الفهرس 
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Abstract
The oral microbiota plays an important role in buccal health and in diseases such as periodontal inflammations, meningitis and dental caries. The cariogenic bacteria accumulated on dental surfaces composed of native oral flora is the primary etiologic agent of dental caries. Plant extracts play an important role in preventing caries and inhibiting the growth of cariogenic bacteria with high efficiency through plant/metal nanoparticles formation by the help of gamma radiation.
In the present study, Fifty plaque samples were collected from fifty participants and isolated on non-selective (Nutrient agar and Malt agar) and selective (MS agar) media. It was noticed that the percentage of the isolated microorganisms were higher in ages ranges between 1-20 years and 41-60 years than in ages between 21-40 years. However, there is no clear difference between the percentages in both genders. After that further screening for streptococcal isolates were made through gram staining and catalase test. It was noticed that among the isolated thirty-seven streptococcal isolates, 18 isolates with percentage of 49% were confirmed to be harboring to S. mutans by RapID STR system test by determination of the bacterial enzymatic spectra. The preliminary selection was carried out according to the highest bioscore, typical biofrequency and implicit probability level in ERIC system.
Among S. mutans isolates, four isolates were selected and lyophilized to be used for further studies and coded as (S1, S2, S3 and S4).
Neem plant parts (bark, leaves and sticks) were extracted separately using three different solvents (acetone, ethanol and deionized water) and prepared in three concentrations (10%, 20% and 50%) in DMSO to test the antibacterial activity of the prepared neem plant extracts against four selected isolates of S. mutans through agar well diffusion assay. It was noticed that acetonic sticks extract at concentration of 50% was the potent extract with inhibition zone diameter (1.80.1, 3.30.2, 3.70.0 and 4.20.3) cm for the isolates S1, S2, S3 and S4, respectively.
On a comparative study between the extracts of neem sticks and pomegranate peels that were extracted separately using three different solvents (acetone, ethanol and deionized water) and prepared in three concentrations (10%, 20% and 50%) in DMSO to test the antibacterial activity of the prepared plant extracts against the four selected isolates of S. mutans through agar well diffusion assay. It was found that the acetonic pomegranate extract at concentration of 50% was promising extract, as the inhibition zone diameter was (3.20.1, 4.20.2, 4.80.0 and 5.00.3) cm for the isolates S1, S2, S3 and S4, respectively.
The morphological changes of S. mutans cell that illustrate the action of acetonic extracts of pomegranate, were observed through SEM. It was noticed that, the cell wall of the bacterial cell was irregular cell wall. Enlargement, deformation and rupture of cells was also observed, in addition to a reduction of biofilm formation.
The FTIR spectra of acetonic pomegranate extract was made to investigate the existed functional groups. The ”C=C stretching and bending vibration of aromatic rings” that related to phenolic and flavonoid compounds was observed followed by a confirmatory test to estimate TPC and TFC and was found to be 233.4213 1.2 and 42.2619 0.4 mg/g extract respectively.
The green synthesizes of ZnO NPs that appears as white precipitation. was obtained by mixing ZnCl solution with acetonic and deionized of PPE separately with and radiated at doses (20, 40, 60 and 80) KGy of gamma radiation.
The UV analysis was carried out to prove the existence and the quantity of biosynthesized ZnO NPs. It was observed that pomegranate/ZnO NPs prepared at 60 KGy, has the highest intensity compared to other gamma doses.
On studying the sensitivity test of biosynthesized ZnO Nps towards S.mutans (S1). It was observed that the sensitivity of ZnO NPs of acetonic and deionized extracts of pomegranate peels at 60 KGy was powerful with higher inhibition zone diameter 5.50.0 and 4.80.0 respectively, due to the small particle size of ZnO NPs compared to acetonic and deionized water PPE and chemically synthesized ZnO NPs.
FTIR analysis of biosynthesized ZnO NPs at 60 KGy confirmed the presence of peaks related to the functional group C=O of amides and carboxylic group of amino acids, -NH of protein related to pomegranate contents that participate in the production, capping and stabilization of ZnO NPs. On the other hand, recognition of Zn-O that verify the presence of ZnO NPs.
TEM and XRD were used to study the particle size, shape and morphology of the biosynthesized ZnO NPs. It was found that biosynthesized ZnO NPs are well dispersed and three shapes were realized as spherical nanoparticles, rod nanoparticles and Triangular nanoparticles with particle size 17.95 nm, 10.29 and 76.98, respectively.
Human oral epithelial cells (OEC) were used in order to determine the cell viability of the bio-produced ZnO-NPs to ensure the safety of biosynthesized ZnO-NPs to be used in further applications. By using SRB assay, the cells were found to be viable to 99% and the concentration of ZnO-NPs required to inhibit 50% from the cells is more than > 100 g/ml.
ZnO NPs/ composite have shown clinically acceptable bond strength values when these antibacterial agents were added to a composite resin as it inhibits the cariogenic bacteria at concentrations of 0.1%, 0.5% and 1% .