Restoring implants using lithium-disilicate,CAD/CAM fabricated restorations

As a result, CAD/CAM technology has been incorporated into an increasing number of dental procedures, enabling dentists and their teams to offer state-of-theart care to patients in half the time of traditional methods.

Moreover, when it comes to implant-supported restorations, CAD/CAM technology efficiently and effectively produces restorations that demonstrate high-strength properties for durable, long-lasting results that can withstand implant forces.

Research has shown that aesthetic, ceramic, CAD/CAM-fabricated molar crowns supported by implants gained high strength values when used in conjunction with adhesive cements, particularly in cases with titanium and zirconia implant abutments.(1,2)

One of the most challenging aspects of a restorative case, however, is matching the abutment, restoration and adjacent dentition in perfect harmony. This is especially difficult with single-unit restoration cases because human dentition exhibits different colours, shades, tones and hues. It never presents one simple colour found on the standard shade guide.

Yet, using highly aesthetic lithium-disilicate value blocks (IPS e.max CAD, Ivoclar Vivadent) milled in the E4D in-office CAD/CAM system, dentists can create restorations that are durable, strong and indistinguishable from surrounding dentition, facilitating the highest level of aesthetics and function.

Material selection/fabrication
The E4D in-office CAD/CAM system enables clinicians to design, fabricate and place first-rate aesthetic restorations in a single visit. The highquality ceramic restorations also demonstrate excellent strength, fit and longevity suitable for a broad range of indications and contribute to predictable outcomes.(3,4)

Among the benefits of utilizing the E4D in-office CAD/CAM system to design and fabricate ithium-disilicate restorations is the ability to capture state of-the-art, powder-free digital impressions. These can be taken from multiple angles for customized accuracy and optimal efficiency. Additionally, both hard and soft tissues can be scanned, depending on the case.

Preparation and margin assessment are completed simultaneously, and high-tech software fab-ricates multiple digital models at once. If needed, sculpting tools facilitate corrections by reimaging, eliminating the need for constructing multiple models or placing temporaries.

During the milling process, the unit’s robust design minimizes vibrations, resulting in micronprecise accuracy for enhanced fit and function of the final restoration.(4)

As dental practices have moved toward inoffice CAD/CAM, innovative ceramic materials have been developed that address material issues regarding strength and aesthetics. These new and improved ceramics are designed to endure CAD/CAM pro cessing without chipping or fracturing. They can be milled to full contour for improved fit and function.(5)

For example, there are many advantages to placing monolithic lithium-disilicate restorations (IPS e.max CAD). These restorations exhibit the same structural and esthetic properties of ceramic, yet demonstrate high-strength resistance to longterm mastication forces.(4) They also blend seamlessly with natural dentition.

Additionally, these restorations are indicated for full-coverage posterior and anterior crowns, although the material itself may be milled for cases requiring thin veneers, minimally invasive inlays and onlays, partial crowns, implant superstructures and three-unit bridges.(5,6)

Research shows that restorations fabricated with CAD/CAM perform better and are more durable
compared to other available restorative options.(4) The lithium-disilicate crystals in the IPS e.max material, in particular, deflect, branch or blunt cracks, increasing the flexural and overall strength of the material to a range of 360 to 400 MPa.(3)

These high-strength characteristics, capacity for milling to full-contour and placement with adhesive bonding or conventional cementation render IPS e.max CAD monolithic restorations practical for restoring in-office implant restorations.(4) Additionally, a strong bond between the restoration and underlying tooth substrates can be achieved.(5)

Case presentation
A 28-year-old patient presented with retained primary molars 55 and 65 (Figs. 1–3). These would be extracted and replaced with implant-supported crown restorations fabricated in-office using the E4D CAD/CAM system and a lithium-disilicate (IPS e.max CAD) material. The Value 1 Impulse blocks were selected because they are ideal for implant crowns, providing the ideal level of translucency.

Implants were placed and the patient was provided with zirconium abutments (Astra Osseo Speed, DENTSPLY). To fabricate the crown restorations, the abutments were scanned using the E4D intra - oral scanner (Fig. 4), and the zirconium abutment margins were marked (Fig. 5).

The E4D ICE software enabled easy viewing of the zirconium margins in subgingival locations (Fig. 6). The E4D design software was used to virtually create the lithium-disilicate crown restorations for the two premolars (Fig. 7). The software also enabled verification of material thickness (Fig. 8). In particular, the E4D Autogenesis software was used to create ideal tooth anatomy and contours, with the buccal area 2 mm thick and the distal area 1.5 mm thick, which was perfect for the lithium-disilicate (IPS e.max CAD) material (Fig. 9).

The Value 1 Impulse blocks (IPS e.max) were milled and fired in one cycle, resulting in highly esthetic and monolithic crown restorations (Fig. 10).

The implant screw access canals were sealed using a provisional inlay material (Systemp.inlay,
Ivoclar Vivadent). To prepare the lithium-disilicate crowns for placement, the internal aspects were etched with 5 per cent hydrofluoric acid (IPS Ceramic Etching Gel) for 20 seconds, then rinsed and dried.

Then, a silane primer (Monobond Plus) was placed inside the crowns for 60 seconds and also on the zirconium abutments as a zirconium primer for 60 seconds, using the phosphoric acid methacrylate and sulfide methacrylate to bond to zirconium. The restorations were then cemented using a universal resin cement, without primers (Multilink, Ivoclar Vivadent).

Conclusion
IPS e.max CAD restorations provide predictable results for restoring implants (Figs. 11–14). The Value Impulse blocks lend to the creation of restorations that blend seamlessly with the adjacent natural dentition, yet they provide the ideal level of translucency to mask zirconium abutments. In this case, the patient was pleased with the natural looking treatment results that were achieved by combining the IPS e.max CAD material with E4D in-office fabrication technology.

References
1. Wolf D, Bindl A, Schmidlin PR, Lüthy H, Mörmann WH. Strength of CAD/CAM-generated esthetic ceramic molar implant crowns. Int J Oral Maxillofac Implants. 2008 Jul-Aug;23(4):609–17.
2. Guess PC, Att W, Strub JR. Zirconia in fixed implant prosthodontics. Clin Implant Dent Relat Res. 2012 Oct;14(5):633–45.
3. Shenov N, Shenov A. Dental Ceramics: An Update. J Conserv Dent. 2010 Oct-Dec: 13(4):195–203.
4. Poticny D, Potincy J, Klim J. CAD/CAM in-office tech - nology innovations after 25 years for predictable, eesthetic outcomes. The Journal of the American Dental Association. 2010;141:55–95.
5. Buehler B. Simple and efficient crown fabrication with an advanced CAD/CAM system. 2012; Dental Tribune.
6. Thompson VP. Durability (reliability) of all-ceramic crowns (Web cast); event.on24.com/eventRegistration/ EventLobbyServlet?target=lobby.jsp&eventid= 163956&sessionid=1&key=B2F0098B49AAEA431E78 38ECF9721EFB&eventuserid=28400352. Accessed April 21, 2010.

This article was published in CAD/CAM the international C.E. magazine of digital dentistry No. 04/2013.