Similarity measure for quality control of dental CAD/CAM-applications

There is no measure for morphometric quality control of dental CAD/CAM-restorations as well as for evaluation of newly developed CAD/CAM-applications. The aim of this study was to (a) establish a 3D-measure for morphological comparisons, (b) to proof its metrical and subjective-visual validity and (c) to explore morphological features which have relevant impact on visual perception. 125 maxillary anterior teeth were chosen from a digital library of 3D data sets and compared by automatic superimposition with a best-fit method. The superimposition was analyzed by a newly defined 3-dimensional similarity measure, called shape similarity value (SSV). With this measure, similarity between symmetrical and non-symmetrical teeth was evaluated and the metrical validity was tested. Additionally, visual evaluation of tooth similarities were performed and analyzed by means of multivariate statistical procedures, to test the correspondence between metrical similarity measure and visual similarity perception. The measure clearly reproduced the similarity of contralateral teeth and the dissimilarity of teeth between different individuals. The coincidence between quantitative similarity measure and visual perception was moderate. In conclusion, the presented 3D-measure can be considered as a first substantial step towards a morphometric quality control of CAD/CAM-restorations of anterior teeth.