The Study Result of Facial Soft Tissue Thickness of Mongolian Children

Subjects

The Craniofacial Collaborative Research Project, a collaborative effort of the Tokyo Medical and Dental University and the Mongolian National University of Medical Sciences, conducted a longitudinal population-based survey of craniofacial growth of Mongolian children between 2013 and 2015. A total of 1842 students, attending the 33rd and 67th elementary and junior high schools of Ulaanbaatar participated. They were screened using a medical examination, questionnaire, cephalometric X-ray images, profile photograph, and mandibula and maxilla impressions. Based on the inclusion criteria, 541 children (225 male and 316 females) (Table 1) were enrolled to have measurements in this study and, their lateral cephalogram was performed between July 2018 and March 2019.

Table 1:Demographic characteristics of research participants.

Children were included in our study if they were 6 to 15 years of age, had normal growth and development, average body mass index, no facial asymmetry, no malocclusion or occlusal deformation, Angle’s Class I occlusion with well-aligned maxillary and mandibular dental arches, overjet and overbite scale within 2-4 mm, cephalograms of normal contrast, no previous history of orthodontic or prosthodontic treatments and no history of maxillofacial or plastic surgery.

The measurements were made on a lateral cephalometric X-ray image.

Cephalograms

Lateral cephalograms of the subjects were taken using a digital cephalometric machine (Veraviewpocs 2D CP X550, Morita, Japan). The subjects were placed in the head holder and asked to look straight ahead to establish the natural head position before adjusting the built-in nasal positioner with a millimeter scale. With teeth in centric occlusion and lips relaxed, the cephalogram was taken at a focus/object distance of 150cm and an object receptor distance of 20cm.

All lateral cephalograms were digitized on a computer by one radiologist with 20 years of experience doing cephalometry to eliminate inter-examiner variability. Using cephalometric software (Winceph 11.0; Rise, Sendai, Japan), eight linear measurements (Figure 1) were obtained for skeletal hard and soft tissue analysis using 16 anthropological landmark points shown in Table 2. Dentists with more than 20 years of experience with cephalometry and image manipulation have validated the landmarks and determined their reproducibility to be 95% using the ellipse method.

Table 2:Hard and soft tissue landmarks.

Landmarks

The anthropological landmarks were identified on each lateral cephalogram. All the required cephalometric landmarks were identified and marked using a cursor/mouse manually. The landmarks and measurements were taken according to the soft tissue cephalometric analysis [1-20].

Measurements

Nine measurements were selected to evaluate the changes in the soft tissue thickness and are as follows: Nasion, Subnasale, Labrale superius, Stomion, Labrale inferius, Labiomentale, Pogonion, Menton.

Statistical analysis

The results were encoded using SPSS 25.0 software, processed after whispering and error checking. The Kolmogorov - Smirnov test method was used to calculate the distribution of the numerical variable, and it was assumed that the p distribution was normal for values higher than 0.05. The Test tested the age-sex relationship for linear contrasts in One-Way ANOVA, and the Independent T-test tested the sex difference. Repeated ANOVA test was used to calculate the difference between the numerical variables of group 3 and above, after determining the distribution, and if there is a normal distribution depending on the distribution. If the p-value is less than 0.01, the difference is considered statistically significant. The reliability of the measurement method was calculated using Dahlberg’s error method [32].

Ethical statement

Ethical approval for this study was obtained from the Research Ethics Committee of the Mongolian National University of Medical Sciences on 08 June, 2018 /approval number 2018-3-10-15/. Before data collection, the parents of all children signed written, informed consent.

Overall data of Mongolian children divided into ten chronological age classes (of 6 and 15 years old) are shown in table 1. General results divided between males and females are shown in Table 3, Figures 2 and 3.

Table 3 shows that facial soft tissue thickness means that standard deviations and values were compared for each age and gender. Statistically significant measurements differed with age, except for stomion (P <0.001). Statistical analysis shows that the thickness of facial soft tissue in Mongolian children increases with age.

Table 4 shows facial soft tissue thickness means, standard deviations and values were compared for gender, and there is no significant difference in gender, but the lower part of the face is slightly thicker for boys. (P <0.01).

A comparison analysis of soft tissue thickness between this study and other populations are shown in Table 5. It differs in most respects from the usual average of children of other nationalities and ethnic groups.

Table 3:Standard average soft tissue thickness of Mongolian children aged 6-15 years / by age and sex /

N=541, SD=Standard Deviation, Test for linear contrasts in One-Way ANOVA. NS-not significant, *p<0.001. All measurements are reported in mm.

Table 4:Standard average soft tissue thickness of Mongolian children / by sex /

N=541, SD=Standard Deviation, Independent T-test. NS-not significant, *p<0.01 All measurements are reported in mm.

In this study, we determined the average mean and standard deviations of facial soft tissue thickness of a relatively healthy Mongolian child aged. 6-15 years (Tables 3 and 4) This is the first study of its kind in Mongolia, so we compared the results of foreign researchers’ measurements of children’s facial soft tissue thickness.

The lateral cephalograms have been shown to be a reliable method of assessing facial soft tissue, and many researchers have used this method in their research [23-25, 27, 30, 31]. Carl Stephen, a laboratory researcher at the University of Queensland, Australia International researchers estimate that there are about 1,290 studies of facial soft tissue thickness in children and 2,200 in adults [22]. Although there are many studies of facial soft tissue thickness on lateral cranial radiographs [23-25], we have clarified this because no such study has been conducted in Mongolia; The lateral cephalograms measurements were compared with American white and African black, black, European, and Asian populations. The measurement error of the study was estimated by the Dahlberg method [32].

Facial soft tissue thickness is affected by a person’s age, sex, ethnicity, lifestyle, and disease. The thickness of the facial soft tissue of a growing child varies. The study and identification of these can be used to diagnose abnormalities and distinguish between normal and abnormal growth and development; It is essential to develop a treatment plan and monitor its effectiveness [33]. The thickness of the soft tissue varies depending on the type and classification of the defect [34, 35].

According to foreign researchers, in most cases, the thickness of the soft tissue of the face of men was higher than that of women. According to Uysal, the thickness of the upper and lower lips and the thickness of the soft tissue of the anterior and inferior margins were statistically significant for the sexes [26]. Also, several studies evaluating the soft tissue thickness of different ethnic groups at different ages have shown that men outnumber women [27-29].

The thickness of the facial soft tissue of Mongolian children did not differ much by sex, but the Stomion part of a girl was thicker than that of a boy and the Menton part of a boy was thicker than that of a girl. (P <0.01) Nasion was 5.9 ± 0.9mm thinner than other parts. is similar to that of Japanese children [12, 16]; less than American [31] and European [21] children; thicker than black children [30].

The thickness of the upper (12.0 ± 1.8) and lower lip (10.7 ± 1.2) of Mongolian children is thinner than that of children of other nationalities. (P <0.01) The thickness of the soft tissue of the anterior margin is relatively thick, and the thickness of the soft tissue of the lower edge is less than that of Japanese children [23]. Facial soft tissue thickness increases at least 0.3-0.5mm per year on average in the Menton-menton area at the age of 9-12 years, and increases by a maximum of 1.2mm in the Stomion area (p <0.01). Stomion, Pogonion for female children aged 9-12 years in terms of growth trends; The Stomion and Upper lip thickness section of the male child is thicker than the other sections.

1. The profile and shape of the face is based in the database of the facial soft tissue thickness.
2. It differs in most respects from the usual average of children of other nationalities and ethnic groups.
3. It is believed that the increase in facial soft tissue thickness varies with age and sex, in addition to the individual characteristics of each child’s growth and development, and the stage of sexual maturation.
4. Soft tissue thickness database of Mongolian children aged 6-15 created and used as a diagnostic and treatment reference in the field of orthopedics, surgery, forensic medicine, anthropology, dermatology, and artificial intelligence base.

None.

The authors declared no conflict of interest.

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