The clinical effectiveness of two dentin adhesives, Clearfil New Bond and Scotchbond 2, was evaluated in two different cavity designs. Group A was without enamel bevel or acid etch and with a butt-joint cavity; and group B had enamel bevel, acid etch, and feather-edged cavities. The retentive rate and marginal adaptation were monitored for 2 years. In the Clearfil system, 21% of group A restorations failed after 2 years, whereas virtually all the group B restorations (99%) were retained. In addition, after 2 years, the total of debonded group A restorations in the Scotchbond 2 system expanded to 13%, whereas no restorations from group B were lost. There was clearly marginal deterioration in time irrespective of the bonding system. Nevertheless, the marginal adaptation of cervical lesions restored with Clearfil New Bond adhesive in combination with Clearfil Ray composite resin revealed fewer defects compared with the Scotchbond 2 adhesive with Silux Plus composite resin restorations. SEM evaluation disclosed composite resin remnants on the dentin surface in cavities with lost fillings, which indicates partial cohesive failure of the adhesive joint.