Research Paper Orthognathic Surgery Three-dimensional computed tomography cephalometric craniofacial analysis: experimental validation in vitro R. Olszewski, F. Zech, G. Cosnard, V. Nicolas, B. Macq, H. Reychler: Three- dimensional computed tomography cephalometric craniofacial analysis: experimental validation in vitro. Int. J. Oral Maxillofac. Surg. 2007; 36: 828–833. # 2007 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. R. Olszewski 1 , F. Zech 2 , G. Cosnard 3 , V. Nicolas 4 , B. Macq 4 , H. Reychler 1 1 Department of Oral and Maxillofacial Surgery, Saint Luc University Clinics, Universite ´ Catholique de Louvain, 10, Av. Hippocrate, 1200 Brussels, Belgium; 2 Department of Internal Medicine, Saint Luc University Clinics, Universite ´ Catholique de Louvain, 10, Av. Hippocrate, 1200 Brussels, Belgium; 3 Department of Radiology, Saint Luc University Clinics, Universite ´ Catholique de Louvain, 10, Av. Hippocrate, 1200 Brussels, Belgium; 4 Communications and Remote Sensing Laboratory, Faculty of Engineering, Universite ´ Catholique de Louvain, 2, Place du Levant, 1348 Louvain-la-Neuve, Belgium Abstract. The development of three-dimensional (3D) cephalometric analysis is essential for the computer-assisted planning of orthognathic surgery. The aim of this study was to transform and adapt DELAIRE’s two-dimensional cephalometric analysis into the third dimension; this transposition was then validated. The comparative advantage of using 3D computed tomography (CT) surface renderings over profile X-rays was analysed. Comparison was made of inter- and intra-observer reproducibility of the cephalometric measurements done on profile X-rays and on 3D CT surface renderings on the same 26 dry skulls. The accuracy was also tested of the measurements done on 3D CT surface renderings (ACRO 3D # ) in relation to those directly taken on dry skulls with the help of a 3D measuring instrument. Inter- and intra-observer reproducibility proved significantly superior (p < 0.0001) following the 3D CT method. There were no significant differences in the accuracy of measurements between the ACRO 3D software and the 3D measuring instrument. The ACRO 3D software was confirmed as being a reliable tool for developing 3D CT cephalometric analyses. Further research may entail clinical validation of the 3D CT craniofacial cephalometric method of analysis. Key words: cephalometry; 3D computer appli- cations; experimental investigation; computer tomography; observer performance. Accepted for publication 4 May 2007 Two-dimensional (2D) routine cephalo- metry still serves non-surgical orthodon- tics in most cases, except those involving disturbances of bilateral symmetry (e.g. some syndromic cases). Two-dimensional cephalometric analyses can be subdivided into two groups: dimensional and topolo- gical. In dimensional analysis, different craniofacial structures are measured with regard to a line or reference plane (e.g. Tweed, Ballard, Steiner, Sassouni, Bimler, Ricketts, Burstone) 11 . In topological ana- lysis, the proportions of the different cra- niofacial structures of a subject are compared in order to provide a facial and mandibular topology (e.g. De Coster, Coben, Delaire, Tuduri, Enlow) 11 . In con- trast, three-dimensional (3D) CT plays a fundamental role in modern surgical treatment planning in terms of the recon- struction, segmentation and virtual manip- ulation of segments 17 . The link between 2D diagnosis and 3D planning could be provided by the development of 3D CT cephalometric analyses. The available data in the literature (BETTEGA,SWENNEN, TREIL) 2,15,16 do not provide any validation Int. J. Oral Maxillofac. Surg. 2007; 36: 828–833 doi:10.1016/j.ijom.2007.05.022, available online at http://www.sciencedirect.com 0901-5027/090828 + 06 $30.00/0 # 2007 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.