الفهرس 
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Abstract
Using conventional dental drilliling machine for a long time, but after the emergence of lasers, some studies began theoretical and practical trying to prove the ability of the laser in cavity preparation. Those studies found that the laser beam Er,Cr : YSGG with wavelength 2780 nm and Er : Yag laser with wavelength 2940nm are the most common types of lasers in cavity preparation. Lasers have many advantages in cavity preparation such as, lack of annoying voice of conventional bur during drilling, reduces the need for local anasthesia in many cases and it is considered a strong potential for infection control when compared with conventional bur. Studies have found that the application of Er,Cr:YSGG laser device in cavity preparation is a distinct and unique application when compared with conventional bur technique. One of the major challenges in restorative dentistry is the problem of shrinkage during light polymerization which generates stress. The shrinkage stress generated within the bonded composite restoration is transferred to the adhesive interface between the cavity walls and the composite resin. This stress pulls away the shrinking composite resin from the cavity walls and results in breaking the weaker adhesive bond with gingival dentin, resulting in marginal gap formation and failure of restoration with pulpal complications. This research is designed aiming to evaluate the effect of Er,Cr:YSGG laser system versus conventional bur on marginal integrity of composite resin for cavity preparation.