Purpose <p>This randomized controlled clinical trial evaluated the influence of guardians’ prior knowledge about silver diamine fluoride (SDF), through the application of an instructional video, on their acceptance and perception of its use in children.</p> Methods <p>The children’s guardians responded to a questionnaire containing questions about the use of SDF. They were randomized into groups: test, received prior information about SDF through a video; control, did not receive prior information. As answer options (yes/maybe/no) for each question, scores were assigned (0–2). The lower the total score (0–24), the better the acceptance and perception. X² and Mann–Whitney tests were used for comparisons between groups.</p> Results <p>Eighty-two participants were included (test, <i>n</i> = 42; control, <i>n</i> = 40). The total score was 6.98 (± 4.33) in the test group and 8.45 (± 4.87) in the control (<i>p</i> = 0.683). Considering the use of SDF in anterior teeth, the test group showed better acceptance (<i>p</i> = 0.027).</p> Conclusion <p>The prior knowledge about the SDF did not, generally, influence the acceptance and perception of the guardians. However, regarding anterior teeth, there was better acceptance and perception by those who received the video about SDF.</p>