Background and Significance The pulp necrosis of permanent immature teeth implies the interruption of the root formation and apical closure. It is then necessary to implement a therapy to induce a calcified barrier at the apical end of the root. The endodontic management of permanent immature teeth is fraught with challenges. Although treatment modalities for vital pulp therapy in these teeth provide long-term favorable outcome, the outcomes from the treatment of pulp necrosis and apical periodontitis are significantly less predictable. Key role of microorganisms in the causing and development of pulpal and periapical diseases have been demonstrated, and their presence in the canal at the time of definitive filling has negative effect on success of the therapy. However, the specificity of microbial load of immature permanent teeth is not completely investigated, nor the influence of the disinfection protocols on treatment success.

Available procedures rely heavily on root canal chemical disinfection of the root canal system, with minimal mechanical instrumentation. Sodium hypochlorite (NaOCl) in different concentrations is the most accepted solution for disinfection of root canal in endodontic. Despite common usage, impossibility of NaOCl to completely disinfect root canal has been noticed. Traditionally, irrigants and medicaments have been chosen for their maximum antimicrobial effect without consideration for their effects on stem cells and the dentinal microenvironment. The balance between disinfection and the creation of an intracanal microenvironment conducive for the proliferation of stem cells requires further investigation. This requires the interpretation of preclinical studies, and this level of evidence should be increased by randomized controlled clinical studies.

Diode lasers have been used in many areas of dentistry, with tendency of good results in canal and dentine disinfection. The bactericidal effect of high-power lasers is based on dose dependent heat generation. Its antimicrobial effectiveness against diverse microorganisms has already been demonstrated.

Photodynamic therapy (PDT) is a two-step therapeutic approach starting with the application of a photosensitizing agent and followed by irradiation with light energy that is spectrally matched to activate the drug. Because its high antibacterial potential, usage of photodynamic therapy as advance to standard protocol in root canal disinfection have been suggested. Studies showed positive effect of photodynamic therapy in the reduction of microbial load in root canal treatment. When a photoactive compound is applied in the root canal system, it is taken up by residual bacteria in the main canals, isthmuses, lateral canals and dentinal tubules. It is also possible that this compound may escape into the periapical tissues. During PDT, light will excite the drug in bacteria within the root canal, but could also potentially affect the apical stem cells that have taken up the drug. Therefore, it is important to determine the therapeutic window whereby host cells are left intact.

Several studies showed wide-ranging spectra of desirable effects of low level power laser (LLLT) on biological tissue. It has been reported to increase cell functional activity, induce cell proliferation, lowers inflammation, releasing of endorphins, thus having analgetic effect. Furthermore, it has been shown that irradiation with a LLLT following photosensitization with phenothiazine chloride had no negative effect on the growth and differentiation of human osteoblastic cells, and did not counteract the biostimulatory effect induced by LLLT. There were no statistically significant differences in the growth and differentiation behavior between the two study groups. Further investigations of PDT on dental stem cells are needed to determine possible biostimulative effect on proliferation and differentiation, and thereby contribute to root development of non-vital permanent immature teeth. Prolonged treatment of young permanent teeth increases possibility of treatment failure. Involvement of a method that could help healing process is desirable.