0.388 Hy_Me_MP° 21.4±10.2 21.7±9.1 17.8±8.3 0.317 Hyoid_MP-Prep° 13.9±5.3 13.4±5.5 11.9±5.2 0.531 Hy_RGn mm 37.6±6.5 34.3±6.9 36.2±7 0.157 Hy_C3 mm 35.5±4.5 32.7±4.5 34.7±3.3 0.031* Hy_S mm 100.2±9.9 93.2±15.2 99.7±8.9 0.068 Sp length (PNS_U) mm 30.9±4 31.2±4.4 31.7±3.6 0.845 NasopharyxatA mm 16.8±3.8 15.1±3.7 14.8±3 0.173 OropharynxatU1 mm 11.9±3.5 10±3.3 10.8±2.7 0.111 HypopharynxatB mm 11.6±4 10.6±3.3 10.9±2 0.540 DeepPharyxatPog mm 14.1±5.9 11.7±3.6 12.4±3 0.085 Part B “Chinese” Variables Post hoctests P-value I/II I/III II/III SNB° 0.124 0.109 0.000*** ANB° 0.000*** 0.001** 0.000*** OverJ 0.018* 0.004** 0.000*** Hy_C3 mm 0.047* 0.857 0.231 Part B “Chinese” Variables Class I (n=15, M=5, F=10) mean±SD Class II (n=69, M=21, F=48) Mean±SD Class III (n=12, M=4, F=8) mean±SD P-value Age y 17.2±4.9 18.3±5.5 14.6±3.5 0.077 FMA° 25.7±3.9 28.4±5.5 25.5±5.4 0.074 SNA° 81.4±3 81.7±2.1 81.5±2.2 0.868 SNB° 79.1±3.1 76.3±2.4 82.1±3.2 0.001*** ANB° 2.3±0.6 5.4±1.5 −0.7±1.7 0.001*** OverB 2.5±1.6 3.5±2.1 2.1±2.3 0.046* OverJ 4.5±1.3 5.8±2.2 3±2.8 0.001*** PNS_V m 62.3±7.3 61.4±7.6 57.8±7.7 0.263 PNS_U m 31±3.7 32±4.6 28.1±5.1 0.025* TGL (TT_V) mm 68.9±5.5 68.1±6.9 64.3±6.4 0.148 T Angle(TT_FH)° 26.6±7.4 26.9±5.6 24.7±5.1 0.488 Hy_Me_MP° 22.4±11.6 25±11.8 19.4±8.5 0.258 Hyoid_MP-Prep° 12.7±6.2 13.5±6.1 11.5±5.9 0.545 Hy_RGn mm 31.3±4.7 30.7±5.6 31.9±5.7 0.760 Hy_C3 mm 33.6±3.9 31.8±4.3 32.3±3 0.340 Hy_S mm 104.6±10.5 101.5±9.9 108.9±29.5 0.203 Part B “Chinese” Variables Class I (n=15, M=5, F=10) mean±SD Class II (n=69, M=21, F=48) Mean±SD Class III (n=12, M=4, F=8) mean±SD P-value Sp length(PNS_U) mm 30.4±3.5 31.9±4.5 28.6±5.5 0.045* NasopharyxatA mm 15.4±2.7 15.8±3.2 14.9±4.6 0.637 OropharynxatU1 mm 9.5±2.3 8.5±2.4 9.5±2.5 0.170 HypopharynxatB mm 9.9±1.7 9.4±2.7 9±2.1 0.662 DeepPharyxatPog mm 11.5±2.9 12.2±3.6 10.6±3.2 0.336 Variables Post hoctests P-value I/II I/III II/III SNB° 0.001** 0.014* 0.001*** ANB° 0.001*** 0.001*** 0.001*** OverB 0.244 0.840 0.082 OverJ 0.093 0.170 0.001*** PNS_U mm 0.706 0.237 0.202 Sp length (PNS_U) mm 0.444 0.560 0.049*

In the case of Group B “Chinese,” statistically significant differences were detected for six parameters. Uvula dimensions (PNS-V) were greater in males (P ≤ 0.01), distance from tongue tip to the V was greater in males (P ≤ 0.05), hyoid bone position ([Hy-Me-MP] [P ≤ 0.01] [Hyoid–MP-Prep] [P ≤ 0.05] [Hy-C3] [P ≤ 0.01], and [Hy-S] [P ≤ 0.05]) were all greater in males. In comparison between skeletal malocclusion classes, there was a statistically significant difference only between Class II and Class III relative to the soft palate length (PNS-U), with Class II cases showing higher results than Class III cases (P ≤ 0.05) [Table 3 “Part B”].

DISCUSSION

The present study evaluated craniofacial characteristics and PAS dimensions in young adult Chinese and Egyptian cases. In spite that, the present study did not include samples from a wide variety of ethnic populations, a lateral cephalogram may be used to make an indirect comparison between our results and that of the past studies on young, healthy populations. Comparing our results with that of Caucasians, Blacks, Hispanics,[43] and Lebanese,[25] the Chinese and Egyptian populations had shorter soft palate (PNS-U) (31.3 ± 4.6 mm in Chinese, 31.2 ± 4.1 mm in Egyptians compared to 44.1 ± 5.6 mm in Caucasians, 46.2 ± 4.7 mm in Blacks, 42.8 ± 6.6 mm in Hispanics and 37.4 ± 4.6 mm in Lebanese). Although some of these discrepancies could be related to the reproducibility of cephalometric landmark identification,[44-46] the contrast may be related to the population race. Our results showed statistically significant differences between genders regarding PAS-related parameters.

Sexual dimorphism is usually reported in healthy adults during the evaluation of pharyngeal morphometry.[21,28] Nasopharynx showed a larger value in females than males without statistical significance in the Chinese group and almost equal values in males and females in the Egyptian group. Chinese males tend to have larger oropharynx, tongue, and hyoid bone areas than females, while Egyptians show a reverse result. This was coupled with significant differences in the measurements of the PAS (PNS_V [P ≤ 0.01], TGL [TT_V] [P ≤ 0.05], Hy_Me_MP [P ≤ 0.01], Hyoid_MP-Prep [P ≤ 0.05], Hy_C3 [P ≤ 0.01], and Hy_S [P ≤ 0.05]) for Chinese and (TT_FH [P < 0.001], Hy_RGn [P < 0.001], Hy_C3 [P < 0.05], Hyoid_MP-Prep [P < 0.05], Hy_C3 [P < 0.01], and Hy_S [P < 0.05]) for Egyptians. These findings are similar to the findings in young adult European from Spain[21] and Hong Kong Chinese.[28] Although the distance between the posterior nasal spine and epiglottic fold showed greater values in Chinese males than in females (P ≤ 0.01), the tongue angle (TT-FH) between epiglottis, tongue tip, and Frankfort horizontal plan showed greater values in Egyptian males than in females (P < 0.001), these findings did not affect the posterior pharyngeal airway space.

Confliction has been reported in the correlation between PAS dimensions and sagittal skeletal patterns. Although some studies have shown a significant correlation between sagittal skeletal malocclusion and PAS size,[21] others have failed to demonstrate such association.[23,24,47] In the present study, significant differences were only demonstrated between Class II and Class III subjects relative to soft palate length (PNS_U), with Class II subjects presenting greater soft palate length in the Chinese group and between Class I and Class II subjects relative to the angle between hyoid bone and Inferior anterior part of the 3rd cervical vertebra (Hy-C3), with Class I subjects presenting greater value in Egyptian group. The above-mentioned discrepancies are likely to be associated with differences in sample anthropometric characteristics, technical differences, and population-related variability.

Small posterior airway dimensions established early in childhood may predispose to breathing disordered during sleep. Soft-tissue changes due to age, obesity, or genetic reasons may cause a further reduction in the available dimension of the oropharynx.[4] Therefore, monitoring it in early life would be beneficial. Lateral cephalogram provides a 2D view of a 3D structure and prevents a volumetric assessment of the structure. Moreover, lateral cephalograms have other shortcomings, including distortion, difficult landmark identification with low reproducibility, uncontrolled magnification, and bilateral structures that can be superimposed, making inaccurate tracing.[48] Many studies compared hand tracing versus digital tracing and concluded that no differences and even digital tracing will be the future and is better in standardization, reproducibility, and ability to enhance the image easier and faster.[49] Although 3D imaging would be the appropriate and best way for measuring the airway using CBCT (Cone-Beam Computed Tomography), enabling accurate detection of changes in the upper airway, and considering the volume and morphology of the upper airway,[50] the technique is not available in all centers and results in a high dose of ionized radiation. Many studies compared conventional lateral cephalograms and those derived from 3D CBCTs showed a non-significant in most[30-33] 2D cephalometric measurements which are also well related to the 3D MRI measurements.[34] Therefore, digital lateral cephalometry is still a valuable and reliable diagnostic tool in airway studies. Using digital cephalometric X-ray combined with digital tracing (Dolphin software) can give highly valuable reproducible information, including airway dimensions and landmarks.[51]

CONCLUSION

Within the limitations of this study

There is no direct clinical implication of this study. However, the study shows a reference of the average size of PAS in both genders of Egyptian and Chinese races

Gender showed a significant influence on the PAS dimensions in Chinese and Egyptian individuals, while sagittal skeletal class had only an impact on soft palate length in Chinese individuals and on hyoid bone – 3rd cervical vertebra angle for Egyptian individual

Sexual dimorphism may account for larger airway dimensions and hyoid bone geometry in Chinese and Egyptian males.

Limitations of the study

There is no direct clinical implication of this study.

This study cannot be used as a way of diagnosing patients with symptoms or a history of sleep disorders.

Recommendations

To make the findings of this kind of study more valuable, further larger-scale studies using CBCT with the inclusion of more airway and soft-tissue volumetric parameters including primary and secondary studies (systematic review and meta-analysis) are needed to assess the similarities and differences between other ethnic groups population.