[Stereolithography models vs. milled 3D models. Production, indications, accuracy].

Anatomic, life-like, three-dimensional models have a definite place in cranio-maxillofacial surgery. Our experience with 541 computer tomographic (CT)-based three-dimensional (3D)-models for diagnostic purposes, preoperative planning and model operations in our department was gained using stereolithographic and milled models. The question of which production method is preferable is a matter of controversy in the literature. Both methods are based on CT and magnetic resonance imaging data, but the differences in production give rise to specific advantages and disadvantages. For comparison we scanned two measurement models, fabricated milled and stereolithographic models, and analyzed the differences concerning accuracy and shape of specific structures. The scan distance (feed) is the limiting factor for the accuracy for both methods. Milled models show the highest precision in the plane of CT scanning--the more oblique the measurements became to this plane, the greater the decrease in accuracy. Hollows and undercuts can only be produced by splitting the model. Stereolithographic models show higher deviations with randomly distributed errors. The mean deviation was 0.81 mm on stereolithography and 0.54 mm on milled models. The accuracy of both methods is sufficient for clinical use. In routine cases the milling method seems to be superior because of shorter production time and lower costs. In special cases, where hollows and fine structures play a major role, stereolithography is the method of choice.