ABSTRACT OBJECTIVE To estimate time in days from the beginning of follow-up up to the development of dental caries in children under 30 months and to assess risk factors potentially affecting the development of the disease. METHODS The study population of the cohort study were children attending public, private, and charitable day care centers in Salvador, Northeastern Brazil, followed up for fourteen months. We used the multivariate Cox regression to estimate risk and Kaplan-Meier method to estimate the caries-free time. RESULTS Of the 495 children studied, 112 developed caries (22.6%). Mean caries-free time was 248.6 (SD = 96.2) days. The comparasion of curves by age group (> 24 months) and children attending public day care showed more caries in a shorter period (p < 0.00).

The following variables were important risk factors for increased rate of caries:

district of origin (HR = 1.88, 95%CI 1.27-2.77), category of day care (HR = 3.88, 95%CI 2.04-7.38), age (HR = 1.77, 95%CI 1.15-2.74), bottle-feeding before sleep time after the age of 12 months (HR = 1.62, 95%CI 1.04-2.51), presence of active white spots (HR = 2.70, 95%CI 1.07-6.80), and living in non-masonry house (HR = 1.68, 95%CI 1.02-2.76). The highest hazard ratio (HR = 4.60, 95%CI 2.80-7.42) was found for previous caries experience. CONCLUSIONS Social variables were considered as of high risk for the development of dental caries.