1. A method for manipulating a virtual dental model, comprising:— (a) providing a 3D virtual model of at least a portion of an intraoral cavity comprising a preparation having a finish line, wherein at least a portion of the finish line is obscured; (b) manipulating said 3D virtual model in the vicinity of said obscured portion of said finish line in a virtual manner such as to create an auxiliary 3D virtual model corresponding to said obscured portion of said finish line; (c) providing topographical data of the finish line from the virtual model and the said auxiliary virtual model.