Introduction Objective parameters may help the decision of how to manage existing dental restorations in patients. Objective This study tested the following hypotheses: i) teaching objective criteria to dental students enhances their criticism toward the indication for replacement of dental restorations; and ii) a complementary practical approach enhances the proportion of correctly indicated treatments compared with a strictly theoretical approach. Method This block-randomized controlled trial involved dental students from a Brazilian university who were randomized to either a didactic/theoretical class group (A, control) or a didactic/theoretical class followed by practical training (group B); both conditions were applied in a moodle-based environment. The proportion of correctly indicated interventions before and after teaching the criteria was compared with using Mann–Whitney U-test (p<0.05), and a comparison between the approaches was established with Wilcoxon test (p<0.05). Result The baseline proportion of correct assignments significantly increased after interventions for both groups (p=0.02), with no significant difference between the interventions (p=0.871). Conclusion The proposed online training enhanced the proportion of correct assignments to restorations, confirming the first study hypothesis. The second hypothesis was rejected because differences between the strategies had no effect on the proportion of correct answers. Focusing on teaching objective criteria for assessment of the quality of restorations would enhance students’ ability to correctly treat them.