A method for adjusting/monitoring an orthodontic appliance worn by a patient. Creating a numerical three-dimensional reference model of at least a part of a patient's arch. Creating a numerical three-dimensional reference model of the teeth of the at least a part of the patient's arch. Acquiring at least one updated image, under actual acquisition conditions, and searching, by deformation of the initial reference model, for an updated reference model corresponding to the positioning of the teeth during the acquisition of the updated image. Determining, depending a comparison model corresponding to an anticipated positioning of the teeth, a comparison model. Comparing the updated reference model with the comparison model. If comparison leads to an unsatisfactory result, creation of a replacement orthodontic appliance, by modification of the orthodontic appliance worn or by creation of a new orthodontic appliance, the replacement orthodontic appliance being configured accordingly.