PREVALENCE OF MALOCCLUSION AMONG YEMENI CHILDREN OF PRIMARY SCHOOLS

Objective: Malocclusion is every difference in the arrangement of teeth beyond the standard of regular occlusion illustrated by anomalies within the dental arches. The purpose of this study was to measure prevalence of malocclusion between primary school children in Sana’a city Yemen. Methods: A cross sectional study was conducted on 1079 school children (546 girls and 533 boys), their age ranged from 7 to 12 years old from public and private schools selected randomly in Sana'a City, Yemen. The prevalence of malocclusion was investigated according to age, gender and school type based on Angle's classification. Results: The study showed that the overall prevalence of malocclusion among school children was 81.1%, in which Class I normal molar association was found only in 18.9% of school children, while Class I malocclusion included the highest percentage of the sample 70.4%, followed by Class II relation 9.5%, and Class III involved only 1.1%. The most prevalent malocclusion trait was spacing 35.7%, whereas the crowding was present in 30.0% of the sample. The deep bite was present in 10.1% followed by anterior crossbite 8.8%, midline diastema 8.6%, anterior open bite 4.5%, posterior crossbite 4.0%, and the least noted malocclusion trait was posterior open bite 0.4%. Conclusion: In conclusion, there was a high rate of malocclusion in school children and significantly increased with age, class I malocclusion was the most common followed by Class II malocclusion, while Class III was the rear. The most prevalent occlusal problem was spacing, followed by crowding. Thus, 7-12 year-olds can benefit from interceptive and preventive oral health procedures which may either entirely prevent or reduce the development of serious types of malocclusions afterward in their lives.


INTRODUCTION
Research and study of dental health problems in Yemen are still modest and limited, although there have been studies that have addressed the problems of tooth decay, gum infections, causes for extraction of permanent teeth and prevalence and pattern of third molar impaction in adults and children 1,2,3,4,5 but no research has touched upon malocclusion. Malocclusion is a problem of the oral cavity scattered around the world, from which the children and adults suffer, not less important than other oral problems. Although dental malocclusion is not a life-threatening condition 6 , the poor periodontal conditions 7 and impaired mastication 8 associated with it provoke the need to explore the prevalence of malocclusion in different age groups. Furthermore, it is one of the most common dental problems, together with dental caries, gingival disease and dental fluorosis 9 . It is considered as dental public health problem, its impact psychologically and functionally is great, and its prevalence among children is high 10 . In addition to that, malocclusion is thought to be a risk factor information and progression of dental caries. Since pediatric patients with malocclusion have challenged the ability to practice effective oral hygiene, this may predispose them to malocclusion 11 . Concerning premature loss of primary teeth, it has been previously stated that the premature loss of primary teeth can affect the normal eruption time of the permanent successors by either retarding or accelerating their emergence 12 . It is considered a predisposing factor for occlusal and space discrepancies in the mixed and permanent dentitions 13 . Consistent with the World Health Organization, the main dental problems should be subjected to regular epidemiological evaluations. Knowledge of a population's epidemiological condition is vital for planning and offering prevention and treatment services 14 . The understanding of the epidemiological status of different characters of malocclusion among the special population is essential for planning the need and provision for orthodontic service to improve the quality of life 15 . Dental malocclusion prevalence among school children have been reported in most countries of the world. There were few studies on the prevalence of malocclusion in Yemen, and only two studies were conducted in Sana'a City in 2014 by Al-Zubair and Ghandour 16 , and Al-Zubair and Al-Almulla 17 . It is clear to see the need to study prevalence of malocclusion in Yemeni school children during mixed dentition period to provide basic values for preventive measures and then to know and reduce the potential irregularities in the developing dental-facial complex in future. The importance of this study comes from the great effects of malocclusion defects on children's oral, systemic and psychological health.

SUBJECTS AND METHODS
This descriptive cross-sectional study was conducted to measure the prevalence of malocclusion among Yemeni school children of primary schools (Government and private) in Sana'a City, Yemen. A total of 1079 boys and girls aged between 7-12 years old from schools of Sana'a were randomly selected and examined, the schools are located in different regions of the city to avoid having children from the same area. The data collection was performed by one examiner; the researcher (Tharwa), by using the standard method 18 . The clinical examination for each child with dental and medical history was formed by simple inspection under adequate light, sometimes if the natural light was insufficient, artificial light from a torch was utilized. All children were examined in a room of the school selected by the principles of the school. Those children who were selected and refused to participate were excluded replaced with new one. Before starting the study, ethical considerations were taken after the approval of the study by the Faculty of Dentistry in Sana'a University, Yemen. The examination was conducted with permission from the concerned education authorities. Permission was obtained from the office of the region education and the principals of the targeted schools and after obtaining informed consent from parents of the participating children The examination assessed the period of dentition and analysis of occlusal data, by using a separate registration chart designed to record the personal data of the subjects (all information and clinical examination).

Statistical Analysis
The data were analyzed by SPSS program (IBM Corp. Released 2012. IBM SPSS Statistics for Windows, Version 21.0. Aromnk, NY: IBM Corp.) and presented by using tables. Percentage (%) was used to describe the qualitative variables. Chi-square with Yate correction and Fisher tests were used to show the significance of the association between the outcomes at the level of significance less than 0.05 (P).

RESULTS
The results in Table 2 indicate that the prevalence of total malocclusion among school children was 81.1%, and there was significant difference between malocclusion according to age group 7-9 years old (84.2%) and 10-12 years (78.1%). Also a similar prevalence of malocclusion was found in boys and girls, government schools, and private schools ( Table  2). The results in (Table 3) indicate that class I malocclusion has the highest proportion of the sample 70.4%, with 73.2% in the 7-9 age group higher than the 10-12 age group (67.8%) (P<0.05). The class II malocclusion was at 9.5%, while the class III had the lowest incidence and was only present in 1.1% of the entire sample.  21.9% were found for age group 10-12 years older more than that of age group 7-9 years (15.8%), also the age difference was significant. The most prevalent malocclusion trait was spacing 35.7%. According to age groups, the highest rate of spacing was found in 7-9 years old 42.0%, comparing to age group 10-12 years old 29.7% (X 2 =17.76, P<0.001), while non-significant difference of spacing malocclusion was found regarding gender and school type ( Table 4). The proportion of school children with dental crowding was 30.0%, with a non-significant difference that in age groups, gender and school type (P > 0.05) (  Regarding gender, no statistical significant difference (P > 0.05) was observed between boys and girls with respect to the prevalence of malocclusion (Table 2), coinciding with Das et al., 27 ; Souza et al., 28 ; Narayanan et al., 20 . According to age groups, the prevalence of malocclusion was more noticeable for the age group 7-9 years compared to the age group 10-12 years, with a statistical significant difference (P < 0.05). This finding is consistent with Morais et al., 23 . Variation in malocclusion can appear between age groups due to age and individual differences, or perhaps a shift from Class II malocclusion to the normal occlusion that occurs from the mesial movement of the first molars in the lower jaw where the second primary molars exfoliated 25 . The prevalence of normal occlusion was found low in the present study (18.9%) comparing with other studies by Alatrach et al., 29 (38.5%), Reddy et al., 22 (48.30%), Al-Zubair and Ghandour, 16  variation of results may be explained by the regional differences, age and sample size, or by the fact of considering normal occlusion as being Class I and maybe by the diversity of the used methodology 26 .
Furthermore, Class I malocclusion included the highest proportion of the sample 70.4% (Table 3). This finding resembles 32 who found that the most common malocclusion was Class I 70.4%.   26 (5.9%). In the present study, the most prevalent malocclusion trait was spacing 35.7% (Table 4). This result higher when compared to Al-Zubair and Al-Almulla 17 (25.8%). This large number of school children with spacing is due to the fact that most of them had a premature loss of teeth mostly the primary teeth losing. There was statistic significant difference between the two age groups, which was found higher for age group 7-9 years old 42.0%, compared to the 10-12 years old 29.7%. By comparing with other studies, this result is much higher than that found by Disha et al., 24 19 (52.6%). According to gender, a non-significant difference in crowding was observed (P>0.05) ( Table 5). This finding is in agreement with Brito et al., 14 , and in disagreement with Souza et al., 28 who found a significant difference between genders (P<0.05) in which the dental crowding in girls was higher than in boys. On the other hand, the results has shown that there is a higher prevalence of dental crowding for age group 7-9 years old than for age group 10-12 years old (Table 5). This result is in agreement with that found by Morais et al., 23 . This may be partially explained by the fact that some dental crowding may have, spontaneously, resolved. Mixed dentition crowding, known as temporary primary crowding, may resolve spontaneously during the stage of mixed dentition 35,36 .

CONCLUSION
There was a high rate of malocclusion in school children and significantly increased with age, class I malocclusion was the most common followed by Class II malocclusion, while Class III was the rear. The most prevalent occlusal problem was spacing, followed by crowding. This study could open the field of specific studies to determine the means for the proper identification, control, and guidance of the environmental factors that could affect the craniofacial structures, which would be the main target of the preventive programs. Thus, 7-12 year-olds can benefit from preventive and interceptive oral health measures, which may totally either prevent or lessen the development of severe forms of malocclusions later in their lives.

AUTHOR'S CONTRIBUTION
This research work is part of a Master's thesis. The candidate is the first author (TAA) to conduct clinical work and thesis. Corresponding author (HAA), second author (KAA) and third author (MAA) supervised the work, revised and edited the thesis draft and the manuscript.