الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Composite resins have replaced dental amalgam in posterior restoration due to the increasing demand of patient for esthetics not only in anterior teeth but also in posterior teeth,1 In addition the easy handling , adequate mechanical properties , ability to bond with tooth structure and moderate cost of composite resins compared to ceramics give composite resins the advantage of being the most popular material in the dental clinics2,3. The long-term performance of any restorative material depends on its marginal integrity and internal adaptation to the cavity walls. On the other hand, one of the main causes responsible for the marginal and internal defects is the polymerization shrinkage of resins that generates stress at the tooth-restoration interface. This is considered among the main problems of composite resins despite of several improvements during the last several years4. The shrinkage generated stresses is transferred to the tooth-restoration interface leading to de-bonding thus causes subsequent microleakage permitting bacterial passage, fluids, and toxins leading to marginal gap formation & recurrent caries5. Over years, the incremental build-up technique of composite resin was considered a gold-standard technique to minimize polymerization shrinkage6 but it has a disadvantages of possible voids formation between the increments. Therefore the manufacturer claimed that bulk fill composite resins can be applied and light cured in one layer (4-5mm thick) were introduced7. These composites exhibit lower volumetric polymerization shrinkage and stresses than hybrid and flowable resin composites and Introduction 2 increased depth of cure8. In addition to the potential advantages of simplifying clinical technique and saving time in cases of deep and wide cavities. Furthermore, bulk placement prevents void incorporation and contamination between composite layers producing more compact fillings 9. However, with high-viscosity resins; it is difficult to gain perfect adaptation to internal cavity walls and proper marginal seal of the cavity margins8.