Monolithic lithium disilicate restorations continue to emerge

The science and research behind Ivoclar Vivadent's IPS e.max restorative material validate its strength, longevity and quality.

Throughout the years, dentists have faced challenges when it comes to prescribing combination restorations such as metal with metal-ceramic or zirconia with zirconia layering ceramic. It’s been in the last decade or so that dental material science has broadened the options available for achieving the accuracy, fit, precision, strength, and esthetics that ultimately determine the extent of treatment success with combination restorations.

As a result, dentistry now has available monolithic restorations-crowns, veneers and other structures pressed or milled to full contour from lithium disilicate (LS2) glass ceramic or yttrium-stabilized zirconium oxide (ZrO2). These alternatives significantly reduce clinical and functional problems experienced in the past with conventional restorations, such as fracturing and/or chipping of veneering porcelain over porcelain-fused-to-metal (PFM) restorations, as well as esthetic issues. Now, dentists can achieve the strength they require for posterior and/or parafunctional habit indications without metal-based restorations, and the esthetics they need for more cosmetically demanding cases.

While the availability of monolithic lithium disilicate and zirconium restorations represents a paradigm shift for everyday dentistry, it’s important for dental professionals to examine the research supporting available material systems. Since its introduction, Ivoclar Vivadent’s IPS e.max system, which includes compatible materials such as lithium disilicate (LS2) glass ceramic, yttrium-stabilized zirconium oxide (ZrO2), and veneering ceramics such as fluorapatite glass-ceramic and nano-fluorapatite glass-ceramic, has been the subject of numerous published articles demonstrating its clinical applications. However, more important as the basis for well-informed treatment decisions are the in vivo and in vitro studies that have been undertaken to validate the materials’ strength, longevity, efficacy and quality.

Lithium disilicate (IPS e.max Press, IPS e.max CAD) is an esthetic and high strength material that can be processed into full-contour restorations. It can be placed with conventional cementation or adhesive bonding techniques, and it eliminates challenges experienced when incompatible materials are combined.1

The material can be pressed as thin as 0.3 mm when minimal tooth preparation is desired while still ensuring strength of 400 MPa.2 Posterior lithium disilicate crowns fabricated to full contour using CAD methods demonstrate monolithic strength of 360 MPa throughout the entire restoration.3

Summary of research
An increasing body of clinical and laboratory evidence has developed in recent years supporting the use of lithium disilicate. In fact, more than 20 clinical and even more in vitro studies have been conducted, and nearly 40 million restorations have been fabricated. The data from this research includes up to 10 years of clinical use for lithium disilicate.

Such research and evidence demonstrate the long-term success these materials have achieved. Highlights include the following:

• Pressable lithium disilicate restorations (IPS e.max Press) demonstrated a 98.4% survival rate across 6 studies.5-10

• Conventional and adhesive cementation work equally well with pressable lithium disilicate restorations.5-10

• Machineable lithium disilicate restorations (IPS e.max CAD) demonstrated a 97.9% survival rate across 6 clinical studies.11-16

• The resulting overall survival rate for IPS e.max restorations is 96.8%.

Conclusion
Monolithic lithium disilicate restorations are emerging as the everyday treatments of choice for high strength and esthetic indirect treatments, whether for the anterior or posterior regions of the mouth. The material offers specific advantages to dentists compared to PFMs, such as the ability to provide strong and durable restorations with highly esthetic characteristics without metal. Although anecdotal case demonstrations support the many applications of monolithic restorations and the versatility of these materials, it is the quality research summarized here that validates the long-term success of the IPS e.max system.  

References
1. Fabianelli A, Goracci C, Bertelli E, Davidson CL, Ferrari M. A clinical trial of Empress II porcelain inlays luted to vital teeth with a dual-curing adhesive system and a self-curing resin cement. J Adhes Dent. 2006 Dec; 8(6):427-31.
2. Sorensen JA, Cruz M, Mito WT, Raffeiner O, Meredith HR, Foser HP. A clinical investigation on three-unit fixed partial dentures fabricated with a lithium disilicate glass-ceramic. Pract Periodontics Aesthet Dent. 1999 Jan-Feb; 11(1):95-106.
3. Kheradmandan S, Koutayas SO, Bernhard M, Strub JR. Fracture strength of four different types of anterior 3-unit bridges after thermo-mechanical fatigue in the dual-axis chewing simulator. J Oral Rehabil. 2001 Apr; 28(4):361-9.
4. Vagkopoulou T, Koutayas SO, Koidis P, Strub JR. Zirconia in dentistry: part 1. discovering the nature of an upcoming bioceramic. Eur J Esthet Dent. 2009;4(2):130-51.
5. Boning K, Ullmann U, Wolf A, Lazarek K, and Walter M. Dreijahrige klinische Bewahrung konventionell zementierter Einzelkronen aus Lithiumdisilikat-Keramik. Dtsch Zahnarztl Z. 2006; 61: 604-611.
6. Etman MK, Watson TF, Woolford M. Early clinical wear of Procera-Allceram restorations and an experimental ceramic. J Dent Res. 2001; 80: 642.
7. Guess PC. Einfluss von Verblendtechniken auf das Versagensverhalten und die Dauerbelastbarkeit von Y-TZP-Dreischichtsystemen. The European Journal of Esthetic Dentistry. 2009; 4: 284-299.
8. Gehrt MA, Rafai N, Reich SSW, Edelhoff D. Outcome of lithium-disilicate crowns after 8 years. IADR Abstract #656. 2010; Barcelona.
9. IPS e.max 4-year clinical performance. The Dental Advisor. 2010: 27.
10. Internal data. Ivoclar Vivadent.
11. Richter J, Schweiger J, Gernet W, Beuer F. Clinical performance of CAD/CAM-fabricated lithium-disilicate restorations. IADR Abstract #82. 2009; Munich.
12. Nathanson D. Clinical performance and fit of a milled ceramic crown system. IADR Abstract #0303. 2008; Toronto.
13. Reich S, Fischer S, Sobotta B, Klapper HU, and Gozdowski S. A preliminary study on the short-term efficacy of chairside computer-aided design/computer-assisted manufacturing generated posterior lithium disilicate crowns. Int J Prosthodont. 2010; 23: 214-216.
14. Fasbinder DJ, Dennison JB, Heys D, Neiva G. A clinical evaluation of chairside lithium disilicate CAD/CAM crowns: a two-year report. J Am Dent Assoc. 2010; 141 (Suppl 2): 10S-14S.15. Bindl A. Uberlebensrate und klinische Qualitat von CAD/ CAM-gefertigten Seitenzahnkronen aus Lithiumdisilikatkeramik. Eine prospektive klinische Studie (Zweijahresbericht). 2011.
16. Sorensen JA, Trotman R, Yokoyama K. e.max CAD posterior crown clinical study. 2009.

Photos 6-9, 12-13 by Dr. Franklin Shull.
Photos 10-11 by Dr. John Nosti.