Oral health-related quality of life is significant in adolescents, as many of their social and psychological coping skills are still developing . The present study assessed the relationship between dietary habits and caries incidence in 12- to 15-year-old adolescents in Shanghai, China.
The caries prevalence and mean DMFT among 12-year-olds were 19.7% and 0.59, respectively. These values are much lower than those seen nationally (41.9% and 1.04, respectively) , and also lower than those seen in other regions like Zhejiang province, China (40.9%; 0.98) , Sichuan province, China (37.2%; 0.86) , Ambala, India (34.3%; 0.82) , and Galicia, Spain (39.6%; 0.98) . The caries prevalence showed an upward trend with increasing age, ranging from 19.7% among 12-year-olds to 32% among 15-year-olds. This may be attributed to the continuous and cumulative process of caries development as well as the increase in erupting teeth with advancing age. Other studies have also reported a similar caries prevalence among these age groups [25, 26]. In our study, the 14- and 15-year-old groups showed the highest overall caries prevalence, signifying a continued decline in oral health. The prevalence of dental caries and the mean of DMFT were higher in females than in males. This may be attributed to the earlier eruption of teeth in females, which could lead to prolonged exposure to cariogenic acids in the oral environment. However, other evidence suggests that the higher caries susceptibility among females may also be attributed to changes in salivary rates and composition induced by gender-specific hormonal fluctuations .
Tooth brushing is a relatively affordable method of reducing dental caries risk, mainly via exposure to fluoride from toothpaste and mechanical plaque removal [14, 28]. The association between tooth-brushing frequency and dental caries may differ depending on the country. Bernabé et al.  reported a reduced 4-year net increment in tooth decay via tooth-brushing twice a day or more compared with once a day or less in a Finnish population. Similarly, Rothen et al.  demonstrated that brushing teeth with a fluoride toothpaste twice daily reduced the incidence of caries in northwest American dental patients. However, in this study, the frequency of tooth-brushing was not associated with the incidence of dental caries. This finding supports a previous cross-sectional study in a Japanese population , possibly due to the design of the study questionnaire. In addition to the frequency of tooth-brushing, the quality of tooth-brushing is also important. Using the current questionnaire, it is impossible to know whether a subject has adopted the correct method of brushing and sufficient time for tooth-brushing. These factors may also affect the incidence of dental caries .
Moreover, beverage consumption patterns have changed in the past 10 years. The consumption of sugar-sweetened beverages has increased annually, while the consumption of water and milk has gradually decreased . A study on the fluid intake of Brazilian teenagers found that soft drinks are the second most consumed beverage, accounting for 10% of teenagers’ daily energy intake . The relationship between the frequency of sugary drinks and caries has been clearly demonstrated in preschool children and adults , with limited data on adolescents. Here, we present the impact of sugary drink consumption on caries incidence based on the most recent data sample of Chinese teenagers. We confirm a statistically significant relationship between elevated sugary drink consumption and dental caries experience.
In this study, we also found that eating vegetables twice a day or more can reduce the risk of caries. This result is similar to that of previous reports. A study by Chin-En Yen et al. found that a high vegetable intake effectively reduced dental caries incidence among 182 children aged 3–6 years . In addition, a study of female university students in Saudi Arabia showed that eating vegetables four times per week or more effectively reduced caries risk (odds ratios = 0.73) . Another study conducted by Japanese scholars including 600 cases of 70-year-old subjects found that vegetable intake was negatively correlated with dental caries incidence . Based on these findings, we speculate that vegetable intake is significantly associated with fewer dental caries, regardless of age.
Our data showed that approximately 20% of participants did not eat breakfast every day. There were significantly impaired eating habits that increased with age, including irregular breakfasts among 12- to 14- year-olds. Interestingly, we found evidence of “recovery” from these patterns and improved eating habits among 15-year-olds, as shown in supplementary Figure 1. This data trend agrees with that previously reported by Bruno et al. . In addition, we found a statistically significant association between irregular breakfast patterns and caries development, with a 1.124 times increased caries risk. Skipping meals may reduce exposure to cariogenic foods, such as breakfast cereals, but irregular meal patterns, like light meals and high-sugar snacks throughout the day [15, 39], may explain the enhanced caries activity. In this study, caries risk caused by irregular breakfasts was lower than that reported in previous studies of Swedish female teenagers  and Polish preschool children . This may be due to differences in the age and gender of the study populations or due to the differences in the diets of Eastern and Western people. Westerners generally consume more sugar in their daily diets than Easterners , and thus, Westerners may have a higher dental caries risk than Easterners.
However, our study has some limitations. We used a food frequency questionnaire to determine food intake frequency, but subjects may not be able to recall exactly what they have eaten over time. A food diary may be a solution to this problem, though it relies on the subject’s compliance. Recently, pre-post meal digital photography proved to be a valid, accurate, and applicable method to assess food intake . In addition, this study was a cross-sectional investigation, and the time course was not considered. Other studies have reported that previous dental caries experience at baseline increases the likelihood of future caries . Thus, a longitudinal study with full consideration of baseline variables is required to confirm the effect of irregular breakfasts, sugary drinks, and vegetable intake on the occurrence of dental caries in the Chinese population.