We describe a novel approach to obtain a good estimate of the complete 3D representation of a tooth given only the crown. The technique is based on the use of statistical model derived from 3D-images of teeth constructed by microtomography. The root is constructed by matching the respective crowns of the two models, defining the optimal registration, and optimizing the statistical model parameters. This method allows us to generate the root efficiently due to the small number of parameters to adjust, and requires none or little interaction from the user. The resultant 3D model is smooth and provides a good approximation of the root shape.