1.Background

Positioned centrally on the face, the nose plays a vital role in identifying race, sex, and other features^1,2). In forensic science, it is used for personal identification¹⁾. Additionally, the airway inside the nose is related to craniofacial development, making it highly important in orthodontics³⁾. The nasal passage influences breathing patterns, which subsequently affect the growth and development of the craniofacial structure. For example, chronic nasal obstruction can lead to mouth breathing, which is associated with altered tongue posture, dental arch development, and even facial skeletal growth. Therefore, it has been observed that individuals with certain nasal types are more prone to developing malocclusions due to the influence of nasal airflow on oral and maxillofacial development. Studies by Allam et al.¹⁾ and He et al.²⁾ have explored these relationships, highlighting the significance of nasal morphology in orthodontics and craniofacial development.

Among these studies, the Nasal Index (NI) classification method is used to categorize nasal morphology and is applied in nasal-related research. The NI classification divides the nose into four types: hyper leptorrhine (very narrow nose), leptorrhine (long and narrow nose), mesorrhine (medium nose), and platyrrhine (broad nose)^4,5). Historically, NI was used in forensic science⁶⁾, but it is now also being utilized in clinical fields^4,7). Therefore, research on the nose is significant in modern society. However, most studies have been conducted internationally^1,2,4-14), indicating a need for related research domestically.

Furthermore, the majority of studies have involved actual measurements of patients or measurements from 2D images obtained through cone-beam computed tomography (CBCT)^1,2,4-14). In such cases, it is difficult to infer precise points, and measurement errors can occur, necessitating research utilizing 3D methods.

2.Objectives

This research seeks to verify the proportions of nasal morphology in malocclusion patients by utilizing a 3D software to model the skull and carrying out measurements and evaluations for NI classification.

1.Ethics statement

This study used CBCT data collected from patients who visited the dental hospital at Dankook University. The CBCT data were analyzed retrospectively after obtaining IRB approval, with a request for exemption from informed consent.

2.Study design

1) CBCT data

To ensure consistency, all data were collected by the same technician, with the Frankfort horizontal plane positioned perpendicular to the floor during imaging. The facial sagittal midline was aligned with the CBCT device (Alphard 3030; Asahi, Kyoto, Japan). Imaging parameters included a gantry angle of 0°, 120 kV, and auto mA. CBCT scanning involved a slice increment of 0.39 mm, a slice thickness of 0.39 mm, a slice pitch of 3, a scanning time of 4 seconds, and a 512 px×512 px matrix. All CBCT data were provided in DICOM format.

2) 3D image production

The provided DICOM files were processed using the 3D program Mimics (ver. 22; Materialise, Leuven, Belgium) to create models in three views: Coronal, Sagittal, and Frontal (Fig. 1). For 3D extraction of soft tissues, masking was performed with Hounsfield unit (HU) settings of Min −507 HU and Max 3,071 HU, and noise was removed using the Edit Mask function. The resulting data were converted to stereo lithography (STL) files using the Calculate Part function. The STL-converted soft tissues were measured using the Distance function.

Fig. 1. Mimics software (ver. 22; Materialise, Leuven, Belgium).

3) Measurements

All measurements were performed with the 3D model adjusted to align horizontally with the Frankfort horizontal plane. Measurements were taken from the highest points, with each measurement repeated three times to calculate the average value. The reliability of the measured data was confirmed (Cronbach’s α=0.623). The NI classification was then performed using the obtained measurements according to the specified parameters and formula.

(1) Measurement parameters

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

Fig. 2. Measurement parameters of nasal index. (1) Nasal height. Distance between N (nasion) and SN (subnasale); (2) Nasal width. Distance between alaria (AL).

Nasal Index Parameters

Parameter	Definition
Nasal height (N-SN)	Distance between N (nasion) and SN (subnasale)
Nasal width (AL-AL)	Distance between alaria (AL)

(2) Formula

The NI classification was performed using the following formula based on the measured values:

3.Sample size

CBCT data from 100 malocclusion patients in their twenties (Class I: 40, Class II: 34, Class III: 26) who visited the dental hospital at Dankook University were provided by the orthodontics department. The sample size was calculated using the G-power 3.1 program (HHU, Dusseldorf, Germany). After selecting F tests in the test family and selecting ANOVA: Fixed effects, omnibus, one-way in the statistical test, Effect size f: 0.25, α err prob: 0.05, Number of groups: 3 were set. Total sample size was calculated to be 90.

4.Statistical methods

The measurement items were analyzed using the SPSS program (version 23.0; IBM Corporation, Armonk, NY, USA). A chi-squared test was conducted to determine the proportions of NI classifications by sex. All statistical analyses were performed with a 95% confidence interval and a significance level set at 0.05.

1.Nasal index proportions of study subjects

Assessment indicated 10 subjects with a leptorrhine NI, 76 with a mesorrhine NI, and 14 with a platyrrhine NI (Table 2).

NI Classification

Nasal type	Range of NI (%)	Number
Leptorrhine (long and narrow)	55.0∼69.9	10
Mesorrhine (moderate shape)	70.0∼84.9	76
Platyrrhine (broad and short)	85.0∼99.9	14

NI: nasal index.

2.Nasal index proportions in malocclusion patients

Evaluation of the NI proportions in malocclusion patients showed that in Class I, there were 5 leptorrhine, 30 mesorrhine, and 5 platyrrhine cases. In Class II, there were 3 leptorrhine, 25 mesorrhine, and 6 platyrrhine cases. In Class III, there were 2 leptorrhine, 21 mesorrhine, and 3 platyrrhine cases. Thus, mesorrhine was the most common type in Class I, Class II, and Class III (Table 3).

Nasal Index Analysis According to Sex

Subject			Nasal type			Entire	p-value
			Leptorrhine	Mesorrhine	Platyrrhine
Malocclusion	Class I	Number	5	30	5	40	0.915
		During malocclusion (%)	12.5	75.0	12.5
	Class II	Number	3	25	6	34
		During malocclusion (%)	8.8	73.5	17.6
	Class III	Number	2	21	3	26
		During malocclusion (%)	7.7	80.8	11.5
Entire		Number	10	76	14	100
		During malocclusion (%)	10.0	76.0	14.0	100.0

3.Nasal index ratio according to sex in malocclusion patients

As a result of comparing the NI types according to sex of malocclusion patients, in Class I, men were classified into 3 Leptorrhines, 15 Mesorrhines, and 2 Platyrrhines, and women were classified into 2 Leptorrhines, 15 Mesorrhines, and 3 Platyrrhines. In Class II, men were classified as 2 Leptorrhines, 12 Mesorrhines, and 2 Platyrrhines, and women were classified as 1 Leptorrhines, 13 Mesorrhines, and 4 Platyrrhines. In Class III, men were classified as 0 Leptorrhine, 13 Mesorrhine, and 1 Platyrrhine, and women were classified as 2 Leptorrhine, 8 Mesorrhine, and 2 Platyrrhine. Accordingly, the Mesorrhine type was observed to be the most common in both men and women in Class I, II, and III. However, it was not found to be statistically significant (p>0.05) (Table 4).

Nasal Index Ratio According to Sex in Malocclusion Patients

Subject		Malocclusion						Entire (n)
		Class I		Class II		Class II
Sex		Male (n=20)	Female (n=20)	Male (n=16)	Female (n=18)	Male (n=14)	Female (n=12)
Nasal type	Leptorrhine	3	2	2	1	0	2	10
	Mesorrhine	15	15	12	13	13	8	76
	Platyrrhine	2	3	2	4	1	2	14
Entire (n)		40		34		26
p-value		0.819		0.630		0.184

The nose is vital for facial reconstruction and is closely related to malocclusion, impacting orthodontic treatment planning^10,11). While international research is abundant, domestic studies are needed^1,2,4-14). This study assessed nasal morphology in malocclusion patients using 3D modeling and NI classification.

1.Interpretation and comparison to previous studies

The results indicated that the nasal morphology in malocclusion patients falls into three categories: leptorrhine, mesorrhine, and platyrrhine. Mesorrhine was the most prevalent type in Class I, Class II, and Class III. This suggests that the nasal proportions in malocclusion patients do not significantly differ by malocclusion class. Comparing these results with studies that analyzed the nose type of the general population, it appears that mesorrhine is also a common nasal type among the general population, as noted by Leong and Eccles¹⁰⁾ in their systematic review. This indirect comparison suggests that malocclusion may not significantly influence the general nasal morphology distribution. According to Dastan et al.¹¹⁾, no significant correlation was found in the airway size differences in malocclusion patients. Similarly, Shokri et al.¹²⁾ observed that Class III patients had generally larger airways, but the differences between Class I and Class II were not statistically significant. Therefore, the nasal morphology observed in malocclusion patients may not have a strong correlation with malocclusion class.

2.Suggestion

This study found that the nasal morphology in malocclusion patients includes leptorrhine, mesorrhine, and platyrrhine types. Mesorrhine was the most common type in Class I, Class II, and Class III. These results can assist in clinical procedures, including surgery and orthodontic treatment, for patients with malocclusion. Additionally, this study may serve as a reference for similar future research.

3.Limitations

This study has some limitations. Firstly, even when measuring the highest points for the NI, slight variations between measurers can occur. To enhance accuracy, the average of three measurements was utilized, and a reliability analysis was performed prior to classification. These measures were implemented to address and reduce the limitations of this study.

None.

Jeong-Hyun Lee has been journal manager of the Journal of Dental Hygiene Science since January 2023. Jeong-Hyun Lee was not involved in the review process of this editorial. Otherwise, no potential conflict of interest relevant to this article was reported.

This study was conducted as a retrospective study. Therefore, the requirement to obtain informed consent was waived. Dankook University (DUDH IRB 2015–12-022).

Conceptualization: Jeong-Hyun Lee, Sung-Suk Bae, and Yun-Ja Hwang. Data acquisition: Ha-Rin Jang, Su-Jeong Kang, and Jeong-Hyun Lee. Formal analysis: Ha-Rin Jang, Su-Jeong Kang, and Jeong-Hyun Lee. Supervision: Jeong-Hyun Lee and Hee-Jeung Jee. Writing-original draft: Sung-Suk Bae and Jeong-Hyun Lee. Writing-review & editing: Sung-Suk Bae, Yun-Ja Hwang, and Jeong-Hyun Lee.

None.

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