CAD/CAM international magazine of digital dentistry

30 I I industry report _ CAD crown design _CAD/CAM technology allows dental profes- sionals to manufacture solid all-ceramic crowns chairside. A digital image of the preparation is captured with an intra-oral camera and the crown is designed accordingly. A variety of ceramics are available for the construction of the crown, for example an aesthetic, easy-to-mill ceramic such as IPS Empress CAD (Ivoclar Vivadent). As this leucite glass-ceramicisweakerthanzirconiumoxide,these crownsmustbeseatedwiththeadhesivetechnique (for example with Syntac/Variolink II or Multilink Automix, all Ivoclar Vivadent). This makes them strong enough to withstand masticatory forces in the long term. IPSe.maxCAD(IvoclarVivadent),whichhasbeen on the market for some time, is a lithium disilicate glass-ceramic that demonstrates a flexural strength of 360 MPa. This ceramic is machined to the desired shape while it is still in its metasilicate or blue state (approximately 130 MPa). Subsequently, the ceramic is crystallised for 20 minutes. During this process, the material attains its final state and ob- tainsitsexcellentmechanicalandaestheticproper- ties.IPSe.maxCADisavailableinalowtranslucency (LT) version, which is suitable for the fabrication of crowns and implant-retained crowns. The high translucency form is intended for the construction ofinlaysandpartialcrowns.Thestainsandglazeare applied before the crystallisation process. As a result, subsequent polishing is unnecessary. Owing to the high strength of the restoration, ad- hesive cementation with a separate dentine con- ditioner is not indicated as long as the thickness of the ceramic is not less than 1.5 mm. Self-adhesive CAD/CAM 4_2012 Fig. 1_Pre-op situation: the buccal wall of tooth #25 was cracked and featured a large, damaged composite filling—a clear indication for a crown. Fig. 2_A digital impression was taken of the preparation and the antagonists and the situation in centric occlusion (CEREC Bluecam) from the buccal aspect (middle). Fig. 3_Semi-automatic alignment of the maxillary and mandibular jaw models with the help of the buccal image. Fig. 1 Computer-aided crown design—Fabrication of CAD/CAM crowns chairside Author_ Dr Andreas Bindl, Switzerland Fig. 3Fig. 2