March 1, 2011
by Andreas Bindl, DDS
IPS e.max® CAD (Ivoclar Vivadent, Amherst, NY) is a lithium disilicate glass-ceramic that demonstrates a flexural strength of 360 MPa. Available to dentists for several years, this ceramic is milled to the desired shape while still in its metasilicate or “blue” state (i.e., approximately 130 MPa). After a 20-minute crystallization/firing process, the material achieves its final physical state and obtains its excellent mechanical and esthetic properties. Because stains and glaze are applied prior to the crystallization process, subsequent polishing is unnecessary.
IPS e.max CAD is available in a low translucency (LT) version suitable for the fabrication of crowns and implant-retained restorations. The high translucency (HT) form is ideal for inlay and partial crown restorations. Due to the high strength of the restoration, adhesive cementation using a separate dentin conditioner is not indicated as long as the ceramic thickness remains 1.5 mm or greater. Self-adhesive cementation materials can be used, and the new self-adhesive composite cement SpeedCEM (Ivoclar Vivadent, Amherst, NY) is particularly suitable for lithium disilicate restorations.
This article describes the preparation, impression taking, digital design, and cementation processes involved in the fabrication and placement of an IPS e.max CAD LT posterior crown restoration. The new SpeedCEM luting cement was used in this case.
A 32-year-old woman presented with a large, damaged composite restoration and extensive decay on tooth #25, as well as a crack that destroyed the dental hard tissue (Fig. 1). It was determined that treatment with a full-coverage crown restoration was indicated. The defective restoration was removed, and the tooth was prepared with a shoulder of approximately 1.0 mm epigingivally.
Digital Impression Taking
Subsequently, the preparation was dusted with contrast spray (IPS® Contrast Spray), and a digital impression was taken (CEREC Bluecam camera). The new CEREC software version 3.80 generated a visual image of the antagonists, which replaced the centric bite record. Then, in order to match the upper and lower teeth, an image of the centric occlusion was captured from the buccal aspect (Fig. 2). The upper and lower teeth were matched semi-automatically (Fig. 3).
The 3.80 software version designed biogeneric occlusal surfaces for the full crown and provided a design proposal for the tooth morphology, which was based on the occlusal surface of the adjacent distal tooth and the antagonist (Fig. 4). The image of the bucco-oral cross-section of the crown allowed verification of the minimum occlusal thickness of 1.5 mm (Fig. 5). The minimal ceramic density (0.2 vol%) during the crystallization process was taken into account by the software and adjusted accordingly.
The appropriately colored IPS e.max CAD block was selected and placed in the milling unit. Once the crown had been milled, the proximal and occlusal contacts were adjusted intraorally (Figs. 6 & 7). In this case, the “white” and “creme” materials from the corresponding stains assortment (IPS e.max® CAD Crystall/Stains) were applied sparingly to the cusp tips, and the “sunset” material was applied to the tooth neck and in the fissures. Immediately afterwards, a spray glaze (IPS e.max® CAD Crystall/Glaze Spray) was applied several times to the outer surfaces of the restoration.
Once the restoration was fully coated with a white-opaque glaze layer, it was fired in a combined crystallization and firing process (Programat® CS furnace, Ivoclar Vivadent) (Figs. 8 & 9). Prior to cementation, the inner surface of the crown was etched with 4.9 percent hydrofluoric acid (IPS Ceramic Etching Gel) for 20 seconds, after which it was silanized (Monobond Plus) for 60 seconds.
A self-adhesive luting cement (SpeedCEM) was placed in the internal aspect of the crown, after which it was securely seated on the preparation by applying even pressure (Fig. 10). Excess cement was light-cured for one second per surface (i.e., mesial, distal, mesio-buccal, distobuccal) using a curing light (bluephase®, Ivoclar Vivadent) in the low-power (LOP) mode at a distance of approximately 5 mm. In this cured state, the cement was removed carefully using a scaler and probe. The cement then was fully cured using the bluephase curing light in the HIP (High Power) mode.
The cement margin was polished. Final inspection revealed the restoration to be in harmony with the overall esthetics and form of the adjacent dentition (Figs. 11 & 12).
CAD/CAM technology enables dental professionals to fabricate monolithic all-ceramic crown restorations chairside. A digital image of the preparation is captured using an intraoral camera, which allows the dental professional to design the restoration accordingly. A variety of ceramics are available from which to mill such restorations, including esthetic and easy to mill lithium disilicate (IPS e.max CAD). To ensure that restorations fabricated from this leucite glass-ceramic remain sufficiently strong long term to withstand masticatory forces, they should be seated according to adhesive protocol (e.g., Syntac®/Variolink® II or Multilink® Automix). OH
Dr. Andreas Bindl, Station für Zahnfarbene & Computer-Restaurationen, Praxis am Zürichberg, Attenhoferstrasse 8a, 8032 Zurich, Switzerland.
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