1. A method for automatically identifying tooth crowns in a virtual three-dimensional model of teeth in a dental arch, comprising the steps of: a) storing said model in a memory accessible to a general-purpose computer, said computer including a processing unit; b) providing machine readable instructions for execution by said processing unit, said instructions comprising instructions operating on said model in the following respects: 1) orientating said model with reference to a plane; 2) automatically determining local maxima of the model and areas bounded by said local maxima; 3) automatically determining saddle points between said local maxima in the model, said saddle points corresponding to boundaries between teeth; 4) determining the position of said saddle points along a dental archform, and 5) for each tooth, automatically identifying a path linking said saddle points comprising a transition between teeth and gingival tissue and between adjacent teeth in said model, and identifying areas bounded by said path and in the direction of said plane as corresponding to one of said tooth crowns.