The final stage of severe infection round the apex of a tooth is granuloma formation, the treatment of which can be a major problem in clinical dentistry. Although granulomas in the early stages can respond to conservative conventional therapy, such as the application of calcium hydroxide, many in the later stage require surgical intervention with the risk of postoperative sequelae and patient downtime. Low reactive-level laser therapy (LLLT) has been shown to reduce inflammation and accelerate wound healing. The present study was designed to assess the role of 830 nm diode laser therapy in conjunction with conservative conventional therapy in the treatment of severe apical granulomas. Thirty-three young male patients with severe apical granulomas participated in the study, 19 of whom were treated with conventional treatments, and 14 with calcium hydroxide combined with 0.5 J/cm² - 2 J/cm² intra- and extraoral diode laser therapy. Significant improvements were seen in the LLLT combination group compared with the control group in the time taken for the resolution of acute postoperative pain (100 vs 500 min) and inflammation (1.6 vs 5.6 days), and long-term tooth remineralization and alveolar bone regeneration (15 vs 33 months). LLLT with the 830 nm diode laser was shown to be safe and effective in combination with conservative conventional therapy in the treatment of severe apical granulomas and was superior to the conventional approach on its own for granulomas of similar severity.