Whenever a hand or a rotary instrument is used to eliminate tooth tissue, the mineralized matrix shatters rather then being uniformly sheared, producing considerably quantities of cutting debris. Much of the debris made up of very small particles of mineralized collagen matrix over the surface of dentin is known as smear layer. The clinical outcome of dental restorations is dependent upon the surface preparations, smear layer formation and hybrid layer which which provides a stable adhesion. Different surface morphology is produced by use of different burs. The thickness of the smear layer is affected by various factors as type of the bur, use of water spray and speed of rotation. Bonding is enhanced when smear layer is completely removed or modifed. The purpose of this in vitro study is to evaluate the effect of different burs on the topography of the smear layer formation and thickness on dentinal surface.