Virtual three-dimensional planning in orthognathic surgery - comparing completely digital workflows

The planning of interventions in orthognathic surgery is increasingly no longer carried out on gypsum models in the articulator, but using three-dimensional digital media. In these processes high-resolution 3D images of the teeth from direct intraoral scanning or the digitisation of gypsum models are combined with information on the cranialfacial morphology in order to plan and monitor movements through the osteotomies. The change in the position of the jaws is the basis for the production of splints using rapid prototyping (RP) technologies. In the first described methodology (bimaxillary procedure), the target occlusion is determined by means of virtual models. Now, in a superimposition of the virtual models with the data of a Cone Beam CT, the necessary displacement of the bony structures of the upper and lower jaw can be calculated (iPlan, BrainLab AG, Feldkirchen). This simulation serves as the basis for intraoperative navigation, which optimally positions the maxillo-mandibular block defined by the target splint without an intermediate splint to the skull. The second workflow uses the same basic principles, but also includes motion information on the lower jaw. This is beneficial for patients without a safe centric relation. In this case, a joint-related initial situation is determined by means of the SICAT function (Sirona GmbH, Salzburg), and this is used for a splint produced by means of RP technology (joint fixing is done by means of positioning plate). The target point (unimaxillary interventions) is created in OnyxCeph 3D Lab (ImageInstruments GmbH, Chemnitz) with an occlusogram of the target position and printed three-dimensionally. The advantages and disadvantages as well as limitations of these digital process chains are presented and discussed with the aid of patient examples. This also takes into account technical aspects in the interaction of different software tools and formats. Keywords: orthognathic surgery, rapid prototyping, 3D planning