The introduction of confocal laser scanning microscopy (CLSM) has provided a valuable new technique for the visualization of bonding structures such as a hybrid layer in dentin (Watson, 1989, 1991). In the case of seven commercially-available dentin bonding systems, it could be demonstrated that the CLSM renders considerably more detailed information than the SEM because of its non-destructive nature and because of the possibility of a distinction between components of bonding agents. With most of the bonding systems, measurements of the thickness of the hybrid layer could be carried out when the primer component was labeled with rhodamine B. It was found that this thickness is significantly increased by increases in etching time and only slightly decreased by increases in the drying time of the dentin and of the primer. When rhodamine B was used for dye penetration tests on four different dentin bonding systems, a leakage within the demineralized zone in the dentin was found in each of the specimens. This structure appears similar to that which Sano et al. (1995) called "nanoleakage". The amount of nanoleakage could not be measured by this method. In the case of enamel or ceramic bonding, a penetration zone was found which corresponded to the etching patterns found in enamel and ceramics, respectively. We conclude that CLSM can offer a wealth of new information about bonding morphology and, therefore, should be used in addition to conventional methods so that the maximum information can be obtained.