Introduction The aim of this study was to assess the prevalence of malocclusion in primary teeth and its predisposing factors.

Methods A randomised representative cross-sectional study was carried out in Belo Horizonte, Brazil, with 1069 preschool children between 60 and 71 months of age. A questionnaire addressing individual and behaviour characteristics of children was self-completed by parents. The oral examination was performed by a single dentist calibrated (κ≥0.82) for the diagnosis of the following types of malocclusions: posterior crossbite, overjet (>2 mm), anterior crossbite, anterior open bite and deep overbite. The chi-square and Fisher's exact tests were used, with the level of significance set at 5%. The study was approved by the Ethics Committee of the Federal University of Minas Gerais.

Results The overall prevalence of malocclusion was 46.2%. The specific prevalence of each malocclusion type was 13.1% for posterior crossbite, 10.5% for overjet, 6.7% for anterior crossbite, 7.9% for anterior open bite and 19.7% for deep overbite. No statistically significant associations were found between malocclusion and breast feeding, bottle feeding, pacifier sucking, finger sucking or nail biting (p>0.05). No statistically significant associations were found between malocclusion and the presence of these habits after 2 years of age (p>0.05). No statistically significant associations were found between malocclusion and parents' report of the occurrence of stuffy nose, open mouth, nose operation, throat operation or sinusitis (p>0.05).

Conclusion The prevalence of malocclusion was high, but the predisposing factors investigated were not associated to the presence of malocclusion.