Predictability of a three-dimensional planning system for oral implant surgery R Jacobs* ,1 , A Adriansens 1 , K Verstreken 2 , P Suetens 2 and D van Steenberghe 1 1 Department of Periodontology, School of Dentistry, Faculty of Medicine, and 2 Laboratory for Medical Imaging Research, ESAT/ Radiology, University Hospital, Catholic University of Leuven, Leuven, Belgium Objectives: To compare 2D CT alone with 2D+3D reconstruction for pre-operative planning of implant placement. Methods: Spiral CT scans of 33 consecutive patients were used for both reformatted 2D and 3D computer-assisted planning. The number, site and size of implants and the occurrence of anatomical complications during planning and implant placement were statistically compared using the percentage agreement and the Kendall's correlation coecients (t). Although planning was performed in 33 patients, implants were only placed in 21 patients. In 11 patients surgery was based on 2D+3D imaging and in ten patients on 2D planning. Results: Agreement between planning and placement of implants was highly signi®cant for the implant sites selected. For 2D based planning and placement, agreement reached 68% (t=0.94). For 2D+3D based planning and placement, agreement attained 73% (t=0.89). For planning and placement of implant size based on 2D images, agreement was 31% and not signi®cant (t=0.23). When based on 2D+3D images, agreement for implant size was 44% (t=0.5). Agreement was not signi®cant for anatomical complications: 69% for 2D planning and 71% for 2D+3D planning (t=0.24 for 2D and t=0.21 for 2D+3D). Conclusions: The 3D planning system is a reliable tool for pre-operative assessment of implant placement. Both 2D and 2D+3D planning have a good predictability for the number and site of the implants but less so for anatomical complications. However, the 2D+3D planning provides a better pre-operative assessment of implant size. Keywords: tomography, X-ray computed; dental implant, endosseous; radiography, dental Introduction When planning the installation of endosseous implants in the maxilla and the posterior mandible, cross- sectional imaging with either reformatted CT or tomography is recommended. 1,2 Conventional tomo- graphy involves less radiation and is a reliable alternative to reformatted CT scans when information is needed on a relatively limited edentulous span. 3 An advantage of multiplanar reconstructed CT is that the combined information re¯ects the three-dimensional anatomy of the structure imaged. The recent introduction of spiral CT has opened new horizons for 3D visualisation. 4 We have previously shown that the use of 2D-CT for pre-operative planning is reliable for predicting the number of implants and the sites, but less good for implant size and anatomical complications. 5 Three-dimensional visualisation has been proposed as a means for overcoming the limitations involved in making a mental 3D transfor- mation. 6 Software programs are available for pre-operative planning by means of interactive placement of the implants, for example SimPlant 1 (Columbia Scienti®c, Inc., Columbia, Maryland, USA). This is, however, limited to 2D-imaging. Attempts have also been made at implant planning with 3D CT. 7,8 It has recently become possible to visualise the anatomical structures in 3D on a computer screen for interactive implant placement. 9 The aim of the present study was twofold: (1) to compare interactive planning on combined 2D+3D CT with conventional planning on 2D reformatted CT; Correspondence to: R Jacobs, Department of Periodontology, Faculty of Medicine, Catholic University of Leuven, Kapucijnenvoer 7, B-3000 Leuven, Belgium Received 9 April 1998; accepted 8 November 1998 Dentomaxillofacial Radiology (1999) 28, 105 ± 111 ã 1999 Stockton Press All rights reserved 0250 ± 832X/99 $12.00 http://www.stockton-press.co.uk/dmfr