The aims of this study were to assess the epidemiology of traumatic dental injuries (TDI) to primary teeth in infants and toddlers between 1 and 3 years of age and investigate whether TDI was related to biological and social factors. A representative sample of infants and toddlers in the city of Belo Horizonte, Minas Gerais, Brazil (n = 519) was examined during a vaccination campaign. The evaluation of clinical signs of previous dental trauma was performed by nine previously calibrated examiners (intra-examiner Kappa = 0.95%; inter-examiner Kappa = 0.88%). Data were analysed through descriptive analysis, the chi-squared test (P < 0.050) and logistic regression. The prevalence of dental trauma was 41.6%. Among the 519 children examined, 193 (37.2%) had enamel fractures, 30 (5.7%) had enamel-dentin fractures and only three (0.6%) had enamel-dentin fractures involving the pulp. Dental care had been performed within the first 24 h in 4.1% of the sample and after 36 h in 0.8% of the sample. There was no statistically significant difference between genders. The most reported aetiologies were falls (28.8%) and collisions (6.8%). There were no statistically significant associations between the prevalence of dental trauma and non-nutritive sucking habits, dental caries or lip incompetence (P > 0.050). Children of mothers with low levels of schooling (0-6 years of study) had a greater prevalence of TDI (P = 0.001). The results of the logistic regression also demonstrated a significant association between dental injury and the Social Vulnerability Index (P = 0.045). Children from families with high social vulnerability (worse living conditions) had a 1.51 (95% confidence interval 1.0-2.2) greater chance of exhibiting TDI. These results can help guide the implementation of health promotion policies.