The goal of this clinical trial is to evaluate if regenerative endodontic treatment using two different forms of demineralized dentin matrix (DDM) can effectively treat immature permanent single-rooted teeth compared to treatment using RetroMTA in patients aged 9 to 15 years. The main questions it aims to answer are: Does the use of DDM improve clinical and radiographic outcomes such as root length, dentinal wall thickness, and apex closure? Is DDM a viable bioactive alternative to RetroMTA as a coronal sealing material in regenerative endodontic procedures? Researchers will compare three groups: one using RetroMTA, one using a DDM-TheraCal LC mixture, and one using TDM-Hydrogel, to see if these materials differ in their effects on regenerative outcomes. Participants will: Undergo two treatment visits including canal disinfection, induction of bleeding to form a blood clot scaffold, Receive placement of one of the study materials over the blood clot as a coronal barrier, Have clinical examinations and CBCT imaging at baseline and multiple follow-ups up to 12 months to assess treatment success through signs, symptoms, and radiographic changes.