OCCLUSAL CHARACTERISTICS OF THE PRIMARY DENTITION AMONG A SAMPLE OF YEMENI PRE-SCHOOL CHILDREN

Objective: The occlusal features change dynamically in the growing children and any disruption in the complex craniofacial growth process may lead to malocclusion, which is a major concern for the pediatric community because of its effects on dental function and beauty, as well as on the child's psyche. The aim of the present study was to study the prevalence of different occlusal traits in the primary dentition of the randomly selected pre-school children from three to five years in the city of Sana’a, Yemen. Methods: The study includes 1106 pre-school children subjected to a dental examination performed in the school premise, using the Foster and Hamilton criteria for occlusal traits. As well as interand intra-calibration tests were conducted for assessing the degree of agreeability. Results: Results of the study showed that the Bilateral flush terminal molar relationship was found in 60%, bilateral mesial step in 27.9%, asymmetrical relationship in 8.5% and distal step in 3.5% of tested children. The Bilateral canine class I was detected in 62.8%, asymmetrical relationship (13.6%), class II (12.5%) and class III (11.1%). Normal over-jet (OJ) of 1-3 mm was identified in 39.2%, decreased OJ <1 mm (32.7%) and edge-to-edge (8.8%). Ideal over-bite (OB) of 1-50% was detected in 64.5% and increased OB of > 50% (19.7%). Conclusion: In conclusion theBilateral flush terminal molar, class I canine relationships, normal overjet (OJ) of 1-3mm were the most commonly found sagittal occlusal traits in the current study. Ideal over-bite (OB) of 1-50% were identified in more than half of the children.


INTRODUCTION
Occlusal traits in the primary dentition are known to have an important bearing on the occlusal relationships in the secondary dentition 1,2 . Malocclusion is ranked third worldwide in dental public health second only to dental caries and periodontal disease 3 . The assessment of the occlusal traits of primary dentition will aid in the prediction of certain malocclusions such as; crowding, cross-bites, and anterior open-bites. This will enable an enhanced and effective preventive and interceptive measures to be constructed at an individual as well as in a larger scale level, all of which would ultimately reduce the degree of malocclusion in the permanent dentition. Therefore, shorten the time taken and simplify the performance of comprehensive orthodontic treatment which can be reflected as a reduction in the psycho-social and monetary impact on the patient and patient's parents 3 . It is important to note that the difference in occlusal traits can be attributed to the differences in the criteria used to define them with differences in their interpretation 4,5,6. Numerous studies have been conducted on the occlusion in the primary dentitionin children of different age groups in different regions of the world 7 . However, by comparison, few studies have been published in the Arab region. By reviewing these studies, one can conclude that the prevalence of different occlusal traits in primary dentition varies between different age groups, populations, and ethnicities around the world 2,7 . As for Yemen, the only published study was directed towards the assessment of occlusal traits among the ISSN: 2456- 8058 26 CODEN (USA): UJPRA3 Yemeni adolescents using canine and incisor classifications 8 . However, no published study was found to reflect on the incidence of occlusal traits in the primary dentition of the Yemeni children. The objective of the current study is as follows: to assess the occlusion in sagittal, transverse and vertical planes namely: the terminal molar relations on the right and left side of the jaw, the primary canine relationship on the right and left side of the jaw, the over-jet (OJ) and over-bite (OB).

SUBJECTS AND METHODS
This was a cross-sectional study conducted in six of the ten randomly selected administrative regions in Amanat Al Asimah, Sana'a City, Yemen. The target population of the study was preschool children aged 3 to 5 years, who attended a randomly selected public and private kindergartens, during the 2018-2019 school time period based on data collected from the Ministry of Education, Sana'a City, Yemen. The sample size (n) required for this study was calculated to be 369 and this was through the utilization of the WHO formula for sample estimation which states that n = z 2 p(1-p)/e 2 Where "n" represents the sample size. "p" as the expected prevalence of malocclusion. "z" as the standard score of 1.96 (95% CI: confidence level). e = maximum tolerable error 5%. For the purpose of increasing the significance level of the findings of this study the sample size was increased from 369 to 1106 pre-schoolers. To calculate the sample, the spread (P) was adopted by 60% 3,9, 10 . In addition, a 1.5 (CF) correction factor was used to compensate the number of students who refused to participate in the study. The study sample (n=1106) was determined through a twostage sampling technique. In the first stage, a random sample was selected from several primary schools (public and private) from each of the six aforementioned provinces. It is followed by the second stage which involves random sampling of pupils from each of the aforementioned selected schools. The inclusion criteria: Healthy Yemeni children. 3-5 years with primary dentition. Pre-school children whose parents / guardians agree. (n=1106). The exclusion criteria: Those with a permanent first molar tooth erupting. Those who have missing teeth due to trauma, extraction, and tooth decay. Preschool children who have received interceptive and preventive orthodontic treatment. Prior to collecting data, medical ethical approval was obtained from the Ethics and Research Committee at the University of Sana'a, followed by approval of education offices in the different administrative district to conduct this study in the schools assigned to them in their respective areas 11,12,13 . Approval was obtained from school officials and parents of students who were randomly chosen through the school's mediator (principal or teacher) to explain the purposes of the study and the type of exam to be taken for their children 14, 15 . The child's permission was obtained before a dental examination. The examiner was trained and calibrated under the guidance of the supervisor at the Department of Pedodontics at the University of Sana'a to reduce the variability of the examiner during data collection. A total of 20 children were examined for both: the intra-examiner and inter-examiner reliability tests. The results were analysed statistically through the utilization of the Cohen's Kappa coefficient 16 . The overall Kappa co-efficient for the inter-examiner and intra-examiner reliability shows a high level of agreement scoring 0.868 and 0.877 respectively. The dental examination was carried out under natural daylight in the school premise. Disposable examination gloves and single use sterile mouth mirrors and explorer as well as sterile metallic mm rulers were made available for each child during the dental examination. Occlusion was assessed while each child was biting on his or her posterior teeth with the jaws in centric relation (maximal inter-cuspation). The criteria of Foster and Hamilton (1969) was used for defining the occlusion 11,12,13 . Occlusal norms were determined based on numerous studies found in the literature 17,18,19 . All of the examined students found to be suffering from malocclusion that would benefit from early interceptive paediatric or orthodontic dental treatment were referred to the paediatric dental clinic at the University of Sana'a, Faculty of Dentistry, to receive the required dental care.

Statistical analysis
The collected data was coded, inserted and analysed using IBM SPSS statistics for Windows, Version 21.0. Armonk, NY: IBM Corp, released 2012. The data were presented using tables, graphs, and pie charts. Basic standard descriptive statistics were calculated in the form of frequency and percentage to describe the qualitative variables. Pearson chi-square with Yate correction and Fisher tests were used to show the significance of the association between the outcome and its risk factors at a level of significance 0.05. Pvalue of less than 0.05 was considered as a statistically significant value. Odd ratio (OR) was calculated in addition to, the 95% confidence interval (CI).

RESULTS
In this study, a bilateral dental examination was performed on a total number of 1106 children aged three to five years old. Figure 1 illustrates that; the Bilateral flush terminal molar relationship was found in 60% (664 out of 1106) of the pre-schoolers. Followed by: bilateral mesial step (27.9%), asymmetrical relationship (8.5%) and distal step (3.5%). Present in 309, 94 and 39 out of the 1106, respectively.   Table 1 shows a significant correlation based on the Pearson's chi-square test between the different molar relationships distribution with the age and school type of the participants but no significant association was found with the gender of the study participants. Table 2 shows that the flush terminal was significantly associated with class I canine, normal OJ (of 1-3 mm sagittal overlap) and ideal OB (of 1-50% vertical overlap), where it was observed in 71.1%, 68.4% and 62.8%, correspondingly. The distal step molar relationship was most frequently seen in pre-schoolers with class II canine, increased OJ (of>3mm) and increased OB (of >50%), where 24.6%, 12.3% and 10.6% were affected, respectively. As for the mesial step molar relationship, it was found to be more commonly associated with class III canine (69.1%) and anterior reverse-bite (66.7%). The asymmetrical molar relationship was most frequently associated with the asymmetrical canine relationship and increased OJ of > 3mm and anterior open-bite, affecting 53.3%, 12.3% and 15.1%, in that order. The Bar chart illustrated in Figure 2 shows that the Bilateral canine class I was detected in 62.8% of the study sample. Ensued by: asymmetrical relationship, class II and class III. Which were detected in 13.6%, 12.5% and 11.1%, respectively. However, as shown in Table 3, no statistically significant affiliation between the distribution differences of the canine relationships with the age, gender, and school type of the study participants. The majority of the study sample ( Figure  3 and Table 4) possess normal OJ of 1-3 mm, which was identified in 39.2% (433 out of 1106) of the children followed by decreased OJ <1 mm (32.7%-362 out of 1106), increased OJ of>3 mm (16.9% -187 out of 1106), edge-to-edge (8.8% -97 out of 1106) and reverse-bite (2.4%-27 out of 1106). But no significant association was found between the prevalence of different OJ relationships with the age, gender and school type of the pre-school study participants.

DISCUSSION
In the current study, Figure 1 shows that the majority of the pre-schoolers (60%) demonstrate a bilateral flush terminal molar relationship followed by the bilateral mesial step ( 26 , who observed that the prevalence of flush terminal and mesial step was similar among their Chinese pre-schoolers.
As well as with Abu Alhaija and Qudeimat 27 , Chebet 28 and Baral et al. 29 who found out that mesial step was more commonly seen than the flush terminal molar relationship among their study participants. In the present study, a significant correlation was observed between the prevalence of different molar relationships and the age of the child as well as the type of their school. However, no significant association was observed between the occurrence of the molar relationship and gender (    Table 2 shows that the flush terminal was significantly associated with class I canine relationship, where it was observed in 71.1%. These findings disagree with the Iranian study conducted by Sahebalam et al., where class II canine occlusion seemed to have coincided with more than half of the flush terminal molar occlusions (62%) 31 . The asymmetrical molar relationship (Figure 1) was the third common molar relationship, seen in 8.5%, which was greater than the results seen among the Kenyan, Indian and Sudanese pre-schoolers 16,20,28 . But, lesser than the Jordanian, Nepalese and Chinese studies 26,27,29 . The distal step (Figure 1) was the least common type of molar relationship (3.5%), which was similar to the results seen among the Jordanian, and Saudi Arabian pre-schoolers 23,27 . Furthermore, the distal step molar relationship observed in this study was most frequently associated with class II canine relationship (Table 2). While, the mesial step among the study participants was more commonly associated with class III canine relationship ( Table 2). These results differ from those observed by Sahebalam et al. 31 , who discovered that class I canine relationship was largely associated with mesial step molars. The Bilateral canine class I relationship was the most prevalent canine relationship in the current study, observed in 62.8% of the participants (Figure 2