الفهرس 
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Abstract
To evaluate and compare the effect of water storage on marginal adaptation of different flowable resin composite restorative systems bonded to dentin cavities. Materials and Methods: Six different flowable composite restorative systems were used, an Ormocer-based composite (Admira fusion flow / Admira bond, Voco), a highly-filled nanohybrid resin composite (Grandio flow/ Futura bond M , Voco) , a self-adhering resin composite (Vertise flow, Kerr), a highly-filled resin composite (G-aenial flow/G-aenial bond, GC-Amerian), a bulk-fill resin composite (SDR flow/prime and Bond universalTM, Dentsply) and a nano-filled resin composite (Z350XT flow/ Adper single bond, 3M ESPE). A total of 120 cylindrical dentin cavities were prepared after removal of buccal enamel in extracted human molars. The cavities were randomly assigned into six groups each n=20. Marginal adaptation was evaluated under a metallographic microscope immediately after polymerization and after 6 months of water storage at 37oC in incubator. The evaluated parameters were GF, MG, DM, MI. All the collected data was statistically analyzed for variables using two-way ANOVA, one-way ANOVA followed by the post hoc tukey test, Student’s Paired t-test, the level of significance at p<0.05. Results: None of the restorative systems examined exhibited completely gap-free restorations either immediately or after 6 months of water storage. The results of two-way ANOVA indicated statistically insignificant interaction between the type of composite restorative system and storage time P=0.849. However, the marginal adaptation was significantly affected by the type of restorative/adhesive system (p<0.001). In time there was a significant effect of storage time (P<0.001). Regarding restorative materials systems tested. The results of one-way ANOVA indicated statistically significant difference (P<0.001). Post hock tukey test results showed that ormocer-based, self-adhering composite restorations exhibited the lowest MG, DM and MI values, while methacrylate-based nano-filled restorations revealed the highest values. The results of Student’s Paired t-test showed no statistically significant difference between the mean values of MG, DM and MI of each group immediately and after 6 months of water storage. Conclusion: Although all examined composite restorations failed to achieve gap-free margins with dentin cavities, the ormocer-based restorative system exhibited the best marginal adaptation at all testing times. Water storage has a negative effect on marginal adaptation of all tested restorative systems.