Dental Tribune Untited Kingdom Edition

April 16-22, 201222 Lab Tribune United Kingdom Edition About the author Lee Culp is Chief Technology Officer, Microdental Laboratory, Dublin, Cali- fornia Prof Edward A. McLaren is Profes- sor, Founder and Director, UCLA Post Graduate Esthetics; Director, UCLA Center for Esthetic Dentistry, Los An- geles, California page 20DTß chemical composition and/ or application. The IPS e.max lithium disilicate is composed of quartz, lithium dioxide, phosphorus oxide, alumina, potassium oxide, and other components.7 These powders are combined to produce a glass melt, which is poured into a steel mould, where it cools until it reaches a spe- cific temperature at which no deformation occurs. This method results in minimal defects and improved quality control (owing to the translu- cency of the glass). The blocks or ingots are generated in one batch, based on the shade and size of the materials. Owing to the low thermal expansion that results during manufac- ture, a highly thermal, shock- resistant glass-ceramic is pro- duced. Next, the glass ingots or blocks are processed using CAD/CAM-milling procedures or lost-wax hot-pressing tech- niques (IPS e.max Press; Fig 11). The IPS e.max CAD blue block is based on two-stage crystallisation: a controlled double nucleation process, in which the first step includes the precipitation of lithium- metasilicate crystals. Depend- ing on the quantity of col- ourant added, the resulting glass-ceramic demonstrates a blue colour. This ceramic has superior processing proper- ties for milling. After the mill- ing process, a second heat- treating process is performed in a porcelain furnace at ap- proximately 850°C, at which temperature the metasilicate is dissolved and the lithium disilicate crystallises. This results in a fine-grain glass- ceramic with 70 per cent crys- tal volume incorporated into a glass matrix. With two crystal types and two microstructures during processing, the IPS e.max CAD material demonstrates distinctive properties during each phase. The intermedi- ate lithium-metasilicate crys- tal structure promotes eas- ily milling, without excessive bur wear, while maintaining high tolerances and marginal integrity. In the blue stage, the glass-ceramic contains approximately 40 per cent volume lithium-metasilicate crystals that are approxi- mately 0.5μm. The final-stage microstructure of lithium dis- ilicate gives the restoration its superior mechanical and aes- thetic qualities. In this stage, the glass-ceramic contains approximately 70 per cent vol- ume lithium-disilicate crystals that are approximately 1.5 μm (Figs 12–15). The laboratory process Once designed and milled, the IPS e.max ceramic resto- rations are then prepared for final aesthetic adjustments. After the milling sprue has been removed, the technician defines surface texture and occlusal anatomy using dia- mond and carbide burs, care- fully avoiding any alteration to the perfected occlusal and interproximal contacts. After- wards, restorations are rinsed to remove surface debris and dried. Then, the milled blue restorations are placed in a conventional ceramic furnace for the crystallisation process. These restorations were digi- tally designed with an incisal cut-back design that will al- low a minimal application of translucent ceramics to mimic the incisal effects found in nature. Contoured to final anatomic shape, the restora- tions are further aesthetically improved by subtle colouring and glazing. Restoration placement Next, five per cent hydrofluo- ric acid (IPS Ceramic Etching Gel, Ivoclar Vivadent) was ap- plied for 30 seconds onto the internal surfaces of the glazed restorations. Then they were rinsed and dried. This was followed by a silane coupling agent (Monobond-S, Ivoclar Vivadent), which was also placed for a minute onto the internal surfaces, and then air-dried. For the final ce- mentation, Variolink Veneer (Ivoclar Vivadent) was used. After excess cement had been removed, final light-curing was done. The occlusal con- tacts were then reviewed and excursive pathway freedom was confirmed. Owing to the correct capture and alignment of the bite-registration infor- mation, few adjustments were required. Conclusion IPS e.max is about restorative options. Dentists and techni- cians now have a material with which they can do ante- rior or posterior restorations. With four different opacities or translucencies available, a variety of creative aesthetic options can be accomplished in a restoration. Dentists and their laboratory ceramists now have the opportunity to be more creative for their pa- tients (Figs 16–18). Editorial note: A complete list of references is available from the publisher. Fig. 11 IPS e.max milling blocks, shown in blue stage Fig. 12 Milled e.max full contour posterior restoration, shown in blue stage Fig. 13 Milled e.max full contour poste- rior restoration, shown in final crystal- lised stain and glaze stage Fig. 14 Milled e.max cut-back anterior restoration, shown in blue stage Fig. 15 Milled e.max cut-back anterior restoration, shown in final crystallised micro-layered and glazed stage Figs. 16–18 Maxillary anterior section restored with CAD/CAM-designed and -milled e.max restorations, using a micro-layering technique for aesthetics Fig. 17 Fig. 18 Precident is a full service private laboratory, located in St George, Bristol. We are Bristol’s premier implant and all ceramic laboratory. Every technician at Precident is highly qualified and skilled to ensure that we can deliver the highest quality of work to our clients. Not only are we Straumann Platinum certified but we are familiar with all leading implant systems on the market. All our technicians are registered at the General Dental Council. We strive to stay on top of technology and the changing Dental market by attending appropriate courses and lectures on a regular basis. Please contact us at: Tel: +44 (0)117 9355 335 Email: info@precident.co.uk Website: www.precident.co.uk Products: • Implants • Metal Ceramic • Veneers • e.Max pressable ceramic • Zirconia (Metal free) • Prosthetics • Chrome Cobalt partial dentures Download our prescription form and free shipping label from our website at www.precident.co.uk now! Daily collection and delivery service in the Bristol and Bath areas.