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ePaper created 2017-10-13, 12:16:31 | version 1.38.0
12 TRENDS & APPLICATIONS Dental Tribune Asia Pacific Edition | 10/2017 Screw-retained implant-supported restoration in the edentulous maxilla A working document for the production of a milled zirconium dioxide framework 1 4 2 5 3 6 Fig. 1: The structure milled in wax to check the fit.—Fig. 2: The framework was fabricated using zirconium dioxide (Zenostar).— Fig. 3: Sintering the framework. Small sintering drops supported the frame- work during sintering.—Fig. 4: Checking the fit of the titanium sleeves after sintering.—Fig. 5: Comparison between the wax structure and the sintered framework.— Fig. 6: The fired framework with IPS e.max Ceram ZirLiner ready for veneering. By Dr Octavian Fagaras & Milos Miladinov, Romania Wfen veneering zirconium dioxide frameworks, manual dexterity and a profound knowledge of tfe materials is required. Tfe correct use of tfe materials is decisive for success. A screw-retained and tferefore condi- tionally removable restoration is a proven concept for tfe implant pros- tfetic treatment of an edentulous maxilla. Zirconium dioxide is a frame- work material tfat can support a long-lasting result. A state-of-tfe-art zirconium dioxide material sucf as Zenostar T (Wieland Dental) and inno- vative ceramic veneering systems (sucf as IPS e.max Ceram, Ivoclar Vivadent) enable natural-looking prostfetic res- torations to be acfieved in an efficient manner. In principle, zirconium diox- ide is a sopfisticated material tfat re- quires correct and skilled application. Introduction to a patient case An implant-supported, screw- retained bridge was planned for the edentulous maxilla. Based on defined backward planning, six implants were inserted into the patient’s jaw. After the healing phase, the implants in the visible region were provided with trans- versal screw-retained abutments. In the molar region, the final bridge restoration would be occlu- sally screw-retained. Important parameter for frame- work production A set-up of the planned resto- ration was used as a basis for the CAD/CAM-supported production (Zenotec, Wieland Dental) of the zirconium dioxide framework. After digitisation in the design software, the framework shape was reduced according to the cut- back technique. This method cre- ated sufficient space for the ve- neer. The digital structure was first milled in wax so that the fit and precision could be checked (Fig. 1). Subsequently, the framework was milled from a Zenostar T disc. Dur- ing framework construction, it was necessary to include sintering drops as an occlusal support for the restoration so that distortion would be prevented during sinter- ing in the Zenotec sintering fur- nace. In doing so, the restoration was not to be separated from the occlusal tongue (Fig. 2). Sintering distortion was avoided with this method. The sintering process was carried out in the compact, high-temperature Zenotec Fire P1 sintering furnace, which is sup- plied with pre-installed pro- grammes. This sintering furnace can also be freely programmed so that other sintering programmes can be used. We selected the “long programme”. The heating-up and cooling-down phases were set as long as possible in order to achieve an exact result. It should be noted that the sintering time should not be shortened. After sintering, the framework had the required fit- ting accuracy. The restoration was perfectly supported with the oc- clusally positioned sintering drops “...when dealing with a complex restoration on a zirconium dioxide framework, correct handling is a major criterion for success.” (Fig. 3). The titanium sleeves could be easily inserted into the frame- work (Figs. 4 & 5). Tfe recommended sintering pro- gramme: • 20–900 °C for 1.5 h (600 °C/h) • Holding time: 900 °C for 30 min • 900–1,450 °C for 2.75 h (200 °C/h) • 1,450 °C for 2 h • Cooling: 600 °C/h; from 1,450 to 900 °C • 900–300 °C for 1.2 h Preparing for veneering The next working steps re- quire not only manual dexterity but also knowledge of the material firing parameters and furnace set- tings. This is the only way to en- sure a balanced temperature dis- tribution in the bonding area be- tween the framework and the ve- neer. This in turn results in a sound bond and uniform shrink- age of the ceramic layer. Slow cool- ing of the restoration prevents the risk of tension in the fired restora- tion, which therefore minimises the risk of delamination. The exact fit of the restoration justifies the long firing time. It should be noted that the programmes must be adjusted ac- cordingly before the ZirLiner bake (IPS e.max Ceram ZirLiner, Ivoclar Vivadent): • long heating-up time • long cooling-down time Ceramic system and framework Our preferred veneering ma- terial (IPS e.max Ceram) consists of low-fusing nano-fluorapatite. The material has a crystal struc- ture similar to that of natural dentition and allows a speci- fically adjustable combination of translucency, brightness and opalescence. The framework (Ze- nostar T) is an ideal base for the ceramic veneer. The defined cut- back enables the framework to be veneered efficiently. The re- duced tooth shape allows the ve- neering ceramic to be applied in an even thickness. This ensures that the is heated uniformly during firing. For the fabrication of the pros- thetic gingiva, we chose IPS e.max Ceram Gingiva materials, with which we achieved a gingi- val area with a lifelike appear- ance. The materials were applied and fired in a similar manner to the dentine and enamel materi- als. layered ceramic Liner bake First, the ZirLiner bake was carried out using the IPS e.max Ceram ZirLiner, a material with multiple functions. On the one hand, the ZirLiner creates a strong bond between the veneer and the framework. On the other hand, it gives the restoration depth of shade and fluorescence. We do not recommend omitting the ZirLiner, as this can increase the risk of cracks and delamina- tion. Before the ZirLiner is ap- plied, the framework must be free from dust and dirt. Contam- ination must be avoided. The IPS e.max Ceram Liner should cover the framework completely; we recommend applying the mate- rial in uneven layers. After a