Estimate the prevalence of dental caries based on clinical examinations and self-reports and compare differences in the prevalence and effect measures between the two methods among 18-year-olds belonging to a 1993 birth cohort in the city of Pelotas, Brazil.

Data on self-reported caries, socio-demographic aspects and oral health behaviour were collected using a questionnaire administered to adolescents aged 18 years (n = 4041). Clinical caries was evaluated (n = 1014) by a dentist who had undergone training and calibration exercises. Prevalence rates of clinical and self-reported caries, sensitivity, specificity, positive and negative predictive values, absolute and relative bias, and inflation factors were calculated. Prevalence ratios of dental caries were estimated for each risk factor.

The prevalence of clinical and self-reported caries (DMFT>1) was 66.5% (95%CI: 63.6%–69.3%) and 60.3% (95%CI: 58.8%–61.8%), respectively. Self-reports underestimated the prevalence of dental caries by 9.3% in comparison to clinical evaluations. The analysis of the validity of self-reports regarding the DMFT index indicated high sensitivity (81.8%; 95%CI: 78.7%–84.7%) and specificity (78.1%; 95%CI: 73.3%–82.4%) in relation to the gold standard (clinical evaluation). Both the clinical and self-reported evaluations were associated with gender, schooling and self-rated oral health. Clinical dental caries was associated with visits to the dentist in the previous year. Self-reported dental caries was associated with daily tooth brushing frequency.

Based on the present findings, self-reported information on dental caries using the DMFT index requires further studies prior to its use in the analysis of risk factors, but is valid for population-based health surveys with the aim of planning and monitoring oral health actions directed at adolescents.