Dento-Skeletal Abnormalities in School-aged Children in Iran: A Cross-Sectional Study

Aim : The aim of this study was to evaluate skeleto-dental abnormalities in 9-11-year-old school children, in

Dento-skeletal abnormalities can affect speech and mastication efficacy. Bruxism, dental trauma, and dental caries are significantly more prevalent in skeletal deformity cases compared to normal cases [9][10][11][12] . Additionally, they may negatively impact on the health of young patients by leading to airway obstructions that contribute to sleep apnea, disturbing gastric pH, and affecting immune function.
Dento-skeletal abnormalities can adversely impact the psychological, emotional, and overall well-being and quality of life in children 13 . Therefore, planning the orthodontic treatment requires understanding the patient's baseline demographics and the prevalence of different skeleto-dental abnormalities among the population.
Thilander et al. evaluated orthodontic treatment needs in children 5-17 years of age and showed the 88% of children had some type of abnormality, and 20% of them greatly needed orthodontic treatments, in Colombia 14 . Keski-Nisula et al. estimated that the prevalence of malocclusion in Finland was 68%-93% depending on the values of unacceptable parameters used 15 . Bittencourt showed the 85% of 6-10-year-old children had some sort of altered occlusion and 53% of them needed preventive orthodontic treatments 16  If preventative dento-skeletal abnormalities are diagnosed, and treated early, their progression thus may be inhibited at an age early, leading to a decrease in the need of extensive challenging, costly treatments. The goal of this study was to evaluate dentoskeletal abnormalities by determining the sagittal relationship, vertical relationship, facial form, and significant asymmetry in school-aged children in Tehran, Iran.

Materials and Methods
Sample size calculation: The target population of the present study was Iranian children in mixed dentition before a growth spurt students in the fourth and fifth grades of elementary school in Tehran, Iran, between the ages of 9-11 years (10 years ± 8months) were selected as the study population.
To have a representative sample, cluster random sampling was applied. In each district, one boys' school and one girls' school were selected from a list of all schools in the district and in each school, students in grades four and five were selected. In 19 districts, a total of 38 schools were selected, and out of 1585 subjects, the data of 1429 children were collected (response rate = 90%).
Participation was voluntary and informed consent was obtained from the participants' parents or legal guardians prior to conducting the study. The study was approved by the ethical committee of the school of dentistry, Tehran University of Medical Sciences (Ethical approval number: IR.TUMS.REC.1394.2003).

Study sample:
The examiners were four orthodontists calibrated previously during the examination on 25 students by a professor of orthodontics (Kappa=0.95). Examinations were carried out in schools. A brief questionnaire including background information and a written anonymous consent form was given to the students to deliver to their parents to be completed and signed for participation in the study and further clinical examination. Clinical examinations included the most important skeletal indices described below.

Frontal view evaluation:
Facial Form: The facial form was recorded with facial index. It is an expression of the ratio between the facial height and the bi-zygomatic facial width. It is used in anthropometry to classify as Euryprosopic (Broad facial form) that is whom transversely wider, Mesoprosopic (Average facial form) that is the average and, Leptoprosopic (Narrow facial form) that is whom vertically relatively tall (figure 1) 21 .    Statistical analysis: Data were analyzed by SPSS version 20 (IBM, Chicago, USA). The Chisquare test was used to compare frequency between subgroups. P-values less than 0.05 were considered significant. Sagittal and vertical jaw relationship, facial form, and asymmetry were evaluated using binary logistic regression analysis.
The epidemiological information in percentage values on the prevalence of individuals with different facial form, discrepancies in sagittal and vertical plane and individuals with significant asymmetry was categorized.
According to the sagittal skeletal relationship, the most prevalent type was convex (63%) that present the skeletal Cl II jaw relationship, followed by straight (32.9%) and concave (4.1%). The straight profile is more prevalent (p<0.0001) in girls (38.8%) than boys (27.1%). The distribution of different types of sagittal skeletal relationship among different demographic features is given in Table 1. Results are weighted according to population of each district and boys/girl's ratio.
In the vertical skeletal relationship, 73.9% of the children had a normal vertical relationship that was more prevalent (p<0.0001) in boys than the girls. 26.1% had some kind of altered relationship, so that, 18.4 % had a long face pattern and 7.8% had a short face pattern. The prevalence of normal face was decreased as the age increased. The distribution of different type of vertical skeletal relationship among different demographic features is given in Table  2. Results are weighted according to population of each district and boys/girl's ratio.
Regarding the facial form in frontal view, the most prevalent was average (79.3%) followed by narrow (14%) and broad (6.7%). The prevalence of average facial form in boys was lower (p=0.27) in boys (78.7%) than girls (79.9%). (Table 3). This study evaluated the significant asymmetry in vertical and horizontal direction but to summarize the vast amount of data we reported the asymmetry in general. Prevalence of asymmetry was 15.2%. As can be seen in Table 4 asymmetry was more prevalent (p=0.016) in boys (17.1%) than in girls (13.2%). Results are weighted according to population of each district and boys/girl's ratio.

Discussion
Dento-skeletal abnormality is endemic and widespread throughout the world after dental caries and periodontal diseases and it is a significant public health burden on children. This demonstrates the great magnitude of the challenge that pediatric dentistry and orthodontics, in particular, need to confront. 23 This study reports the prevalence of skeletal relationship in the sagittal, vertical, and transverse planes among 9-11-year-old school children.
In this study, we evaluated the sagittal skeletal relationship by a careful examination of the soft tissue of facial profile that yields the same information, though in less detailed for the underlying skeletal relationship. This was done with assessing the relationship between two lines, one dropped from the bridge of the nose to the base of the upper lip, and a second one extending from the point down to the chin that indicate the profile convexity and concavity. Profile convexity or concavity results from a disproportion in the size of the jaws so that a convex profile indicates a Class II jaw relationship and a concave profile indicates a Class III relationship 6 . The above method has been introduced by Proffit WR and has been used previously to assess the sagittal skeletal relationship 5,22 .
The results showed that more than 60% of the 9-11 years old Iranian children had a convex profile, which was more prevalent in the boys than the girls. In contrast, the straight profile was more prevalent in girls than the boys. This may be related to the mandibular horizontal growth during the growth spurt and is more pronounced in girls during these years. Eslamipour et al, reported that the Class II skeletal relationship was the most prevalent (51.5%) among the patients who need orthognathic surgery 19 .
Different studies found similar variations in the occurrences of skeletal jaw relationships with respect to ethnicity. Jones found that the most common skeletal relationship among Saudi orthodontic patients was Class I followed by class II and Class III 24 . Al-Jundi and Riba showed the majority of Saudi Arabian patients were skeletal Class I followed by Class II and Class III 25 . Farawana found the Class I skeletal relationship as the most predominant in the Iraqi population, followed by Class II and Class III 23 . Zhou reported Class I jaw relationship as the most common relationships among the Chinese population followed by Class III and Class II 26 . Halwai showed the most common skeletal jaw relationship was skeletal Class II followed by Cl I and Cl III in Midwestern Nepal 13 .
Many studies described a variable prevalence of skeletal jaw relationships among Iranian children, all reporting the lowest level for skeletal Class III. The prevalence of dental malocclusion also reported by Borzabadi-Farahani and Akbari in Iranian children that they showed the most prevalent malocclusion was Cl I followed by Cl II, and the lowest was Cl III, although, the most prevalent malocclusion among the patients in need of orthognathic surgery was the Cl III malocclusion (45.6%) 18,19,20,27  showed the prevalence of facial form and asymmetry was significantly different in different gender, so that, the prevalence of broad facial form and asymmetry were more prevalent in boys than the girls.
The prevalence of average facial form in our study was 79.3%, narrow facial form was 14%, and the broad facial form was 6.7%. This study evaluated the significant asymmetry in vertical and horizontal direction. To summarize the high variant data, we reported the asymmetry in general. Of all children, 15.2% had degrees of asymmetry in their face.
Anistoroaei et al concluded that facial asymmetry was present in 4.7% of patients, they also conducted that a significant correlation was evidenced between facial asymmetry and type of malocclusion, age, and type of dentition 31 .
However, Ferrario showed that no significant gender-or age-related differences were found for both metric and percentage indices of individual asymmetry 32 . Similar findings were reported by Farkas for adult males and females and by Burke for children aged 7-20 years 33 . Conversely, in a recent 3D study, the nose was more asymmetric in boys aged 9 years than in girls of corresponding age, although, mandibular asymmetry was greater in 6-year old boys than in girls of comparable age, no gender differences were observed in older individuals 34 . Studies conducted by Proffit and Sarver assessing facial asymmetries in orthodontic patients clinically found a prevalence of ranging 12-37% in the US, 23% in Belgium, and 21% in Hong Kong 35 . In Brazil, Boeck assessed the prevalence of the skeletal abnormalities. Their findings revealed a prevalence of 32% of asymmetry in their population 36 . Although both the methods of assessment and the definitions of malocclusions vary in different studies, and their findings should be compared with caution, the present results do not seem to significantly differ from those reported earlier.
The results obtained in this study revealed that the prevalence of dento-skeletal abnormalities was high and the majority of the Iranian school aged children, 9-11 years, have at least one dento-skeletal abnormality, even though it is commonly preventable.