Site preparation for oral implants is a delicate surgical procedure. In the ITI F-type and Bonefit implant systems, two cylindrical burs are available. Experiments were performed to verify the clinical experience that the longer bur is more accurate in defining the direction of implants. Several preparations were made in six human femur heads. The purpose of the experiments was to investigate the difference in parallelism between preparations made with the standard cylindrical bur and the bur with the long shaft. The results showed that the bur with the longer shaft was preferred for obtaining an accurate direction and parallelism of the implants. Keywords: ITI implant, operation technique, parallelism, radiologic registration