الفهرس 
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Abstract
To evaluate and compore the clinical performance, Streptococcal and fungal adhesion, marginal adaptation, and surface microhardness of one Silorane-based and two methacrylate-based resin composites. METHOD AND MATERIALS: 1. Clinical Investigation: Forty patients with normal occlusion, each with three restorations either class I or II under occlusion. Only those who demonstrated good oral hygiene were enrolled to join this study .A total of 120 restorations were placed, 30 restorations from each material: Silorane-based composite, Filtek P90; nanofilled composite, Artiste; microhybrid composite, Quixfil. One operator placed all the restorations according to according to the manufacturers’ instructions. Each restoration was clinically evaluated immediately following finishing and polishing (baseline), after 6 months, 1 year and 1.5 years by two independent examiners. Restorations were evaluated using United States Public Health Service (USPHS). The changes in the USPHS parameters during the 1.5 years were analyzed, Comparison between different materials at the same time was performed with the Kruskall–Wallis test (K.W.) followed by a pair wise Mann–Whitney U-test. Comparison between the different recall examinations was calculated by a Friedman test followed by a paired Wilcoxon test at P <0.05 level of significance. Results: all the restorations showed only minor changes, and no differences were detected between their performance at base-line and after 18 months. Only one microhybrid had failed after 12- months. Regarding the clinical performance, there was no statistically significant difference among the material tested (P <0.05). 2. Microbiological and laboratory Investigations. Ninty cylindrical specimens (10 x 2) made of the tested composite were polished with Sof-Lex polishing discs. The average surface roughness (Ra) after polishing was measured using optical profilometry for sixty specimens ( n=20) that were used for microbiological investigations, the other thirty specimens were used for microhardness test. Conclusion: 1.Silorane-based composite showed a satisfactory clinical performance after 18 months as methacrylate-based composite. Nanofilled composite showed the smoothest surface between the tested composites. All the tested restorative systems failed to achieve gap-free margins at all testing times. Silorane-based composite restorations exhibited the best marginal adaptation and the best marginal stability among the tested composite systems at all aging periods. Microhybrid resin composite demonstrated the highest microhardness value while both Silorane group and nanofilled group demonstrated comparable microhardness values. Silorane-based resin composite presented the least S.mutans and C albicans adhesion values.