Dental caries prevalence and associated factors among 12-year-old children in Shanghai: a cross-sectional study

Dental caries remains one of the most prevalent chronic diseases among children globally. This study aimed to determine the current prevalence of dental caries and identify key factors associated with caries among 12-year-old children in Shanghai based on a theory-informed analytical framework, to inform targeted prevention strategies. A school-based cross-sectional survey was conducted in 2024. A total of 2570 children aged 12 years were selected from 16 districts of Shanghai using a multi-stage, stratified, cluster sampling method. Data were collected through oral clinical examinations performed by calibrated dentists using WHO criteria and a structured questionnaire covering socio-demographics, dietary habits, oral hygiene behaviors, knowledge, attitudes, and dental service utilization. Caries experience was assessed using the DMFT index. Univariate analyses (Chi-square test, Mann-Whitney U test, Kruskal-Wallis H test) were conducted. For multivariable analysis, covariate sets were determined using a directed acyclic graph, and modified Poisson regression with robust variance was employed to estimate prevalence ratios. Cross-tabulation and the Chi-square test were used to analyze the distribution differences in the intake frequency of five major cariogenic foods between genders. The overall caries prevalence was 19.65%, with a mean DMFT of 0.41 ± 1.04. Multivariable analysis using modified Poisson regression revealed that lower paternal education level (prevalence ratio PR = 1.344, P = 0.012), female sex (PR = 1.524), suburban residence (PR = 1.238), and higher frequency of dessert and candy intake were significantly associated with increased caries. Compared with children consuming desserts ≤ 1 time/week, those consuming desserts ≥ 1 time/day had a higher caries prevalence (PR = 1.391, P = 0.003), with a dose-response gradient observed across intake categories. A similar pattern was found for candies (≥ 1 time/day vs. ≤1 time/week: PR = 1.458, P = 0.001). Brushing time and brushing specific surfaces were not significantly associated with caries. Children without fissure sealants had a lower caries prevalence than those with sealants (PR = 0.749, P = 0.001). Higher oral health knowledge was paradoxically associated with higher caries prevalence (PR = 0.735, P = 0.027). Girls had higher intake of solid sweets, while boys consumed more sugary beverages. The caries prevalence among 12-year-old children in Shanghai is relatively low, yet significant differences exist by sex, region, and socioeconomic factors. Dietary behaviors—particularly frequent dessert and candy intake—were the primary modifiable factors. The inverse association between fissure sealants and caries likely reflects indication bias. The paradoxical knowledge–caries association suggests reverse causality. Bridging the knowledge–behavior gap remains a priority for prevention.