1997;128;297-307 J Am Dent Assoc

MA Rosenblum and A Schulman A review of all-ceramic restorations

jada.ada.org ( this information is current as of April 8, 2011 ):The following resources related to this article are available online at 

http://jada.ada.org/cgi/content/abstract/128/3/297in the online version of this article at:

including high-resolution figures, can be foundUpdated information and services

http://jada.ada.org/cgi/collection/restorativesRestoratives   : subject collectionsThis article appears in the following

http://www.ada.org/prof/resources/pubs/jada/permissions.aspthis article in whole or in part can be found at:

of this article or about permission to reproducereprintsInformation about obtaining

© 2011 American Dental Association. The sponsor and its products are not endorsed by the ADA.

on April 8, 2011

jada.ada.orgD

ownloaded from

i T O Y

To select the most

appropriate type of

all-ceramic system

for clinical use, the

clinician must be fa-

miliar with the differ-

ences between sys-

tems. This article

discusses five cate-

gories of all-ceramic

restorative systems

relative to their pro-

cessing techniques,

strength and wear

characteristics. The

authors present and

compare results of

published in vitro

studies and short-

term clinical studies.

A Review of :_

All-Ceramic

ince the introduction of the first successful porcelain-fused-to-metal

system in the early 1960s,' there has been increasing demand for ce-

ramic restorative materials. As recently as 1990, of the estimated 35

million crowns placed by private practice dentists, more than 71 percent had

porcelain as one of the components.2 This popularity may be the result of

porcelain aesthetics. Porcelain is the most natural-appearing synthetic re-

placement material for missing tooth substance. It is available in a range of

shades and translucencies for achieving lifelike results. Historically,

strength concerns compromised some of the beauty of porcelain crowns.

Because of the relatively low tensile strength and brittleness of the porce-

lain, it has been generally fused to a metal substrate to increase resistance

to fracture.3 However, this metal base can affect the aesthetics of the porce-

lain by decreasing the light transmission through the porcelain and by creat-

ing metal ion discolorations. In addition, some patients have allergic reac-

tions or sensitivity to various metals. These drawbacks, together with the

material and labor costs associated with metal substrate fabrication, have

prompted the development of new all-ceramic systems that do not require

metal, yet have the high strength and precision fit of ceramo-metal systems.

MARC A. ROSENBLUM, PH.D., D.M.D.; ALLAN SCHULMAN, D.D.S., M.S.

JADA, Vol. 128, March 1997 297

on April 8, 2011

jada.ada.orgD

ownloaded from

C~KOVER STORY

Figure 1. Whiteware compositions composed of clay, feldspar and silica (quartz).

In this article, we describefive categories of all-ceramicsystems:- conventional (powder-slurry)ceramics;

castable ceramics;-machinable ceramics;-pressable ceramics;

infiltrated ceramics.

CERAMIC VS. PORCE-LAIN: WHAT'S THEDIFFERENCE?

Ceramics. Ceramics are usu-

ally defined in terms of whatthey are not: nonmetallic (notmetals) and inorganic (notresins). To distinguish themfrom rocks and minerals, thevast majority of which are alsoinorganic and nonmetallic, ce-

ramics are additionally definedas man-made solid objectsformed by baking raw materi-als (minerals) at high tempera-tures. The term "ceramics" is

derived from the Greek word"keramos" meaning "burntstuff."

Although the methods of ob-taining and purifying the rawmaterials and the technology offabricating these raw materialsinto useful objects have beensignificantly advanced sinceancient times, some methodsand techniques have notchanged. For example,

stoneware and pottery are stillmade from impure clays, sandand feldspar minerals, and are

baked in ovens called kilns.These objects are made by firstpulverizing the raw materialsinto fine particles or powders,then adding water to obtain a

consistency suitable for shap-ing and molding. The "green"(unbaked) objects are dried andare placed in a kiln and heatedto sufficiently high tempera-tures to make the individualparticles coalesce into a solidmass. The coalescence of theparticles is often referred to as

"sintering," and the processusually results in a net shrink-age and strengthening of thesolid mass.

The newer types of ceramicdental restorative materialsused for all-ceramic crowns, ve-neers and inlays are eithervariations of feldspathic porce-

298 JADA, Vol. 128, March 1997

VI n dentistry, we use

three differenttypes of porcelain

compositions, depend-ing on their application.

A

on April 8, 2011

jada.ada.orgD

ownloaded from

COVER STORY

lain (for example, Optec HSP,Jeneric/Pentron; In-Ceram,Vident; Cerec, Vident; Celay,Vident; IPS Empress, IvoclarNorth America; and OptecPressable Ceramic, Jeneric/Pentron) or are made of entirelydifferent compositions (for ex-ample, Dicor, Dentsply, L.D.Caulk Division; Duceram LFC,Degussa Corp.). Themethods used for fabri-cating some of theserestorations are quitedifferent from thoseused for ceramo-metalrestorations and porce-lain jacket crown, orPJCs.

Porcelain. A specifictype of ceramic widelyused for nearly 3,000years, traditional porce-lain is composed ofblends of three natural-ly occurring minerals:pure white clay, quartzand feldspar. Whenthese three ingredientsare pulverized, blended,formed into shapes andbaked, they composewhat is known as white-ware, so named becausetheir color is white after Figurethey are baked. crystaPorcelain is a type of graphwhiteware that has rel-atively high strength andtranslucency. Other types ofwhiteware include tile, electri-cal insulators and sanitaryware (used, for example, insinks and toilets) (Figure 1).

In dentistry, we use three dif-ferent types of porcelain compo-sitions depending on their appli-cation. One is for denture teeth,one is for ceramo-metal applica-tions and another is for all-porcelain restorations (PJCs, ve-neers and inlays).- Denture tooth porcelain be-

gins as a mixture of powders offeldspar, clay and quartz. This isreferred to as high-temperatureporcelain in some dental materi-als textbooks.4- Feldspathic dental porcelain,used for ceramo-metal restora-tions, begins as a mixture ofpowders of potassium feldsparand glass. This type of porcelain

D 2. Scanning electron micrograph of leucIs in a dental porcelain composition (phecourtesy of Dr. T.K. Vaidyanathan).

composition can also be used forfabricating porcelain veneersand inlays.- Aluminous porcelain, used inPJCs, is composed of mixturessimilar to that of feldspathicdental porcelain with increasedamounts of aluminum oxide.

These three types of dentalporcelain also contain pigmentsand opacifying agents to createvarious shades and translucen-cies. After baking, all three typesof porcelain contain similar com-ponents: small crystals (leucite

and/or other alumino-silicatecrystals) embedded in a silicateglass (a noncrystalline, amor-phous matrix). The relativeamounts of crystal and glass de-pend on the specific type ofporcelain in question. Leucite (areaction product of potassiumfeldspar and glass) is a particu-larly important component in

dental porcelain becauseit affects the optical prop-erties, thermal expan-sion, strength and hard-ness of the porcelain(Figure 2).

CERAMICS ASRESTORATIVEMATERIALS

Much has been writtenabout the desirable prop-erties of ceramic dentalrestorative materials:their lifelike optical prop-erties, biocompatibility,durability and etchability(ability to be bonded).However, two major prob-lems arise in their use indentistry: their potentialfor brittle, catastrophicfracture, and their poten-tial to cause abrasive

mite wear of opposing toothDto- structure.

Brittle fracture is gen-erally attributed to the

rapid, uninterrupted propaga-tion of cracks through the bulkof the ceramic material, usuallybeginning at a flaw in the mate-rial. The flaw can be a microc-rack in the surface (for example,created during occlusal adjust-ment with a diamond stone), orit can be a subsurface porosity(for example, from a processingerror during the buildup andbaking of the porcelain). In gen-eral, ceramics have relativelylow tensile strength because ofthe presence of flaws. Improving

JADA, Vol. 128, March 1997 299

on April 8, 2011

jada.ada.orgD

ownloaded from

8COVER STOBY-

the fracture resistance of dentalporcelain provided the impetusfor fusing it to a metal sub-strate. For additional strength,small crystals can be dispersedwithin the ceramic structure toimpede the propagation ofcracks.

The abrasive wear of oppos-ing tooth structure is a seriousclinical problem. The amount ofwear is influenced by the hard-ness of the ceramic materialand its surface roughness as itfunctions against natural toothstructure. The effects of abra-sive wear are particularly no-ticeable and destructive whenlingual ceramic surfaces of amaxillary anterior crown func-tion against the incisal and fa-cial surfaces of mandibular an-terior teeth. Glazed porcelaincan be less abrasive than porce-lain with a roughened surface5(for example, from occlusal ad-justment).

The evolution of ceramic andporcelain materials has been abattle for the ideal strength-aesthetic combination. The firstall-ceramic crowns introducedby Land in 19036 were relativelyweak materials with limitedclinical use. In 1965, McLeanand Hughes7 formulated alumi-nous porcelain compositionsthat are still in use today.These materials are composedof feldspathic porcelain to whichapproximately 50 percent alu-minum oxide is added to in-crease the strength and bakingtemperature. As such, alumi-nous porcelain compositions canbe used as cores to replace themetal substructure used in cer-amo-metal constructions. Theyare veneered with conventionalfeldspathic porcelain to repro-duce the contour and shade of anatural tooth. Because alumi-nous porcelain shrinks during

the baking procedure, the fit offinished aluminous crowns isgenerally much poorer thanthat of ceramo-metal crowns.Although aluminous crowns areconsidered more lifelike in ap-pearance than their ceramo-metal counterparts, their suc-cessful fabrication is extremelytechnique-sensitive. The clinicalfracture reported for thesetypes of restorations is relative-ly high: 2 percent for anteriorcrowns8 and 15 percent for pos-terior crowns.9

More recently, newer typesof all-ceramic restorations havebeen developed that may proveto have a lower incidence ofclinical fracture for three im-portant reasons:- all-ceramic restorationstoday consist of stronger mate-rials and involve better fabri-cating techniques;- most all-ceramic restora-tions can be etched and bondedto the underlying tooth struc-ture with the new dentin adhe-sives;- with greater tooth reductionthan what was previously usedfor PJCs, clinicians now pro-vide laboratory technicians withenough room to create thickerand stronger restorations.

CLASSIFICATION OF ALL-CERAMIC SYSTEMS

The following general types ofall-ceramic systems are current-ly available:- Conventional powder-slurry ceramics. These prod-ucts are supplied as powders towhich the technician addswater to produce a slurry,which is built up in layers on adie material to form the con-tours of the restoration. Thepowders are available in vari-ous shades and translucencies,and are supplied with charac-terizing stains and glazes.- Castable ceramics. Theseproducts are supplied as solid ce-ramic ingots, which are used forfabrication of cores or full-con-tour restorations using a lost-wax and centrifugal-casting tech-nique. Generally, one shade ofmaterial is available, which iscovered by conventional feld-spathic porcelain or is stained toobtain proper shading and char-acterization ofthe final restora-tion.- Machinable ceramics.These products are supplied asceramic ingots in variousshades and are used in comput-er-aided design-computer-aidedmanufacturing, or CAD-CAM,procedures. The machinedrestoration can be stained andglazed to obtain the desiredcharacterization.- Pressable ceramics. Alsosupplied as ceramic ingots,these products are melted athigh temperatures and pressedinto a mold created using thelost-wax technique. The pressedform can be made to full con-tour, or can be used as a sub-strate for conventional feld-spathic porcelain buildup.- Infiltrated ceramics. Theseproducts are supplied as twocomponents: a powder (alu-

300 JADA, Vol. 128, March 1997

on April 8, 2011

jada.ada.orgD

ownloaded from

COVEH STORY

minum oxide or spinel), whichis fabricated into a porous sub-strate, and a glass, which is in-filtrated at high temperatureinto the porous substrate. Theinfiltrated ceramic is then ve-neered using the conventionalfeldspathic porcelain technique.

CONVENTIONAL POW-DER-SLURRY CERAMICS

Optec HSP. Optec HSP hasgreater strength than conven-tional feldspathic porcelain as aresult of an increased amount ofleucite.Y' The manufacturer dis-perses the leucite crystals in aglassy matrix by controllingtheir nucleation and crystalgrowth during the initial pro-duction of the porcelainpowder. " Because of its in-creased strength, Optec HSPdoes not require a core whenused to fabricate all-ceramicrestorations, as is necessarywith aluminous porcelain PJCs.The body and incisal porcelainsare pigmented to provide thedesired shade and translucency.The leucite and glassy compo-nents are fused together duringthe baking process (at 1020 C).12The buildup and contouring ofthe crown is accomplished usingthe powder-slurry technique ona special semipermeable diematerial. Optec HSP does notrequire special processingequipment beyond what is usedfor ceramo-metal restorations.

These restorations fit accu-rately; however, their increasedleucite content contributes tothe relatively high in vitro wearof opposing teeth, as reported ina recent laboratory study.5There are no published clinicalstudies of Optec HSP.Duceram LFC. This is a

relatively new category ofrestorative material, referred toas "hydrothermal low-fusing ce-

Figure 3. Inlay made from Celay (Vident) (photograph courtesy of Dr.C. Moglianesi).

ramic." It is composed of anamorphous glass containing hy-droxyl ions. The manufacturerclaims'` that this noncrystallinestructure has greater density,higher flexural strength,greater fracture resistance andlower hardness than feldspathicporcelain (causing less abrasionagainst tooth structure thanleucite-containing systems). Thehigher flexural strength resultsfrom an ion exchange mecha-nism of hydroxyl ions, which issaid to also promote a healing ofsurface microcracks. The lowerhardness results from the ab-sence of leucite crystals in thismaterial.

Duceram LFC is used for thefabrication of ceramic inlays,veneers and full-contourcrowns. The restoration is madein two layers. The base layer isDuceram Metal Ceramic (aleucite-containing porcelain); itis placed on a refractory dieusing standard powder-slurrytechniques and then baked at930 C. Over the base layer,Duceram LFC is applied usingthe powder-slurry technique

and baked at a relatively lowtemperature (660 C). The mate-rial is supplied in a variety ofshades and can be surface-char-acterized with compatiblestains and modifiers. The fabri-cation process requires no spe-cial laboratory techniques orequipment.

There are no clinical studiessubstantiating the manufactur-er's claim that the material isless abrasive to tooth structurethan feldspathic porcelain.However, the results of a one-year clinical study recently con-ducted for the manufacturerseem to indicate that the mate-rial wears at a rate equivalentto that of natural tooth enamel(Shotwell J, Beard CC, Lang B,Lang BR, unpublished data,1990).

CASTABLE CERAIVUICSYSTEMS

Dicor. This is a polycrystallineglass-ceramic material, initiallyformed as a glass and subse-quently heat-treated under con-trolled crystallization conditionsto produce a glass-ceramic ma-

JADA, Vol. 128, March 1997 301

on April 8, 2011

jada.ada.orgD

ownloaded from

COVER STORY

Optec HSP 146 MPa'0 Higher thanl that of Special die No core material; i-(Jeneric/ conventional feld- material form thranluoency andPentron) spathic porcelain due shade throughout; etch-

to high leucite corntent5 able forbohding totooth

Duceram LFC 110 MPa13 Close to hardness of Special die Low fiusing tempera-(Degussa) natural tooth owing material ture; can be charac-

to absence of leuicite terized with suirfacestains

r ~~~~~~~~~~~~~~~~~~~~~~~~~kDlcor 152 MPal Same as that of tooth Special invest- Surface stains (aes-(Dentsply, L.D. (softer than conven- ment and casting thetics) can be lost toCaulk Division) tional feldspathic equzipment abrasion and acidu-

porcelain)'; however, lated fluoride (DicorDicor Plus is as hard Plus is more stable);as conventional feld- etchable core forspathic porcelain bonding to tooth

Cerec Vltablocs 93 MPa26 Similar to that of con- Siemens Cerec Regarding all mate-Mark I (Vident) 9ventional feldspathic CAD-CAM rials in this group:

porcelainr System; milling ~ Can be character-of a ceramic ized with surfaceingot from a digi- stainis; the stainstized optical scan may be lost to abra-

sionCerec 152 MPa26 Similar to that of Same as above - The gap betweenVitablocs Mark eaamel27 the restoration andll (Vident) tooth is wider than

that in other all-ce-ramic systems; wear

Dicor MGC 216 MPa28 Between those of Same as above of the resin cement(Dentspiy, L.D. Cerec Vitablocs Mark in this gap may haveCaulk Division) I aDd Cerec Vitablocs clinical significance

Mark 1127 - Etchable for bond-ing to tooth struc-

Celay (Vident) Same as Same as that of Cerec Celay Copy- tuirethat of Vitablocs Mark 1130 Milling System;Cerec milling of a ce-Vitablocs ramic ingot fromMark I130 a direct pattern

UPS Empress 126 MklPa Possibly higher than Special o-ven, die Core material is(Ivoclar North i6itially; that ofconventiojnal feld- material and shaded and translui-America) 160-182 spaxthic porcelain owing molding proce- cent; etchable for

M:Pa after to increased leuzcite dure bonding to toothheat treat- content after heatment24 treatment

Optec PF.ssatie 165 MPa37 Same as above Same as above Same as aboveCeramic(JenedcAPeronb)

In-Ceram 450 Mpa17'20 Same as that of conr- Special die mate- Core material is more(Vident) 0ventionial feldspathic rial, high-tem- opaque than other

porcelain perature oven types; not etchablefor bonding to tooth

* ft*Wu~estength re f various iatW.M

302 JADA, Vol. 128, March 1997

on April 8, 2011

jada.ada.orgD

ownloaded from

COVER STORY

Figure 4. A. Lower anterior teeth before treatment.B. IPS Empress (Ivoclar North America) porcelainveneers on a laboratory model. C. Lower anteriorteeth with bonded porcelain veneers. (Photographscourtesy of Dr. David Ehrenberg.)

terial."4 The fabrication methoduses lost-wax and centrifugal-casting techniques similar tothose used to fabricate alloycastings.A full-contour transparent

glass crown is cast at 1350 C,then is heat-treated at 1075 Cfor 10 hours. This heat treat-ment (known as "ceramming")causes partial crystallization(55 percent) of tetrasilic mica-like crystals.11 The crystalsfunction in two ways: theycreate a relatively opaque ma-terial out of the initially trans-parent crown, and they signifi-cantly increase the fractureresistance and strength of theceramic. These crystals are alsoless abrasive to opposing toothstructure than the leucite crys-tals found in traditional feld-spathic porcelains.15 To achievethe appropriate shade, the col-orant stains are baked on thesurface of the glass-ceramicmaterial.

There has been some evi-dence that the stain layermight be lost during occlusaladjustment, during routinedental prophylaxis or throughthe use of acidulated fluoridegels.16 Dentsply (TrubyteDivision) has introduced Dicor

Plus, which isa shaded feld-spathic porce-lain veneer ap-plied to theDicor sub-strate.'7However, asDicor Plus is afeldspathic porcelain that con-tains leucite, it is expected thatthese restorations will be asabrasive to teeth as other feld-spathic porcelains.

Dicor crowns and veneershave been demonstrated to fit ac-curately in clinical and laborato-ry studies.18 The process requiresa special high-temperature, elec-tric-heated casting unit.

Short-term clinical studiesverify the efficacy of the Dicorsystem for use in veneers andinlays.9'20 Failure rates as highas 8 percent (fracture of therestorations) have been report-ed.'9 Failure rates as high as 35percent for full-coverage Dicorcrowns not bonded to the un-derlying tooth structure havebeen reported.2'

MACHINABLE CERAMICS

The ceramic ingots used inCAD-CAM restorations do notrequire further high-tempera-

ture processing. They areplaced in a machining appara-tus to produce the desired con-tours. This is followed by oc-clusal adjustment and thenpolishing, etching and bondingthe restoration to the preparedtooth. The CAD-CAM process isdiscussed in detail in the litera-ture.22-24 The different types ofceramic ingots used in the pro-cess are as follows.

Cerec Vitablocs Mark I.This is a feldspathic porcelain,which was the first compositionused with the Cerec system(Siemens). It is similar in com-position, strength and wearproperties to feldspathic porce-lain used for porcelain-fused-to-metal restorations.

Cerec Vitablocs Mark II.This is a feldspathic porcelain ofincreased strength,2' and has afiner grain size than the Mark Icompositions; an in vitro evalu-ation shows that this produces

JADA, Vol. 128, March 1997 303

on April 8, 2011

jada.ada.orgD

ownloaded from

G~KOVER STORY

-~~ ~ ~~~ ~ ~~~ ~ ~~~ ~ ~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~ ~~~ ~ ~~~ ~ ~~~ ~ ~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Figure 5. Inlay made from Optec Pressable Ceramic (Jeneric/Pentron)(photograph courtesy of Dr. David Ehrenberg).

less abrasive wear of the oppos-

ing tooth structure.26 There are

no published clinical studies as

yet to support this claim.Dicor MGC (Dentsply,

L.D. Caulk Division). This isa machinable glass ceramiccomposed of fluorosilicic micacrystals in a glass matrix. It hasgreater flexural strength thanthe castable Dicor (discussedearlier) and the Cerec composi-tions (Table).27 This material issofter than conventional feld-spathic porcelain and producesless abrasive wear of the oppos-ing tooth structure than CerecMark I and more wear thanCerec Mark II in an in vitrostudy.26

Celay. This material can beused for CAD-CAM-producedrestorations or used in the copy-

milling technique (Figure 3).28 Itis a fine-grained feldspathicporcelain that is said to reducethe wear of antagonist toothstructure; however, there are no

clinical studies to substantiatethis claim. The manufacturerclaims that this material isidentical in composition to

Cerec Vitablocs Mark II (E.Perry, Celay product manager,Vident Inc., personal communi-cation, 1996). On this basis, itwould be expected that the phys-ical and clinical properties ofCelay are also identical to thoseof Cerec Vitablocs Mark II.

All the aforementioned sys-tems can be characterized withstains after milling and occlusaladjustment. Machinable ceram-

ics have been evaluated in some

limited clinical studies.93'These studies have shown thatthe gap between the restorationand tooth structure is consider-ably wider than that in othertypes of all-ceramic restora-tions. This gap can be filled inwith composite resin cements,but the cement itself is subjectto wear. This wear may be self-limiting after three to fouryears.3031 Clinical fracture seemsto be related to insufficientdepth of tooth preparation andinadequate bonding to the toothstructure during cementation.

PRESSABLE CERAMICS

IPS Empress. This is a type offeldspathic porcelain suppliedin ingot form. The ingots are

heated and molded under pres-

sure to produce the restora-tions. A full-contour crown iswaxed, invested and placed in a

specialized mold that has an

alumina plunger. The ceramicingot is placed under theplunger, the entire assembly isheated to 1150 C and theplunger presses the molten ce-

ramic into the mold.32'33 Thefinal shade of the crown is ad-justed by staining or veneering(Figure 4). In the veneeringtechnique, the original wax-upis cut back by about 0.3 mil-limeters. After molding andbaking as described, feldspathicporcelain is added to the surfaceto obtain full contour and thecorrect shade.

The flexural strength hasbeen shown to improve undersubsequent heat treatments as a

result of the growth of additionalleucite crystals.34 For example,the flexure strength of the heat-pressed material is in the rangeof 126 megapascals, or MPa;with subsequent heat treat-ments, the strength increases tothe 160- to 182-MPa range.

304 JADA, Vol. 128, March 1997

V

A 11 the systemsappear to haveadequate

strength for single units.Their ability to be bond-ed to tooth structure isan additional strength-emng mechanism.

A

on April 8, 2011

jada.ada.orgD

ownloaded from

COVER STODY

Figure 6. Crowns made from In-Ceram (Vident) (photographs courtesy of Dr. Carlos Moglianesi).

One short-term clinicalstudy35 has been published thatreports no clinical fractures of10 IPS Empress inlays; howev-er, one-third of the restorationsshowed a marginal gap after 11/2years of evaluation.

Optec Pressable Ceramic.Optec OPC is also a type offeldspathic porcelain with in-creased leucite content, pro-cessed by molding under pres-sure and heat. The OPC systemcan be used for full-contourrestorations (inlays, veneers,full crowns) (Figure 5).Alternatively, it can be used asa core material, which is ve-neered using conventional pow-der-slurry techniques with ahigh-leucite-content feldspathicporcelain, similar to Optec HSPporcelain. The manufacturerclaims that the crystallineleucite particle size has been re-duced and the leucite contentincreased, resulting in an over-all increase in flexural strengthof OPC.36 There are no pub-lished clinical studies of OptecOPC; however, because of itshigh leucite content, it can beexpected that this porcelain'sabrasion against natural teethwill be higher than that of con-ventional feldspathic porcelain.

Both Optec OPC and IPSEmpress produce strong,

translucent, dense and etchableceramic restorations. The mate-rials are especially useful infabricating ceramic veneers.Both systems require specialequipment (pressing oven anddie material) to fabricate therestorations.

INFILTRATED CERAMICS

In-Ceram. This ceramic mate-rial is composed of an infiltratedcore veneered with a feldspathicporcelain. The core is initiallyextremely porous, and is com-posed of either aluminum oxideor spinel (a composition contain-ing aluminum oxide and magne-sium oxide). This porous struc-ture is subsequently infiltratedwith molten glass. The spinelcores are more translucent thanthe aluminum oxide cores, butsome strength has been sacri-ficed for the translucency.

The core is made from fine-grained particles37 that aremixed with water to form a sus-pension referred to as a "slip."38The slip is then placed on a gyp-sum die and baked at 1120 Cfor 10 hours to produce theopaque, porous core. At thisstage, the material is very frag-ile and must be handled careful-ly. Next, an appropriate shadeof glass powder is applied to thecore, which is baked again at

1100 C for four hours. Duringthis process, the molten glassinfiltrates the porous aluminacore by capillary action.39 Thisconfers the selected shade tothe core (although it remainsfairly opaque), and increasesthe strength of the core to about20 times its originalstrength.40'41 The aluminumoxide or spinel crystals limitcrack propagation and the glassinfiltration reduces porosity.39Vitadur N (Vident) aluminousveneering porcelain is then ap-plied using conventional pow-der-slurry techniques to createthe proper shade and contour.

The restorations producedwith aluminum-oxide-infiltrat-ed cores have extremely highflexure strength (in the 450-MPa range)42; this is thestrongest all-ceramic dentalrestoration presently available.The core of aluminum oxide orspinel is so dense that tradition-al internal surface etching toimprove the bond to tooth struc-ture is not possible.43 (The man-ufacturer recommends sand-blasting and the use of a resincement such as Panavia 21TC[J. Morita] for final cementa-tion). These restorations pro-vide an accurate fit. Because ofthe opaque alumina core, thetranslucency of the final

JADA, Vol. 128, March 1997 305

on April 8, 2011

jada.ada.orgD

ownloaded from

COVER STORY

restoration may not be as life-like as that seen with other sys-

tems (Figure 6). This materialrequires specialized equipmentto fabricate a restoration.

In a 21/2-year clinical study of61 full-coverage single unitsand 15 multiple-unit bridges,"researchers reported that nosingle units fractured, and twoof the 15 bridges failed becauseof fractured abutments.

COMPARISON OF THEALL-CERAMIC SYSTEMS

Strength. All the systems ap-

pear to have adequate strengthfor single units. Although theresistance to fracture of mostall-ceramic crowns may be sig-nificantly less than that of cer-

amo-metal crowns, their abilityto be bonded to tooth structurecan be considered an additionalstrengthening mechanism to in-hibit fracture of the restoration.- Dicor, a castable glass-ce-ramic with tetrasilic fluoromicacrystals, is strengthenedthrough the partial recrystalliza-tion ofglass through a cerammingprocess.

In-Ceram, a high-alumina-content substructure infused witha low-fusing glass, is strengthenedthrough glass infusion. The re-

ported flexural strength valuesare the highest for the all-ceramicsystems, and may qualify the ma-terial for use in multiple-unitbridges.- IPS Empress and OptecPressable Ceramic are hot-pressedleucite-reinforced ceramics; theyare strengthened by dispersion ofleucite crystals throughout theirinternal structure. Optec HSPalso is strengthened though inter-nal dispersion ofleucite crystals; itis fabricated using conventionalporcelain build-up techniques.~ Duceram LFC, a hydrother-mal ceramic, is strengthened by

an ion exchange mechanism in-volving hydroxyl ions. This issaid to decrease surface mi-croflaws and increase fractureresistance.

Fabrication techniques.With the exception of OptecHSP and the Duceram system,the all-ceramic systems use spe-

cialized equipment and tech-niques. This could be considereda disadvantage because of theadded cost of fabrication to thetechnician.

Marginal fit. With the ex-

ception of the machined ceramicrestorations, the fit of the all-ce-

ramic crowns to the underlyingtooth structure can be extreme-ly accurate. Compensation fordiscrepancies or gaps can bemade by using resin cements.Wear of opposing tooth

structure. While no clinicaldata are yet available compar-

ing abrasive wear of the fivesystems, all of the leucite-con-taining all-ceramic materialsdescribed above can be expectedto wear opposing natural teeth.The abrasion is a byproduct ofthe leucite crystals within all-ceramic restorative materials.The materials with the greateramount of leucite (IPS Empress,Optec HSP and Optec OPC)would be expected to create

greater clinical wear. Dicor(without the Dicor Plus veneer)and Duceram would be expectedto create minimal or no wear

against natural tooth structure.

SUMMARY

We have discussed five cate-gories of all-ceramic systems re-

garding their processing tech-niques, strength and wear

characteristics. These systemsare all currently in use by den-tal laboratories for the fabrica-tion of all-ceramic restorations.The table compares the physicalproperties of these systems (asdetermined by in vitro studies).The choice of the most appropri-ate all-ceramic system dependson the particular clinical situa-tion. That is, the stronger mate-rials should be used in stress-bearing situations (posteriorteeth), and the softer materialsshould be used in situations inwhich tooth abrasion may becritical (lingual surfaces ofupper anterior teeth). In thehands of adequately trainedand skilled technicians, the aes-

thetic results of all these sys-

tems can be excellent.Although in vitro studies

have shown significant differ-ences in the strength and hard-ness of some of these materials,the results of long-term clinicalstudies are not yet available.Until long-term clinical success

has been proven, cliniciansshould use these restorationsselectively. They should be usedcautiously in situations inwhich there are high stress lev-els or there is the potential forabrasion of opposing toothstructure.No currently available

restorative system can be con-

sidered the ideal replacementfor natural tooth structure.However, in recent years there

306 JADA, Vol. 128, March 1997

v -VU n~itil long-term

clinical success

has been

proven, cliniciansshouild use theserestorations selectively.

A

on April 8, 2011

jada.ada.orgD

ownloaded from

COVER STORY

Dr. Schulman Ifeaaor and &ass

head, DivisionReatorative ani

ProsthodonticSciences (DartlMaterials), NewUniversity CoiltDentistry, Nows

has been agreat amouof attentiorgiven to re-

Is pro-Societeof,d

talw York

wge ofvYork.

amt

search on anddevelopment of

ceramic systems for restorativeuse. Ceramics are playing an in-creasingly important role inrestorative dentistry, and fur-ther improvements in fractureresistance and wear propertieswill no doubt enhance theirrestorative use.

1. Weinstein M, Katz S, Weinstein AB. Fusedporcelain-to-metal teeth. U.S. Patent no.3,052,982, Sept. 1962. Washington, D.C.: U.S.Patent Office.

2. American Dental Association SurveyCenter. 1990 Survey ofdental restorations. In:Survey of dental services, 1990. Chicago: ADASurvey Center.

3. McCabe JF. Anderson's applied dental ma-terials. 7th ed. Oxford: Blackwell Scientific;1990:73.

4. Craig RG. Restorative dental materials. 7thed. Chicago: Mosby; 1985:437.

5. Seghi RR, Rosenstiel SF, Bauer P. Abrasionofhuman enamel by different dental ceramicsin vitro. J Dent Res 1991;70(3):221-5.

6. Land CH. Porcelain dental art. DentCosmos 1903;45:437-44.

7. McLean JW, Hughes TH. The reinforce-ment of dental porcelain with ceramic oxides. BrDent J 1965;119:251-67.

8. McLean JW. Perspectives of dental ceram-ics. Dental ceramics. In: Proceedings ofthe 1stInternational Symposium on dental ceramics.Chicago: Quintessence; 1984:13 40.

9. American Dental Association. Recent devel-opments in materials and processes for ceramiccrowns. JADA 1985;10(4):548-9.

10. Vaidyanathan TK, Vaidyanathan J,Prasad A. Properties ofa new dental porcelain.Scanning Microsc 1989;3(4):1023-33.

11. Anusavice KJ. Recent developments in re-storative dental ceramics. JADA 1993;124:72-84.

12. Optec HSP laboratory technique manual.Wallingford, Conn.: Jeneric-Pentron Inc.; 1988.

13. Komma 0. Hydrothermal dental ceramicsystems. Technical report. Rosbach, Germany:Ducera Dental Company; 1993.

14. Dickenson AJG. A comparison oftheCerestore and Dicor systems. In: Proceedings ofthe International Symposium: Alternatives tothe use oftraditional Porcelain. Amsterdam,The Netherlands. 1986:1-24.

15. Grossman DB. Processing a dental ceram-ic by casting methods. Ceramic Eng Sci Proc1985;6(1-2):19-40.

16. Anusavice KJ. Degradability ofdental ce-ramics. Adv Dent Res 1992;6:82-9.

17. Anusavice KJ. Benefits and limitations ofrestorative dental ceramics. In: Symposium onesthetic restorative materials. Chicago:American Dental Association; 1991:73-9.

18. Adair PJ, Hoekstra KE. Fit evaluation of acastable ceramic (IADR Abstract no. 1500). JDent Res 1982;61:345.

19. Stenberg R, Matsson L. Clinical evalua-tion ofglass ceramic inlays (Dicor). ActaOdontol Scand 1993;51(2):91-7.

20. Barnes DM, Blank LW, Gingell JC, LattaMA. Clinical evaluation of castable ceramic ve-neers. J Esthet Dent 1992;4:21-6.

21. Moffa JP, Lugassy AA, Ellison JA. Clinicalevaluation of castable ceramic matexial: three-year study (IADR Abstract no. 43). J Dent Res1988;67:118.22. Mormann WH, Brandestini M, Lutz F,

Barbakow F. Chairside computer-aided ceramicinlays. Quintessence Int 1989;20:329-39.

23. David SB, LoPresti JT. Tooth-colored pos-terior restorations using Cerec method(CAD/CAM)-generated ceramic inlays.Compend Contin Educ Dent 1994;15(6):802-10.

24. Leinfelder KF, Isenberg BP, Essig ME. Anew method for generating ceramic restorations:a CAD-CAM system. JADA 1989;118:703-7.

25. Schwickerath H. The strength characteris-tics ofCerec [in German]. Quintessenz1992;43:669-77.26. Kreji I. Wear ofCerec and other restorative

materials. International symposium on comput-

er restorations. Chicago: Quintessence; 1991.27. Grossman DG. Biaxial flexure strength of

CAD/CAM materials (IADR Abstract no. 1341).J Dent Res 1991;70:433.

28. McLaren EA, Sorensen JA. Fabricating ofconservative ceramic restorations using copy-milling technology. Quintessence Dent Technol1994;17:19-25.29. Gladys S, Van Meerbeek B, Inokoshi S, et

al. Clinical and semiquantitative marginal anal-ysis offour tooth-coloured inlay systems at 3years. J Dent 1995;23(6):329-38.

30. Isenberg BP, Essig ME, Leinfelder KF.Three year clinical evaluation ofCAD/CAMrestorations. J Esthet Dent 1992;4(5):173-6.

31. Heymann HO, Bayne SC, Sturdevant JR,Wilder AD, Roberson TM. The clinical perfor-mance ofCAD-CAM-generated ceramic inlays:a four-year study. JADA 1996;127:1171-81.32. Behnm G. IPS Empress: a new ceramic

technology. Ivoclar Vivadent report no. 6.Amherst, N.Y.: Ivoclar-Williams-Vivadent; 1990.

33. Holland W, Frank M. Materials science ofEmpress Glass Ceramics. Ivoclar-Vivadent re-port no. 10. Amherst, N.Y.: Ivoclar-Williams-Vivadent; 1994.

34. Dong JK, Luthy H, Wohlwend A, ScharerP. Heat-pressed ceramics: technology andstrength. Int J Prosthodont 1992;5:9-16.

35. Krejci I, Krejci D, Lutz F. Clinical evalua-tion ofa new pressed glass ceramic inlay mate-rial over 1.5 years. Quintessence Int1992;23(3):181-6.36. Panzera C. OPC, the new and improved

pressable ceramic. Optec product literature.Wallingford, Conn.: Jeneric/Pentron; 1996.

37. Kappert HF. I-Ceram: testing a new ce-ramic material. Quintessence Dent TechnolSpecial reprint; 1993.

38. Probster L, Diehl J. Slip casting aluminaceramics for crown and bridge restorations.Quintessence Int 1992;23:1-31.

39. McLean JW. The science and art of dentalceramics. Oper Dent 1991;16:149-56.

40. Sorensen J, Knode H. In-Ceram all-ceram-ic bridge technology. Quintessence DentTechnol Special reprint; 1992.

41. Claus H. Vita In-Ceram, a new system forproducing aluminum oxide crown and bridgesubstructures. Quintessenz Zahntech1990;16:35-6.42. Seghi RR, Sorensen JA, Engelman MJ,

Roumas E, Torres TJ. Flexural strength ofnewceramic materials (IADR Abstract no. 1521). JDent Res 1990;69:299.

43. Christensen GJ. Ceramic vs. porcelain-fused-to-metal crowns: give your patients achoice. JADA 1994;125(3):311-4.

44. Probster L. Survival rate ofIn-Ceramrestorations. Int J Prosthodont 1993;6:259-63.

JADA, Vol. 128, March 1997 307

Dr. Rosenblum Is aclinical associate pro-fessor, Depa e orProsthodontlcs andBlomaterils andDeparbtmnt ofGeneral and HospitalDentisry, Unhivrsityof Medicine and

Dentisr of NewJers, NewakAddrss rapunt re-

quedst to Dr.

Rosenblum at

UMDNJ, UniversityHelghts, 10 BergenSt., Newark, N.J.

07103-2400.

on April 8, 2011

jada.ada.orgD

ownloaded from