Effect of different types of smear layers on dentin and enamel shear bond strengths

Clinically, dentin is usually shaped with burs prior to dentin bonding. In the laboratory, almost all bonding studies are done on dentin prepared with sandpaper. This work compared the shear bond strengths of Scotchbond/Silux to enamel and dentin prepared with slow or high-speed burs, sandpaper (320 versus 600-grit SiC) and a low-speed diamond saw. There were no statistically significant differences among bonds made to enamel versus dentin smear layers. Dentin smear layers created with slow-speed burs and 320 or 600 grit SiC gave similar bond strengths. Scanning electron microscopic examination of both sides of the sheared bonds indicated a cohesive failure of the smear layer. That is, the forces holding the smear layer together seem to limit the ultimate bond strength of Scotchbond/Silux.