The present study has been performed to determine the dental caries prevalence, Decayed, Missing, and Filled Teeth (dmft and DMFT indexes) and the associated factors among 9 - 11 years old children. In the present study, the prevalence of permanent and permanent dental caries was 39.73% and 67.72% in students, respectively. The results of a 2015 Kumar study of Indian students showed that 47 % of them had tooth caries [18]. The results of a study by Zhang on Chinese students also showed that the prevalence of dental caries was 40%[19]. The results of a study on your children in Ethiopia showed that 36.3 % had caries[4].
The results of present study indicated that 90% of students use the toothbrush, 25% mouthwash, and 18% dental floss. In study by Mohamadkhah, tooth brushing, flossing, and use of mouthwash have been reported as 69 %, 34 %, and 69%, respectively[20]. Also, the study by Babaei indicated that 59.5% of students brush their teeth daily [21]. In the study by Halboub, the frequency of tooth brushing (less than twice per day) was reported as 24%[22]. Considering the discrepancy of the age group across different studies, the different findings seem to be normal. Furthermore, since sometimes flossing can cause the incidence of pain, gum bleeding, and discomfort, the person is discouraged to floss or to care for oral and dental health. Lack of proper knowledge about flossing especially in the regions in which food residual may remain could be a reason for the low percentage of flossing.
In the present study, the rate of decayed, missing and filled teeth was the highest in the permanent teeth of 11 years old and in the primary teeth of 9 years old. Overall, the dmft and DMFT indices showed the highest values at 9 and 11 years, respectively. It seems that since the age of 9 years old, children have more primary teeth and the dmft index in this group is more likely than other age groups. Also in the age group of 11 years old, since children have more permanent teeth, the DMFT index is more likely than other age groups.
Based on the logistic regression results, in this study the girls had a higher rate of tooth decayed and repair compared to boys, and had overall a higher DMFT; this index was likely to be twice as large in girls than in boys. The results of Amirabadi and Nag studies, in line with the results of the present study, showed that girls had a higher rate of caries and repair than boys and overall DMFT index[23, 24]. The results of the study by Shaffer showed that girls in comparison to boys have 1.5 times fewer damaged teeth, and the DMFT of boys is larger than that of girls' [25]. This incongruence in the results of the studies can be due to the different age of the target groups or the method of knowledge acquisition by students regarding oral and dental health. Furthermore, physiological and behavioral differences in girls and boys, earlier growth of teeth in girls, and the high percentage of girls at home causing more consumption of sweets can justify the higher DMFT in girls[26].
In the present study, the rate of decayed, missing teeth, and DMFT index were higher in students living in villages as compared to city-dweller students. Furthermore, the rate of filled teeth was higher in the urban regions, while the rate of missing and decayed teeth, as well as dmft index, were higher in the rural region. In that study by Babaei, the place of residence of children, in terms of living in a city or village, had a significant relationship with the rate of dental decayed [8]. The reason of these discrepancies can be different access to dental care services, lower priority of oral and dental healthcare in comparison to other needs, differences in implementation of healthcare and preventive programs of oral and dental health, weakness in implementing educational programs, economic and cultural differences, and lack of supervision by parents regarding proper teeth cleaning by children. The results of Arora's study showed that the rate of DMFT in urban students was lower than that of rural students, which was in line with the results of the present study[27]. In the study by Gorbatova, no difference has been reported between rural and urban regions. The similarity of service provision in both rural and urban regions in the mentioned study has been reported as the reason for the discrepancy with the results of the present study[28].
In the present study, it was found that the students whose fathers and mothers had academic education had lower DMFT index as well as a lower rate of decayed and missing teeth in both permanent and primary teeth while having a higher rate of filled teeth. In the study by Pakpour, the maximum positive and significant correlation was observed between the fathers' level of education and filled teeth of children [29].
The results of the studies of Abbass, Mohebi, and Nurelhuda showed that there was a significant relationship between parents 'education and students' oral health status, which was in line with the results of the present study[14, 30, 31]. Concerning the importance of teeth and their role in proper nutrition, providing beauty and formation of speech in the early years of life, developing caries can signal a major defect in the early stages of development for the child's health. In this regard, parental education can be one of the principal factors in promoting the dental and oral health status of children. Furthermore, higher parental education level leads to their better awareness about oral and dental health status and eventually greater supervision of parents on the oral and dental health of children.
The results of this study also showed that father unemployment is an important factor for the high rate of decay. There is also a significant relationship between a mother’s employment and dmft index. Shaghaghian found the mother's job as one of the important factors for a student’s dental decayed [32]. The results of studies have shown that the average social status of the family is associated with dental caries, where children with a higher socioeconomic level have fewer decayed, missing, and filled teeth [33, 34]. Low socioeconomic status of families can be associated with poor eating habits and unhealthy lifestyles and can be effective in causing dental caries in children[35].
Based on the results acquired in this study, those with no health insurance had a higher dmft and more decayed teeth. Considering the huge dentistry costs, it seems that lack of health insurance can be a reason for no referral and dental restoration. In this regard, Babaei reported that 41.1% of students cited the expensiveness of dentistry costs as the reason for not referring to a dentist [8]. The results of the study by Amirabadi also showed that DMFT is higher among the students who do not refer to a dentist for annual examinations than among other students [23]. Nevertheless, this problem can be mitigated to some extent through the support of dental insurance companies and governmental support.
The results of this study indicated that students who used mouthwash had higher DMFT index as well as a greater rate of decayed in both permanent and primary teeth. As a justification, usage of these products is recommended for some special cases, because long-term and improper use of mouthwashes can lead to adverse consequences and damages to dental health. It seems that in the present study the students had not used mouthwash properly, and thus damaged their teeth. The results showed that the usage of mouthwash alongside regular tooth brushing contributes to better oral and dental health [20]. On the other hand, based on the results, not all mouthwashes available in the market are useful and some of them can damage the teeth. Hence, the use of mouthwash should be prescribed by a dentist [36].
Based on the findings of the present study, it was observed that not flossing leads to increased dmft index as well as the rate of decayed, while tooth brushing results in reduced dmft along with the rate of decayed in primary teeth. Flossing as a means for taking care of oral and dental health can help in the removal of dental plaques mechanically thereby removing the plaques that form between teeth [36]. The results of a study showed that the students who regularly floss have better oral and dental health compared to those who floss occasionally [37].
Also, in the present study, those who brushed their teeth had a lower DMFT compared to other students, though there was no significant relationship. The results of a meta-analysis study indicated that the students who floss regularly are 1.5 times less likely to suffer dental caries and problems in comparison to those who toothbrush occasionally and irregularly [38]. It has also been found that improper use of a toothbrush can cause damage to the teeth [36]. Possibly, in the present study, the students had not been trained about the proper way of tooth brushing and they may have damaged their teeth unintentionally. Furthermore, since dental caries is a multidimensional disease, the lack of a statistical relationship may be justified.
The present study also showed that DMFT is higher and dental caries are more frequently observed in fourth and younger children; this value is 1.38 times greater in fourth children and younger compared to first to third children. In primary teeth, the number of restored teeth is higher in students who are the first, second, or third children. In this regard, Al-Meedani, found that the oral and dental health of children in populated families is poorer than in less populated families[39]. It can be justified that the attention of parents to children diminishes as their number increases; thus the opportunity for educating them and raising awareness in them about the impact of decay-causing materials on their dental health and supervision on oral as well as dental health diminish.