Purpose: The aim of this retrospective study was to introduce a novel technique of a double-scan protocol with markerfree registration and compare it to the already-used techniques regarding the accuracy of registration.

Materials and methods: Fifty-nine fully edentulous patients underwent double-scan procedures by three different methods: the barium sulfate method for 11 patients; the gutta-percha method for 26 patients; and the marker-free method for 22 patients. Point-to-point registration of the two scans was followed by a voxel-based surface "best fit" registration. The mean registration error of each case was digitally recorded. Differences in registration error between groups were evaluated using one-way analysis of variance (ANOVA).

Results: The accuracy of the registration showed no significant differences according to the method (P = .719).

Conclusion: The marker-free procedure was presented as a novel technique for registration of the scans in the double-scan protocol. There was no significant difference in the accuracy of the registration between the three techniques: marker-free, gutta-percha markers, and fully radiopaque barium sulfate scan appliance. Therefore, the marker-free technique might be a viable option for the double-scan protocol.