Taraneh Movahhed - Dental School, Mashhad University of Medical Sciences, Iran.
Maryam Mehrabkhani - Dental School, Mashhad University of Medical Sciences, Iran.
Mohsen Arefnezhad - Kashmar School of Nursing, Mashhad University of Medical Sciences, Iran.
Shokouh Sadat HAmedi - School of Persian and complementary medicine, Mashhad University of Medical Sciences, Iran.
Reza Zare Mahmoudabadi - Dental School, Mashhad University of Medical Sciences, Iran.
Fariba Ghanbari - Dental School, Mashhad University of Medical Sciences, Iran.
Mahjube Rostami - Dental School, Mashhad University of Medical Sciences, Iran.

Background: Chemical agents, such as Chlorhexidine are used as one of dental plaque control strategy. Researchers are looking for a natural and economic substitute with same antibacterial efficacy and less complications. The aim of this study was to evaluate the antimicrobial efficacy of the Khorasan Razavi walnut green husk extract with and without adding ZnO nanoparticles (nZnO) on  (S. mutans). Methods: In this in vitro study, antimicrobial effect of the Hydro-ethanolic extract of WGH, was evaluated. Broth Dilution and Agar diffusion methods were used with ۹۰ tubes containing different dilutions of WGH extract (۱۰۰ to ۰.۰۰۶ mg/ml). ZnO nanoparticles (nZnO) were added to ۴۵ tubes. Streptococcus mutans was exposed to ۱۵ different serial concentrations of study extracts, from ۱۰۰ mg/ml to ۰.۰۰۶ mg/ml. Minimum inhibitory concentration (MIC) of the study extracts were determined and zone of inhibition diameter was compared to positive controls (chlorhexidine ۰.۲%, nZnO), and negative control (sterile distilled water). The differences between the mean diameters, were analyzed by independent sample T- teS. Results: Minimum inhibitory concentration (MIC) of study extract was found to be ۵۰ mg/mL, with adding nZnO, MIC was reduced to ۳.۱۲ mg/mL. Mean diameter of inhibition zone at ۳.۱۲ mg/ml with and without adding ZnO nanoparticles were ۱۷.۶۷±۰.۵۷ mm and ۸±۰.۰۰۱ mm, respectively, (p-value< ۰.۰۰۱). Conclusions: Adding nZnO could be enhanced antimicrobial efficacy of the WGH extract against S. mutants, while it was still less effective than chlorhexidine.

Keywords: Dental decay, Nanoparticles, Streptococcus mutans, Walnut green husk, Zinc oxide.