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Dental TribuneAsia Pacific Edition | 4/201612 TRENDS&APPLICATIONS Full-arch implant-supported su- perstructures can be achieved by various methods. Depending on the bone quality and number of implants,thepatient mayeitherre- ceive a fixed or removable implant restoration. If a fixed prosthesis is indicated, the superstructure may either be cemented or, alter- natively, screwed directly to the implant fixture, depending on the clinical situation. In the case described here, we opted for a cemented zirconium oxide bridge. Monolithic crowns were used in the posterior region. Fortheanteriorregion,thecrowns were cut back and veneered. Translucent zirconium oxide (Zenostar T, Wieland Dental) was used for the framework and IPS e.max Ceram for the veneering of the anteriors. These materials al- lowed us to achieve the desired strength and aesthetics. When the patient came to our dental lab, she wore a classic full- arch denture in her upper jaw. She was unhappy about the aesthetic appearance, functional qualities and the loose fit of the denture. Her oral condition was assessed with digital volume tomography (DVT) to confirm that adequate bone quantity was available to facilitate the anchorage of the implants. Although the placement of four implants would have provided adequatestabilityforaremovable denture, the patient asked for a fixed all-ceramic reconstruction. Having discussed the treatment options with her, we abandoned the idea of providing an implant- supported denture based on the “All-on-4” concept and instead chose to manufacture a fixed, im- plant-retained bridge. The frame- work would be made of zirconium oxideandtheanteriorteethwould be individually veneered. Based on the DVT examination, seven implants (Replace CC, Nobel Biocare) were planned and placed. An adequate primary stability of 30to35Ncmwasachieved.During the healing phase, the patient woretheexistingdenturethathad been relined with soft silicone. After a six-month healing pe- riod, a satisfactory level of os- seointegration was achieved, without any signs of bone resorp- tion or inflammation. The im- plants were uncovered and gin- giva formers inserted. Two weeks later, an impression was taken to transfer the position of the im- plants to the dental lab. After model fabrication, appropriate abutments were selected and adapted to achieve a common in- sertdirectionforthebridge(Fig.1). Digital technology was used to manufacture the temporary bridge. The model was scanned with a Zenotec D800 lab scanner (Wieland Dental) and the tempo- rary bridge was designed with the 3Shape dental design software. Milling was carried out in a Zenotec select S2 milling unit (Wieland Dental) using a PMMA material (Telio CAD). Framework fabrication Since the patient was satisfied withtheshapeandfunctionofthe temporary restoration, we used it asthebaseforthefinalrestoration design. The natural wear facets that formed during the tempori- sation period should be reflected in the final restoration. A conven- tional impression of the oral sit- uation was taken in the practice. In the lab, a model and a gingival mask were prepared and scanned. First, the working model together with the temporary bridge was digitalised. Then we scanned the model together with the abut- ments, the opposing jaw model and the bite registration. Finally, the abutments were scanned indi- vidually one after the other be- cause the abutment shoulders were located subgingivally and could therefore not be captured accuratelyenoughwiththemodel scan alone (Figs.2a & b). CAD construction First, the position of the digi- tised model was defined in the de- sign software according to the common insert direction of the abutments. In a second step, the shoulder lines of the abutments were marked and the thickness of the cement gap was defined. The shoulder line represents the “preparation margin” of the restoration. In this case, we set the cement gap to 0.2 mm and the cement space to 0.4 mm. The thickness of the cement gap at the marginalborderwassetto0.1mm. From our experience, these set- tings result in an excellent accu- racy of fit of the restoration on the model and in the patient’s mouth, eliminating the need for later ad- justments. At the end, the design of the restoration was checked once more against the individual design parameters. If the wall thickness is lower than the mini- mumacceptable,thesoftwarewill issue a warning and enable an automated remediation step. The final restoration was de- signed using the full-contour long-term temporary as a basis. The full contours of teeth 13 to 23 were reduced by 0.9 mm on the vestibular aspect to make space forthepartialveneers(Figs.3a&b). The incisal border was left fully contoured as a large number of functional movements occur in this area. The fully contoured shapes of the posterior teeth and thepalatalsurfacesoftheanterior teethwereleftunalteredtoensure a maximum level of strength in the final restoration. There was a risk that the abutments might shimmerthrough.Forthisreason, we decided to use translucent zir- conium oxide. The layer thickness appeared to be adequate to mask the abutments. Milling The completed CAD design di- vides a basic crown framework into18,000to20,000coordinates and generates a harmonious sur- face texture and perfect marginal seal. The completed design was transferred 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 informa- tion on the specified cement gap, implantaxesandrestorationmar- gins. The CAM software uses this information to calculate milling parameters that distinguish be- tween the different areas of the restoration. For instance, when milling the restoration margins, the unit reduces the speed, infeed and feed rate to prevent thin crown margins from breaking or fracturing. As a result, even wafer- thin cervical margins having a thickness of as little as 0.1 mm can be reliably milled and require only very little reworking after the sintering process. In less sensitive areas, the unit uses a higher milling speed. After the output format has been entered, a milling strategy using 2.5 mm, 1.0 mm and 0.7 mm burs was selected for the produc- tion of the bridge. The option of using a 0.3 mm bur was not taken as it was not needed for the restoration in question. Next, the job was placed in a virtual Zenostar blank (Fig.4). We decided to use a translucent, pre-shaded Zenostar T zirconium oxide disc in the shade T sun, because the posterior teeth from 14 to 16 and 24 to 26 were planned to be re- storedwithmonolithiczirconium oxide. The warm, reddish shade of this disc closely matches the se- lected tooth shade and allows the A–D shades to be recreated effi- ciently and reproducibly. A sinter support structure was designed to allow the restoration to be sintered in an upright posi- tion in the Programat S1 sintering furnace. The sinter frame min- imises distortion during sintering and is instrumental in achieving a high accuracy of fit in long-span objects. Finally, the program cal- culated the milling data in a process that took less than three minutes to finish. Then, the milling operation was started. This process was achieved in a Zenotec select S2 milling unit that features 5-axis operation and an 8-disc material changer (Wieland Dental). The absolute precision with which this unit Fixed aesthetic restorations Combining implantology with dental CAD/CAM technology By Dr Dario Žujic,DTVelimir Žujic,Croatia & DT Dragan Stolica,Slovenia 1 2a 2b 3a 3b 4 5 6 7 Fig.1:Thesevenimplantsin theedentulousjawwere tobeconnected toafixedbridgemadeofzirconiumoxide.—Figs.2a&b:Digitizedmodelwith temporaryrestorations (above)andabutments(below).—Figs.3a&b:First,therestorationwasdesignedinfullcontourandthencutbackinthevisibleaestheticregion.—Fig.4:Nestingofthebridge frameworkintheCAMsoftware.—Fig.5:Aftermilling:highprecisionresultwithframeworkpriortosinteringexcellentmarginalaccuracy(incisal,occlusal).—Fig.6:Shading the interior crown surfaces and basal surfaces.—Fig.7: Customised framework prior to sintering. DTAP0416_12-15_Zujic 30.03.16 15:18 Seite 1 567 DTAP0416_12-15_Zujic 30.03.1615:18 Seite 1