Feature curves based cephalometric superimposition

The analysis of the spatial changes of the craniofacial structures for orthodontic treatment or surgery always relies on the superimposition of cephalometric tracings taken at different times. The errors in the manual measurement of superimposition may be arisen from the bad cephalogram quality, the facial growth, and the orthodontist's experience. In this paper, the computerized superimposition is developed for alleviating the problems mentioned above. This procedure contains three parts: 1. To digitize and calibrate the cephalogram through the CCD camera; 2. To extract the feature curves for the cranial base using the best oriental edge detector and Hough transform, and for the mandible using the Laplacian of Gaussian and grouping; and 3. To automate the superimposition based on the clinically available procedure and finally to display the associated results. The complete procedure typically takes 5 to 6 minutes of computation. The precision for the cranial base superimposition is about 0.312cm, and the mandible about 0.005cm. The difference between the superimpositions of the proposed system and the manual measurement is about 0.95cm in the cranial base, 0.98cm in the maxillary, and 1.26cm in the mandible.