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CAD/CAM - international magazine of digital dentistry

concluded the survival rates for IPS Empress inlays and onlays ranged from 96 per cent at 4.5 years to 91 per cent at seven years. IPS Empress crowns had asurvivalraterangingfrom92percentto99percent at three to 3.5 years. Forbothcrownsandonlays,mostfailuresweredue to bulk fracture.2 In general, IPS Empress has higher failure rates in the posterior than the anterior and higher fracture rates on molars compared with pre- molars.3–6 Therefore, IPS Empress is an excellent material choice in the anterior for aesthetically de- manding patients. However, alternative materials exist for posterior use. _Case presentation A new patient called the office and said his crown “exploded.” He presented to the clinic with the crown missing on tooth #9 (Fig. 1). The E4D Dentist System was used to make a digital impression of the prepa- ration and the bite registration. Using the intuitive design features in the E4D software, a restoration was designed (Fig. 2). An IPS Empress CAD Multi A1 restoration was milled and characterized using IPS Empress Universal Stains. For delivery, the crown waspreparedbyetchingwith4.9%hydrofluoricacid for 60 seconds and silanated for 60 seconds with Monobond-Plus (Ivoclar Vivadent). The tooth was pumiced; Optibond XTR (Kerr) was applied and cured for 20 seconds; and Nexus 3 resin cement (Kerr) was used to bond the crown (Fig. 3). The use of IPS Empress has been selective partly because of the popularity of IPS e.max CAD (lithium disilicate). IPS e.max CAD comes in a lithium metasil- icate state (blue colour) that is not fully crystallized but can be easily machined. The milled restoration is then placed in the oven for 19 to 26 minutes to crys- tallize the glass. During crystallization, the lithium metasilicate crystals are replaced with lithium dis- ilicate crystals, increasing flexural strength from around 160 MPa to 360 MPa. IPS e.max was introduced to the market in 2006. Gehrt and colleagues followed 104 IPS e.max crowns in 44 patients and found the corresponding survival rate for all restorations was 97.4 per cent after five years and 94.8 per cent after eight years of clinical servicewithlocationnotsignificantlyimpactingsur- vival rate.7 These results were for IPS e.max press restorations that were cut back and veneered. It Fig. 3_An IPS Empress DAC Multi A1 restoration is milled and custom characterized using IPS Empress Universal Stains. Figs. 4–6_In this case, a patient who was not happy with the aesthetics of an amalgam restoration presented with recurrent caries on the mesial of tooth #13. The E4D Dentist System was used to make a digital model, and restorations were milled out of IPS e.max CAD HT A2 blocks. I 07 CE article _ practical lessons in CAD/CAM I CAD/CAM 3_2013 Fig. 4Fig. 3 Fig. 6Fig. 5