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Dr. Edward Narcisi discusses metal-free materials

Dec. 1, 2006
Dr. Dalin: The time to begin the process of going metal-free has come upon the dental profession.

The Dalin Exchange | Jeffrey B. Dalin, DDS, FACD, FAGD, FICD

Dr. Dalin:The time to begin the process of going metal-free has come upon the dental profession. Our patients are asking to have their old restorations replaced with something more esthetic and biocompatible. We all know the advantages of going all ceramic: superior esthetics, no thermal conductivity discomfort, no metal reactions to the gingival tissues, better light transmission through the restoration, and no exposed metal margins. However, as this area of dentistry explodes in popularity, so does the confusion that goes along with the continual introduction of new materials. I am thrilled to be able to sit down and talk with you. If there is anyone who can help clear up the confusion out there, it is you, Ed. Let’s get right down to business. The way I see it, there are six main categories of ceramic materials available for use: feldspathic porcelain, leucite systems, castable glass, glass-infiltrated alumina systems, aluminous core, and zirconium oxide. I would like to go through each one of these systems, one-by-one, discussing the positives and negatives of each.

Dr. Narcisi: Jeff, I’m glad you’re giving me the opportunity to help clear up a very confusing situation in our profession. It seems that almost daily, a new ceramic product is introduced to the marketplace. It is very difficult to stay on top of all of these new materials. I will try to very simply describe the different categories of ceramic materials. They are listed here from weakest to strongest.

Feldspathic porcelain: Simply put, feldspathic porcelains are most suited as layering porcelains. They are the porcelains that are veneered over metal-ceramic and all-ceramic restorations. There is certainly a strong indication for the use of feldspathic porcelain in the fabrication of porcelain veneers. In the hands of a talented ceramist, feldspathic porcelains are capable of producing beautiful porcelain veneer restorations. Unfortunately, feldspathic porcelains do not have the strength required to be used confidently in any other capacity or in the posterior dentition. Feldspathic restorations need to be bonded to an etched surface with adhesive composite resin cement.

Leucite-reinforced ceramic: Leucite has been widely used in traditional dental ceramics as a means to modify the coefficient of thermal expansion. With the introduction of pressed leucite-reinforced ceramics, such as IPS Empress (Ivoclar Vivadent), the increased volume of leucite is responsible for the significant increase in flexural strength. The leucite reinforcement also increases toughness, strength, and modifies the wear rate that is now similar to natural tooth enamel. The leucite-reinforced systems allow fabrication of porcelain veneers, anterior crowns, and inlays and onlays. They are not indicated for posterior crowns or fixed bridges. Leucite-reinforced restorations need to be bonded to an etched surface with adhesive composite resin cement.

Castable glass: Castable glass ceramic would be represented by the Dicor system (Dentsply International). This type of system utilizes the lost-wax technique to produce a glass casting of the restoration. The casting is then heat-treated or “cerammed,” which increases the strength and toughness of the glass ceramic restoration. Again, this type of restoration is best suited for anterior dentition. Unfortunately, at the time of the Dicor system’s release, the existing adhesive and resin bonding systems were not capable enough to properly support these restorations, which led to premature failures.

Glass-infiltrated alumina: Vident introduced a slip casting system that utilizes fine-grained alumina. The cast alumina is heat-treated, or sintered, and then a glass infiltrate is applied and heat-treated again. This process creates the glass-infiltrated alumina core we know as In-Ceram. The In-Ceram core is then veneered with feldspathic porcelain. Indications include anterior and posterior crowns and three-unit anterior bridges. Conventional crown and bridge (C&B) cementation techniques can be used.

Aluminous core: Alumina core restorations have been popularized by Nobel Biocare with the Procera system. Procera produces CAD/CAM copings, which are then layered with feldspathic veneering porcelains that are then fired to provide the color and form of the restoration. This type of restoration now approaches the strength of traditional PFMs with the esthetic advantage of ceramic. Indications are anterior and posterior single-unit crowns and anterior and posterior three-unit bridges. These restorations can be cemented with conventional C&B cement techniques.

Zirconium oxide: Zirconium restorations are the latest technological advancement in the all-ceramic category. Solid blocks of zirconium oxide, either presintered or sintered, are manufactured and optimized industrially so that the material qualities remain unchanged through the complete production process. Using CAD/CAM technology, the solid blocks are then milled to the desired restorative design with tremendous marginal accuracy. Zirconium restorations have outstanding physical and mechanical properties, such as density, compressive strength, bend strength, tensile strength, and modulus of elasticity. The zirconium-core restorations are then veneered with specific veneering porcelains. Indications are anterior and posterior single-unit crowns and anterior and posterior bridges with pontic spans up to 48 mm (Everest ZS, KaVo). Once again, conventional C&B cementation techniques can be used.

Dr. Dalin:I know I asked you for a lot of information here, but you know as well as I do that a dental laboratory can only invest in a few of these different technologies. They may be recommending one type of ceramic over another based on their investment in equipment and materials. I am totally confused by all of the different brands and the different categories they might fall into. The information you just provided helps me better understand what to ask of my labs. Let’s go through some of the big-name products. Can you tell me in which category they fall? And feel free to add some other brands that I have omitted.

Dr. Narcisi:

Lava: This is 3M ESPE’s zirconium system. Lava allows for CAD/CAM fabrication of a presintered zirconium core, which, in combination with specially designed veneer ceramic, is an ideal choice for all-ceramic restorations, including three-unit bridges. Conventional C&B cementation can be used.

Procera Alumina: This is Nobel Biocare’s alumina core material. The core is produced using CAD/CAM design and milling technology at a designated Nobel Biocare facility. After the core is completed, it is sent back to the laboratory for veneering with Nobel-Rhondo Alumina veneering porcelain. Procera is indicated for single-unit anterior and posterior crowns, and anterior and posterior bridges up to 53 mm and, most recently, porcelain veneers. With the exception of the porcelain veneers, all other restorations can be cemented conventionally. The porcelain veneers should be bonded to an etched surface with adhesive resin cement.

Procera Zirconia: This is Nobel Biocare’s zirconium CAD/CAM material. The cores and frameworks are milled at designated Nobel Biocare facilities, then sent back to the laboratory for veneering with Nobel-Rhondo Zirconia veneering porcelain. The zirconia material is indicated for single-unit anterior and posterior crowns, anterior and posterior bridges up to 60 mm, implant bridges up to 60 mm, and implant abutments. The restorations can use conventional cementation techniques.

In-Ceram: In-Ceram is a family of products from Vident. It includes In-Ceram Alumina, In-Ceram Spinell, In-Ceram Zirconia, and In-Ceram YZ. In-Ceram Alumina, Spinell, and Zirconia are all glass-infiltrated porcelains. They all use the Vita In-Ceram slip technique. In this technique, the ceramist fabricates the coping or framework by hand, which is then sintered and finally glass infused. The copings and frames are then veneered using proprietary veneering porcelains VM7 (for alumina) and VM9 (for zirconia). In-Ceram Alumina is indicated for anterior and posterior crowns and three-unit anterior bridges. In-Ceram Spinell is indicated for anterior crowns. In-Ceram Zirconia is indicated for anterior and posterior crowns, and anterior and posterior three-unit bridges. In-Ceram Zirconia is a hybrid zirconia, which means it is approximately 30 percent zirconia and 70 percent alumina. Therefore, it does not have the strength of industrially manufactured zirconia. In-Ceram also offers In-Ceram YZ, which is an industrially manufactured zirconia with all the strengths of that category of material. This material is in the form of solid blocks of zirconia, which are then milled using CAD/CAM technology. The cores and frameworks are then colored, sintered, and finally veneered with Vita’s VM9 veneering porcelain. In-Ceram YZ is indicated for anterior and posterior crowns, and anterior and posterior bridges up to 40 mm. All of the In-Ceram materials can be conventionally cemented. In-Ceram also markets a product called InVizion. InVizion is a trademarked name for a crown made from milled In-Ceram YZ and veneered with Vita’s VM9 porcelain.

IPS Empress: This is a leucite-reinforced ceramic manufactured by Ivoclar Vivadent. With more than 25 million restorations fabricated, it has a proven track record. IPS Empress is indicated for porcelain veneers and anterior crowns where ideal esthetic results are required. IPS Empress also can be used to fabricate inlays and onlays. This material should be bonded to an etched surface with adhesive resin cement.

Cercon: This is Dentsply’s CAD/CAM zirconium product. Cercon is indicated for anterior and posterior crowns and anterior and posterior bridges up to 47 mm. The zirconium frame is optimally veneered with Cercon Ceram KISS or Ceramco PFZ veneering porcelain. A conventional cementation technique can be used.

Everest: This is a CAD/CAM system from KaVo. This system can CAD/CAM frameworks from solid blocks of zirconium (two types: sintered and presintered), leucite-reinforced ceramic, and titanium. The presintered Everest ZS material can produce frameworks for bridges up to 48 mm. Everest can be used for veneers, anterior and posterior crowns, and anterior and posterior bridges. With the exception of porcelain veneers, the remaining restorations can be conventionally cemented.

Wol-Ceram: Wol-Ceram is a unique core fabrication technique. Wol-Ceram utilizes CAD/CAM technology in conjunction with ELC (Electro Layered Ceramic) technology. The original die is scanned to precisely design the intended core or framework in 3-D. The original working die is then dipped into a solution of In-Ceram Alumina, Spinell, or Zirconium. (It must be noted that the In-Ceram Zirconia used in the Wol-Ceram system is a hybrid zirconia, therefore it has a strength characteristic of approximately 30 percent less than solid milled zirconia.) The core or frameworks created are then milled to the final specifications of the computer design. The cores or frames are then veneered with material-specific veneering porcelain. Unique to this system is the fact that the electro layer technology allows precise marginal adaptation to any margin preparation design, from a feather-edge to a shoulder. Wol-Ceram can be used for anterior or posterior crowns and anterior or posterior three-unit bridges. A conventional cementation technique can be used.

IPS e.max: Ivoclar Vivadent’s IPS e.max system can best be described as a family of ceramic products. The system contains five products: e.max Press, e.max ZirPress, e.max ZirCAD, e.max CAD, and e.max Ceram. The e.max Press is a glass ceramic ingot (lithium disilicate) that can be pressed to form the core for anterior and posterior crowns, and anterior three-unit bridges. The e.max ZirCAD is a solid block of zirconium, which can be milled with CAD/CAM technology into single-unit anterior and posterior crowns and anterior and posterior bridges. The e.max CAD is the same material as the e.max Press, but in block form for CAD/CAM fabrication of single-unit anterior and posterior crowns and anterior three-unit bridges. The e.max ZirPress is a fluoroapatite pressable ingot, designed to be pressed onto the ZirCAD cores and frameworks. The e.max ZirPress can then be cut back and veneered with e.max Ceram, which is a nano-fluoroapatite glass ceramic. The e.max Ceram is the veneering porcelain compatible with all of the e.max core and framework materials. All of the e.max restorations can be cemented via conventional cementation techniques. Ivoclar Vivadent designed their family of ceramics so that IPS e.max in combination with IPS Empress would enable the clinician and the laboratory to fabricate any all-ceramic restorations.

Dr. Dalin:Should we take a moment to discuss cements that we can use to place all of these different types of ceramic restorations? Can one type be used for all of these, or should we have a few different types to use depending on which family or brand of ceramic material we choose?

Dr. Narcisi: Given all of the options listed above, some discussion should follow as to which cements would be best suited for the modality chosen. In theory, when conventional cementation is listed as a possibility, any crown and bridge luting cement can be used, including: zinc phosphate (e.g., Fleck’s cement); polycarboxylate (e.g., 3M ESPE Durelon); glass ionomer (e.g., GC Fuji I); resin modified glass ionomer (e.g., 3M ESPE RelyX Luting; GC Fuji Plus). When an etched tooth surface and an adhesive composite resin cement is required (e.g., Ivoclar Vivadent Variolink II; Kerr Nexus 2), then a dedicated bonding protocol must be followed.

There is a new family of cements known as “self-etch/self-adhesive resin cements.” Examples include 3M ESPE’s RelyX Unicem, Kerr’s Maxcem, and Ivoclar Vivadent’s Multilink. This new generation of cements is indicated for all cementation needs except porcelain veneers. The resin cement category can be divided into light-cure only (e.g., RelyX Veneer Cement), dual-cure (e.g., Variolink II), or self-cure (e.g., Kuraray Panavia 21). Light-cure cements are indicated for restorations that are 2 mm or less in thickness and that are fairly translucent, typically, porcelain veneers. Dual-cure and self-cure cements are required for restorations that are thicker than 2 mm or are more opaque, typically, inlays, onlays, crowns, and bridges.

Dr. Dalin:Ed, thank you so much for helping me maneuver through the maze of all of these ceramic choices. I’m sure you’ve helped make our practice lives better with this information. We will now be able to make better decisions with the restorations we design and deliver to our patients.

Dr. Narcisi: With the multitude of ceramic systems, ceramic materials, cements, and restorative options, the task of deciding the best option for each situation for each patient can be daunting. The clinician may choose a functionally capable material with ideal esthetics for anterior single-unit restorations, and then choose a material designed for maximum strength with a slight sacrifice in esthetics for a multi-unit restoration in the posterior dentition. The combinations are tremendous but, ultimately, the dentist must understand which materials for which situation would be most appropriate for that patient. The fact that dentistry has so many wonderful solutions is exciting, but certainly it increases the dentist’s responsibility to acquire the necessary clinical techniques and material knowledge.

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Edward M. Narcisi, DMD, maintains a full-time general practice in Pittsburgh, where he utilizes all the techniques of esthetics in treating patients. Dr. Narcisi has lectured extensively on esthetic, reconstructive, and implant dentistry. He has served as Assistant Professor in the Department of Restorative Dentistry and Clinical Director of Aesthetic Dentistry at the University of Pittsburgh School of Dentistry. Dr. Narcisi also participates as a consultant to a number of dental manufacturers, and has been named to the Editorial Board of “Reality.” Contact him by e-mail at [email protected] or call (412) 373-9447.

Jeffrey B. Dalin, DDS, FACD, FAGD, FICD, practices general dentistry in St. Louis. He also is the editor of St. Louis Dentistry magazine, and spokesman and critical-issue-response-team chairman for the Greater St. Louis Dental Society. He is one of the co-founders of the Give Kids A Smile Program. Contact him by e-mail at [email protected], by phone at (314) 567-5612, or by fax at (314) 567-9047.