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46 I I meetings _ 9th Ceramics Symposium CAD/CAM 1_2010 luting is that no retention forms are necessary whatsoever. Depending on the type of material, ceramics have translucent properties; thus, ac- cording to Dr Kurbad, dark fillings can be a dif- ficult foundation. Pronounced discolouration of the crown stump requires greater substance removal, in order to allow the ceramic a greater thickness. _Toughness versus resistance “The fracture toughness of the ceramic is more important than its resistance,” explained Prof Ul- rich Lohbauer (University of Erlangen-Nürnberg, Germany) in his talk on Fracture mechanics of all-ceramicrestorations.Hence,itisanimportant accomplishment that in the structure of zirco- nium dioxide ceramic (ZrO2), volume-expanding compressive forces block the propagation of micro-cracks. The fracture toughness explains the high survival probability of crown and FDP frameworks of ZrO2 in clinical long-term studies. However, there has been recent discussion about veneeringfracturesonZrO2 frameworks3 because the veneer ceramic (feldspar) has a much lower crack toughness than ZrO2. In designing the crowncopings,itisthereforeimportanttoensure thatcuspssupporttheveneeringlayer(Figs.2&3). After grinding (fine diamond), Prof Lohbauer rec- ommended polishing the restoration’s surface (checkwithloupes)duringinsertionor,betteryet, sending it back to the dental laboratory for final firing. In selecting the ZrO2 blank, Prof Lohbauer advised using only original materials from qual- ity-conscious ceramic manufacturers and with proven clinical suitability, and adhering to the procedure for the veneers. This is to ensure that framework and veneering materials match. _From wax knife to mouse Master Dental Technician Volker Brosch (Ger- many) demonstrated the switch from wax knife to electronic framework design, comparing the workflow in conventional dental engineering with the CAD/CAM technique. The digitally con- structed datasets can be used to construct both the temporary and definitive restorations. Fully anatomical anterior and posterior crowns can be made from the millable LS2 blanks, and multi-unit bridges up to the second premolar can also be manufactured from this pressable ceramic of increased strength. Where aesthetic demands are particularly high, the cut-back procedure is used—the fully anatomical crown is anatomically grounddownbythethicknessoftheenamellayer and then fuse-on veneered. Recently, Brosch has made singly designed veneers of fluorapatite pressable ceramic, digitally modelled and then sintered onto the ZrO2 frameworks (Figs. 4 & 5). Unique in dentistry is the multi-centre field study by the SDC, in which dentists in private practice can compare their findings/results on all-ceramic restorations anonymously and in- dividually with other participating practices. At the time, over 5,700 restorations from more than 200 practices constituted the basis of the results. After evaluating over 3,000 follow-up examina- tions, Dr Reiss, who heads this quality-control study, recapitulated that the survival rate of in- lays, onlays, partial crowns, and crowns of silicate FIRST AUTHOR N CERAMIC TIME FAILURE RATES (IN %) (IN MONTHS) ANT. PM M Pospiech 2004c 35 Lava 36 – – 0° Suárez 2004c 10 In-Ceram Zr 36 0° 5.5 Raigrodski 2006c 20 Lava 31 – 0* 0* Sailer 2007a 33 DCM 53 – 26.1°* Molin 2008a/c 19 Denzir 60 0 0 0 Tinschert 2008a/c 65 DSC 37 0° 0* Wolfart 2008c 24 Cercon 45 – 4* Wolfart 2008c 37 Cercon ext-br. 46 – 8.1°* Beuer 2009c 21 Cercon 40 – 9.5 Eschbach 2009c 60 In-Ceram Zr 60 – – 3.2* Wolfart 2009a/c 36 e.max Press 86 0° 6.7* a adhesive luting c conventional luting ° up to 25 % additional fractures * 2.2–4.8 % structural fractures Failure rates of all-ceramic fixed dental prosthesisTable I _Failure rates of all-ceramic bridges. ZrO2 frameworks remained largely fracture-free; chipping interfered with clinical success. (Table courtesy of Prof Matthias Kern, Germany)