The antimicrobial effects of zinc oxide-calcium hydroxide mixture fillers: determining the ideal mixture ratio

BACKGROUND AND OBJECTIVES: Although zinc oxide (ZO)-calcium hydroxide (CaOH) mixtures have been successful regarding their absorption rate compatibility with dissolving primary teeth, no study has been conducted on the appropriate mixture ratio to obtain effective antibacterial properties. In this study, we compared antibacterial activity of CaOH-ZO pastes using different mixture ratios sagainst Enterococcus faecalis as an important bacterium in root canal treatment failure. MATERIALS AND METHODS: Seven types of pastes were prepared in our laboratory. The first group included one gram of ZO+eugenol, second group included one gram of CaOH+distilled water, third group included 0.5gram ZO+0.5gram CaOH+distilled water (1:1), forth group included 0.75gramCaOH+0.25gramZO+distilled water (3:1), the fifth group included 0.33gram of CaOH+0.66gram of ZO+distilled water (1:2), the sixth group included 0.75gram of ZO+0.25 CaOH+distilled water (3:1), the seventh group included 0.66 gram CaOH+0.33 gram ZO+distilled water (2:1), and the final group included one gram of gelatin+distilled water (as the control group). These pastes were compared regarding their antibacterial effects against Enterococcus faecalis using agar diffusion and microdilution methods. RESULTS: Except for the control group, all prepared pastes showed antibacterial properties. Order of minimum inhibitory concentration for pastes were as followed: CaOH-ZO (1:3)=CaOH-ZO (1:2)>CaOH-ZO (1:1)>CaOH-ZO (3:1)=CaOH-ZO (2:1)>CaOH=ZO-eugenol. Order of minimum bactericidal concentration, which shows a weaker bactericidal effect, according to type of paste, were as followed: CaOH-ZO (1:3)>CaOH-ZO mixture (1:2)>CaOH-ZO mixture (1:1)>CaOH-ZO mixture (3:1)=CaOH-ZO (2:1)>CaOH=ZO-eugenol. Only CaOH-ZO (1:3) and CaOH-ZO (1:2), showed significantly weaker MICs and MBCs (p < 0.001). CONCLUSION: Considering the limitations of an in-vitro study, in terms of anti-bacterial effects against Enterococcus faecalis, CaOH-ZO mixture (2:1) is equivalent to ZO-eugenol as the most commonly used material in polypectomy of primary teeth.