Abstract: Regenerative endodontic treatment for young permanent teeth after unsuccessful root canal therapy is challenging and rarely reported, and requires long-term follow-up for efficacy assessment. This case demonstrates a regenerative endodontic treatment for the mandibular second premolar. The periapical inflammation of this tooth was caused by inadequate filling. The outcome was favorable after 36 months of follow-up. Clinical examination and imaging revealed that the tooth exhibited normal percussion responses, and the low-density images of periapical inflammation disappeared. The infection control of the affected tooth was achieved, and the pulp regeneration was induced.

Key words: regenerative endodontic treatment, root canal retreatment, young permanent teeth, periapical periodontitis