Background <p>Postoperative pain, facial swelling, and trismus are common sequelae following the surgical extraction of impacted mandibular third molars. This study aimed to compare intramucosal dexamethasone injection and peri-extraction photobiomodulation therapy in controlling these postoperative outcomes.</p> Methodology <p>An open-label, split-mouth randomized controlled trial was conducted on 30 patients undergoing bilateral surgical removal of impacted mandibular third molars. One surgical site received an intramucosal dexamethasone injection (Group 1), while the contralateral site was treated with peri-extraction photobiomodulation therapy (Group 2). Postoperative pain, facial swelling, and mouth opening were evaluated at predetermined time intervals.</p> Results <p>Sixty surgical sites (30 per group) were analyzed. Both groups demonstrated significant (<i>p</i> = 0.000**) reductions in postoperative pain, swelling, and trismus. Group 1 showed significantly lower pain scores on the 2nd (<i>p</i> = 0.000**) and 7th postoperative days (<i>p</i> = 0.000**). Group 2 exhibited greater, though statistically nonsignificant (<i>p</i> = 0.150), improvement in mouth opening on the 7th postoperative day.</p> Conclusion <p>Both treatment modalities are effective in reducing postoperative morbidity following impacted mandibular third molar surgery. Intramucosal dexamethasone provides superior pain control, whereas photobiomodulation therapy is associated with improved postoperative mouth opening.</p>