PREVALENCE OF PREMATURE LOSS OF PRIMARY TEETH AT THE AGE OF 6-10 YEARS IN SANA'A CITY, YEMEN

Background and Objectives: Primary teeth and the integrity of the primary teeth are very important for the normal growth and progress of the occlusal relationships and the dentofacial structures. Premature loss of the primary teeth may lead to the loss of the arch length needed for the eruption of permanent teeth and thus lead to rotation, crowding, and impaction of permanent teeth. This study aimed to determine the prevalence of premature loss of primary teeth among children aged 6-10 years in Sana'a city, Yemen. Materials and methods: This observational cross-sectional study included 1091 children, aged 6-10 years. An experienced examiner the first author carried out all clinical examinations under natural light. Data were collected including age and missing teeth. Results: The results showed that 26% of the sample suffered premature loss of primary teeth with no significant difference between the sexes (P> 0.05). There was low in prevalence of premature loss of primary teeth in 10 years (17.7%), while the rate raised to 29.7%, 31.6%, and 31.7% in 6,7 and 9 years respectively. When considering the number of teeth, the prevalence of one premature loss was 10.8%, followed by two premature losses (9.8%), while the loss rate of 3 or more was5.4%. Considering dental arch 61.8% of loss was Mandible loss, while the loss in Maxilla was 38.1% only. The most common missing tooth is the first lower right primary molar (17%). Conclusion: The prevalence of premature loss in current study is similar to that of developing countries, the rate was low at 10 years for children, while the rate increased at 6,7 and 9 years; most of the loss was in the lower jaw and the most common missing tooth was the right lower primary molar. This result determines the importance of increasing awareness of this problem and focusing on the need for more preventive efforts to maintain healthy and natural teeth that improve the chewing function and aesthetic appearance of children and the entire population.


INTRODUCTION
Dental research is still limited in studying dental problems in Yemen, however some recent studies have been conducted that discussed the prevalence of malocclusion, the causes of permanent tooth extraction in general dental practices, the spread of the retromolar canal, and the prevalence and causes of traumatic dental injuries 1-4 . The primary teeth and the integrity of the primary teeth are very important for the normal growth and progress of the occlusal relationships and dentofacial structures. Preserving the primary teeth until they are naturally exfoliated is one of the most important goals of pediatric dentistry 5 . An early or premature loss is known as the loss of a primary tooth before the time of natural exfoliation 5, 6 . Early loss of primary teeth is a public health problem. A tooth is lost prematurely if it is lost from a dental arch within a year before the normal age of exfoliation 7 . There are local and systemic factors that cause early loss of primary teeth. Local factors include tooth decay, which is the most common cause, inadequate nutrition, bad oral health, trauma, periodontal disease and premature root ISSN: 2456-8058 43 CODEN (USA): UJPRA3 resorption 8- 10 . There are a number of systemic diseases such as diabetes, phosphate deficiency, leukemia, hyperthyroidism, etc., whose effects on the oral cavity may make the teeth subject to exfoliation 11 . It is generally accepted that premature loss of deciduous teeth is associated with malocclusion of permanent dentations, such as tooth rotation, extrusion of antagonist teeth, dental crowding, development of habits, and disorders of craniofacial development, especially post-dental impaction and reduction of the length of the dental arch 12-14 . Early loss of the primary teeth leads to early or late eruption of successor teeth 10 .
The reason for choosing this topic is to determine the prevalence of early loss of primary teeth in Yemen, as this is of importance in preventive treatment planning and shows the extent of the need to spread knowledge of such a problem between the medical community and society in general.

SUBJECTS AND METHODS Study Design:
A cross sectional study was conducted. Study Population: The target population was students of both genders, aged 6 to 10 years, chosen from public and private primary schools that are located in the five districts.
All children should match the study inclusions criteria a) 6 to10 years old, b) a tooth was considered to be prematurely lost if it was missing from the dental arch one year before its natural age of exfoliation 15 , and c) The study subjects provided informed consent from their parents and presented for examination on the day of screening. However, the exclusions criteria included: a) Non-Yemeni children and b) medically compromised children.
Sample size: The sample size was calculated using EPI version 7, based on the following assumptions: a) The total number of students in the five Sana'a City districts is 101,590 according to the Ministry of Education; b) The previous recurrence of early loss of primary teeth is estimated to be approximately 51%, with a 99.9% confidence level and with a margin error of 0.01. From previous assumptions, 1091 participants are needed to give significant results out of the total population. Study area and sampling type: Multistage sampling method which the first Stage: from the ten districts we chosen randomly five districts: from the south Alsabein district, from the north Al-Thwarh district, from the west Azal district and Al-wahda; and from the middle the Old Sana'a district. The second stage: In each district, we considered that all private and public schools are included in the study, then we randomly selected sixteen public schools and ten private schools which represent nearly 10% of total number of schools according to Education, 2018. The Third stage: In all randomly selected school, we considered that all the classes of students aged from 6 to10 years old are included in the study. Then we randomly selected one class from each level. Finally, selection from the selected classes was systemically random; so that we can reach the sample size target.

Data collection and clinical examination:
An experienced examiner the first author performed all clinical examinations under natural light. Data including age and missing tooth was collected. Ethical consideration: The study was approved by the research ethics committee of Faculty of Dentistry, University of Sana'a. Statistical analysis: Data were analyzed statistically using SPSS 21. Data were presented using tables. The percentage (%) was used to describe the qualitative variables. Pearson's Chi-Square test was used to show the significance of the association between outcomes at a significance level less than 0.05 (P).

RESULTS
The result revealed that of the 1091 children included in this study group, 284 (26%) had a premature loss of their primary teeth (Table 1). Both males and females had roughly the same prevalence: 26.2% and 25.8%, respectively. There was a significant (p<0.05) decrease in the prevalence of premature loss of primary teeth at 10 years (17.7%), while the rate increased nonsignificantly to 29.7%, 31.6%, and 31.7% in children aged 6, 7 and 9 years, respectively ( Table 2). The results showed that a total of 543 primary teeth were lost prematurely. The most commonly lost tooth was 84 (mandibular right first primary molar) with significant rate (17%) of the total (p<0.05), followed  Table 3). When considering the number of teeth, the prevalence of one premature loss was 10.8%, followed by two premature loss (9.8%), while 3 or more loss was 5.4% and the variation was not statistically significant (Table 4).  Considering the dental arch a significant rate equal to 30.8% of the loss was the mandible (p <0.05), while loss in Maxilla was 19% only (Table 5). Table 6 shows the distribution of premature loss according to dental quadrant among male and female children aged 6-10 years. The result showed that the mandibular right side had the highest incidence of the early loss (15.7%), followed by the incidence of early loss on the mandibular left side (15.1%), then the incidence of early loss on the maxillary right side was 10.3% and the incidence of early loss on the maxilla left was 8.7%, and the differences were statistically nonsignificant.

DISCUSSION
Premature loss of primary teeth is the most common local factor that leads to malocclusion. Many practitioners prefer to extract the primary teeth rather than treat them because it is often complicated 16 . On the other hand, most parents believe that it is not necessary to treat the primary teeth because they will be replaced in any way 16 . The harmony of the permanent teeth interferes with the premature loss of the primary tooth and the main effect of this loss is the congestion caused by the migration of the adjacent teeth 13,17 . Knowledge of the pattern and causes of tooth extraction will increase the knowledge of the dental practitioner in order to provide better information about the prevalence of dental disease, availability of dental care, and behaviors towards tooth mortality [18][19][20] 22 . Compared to other studies conducted in Saudi Arabia, Yemen and Denmark, early loss of primary teeth was (51%), (40.5%) and (47.3%) respectively and it is higher than this study 5,23, 24 . This difference may be due to the higher rate of decaying deciduous teeth. In general, the increase in the rate of early loss of primary teeth may be a result of parents and dentists believing that prevention and treatment of a primary tooth is unnecessary because the teeth will eventually be extracted. Some socio-demographic variables in this study showed that there was no statistically significant difference in premature loss of primary teeth between boys and girls. This result was similar to previous studies 15, [24][25][26] . This indicates that premature loss is due to poor oral hygiene, not related to children sex.
Comparison of a study conducted in Brazil by Almeida-Heilborn et al., 10 , there was a significant difference between the sexes, with premature loss being more in males than in females. This may be a result of a prolonged period of feeding male infants due to a preference for sons which could be a causative factor for the high incidence of decay-filled (dft) scores among male individuals leading to increased loss of primary molars in a male individual as confirmed by Saravanan et al., 27 . There was a decrease in the prevalence of premature loss of primary teeth at 10 years (17.7%), while the rate increased to 29.7%, 31.6%, and 31.7% in children aged 6, 7 and 9 years, respectively ( Table 2) which confirms the result reported by previous studies 6, 9,16 . In this study the teeth more frequently lost was 84 (the right lower molar) with (17%), followed by 74 (the lower left primary molar) with (16%), which was consistent with studies conducted by many researchers in the developing countries 6,15,16,26,28 . These findings could be a result of the chronological age of the first and second primary molar eruption. Because the first primary molars erupt early and stay in the oral environment for a longer period. These teeth are more prone to tooth decay. Moreover, dentists usually prefer to preserve the second primary molar to prevent space loss during the eruption of the first permanent molar. This explains why the first primary molars are more commonly extracted compared to the second primary molar, which leads to repeated early loss of the primary first molars 29 . The colonization of mutant streptococci is the main cause of early loss of primary molars. Increase of the mutant streptococcus colony towards primary molars due to anatomy of the occlusal fissured surface in nature and the proximal concave surface 30 . Compared to the study carried out in Romania by Andronic 31 , the tooth most affected by premature loss was the second primary molar of the mandible. This difference may be the result that each group has its own characteristics depending on the region in which you live and the health education. In this study, premature loss of only one tooth constituted the highest percentage of the total study group agreed upon with a study conducted by Al-Asadi 32 . This shows that preserving the natural teeth throughout the life of the children, either by preventing dental diseases or providing treatment for them, was the main goal of the children's clinic. In this study, the mandibular arch had more premature loss of the primary teeth than the upper jaw, which is similar to previous studies conducted in developing countries 6,15,22,28,31 . The increased rate of premature loss of primary teeth in the mandibular arch may be due to food packaging and plaque accumulation compared to the abundance of saliva and its anticarious effect on the maxillary molar teeth 16 .
The current study showed that the greater loss of primary teeth in the right quadrant of both jaws than in the left quadrant is consistent with other studies conducted by Ahmed et al., 15 and Ayachandar et al., 26 .
Due to the reduced level of cleaning and chewing powers, this leads to plaque accumulation on the right side, as emphasized by Lotto 33 and Park et al., 34 .

CONCLUSION
The prevalence of premature loss is similar or roughly lower the rate in developing countries, the rate was low in 10 years children, while the rate raised in 6,7, and 9 years; and most of the loss in dental arch was in mandible and the most common missing tooth was the right lower first primary molar. This result determines the importance of raising awareness about this problem and focusing on the need for more preventive efforts to maintain healthy and natural teeth that improve the chewing function and aesthetic appearance of children and the entire population.

AUTHOR'S CONTRIBUTION
This research work is part of a Master's thesis. The candidate is Kadija Ahmed Omer Bamashmoos to conduct clinical, field works and thesis. Corresponding author (HAA), second author (AHA), and the rest of the authors supervised the work, revised and edited the thesis draft and the manuscript.

ACKNOWLEDGMENTS
Authors acknowledge the financial support of Sana'a University, and Alhasani clinic and Dental Center in IBB City, Yemen.