CAD/CAM - international magazine of digital dentistry

28 I I industry report _ lithium disilicate or hybrid layering techniques, which have been used for years with IPS Empress Aesthetic (Ivoclar Vivadent). The HT ingot is meant for stain and glaze techniques. Choosing one of these four different aesthetic options depends on the preparation and the tech- nique to be used in order to match the adjacent dentition or restorations. In addition, the labo- ratory can select the processing choice that is appropriate for the selected restoration. IPS e.max includes press and CAD/CAM options because lithium disilicate can be pressed from ingot form or milled from a block form. If the CAD/CAM option is used, the technician will design the restora- tiondigitallyratherthanperformafullwax-upand invest/press. _Preparation options If LT or HT ingots will be needed, then dentists can have flexibility with their preparations because ofthetranslucentmargins.Thisisthesituationwith partial preparations (for example inlays, onlays and veneers)—the margins can be placed wherever clinically proper. IPS e.max’s translucency enables dentists to place the margins virtually anywhere on the restoration, blending seamlessly with the natural dentition. Dentists can use a traditional preparation of 1.0 to 1.5 mm reduction (for example a full-crown preparation) if they need more opaque materials (for example HO and MO). Because the resulting restoration will have a slight opacity, the margins will be equi-gingival or slightly sub-gingival. In either case, the material will be fully layered to create the final restoration. IPS e.max provides the choice of using traditional or creative preparation designs. _Cementation options Because lithium disilicate can be fully light-cure bondedorcementedusingaself-etchingprimerwith conventional resin-cement techniques, IPS e.max also provides options for cementation. Conven- tional self-etching primer cement is ideal for full crowns. For partial and veneer preparations for whichadhesiveprotocolwillbeused,fulllight-cure bonding is preferred. _Case study A 42-year-old female presented with disco- loured teeth that had been repaired with various composite restorations placed throughout the years(Fig.5).Alingualamalgamrestorationintooth #12andcompositerestorationsinteeth#23,21,11 and13showedrecurrentdecaythatwasdiagnosed with digital X-rays. She possessed a negative med- ical history and good oral hygiene with resultant periodontal health and asymptomatic teeth. Treat- ment options of zirconia or porcelain-fused-to- metal crowns or CAD/CAM all-ceramic restorations were discussed with the patient. Ultimately, CAD/CAM all-ceramic restorations were tested. When proper preparation and occlusal designconsiderationsarefollowed,properlyplaced CAD/CAM-designed and -milled restorations have been extremely successful. The patient made a preparationappointment,duringwhichtheexisting restorations were removed, and teeth #23 to 13 were prepared for all-ceramic veneer restorations, following accepted CAD/CAM glass-ceramic prep- aration guidelines (Fig. 6): adequate clearance, rounded internal aspects, and equi-gingival butt- joint margins were ensured. Once the preparations were completed, conventional impressions were taken and poured in high-quality, laser-reflective dental stone. Laboratorycommunication The dentist is to the dental technician what the architect is to the builder. Each has a primary role in indirect restorative dentistry, which is to imitate naturalfunctionandaestheticsperfectlyandtrans- late that into a restorative solution. The commu- nication between the clinician and technician en- tails a thorough transfer of information, including Fig. 8_Computerised image of digital 3-D model. Fig. 9_Computerised 3-D digital composite file, showing preparation, provisional models and digital restoration design. Fig. 10_Final digital restorations, with cut-back design for the micro-layering of enamel ceramics. CAD/CAM 1_2012 Fig. 8 Fig. 9 Fig. 10