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The demand for posterior aesthetic restorations has dramatically increased in recent years. Several new materials have been developed with improved aesthetic, adhesive and mechanical properties. However microleakage elimination, especially if the margins are on dentine or cementum, and attainment of optimum mechanical properties for posterior use, are still questionable. The results of the present study also showed that no material was able to eliminate microleakage completely at dentine or cementum margins. However, composite resin restorative materials based on nano-technology showed better marginal seal as compared to the other tested materials. Therefore, clinicians should be careful when placing aestehtic restorations in the posterior teeth.

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