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CAD/CAM - international magazine of digital dentistry

28 I I opinion _ CBCT It is remarkable that the wax thickness does not significantly influence the accuracy of the radi- ographic scan and consequently the results of the CA. The software is able to recognise the presence andsizeofthespheresintheCBCTscanandmatches them to those corresponding areas on the cast. This is currently the only method that allows for an overlap with an error margin of less than 0.1 mm.7 Once the data has been collected, it is possible to perform different kinds of analyses before the surgical treatment. The software presents powerful segmentation tools that allow the splitting of the maxillo-facial complex from the mandible, provid- ing two separate images. This feature is relevant in orthodontic and sur- gical planning for calculating bone movement. The clinician can select the tissues to be moved following a procedure similar to the manual one. For example, it is possible to select the osteotomic lines in order to simulate a forwards or backwards mandible shift, finding the exact shift needed (in mm) to properly correct the malocclusion (Fig. 6). Once the bone correction has been finalised, it is possible to create a 3-D orthodontic model and display the resulting dental correction to be ob- tained by the end of the treatment. Finally, shifting back the bone structure (and the dentalarchwiththefinalmodel)totheoriginalmal- occluded position, it is possible to obtain the target cast to be reached before the surgical treatment. On the cast, it is then possible to build successive imagesusingCAD/CAMtechniquestotrackprogress towards orthodontic pre-surgical treatment.8 Virtual surgery has a twofold objective: firstly, to verify that the planned shifts are in fact feasible; and secondly, to position the cast according to the ratios needed to build the surgical splint, which will be used during the surgical procedure. The digital cast superimposition reduces the treatment plan- ning phase, as it is not necessary to reveal the facial arch or to use the articulator. In fact, all the data can be sourced from the combination of the CBCT and cast scans. Recent studies focus on the en- hancementofthesystemthroughthedevelopment of an intra-oral scanner, which will allow direct 3-Dimpressions,skippingtheconventionalimpres- sions, which—although precise—can be influenced by manual errors.9,10 Although complex, using software offers many advantages because it enhances both orthodon- tic and surgical techniques, while ensuring a very high quality result. In fact, a CAD/CAM technique allows for a standardised procedure and easy qualitychecking,incomparisontotraditionaloper- ator-performed techniques, which are open to in- accuracies. _Creating customised multi-bracket appliances In virtual orthodontic and surgical planning, it is possible to create a digital orthodontic model once Fig. 5_Reference aligner. Fig. 6_3-D rendering and selection of anatomic structures. Fig. 7_Pre- and post-treatment maxillary superimposition. Fig. 8_Pre- and post-treatment mandibular superimposition. CAD/CAM 2_2012 Fig. 5 Fig. 6 Fig. 7 Fig. 8