The Association between Malocclusion and Dental Caries among Yemeni SchoolChildren in Sana’a City

Background: Even though few studies have documented malocclusion in different age groups in Yemen, the literature on the prevalence of malocclusion in mixed dentition is scarce or non-existent. Dental caries is another common condition that affects overall health. However, its link to malocclusion in mixed dentition is unknown in Yemen. Objectives: The purpose of this study was to determine the prevalence of malocclusion and its association with the experience of caries in schoolchildren between the ages of 7 and 12 in Sana’a, Yemen. Methods and subjects: A cross-sectional study was conducted on 1079 students (546 girls and 533 boys) between the ages of 7 and 12 years from government and private schools that were randomly selected in the city of Sana’a, Yemen. WHO criteria were used to assess the prevalence of dental caries (dmft) for deciduous teeth; and malocclusion was investigated by Angle’s classification. Results: This study showed that the overall prevalence of malocclusion among school children was 81.1%, in which Class I normal molar relationship was found only in 18.9% of school children, while Class I malocclusion involved the highest percentage of the sample 70.4%, followed by Class II relation 9.5%, and Class III involved only 1.1%. The prevalence of dental caries among school children in this study was very high, in which the proportions were 92.4% for primary teeth, and significantly increased with age. On the other hand, the study revealed positive association of malocclusion with dental caries (dmft) among school children, which was statistically significant (P<0.05). Conclusion: The prevalence of malocclusion in our study was consistent with other studies reported worldwide, which ranged between 19.6% and 90%. Moreover, the association between malocclusion and dental caries in primary dentition was of great significance as children with malocclusion were presented to experience higher caries than children without malocclusion.


Introduction
Researches and studies on dental health problems in Yemen are still modest and limited, despite the presence of studies that dealt with problems of tooth decay, gingivitis, causes of permanent tooth extraction and spread, formation of biofilms after introduction of fixed orthodontic devices and susceptibility to of Candida to antifungal drugs and the pattern of third molar impaction [1][2][3][4][5][6][7][8][9], but only one research deals with malocclusion [10] and this is the second study that deals with malocclusion and the first study that studies malocclusion and its relationship to dental caries. Malocclusion can be defined as an irregularity in the teeth or a malfunction of both arches outside of what is acceptable as normal. Malocclusion is thought to be a risk factor in the formation and progression of tooth decay [10,11].
Malocclusion is the most common oral problem, along with tooth decay, gum disease, and fluorosis [11]. According to international studies and the World Health Organization, major dental problems should be subjected to periodic epidemiological surveys; knowing the population's epidemiological situation is vital to planning and providing prevention and treatment services [10][11][12][13][14][15].
The causes of malocclusion can be genetic or environmental, and/ or a combination of both factors, along with various local factors such as negative oral habits, dental abnormalities, the shape of the teeth and the location of their growth, can cause the malocclusion [10][11][12][13][14][15]. The prevalence of malocclusion varies from country to country and between different age groups and nationalities [10][11][12][13][14][15]. Globally, epidemiological studies of malocclusion show the prevalence to be  [15][16][17]. Primary dental caries and premature loss are predisposing factors to occlusion and void anisotropy in mixed and permanent teeth [10, 16,17]. Dental caries is the most common oral disease in Yemen and around the world regardless of the fact that it can be prevented [6,8,18,19] because its etiology is complex and there are many unexplained interactions between confounding factors and unknown risk factors; it is the most prevalent oral health problem worldwide [6,10,18,19].
Even though one study has documented malocclusion in children groups in Yemen [10], the researches on the prevalence of malocclusion in mixed dentition is scarce or non-existent. Dental caries is another common condition that affects overall health. However, its link to malocclusion in mixed dentition is unknown in Yemen. The purpose of this study was to determine the prevalence of malocclusion and its association with the experience of caries in schoolchildren between the ages of 7 and 12 in Sana'a, Yemen.

Subjects and Methods
This descriptive cross-sectional study was conducted to measure the prevalence of malocclusion associated with dental caries among Yemeni school children in primary schools (government and private) in Sana'a, Yemen. A total of 1079 boys and girls aged 7-12 years from Sana'a schools were randomly selected and screened, and the schools are located in different areas of the city to avoid having children from the same area. The criteria for each assessment of malocclusion described by Angle, (1899) [20] divide the malocclusion into different categories based on the occlusal relationships of the first molar. Teeth affected by dental caries and their restoration/extraction as a result of dental caries were recorded using World Health Organization, (1997) [21]. Data were collected by one examiner who is the first researcher using the standard method [22]. The clinical examination for every child with a history and medical history was formed by a simple examination under sufficient light, sometimes if the natural light was insufficient, artificial light from a torch was used. All children were screened in a school room chosen by the school's principles. Children who were selected and refused to participate were replaced by new ones.
Before starting the study, ethical considerations were taken after the approval of the Faculty of Dentistry at Sana'a University, Yemen, for the study. The test was administered with permission from the relevant educational authorities. Permission was obtained from the District Education Office and the target school principals, after informed consent was obtained from the parents of the participating children.

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. Mean and standard deviation was used to describe the quantitative variables for the normally distributed data. 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 malocclusion rate was 81.1%, there was an association between malocclusion and the younger age group (7-9 years) of 84.2%, odds ratio=1.5 (CI=1.1-2), p=0.01. There was no significant association between malocclusion and sex or school type (Table 1). Class I malocclusion had the highest percentage of sample 70.4%, with 73.2% in age group 7-9 higher than age group 10-12 (67.8%) (P<0.05). Class II malocclusion was 9.5%, while Class III had the lowest incidence and was present in only 1.1% of the entire sample. According to age, there was a significant difference with Class II malocclusion (P<0.05). On the other hand, normal Class I occlusion was in 18.9% of the sample. It was found that 21.9% of the age group 10-12 years was greater than the age group 7-9 years (15.8%), and the age difference was significant (Table 2, Figure 1). The prevalence of caries in the deciduous teeth was present at 92.4% as shown in figure 2. There was a significant association between dmft (dental caries) and malocclusion with a rate of 82.1% positive caries in positive malocclusion with the associated odds ratio equal to 2.13 times, interval Confidence=1.30-3.48; P<0.05. There was also a significant association between missing primary teeth and malocclusion with a rate of 99.7% positive malocclusion with an associated odds ratio of 106.64 times, confidence interval=14.88-764.46; P<0.001 (Table 3, Figure 3).

Discussion
The current cross-sectional study was carried out to assess the prevalence of malocclusion and dental caries among 7-12 year-old children in Sana'a city, Yemen. Most studies [14][15][16][17][18][19] that evaluate the prevalence of malocclusions use samples that include various age groups. The present study covered an age group which orthodontic clinics are the most sought after due to the emergence of clinical situations that involve alterations in the arches and faces. This could be attributed to the normal sequence of eruption in 9-year olds as many deciduous teeth exfoliate at this age. Moreover, this is a   period of growth and development during which many professional interventions can be made, leading to numerous benefits for these individuals [10, 14,15]. Malocclusion in this study was present in 81.1% of the school children ( Table 1). The high rate of malocclusion in the current studies can be explained by the high prevalence of factors that lead to malocclusion among our tested children, including extra teeth, missing teeth, affected teeth, or abnormally shaped teeth. Ill-fitting dental fillings, crowns, appliances, fixings, or braces, as well as misalignment of jaw fractures after severe injury, are also known to cause malocclusion [10][11][12][13][14][15]. In addition to thumb sucking, tongue thrusting, pacifier use after the age of three, and prolonged use of the bottle [19]. Moreover, the lack of chewing stress during growth can cause overcrowding of the teeth. Children who chewed hard gum for two hours a day showed increased facial growth [21][22][23]. Animal experiments showed similar results. In an experiment with two groups of rock hyrax fed hard or soft copies of the same foods, animals fed more soft food had a narrower face and shorter jaw and thinner jaws than animals fed on solid food [24].
The results obtained in the present study proved that the prevalence of dental caries is high in Sana'a City, and significantly increases with age, in which the percentages of dmft was 92.4%, (Table 3, Figure  2). This result comes in agreement with many studies reported a higher prevalence of dental caries by Gandeh MB, et al. [39]; Al-Haddad KA [40]; Wyne AH, et al. [41]; and Al Agili DE, et al. [42]. Increased tooth decay in developing countries is due to a combination of factors, including eating carcinogenic foods, exposure to fluoride, socioeconomic status, race, health, age, access to oral health services and other lifestyle factors [43,44]. The association between caries and malocclusion between the study subjects was statistically significant and that was present in primary teeth (dmft) 82.1% (Table 3, Figure  3). This finding is consistent with the findings of Gabris K, et al. [18];    Mtaya M, et al. [14]; Shivakumar KM, et al. [15]; Singh A, et al. [19]; Buczkowska-Radlinska J, et al. [17]; and Baskaradoss KL, et al. [16] that demonstrated a positive association between caries prevalence and malocclusion. However, it differs with some other studies by Asahi K, et al. [45]; and Aamodt K, et al. [46], who did not report statistically significant association between caries and malocclusion.

Conclusion
The results of the current study showed that there is an increase in the prevalence of malocclusion among schoolchildren from 7 to 12 years old. The study showed that the prevalence of dental caries was very high in the deciduous teeth, and there was a significant association of the total dmft component with malocclusion (P<0.05). The results of this study provide the basic data for implementing preventive programs in schools in order to take immediate action and obtain more oral health awareness programs through early interception treatment to reduce factors that prevent the development of dental arch as well as structural jaw growth.