Association between baseline oral examination status and out-of-pocket dental expenditure trajectories in South Korea: a longitudinal panel study

Oral examinations are an important component of preventive oral care, but their association with dental expenditures may vary over time. Evidence on long-term out-of-pocket dental expenditure trajectories in relation to oral examination status remains limited. This study examined this association using data from the Korea Health Panel (KHP). We analyzed 6,256 adults observed across eight annual waves of the KHP from 2011 to 2018. Baseline oral examination status was derived from self-reported usual examination frequency, assessed without a fixed recall period. Piecewise latent growth models incorporating inverse probability weighting and covariate adjustment were used to estimate differences in baseline expenditure and rates of change during 2011–2013 and 2014–2018. Age- and household-income-specific analyses and formal interaction tests were conducted as exploratory assessments of heterogeneity. Sensitivity analyses used log-transformed expenditures. Regression coefficients for the primary analysis are expressed in units of 10,000 KRW. The oral examination group had a higher baseline level of out-of-pocket dental expenditure than the no-oral-examination group (β = 5.35, 95% CI: 3.44 to 7.26; p < 0.001) and a lower annual rate of expenditure change during 2011–2013 (β = −3.08, 95% CI: −4.47 to − 1.69; p < 0.001). During 2014–2018, the between-group difference in the annual rate of change was modestly positive (β = 0.66, 95% CI: 0.01 to 1.32; p = 0.049), but this later-period finding was not statistically significant in the log-transformed sensitivity analysis. Formal interaction tests provided no statistically significant evidence of heterogeneity by age or household income. Baseline oral examination status was associated with a higher initial level of out-of-pocket dental expenditure and a lower early rate of expenditure change. These two findings were consistent under log transformation, whereas the later-period finding was sensitive to outcome specification. The results demonstrate the importance of distinguishing initial expenditure levels from subsequent rates of change rather than relying solely on average expenditure differences. Further research should examine repeated oral examination behavior, service-specific expenditures, and the role of access to appropriate follow-up care.