Zirconia-Based Ceramics: Material Properties, Esthetics, and Layering Techniques of a New Veneering Porcelain, VM9

Edward A. McLaren, DDS*Russell A. Giordano II, DMD, DMedSc**

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n the search for the ultimate estheticrestorative material, many new all-ceramicsystems have been introduced to the mar-

ket1–3; the use of all-ceramic materials is increasingat almost an exponential rate. Ceramics offer thepotential for excellent esthetics, biocompatibility,and long-term stability.1–3 One material currently ofgreat interest is zirconia. Zirconia is the strongestand toughest ceramic material available for use indentistry today.4 Zirconia has the potential to allowfor the use of reliable, multiunit all-ceramic restora-tions for high-stress areas, such as the posterior re-gion of the mouth.

Although still too new to have generated 5-and 10-year studies, in 2 years of using zirconia

frameworks for single crowns and some shortfixed partial dentures (FPD) at the UCLA Schoolof Dentistry and Boston University, the authorshave yet to encounter a single failure. Three-yeardata from studies in Germany and Switzerland,where zirconium-core technology was developed,are now emerging; these report no fractures ofthe zirconia frameworks.5

Zirconia frameworks are available from severalcomputer-aided design/manufacturing (CAD/CAM)systems, such as Vita YZ from CEREC inLab (Sirona,Bensheim, Germany), Lava (3M/ESPE, Seefeld, Ger-many), Cercon (Dentsply/Degussa, York, PA, USA),and Procera Zirkon (Nobel Biocare, Göteborg, Swe-den). In addition to new framework materials, ve-neering porcelains are being engineered with finemicrostructures to improve the clinical benefits forthe patient. Concomitantly, the microstructures cre-ate improved optical properties that more closelymimic the properties of natural teeth (Figs 1 and 2).The understanding of color science relative to teethhas improved in recent years, as some manufactur-ers have improved shading to be able to moreclosely replicate the shades of natural teeth.6

* Associate Professor; Director, UCLA Center for EstheticDentistry, UCLA School of Dentistry; and private practicelimited to prosthodontics and esthetic dentistry, Los Angeles, California, USA.

** Associate Professor and Director of Biomaterials, BostonUniversity, Goldman School of Dental Medicine, Boston,Massachusetts, USA.

Correspondence to: Dr Edward A. McLaren, UCLA School ofDentistry, Room 33-021 CHS, PO Box 951668, Los Angeles,CA 90095-1668, USA.

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VM9 (Vident/Vita, Brea, CA) is one such materialwith a fine microstructure and improved optics; it isspecifically designed to be used on Vita YZ zirco-nia but has a thermal expansion coefficient tomatch other zirconia materials such as Lava, Cer-con, and Zirkon. The purpose of this article is todiscuss the material properties of the new zirconiacore systems, esthetic optimization of core designand use of core bonding agents, and the materialproperties and specialized esthetic veneering tech-nique of a new porcelain specifically designed forsolid-sintered zirconia frameworks.

MATERIAL PROPERTIES AND FABRICATION TECHNIQUES

Zirconia (ZrO2) is an oxidized form of the zirconiummetal, just as alumina (Al2O3) is an oxidized formof aluminum metal. Zirconia may exist in severalcrystal types (phases), depending on the additionof minor components such as calcia (CaO), magne-sia (MgO), yttria (Y2O3), or ceria (CeO2). Thesephases are said be stabilized at room temperature

by the minor components. If the right amount ofcomponent is added, one can produce a fully sta-bilized cubic phase—the infamous cubic zirconiajewelry. If smaller amounts are added, 3 wt% to 5wt%, a partially stabilized zirconia is produced. Thetetragonal zirconia phase is stabilized, but understress, the phase may change to monoclinic, with asubsequent 3% volumetric size increase. This di-mensional change takes energy away from thecrack and can stop it in its tracks. This is called“transformation toughening” (Fig 3). Also, the vol-ume change creates compressive stress around theparticle, which further inhibits crack growth.

Natural teeth often contain many cracks in theenamel, which do not propagate through the en-tire tooth. These cracks can be stopped by theunique interface at the enamel-dentin junction.7

The ability to stop the cracks as they enter the zir-conia core structure mimics the effect seen in natu-ral teeth. Furthermore, the core may be able to re-sist high-stress areas internally, such as sharp lineangles in the tooth preparation, grinding damageduring internal adjustment, and stresses generatedby chewing or thermal changes in the mouth.

Fig 2 Section of veneered natural tooth with VM9 displays similar natural tooth optics.

Fig 1 Section of natural tooth displays opalescence, fluorescence, and iridescence under specialized light.

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Transformation toughening helps give zirconiaits excellent mechanical properties: high flexuralstrength—900 MPa to 1.2 GPa—and toughness—7 to 8 MPa·m–0.5 (Fig 4). Other beneficial proper-ties include good biocompatibility.8,9 The mechani-cal properties may allow for decreased copingthickness and connector sizes, helpful becausetooth reduction is often less than desired. Also, itmay be possible to make longer-span FPD frame-works of four, five, or six units.

Several dental laboratory milling systems (Fig5) are designed to fabricate frameworks from azirconia-containing material. There are two basicapproaches to using near 100% zirconia. One isto mill 100% dense, sintered zirconia directly. Thisapproach requires a rigid milling unit, which trans-lates to a large, heavy machine, as it is difficult tomachine dense zirconia. Mill times for a coping

range from about 2 to 4 hours. This approach hasan advantage in that no post-milling sintering is re-quired. There is no shrinkage; what you see is whatyou get. The obvious drawback is the extendedmilling time and wear of the milling burs.

Another approach is to mill a partially fired zir-conia block. The blocks are about 50% dense. Be-cause they are only partially fired, the blocks areweak but easy to mill. However, the milled frame-work must be fired for 6 to 8 hours to increase thedensity of the restoration. A large amount ofshrinkage occurs, and this must be compensatedfor during the milling process (Fig 6). Oversizedframeworks are fabricated, relying on a computerto enlarge the pattern correctly to compensate forshrinkage and provide a reliable fit. Each block hasa barcode containing the density for that block.The milling system then computes the proper de-

Transformation Toughening

Partially stabilizedcrystal phase change

3% Volume Increase

Stress

Tetragonal Monoclinic

Fig 3a Phase change from a tetragonal-shaped crystalto a monoclinic form of crystal.

Crack stopping

Volume increaseEnergy transferCompressive stressMicrocracks

Transformation TougheningCrack

Fig 3b Closing of microcracks because of the crystalvolume increase caused by the phase change.

YZ Zirconia

Cercon

InCeram Zirconia

Procera Alumina

InCeram Alumina

InCeram Spinel

Empress 2

Empress 1

Omega 900

Conventional

VM9

0 200 400 600 800 1000 1200

Mean flexural strength (MPa)

Fig 4 Flexural strengths of various ceramic core systems.Note the high strength of the two zirconia systems tested.

Fig 5 CEREC inLab, Cercon, and Lava systems.

gree of oversizing needed to compensate for theshrinkage to full density. Thus, the homogeneity ofthe block and density measurement is a key to thesuccess of this approach. Vita YZ, Cercon, andLava take this approach, which is somewhat similarto the Procera technique in that compensation forshrinkage of the oversized framework must be per-formed. All of these materials are about 95% zirco-nia, with the rest made up of yttria and some natu-ral impurities.

MATERIAL TESTING, VM9 VENEERINGPORCELAIN

VM9 is a newly released veneering porcelain de-signed for these zirconia frameworks. VM9 is thelatest in a series of Vita veneering materials with arefined particle size (Fig 7). Ceramics processingliterature shows that reduction of particle size in aceramic generally increases the strength andtoughness of the material.10 There are other clini-cal benefits as well; these include improved wearkindness and polishability.11 Research on the prop-erties of veneering porcelains, ceramics, and resincomposites is ongoing in the laboratory of one ofthe authors as part of a comprehensive analysis ofmechanical properties, surface finish, polishability,and wear of various restorative materials.

Wear in the oral cavity is a complex process de-pendent on the load applied to the teeth and en-vironmental factors that interact with the specificrestorative material and the patient’s enamel,which varies from person to person. Two major

determinants of “enamel wear kindness” are sur-face finish and microstructure.12 Porcelain with a re-fined structure should produce a wear-kind sur-face, which is easily polished or glazed. Older-styleporcelains with coarse structures may producerougher surfaces, which might wear opposingenamel at an accelerated rate. It is also importantto properly sinter (fire) the veneering porcelain, aseven fine-grained but underfired porcelain isrougher and thus more abrasive.13

In the authors’ tests, restorative materials werefabricated into rectangular sections 2 mm 3 10mm 3 16 mm. Enamel pieces were sectioned fromfreshly extracted teeth and loaded into a holder tocreate an overall size equivalent to the restorativesamples. Enamel pins were trephined from freshlyextracted teeth. A modified toothbrush abrasionsystem was used to mount the pins on a brass rod.The enamel pins contacted the test materials. Aload of 400 g was applied to the pin. The systemwas run at 160 cycles/min for 60,000 cycles underwater. The load and cycling parameters representa common value determined from an extensive lit-erature search on wear testing of dental restorativematerials. Restorative samples were polished usinga series of diamond wheels and pastes.

The results shown in Fig 8 demonstrate the lowenamel wear for the refined new veneering porce-lains—VM7, VM9, and materials with fine crystalstructures, such as Omega 900 (Vita) and MkIICEREC blocks. In Fig 9, the data displayed havebeen normalized with respect to enamel. The wearratio attempts to include both material and enamelloss and compensate for differences in enamel

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6 7

Fig 6 Vita YZ block after machiningbut before complete sintering (top),and the same framework after com-plete sintering. Note the significantshrinkage.

Fig 7 Scanning electron micrographof the VM9 material demonstratesthe fine grain structure. Fine mi-crostructures correlate directly togreatly reduced abrasion potentialof these types of materials.

samples. Wear ratios closest to 1 indicate wearthat most simulates enamel versus enamel. Again,fine-structured porcelains have values close to thatachieved with natural human tooth enamel againstenamel. The mean roughness value for each mate-rial was measured before and after wear testing(Fig 10). The roughness data describe both thesmoothness of the surface that may be achievedduring polishing as well as material resistance tosurface abrasion during clinical service. Increasedplaque accumulation may occur as the restorationsurface becomes rougher during clinical service.Roughness values also correlate well with materialswith a fine microstructure.

As part of the analysis of new materials, strengthtesting of VM9 was conducted and compared to

other veneering materials. Porcelains were mixedusing a standard water:powder ratio and vibratedinto silicone molds to form standardized bars 2 mm3 4 mm 3 25 mm. The bars were condensed andfired according to the manufacturer’s recommenda-tions. Ten bars per group were tested in three-pointflexure using an Instron universal testing machine(Canton, MA, USA) with a cross-head speed of 0.5mm/min, and strength values were automaticallycalculated using the standard formula for three-point bending contained in the Instron software (Fig11). Compared to other veneering materials, thosewith a refined particle size, such as VM9, VM7, andOmega 900, have values significantly higher thanthose of other porcelains in a similar class.

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1.4

1.2

0.8

0.6

1

0.2

0.4

0VM7

MKIIMz100

VM9

Creation

Softspar

Enamel

Omega 900d.Sign

Finesse

Vita Alpha

Rat

io

Material loss >1Enamel loss >1

Fig 9 Normalized wear values of the various veneermaterials. The left half of the graph represents increas-ing abrasiveness of enamel and less attrition of the testmaterial relative to enamel. The right half of the graphrepresents increasing attrition of the test material andless abrasiveness of enamel.

2.5

2

1.5

1

0.5

0VM7

MKIIMz100

VM9

Creation

Softspar

Enamel

Omega 900d.Sign

Finesse

Vita Alpha

Vol

ume

loss

(m

m3 )

Fig 8 Wear of the opposing enamel from the varioustest materials. The red bar represents enamel wearagainst enamel. Everything to the left of the red barrepresents enamel worn less than enamel wore enamel.

VM7

VM9

Ceramco 2

All-Ceram

Creation

Softspar

Omega 900

d.Sign

Finesse

Alpha

LFC

0 50 100 150 200

Flexural strength (MPa)

Fig 11 Flexural strength of the various veneeringporcelains.

0.50.45

0.350.3

0.4

0.20.25

0.150.1

0.050

VM7MKII

Mz100VM9

Creation

Softspar

Omega 900d.Sign

Finesse

Rou

ghne

ss (

mic

rons

)

BeforeAfter

Fig 10 Mean roughness data of test materials beforeand after testing. There is a close correlation betweenroughness and abrasiveness.

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OPTIMIZING ZIRCONIA ESTHETICS

Exciting as the new developments in zirconiamilling technology are, little attention has beenpaid to the optical behavior of the various zirconiacore systems relative to core design to optimizeesthetics. Zirconia, while somewhat translucent, isas opaque as metal if used at certain core thick-nesses and with certain cement combinations.Also, if the core is thicker than it needs to be,opacity is increased, and room for the veneeringporcelain is used up. This would in fact be worseesthetically than a properly designed porcelain-fused-to-metal (PFM) restoration with a thin metalframework used in the same situation, becausethere would be more space for the veneeringporcelain for the PFM (Figs 12a and 12b). Thus,core design (ie, facial thickness) in the estheticzone will have a detrimental effect on esthetics.

Typically, cores have been recommended to be0.5 mm thick on the facial aspect, with 0.6 mm theonly option at this time for the Procera zirconiacopings. The authors have found 0.5 mm of the

zirconia (especially the white material) to be tooopaque for incisors in most clinical situations. TheCEREC system, which uses the Vita YZ material,and the Lava system allow for thinner frameworksto be fabricated for incisors. These systems allowfor the framework to be fabricated with a facialthickness of 0.3 mm (Fig 13), which is as translu-cent as 0.8-mm-thick pressed glass of the sameshade. If absolutely necessary for a single incisor,the authors will thin the coping to 0.2 mm on thefacial aspect to allow maximum translucency. Thebest technique found was to use the NoritakeMeister diamond-impregnated knife-edged wheel(Noritake Dental Supply, Aichi, Japan) (Fig 14).This wheel generates little heat and has not cre-ated cracking problems with the core. After treat-ment with the wheel, the core is aluminous oxideair abraded with 50-µm Al203 at 50 psi to cleanthe contaminants.

Most manufacturers use an achromatic or whiteform of zirconia for the cores. For high-valueshades, eg, 0 or 1 Vita 3D Classical (A0, A1 VitaClassical), the white core works fine. For lower

12a 12b

Fig 13 Comparison of 0.3-mm zir-conia core sample against 0.8-mmEmpress veneer (Ivoclar Vivadent,Amherst, NY) demonstrates similaror greater translucency in the dimen-sions that are actually used. Note:the black line and white backgroundshow through more on the Lavasample on the right than on thepressed-glass sample on the left.

13

Figs 12a and 12b Before and afterviews of a PFM restoration with aCaptek substrate (Captek/PreciousChemicals, Altamonte Springs, FL).

value and higher chroma shades, the white-shadedcore can be problematic. Both the Lava and VitaYZ systems allow for colored cores. The Lava corescome in seven different colors and the Vita YZ infive colors. The core shade that corresponds to thedesired tooth shade is chosen. In the authors’ ex-perience, it is much easier to match the translu-cency and chroma of natural teeth if the correctshaded core is chosen versus using the white zirco-nia core material.

Core Bonding/Shading Agents

One strategy used to color or shade the core forthe white zirconia was to develop “core-shadedporcelains.” Company testing also found that thebond of the normal body porcelains fired and nor-mal temperatures created a weak bond of the ve-neering porcelain to the zirconia framework. Thematerials developed to solve both of these prob-lems were essentially high-chroma opaque materi-als used to shade the core and create a “bonding”layer to which the porcelain fused on subsequentporcelain firings. The materials are fired at a highenough temperature to melt the material to effec-tively wet the surface of the zirconia, creating botha micromechanical and chemical bond. After firing,the core basically looks like opaqued metal, whichwould obviously negatively affect the esthetic re-sult (Fig 15).

The authors found a much more esthetic alterna-tive to obtain the desired results of a bonding layerand developing core color. Translucent fluorescentliners or shoulder powders can be used as thebonding layer and to develop core color. With theVM9 system, the material called the Effect Liner isplaced over the whole core in a thin layer (about0.1 mm); this is fired 70°C higher than the normalrecommended firing temperature for this material(Fig 15). This will melt the material, creating a thinlayer that wets the zirconia surface. The surfaceshould look like a “low glazed” porcelain surface.For 0 and 1 value shades, the authors use a mixtureof 50% Effect Liner 1 and 50% Effect Liner 2; forvalue 2, Effect Liner 2; and for value 3, Effect Liner

3. It is important to note that this is used instead ofthe effect bonder. The coping is now ready forporcelain margin techniques and porcelain layering.

A recent study by Dr Giordano, as yet unpub-lished, of shear bond strength of veneering porce-lains to zirconia found that using a dentin washlayer fired at approximately 950°C improves thebond strength of VM9 to Lava. This procedure isalso a good substitute for the VM9 bonding mate-rial when using Vita YZ as the substructure. How-ever, it must be noted that veneering porcelainsappear to have different bond strengths depend-ing on the zirconia and initial fired veneer layer.

THE SKELETON LAYERING TECHNIQUEAND VM9

The VM9 material is different enough from previousmaterials that the authors have found from experi-ence that a slightly altered building technique isnecessary to maximize the esthetic results. A num-ber of years ago, a simplified porcelain buildingtechnique was described for building Alpha (Vita,Bad Säckingen, Germany)—the “skeleton builduptechnique.”14 This technique was adapted for usewith the VM9 material. The skeleton buildup tech-nique is a combination of many techniques brokendown further into distinct manageable and easilycorrectable steps. It is so named to create animage of a structure that is built from the skeletonoutward, one layer at a time; layers are individuallycompleted (fired) prior to veneering the skin(enamel surface), thus allowing maximum control ofboth shape and shade.

Porcelain Margin

Zirconia cores are slightly more opaque thandentin; thus, it is ideal to design the framework toallow for a more translucent porcelain margin ma-terial to be placed. There is a misconception thatthe margin material should have the same translu-cency as dentin. If the marginal area were at allvisible, it would be noticeable unless the margin

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material also had the exact same chroma and hueas the surrounding tooth structure. It is actuallyideal for the marginal material to be slightly moretranslucent than the surrounding tooth structure sothat it blends in by picking up some color from thetooth, the so-called contact lens or chameleon ef-fect. As with metal or more opaque ceramic cores,a porcelain margin is mandatory for ideal esthetics.

The benefit over metal ceramics is that theframework only needs to be shortened slightly toallow enough light through to illuminate the gingi-val area to create a natural effect (Fig 16). The zirco-nia cores can be designed on the computer with ashortened framework. It is only necessary to shortenthe framework 0.5 to 0.7 mm on the facial aspect.With the VM9, the authors use the Effect Linerporcelains with a direct lift technique for the porce-lain margin; 30% Effect Liner 1 with 70% Effect Liner2 works for the brighter shades (Figs 17 and 18).

The material has a fluorescence similar to that ofnatural dentin, which is most valuable at the mar-gin or gingival area and of less importance in otherareas of the restoration. Fluorescence adds about3% of the light we see reflected off natural teeth,thus having minimal effect on optics in the middleand incisal regions of the crown, but in the gingivalarea, fluorescent materials act as light carriersmuch like a fiber optic. Light is carried from themarginal area, helping to illuminate the marginalgingiva and giving a more natural appearance tothe restoration and the gingiva in this area.

Base Dentins

Base dentins are new materials to replace the tra-ditional opaque dentins from other systems. Thechroma and opacity are between those of con-ventional opaque dentins and dentins. The mate-rial could be used without dentin in thin areaswhere chroma is needed but little space is avail-able for the dentin layer or for a basic shadeguide buildup technique. If additional chroma isneeded, Effect Chroma modifiers are added to

the base dentin. They are chosen based on theshade analysis and whether the shade is yelloweror redder than the chosen shade. Generally,about 10% to 20% of the modifier is all that isnecessary. The base dentins of the desired shadeare built to mimic dentin that needs to be re-placed, generally about 0.4 mm thick, allowingabout 0.2 to 0.3 mm for the conventional dentins.If less than 0.6 mm is available for the basedentin–dentin combination, use base dentin only,with the added Effect Chroma if necessary.

To create the illusion of reality even for ableached tooth effect, it is necessary to build insubtle intratooth color contrasts (ie, color zones)when building the base dentin and dentin. Thereare at least three distinct contrast zones within atooth. As a general guide, the chosen base shadeis placed in the middle third, slightly higher inchroma and lower in value in the gingival third,and slightly lower chroma and value in the incisalthird (Fig 19). This layer should be slightly over-built at this point, and it is then fired (Fig 20).Slight overcontouring after firing is easily con-toured with a bur.

Dentins

The dentins with the VM9 are more translucentthan traditional dentins and are designed for themultilayer buildup techniques currently beingtaught. The dentin material should not be usedwithout the base dentin, as it is too translucent byitself and the core will show through. For a basicshade guide, building technique dentins are notnecessary and only the base dentins need to beused. For a polychromatic and more natural result,dentin materials are overlaid over the fired basedentin layer using the same color or contrastscheme as the base dentins; generally, 0.2 to 0.3mm is the correct thickness with about 0.4-mmthickness of the base dentin. Again, it is best toslightly overbuild the dentins, which can be ad-justed after firing (Figs 21a and 21b).

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Incisal Framing

The enamel structures (layer) are started by build-ing up what has been termed the incisal frame;essentially, it is the lingual half of the incisal edge.With the internal structure (skeleton) of the basedentins and dentins fired, it is easier to control theposition and dimensions of the enamel materials.The lingual wall of the incisal edge (incisal frame)is built up with a 50/50 mixture of Effect EnamelLight and the light-blue translucent Effect Enamel9 for light shades, and for shade 3 value (A3 withthe old shade system) and darker, a 50/50 mixtureof Enamel Dark and Window (clear). This is thenfired. Because of the small volume of porcelain,firing shrinkage is minimal, thus affording maxi-mum positional control of the incisal edge. Slightoverbuilding can be adjusted after firing, andslight underbuilding can be corrected by addingmore porcelain and refiring prior to going to thenext layer (Figs 22a and 22b).

Internal Effects

Internal incisal edge effects called mamelonsneed to be created to mimic a natural tooth. Spe-cial high-chroma porcelains called mamelon pow-ders were developed for this purpose. Threemamelon powders come with the kit. The authorshave found that mixing MM1 and MM3 50/50 forthe mamelon effects did not end up overdoneand worked quite well with most shades. Themamelons are layered on top of the fired dentinusing a stain-type liquid to create mamelon ef-fects (Fig 23). They are placed on thin and “drawnout” to a thin, feathery appearance with a brush.Other effects are created in the same manner.These are then vacuum fired to only 875°C to setthem on the surface. Firing to 875°C will not affectthe internal microstructure of the fired dentins andenamels, thus minimizing the potential devitrifyingeffect of multiple firings. After firing, the appliedEffect powders will appear chalky, as they are in-completely sintered at this point (Fig 24). Wettingthe surface with a glycerin-type liquid will alter the

refractive index to allow viewing the fired effects.This step can be repeated as many times as nec-essary until the desired effects are obtained. If theeffects are excessive, it is a simple matter to re-move them prior to proceeding to the next layer.With a full-contour buildup technique, effects can-not be viewed until after complete sintering. If un-desired effects are created, complete stripping ofthe crown may become necessary.

Enamel Skin

The enamel or translucent layer is placed next;this is termed the “skin layer.” VM9 has 11 differ-ent translucent materials, termed Effect Enamels.There are also three translucent pearlescentenamels that are useful to recreate a bleachedtooth effect. The authors found the pearlescentenamels (Effect Pearls) to be too bright to be usedstraight. If they need to be used to create a brightreflective zone, they should be cut with 50% EffectNeutral. There are also three translucent highlyopal porcelains for cases that require a bluish orwhitish opal effect. For bright cases, the EffectOpal 1 is cut with 50% Effect Neutral 1 and usedover most of the facial surface; this gives a believ-able bright result (Fig 25). Also, Effect Opal 3(bluish opal) looks good when used at the mesialand distal incisal corners. Generally, in the gingivalthird, the light yellow/orange Effect Enamel 4used in about 0.2-mm thickness gives a slightwarmth to this region (Fig 25).

Because of the exact control of the internal lay-ers (skeleton), the precise control of the enamel/translucent layer (skin) is fairly easy. Overbuildingis preferred at this point to allow slight contouringof the porcelain after firing, rather than a secondaddition of translucent porcelains to completecontour. If an incisal halo effect is desired, it is cre-ated by placing a thin bead of a mixture of dentinand enamel porcelain at the incisal edge of the fa-cial translucent layer; also, any slight correctionsof form can be completed by the addition of smallamounts of translucent porcelains. This is thenfired to complete the buildup (Fig 26). If, after the

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Fig 14 Using the Noritake wheel to thin the zirconia core. Fig 15 Core with bonder (maxillary right central incisor),which is too opaque, and adjacent core (left central in-cisor), with fluorescent liner used as the bonder, whichdemonstrates better apparent translucency.

Fig 16 Necessary core cutback formarginal esthetics.

Fig 17 Placing the porcelain margin. Fig 18 Porcelain margin after it isfired.

Fig 19 Built-up base dentins and zone contrast scheme.

Higher chromaLower value

Base shade(Slightly brighter)

Lower chromaLower value

Fig 20 Base dentins are fired.

Figs 21a and 21b Dentins are built up and fired.

Figs 22a and 22b Incisal framing is built up and fired.

Fig 23 Internal (mamelon) effects are built up withmedium-viscosity glaze liquid.

Fig 24 Internal effects are fired at 875°C under vac-uum.

Fig 25 Enamel skin layer is built up with mostly EffectEnamel 1 and Effect Enamel 4 in the gingival third.

Fig 26 Enamel skin layer is fired.

Fig 27a Preoperative condition of two all-ceramic crowns; thepatient is unhappy with the discolored or dark area on the maxil-lary right central incisor.

Fig 27b Final crowns are a zirconia core with VM9. Note the ef-fective masking of the discoloration of the right central incisorwithout an opaque appearance.

27a

27b

Effect enamel 4(Light yellowish-orangetranslucent)

Effect opal 3(Blue opal)

Effect opal +Effect neutral

skin bake, the contour is insufficient, a correctionbake is completed by adding the necessary mate-rial to full contour and firing.

Contouring and Glazing

Contouring and surface texture are completed asnecessary using diamonds and stones. It is notpossible to cover all the steps in contouring andglazing in the scope of this article. It is importantto note that natural teeth, even old teeth, havesome surface texture. Proper contour and textureare prerequisites for natural-looking restorations.Figures 27a and 27b show before and after viewsof the case discussed in this article and treatedusing the new VM9 material as described.

DISCUSSION

CAD/CAM-generated zirconia crowns and FPDsoffer an alternative to conventional PFM restora-tions, as the physical properties are exponentiallyimproved over previous materials. It is importantto note that long-term clinical data on whetherzirconia can serve as a replacement for metal ce-ramics, especially for FPDs, are as yet unavailable.Even with improved physical properties, manyprocessing and clinical issues will affect a mate-rial’s performance.

Material testing of a new veneering porcelainhas demonstrated improved flexural strength anddecreased abrasiveness compared to previous-generation veneering porcelains. This is believedto directly relate to the fine microstructure in thenewer materials; thus, microscopically, they aresmoother. These finer-grained materials have abra-siveness similar to that of enamel, which is ulti-mately what is desired from a restorative material.

The skeleton buildup technique was reviewedand adapted for use with the VM9 material for zirco-nia frameworks. This technique might seem rathertime intensive, but actually the time spent buildingporcelain is the same as for other techniques. Theonly difference is the oven time; as long as the ce-

ramist has other work while the restoration is bak-ing, there is no actual increase in labor time. Thebenefit of this technique is complete control of eachbuildup step, with the ability to view each fired layerand adjust it as necessary prior to proceeding. Thetechnique is also a great teaching tool.

REFERENCES

1. Giordano RA. Dental ceramic restorative systems. Com-pend Contin Educ Dent 1996;17:779–794.

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