OBJECTIVE To determine whether the shaping of oval-shaped root canals using 2 different preparation techniques resulted in significant morphologic differences. STUDY DESIGN Forty lower premolars with oval-shaped root canals were divided into group A, instrumented with the Anatomic Endodontic Technology (AET) system, and group B, treated with ProTaper instruments. A modified Bramante technique was used to analyze changes in root canal diameters (DeltaD), changes in surface area (DeltaA), and the change in buccolingual and mesiodistal ratio (DeltaR). The data were subjected to a Student t test at a significance level of P < 0.05. RESULTS Statistically significant differences were found between the 2 groups at coronal and middle levels. There was no statistically significant difference at the apical level. CONCLUSIONS The 2 techniques produced a significant difference in the ultimate shape of the coronal and middle portions of oval-shaped root canals, with the AET system removing more tooth structure at these levels. However, no differences were observed at the apical third.