impression. The fully automated grinding process (with the use of 6 axes, and not 3, as previously) and the use of smaller diamond

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1 Prosthetic dentistry Cluj-Napoca 2 3 Corresponding author: Burde.Alexandru@umfcluj.ro The Cerec system (an acronym for Ceramic reconstruction) is a compact computer integrated imaging and milling system created to eliminate as much as possible human input and errors during various lab procedures. The advantages of the Cerec system include a more economical restoration, comparatively with a conventional one, due to the cost savings generated by the elimination of conventional impression and temporary restoration. [1] Created in 1985 by Mörmann and Brandestini, the Cerec System has been constantly improved, as follows: the initially Cerec 1 COS. 1.0 has been replaced, in 1991, by COS. 2.0 version; in 1993, 2 COS. 4.2 was able to mill not only veneers but also inlays, onlays and full ceramic crowns. The improved features of Cerec 2 are: the software for the camera and imaging process, which adds contouring aspects to the design capabilities; impression. The fully automated grinding process (with the use of 6 axes, and not 3, as previously) and the use of smaller diamond automatically generated occlusion and free cavity design [1]. The detachable cover of the 3D camera in Cerec 2 enables sterilization. Cerec 2 has improved features for camera and image processing and design, which enhance the automate calibration function and add contouring aspects to the design capabilities The central processing unit is more powerful in terms of speed, memory and storage, and colour and graphic capabilities have been also added [1]. Equally, due to an optimized optical beam path by means of symmetrical bean geometry, major measurement errors in measuring the volume of a restoration operation have been brought down to less than +/- 25 micrometer [1]. The most recent version of the CAD CAM system allows tridimensional visualization of the projected restoration, with virtual seating capabilities. dimensions before machining. The grinding process lasts usually 2-8 minutes. Cerec 3 was elaborated in the year 2000, and in 2003 the 3D version software, which enables 3D visualization of the casts, was launched. was elaborated in 2005 and were able to mill inlays, onlay, veneers, on using ceramic blocks up to 20 mm. In 2008, Sirona produced the MCXL milling unit with an average 4 min working time per crown. Milling of bridges, as well as of surgical guides and dies for implants - the MCXL unit - using blocks up to 40 mm, became thus possible. zirconia dentures containing up to 12 elements can be milled, using a block up to 85 mm. Cerec developed the imaging features of the preparation in time, so that, nowadays, it can be performed in various ways: RedCam, BlueCam or Omnicam. The RedCam uses infrared light, International Journal of Medical Dentistry 313

2 Sorana BACIU, Alexandru-Victor BURDE, Alexandru GRECU, Mariana CONSTANTINIUC needing coating of the preparation with opaque powder and manual focusing. In 2009, Sirona launched CEREC Acquisition Center (AC) equipped with Bluecam. It uses UV light, coating with powder and electronic focusing. Omnicam, the latest version, uses a live colour camera and no powder for image capture. The use of different milling materials grants highly aesthetic reconstructions. Some of the and veneering/staining stage (presintered raw blocks of zirconium oxide), while other materials are found as completely sintered blocks. The last ones have increased hardness, so they are too tough to be milled or they wear the burs very quickly. The presintered blocks are softer, easier to mill and they have a violet color, for reminding the practitioner that, after milling, they have to be sintered (presinterized blocks - 150Mpa; after sintering 400Mpa). The presintered zirconium blocks - included in this category - have a bright, white color and are used to obtain either fully contoured crowns or copings, to be subsequently veneered with ceramic layers. The zirconium oxide partially stabilized with Ytrium oxide enhances the mechanical properties of the material and prevents cracks [2]. The material demonstrates excellent physical and chemical characteristics. At 2,700 o C, its melting point is ceramic materials, which improves stability, zirconium is softer, which means shorter milling times, reduced instrument wear, as well as higher precision. Sintering will shrink the restoration by 18-25%, but this is factored into the design so that the computer automatically oversizes the contour of restoration, to allow preservation of dimensional precision [2]. Consequently, it can be employed in both lateral and anterior areas for patients with high aesthetic expectations. Nowadays, the materials that can be used with the CAD CAM technique can be divided as follows: 1. Feldspathic ceramics (materials containing feldspar as a major crystalline phase within a glassy matrix), monochromatic Vita Mark II blocks (which have to be selected slightly darker than the tooth colour) [1], polychromatic blocks - Vita Trilux Forte, Vita Real Life - (the latter having a new feature, namely the inner side, the core of the block having a different colour, so that it can very well imitate the shades of dentin), 2. Empress CAD leucite reinforced ceramic blocks with 2 translucency degrees, 3. IPS e.max CAD lithium disilicate blocks. Lately, blocks made out of a mixture between composite resins and ceramic particles (Vita Enamic), or blocks containing zirconium particles embedded in a composite resin (Vita Suprinity) have been elaborated. Both are milled, stained the sintering process. Vita Suprinity, a new glass homogeneous structure which assures excellent material quality and consistent high load capacity, as well as long-term reliability. Moreover, the material offers outstanding processing characteristics, such as easy milling and polishing. Thanks to the excellent this new glass ceramic material, Vita Suprinity provides excellent aesthetic properties. Tooth preparation was performed following all typical ceramic guidelines. For the impression, the wash-technique, and putty and low-viscosity condensation silicone Optosil/Xantopren (Heraeus Kulzer) were applied. The master cast with removable dies was immediately obtained by pouring into the impressions a special class during optical scanning. The casts were mounted into an articulator (Protar5) by means of an occlusion impression. 314 v 18 pp

3 PARTICULARITIES OF LABORATORY PROCEDURES FOR OBTAINING AN AESTHETIC OVERLAY WITH CEREC TECHNOLOGY The removable die with the preparation and the whole master cast is scanned using the Cerec of the preparation was achieved by aligning the camera with the insertion path and subsequent storage in the computer. The modelled morphology and landmarks can be improved by redesigning the mesio-distal The image is cropped so that only the removable die with the preparation can be seen The preparation margins, as well as the marked with the software which assists this step An important feature is that the Cerec system automatically blocks out any undercuts during the optical impression, yet care should be taken not to allow excessive undercuts, especially at the basis of the cusps, because they will be cannot act as a dentin replacement/substitute [3] To obtain an integrated occlusal morphology, the following steps are to be considered [4]: establishing the cervical limit of the preparation, marking the contour height of the neighboring teeth, so that the correct mesio-distal diameter can be approximated, verifying the position of the mesio-distal groove, and marking the tips of the cusps. After that, the computer establishes the height of the restoration contour and its occlusal limit and, by connecting the established lines, the anatomy of the improved reconstruction Fig. 5 Fig. 6 The wax pattern was made on the removable Fig. 1 For the present overlay, a VitaMark II block shade A2 was selected. The shade of the ceramic block had to be slightly darker than the colour of the restored tooth, as suggested by Goldstein, International Journal of Medical Dentistry 315

4 Sorana BACIU, Alexandru-Victor BURDE, Alexandru GRECU, Mariana CONSTANTINIUC main characteristic of this material is its homogenous structure, obtained by including 4 micrometer small particles into a feldspathic scaffold with 3D-microrelief, which improves adhesion during cementation [5]. The fully automate grinding process uses grinding units roughness of the internal walls of the overlay can be also chosen to improve adhesiveness during for 7 min. Additional natural appearance is achieved with stain. Fig. 13 Fig. 14 Try-in and cementation have been done carefully, with very little pressure. These are demanding operations, because of the relatively fragile nature of the ceramic material, and need for a nearly perfect moisture control and use of composite cements. Considering the fragility of the material, occlusal evaluation and adjustment were delayed until after cementation. surface of restoration, to increase both the surface area and micromechanical bonding of the composite to the ceramic restoration. A white procedure. Applying a silane coupling agent aimed at facilitating the chemical bonding of the composite cement. Then, the preparation surfaces were etched, the enamel-dentin bonding system cement was mixed and the restoration was shaped diamond instruments, and also carbide surface. Limitations of the Cerec system are represented by the inability to replicate internal staining (only external shading Vita Shading Paste and Glaze Vivadent) and also by the larger marginal gaps than in the traditional methods [1]. exhibited in early stages improved in time. The automate fully grinding process used nowadays results in higher accuracy, automatically generated occlusion, free cavity design, overlays production, as well as various anatomical veneer preparations with incisal edge cover [1]. As to et al. [6] found out an average thickness of 89 microns on the occlusal cavosurface margins, and reported a very good state of the restorations after 2 years, with a cement loss of only 50 microns. In a 3 year-study, Isenberg Essig Leinfelder [7] reported that none of the restorations exhibited secondary caries throughout the three year period. In the beginning, occlusal positive and negative landmarks were badly reproduced, and the marginal gap was higher than in other improved and reproduction of occlusal morphology was also possible. With the high resolution of the intraoral scanner in Cerec 3 (25 μm) and the quality of reproductibility of the milling unit (±30 μm), high standard parameters were obtained [8]. Studies on 2,328 chair side inlays/onlays showed a surviving rate of 95.5% after 9 years [9] An 18 year-study performed on 1,011 inlays/ onlays showed a surviving rate of 84.4% [10]. 316 v 18 pp

5 PARTICULARITIES OF LABORATORY PROCEDURES FOR OBTAINING AN AESTHETIC OVERLAY WITH CEREC TECHNOLOGY Another 9.5 year-study [11] performed on 617 veneers gave a surviving rate of 94%. The Cerec2 system using VitaMark II blocks can be employed in both lateral and frontal areas, for patients with aesthetic expectations, as it combines good aesthetics by external staining with good resistance to occlusal force. Marginal adaptation has been improved and greater translucence of the margins was achieved, because of the absence of metallic structures. The are recorded for both patient and dentist. The system permits fabrication on various types of single unit reconstructions, as well as elaboration and certain ceramic blocks. Still, one should not forget that, although computer-generated restoration for the patients, some of them may colour perfectionists. However, as Massek (quoting Goldstein- Esthetic in Dentistry) showed, predictable results can be obtained by Acknowledgement 1. Goldstein RE. (1998) : Second Edition. Vol 1. B.C. Decker, p: Sironi D, Pasceta R, Romeo G. (2005) Precision in. Quintessence Pub Co, p: Roberson TM, Heymann HO, Swift EJ. (2001) Operative Dentistry. 4 th ed. Mosby, p: Bratu D, Nussbaum R. (2009) Bazele Clinice si Tehnice. 1 st ed. Medical Publishing House, p: SUPRINITY html 6. Sturdevant JR, Bayne SC, Heymann HO. (1999). Journal of Esthetic and Restorative Dentistry, 11(4): Isenberg BP, Essig ME, Leinfelder CF. (1992) Three-. Journal of Esthetic and Restorative Dentistry, 4(5): Fasbinder D J. (2006). In Mörmann WH: Berlin, p: Posselt A, Kerschbaum T. (2003) [in German]. Dentistry, 6(3): Reiss B. (2006) Practice 11. Wiedhahn K. (2006) International Journal of Medical Dentistry 317