The purpose of the present study was to assess the effects of dentist-patient communication via social media on dental anxiety and to determine the appropriate timing of such communications. In this randomized, double-blinded and controlled trial, we used Instagram's quick replies system to answer patients' questions to alleviate dental anxiety for patients undergoing impacted teeth extraction under local anesthesia. Patients were assigned randomly into four groups according to the timing of such communications: only after (group 1, n = 36), only before (group 2, n = 35), before and after the operation (group 3, n = 36), and a control group who received no communication on social media (group 4, n = 36). Dental anxiety was evaluated one week before (pre-op) and after the operation (post-op) using recognized assessment scales -the Spielberger's State-Trait Anxiety Inventory, Modified Dental Anxiety Scale (MDAS), and Visual Analogue Scale (VAS). The results showed that the post-op values of group 4 had higher anxiety scores than the groups 2 and 3 according to VAS (p < 0.05). Within the groups, the anxiety levels showed a decreasing trend after surgery according to MDAS and VAS scores (p < 0.05). The results of this study suggest that communication with patients before the operation is sufficient to reduce their dental anxiety.