Effects of composite thickness on the shear bond strength to dentin

The manufacturers of some condensable posterior composites claim that their products can be placed in bulk and light-cured in 5-mm-thick increments. This study compared the shear bond strengths of three composite resins when bonded to dentin in 2- and 5-mm-thick increments. Overall the bond strengths were adversely affected by the composite thickness (p < 0.0001). The shear bond strength of each composite tested was much lower when polymerized in a 5-mm increment than in a 2-mm increment of composite (p < or = 0.0005). The two condensable composites tested had a lower bond strength than the conventional composite when polymerized in a 5-mm bulk increment (p < or = 0.01).