CADCAM Update Technologies and Materials and Clinical Perspectives

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New CAD/CAM systemsand tech-nologies are being introduced to the den-tal marketplace at an ever-increasing rate.Most dental companies that are involvedwith restorative dentistry are already in themarket or are in the process of develop-ing a system or material for the CAD/CAMmarket. To give the reader an idea of howindustry or business views the dental mar-ket, TDS, whose parent company makesNike shoes, recently has entered theCAD/CAM market.Because of the growingconfusion as to what these technologiesare, what they will do, and, more impor-tantly, what the clinical and laboratoryguidelines for using these materials andtechniques are, this article will addressthe important points of these topics.

CAD/CAM TECHNOLOGIESAND MATERIALSAdvances in dental ceramic materials andprocessing techniques, specifically CAD/CAM and milling technology, have facil-itated the development and applicationof superior dental ceramics.CAD/CAM al-lows the use of materials that cannot beused by conventional dental processingtechniques. Tightly controlled industrialceramic processing can produce increasedmicro-structural uniformity, higher den-sity, lower porosity, and decreased resid-ual stresses. Such improvements have thepotential to improve clinical predictabil-ity. CAD/CAM has become somewhatsynonymous with zirconia, but systemsare available that can machine any type ofceramics, ie, glass ceramics, interpenetrat-ing (infiltration ceramics) materials, andsolid-sintered monophase ceramics suchas zirconia.

Problems and complaints with earlysystems focused on the machining accu-racy of a particular system and not with

the materials used with the system. InitialCAD/CAM systems produced restorationsthat had poor marginal fidelity with ageneral lack of internal adaption to the dieas a result of low-resolution scanning de-vices and inadequate computing power.Technological advances in new systemsand software development, coupled withspecific clinical and laboratory techniques,have minimized or eliminated these prob-lems so that marginal integrity and in-ternal adaptation can be excellent.1

Recently, several strategies using differ-ent CAD/CAM processes and differentmaterials that can manufacture all types ofall-ceramic restorationsfrom inlays toonlays and from veneers to crowns to fixedpartial dentureshave been developed.

CAD/CAMTECHNOLOGIES AND GLASSCERAMIC MATERIALSGlass ceramic materials are primarily aglass matrix material that has a fine, even-ly distributed crystalline phase. These mat-erials generally have translucency verysimilar to tooth structure, which makesthem ideally suited for inlay and onlay ap-plications (Figure 1 and Figure 2).They canbe fabricated with a conventional powerliquid technique or they can be industri-ally processed into a dense machineableblock. Two companies fabricate materi-als in block form for the CEREC inLabsystems (Sirona Dental Systems,Charlotte,NC); VITA (Vident, Brea, CA) makesthe Vitablocs Mark II and VITA BlocEsthetic Line materials and Ivoclar Viv-adent (Amherst, NY) makes the ProCADand IPS e.max CAD materials. Glass cer-amic materials are ideally suited for more

conservative restorations (ie, inlays,onlays,and veneers).The only commercial systemfor generating inlays, onlays, and veneers

is the CEREC inLab system (Figure 3).This system is an evolution from the den-tist-based CEREC III (Sirona Dental Sys-tems) system that is used for generatingone-visit inlays and onlays.The system isa self-contained scanning and millingunit, and it is also designed to fabricatesingle copings and 3-unit fixed partial den-ture frameworks using interpenetratingphase compounds and zirconia. The den-tist prepares inlays and onlays by standardtechniques and sends the impression tothe laboratory. The authors experiencewith the system has shown that overflar-ing or beveling the preparation should beavoided. In the laboratory a die is gener-ated and placed in the system and optical-ly scanned (Figure 4). A virtual die is thendisplayed on the monitor and the rest-oration, with occlusion, is designed by thesoftware. The die is then replaced with aglass-ceramic block of the desired materi-al and the restoration is machined. Thesystem will give excellent margins that areclean, confluent,noncorrugated,and non-beveled and, ideally, a close to butt-jointmargin preparation.

For veneers, the same glass ceramicmaterials are used.Dies are generated andscanned as in inlay/onlay applications.Theveneers are machined from the appropri-ate shade and translucent material.For the

best esthetics, the machined veneback in the laboratory in the incthird to one half and enamel or cent porcelain is built up (or stackthen fired (Figure 5 and Figure

98 INSIDE DENTISTRYNOVEMBER/DECEMB

LAB

taLkLaboratory perspectives from the inside o

CAD/CAM Update: Technologies andMaterials and Clinical PerspectivesEdward A. McLaren, DDS, MDC, and Lu Hyo, MDC

Edward A. McLaren, DD

Adjunct Associate

UCLA Center for Esthetic D

Founder and

UCLA Master Dental Ceramist

UCLA School of D

Los Angeles, C

Private Practice limited to Prosthodo

Esthetic D

Los Angeles, C

Master Dental

Assistant

UCLA Master Dental Ceramist

UCLA School of D

Los Angeles, C

Figure 1 Image of an onlay machined from aVita Mark II glass ceramic block.

Figure 2 Cementation of a glass ceraand inlay after staining, glazing, and po

Figure 3 The CEREC inLab system. Figure 4 Prepared die placed in the system

ready to be scanned.

Figure 5 A glass ceramic veneer that has

incisal one third cut back and ready for translu-

cent porcelains to be applied.

Figure 6 Applying translucent porcela

the incisal one third to create a more n

effect.


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benefit of veneers fabricated by this tech-nique is that it is much safer to try them inintraorally because the ceramic is muchtougher than veneers fabricated by con-ventional porcelain techniques. Also, ifnecessary,the restorations can be easily re-

fired just like a conventional porcelain-fused-to-metal (PFM) or high-strength all-ceramic crown. The disadvantage of thistechnique is that the veneers need to beabout0.9 mm or thicker for optimal esth-etics. The author uses veneers with thistechnique; the veneer thicknesses are about0.9 mm or more.The author uses conven-tional veneers for veneers thinner than0.9 mm (Figure 7). It is important to notethat the clinical situation should dictatethe material and technique selected (ie, ifthinner, more conservative veneers arethe desired clinical result,then teeth shouldnot be over-prepared to use machined or

pressed glass ceramic materials). The sys-tem does not lend itself to knife-edge orno-preparation margin techniques. Thebest results for these situations are obtainedwith a medium chamfer preparation.

CAD/CAM TECHNOLOGIESAND INTERPENETRATING(INFILTRATION CERAMICS)PHASE MATERIALSThis class of materials uses a partially sin-tered crystalline matrix of a high modulus(stiff) material, in which there is a junc-tion of the particles in the crystalline phase(Figure 8). The crystalline phase consistsof alumina,an alumina/magnesia mixture,or an alumina/zirconia mixture.The mate-rial is supplied in block form (Figure 9)and only supplied for the CEREC inLabsystem. The framework made from any ofthe three materials is then infiltrated with

a low-viscosity lanthanum glass at hightemperature (Figure 10).The ceramic phaseand the glassy phase form a continuousinterconnecting meshwork.The final struc-ture is about 85% crystalline and 15%glass. The materials are virtually the sameas the VITA In-Ceram (Vident) material .The big difference is the material is ma-chined from a block rather than a slurrymixture of powder and liquid being builtup with a brush. The alumina/magnesiamixture is a very translucent core mate-rial and, in the authors opinion,is ideal forwhen anterior crowns are indicated andmaximum translucency is desired (Figure11 and Figure 12).The material has shownexcellent clinical results for single poste-rior crowns of either the alumina or zir-conia-infiltrated core; thus, it can berecommended for single posterior crowns.Because of the better physical properties

of the solid sintered zirconia, the authoruses cores from this material for all-cer-amic posterior crowns. There are a cou-ple of systems on the market that useelectroplating technology (one exampleis WolCeram, MicroDental Laboratories,Dublin, CA) to plate the alumina ma-terial to a masterdie. It is then infiltratedwith the same glass as in the convention-al In-Ceram technique or the CAD/CAMtechnique. These systems should performas well as the conventional In-Ceram mate-rial because it has very similar physicalproperties; thus, it can be recommendedfor single posterior crowns. The system

has been recommended by some terior bridge applications, but thno published clinical studies supthese plating systems for use in pbridges. The In-Ceram alumina is not recommended for posteripartial dentures (bridges) by thefacturer. The authors personalence would agree with that, as ovof the posterior bridges fabricatthe alumina material failed by

The system has proved to be safefective for 3-unit anterior bridges

Preparations ideally should bheavy chamfer to shoulder. Shangles need to be rounded as nonCAD/CAM systems machine wsharp line angles. Sharp line analso concentrate stress and lead tothan normal fracture. PreparatSpinell anterior restorations shoufor 1.2 mm of crown thickness festhetics. Because of the greaterof the alumina or the zirconia m1.5 mm of space is necessary for idetics, which is the same as a PFM

SOLID SINTEREDMONOPHASE CERAMICSSolid sintered ceramics have thepotential for strength and toughnbecause of high firing temperatusintering shrinkage techniques, thnot available to use as high-strengthworks for crowns and fixed partial until recently. Solid sintered monceramics are materials that are by directly sintering crystals togethout any intervening matrix to formair-free, glass-free, polycrystallinture (Figure 13).There are several processing techniques that allow rication of either solid sinteredinous oxide or zirconia oxide fram

There are three basic techniqfabricating solid sintered monophamic frameworks for porcelain ation.One system,DCS Preciscan (min the United States by Dentsply Amachines from a solid sintered bmaterial the final desired frameworThis system is expensive and has nven cost effective as a result of the emachining time and manual labosary to adjust and fit the coping.Sthe Procera system (Nobel BiocarLinda,CA) employs an oversized dslurry of either aluminous oxide

nia oxide is applied to the die,subly fired, fullysintered, and shrunk scanned die. The Procera system the ability to fabricate custom abfor regular platform Brnemark i(Figure14 and Figure15). The thirod machines an oversized copingpartially sintered block of zirconmaterial, which is then fired to tering temperature and then shfit the die. Most of the systemsmarket today use some variationtype of technology. Examples osystems are the CEREC InLabuses VITA YZ [Vident] and Ivocla


Figure 7 Layered glass ceramic veneers in-

situ. The veneers are about 1 mm thick.

Figure 8 SEM of In-Ceram showing the partial-

ly sintered crystalline phase with the intervening

glass phase.

Figure 9 Block of In-Ceram material for

machining in the CEREC inLab system.

Figure 10 Glass-infiltrated In-Ceram coping. Figure 11 Intraoral view of a transilluminated

Spinell coping. Note the natural translucency.

Figure 12 Single central on tooth No.9 made

out of Spinell and Vita VM7 (Vident).

Figure 13 SEM of the densely sintered zirconia. Figure 14 Image of custom zirconia implant

abutment made with the Procera system.

Figure 15 Final Vita YZ coping veneered with VM9.

Figure 16 Figure of the Lava and inLab CAD/CAM systems.


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materials), Lava (3MESPE, St. Paul,MN) Cercon (Dentsply,York, PA),Everest(KaVo, Lake Zurich,IL),and TDS systems(Figure 16). These systems scan the pre-pared die, and then the software createsvirtual dies and frameworks.An oversizedframework is created through a CAMprocess, which is then fully sintered in aspecial oven. The VITA YZ and the Lavasystems also allow for internal shading ofthe core material. In the authors experi-ence, the white zirconia is too reflectiveand thus the final result is too opaque.The recommendation is to use a sys tem

that allows internally colored cores.Thetwo systems that allow internally coloredzirconia cores of different shades are theVITA YZ system machined on the CERECinLab; this system is marketed as in-Vizion (Vident), and the Lava system(Figure 17 and Figure 18). Some systemsallow the external application of color onthe surface of the white core but this alsohas the potential of being too opaque.

Zirconia oxide, sometimes called zir-con, has unique physical characteristicsthat make it twice as strong and twice astough as alumina-based ceramics. While

the reported values for flexural strengthof this new material range from over 900MPa to 1,100 MPa,4 it is important to notethere is no direct correlation between flex-ural strength (modulus of rupture) andclinical performance. Generally, strongermaterials have performed better but thereare many factors that contribute to a mater-ials clinical success along with the flexuralstrength of the material.A more importantphysical property is fracture toughness,

which has been reported to be between 8MPa m1/2 and 10 MPa m1/2 for zirconia.3

This is significantly higher than any previ-ously reported ceramic, and roughly twicethe amount reported for the aluminamaterials. Fracture toughness is a measureof a materials ability to resist crack growth(ie, a measure of the amount of energynecessary to cause crack growth). Clin-ically, restorations are not loaded to fail-ure as is done in a flexural strength test;instead,millions of subcritical loads (chew-ing) are applied. Materials ultimately failbecause of this cyclic fatigue by crackpropagation. Thus, materials with higherfracture toughness are more ideal clini-cally as it takes more energy to cause crackgrowth. Other factors such as stress corro-sion (chemically assisted crack growth)and residual flaws in the material greatlyaffect the final strength of a finished mat-erial and are discussed elsewhere.5

CLINICAL INDICATIONSThere have been relatively few clinicalstudies reporting on CAD/CAM-gen-erated, all-ceramic, zirconia-corebasedcrowns that have included large samplesizes or long follow-up periods. Ideally,follow-up periods would be at least 5 yearswith sample sizes of several hundred

units.Long follow-up periods are nbecause it takes several years for facause failure. The author has pla300 VITA YZ and Lava restoover the last 36 months with esuccess. To date there have been nnia core fractures observed; thebeen a few cases of porcelain delafrom some of the early crownsdetermined that inappropriate fthe porcelain to the core was th

Proper firing of a bonding layer oain to the core is necessary to creable porcelain/zirconia core interflaboratory technique for doingcovered elsewhere by the authorbased on this early success, zircorestorations can be recommendedgle units anywhere in the mouth.

For fixed partial dentures, rclinical data has been short term buising.This and many anecdotal resuccess would indicate that high-ceramic frameworks subsequeneered with porcelain should perclinically acceptable standards foanterior and posterior fixed parttures as long as accepted guidelmaintained. It is important to nwhile several studies are being ior are already ongoing (includingUCLA) using CAD/CAM technothe fabrication of posterior fixeddentures, no large-sample,long-te

yet exists to justify their ubiquitoEarly results look extremely probut the effects of fatigue and chcorrosion take time to manifeeffects. Clinical use of these mateposterior fixed partial denturesstill be considered experimentapoint and patients should be fullmed of possible effects.

CLINICAL GUIDELINES

PreparationsThe correct reduction for the rooessary for the esthetic fabricatizirconia all-ceramic crown is the for esthetic PFM restorations.Evof restorations in which the authformed all clinical and ceramicdures has led to the determinat1.5 mm of labial overall crown thwas the minimum ideal dimenpredictable esthetics and shadeduction. The core can be thinne

mm on the facial, which leaves r1.2 mm of porcelain. A minimmm of crown thickness is requthe lingual walls. Incisal edge thcan be as little as 1.5 mm, but 2ideal esthetically. Posteriorly, it isary to have 2.5 mm of occlusation for both esthetic all-cerammetal-ceramic restorations, espenatural, unworn occlusal anatomsired in the final restoration. Thethe author has found to accompreduction is the 2-mm Reductiofrom Kerr Corporation (Orangethe 2-mm guide passes with on

Figure 17 Image of a single central (tooth No.

8) inVizion crown (inVizion is the trade name for

the VITA YZ material and the CEREC inLabCAD/CAM system).

Figure 18 Image of a single central fabricated

with a Lava core.

Figure 19 Using the Kerr 2-mm Reduction

Guide to judge occlusal reduction.

Figure 20 Image of ideal preparation for scan-

ning and machining. Note the very rounded

occlusal line angles and generally flatter occlusal

preparation than what might have been for a PFM.


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binding through the occluded opposingarches then there is close to 2.5 mm of inte-rocclusal space (Figure 19). As with thepreviously mentioned machinable ma-terials, ideally preparations should be a360 heavy chamfer to shoulder andsharp line angles should be avoided. Prep-aration line angles need to be rounded assharper line angles are not easily milled(Figure 20).

Lab ConsiderationsOne of the main benefits of zirconia isusing the same ceramic or veneer mate-rial for all clinical situations. Porcelainsfor zirconia frameworks can be used forporcelain veneers (Figure 21 and Figure22),crowns,and fixed partial dentures.Theonly other porcelain a laboratory wouldneed is a metal-ceramic material.

There are some tricks to working withthe zirconia cores to get the best estheticresults. Zirconia cores are slightly moreopaque than dentin, so it is ideal to designthe framework to allow for a more trans-lucent porcelain margin material to beplaced. There is a misconception that themargin material should have the sametranslucency as dentin. If the marginalarea were at all visible it would not benoticeable unless the margin materialalso had the exact same chroma and hue asthe surrounding tooth structure. It is actu-ally ideal to have the marginal material to

be slightly more translucent than the sur-rounding tooth structure so that it blendsin by picking up some color from thetooththe so-called contact lens orchameleon effect. So, just as with metalor more opacious ceramic cores, a porce-lain margin is mandatory for ideal esth-etics. The benefit over metalceramics isthat the framework only needs to beshortened slightly to allow enough lightthrough to illuminate the gingival area to

create a natural effect (Figure 23).

REFERENCES1. McLaren EA, Terry DA. CAD/CAM systems,

materials, and clinical guidelines for all-

ceramic crowns and fixed partial dentures.

Compend Contin Educ Dent. 2002;23(7):

637-654.

2. Sorensen JA,Kang SK, Torres TJ, Knode H.

In-Ceram fixed partial dentures: three-year

clinical trial results.J Calif Dent Assoc. 1998;

26(3):207-214.

3. McLaren EA, Giordano RA. Zirconia based

ceramics: material properties, esthetics,

and layering techniques of a new

VM9. Quintessence Dental Tech

28:99-111.

4. White SN, Miklus VG, McLare

Flexural strength of a layered z

porcelain dental all-ceramic system

Dent. 2005;94(2):125-131.

5. Sorensen JA, Berge HX, Edelho

of storage media and fatigue

ceramic strength [abstract]. J

2000;79:271. Abstract 1017.

Figure 21 Layering zirconia porcelain on a

refractory die for porcelain veneer fabrication.

Figure 22 Clinical case of veneers on teeth

Nos. 6 through 11 made with VM9 using the

refractory technique.

Figure 23 A zirconia framework on the die

demonstrating a 0.5-mm facial cutback of the

core for a porcelain margin.

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