Objectives: The aim of this study was to determine the effect of MTAD on the expression of virulence factors of Enterococcus faecalis (E.faecalis) considering the role of Gutta-percha/AH26 or Resilon/RealSeal SE as root canal obturating materials. Materials and Methods: One-hundred and forty-four single-rooted human teeth were instrumented to a standardized apical size. Root canals were infected by E.faecalis (ATCC 29212). Ninety teeth were irrigated with MTAD and randomly divided into three groups. In two groups, root canals were obturated by either Gutta-percha/AH26 or Resilon/RealSeal SE. Root canals were kept unobturated in the third group. The remaining 54 teeth received no final irrigation. All groups were then subdivided into three timepoint subgroups in which dentin powder was obtained from each sample to determine the expression of specific virulence factors of E.faecalis (efa, esp, gel, fsr) using real-time reverse transcription polymerase chain reaction (RT-PCR). Statistical analysis was performed by one-way analysis of variance (ANOVA) and Tukey’s post-hoc test. The statistical power was set at P-value ≤0.05. Results: MTAD was effective against the expression of most of the tested virulence factors, and Gutta-percha/AH26 increased the antibacterial efficacy of MTAD. Conclusions: MTAD could inhibit the expression of some known virulence factors of E.faecalis at the majority of tested timepoints. This may partly explain some of the mechanisms of antimicrobial efficacy of MTAD against this resistant microorganism which is known as one of the main causes of failure of root canal treatment.

Objectives This study aimed to evaluate the cytotoxicity of minimum antibacterial values of medicaments used in endodontic regeneration on stem cells. Materials and Methods “Minimum inhibitory concentration,” “minimum bactericidal concentration,” and “minimum biofilm inhibitory concentration” of triple and double antibiotic paste, a modified triple antibiotic paste (minocycline replaced by clindamycin), Augmentin, and calcium hydroxide were determined using Enterococcus faecalis (ATCC 29212) by microtiter plate method. Direct cytotoxic effects of drugs were evaluated by lactate dehydrogenase and water-soluble tetrazolium salt-1 assays using stem cells of apical papilla obtained from immature third molars via enzymatic digestion. Statistical Analysis Data were analyzed using IBM SPSS Statistics 24, one-way analysis of variance and post hoc comparisons. The statistical power was set at p < 0.05. Results All medicaments caused similar cytotoxicity and cell proliferation at “minimum inhibitory concentration” (p > 0.05) except Augmentin which was significantly more toxic than others (p < 0.05). At “minimum bactericidal concentration,” calcium hydroxide was more toxic than other drugs (p < 0.001), but its adverse effect on cell proliferation was the same as Augmentin (p > 0.05). Triple and double antibiotic paste revealed similar favorable effects in terms of toxicity and proliferation rate at most of the tested concentrations (p > 0.05). At “minimum biofilm inhibitory concentration” both the modified paste and Augmentin caused less proliferation rate than triple and double antibiotic paste (p < 0.001and p < 0.05, respectively) and Augmentin induced more cytotoxicity (p < 0.05). Conclusions Considering the antimicrobial potency, triple antibiotic paste seems to be the safest drug for the stem cells of apical papilla, while Augmentin may have some adverse effects.