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CAD/CAM - international magazine of digital dentistry

| case report aesthetic restorations 22 CAD/CAM 2 2016 strengthinthefinalrestoration.Therewasariskthat the abutments might shimmer through. For this reason, we decided to use translucent zirconium oxide. The layer thickness appeared to be adequate to mask the abutments. Milling The completed CAD design divides a basic crown framework into 18,000 to 20,000 coordinates and generatesaharmonioussurfacetextureandperfect marginal seal. The completed design was trans- ferred to the CAM unit. We use the V3 CAM version, which gives us the option to choose between various output formats. The Zenocam 3.2 format is our preferred output option because, in contrast to the open STL format, it provides information on the specified cement gap,implantaxesandrestorationmargins.TheCAM software uses this information to calculate milling parameters that distinguish between the different areas of the restoration. For instance, when milling therestorationmargins,theunitreducesthespeed, infeed and feed rate to prevent thin crown margins from breaking or fracturing. As a result, even wa- fer-thin cervical margins having a thickness of as little as 0.1 mm can be reliably milled and require onlyverylittlereworkingafterthesinteringprocess. In less sensitive areas, the unit uses a higher milling speed. After the output format has been entered, a milling strategyusing2.5mm,1.0mmand0.7mmburswas selectedfortheproductionofthebridge.Theoption of using a 0.3 mm bur was not taken as it was not neededfortherestorationinquestion.Next,thejob was placed in a virtual Zenostar blank (Fig. 4). We decidedtouseatranslucent,pre-shadedZenostarT zirconiumoxidediscintheshadeTsun,becausethe posterior teeth from 14 to 16 and 24 to 26 were planned to be restored with monolithic zirconium oxide. The warm, reddish shade of this disc closely matches the selected tooth shade and allows the A–D shades to be recreated efficiently and repro- ducibly. A sinter support structure was designed to allow the restoration to be sintered in an upright position in the Programat S1 sintering furnace. The sinter frame minimises distortion during sintering and is instrumental in achieving a high accuracy of fit in long-span objects. Finally, the program calculated themillingdatainaprocessthattooklessthanthree minutes to finish. Then,themillingoperationwasstarted.Thisprocess wasachievedinaZenotecselectS2millingunitthat features 5-axis operation and an 8-disc material changer (Wieland Dental). The absolute precision with which this unit works was evident in the ex- cellent milling results obtained on the occlusal and palatal surfaces and at the incisal edge (Fig. 5). Customising the framework Oncethemillingwascompleted,theframeworkand the sinter support structure were separated from Fig. 5: After milling: high precision result with framework prior to sintering excellent marginal accuracy (incisal, occlusal). Fig. 6: Shading the interior crown surfaces and basal surfaces. Fig. 7: Customised framework prior to sintering. Fig. 8: After sintering: smooth colour transition and ideal basic shade for completing the bridge. Fig. 9: Comparison between white opaque zirconium oxide (superimposed simulation at the top margin) and the Zenostar Zr framework. Fig. 10: After the liner and foundation firing… Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 22016

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