الفهرس 
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Abstract
This study was designed to investigate the antibacterial effect of silver and gold nanoparticles on different bacterial strains (Streptococcus mutans, Staphylococcus aureus, and Lactobacillus acidophilic bacteria).A total of 180 extracted single rooted maxillary anteriorteeth wereused in this study. Teeth were randomly divided into 3experimental groups (n=180), according to the bacterial strains: group I(Streptococcus mutants)(n=60),group II (Staphylococcus aureus) (n=60) and group IІІ (Lactobacillus acidophilus) (n=60). Decapitations of the crown were done, and then pulp tissueswere extirpated from all root canals. The root canals of the collected teeth were enlarged mechanically using the Protaper nickel-titanium rotary system. The Gates Glidden drills were used to flare out the coronal portion of the canal with maintenances 1mm of the apical constriction to obtain enough width able to contain 25μlof bacteria and 25 μl from metallic nanoparticles (silver or gold).. The bacterial suspensionwas formed from different strains of aerobic and anaerobic bacteria, which was standardized to 0.5 McFarland.The prepared root canals(n=180) were divided into 3 main groups (60 each) (group A, group B, and group C) according to the type of bacterial strains: group A: Lactobacillus acidophilic bacteria (n=60), which subdivided into subgroups:group A1: consist of 20 prepared root canals, each one inoculated with 25μlof Lactobacillus acidophilus bacterial suspension and 25μl of distilled water. group A2: consist of 20 prepared root canals each one inoculated with 25μl of Lactobacillus acidophilus bacterial suspension and 25μl of silver nanoparticles. group A3: consist of 20 prepared root canals each one inoculated with 25μl of Lactobacillus acidophilus bacterial suspension and 25μl of gold nanoparticles.