Introduction There is a lack of evidence supporting the protective effect of breastfeeding on occlusion in primary dentition. The aim of this study was to examine the effects of predominant (PB) and exclusive breastfeeding (EB) on malocclusion adjusting for recognised risk factors.

Methods A cross-sectional study was carried out nested in a population-based birth cohort from Pelotas, Brazil which started in 2004. A sample of 1129 children aged 5 years old underwent dental examination. Anterior open bite, posterior cross bite, canines relationship, and overjet, were recorded according (1) Foster- Hamilton criteria and (2) WHO criteria. A history of breastfeeding and non-nutritive sucking habits was collected at interview with the child's mother. Data were analysed using multivariable Poisson regression controlling for potential confounders.

Results The mean duration of EB and PB were higher among children free of malocclusions; the longer the duration of breastfeeding, the lower the prevalence of malocclusions. The concomitant presence of PB for at least six months and the non-regular use of pacifier until two years of age show a protective effect for crossbite following adjustment for confounders. The longer the duration of EB the lower the prevalence of moderate or severe WHO malocclusion. A dose-response relationship between duration of EB or PB and the prevalence of malocclusion was observed. This was reduced or eliminated if pacifier use is introduced early in the child's life.

Conclusions Given that breastfeeding is a protective factor for several childhood diseases, our findings indicate that the common risks approach is the most appropriate way for the prevention of malocclusions.