International Journal of Computerized Dentistry, 01/2011

The digital intraoral impression has become a central part of the CAD/CAM technique. The objective of the present study was to compare the accuracy (trueness and precision) of digital impressions of the full arch with that of conventional impressions on the in-vitro model. For this purpose, a master model was acquired with a new reference scanning process, the measuring trueness of which was ± 4.1 µm and the precision ± 2.5 µm. On the one hand, conventional impressions and then plaster models (n = 5) were produced from this master model, and on the other hand, digital impressions were made with the Cerec AC Bluecam and the Lava COS system (each n = 5). The plaster models were also scanned with the reference scanner. The available data records were superimposed and the differences determined. The deviation from the master model defines the trueness of the impression method. The deviations of the models among one another demonstrate the precision of the method. The trueness of the impressions was 55 ± 21.8 µm in the conventional impression group, for digital impressions with Cerec Bluecam it was 49 ± 14.2 µm and for digital impressions with Lava COS 40.3 ± 14.1 µm. The precision was 61.3 ± 17.9 µm for conventional impression with Impregum, 30.9 ± 7.1 µm for digital impression with the Cerec Bluecam and 60.1 ± 31.3 µm for digital impression with Lava COS. These invitro results show that accuracy of the digital impression is similar to that of the conventional impression. These results will have to be confirmed in further clinical studies. Keywords: digital impression, CAD/CAM, accuracy, trueness, precision, Cerec Bluecam, Lava COS

CAD/CAM methods are also being used ever more frequently to produce fully anatomical restorations. These automated, computer-assisted methods play an outstanding role in generating occlusal surfaces. This study examines whether such computer generated occlusal surfaces are comparable with those which an experienced dental technician functionally waxes-up in the individually controlled articulator. A comparison of the occlusal surfaces in twelve posterior teeth of eleven functionally healthy patients showed differences ranging from 380 to 530 µm related to the mean difference in volume between both types of occlusal surface. Furthermore, a mean pixel deviation of the superimposed occlusal surfaces of 5.12 ± 1.951 µm (min: 2.49 µm, max: 9.16 µm) was observed. These deviations were found for both functionless surfaces and occlusal surface areas of the functional occlusion. Thus, comparable occlusal surfaces can be achieved with computer generated methods, but they do not quite achieve the result of functionally waxed-up occlusal surfaces in the individually programmed articulator. Keywords: functional occlusion, dynamic occlusion, occlusal surface design, computer generated occlusal surfaces, CAD/CAM method, CAD/CAM occlusion

Two new developments extend the spectrum of the Cerec applications: Cerec-Connect: The entire mandible and maxilla can be scanned, as well as their relationship to one another, with the intraoral scanner. Multilayer technique for up to four-unit fixed dental prostheses (FDPs): the CAD-on technique from Ivoclar is the latest procedure in which a zirconium oxide framework and a veneer structure of e.max-CAD are bonded together by ceramic. Intraoral data acquisition with Cerec-Connect, design with Cerec-inLab and fabrication of the three-unit FDP are described and illustrated with a clinical case, and further developments are suggested. Keywords: Cerec FDP, multilayer FDP, CAD-on technique, lithium disilicate FDP, impression-free dentistry

The success of all-ceramic crowns and increased patient demand for metal-free, tooth-colored restorations has led to the development of many different restorative systems for all-ceramic fixed dental prostheses (FDPs). The most recent core materials for all-ceramic FDPs are the yttrium-tetragonal zirconia polycrystal (Y-TZP)-based materials. Yttrium oxide is a stabilizing oxide added to pure zirconia to stabilize it at room temperature and to generate a multiphase material known as partially stabilized zirconia. This exhibits very high flexural strength and fracture toughness along with good biocompatibility and excellent esthetics. This clinical report describes the use of the Lava All-ceramic system, based on Y-TZP, for the fabrication of two fixed dental prostheses (FDPs) in the maxillary anterior region of the patient, restoring both esthetics and function. Keywords: all-ceramics, esthetics, crowns, fixed dental prostheses, CAD/CAM technology, zirconia

Digital acquisition of the clinical situation in the mouth seems much more logical than digitizing the impressions. Intraoral scanning systems are laser supported or video based. The retraction of the gingiva plays a special part in the accurate display of the preparation border. The working procedures in the dental practice and in the dental laboratory have been changed fundamentally by this new technology. Workable solutions are already available and rapid further developments can be expected in the near future. Keywords: CAD/CAM, digitization, impression, intraoral scanner, model production