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ePaper created 2015-03-06, 14:42:46 | version 1.33.01
I 25 review _ CAD/CAM I CAD/CAM 1_2015 take a traditional impression, after which a stone model is poured and the laboratory scans the stone model. The digitalisation of the dies was performed by a laser scanner (Cercon eye, DeguDent) and the substructures were designed on the CAD programme ofthesystem.Digitalimpressionsystemsaredesigned to electronically transmit the recorded data file to the dental laboratory for restoration fabrication. Efficient chairside assistants will increase the overall production of dental practices by aiding dentists in completing their procedures more quickly and more effectively. Other systems are also used by laboratories to createcopings,substructures,andabutmentsbyCAM, afterwhichhandfabricationofanyrequiredceramics and finishing is conducted either by the same labo- ratory or by the laboratory that scanned and referred thecaseformillingofthesubstructure.Ceramicblocks for laboratory-milled restorations are available as zirconia (zirconium oxide) and lithium disilicate glass blocks.Zirconiumoxidecanbeusedtocreateaccurate and strong copings and bridge substructures. After milling,theunitcanbeadjustedusinganexternalliner (Zirliner, Ivoclar Vivadent) that enables characteri- sation before the outer ceramic suprastructure is created. The external ceramic layer can be created eitherusingpressceramics(inthesamemannerasfor atraditionalbridge)orlayeringceramicmaterialonto thesubstructureusingafinebrushandpowder/liquid. Advantages of a laboratory CAD/CAM milled restoration include reduced chairside time and in- creased accuracy. Since a stone model is not used, stone pouring errors are eliminated as well as errors associatedwithabrasionoftheadjacentandopposing teeth due to manipulation of the models during fab- rication that could result in overcontouring, tight contacts, and excessive occlusal height. In addition, reduced time is required for fabrication of the sub- structure. _Materials CAD/CAM restorative materials are currently available in number of sizes in many shades and translucencies, including multiple shades within one dense gradated restorative block. The material used depends on functional and aesthetic demands and on whether a chairside or laboratory CAD/CAM restorationisfabricated.13 A range of dental ceramic substrates have been developed for chairside machining and are re- presented as prefabricated blocks, manufactured using processing routes identified to reproducibly control the resultant ceramic composition and microstructure.14–16 ForchairsideCAD/CAMrestorations,anaesthetic, strong material requiring minimal post-milling aesthetic adjustment to minimise chairside time is needed.17–19 Leucite-reinforced glass ceramics (IPS EmpressCAD,IvoclarVivadent;ParadigmC,3MESPE) and lithium disilicate glass ceramics (IPS e.max, Ivoclar Vivadent) can be used for chairside and laboratory CAD/CAM single restorations. Leucite- reinforced material is designed to match the den- tition for strength and surface smoothness and to offeraestheticresultsbyscatteringlightinamanner similar to enamel.20 A study has been done to evaluate and compare the marginal gap, internal fit, and fracture load of resin-bonded,leucite-reinforcedglassceramicmesio- occlusal-distal (MOD) inlays fabricated by computer- aideddesign/manufacturing(CAD/CAM)orhotpress- ing: as a result, they provided clinically acceptable marginal and internal fit with comparable fracture loadsafterluting.21 Ceramicblocksforlaboratory-milledrestorations are available as zirconia (zirconium oxide) and lithium disilicate glass blocks. Zirconium oxide (IPSe.maxZirCAD,IvoclarVivadent;Cercon,DENTSPLY Ceramco) can be used to create accurate and strong copings and bridge substructures. Zirconia offers some significant physical properties that are ad- vantageous for dental restorations besides its high strength. It has a similar colour to natural teeth, which reduces the need to opaque it or mask it as would be done for a metal substructure. Zirconia also has good opacity. This may be an advantage when trying to block out underlying discolored teeth or restorative materials. It may also be a disadvantage when trying to develop a more trans- lucent appearance to the crown. Some manufactur- ers can colour the zirconia substructure to simulate dentine shades to improve the desired aesthetic result.22 After milling, the unit can be adjusted using an external liner (Zirliner, Ivoclar Vivadent) that enables characterisation before the outer ceramic supra- structure is created. The external ceramic layer can be created either using press ceramics (in the same mannerasforatraditionalbridge)orlayeringceramic material onto the substructure using a fine brush andpowder/liquid. CompositeresinblocksarealsoavailableforCAD/ CAM restorations.23 Another option is the use of a new resin nanoceramic block that consists of ceramic clusters within a highly cross-linked resin matrix. The resulting block is homogenous, and the restoration can be CAD/CAM-milled chairside or in the laboratory. CAD0115_22-26_Kassis 02.03.15 12:47 Seite 4 CAD0115_22-26_Kassis 02.03.1512:47 Seite 4