This is an epidemiological study conducted in Cabo de Santo Agostinho, in the southeastern part of Pernambuco, Brazil, which has a population of approximately 185,123 inhabitants . The sample was comprised of 320 preschoolers aged from three to four years who were attending municipal kindergarten.
The calculation of sample size considered that a previous pilot study on ECC indicated a prevalence of 22.3%, with a 95% confidence interval and a 5% standard error. This resulted in a sample of 266 children, and after adding 20% to avoid data loss, a sample size of 320 children was established.
The pilot study was conducted with 10% of the sample in the yards of the schools, in a knee-to-knee position, with natural light and using a dental mirror and wooden spatula. Children received oral hygiene instruction and supervised tooth brushing before the exam. The children who took part in this trial were included in the final sampling.
This study was approved by the Ethics Committee of the University of Pernambuco. (Protocol No. 119/12). Consent for undertaking the research was obtained from the school principals, and consent to perform the examinations came from the parents or guardians. Only the children of those parents or guardians who returned the signed permission forms were included in the study.
The examinations were performed by a calibrated examiner for visual exam following criteria established by the World Health Organization . Kappa coefficients for intra-examiner agreement was K = 0.90.
Cavitated carious lesions in children younger than 71 months were classified as ECC, according by Drury et al. . The individuals with syndromes that impact the oral cavity were excluded from the sample to avoid confounding factors.
In addition to the oral examination, children were measured and weighed to assess nutritional risk as proposed by the CDC (Center for Disease Control) , which analyses the BMI (Body Mass Index) curve by age and sex from 2–19 years of age. The child was considered to be underweight when the value was below the 5th percentile, normal weight when between the 5th (inclusive) and below the 85th, overweight when between the 85th (inclusive) and 95th and obese when above the 95th percentile. The measurement of body weight was recorded by the researcher, with the child standing with minimal clothing without shoes on a portable calibrated scale with a precision of 100 g, and the height was measured with a tape strip scale.
The examiners administered a questionnaire, which was previously validated in a pilot study, to parents and guardians at the pick-up time at school in order to obtain information on family income. To determine the gestational age and birth weight, we accessed the vaccination and the local maternity hospital records that followed the WHO criteria , indicating preterm to be less than 37 weeks. The WHO criteria  for adolescent pregnancy included girls from 10 to 19 years of age. The classification for birth weight included very low birth weight (less than 1500 g), low birth weight (less than 2500 g) and normal birth weight (equal to or greater than 2500 g).
After data collection and the categorization of variables, we created a database for statistical analysis using SPSS (Statistical Package for Social Sciences) version 17. To test the association between two categorical variables, the chi-squared test was used. To explain the prevalence of early childhood caries and its association with the other risk factors, we chose the Poisson regression test, which is similar to logistic regression, with the advantage that the prevalence ratio (PR) is more stable and the value for OR varies in a smaller range. The margin of error was 5%.