Computer implemented method for aligning a three-dimensional model (6) of a patient's dentition to an image of the face of the patient recorded by a camera (3), the image including the mouth opening, comprising: estimating the positioning of the camera (3) relative to the face of the patient, retrieving the three-dimensional model (6) of the dentition of the patient, rendering a two-dimensional image (7) of the dentition of the patient using a virtual camera (8), carrying out feature detection in a dentition area in the mouth opening of the image (1) of the patient recorded by the camera (3) and in the rendered image (7), calculating a measure of deviation between the detected feature images of the image taken by the camera (3) and the detected feature image of the rendered image, varying the positioning of the virtual camera (8).
