Pathways from socioeconomic inequalities to dental caries disparities: oral health literacy versus behaviors in 35- to 44-year-old adults in Guangdong, China

Dental caries remains a significant public health challenge with marked socioeconomic inequalities. However, the underlying mechanisms remain poorly understood. This study examined whether oral health literacy or oral health behaviors mediate the relationship between socioeconomic status and dental caries outcomes, and assessed the differential contributions of these two pathways. A population-based cross-sectional study was conducted from September 2021 to July 2022 among 35- to 44-year-old adults in Guangdong Province, China. Structural equation modeling tested relationships among socioeconomic status (SES: education, urban/rural residence, insurance), oral health literacy (OHL: 8 knowledge items on caries etiology and prevention; 4 attitude items on oral health importance), oral health behaviors (OHB: preventive behaviors including brushing, mouthwash, interdental cleaning; treatment completion behaviors including Care Index reflecting caries treatment completion rate and Restorative Index reflecting treatment coverage), and oral health outcomes (OHO: caries status, DMFT). Among 401 participants, the structural model demonstrated acceptable fit (χ2/df = 2.88, CFI = 0.927, TLI = 0.902, RMSEA = 0.068, SRMR = 0.074). While SES significantly influenced both OHL (β = 0.452, p < 0.001) and OHB (β = 0.329, p < 0.001), a critical knowledge translation failure emerged: OHL showed no pathway to OHB (β = -0.094, p = 0.303), indicating that oral health knowledge and positive attitudes did not translate into health behaviors. Neither SES (β = -0.003, p = 0.932) nor OHL (β = -0.051, p = 0.254) directly affected oral health outcomes. Only OHB, particularly treatment completion indicators (CI: λ = 0.998; RI: λ = 0.647), predicted OHO (β = 0.788, p < 0.001), explaining 61.8% of variance. The SES-OHO relationship was completely mediated through OHB (β = 0.259, p < 0.001), with no mediation through OHL. Socioeconomic inequalities in dental caries operate exclusively through differential oral health behaviors, particularly treatment-seeking completion, rather than through differences in oral health knowledge or attitudes. The disconnection between oral health literacy and behaviors suggests that interventions should prioritize enabling treatment completion capacity over knowledge enhancement to reduce oral health disparities.