CAD/CAM - international magazine of digital dentistry

I 31 industry report _ lithium disilicate I CAD/CAM 1_2012 occlusalinterproximalcontactareasand,finally,the gingival margins of the preparation. Using input and neighbouring anatomic detail asabasis,thesoftwarewillplacetherestorationsin an appropriate position—but not to the clinically ideal location. Instead, the operator relies on his or her knowledge of form and function and experi- ence to reposition and contour the restoration. As the crown’s position and rotation are fine-tuned, the software’s automatic occlusion application will readjust each triangular ridge and cusp tip—and the restoration’s contours, contacts and marginal ridges—employing the preferences and bite-regis- tration information. The virtual restoration adapts all parameters in relation to the new position. In- stantaneously, the position and intensity of each contact point is illustrated graphically and colour mapped, where it can easily be modified based on the operator’s and clinician’s preferences. Through a variety of virtual carving and waxing tools, customisation and artistry are also possible. These tools can be used to adjust occlusal anatomy, preferences and contours, reflecting actual labo- ratory methods. Each step in the process is updated on the screen; therefore, the effect of any changes is immediately apparent. For this case, three files wereloadedintothecomputersoftwareforrestora- tion design. Scans of the preparations, provisional restorations and opposing dentition were joined to form a composite file that represented the patient’s oral situation accurately (Fig. 9). Once the final vir- tual restorations have been completely designed (Fig. 10), the milling chamber with the predeter- minedshade,opacityandsizeoftheIPSe.maxblock is loaded, an on-screen button is pressed, and an exact replica of the design is produced in ceramic in a short time. Glass-ceramics are categorised according to their chemical composition and/or application. The IPS e.max lithium disilicate is composed of quartz, lithium dioxide, phosphorus oxide, alumina, potas- sium oxide, and other components.7 These powders are combined to produce a glass melt, which is poured into a steel mould, where it cools until it reaches a specific temperature at which no de- formation occurs. This method results in minimal defects and improved quality control (owing to the translucency of the glass). The blocks or ingots are generatedinonebatch,basedontheshadeandsize of the materials. Owing to the low thermal expan- sionthatresultsduringmanufacture,ahighlyther- mal, shock-resistant glass-ceramic is produced. Next, the glass ingots or blocks are processed using CAD/CAM-milling procedures or lost-wax hot-pressing techniques (IPS e.max Press; Fig. 11). The IPS e.max CAD blue block is based on two-stage crystallisation: a controlled double nucleation pro- cess, in which the first step includes the precipita- tion of lithium-metasilicate crystals. Depending on thequantityofcolourantadded,theresultingglass- ceramic demonstrates a blue colour. This ceramic hassuperiorprocessingpropertiesformilling.After Fig. 12_Milled e.max full contour posterior restoration, shown in blue stage. Fig. 13_Milled e.max full contour posterior restoration, shown in final crystallised stain and glaze stage. Fig. 14_Milled e.max cut-back anterior restoration, shown in blue stage. Fig. 15_Milled e.max cut-back anterior restoration, shown in final crystallised micro-layered and glazed stage. Fig. 13 Fig. 15 Fig. 12 Fig. 14