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ePaper created 2015-09-09, 12:07:54 | version 1.38.0
I case report _ implant restorations plate (bite rim). In the upper jaw, the occlusal rim was shaped in such a way that 2 mm of the edge was vis- iblewhentheupperlipwasinrestposition.Thelower edgeoftherimwasalignedparalleltothebipupillary plane and smoothly followed the curve of the lower lip when the patient smiled. On the maxillary rim, the midline,thesmilelineandthelineofthecanineswere outlined. A facebow was used for the transfer of the maxillary position in relation to the base of the skull. Once all of the relevant ratios had been obtained, the models were mounted on the articulator (Fig. 5). The difficulty of this case was that we had to make allowance for the existing mandibular restoration in thedesignofthemaxillaryrehabilitation.Theimplant axes of the mandibular prosthesis in particular posed some problems. Shade selection was dictated by the mandibular restoration and, consequently, our room for decision-making was reduced to deciding on the shape of the teeth. To this end, a photograph of the patientasayoungadultwasuseful,asitwasherwish that the shape and size of her teeth as they were when she was young should be re-established in the prosthetic reconstruction. With the aim to attain as perfectaprosthesisaspossibleandtomakethemost of the available space, we created a wax set-up using prefabricated denture teeth (SR Phonares II, Ivoclar Vivadent). _Primary structure A try-in of the set-up was performed to check the phonetics, aesthetics and occlusion (Fig. 6) and then a silicone key was created over the set-up. This acted as a guide in the subsequent working steps. In order to manufacture the primary structure, the four tita- nium abutments were customised (Fig. 7), the result- ingabutmentswerescannedtogetherwiththemodel and set-up (double scan), and these datasets were imported into the design software. The CAD program proceeded to suggest the shape, height and angula- tion of the telescope crowns, which we adjusted and optimised as required (Fig. 8). The primary telescopes were milled from zirconia and sintered to their final density at 1,500 °C. After the accuracy of fit had been checked, the zirconia crowns were permanently bonded to the titanium abutments (Multilink Hybrid Abutment, Ivoclar Vivadent). Finally, the zirconia tel- escopeswereadjustedusingalaboratoryturbineand parallelograph.Thewallsofthetelescopesweregiven a 2-degree incline and smoothed using appropriate diamond grinding tools and sufficient water-cooling (Figs. 9 & 10). _Secondary structure The primary crowns could now be prepared for manufacturing the secondary crowns by means of the electroforming technique. For this purpose, the zirconia surfaces were covered in a thin coating of conductive silver using the airbrush method. Upon completion of the process, the galvanised gold crowns were detached from the telescopes and the conductive silver coating was removed with a so- lution containing nitric acid. In the process, a highly accurate secondary structure was obtained. _Tertiary structure All of the components were repositioned on to the working model. Before the tertiary structure was fabricated, the electroformed crowns were covered Fig. 11_Intra-oral bonding of the electroformed secondary structure with the tertiary structure. Figs. 12 & 13_Detailed view of the completed denture: customised prefabricated teeth and soft-tissue parts. 24 I CAD/CAM 3_2015 Fig. 11 Fig. 12 Fig. 13