1.Background

Facial contouring is a field of interest in anatomy, anthropology, plastic surgery, and artists, and is now an essential part of forensic science due to individual iden-tification¹⁾. In particular, facial features are affected by factors such as race, age, and culture²⁾. The nose is located at the center of the face^3,4) and can determine race and sex⁵⁾.

Research using the nasal index (NI) classification method to classify the shape of the nose is currently in progress. In the NI classification method, four nose shapes are classi-fied: leptorrhine (long and narrow nose), mesorrhine (me-dium nose), and platyrrhine (broad nose)^6,7). In the past, NI was used in forensic medicine to evaluate remains⁸⁾, but now it is used in various clinical surgeries^5,9). Therefore, the shape of the nose is important in modern society. However, domestic research is needed as most research is being conducted abroad^1-6,9-15).

In addition, in most previous studies, patients were actually measured and classified^1-6,9-15). However, when the actual measurement is performed on the patient, it may be difficult to measure at an accurate point as the soft tissue is measured. Therefore, studies using cone beam computed tomography (CBCT), which can check bone and soft tis-sue at once, is needed.

2.Objectives

In this study, after 3D modeling of the skull using a 3D program, the goal is to confirm the ratio of the nose shape of Koreans through measurement and evaluation for NI classification.

1.Ethics statement

The CBCT data of this study were retrospectively ana-lyzed and proceeded after IRB approval at the Dankook University Dental Hospital.

2.Study design

All radiographs were performed by the same technician, and the Frontkfort Horizontal Plane (FH Plane) was taken perpendicular to the floor to reduce the difference in skull size for each patient. Imaging was performed after mat-ching the sagittal midline of the face with CBCT (Alphard 3030; Asahi, Kyoto, Japan). The shooting conditions were a gantry angle of 0°, 120 kV, and auto mA. CBCT Sanning was slice increment, 0.39 mm; slice thickness, 0.39 mm; slice pitch, 3; scanning time, 4 seconds; matrix, proceeded with an image scale of 512×512 px. All CBCT data were then provided in Digital Imaging and Communications in Medicine (DICOM) format.

The provided DICOM was modeled using Mimics ver.22 (Materialise Co., Leuven, Belgium) 3D program to model the patient’s skull and soft tissues into three views: coronal, sagittal, and frontal (Fig. 1). To extract soft tissue in 3D, Hounsfield unit (HU) was set to a minimum of 507 HU, a maximum of 3,071 HU, and masking was performed. The produced data was converted into a stereolithography (STL) file using the calculate part function. The skull and soft tissues converted to STL were measured for each item through the distance function.

Fig. 1. Mimics Software (ver.22; Materialise Co, Leuven, Belgium). N: nasion, SN: subnasale, AL: alaria.

Measurements for all items were done based on the highest point after horizontally adjusting the Frankfort hori-zontal line. In addition, all measurements were evaluated after calculating the average value after measuring three times. In addition, the reliability of the measured data (Cronbach’s a=0.623) was confirmed through reliability analysis. The classification was performed by substituting into the formula according to the NI classification method. The measurement items and formula are as follows:

(1) Measurement metrics

The measurement metrics were the height and width of the nose (Table 1, Fig. 2).

Table 1

Nasal Index Metrics

Parameter	Definition
Nasal width (al-al)	Distance between Alaria (al)
Nasal height (n-sn)	Distance between N (nasion) and SN (subnasale)

Fig. 2. Measurement Parameters of nasal index. (1) Nasal width is the Distance between Alaria (AL);(2) Nasal height is the Dis-tance between nasion (N) and subnasale (SN).

(2) Measurement formula

Based on the above measured values, NI classification was performed through the formula below.

3.Sample size

This study was conducted on participants in their 20s with relatively less skin aging, as measurements were con-ducted on soft tissues. Therefore, CBCT data of 100 patients (50 males and 50 females) in their 20s who visited the Dankook University Dental Hospital were provided by the Department of Orthodontics. In addition, the number of study participants was calculated through the G-power ver. 3.1 (HHU, England) program.

4.Statistical methods

To confirm the ratio of measurement metrics, analysis was performed using the SPSS ver. 23.0 (IBM Co., Armonk, NY, USA) program. In addition, a cross-analysis was con-ducted to confirm the ratio of NI categories between sexes. A t-test was conducted to determine the mean difference in NI according to sex. All statistics were performed with a post hoc test set at 95% confidence interval and signi-ficance level at 0.05.

1.Nasal index ratio

On evaluating the nose ratio, 10 patients had a lepto-rrhine (long and narrow) type with an NI of 55%∼69.9%, 76 had a mesorrhine (moderate shape) type with an NI of 70%∼84.9%, and 14 had a platyrrhine (broad and short) type with an NI of 85%∼99.9%. However, hyperlep-torrhine (very narrow) and hyperlatyrrhine (very broad/ wide) were not observed (Table 2).

Table 2

Nasal Index (NI) Classification

Nasal type	Range of NI (%)	Number
Leptorrhine (long and narrow)	55∼69.9	10
Mesorrhine (moderate shape)	70∼84.9	76
Platyrrhine (broad and short)	85∼99.9	14

2.Comparison of nasal index averages by gender

On comparing the average NI by sex, it was confirmed that the average for males was 76.16 and for females was 77.84, which was higher for females on average. In addition, it was confirmed that both sexes had an average meso-rrhine (moderate shape) shape. However, no statistically significant results were confirmed (p>0.05) (Table 3).

Table 3

Comparison of Nasal Index Averages by Sex

Sex	Mean (standard deviation)	p-value
Male (n=50)	76.16 (6.78)	0.230
Female (n=50)	77.84 (7.16)

p-value was obtained by t-test.

3.Nasal index ratio comparison between sex

On evaluating the nose ratio, five males had a lepto-rrhine (long and narrow) type with an NI of 55%∼69.9%, 40 had a mesorrhine (moderate shape) type with an NI of 70%∼84.9%, and five had a platyrrhine (broad and short) type with an NI of 85%∼99.9%. In females, five had a leptorrhine (long and narrow) type with an NI of 55%∼69.9%, 36 had a mesorrhine (moderate shape) type with an NI of 70%∼84.9%, and nine had a platyrrhine (broad and short) type with an NI of 85%∼99.9% (Table 4).

Table 4

Nasal Index Analysis According to Sex

Participant	Nasal type			Entire	p-value
	Leptorrhine	Mesorrhine	Platyrrhine
Sex					0.508
Male
Number	5	40	5	50
Expected frequency	5	38	7	50
Female
Number	5	36	9	50
Expected frequency	5	38	7	50
Entire
Number	10	76	14	100
Expected frequency	10	76	14	100

1.Interpretation

The nose is fixed in the center of the face and is the most important structure for facial restoration¹²⁾. Studies related to the nose are in progress, but most are foreign studies^1-6,9-15), and domestic studies are needed. This study aimed to confirm the ratio of Korean nose shape through 3D mea-surement.

2.Key results and comparison

The ratio of the nose of Koreans was observed in the leptorrhine, mesorrhine, and platyrrhine types, but the hyper-leptorrhine and hyperlatyrrhine types were not observed. The leptorrhine type was observed in 10 patients, mesorrhine type in 76 patients, and platyrrhine type in 14 patients. It was observed that Koreans have a high proportion of the mesorrhine type. According to a study by Mohammed et al.¹¹⁾, leptorrhine, mesorrhine, and platyrrhine types were observed in Adonis, Nigeria, and a high proportion of mesorrhine was reported, similar to the present study. However, according to Ray et al.¹²⁾, Lebanese, Dasmachus, Greeks, and Western Europeans reported that the lepto-rrhine type was more common. Consequently, it was found that the shape of the nose was different between the races. It appears that the shape and size of the nose are affected by the climate and environment, resulting in different shapes¹³⁾. According to previous studies, the leptorrhine type was reported to be highly distributed in cold and dry climates, and the platyrrhine type was reported to be highly distributed in humid and warm climates^16,17). The leptorrhine type appears to be highly distributed in Europe, which has a relatively dry climate, and the platyrrhine typ appears to be highly distributed in Africa, which has a relatively warm climate. It has also been reported that this phenomenon changes depending on the environment to ensure efficient breathing¹⁷⁾. Leong and Eccles¹³⁾ According to research, it has been reported that if the nose is small and flat, it is easier to adapt to less turbulent airflow, and the resistance of the nasal airway is low, so it adapts better to hot and humid environments. Therefore, when judging the shape of the nose, race is important, but climate and environment are equally important.

As a result of evaluating the nose ratio, the leptorrhine type was found in the same ratio as 5 males and 5 females. For the mesorrhine type, there were 40 males and 36 females, and the proportion of males was smaller than that of females. As for the platyrrhine type, there were 5 males and 9 females, and there were more females than males. Therefore, it was observed that the proportion of the mesorrhine type was high in all sexes. Aung et al.¹⁴⁾ reported that both Chinese males and females had a high proportion of the mesorrhine type, similar to this study. According to a study by Ray et al.¹²⁾, Nepal and India also reported a high proportion of mesorrhine types, similar to this study. However, Turkey and Iran had a high propor-tion of the leptorrhine type, and Nigeria’s Igbo region reported a high proportion of the platyrrhine type. Ryu et al.¹⁵⁾ reported that the shape of the skull, the nose, and the nostrils of the skull have a correlation. Therefore, Asians with similar facial shapes are judged to have a high pro-portion of mesorrhine types. As a result, it seems necessary to compare the shape of the nose with the shape of the face.

3.Suggestion

In this study, we observed the nose shape ratio of Koreans: leptorrhine (long and narrow) type, mesorrhine (moderate shape) type, and platyrrhine (broad and short) type. The nose is a structure that requires aesthetics because it is located in the center of the face. This is an area of great interest in various clinical trials. Accordingly, the data from this study comparing the shape of Koreans’ noses is expected to be helpful in aesthetic research and clinical surgery. In particular, the nasal cavity, which determines the shape of the nose, is very important in the dental field. The nasal cavity is a breathing space; if breathing incorrectly, it can affect changes in the facial skeleton and cause malocclusion. Therefore, based on the results of this study, it is expected to be helpful in proce-dures and surgeries, such as orthodontic treatment and pediatric dentistry. This study will also be helpful for similar research in the future.

4.Limitations

This study had some limitations. It was considered that there was a slight difference according to the measurer even if the same mark point is used in the measurement of the 3D extracted nose. Accordingly, the average of the measured data was analyzed for reliability, and classi-fication was performed after confirming the reliability of Cronbach’s a=0.618. This way, we tried to improve the limitations while conducting the study, and more supple-mentary studies will be needed in the future.

None.

No potential conflict of interest relevant to this article was reported.

This study was approved by the institutional review board of Dankook University (IRB approval no. DKUDH IRB 2020-01-007).

Conceptualization: Jeong-Hyun Lee. Data acquisition: Min-Gyu Park and Jeong-Hyun Lee. Formal analysis: Min-Gyu Park and Jeong-Hyun Lee. Supervision: Sung- Suk Bae and Jeong-Hyun Lee. Writing–original draft: Hee-Jeung Jee and Jeong-Hyun Lee. Writing–review & editing: Sung-Suk Bae and Jeong-Hyun Lee.

None.

Raw data is provided at the request of the corresponding author for reasonable reason.