Tehran University of Medical Sciences Journal of Craniomaxillofacial Research 2345-5489 8 2 2021 10 02 76 83 Gholamreza Shirani Department of Oral and Maxillofacial Surgery, Craniomaxillofacial Research Center, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. Mohammad Reza Reshadi School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. 2021 07 26 2021 09 05 Purpose: This study aimed to assess the effect of light-emitting diode (LED) phototherapy on pain and trismus following surgical extraction of impacted mandibular third molars. Materials and Methods: This double-blind randomized controlled clinical trial evaluated 50 patients between 20 to 35 years requiring extraction of their impacted mandibular third molars. The patients were randomized into two groups of LED phototherapy and control by flipping a coin. Patients in the LED group underwent LED phototherapy immediately after surgery with red light at 618nm wavelength, 20 mW/cm2 power density and 4 J/cm2 energy density in continuous-wave mode (irradiated area: 3.15cm×1.5cm=4.725cm2). The LED device was used in off mode in the control group (as placebo). The level of postoperative pain was measured by the numerical rating scale, and trismus of patients was evaluated by measuring the maximum mouth opening (MMO). The two groups were compared by the Mann-Whitney and NPar tests. Results: The mean difference in MMO postoperatively, compared with baseline, was lower in the LED group than the placebo group but not significantly (P=0.465). The two groups were not significantly different regarding the level of pain. Conclusion: LED phototherapy with the parameters applied in this study failed to significantly decrease the level of pain and trismus following surgical extraction of impacted mandibular third molars. Keywords: Impacted mandibular third molars; LED; Phototherapy; Trismus; Pain. https://jcr.tums.ac.ir/index.php/jcr/article/view/379 https://jcr.tums.ac.ir/index.php/jcr/article/download/379/326