Introduction: The purpose of this study was to determine the effect of low-level laser therapy on orthodontic pain after the first canine retraction force. Method: This single-blind split-mouth placebo-controlled randomized clinical trial was performed in 30 orthodontic patients requiring bilateral canine retraction in Shahed University. Once canine retraction was initiated, a single dose of diode laser radiation (660 nm, 80 MW, and 3.8 J/cm2 density, diameter of the optical fiber tip: 0/45cm2) was administered to a randomly selected maxillary or mandibular quarter for 30 s. The other quarter served as the placebo side and was treated using the same device without turning on the laser. On the first, second, fourth, and seventh days, the patients rated the pain they experienced on each side at home by using visual analog scale-based questionnaires. Changes in pain were analyzed using non-parametric analysiswith SPSS software. Results: In patients who experienced pain,a significant pain reduction was notedon the first and fourth days after low-level laser therapy on the experimental side compared to that on the placebo side (P <0.05). Conclusions: A single dose of diodelaser therapy (660nm)can be an efficient modality to reduce the orthodontic pain associated with canine retraction

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