The present randomized controlled split mouth clinical study aimed to investigate the efficacy of Er,Cr:YSGG laser irradiation on pain reduction and healing rate of recurrent aphthous stomatitis. 40 patients with RAS were recruited for this study and RAS ulcerations of each patient were randomly assigned to the control or test group. In the test group, Er,Cr:YSGG laser with non-contact mode was to irradiate RAS lesions. In the placebo group, RAS lesions were irradiated with the same device without laser emission. Pain was evaluated with visual analog scale (VAS) while a clinician graded healing of RAS (HRAS). In the placebo group at immediate; scores of VAS presented no statistically significance; in the test group, laser application showed significant pain reducing, at 1st day control. In...