Is the Significant Caries Index in low-caries populations still significant?

Objectives: In the era of robust caries decline in adolescents we wanted to investigate developments in caries inequalities and whether SiC is still a significant index as specific to describe the high caries risk fraction.

Methods: Caries data for 12-year-olds were derived from the Third and Fourth German Oral Health Studies (DMS III/IV), cross-sectional studies conducted in 1997 (n=1.043) and 2005 (1.383). DMFT, SiC were calculated, Lorenz curves were plotted and Gini coefficients to assess inequalities in the distribution of dental caries were estimated for all subjects (GI (total)) and for the SiC fraction (GI (SiC)) from the outputs.

Results: In DMS III 41.8% of the 12-year-olds were caries-free, mean DMFT was 1.7 (95%-CI:1.6;1.8), and GI (total) was 0.61. SiC was 4.1 (95%-CI:3.9;4.3) including DMF teeth > 1 ≤ 16. GI (SiC) was 0.2. In DMS IV 70.1% of the 12-year-olds were caries-free, mean DMFT was 0.7 (95%-CI:0.6;0.8), and GI (total) was 0.81. SiC was 2.1 (95%-CI:2.0;2.3) including 0 DMF teeth ≤ 14. GI (SiC) was 0.42.

Conclusion: Though DMFT and SiC declined between DMS III and IV Gini coefficients increased over time. On the one hand these results indicate a general benefit of caries prevention in 12-years-olds including high risk individuals. On the other hand GI demonstrated increasing caries inequalites. In DMS IV even caries-free subjects were part of SiC demonstrating that in low-caries populations the SiC might not set a meaningful cut-off to describe the high risk fraction.