Introduction Dental diseases and disorders can negatively impact on the quality of life of preschool children and their families. Socioeconomic and demographic characteristics may confound those effects, but this issue has been scarcely studied in this age group.

Objective To evaluate the effects of untreated dental caries, dental pain and malocclusions on the oral health-related quality of life (OHRQoL) of 5-years-old children and their families, adjusting for mothers' schooling, household income, sex and children skin colour.

Methods A subsample of 1129 children from the 2004 Pelotas, Brazil, Birth Cohort study, was investigated in 2009. Children were dentally examined and their mothers were interviewed at home. The outcome, OHRQoL, was assessed by the Brazilian version of Early Childhood Oral Health Impact Scale (ECOHIS) using child and parental subscales and total scores as discrete variables. Multivariable Poisson regression models were performed to estimate the association between the outcome and the co-variates.

Results The multivariable adjusted model showed that dental pain had a great impact on child (IRR 4.50 95% CI 3.58 to 5.65) and parental (IRR 3.05 95% CI 2.25 to 4.13) quality of life. The severity of high levels of untreated dental caries had also a negative impact on children (IRR 2.01 95% CI 1.56 to 2.59) and their family (IRR 3.75 95% CI 2.58 to 5.45) quality of life. Malocclusions had impact only on the total score (IRR 1.32 95% CI 1.09 to 1.60) and the family subscale (IRR 1.40 95% CI 1.08 to 1.81).

Conclusions Dental problems were associated with lower scores of OHRQoL of children and their families regardless potential confounders.