In order to define cases and controls, the CPQ8-10 scores were analyzed using the two-step cluster method. The log-likelihood distance measure was used. Two-step cluster analysis considered the 25 items of the Brazilian version of the CPQ8-10 separately and compared the mean of one item within each cluster to the overall mean of the same item in the total sample . The case group included those children who experienced a higher negative impact on OHRQoL whereas controls showed a lower negative impact on OHRQoL. Cases and controls were individually matched by school and gender.