Disclosed is a method for designing tooth surfaces of a digital dental prosthetic item existing as a 3D data set using a first 3D model of a preparation site and/or of a dental prosthetic item and a second 3D model, which second model comprises regions which match some regions on the first 3D model and regions which differ from other regions of the first 3D model, the non-matching regions containing some of the surface information required for the dental prosthetic item, wherein at least three pairs (P1, P2, P3) of points (P11, P12; P21, P22; P31, P32) corresponding to each other are selected on the matching region on the first 3D model (A) and the second 3D model (A′), that the positional correlation of the second 3D model with reference to the first 3D model is determined with reference to the at least three pairs (P1, P2, P3), and that portions of the non-matching regions of the first and second 3D models are implemented for designing the tooth surface of the dental prosthetic item taking into consideration the positional correlation of these models relative to each other.