The regional bond strengths of three current-generation bonding systems (All Bond 2, Scotchbond Multi-Purpose, and Clearfil Liner Bond 2) were measured in natural wedge-shaped defects in the cervical area of extracted human teeth. A microtensile testing method was used to compare the strengths of resin bonds made to occlusal margins with those made to gingival margins. Controls consisted of normal teeth which had artificial wedge-shaped defects, of the same depth and dimension, created with a high-speed bur. The results indicated that there were no regional differences in bond strength, although bonds made to natural lesions were from 20 to 45% lower than those made to normal dentin in artificially created wedge-shaped defects, depending on the bonding agent. Scanning electron microscopy revealed that Clearfil Liner Bond 2 created the thinnest hybrid layers, which were difficult to measure in the natural lesions. The natural lesions contained sclerotic dentin, whereas the artificial lesions were composed of normal dentin. Although the bond strengths to sclerotic dentin were lower than those to normal dentin, the absolute values (ca. 16 to 17 MPa) were high relative to previous-generation bonding agents.
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