This study aimed to determine the relationship between tooth decay with stress and BMI in elementary school students. Based on the results of logistic regression, the following variables were effective factors in tooth decay: father's level of education, family economic status, experience of toothache in the past year, oral health status, frequency of tooth brushing, flossing, stress, and BMI.
The results of the present study showed that the prevalence of tooth decay among the participating students was 76.9%, which was at a high level. One of the possible reasons for this high prevalence can be the sampling at the clinic level because people usually go to medical centers who have dental problems. Therefore, the prevalence of tooth decay among these people is higher than the samples available in school. The results of this section were consistent with the results of studies by Basir et al. (36), Hamissi et al. (44), Panahi et al. (45), Nabipour et al. (46), and Namal et al. (47), that this rate in these studies have been reported 75.6%, 75.5%, 75.2%, 71.8%, and 76.8%, respectively. Also, the prevalence of tooth decay in the studies of Alghamdi et al. (48), Jain et al. (49), Kalantari et al. (50), Nematollahi et al. (51), Dawkins et al. (52), and Singh et al. (53) were estimated 48.4%, 63.6%, 83.9%, 49.7% and 40%, respectively, which were not consistent with the results of the current study. Possible reasons for this discrepancy include the following: the age of the children studied in these studies was different from the present study, differences in oral health status and dental care between cultures, cities, villages, and countries around the world.
The results of the present study showed that "stress" was at a low level among the participating students. One of the possible reasons for the low level stress in the present study could be the completion of the stress questionnaire by parents, because sometimes the internal states of children's stress may be ignored by parents. In line with the present study, a study by Talbot et al. reported the prevalence of stress at a low level (54). The results of the studies of Tanganelli et al. (55) and Calais et al. (56) were not in line with the results of this part of the present study. Possible reasons for this discrepancy may be due to differences in factors such as the age of children and stress assessment tools in these studies compared to the present study.
The results of the present study indicated that the mean BMI among the participating students was in the normal range. In this regard, it can be said that the majority of participating students probably had healthy eating habits and tried to do sports such as walking or exercise even during a coronavirus pandemic. The approach of parents and their educators in the field of proper nutrition can also be effective in this regard. This results were consistent with the results of studies by Panahi et al. (40), Zare-Zardiny et al. (57), Wei et al. (58), Liang et al. (59), Mohammadi et al. (60), and Jang et al. (61). In terms of BMI in all the above studies, the majority of people were in the normal range.
The results of the present study revealed that the "father's level of education" was one of the factors affecting tooth decay. This part of the results was consistent with the results of studies by Chu et al. (62), Panahi et al. (45), Nematollahi et al. (51), KAZEROUNI et al. (63), Namal et al. (47), Mohebi et al. (64), and Kalantari et al. (50). The results of the present study also indicated that the family economic status was one of the factors affecting tooth decay. The results of the studies of Alghamdi et al. (48), Chu et al. (62), Goodarzi et al. (76), Jamelli et al. (65), and Prashanth et al. (66) were in line with these results. In justifying the possible reasons for these two results, it can be pointed out that as the father's level of education increases, his level of awareness increases. Also, with the increase in the father's level of education, the family economic status will probably improve and the rate of visits to the dentist for examination increases. Finally, the combination of three factors of higher awareness, better economic status, and more visits to the dentist, will improve the oral health status of children.
The results of the present study showed that the experience of "toothache past year" was one of the factors affecting tooth decay. This result may indicate that factors such as adopting oral health behaviors and properly educating them to children, taking seriously the initial pain reported by children and timely action by parents can reduce the rate of primary decay. In this regard, the studies of Faezi et al. (67), Ferraz et al. (68), and Adeniyi et al. (69) also reported similar results to those of the present study. Also in line with the present study, in the study of Prasai Dixit et al., It was pointed out that toothache among children aged 8 to 12 years had a direct effect on the rate of tooth decay (70).
Based on the results of the present study "oral health status" was one of the factors affecting tooth decay. Mohiuddin et al. (71), Schwendicke et al. (72), and Akinyamoju et al. (73) reported similar results on the relationship between oral health and tooth decay. They stated that poor oral health status in children and adolescents, along with factors such as irregular dental examinations and less awareness of the principles of oral health, can affect the rate of tooth decay. However, contrary to the results of the present study in the study of Panagiotou et al. (35), no relationship was observed between oral health and tooth decay in children. One of the possible reasons for this discrepancy could be the difference between the two studies in terms of the sample population, because the above study was conducted among adolescents in addition to children.
According to the results of the present study, the frequency of tooth brushing and flossing were other factors affecting tooth decay. In this regard, it can be said that these two results were largely expected, indicating the vital and important role of oral health behaviors in promoting dental health. This part of the results was consistent with the results of studies by Guadagni et al. (74), Taani et al. (75), Faezi et al. (67), Goodarzi et al. (76), and Prasai Dixit et al. (70).
As the results of the present study revealed, stress was one of the factors affecting tooth decay. Similarly, in the study by Cynthia et al., students with moderate and high levels of stress were at greater risk for tooth decay than those with low levels of stress (34). The results of the studies of Masoudi et al. (77), Kisely et al. (78), Delgado et al. (79), Jain et al. (80), and Honkala et al. (81) were in line with these results. Contrary to the results of the current study, in the studies of Hubbard and Workman (82) and Panagiotou et al. (35), no relationship was observed between stress and tooth decay in children. In justifying this discrepancy, we can point to possible differences in the rate of tooth decay and stress, as well as differences in stress measuring tools and indexes used in these two studies compared to the present study. Also, differences in the family economic status, students' ages, cultures and educational systems of different regions, and different approaches of parents and educators regarding stress and oral health of students could also be effective in this regard.
The results of the present study showed that BMI was one of the factors affecting tooth decay, so that students with higher BMI had more decayed teeth. In this regard, it can be said that these children probably had unhealthy eating habits than others, so the risk of tooth decay was higher among them. Similar to these results, in the studies of Amiri et al. (83), Bafti et al. (84), Yan-Fang Ren et al. (85), Thomas Modéer et al. (86), Kor et al. (87), Wei et al. (58) also, more tooth decay was observed among children with higher BMI.
In contrast, studies by Mohammadi et al. (60), Liang et al. (59), and Jang et al. (61) reported an inverse relationship between BMI and tooth decay. They stated that obese children with higher BMI had less tooth decay and those with lower BMI showed more signs of decay. The reason could be the reduction in the intake of essential minerals such as calcium, that could be due to poor economic status and nutritional problems of children. However, Wu et al. (88) and Dikshit et al. (89) in their studies did not report any relationship between BMI and tooth decay. In general, all the studies mentioned in this paragraph were inconsistent with the results of the present study. In justifying this discrepancy, the possible differences in the rate of tooth decay and the prevalence of different categories of BMI in these studies compared to the present study can be considered. Also, differences in the family economic status, students' ages, cultures and educational systems of different regions, and different approaches of parents and educators regarding stress and oral health of students could also be effective in this regard.
It seems that the present study is the first study that simultaneously has measured the effect of two variables of body mass index and stress on tooth decay. It is suggested that the results of this study be used in designing interventions to prevent tooth decay among students. In addition, the target group in this study were students referred to the pediatric dental clinic of the faculty of dentistry of Qazvin University of Medical Sciences. Therefore, the results of this study cannot be generalized to other groups of students. Therefore, it is recommended that this study be conducted among students in other cities as well as among different groups of students (in terms of education, gender, age, and place of residence). One of the important limitations of this study was that due to the covid-19 pandemic and school closures, sampling was done through convenience sampling method at the pediatric dentistry clinic. In addition, the relatively small number of samples and self-reported data collection were other limitations of this study.