Age-Stratified Association Between CPI Screening Categories and Caries Experience in the Permanent Dentition of Children and Adolescents from Southwest Romania: A Multicenter Cross-Sectional Clinical Study

Background/Objectives: Dental caries and gingival inflammation share several biofilm-related determinants. This study evaluated the association between Community Periodontal Index (CPI) screening categories and permanent-dentition caries experience in a consecutively recruited clinical sample of children and adolescents from Southwest Romania. Methods: The multicenter cross-sectional study included 638 participants aged 6–19 years, analyzed as 6–12 years (n = 407) and 13–19 years (n = 231). Analyses included nonparametric comparisons, adjusted Poisson models, a formal CPI-by-age-stratum interaction, continuous-age sensitivity analyses, and generalized Poisson models allowing underdispersion. Results: Mean DMF-T was 4.71 ± 2.55 and 4.93 ± 2.58 in the younger and older strata, respectively. CPI correlated strongly with DMF-T (rho = 0.743 and 0.749; both p < 0.001). Adjusted expected DMF-T counts were higher for CPI 1 and CPI 2 than for CPI 0 in both strata. There was no statistical evidence that the CPI–DMF-T association differed by age stratum (global interaction p = 0.749) or continuous age (p = 0.552). Plaque Index adjustment markedly attenuated CPI estimates; the extent of residual CPI association was sensitive to count-model specification. Conclusions: Higher CPI categories were associated with greater cumulative caries experience in this clinical sample, but the findings do not establish temporality, causality, or predictive validity. Unequal numbers of erupted permanent teeth and CPI-eligible sextants may have contributed to the observed gradient because these quantities were not retained analytically.