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Compendium

Jul/Aug 2012, Volume 33, Issue 7
Published by AEGIS Communications


CAD/CAM Converging Technologies, Improved Milling Materials Expand Dental Applications

John A. Sorensen, DMD, PhD

Computer-aided design/computer-aided manufacturing (CAD/CAM) technologies have assumed a significant role in restorative dentistry and laboratory technology. Developments in software now enable technicians to rapidly and systematically design and mill a full arch of restorations. Digital technology advancements have evolved CAD/CAM systems beyond milling restorations to the point where technologies have merged to expand clinical functions for diagnosis, treatment planning, and generation of implant surgical guides.

For example, the E4D Compass™ system (D4D Technologies, www.e4d.com) can take cone beam computer tomography (CBCT) data and combine it with a scan of teeth or casts and virtually plan the placement of the implant, generating the surgical guide and later milling the restoration supported by the precisely placed implant. Another example of such a system, which the author uses, is the SCANORA® 3D CBCT system (Soredex, www.soredex.com). The digital files can then be used to plan each case. Similarly, Sirona marries its GALILEOS® CBCT with the CEREC® system (Sirona Dental Systems, www.sirona3D.com).

Design capabilities of many laboratory CAD/CAM systems are being refined every day. For example, based on automotive industry programs to design cars, Delcam Healthcare Solutions (www.delcam.com) entered the dental field, producing a sophisticated CAD/CAM system of dental laboratory design software, a scanning system, and different levels of milling machines. Resourceful dental laboratories have combined several advanced design software systems and then further customized the design and milling software—eg, Burbank Dental Laboratory’s Smart 1 System (www.burbankdental.com) creates highly customized implant-supported hybrid frameworks and then utilizes the Röters TEC milling system. The Burbank system adds the flexibility of milling in either titanium or chrome cobalt when faced with limited vertical height dimension situations. With the Smart 1 System, the frameworks can be so completely customized, they appear to be handmade (Figure 1 and Figure 2).

Advances made in milling block materials have significantly increased clinical reliability, efficiency, economy, and esthetic results in both the clinical and laboratory applications of CAD/CAM. The IPS Empress® CAD system (Ivoclar Vivadent, www.ivoclarvivadent.com), although a leucite-glass ceramic–based ceramic, is not as strong as lithium-disilicate ceramic but is well suited for chairside CAD/CAM production of crowns that require only polishing. With adhesive cementation, these restorations have established a long history of high clinical success rates. Improving further on this concept, Ivoclar Vivadent developed the IPS Empress® CAD Multi® block, which is comprised of four to eight layers of chroma, translucency, and transitions that beautifully simulate the different layers of a natural tooth, producing an extremely esthetic restoration that requires only polishing after chairside milling.

The lithium-disilicate glass-ceramic–based IPS e.max® system (Ivoclar Vivadent) enables a variety of fabrication technologies for producing high-strength restorations either chairside or in the laboratory. E.max CAD® starts as a semi-sintered blue block, which is easily milled in the CEREC® 3 (Sirona) or E4D systems. Once milled, the restoration is oven-fired to attain maximum strength with no net shape change to produce accurately fitting restorations. The lithium-disilicate form can either be used as a substructure for application of veneer porcelain or milled to full contour. The inherent translucency of the ceramic produces a highly esthetic restoration, eliminating the need for veneering on most posterior teeth. The innovative e.max CAD-on® system utilizes CAD/CAM technology to mill high-strength lithium-disilicate veneer for zirconia substructures.

The e.max lithium-disilicate system has great durability, with a flexural strength of 360 MPa to 400 MPa. When fabricated to full contour, the monolithic structure, in the author’s opinion, is one of the most robust ceramic systems available. Even in reduced-thickness clinical situations the lithium disilicate performs well. With the outstanding esthetics conferred by the lithium-disilicate microstructure—even as a monolithic crown—this system is an excellent option for routine restoration of posterior teeth, whether fabricated by chairside milling or a laboratory technician. For most chairside-fabricated restorations, no porcelain-oven glazing or staining is necessary. By merely using a polishing system designed for lithium-disilicate ceramics (eg, Dialite® LD, Brasseler USA, www.brasselerusa.com), an extraordinary quality finish and polish that rivals that of any glazed or polished indirect restorative system can be rapidly achieved.

Zirconium-oxide CAD/CAM restorations have become extremely popular in recent years, thanks largely to the simple and fast milling strategy of semi-sintered zirconium oxide, which has ushered in an explosion of systems to the dental marketplace. CAD/CAM fabrication systems are available from many major companies—including Lava™ (3M ESPE, www.3MESPE.com), Cercon® (DENTSPLY International, www.dentsply.com), e.max® ZirCAD (Ivoclar Vivadent), Zenotec (WIELAND Dental Systems, Inc., www.wieland-dental-systems.com), and Prettau® (Zirkonzahn, www.zirkonzahn.com)—as well as from a myriad of smaller companies.

While the zirconia substructure is nearly indestructible even for 3- and 4-unit bridges,1,2 in the early days chipping of the veneering porcelain was a persistent problem.2 Improvements made in substructure design, processing protocols, and layering materials for zirconia ceramics have significantly reduced chipping of the veneering porcelain.3 New design strategies for traditionally layered zirconia substructure systems that eliminate the lower-strength veneering ceramic have led to a nearly indestructible full-contour zirconia crown. Restoration fabrication is greatly simplified by making only effective polishing necessary. The monolithic zirconia crown reliably restores even second molars in bruxers. The author has routinely used this approach for more than 9 years with no failures.

An in vitro wear study measured loss of human tooth structure against a variety of full-crown materials.4 The enamel wear from antagonist-polished Lava zirconia (3M ESPE) was similar to a gold-platinum alloy (Aquarius, Ivoclar Vivadent). Similarly, enamel wear from a lithium-disilicate ceramic (Empress 2, Ivoclar Vivadent) was not different from the gold alloy. Given the advantageous wear characteristics of these modern ceramics, it is important for clinicians to understand how to best optimize the antagonist restoration surfaces through proper adjustment and polishing during delivery.

Prevalent trade names of full-contour monolithic zirconium-oxide restorations include Lava™ Plus (3M ESPE), BruxZir® (Glidewell Laboratories, www.glidewelldental.com), Zir-MAX® (Burbank Dental Laboratory), Cercon® ht (DENTSPLY), and Diazir® (Diadem Precision Technology, www.diademprecision.com). While the quality, homogeneity, flaw content, and particle size of the zirconium oxide may vary between manufacturers’ systems, they all possess superior polishing qualities.

3M ESPE recently introduced the Lava™ Plus All-Zirconia Monolithic System®, a highly esthetic system that comes in a wide selection of shades matched to the VITA® Classic Shade Guide (Vident, www.vident.com). This highly translucent monolithic zirconia is highly compatible with the Dialite® ZR polishing kit (Brasseler USA) to produce an extremely esthetic full-contour crown despite being all-zirconia.

Milled composites also have the advantage of being able to be rapidly fabricated, adjusted, and polished chairside, unlike some ceramic systems. Manufacturers’ efforts to improve the physical properties of composite resins with higher filler ratios and new filler strategies and resin chemistries have resulted in improved strength and wear resistance of milled restorations. One example of an improved material is Lava™ Ultimate (3M ESPE).

In addition to custom-milled zirconia implant abutments, products like Atlantis™ (DENTSPLY) offer titanium and gold anodized titanium; Atlantis and Procera® (Nobel Biocare, www.nobelbiocare.com) offer zirconia abutments with a variety of shades.

Indeed, as technologies converge and milling materials advance, CAD/CAM dentistry progresses.

References

1. Sorensen JA, Lusch R, Yokoyama K. Clinical Longevity of CAD/CAM Generated Y-TZP Posterior 3- and 4-unit Fixed Partial Dentures [abstract]. International Association for Dental Research (IADR). 2006. Abstract 270.

2. Heintze SD, Rousson V. Survival of zirconia- and metal-supported fixed dental prostheses: a systematic review. Int J Prosthodont. 2010;23(6):493-502.

3. Beuer F, Edelhoff D, Gernet W, Sorensen JA. Three-year clinical prospective evaluation of zirconia-based posterior fixed dental prostheses (FDPs). Clin Oral Investig. 2009;13(4):445-451.

4. Sorensen JA, Sultan EA, Sorensen PN. Three-Body Wear of Enamel Against Full Crown Ceramics. J Dent Res. 2011;90(special iss A). Abstract 1652.

Related content: Scan this code to visit Compendium’s Special Report page online, or go to dentalaegis.com/go/cced190. The page features exclusive video commentary on CAD/CAM from Dr. Louis Rose, editor-in-chief, as well as an online archive of Special Reports on a range of topics.

About the Author

John A. Sorensen, DMD, PhD
Director
Pacific Dental Institute
Portland, Oregon


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Image Gallery

Figure 1  Due to severe vertical height constraints a full metal framework crown was designed. CAD drawing of design.

Figure 1

Figure 2  Milled hybrid titanium framework with molar full crowns.

Figure 2