Prevalence of Orthodontic Malocclusion in School Children in the North East of Slovenia: Retrospective Epidemiology Study

Background: Dental malocclusions exhibit the third-highest prevalence among oral pathologies. The occlusion is evaluated in primary, mixed and permanent dentition. Most orthodontic patients were treated in the early permanent dentition. Early detection of dental anomalies is important to prevent complications and can have short-term and long-term benets. The epidemiological data on the prevalence of malocclusion is an important determinant in planning appropriate levels of orthodontic services. Dentists have the responsibility to recognize, diagnose, and manage or refer to abnormalities. Data from researches showed that is the incidence of malocclusions from 11% to 93%. The study aim is to nd out, the prevalence and species of malocclusion of school children in 4 school years, how they are registered by general dentists. Results: The research was conducted in 4 consecutive school years on schoolchildren from 1. to 9. class. Dentists have registered the presence and type of malocclusion. They are made statistical data percentage of children with malocclusion and percentage of representation malocclusion and statistical difference between genders. The percentage of malocclusion was the lowest in the 1. class. The highest percentage of malocclusion was in 7. class. The most common types of malocclusion were deep bite, crowding cross bite and II class of Angle's. The upper lateral incisive was the most common missing tooth (aplasia). Conclusion: The high percentage of malocclusion at the end of school (15-year-old) about 50% and the low number of children in orthodontic therapy.

A systematic and well-organized dental care program for any target population in a community requires some basic information, such as the prevalence of the condition. (16) The epidemiological data on the prevalence of malocclusion is an important determinant in planning appropriate levels of orthodontic services. (17) Dentists have the responsibility to recognize, diagnose, and manage or refer abnormalities. (18) The source of data is systematic examination of school children. Their examinations do dentists in children and youth dentistry. They are rst stairs upon detection of malocclusions and referral to an orthodontist. It is important, that recognize early some malocclusions and refer to orthodontist for therapy. But sometimes is noted and refer malocclusion, which is not for orthodontic therapy. They may be temporarily condition in physiological tooth exchange. Therefore can be di cult access to orthodontic therapy for those who really need it. Children are the ideal population for prevention, development monitoring, determining the effectiveness of prevention programs and it can modi cation/ update preventive program based on epidemiological studies.
Data of researches showed, that is the incidence of malocclusions from 11-93% (19,20) and these variations are di cult to explain. (17). The prevalence of malocclusions in primary dentition in Brazilian children was 75,8%. (21). Gelgor was in your study found, that only 10% of adolescents had correct occlusion. (22) How is it in the area of Murska Sobota, Slovenia? In Slovenia, the preventive program has its legal basis. (23) The Health center in the city Murska Sobota, which is in the north east of Slovenia, takes care of the implementation of preventive examinations for 11 elementary schools and 5 branch schools. The health center has been doing regular systematic examinations of elementary school pupils for more decades.
Unfortunately, in 2020 due to COVID-19 pandemic, could not inspect all pupils. Dentists for children and youth at a systematic examination identify the anomaly and, if necessary, refer it to an orthodontist. They are a key factor in identifying malocclusions and referral to a specialist, therefore, their knowledge and involvement are essential.
The aim of the study is to nd out, the prevalence and species of malocclusion of school children in 4 school years, how they are registered by general dentists.

Methods
The research was conducted in 4 consecutive school years, retrospective epidemiology study, beginning with 2015/16 (to 2018/19). The school year in Slovenia starts always in September and ends in June the following year. Students start attending school with 6 years (1st class) and end their primary education with approximately 15 years (9th class). In the 6th class, they are 12 years old. Data was obtained after systematic examinations of students, which was done once a year. Systematic examinations were carried out by 4 dentists in their ordinations. Pupils were examined on the chair with a dental mirror, a sond, a puster, and the light. Anomalies were registered by Angle's classi cation (II and III class), edge-to-edge (tete-a-tete), deep bite, open bite, crossbite, aplasia, crowding (tight condition), ectopic outgrowth and dens supernumerary. The condition was noted in the following form and includes the following data: the type of anomaly and is it pupils in orthodontic therapy, pupil's name, pupil's surname, school, class, date, and signature of the dentist. Children with systematic diseases, which may affect the occurrence of anomalies, did not register. Children in orthodontic therapy were registered »in orthodontic therapy«. Their anomalies were not registered. Anomalies, which were registered: The completed form was sent to a specialist in paediatric dentistry, who did the data processing. Statistical data are  The highest percentage of anomalies was in the 7th class (13-year-old). The lowest percentage of anomalies was in 1st class (6-year-old). The most common occlusal anomalies were deep bite (21.7%), crossbite (20%) and crowding (14.7%) of registered anomalies (Table 1).
In the population were present 12 children with aplasia. 1 child was missing teeth 15, 35, 12 and 22. 5 children were missing teeth 12 and 22. 2 children were missing teeth 35 and 45. 1 child was missing the tooth 12. 1 child was missing the tooth 22. 1 child was missing the tooth 31. 1 child was missing the tooth 42.
In the population were 29 children with the Angle's III class. Table 2 The number of children, who were in orthodontic therapy. The children have been treated since 4th class (10-year-old). The most number treated children are in 8th class (14 year-old) ( Table 2). Chi-Square test showed that percentage of girls with malocclusions was higher than that of boys (Table 3).
School year 2016/17 In the population were 19 children with the Angle's III class. Table 5 The number of children, who were in orthodontic therapy.  Table 5). Chi-Square test showed that was both genders equally represented (Table 6).
School year 2017/18 The highest percentage of anomalies was in the 7th class (13-year-old). The lowest percentage of anomalies was in 1st class (6-year-old). The most common occlusal anomalies were II class-Angle's (29%), deep bite (21.8%) and crowding (14.2%) of registered anomalies ( In the population were 54 children with the Angle's III class. Table 8 The number of children, who were in orthodontic therapy. The children have been treated since the 5th class (11-year-old). The most number treated children are in 9th class (15-year-old) ( Table 8). Chi-Square test showed that percentage of boys with malocclusions was higher than that of girls (Table 9).
School year 2018/19 The highest percentage of anomalies was in the 3rd class (9-year-old). The lowest percentage of anomalies was in 1st class (6-year-old). The most common occlusal anomalies were II class-Angle's (30.4%), deep bite (22.3%) and crowding (16.9%) of registered anomalies (Table 10) In the population were present 16 children with aplasia. 7 children were missing teeth 12 and 22. 1 child was missing the tooth 31. 1 child was missing the tooth 41. 2 children was missing the tooth 12. 2 children was missing the tooth 22. 1 child were missing teeth 22 and 42. 1 child was missing the tooth 15. 1 child was missing the tooth 45.
In the population were 43 children with the Angle's III class. Table 11 The number of children, who were in orthodontic therapy. The children have been treated since the 5th class (11-year-old). The most number treated children are in the 7th class (13-year-old) ( Table 11). Chi-Square test showed that percentage of boys with malocclusions was higher than that of girls (Table 12).

Discussion
The highest percentage of anomalies was at the age of 13. The lowest percentage of anomalies was at the age of 6. The most common anomalies were deep bite, cross bite, crowding and II class of Angle's. The most commonly missing teeth (aplasia) were 12 and 22 (together or separately), 35 and 45 (together or separately). Orthodontic therapy started at the age of 10/ 11. The most number treated children with orthodontic therapy were at the age of 15. Chi-Square test showed that was statistically difference at two groups-boys had more anomalies.
The weakness of the study was that not used orthodontistic measures. But this was not the aim. It was not known how many children were directed to ortodontists. The strengt of the study is that the study lasted four years and was determined the prevalence and variants of orthhodontic anomalies, as found by general dentists. They had the obligation to recognize the anomaly and to direct to orthodontist. The study can illustrate the uctuation of orthodontic anomalies over 9 years, the years when the greatest changes in growth and development are present. In the study was found, that had cases with the aplasias and that are the most commonly missing teeth upper lateral incisive and lower second premolar. If several anomalies were to be attributed to a transitional phase resulting in physiological exchange (in the early mixed dentition), there was a big disparity between percentages of anomalies and numbers of children in orthodontic therapy. Especially if early orthodontic treatment would be bene cial and desirable especially to enhance skeletal and dental discrepancies and correct habits, dysfunction and malocclusion in their early stages. (24) Many studies were published to describe the prevalence and types of malocclusion, when examining a certain population, it is di cult to compare (varying methods and indexes to assess occlusal relationships). (25) The result in the study showed a higher percent of malocclusion, than Bandaru's study. (26) The percent of hypodontia in that study is lower than in Kazanci's study. (27) To clarify the need for orthodontic treatment and planning service, it would be good to add orthodontic ndings. Then we would more likely get a more accurate answer to what it is a small number of children with orthodontic therapy. The monitoring same children over the years could be a good source of information on the development of occlusion (maybe an idea for the next study).

Conclusion
There was the lowest percentage of malocclusion in deciduous dentition.
The high percentage of malocclusion at the end of school (15-year-old) about 50%.
The low number of children with ortodontic therapy is 15-years-old.
Systematic examinations are a good source of prevalence information and start point for further planning.
A preventive program is needed to update to reduce the high prevalence of malocclusion.

Declarations Ethics approval and consent to participate
The study used the data from systematic examinations. The parents/ legal guardians of the students signed a statement that the students are participating in the implementation of the program. Written