This study was performed in vivo over a 6-month period to assess restorative margins in Class V restorations placed with different techniques. The margins were evaluated quantitatively under the scanning electron microscope using the replica technique. Results indicated that the sandwich technique using a glass-ionomer cement base and a composite resin restoration was not able to prevent marginal gaps in dentin. However, the experimental Gluma/Clearfil system resulted in a quality of dentinal margins not statistically significantly different from that of enamel margins. These in vivo findings substantiate in vitro results.