Introduction: Dental injuries occur mostly in school therefore the level of teachers' knowledge in this area is particularly important considering that their immediate and appropriate attitude may depend the dental prognosis. Objectives: Assess elementary teachers' knowledge, of public schools of Oporto city, about dental trauma. Material and Methods: Cross-sectional study that used a self-administered questionnaire distributed in 49 schools, whose data were analyzed by SPSS program. To proportions comparison between participants were used the Chi-square, Fisher exact and the nonparametric Mann-Whitney tests. The logistic regression was used to quantify the relationship between teacher's features and their knowledge about dental trauma through adjusted odds ratios and respective confidence intervals to 95%. Results: 329 teachers (74.9%) delivered a full questionnaire. It was found that 40.1% had already witnessed dental injuries however only 2,5% had training in this area. Facing a dental fracture most teachers didn't know that the fragment could be reused, as well as in an avulsion condition only 6.7% knew that they could reposition the avulsed tooth. It was also observed that most teachers answered wrongly to other questions related to dental trauma in school context. Discussion: It's verified the existence of a low level of knowledge about dental injuries in this population and it has been found that most teachers are not qualified to manage a traumatic dental injury. Conclusions: Teachers, as first entity to deal with these traumatic injuries, should be trained to contribute, along with the pediatric dentist, for the improvement of treatment provided to the child. Keywords: dental trauma, school oral health promotion, elementary teacher, knowledge, attitude, preventive dentistry