A comparison of maxillary sinus diameters in Chinese and Yemeni patients with skeletal malocclusion

This retrospective study was authorised by the China Medical University Stomatological Hospital’s research ethics committee in Shenyang, Liaoning (No CMUKQ-2022-034). All actions were performed in accordance with the applicable regulations and laws.

Based on a study by Shrestha et al. [16], who examined CBCT analysis of maxillary sinus volume in various craniofacial patterns, the sample size was calculated with an alpha value of 0.05 and a power of 95%. Based on the sample size of this study, 27 subjects were included. The sample size for each skeletal malocclusion group was increased to 30 participants.

In this study 180 cephalic (LC) radiographs were included. The LC was obtained from Chinese participants who were selected retrospectively from orthodontic patients with various types of skeletal malocclusion at China Medical University Stomatology Hospital (Shenyang, China). The LC was taken from Yemeni participants with various types of skeletal malocclusion, who were retrospectively selected from orthodontic patients at Taiz University stomatology Hospital clinics (Taiz, Yemen), and the list of included participants was sent via email.

The following inclusion criteria were applied: (1) no pathological findings in the maxillary sinus; (2) no craniofacial anomalies, no visible facial discord or cleft palate and lip; (3) no prior orthodontic treatment; (4) images for individuals under 18 years ago were excluded from the study because of incomplete sinus development [5]. Cephalometric images displaying alterations in the sinus surface morphology caused by trauma or pathological statuses were excluded from the study. Images with poor quality, which caused difficulty in observing the maxillary sinuses, were excluded.

The individuals were classified into two major groups based on ethnicity: the first group included Chinese patients, whereas the second group included Yemeni patients. Each ethnic group contained 90 patients, 45 men and 45 women, and in each ethnic group, Wits appraisal and ANB angle were used to divide the patients into three groups (0 < ANB ≤ 4, − 1 ≤ Wits ≤ 0) classified as skeletal Class 1, whereas ANB > 4, Wits > 0 is skeletal Class 2, and ANB ≤ 0, Wits <  − 1 is skeletal Class 3. Each group contained 30 patients: 15 men and 15 women.

The dimensions of the sinuses were compared in every ethnic group in accordance with the gender of the subject and skeletal malocclusion classes to determine whether gender subjects with different skeletal malocclusion classes and ethnicity are factors affecting the sinus dimension.

The LC was entered using WinCeph 9.0 (Rise Corporation, Sakuragaoka Cho Shibuya Ku, Tokyo, Japan). The right and left sinuses were differentiated, and the left side was correctly traced. The patients were turned to the left when the lateral cephalograms were taken, the left sinus contour was more posterior than the right [3]. The maxillary sinus index was measured as follows [14]: As shown in Fig. 1a, b, (1) a vertical line has been drawn from Su and In to determine the maxillary sinus height (Su refers to the highest point, whereas In refers to the lowest point), and (2) a horizontal line has been drawn from An to Po to define the length of the maxillary sinus (An denotes the frontest point, whereas Po denotes the most backward point). All landmarks and cephalometric measurements used in this study are described in Additional file 1.

In evaluating the significant error of the radiographic measurement, the primary examiner and another observer remeasured randomly selected cephalometric radiographs of 30 patients 3 weeks after the initial measurements. Apart from calculating the percentage of total variation that could be attributed to measurement errors, the mean measurement difference between the primary and secondary measurements for each variable was also calculated.

IBM SPSS Statistics, version 21 for Windows (IBM Corp., Armonk, NY), was used to perform statistical analysis. In determining the reliability and reproducibility of measurements, the intra-class correlation coefficient (ICC) was used. In checking the normal distribution of the data, we used The Shapiro–Wilk test. In comparing mean values amongst groups, we used one-way ANOVA and Tukey’s post hoc test. Data were analysed in accordance with gender, skeletal malocclusion and nationality. The mean and standard deviation for each group were calculated, with the significance level set at P 0.05. The maxillary sinus parameters were evaluated using a simple t-test of total sample data based on nationality and gender groups combined or subdivided separately. Furthermore, we used one-way ANOVA to estimate sinus morphometric data for both malocclusion groups and nationality subgroups. Furthermore, in comparing the mean values amongst the groups, we used the Tukey post hoc test. Pearson’s correlation coefficient was used to calculate the correlation between sinus dimensions and cephalometric indices.

Maxillary sinus dimensions change with gender. Based on the findings of the present study, men and women have varying maxillary sinus diameters. This difference is similar to that of other studies [26‐28], which considered gender factors. Considering that men showed greater height, length and surface area than women, they had mentioned two possible interpretations. Firstly, according to Enlow [29], men require a larger lung to support their substantially larger body organs and muscles. Second, men required a significant airway that began at the nose and extended to the nasopharynx. In another way, the physiological changes and structure of the nasal cavity resulted from respiratory-related requirements, such as humidification and warming of breathed air. In addition, the maxillary sinus increases in size because of the filling of remnant space inside the nasomaxillary complex. The maxillary sinus surface area of men is related to body height and weight in the international literature reported by Ariji et al. [30], which may explain why men’s sinus dimensions rise more than women.

The current study shows the mean value of maxillary sinus amongst Yemeni of different gender in accordance with height (34.02 ± 4.54 mm in men and 29.84 ± 4.98 mm in women), length (36.26 ± 4.94 mm in men and 33.49 ± 4.64 mm in women) and surface area (1029.64 ± 214.10 mm² in men and 800.62 ± 208.87 mm² in women) and amongst Chinese of different gender in accordance with height (41.13 ± 3.96 mm in men and 37.80 ± 4.11 mm in women), length (40.39 ± 3.63 mm in men and 38.59 ± 3.67 mm in women) and surface area (1282.52 ± 186.72 mm² in men and 1154.61 ± 148.92 mm² in women). This result has shown statically non-significant difference, as shown in the tables of results. These results are consistent with those of previous studies conducted by Sharma et al. [31]and Uthman et al. [26]. However, other studies showed results lower than these measures [27]. Furthermore, other studies [28, 32] have reported wider and higher maxillary sinuses than our results. However, a survey by Uchida et al. [33] used the cadaver skull and reported no statistically significant difference regarding sides, age or gender.

The maxillary sinus dimensions of various skeletal malocclusions were measured in this study. Our findings in the overall group revealed that the skeletal Class II group had significantly larger dimensions than the Classes I and III groups. Except for height, which appeared almost equal in the two groups, skeletal classes I and II were not statistically significant.

In addition, amongst Yemenis, the results showed a significant statistical difference in mean sinus’s height, length and surface area in skeletal Class II malocclusion. However, sinus height was greater in the skeletal Class I group. For Chinese, the surface area in the skeletal Class II group was greater than that in the rest of the groups, with an approximately equal height and length in all malocclusion groups. These variations could be due to the use of a two-dimensional lateral cephalogram, a small number of samples, ethnic differences in the samples and the age of the samples utilised in our study not being standardised.

All the findings in the current study revealed that the maxillary sinus diameter was more significant in skeletal Class II than in Classes I and III. Thus, other studies [16, 34‐36] considered malocclusion factors. Dibbets et al. [37] and Hopkin et al. [38] interpreted these results as they concluded in their research that men have a bigger cranial base than women, and individuals with skeletal Class II malocclusion have a bigger cranial base than those with Class I or Class III malocclusion. Patients with bigger cranial bases usually have larger maxillary sinuses. Consequently, he suggests that the mean value of male skeletal Class II malocclusion is the highest. These results were in accordance with the ones found in this study.

In the current study, the maxillary sinus dimensions did not exhibit a static significance with ethnicities, except for the surface area of the sinus, which showed statistical significance (P < 0.05). This might result from the small sample sizes within each ethnic group. However, the sinus surface area showed a significant increase. Based on our findings, the dimensions of the maxillary sinuses differ from ethnicity to ethnicity, as the dimensions of the sinus were larger in Chinese than in Yemeni. These differences may be due to the ethnic differences found by Rhee et al. [39]. When they compared Caucasian and East Asian people’s attractive faces, particularly midfacial width measurements, they found that the width and height of the middle of the face in East Asian people were greater than those of Caucasians. This conclusion is consistent with previous studies performed on people of different races and geographic regions [18, 40].

Notably, these factors could differ from the maxillary sinus surface area values. As shown by Kawarai et al. in a study of computed tomography scans of Japanese ancestry, the MSV was greater in Japanese than in people of other races (mean right MSV: 23.6 cm³, mean left MSV: 20.9 cm³). This outcome was linked to variances in this ethnicity’s height–weight ratio and differences in volume measurement methods [40]. In addition, Fernandez conducted research on cadavers from Europe and Zulu of different ethnicities and gender and concluded that the MSV of the two races differed statistically [18].

Regarding the association amongst dimension, maxillary sinus surface area and skeletal parameters, the current findings revealed a substantial relationship between maxillary sinus length, height, surface area, SNA and SNB angles. The maxillary sinus dimensions increased with the increase of SNA and SNB angles. Endo et al. [3] reported the same conclusion.

In addition, the maxillary length was related to sinus height, length and surface area. Therefore, a greater maxillary length is associated with an increase in sinus height, length and surface area, which can be explained by the increased midface length associated with relative prognathic maxillary cases.

Moreover, sinus height had a significant relationship with the length of the mandible, and sinus height was higher amongst patients with a longer mandible, which could be explained by the considerable mandible length linked with the retrognathic maxilla and prognathic mandible situations, as shown in skeletal Class III skeletal malocclusion.

The current study found a relationship amongst NA–APOg, NA–FH angle and the maxillary sinus surface area, indicating a tendency for maxillary prognathism in patients with a greater maxillary sinus surface area. Meanwhile, the dimension and surface area of the sinus have a considerable inverse relationship with the gonial and GoGn–Sn angles, with the dimension and surface area of the sinus decreasing as the degree of these angles increases.

These findings have various dental implications. Orthodontic movement of teeth in the posterior maxillary area requires special consideration when the maxillary sinus is large, as in males, and skeletal Class II skeletal malocclusion. Based on case studies by Park et al. [41] and oh et al. [42], closing the spaces caused by the loss of the posterior maxillary teeth through the maxillary sinus is complex. In obtaining a positive result, modest forces must be used to increase treatment duration. When the posterior root apices protrude into the maxillary sinus, intrusion of teeth can be difficult and slow, and extremely little force is necessary [9, 43]. Likewise, insertion of TADs in the maxillary posterior buccal areas also requires special consideration. In such cases, orthodontic mini-plates may be used as an alternative to mini-implants [44].