A method for generating a three-dimensional reconstruction of a patient's dental arch, called an extended optical impression, comprising the following steps implemented under the control of a practitioner: - obtaining at least one global two-dimensional image of the acquired dental arch with a first image sensor having a relatively wide field of view and relatively low precision, and generating by first digital data processing means a global, relatively coarse three-dimensional reconstruction of the dental arch from said two-dimensional image; - acquiring a plurality of respective local two-dimensional images of respective associated sectors of the dental arch with a second image sensor having a relatively more restricted field of view and a relatively higher precision than the first image sensor, and generating by second digital data processing means respective local three-dimensional reconstructions, relatively more precise than the global three-dimensional reconstruction, of said associated sectors of the dental arch; - merging, by a merging algorithm performed by third digital data processing means, the global three-dimensional reconstruction and local three-dimensional reconstructions into a single total three-dimensional reconstruction wherein the local three-dimensional reconstructions are respectively substituted with portions of the global three-dimensional reconstruction that correspond to the associated sectors of the dental arch, the global reconstruction playing a role of absolute spatial guide, said merging comprising a setting of the local three-dimensional reconstructions in the global three-dimensional reconstruction, said setting being adapted to minimize a distance between the point clouds corresponding to each of the associated sectors of the dental arch and the corresponding point cloud of the global three-dimensional reconstruction. - obtaining at least one global two-dimensional image of the acquired dental arch with a first image sensor having a relatively wide field of view and relatively low precision, and generating by first digital data processing means a global, relatively coarse three-dimensional reconstruction of the dental arch from said two-dimensional image; - acquiring a plurality of respective local two-dimensional images of respective associated sectors of the dental arch with a second image sensor having a relatively more restricted field of view and a relatively higher precision than the first image sensor, and generating by second digital data processing means respective local three-dimensional reconstructions, relatively more precise than the global three-dimensional reconstruction, of said associated sectors of the dental arch; - merging, by a merging algorithm performed by third digital data processing means, the global three-dimensional reconstruction and local three-dimensional reconstructions into a single total three-dimensional reconstruction wherein the local three-dimensional reconstructions are respectively substituted with portions of the global three-dimensional reconstruction that correspond to the associated sectors of the dental arch, the global reconstruction playing a role of absolute spatial guide, said merging comprising a setting of the local three-dimensional reconstructions in the global three-dimensional reconstruction, said setting being adapted to minimize a distance between the point clouds corresponding to each of the associated sectors of the dental arch and the corresponding point cloud of the global three-dimensional reconstruction.