Background: The regenerative function of stem cells from the apical papilla (SCAPs) is affected by the presence of bacteria from infected root canals. Living microorganisms influence SCAP function but the effect of inactive bacteria and its components on SCAPs needs further investigation. Aim: To investigate the effect of residual bacterial products on the proliferation of SCAP under anaerobic conditions. Methods: Five opportunistic bacterial strains from infected dental root canals namely Fusobacterium nucleatum, Enterococcus faecalis, Actinomyces gerensceria, Slackia exigua, and Peptostreptococcaceae yuri, and two probiotic strains Lactobacillus gasseri, Lactobacillus reuteri were used in this study. SCAPs collected from three healthy young patients were exposed to UV-inactivated bacteria or bacterial DNA. Real-Time Cell Analyzer (RTCA) was used to determine real-time proliferation of SCAPs after 80 hours exposure of inactivated bacteria or their DNA. Results: UV killed Fusobacterium nucleatum and Enterococcus Faecalis DNA affects proliferation of stem cells from dental apical papilla as monitored in real-time. Inactivated probiotic species do not affect SCAPs in terms of proliferation. Conclusion:  Inactivated bacteria can affect SCAP function by modulating their proliferation. Further investigations studying SCAP modulation and differentiation are warranted to understand and improve regenerative endodontic procedures.