Prosthodontics

All-ceramic posts and cores: The state of the artSpiros O. Koutayas, DDS, CDT'/Matthias Kern, DMD, PhD"

Metal posts used to restore endodonticaily treated teeth may shine through aii-ceramic crowns and thingingival tissue. When nonprecious alloys are used, corrosion products may iead to discoioration. All-ceramic posts and cores can be used in combination with aii-ceramic crowns to prevent these probiems.Aii-ceramic posts and cores are highiy biocompatibie and wili aimost always increase the transiucency ofan aii-ceramic restoration. The purpose ot this articie is to describe the fabrication of aii-ceramic posts andcores, using high-toughness ceramic materiais such as aiumina or zirconia ceramics, through 4 differenttechnigues: the slip-casting technique: the copy-miiling technique: the 2-piece technique, which invoives aprefabricated zirconia ceramic post and a copy-milled alumina or zirconia ceramic core, and the heat-press technigue. which involves a prefabricated zirconia ceramic post and a heat-pressed giass-ceramiccore, indications, contraindications, advantages, and disadvantages of the different techniques are com-pared. (Quintessence Int 1999:30:383-392)

Key words: all-ceramic post and core, copy-milling technique, endodontically treated tooth,heat-press technique, slip-casting technique, two-piece technique

Endodontically treated teeth often need a post andcore as foundation for the final restoration.' The

restoration of anterior nonvital teeth with metal postsand cores and ail-ceramic restorations may lead tocompromised esthetics because of the semitranslu-cence of ceramics and the opacious metai suhstruc-ture of tiie underiying post and core.- Depending onthe thickness and the opacity of the iuting cementand the aii-ceramic restoration, the metal post andcore may shine through or at least decrease the depthof transiucency of the restoration.' In addition, metalposts may also shine through in the cervical rootareas, thus altering the appearance of thin gingival tis-sue.'' Furthermore, especially when nonprecious ai-Ioys are used for post-and-core fahrication, corrosionproducts may deposit in the gingival tissues or causeroot discoloration. '

'Clinical and Research Associale, Deparlmenl of Prcslhoaonlics,University of Freibjrg, Freiburg, Germany.

•"Professor ano Chaitman, Department of Prosthoflontics, University o(Kiel, Kiel, Germany.

Reprint requests : Prof Dr Matthias Kern, Klinik für ZaiinärzflieheProtlielik, Propâdejfii( und Werkstoffkunde, Klinikum der Christian-AI brechts-Universität Kiel, Arnold-H elfe r-Stras se 16, 24105, Kiel, Germany.E-mail: mkern@proth.uni-kiel.de

Different techniques have been proposed to solvethe problem of the grayish coronal discoloration andto achieve the necessary masking when ail-ceramicrestorations are cemented to teeth restored with metalposts and cores. The appiication of an opaque porce-lain to the metai core," or the use of an opaciousluting cement,' gives a rather intense and opaque ap-pearance to the restoration, especiaiiy when a glass-ceramic restoration is piaeed. Resin veneering of thecast core' and veneering of the metal core with shoui-der porcelain,^ have also been recommended. How-ever, with these methods, the metal posts still mayshine through in the cervicai and root areas.

Almost simultaneously with the introduction of thecurrent all-ceramic systems, the use of the ail-ceramieposts and cores was suggested as an aiternative tosolve the esthetic probiems that metal posts and coresexhibit. In 1989. Kwiatkowski and Gelier"* describedthe clinical application of giass-ceramic posts andcores (Dicor, Dentspiy) and, in 1991, Kern andKnode" introduced posts and cores made of glass-infiltrated aluminum oxide ceramic {In-Ceram, VitaZahnfabrik). In 1995, Pissis^ proposed a "monobloc"technique for the fabrication of a post and core and acrown as a single component made out of glass-ceramic material (IPS-Empress, Ivodar). In 1994 and1995, Sandhaus and Pasche'^ and othersi^" intro-duced prefabricated zirconia ceramic endodonticposts to restorative dentistry. Sandhaus and Pasche'also suggested the use of zirconia ceramic for the fab-rication of a core buildup and post in 1 piece.

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Fig la Rigiil lateral incisor that pre-sents moderate rooi and gingivai tissuediscoloration caused by a nonpreciousmetal post and core.

Fig 1b Corrosion products in the root,after the nonprecious post has been re-moved.

The major advantage of an all-ceramic post and coreis its dentinlike shade. The positive contribution of thedentin shade ceratiiic core is related to the deeper dif-fusion and absorption of tlie transmitted iight in the ce-ramic core mass. An ail-ceramic restoration transmits acertain percentage of the incident light to the ceramiccore and post on which it has been piaced.'''" Thus,with all-ceramie posts and cores, the color of the finalrestoration will bc derived from an internal shade simi-lar to the optical behavior of the natural teeth. In addi-tion, a ceramic post does not reflect intensively throughthin gingivai tissues, and it provides an essential depthof translueeney in the eervieal root areas, All-eeramieposts and cores, as metal-free constructions, provide anexeelient bioeompatibiiiti,' and do not exhibit galvanieeorrosion^'""" (Figs la and lb).

Relatively low fracture strength and fraeture tough-ness are the main obstaelcs for an extended use of eon-ventional dental ceramies as post-and-core materials.Tbere are few research data on the fracture strength ofall-ceramic posts and cores, and for clinical behavior nolong-term clinical data are provided in the literature.Apart from the fracture strength, the fracture toughnessof a ceramic material seems to bc more predictive of itsfailure rate.'" ffigh-toughness ceramics, such as theglass-infiltrated alumina ceramic In-Ceram'" and thedense-sintered alumina ceramic Procera (Nobel Bio-care),'* show a 3 to 6 times higher fiexurai strength andfracture toughness than do conventional feldspathic andgiass ceramics, "*' ' Contemporary' zirconia powder tech-nology contributes to the fabrication of new biocompati-ble ceramic materials \vith improved meehanical prop-erties, ie, further increased tlexural strength and fracturetoughness. "•'' Therefore, zirconium oxide ceramic seemsto bc a very promising material for the fabrication of ail-ceramic posts and cores.' -'"

Tbe purposes of this review article are to describe 4different techniques of all-eeramic post-and-core con-

struction with high-toughness ceramic materials and tocompare their clinical indications and contraindicationsas weli as their advantages and disadvantages.

SLIP-CASTING TECHNIQUE

The fabrication of all-ceramie posts and cores by useof the slip-casting technique was described by Kemand Knode in 1991," Since then, this technique con-cept has been slightly modified, ' With this technique,the core buildup and tbe post are made in 1 piecefrom the aluminum oxide eeramie material, In-Ceram,Because of tbe limited fracture strength'*" and the un-known long-term ciinical prognosis of In-Ceram as apost-and-core material, this method should be usedonly in wide root canals without a crucial reduction ofthe circumferential dentin structure,"

The preparation of the root canal is similar to thepreparation for a metal post and core. Possible under-cuts are eliminated manually with standardized ream-ers during the root canal preparation. At the coronalend of the root canal, a small inlay cavity is preparedto prevent rotation of the finished post and core. Thetooth preparation for an all-ecramic crown requires a90-degree shoulder with a rounded internal angle or adeep chamfer witb a width of 1,0 to 1,2 mm circumfer-entialiy. As the preparation is finished, ail line anglesshould be slightly tapered.

A prefabricated plastic or metal post is placed intbe root canal and a bigb-precision impression istaken. After tbe master east is set, the tooth die is sec-tioned and the preparation margins are exposed andmariiedwith lni<. The die is dtiplicated, and a seeonddie is cast with the special In-Ceram plaster. The du-plicated die is used for formation of the post duringthe slip casting. After its hardening and removal fromthe impression, the bottom of the seeond die is ground

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with a carbide bur until a tiny opening appears.During the slip casting, this hole serves as an externalrelief that prevents air impaction in the slip mass. Inaddition, it is a rehable indicator of the slip injection'scompletion."" Finally, horizontal and vertical sec-tions, which must not reach the root eanal are madeon the die with diamond disks. This procedure is nec-essary to prevent a post fracture, which might occurthrough the shrinkage of the In-Ceram plaster duringthe sintering process" (Fig 2).

As an alternative method, the working die can beseparated into 2 pieces by the insertion and a slight ro-tation of a sharp knife in a drain channel cut along thedie. These 2 parts are glued together again with eyano-acrylate adhesive. The adhesive is burned out whenthe furnace is heated to lOO^C, so that no force is ex-erted by the shrinking die at higher temperatures.^'

A waxup of the core is then made on the masterdie, and the occlusal clearance is confirmed on an ar-ticulator. A 5.0-mm-diameter wax sprue is attached tothe incisai edge of tbe core, providing later the en-trance for the slip injection. Two putty silicon molds ofthe waxup and the master cast are fitted together withinternal retentive undercuts. After the removal of thewaxup, the die of the special In-Ceram plaster isadapted between, and finally the 2 silicon molds are¡cined with rubber rings. With this procedure, a voidspace, previously occupied by the core waxup and thesprue, is provided for the slip injection.

The alumina slip is mixed and ultrasonically vibratedto a homogenous consistency according to the manu-facturer's instructions and then is injected through theinjection spine of the silicon mold. After the slip hasdried, the core is carefully carved to its final shape witha scalpel. One eoat of Stabilizer (Vita Zahnfabrik) isapplied to the finished core. The sintering is done ac-cording to the regular firing cycle settings for the In-Ceram ceramic, as recommended by the manufacturer.After sintering, the all-ceramic post and core is fitted tothe master cast. Then it is checked for possible micro-cracks by the use of méthylène blue liquid.

For the subsequent glass-infiftration firing, the postand core is placed on a platinum foil and is coveredwith a mixture of lanthanum-glass powder and thespecial liquid supplied with tbe In-Ceram system {Figs3a atid 3b). The excess glass is removed with coarse-grit diamond grinding and 50-pm air abrasion (Figs 4aand 4b). Then the all-ceramic post and core is fittedagain to the master cast."' ^

After the fit of the all-ceramic post and core ischecked in the patient's tooth, the post and core is ad-hesively cemented. Rubber dam is applied for moisturecontrol. The root canal is roughened with a diamond-coated reamer and cleaned with 70% alcohol. A self-curing dentin adhesive agent is used prior to cementa-

Fig 2 Stages of the slip-casting technique' (left lo rigiit) slip-casting before sintenng; sintered post and core: and glass-infil-tiated post and core.

tion with a self-curing resin cement. If a phosphatemonomer eontaining resin composite (eg, Panavia 21,Kuraray) is used for the cementation, the In-Cerampost and core need only be sandblasted-^ and ultra-sonicaily cleaned in 96% alcohol. After the resin ce-ment has set, the excess cement is removed by dia-mond grinding, and the tooth preparation is finalizedwith finishing diamonds {Figs 5a and 5b).

COPY-MILLING TECHNIQUE

Recently, the glass-infiltrated alumina ceramic, In-Ceram, and its fabrication process have been adaptedto the Celay copy-milling method (Mikrona), as an al-ternative to the slip-casting technique. The Celay sys-(gfj 2t-î8 involves a rnanually guided copy-millingprocess in which a predesigned resin pattern is surfacetraced and copied in ceramic. The ceramic substruc-tures are prefabricated blanks made of presintcrcd alu-minum oxide ceramic (Celay Alumina Blanks, VitaZahnfabrik), In-Ceram ceramic restorations madewith the Celay method present a 10% higher flexuralstrength (about 500 iVlPa) than do conventional In-Ceram restorations.^^

This method can be used for inlay, onlay, veneer,'"and crown-and-bridge framework fabrication,"'" aswell as for copy-milled In-Ceram posts and cores. Theclinical indications and procedures are similar tothose of the conventionally slip-cast posts and coresalready described.

For the copy-milling technique, the resin "pre-post-and-eore" pattern can be made by a direct or an indi-rect method. The direct method presupposes that the

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Fig 3a in-Ceram alumina sin- Fig 3b Aii-ceramic post and Fig 4a Aii-ceramic post and Fig 4b Giass-infiitraled ail-ce-tered aii-ceramic post and core piaced on piatinum foil and cote after giass inliitration. ramie post and core after sard-

covered with a ianthanumoxide-giass mixture for theglass infiltration.

blasting.

Fig 5a Patient treated with aii-ceramic alumina posts and coresin the maxiiiary nghi central incisor, lett lateral incisor, and lefl ca-nine. (Courtesy of Dr M B Hürzeier, Munich.)

Fig 5b Finai resuit after the placement of in-Ceram aiumina (ceramic crowns.

resin analog of the post and core is modeled on thepatient's tooth, similar to the conventional techniquefor casting metal posts and cores. This intraoralmethod is simplified by the use of prefabricated plasticor metal posts in combination with the appropriateroot canal system (eg, ER-Systcm, Brassclcr) and alight-curing resin composite for the modeling of thecore (eg, Celay-Tech, ESPE).

For the indirect method, an impression of the pre-pared looth is taken and a working cast is poured out ofplaster The resin pre-post and core is modeled as in theindirect fabrication method for metal posts and cores. ^For the molding of the internal inlay of the post andcore, a light-curing resin with increased viscosity [eg,

Visioform, ESPE) can be used to simplify the handling.After the resin pre-post is completed, it is

mounted to the tracing chamber of the Celay ma-chine. The pre-post is mounted vertically, so that theincisai edge of the core is attached to a jig of the re-tentive device and the end of the post is connectedto a pin on top of the cup holder. Then, the resinpattern is surface traced and copied in ceramic bysynchronized grinding in the milling chamber {Fig6), For a precise fit, special attention should be paidwhen the internal inlay is milled. After completion ofthe copy-milling process, the ceramic post and coreis cut off with a diamond disk, fitted to the masterdie, glass-infiltrated, and finished as described above.

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Gutta-percha lili in g

Cementum

Cerapost

Ceramic core In-Ceram

Ali-oeramic crown

Spinel core

Fig 6 Synchronized copy milling ot an ail-ceramic pûui and corein the Celay machine.

Fig 7 Two-piece technique concept tor an ali-ceramic post-and-core construction, combined with a spinei aii-ceramic crown

TWO-PIECE TECHNIQUE

Because the fracture strength of In-Ceram posts andcores is less than that of metal posts and cores, "* In-Ceram posts and cores have only been recommendedfor wide root canals." Tn cases of regular root canals(smaller than ISO 110), In-Ceram ceramic does notseem to provide a sufficient strength; for that reason,until presently, an all-ceramic post and core was notrecommended for such eases. After the recent devel-opment of zirconia ceramic posts, it became possihleto combine both materials. For a 2-piece post-and-core constmcfion, a post made of yttrium oxide-par-tially stabilized zirconia (ER-Cerapost, Brasseler) isused in conjunction witb an all-ceramic core made ofalumina or alumina-magnesia'-* ceramics, fabrieatedeitber by the copy-milling or the slip-casfing technique(Fig 7). The zirconia ceramic posts are commerciallyavailable in three ISO sizes (050, 090, 110} and sup-plement the existing ER-Post system (Brasseler)."

This technique is also applicable for both direct andindirect fabrication methods. For the direct method,the root canal is prepared, and the selected zirconiaceramic post is tried in, A core is formed intraorally byadapting the light-curing resin composite Celay-Techto the inserted post. After the removal of the resin corefrom the post, the core is copied in ceramic in theCelay machine. For the indirect fabrication method, animpression of the inserted post is taken, and a workingdie is cast The core is then formed with the light-cur-ing resin composite Celay-Tech on the master cast (Fig8). Finally, it is also copied into ceramic (Fig 9a).

As an alternative to the copy-milling core fabrica-tion, the slip-casting technique can be used as de-scribed earlier, with a minor modification. A plasticpost of the ER-System is inserted in the root canal of

Fig 8 Modeiing of the oores with lighi-ouring resin based on awaxup mold.

the special In-Ceram plaster die. This plastic post pro-vides accurate space for the zirconia ceramic post anddoes not cause any problems because it is burned outduring the sintering firing. After the core waxup andthe two silicon molds are made, the slip is injected asdescribed for the slip-casting technique.

After glass-infiltration firing (Fig 9b), the infiltratedalumina core and the zirconia post are sandblastedand ultrasonically cleaned in 96"/o alcohol. For cemen-tation, an adhesive resin (eg, Panavia 21, Kuraray) isapplied to the bonding surfaces of tbe post and core,and then they are hotb iuted to the abutment tooth.Primarily, the ceramic core is placed on tbe preparedtooth and immediately afterward the post is insertedin the roof canal through the canal of tbe core (Figs10a to 10c). Finally, after setting of the luting resin, thepost is shortened at its protruding occlusai end, andfhe toofh preparation is finished.

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Fig 9a Zirconia post with acopy-milled alumina ceramiccore.

Fig 9b Zirconia post with analumina core, after glass infil-tration of the core (2-piecetechnique).

Fig 10a Zirconia post insertedthrough the ceramic core canal.

Fig 10b Aif-inhiüiting gel, ap-plied until the resin cement hasset.

Fig 10c Final restoration after cementation Fig 11 Heat-pressed glass-ceramic mate-riai onto a zirconia post.

When a sufficient amount of a caries-free toothsubstance is available, instead of the ceramic corebuildup, a seif-euring resin composite buiidup can alsobe used in combination with a zirconia post.' ' ^

HEAT-PRESS TECHNIQUE

Tbe heat-press technique has recently found applicationto an all-ceramic post-and-core construction. It is basedon the well-known IPS Empress system (Ivoclar). Inthis system, a castable, precerammed leucite-reinforced

glass-ceramic material is heated and pressed in an in-vestment mold after the burnout of the wax analog(lost-wax technique).^* In the heat-press technique, aglass-ceramic core (EmpressCosmo, Ivoclar) is heat-pressed over a prefabricated zirconium dioxide post(CosmoPost, Ivoelar), and therefore both materials arefused into a solid post-and-core restoration.

For the root canal preparation, special reatners(CosmoPost Set, Ivoelar) are used so that the canalean receive a zirconia post with the appropriate di-ameter (1.4 or 1.7 mm). After the impression is taketiand the master cast is constructed, the eore wax pat-

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Fig 12a Maxillary lett lateral incisor beforetreatment.

Fig 12b Finished tooth preparation alter Fig 12c Maxillary leff lateral incisor after finalbonding of fhe posl and core. cementation of a glass-ceramic restoration.

tern can be molded in the laboratory. An intraoral di-rect method can also be employed with the use of aself-curing resin (GC Pattern, GC) after insertion ofthe post in the root canal. Then, the heat-press proce-dure, which is identical for both methods, is followed.A 3.0-mm-diameter and 6,0- to 8,0-mm-long waxsprue is attached to the core with an inclination thatallows a uniform flow and expansion of the glass ce-ramic. At that time, the post and core is invested in aphosphate-bonded refractory die material. The heat-press procedure is performed in a specially designedfumace (IPS-Empress EP 500, Ivoclar), The ceramicingot is first heated at 1,1SO°C and then is pressedwith 0.3 to 0,4 MPa pressure under vacuum (Fig 11),After cooling and divestment, the post and core, as asolid, all-ceramic construction, is fitted to the mastercast. Then, it is tried in the patient's mouth andadhesively cemented as previously described (FigsI2ato 12c).

DISCUSSION

An impetus for the rapid development of ceramictechnology is the contribution to metal-free prostb-odontic restorations, which provide increased esthet-ics and improved material strength.''

Ail-ceramie posts and cores fulfill the esthetic claimswhen combined with all-ceramic restorations, and forthat reason they early possessed a place among reviewsof all-ceramic systems'' (Figs 13a to 13c), The depth oftransiucency of the ail-ceramic crowns depends on theóptica! properties of the ceramic and on the refractionindex oí the luting cement,'-'"•" Because of theirdentinlike shade, obtained by glass infiltration, all-ce-ramic posts and cores increase tbe depth of transiu-

cency and give a natural appearance to the final all-ce-ramic restorations. By avoiding the root discolorationthat can arise with metal posts, ali-eeramic posts andcores provide an enhanced color match at the soft tis-sue-ceramic interlace.""•'>

tn-Ceram Alumina has been suggested for the all-ceramic post-and-core construction because it showshigh biocompatibility, increased flexura! strength, andan accurate fit.'' "-''-'-' The all-ceramic posts and coresmade of alumina ceramic by both slip-casting andcopy-milling techniques are clinically acceptablerestorations, but iongitudinal clinical studies areneeded to confirm their use. However, ceramic materi-als are often liable to fracture, because they cannot ab-sorb tensile stress as metals and polymers do, tbroughdeformation. Alumina also exhibits a britde bebaviorand has a relativeiy low fracture toughness. It is sensi-tive to microstructural flaws, which lead to poor resis-tance to stress concentration or mechanical im-pact.''•''••' Therefore, the superficial mierocracks thatmight develop during the processing of high-toughnessceramic materials should be avoided.

In 1995, Kern et al-"* showed, in an in vitro study,that anterior posts and cores made of the aiumina ce-ramic In-Ceram have a fracture strength of 168.5 +47,8 N, Tbis strength increased to 342.0 N ± 50.9 Nwben In-Ceram crowns were resin-bonded to tbe re-stored natural teeth. This means that the fracturestrength of the restored tooth complex is increased sig-nifieantly after the finai cementation of the all-ceramicrestoration. However, compared to untreated teethand teeth restored with metal posts and cores, thefracture strength was reduced to about 50%. Leibrocket a F also reported that the fracture strength of postsand cores made of the glass-ceramic iPS Empress var-ied between 80 and 287 N,

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Fig 13a Anterior teeth Detore treatment. (Courtesy ot DrAltmann, Friedrichshafen, Germany.)

Fig 13b Cemented ali-oeramic pests and cores, fabricatedusing the 2-piece technique.

Fig 13c Anteriûi teeth alter placemen! of den se-sintered alurninacrowns

The preparation of a root canai inlay prevents postrotation but may also result in a stress concentrationthat may lead to failure under functional fatigue.•' ••'The need for a canal inlay may be reconsidered for ad-hesively cetnented all-ceramic posts and cores.Because of the adhesive fixation, the whole restorationbehaves as 1 unit, and an antirotationai inlay mightnot be necessary.'-'

To overcome these limitations, yttrium oxide-par-tially stabilized zirconia posts have been developedespecially for dental use.''* Lately they have beenunder in vitro'" and in vivo^' evaluation. Yttriumoxide-partialiy stabilized zirconia eeramies are bio-compatible materials commonly used in medicine.""They exhibit a better fracture toughness than do alu-mina ceramics.^'''^ The toughening mechanism is re-lated to a niartensitic-like transformation, occurring atthe tip of an induced microcrack, of tetragonalmetastable to a monochnic state.^^'" Because of thisstrengthening-phase transformation, zireonia ceramicsare espeeially indicated for the post-and-core con-

struction and seem to be suitable for the highly loadedoral environment.

Regarding the fabrication techniques for all-ceramicposts and cores, undetected voids in the slip mass arethe main limitation of the slip-casting technique.Because of the controlled tnanufacturing process ofthe Ceiay ceramic blanks, the flexural strength of thecopy-milled posts and cores is greater than that ofconventional slip-cast In-Ceram ceramic posts andcores. However, the Celay system is not designed forall-ceramic post-and-core fabrication, so there arctechnical problems associated with the pre-post ad-justment in the Celay machine. In addition, the post'sapical end is not perfectly tnilled because it is fixed tcthe retentive device; thus, a careful manual adjustmentis required when the post and core is fitted.

The 2-piece technique is a very promising tech-nique because it combines the excellent mechanicalproperties of the zirconia ceramic post and the opticalproperties of the alumina or spinel core, which is eas-ily fabricated with the Celay system. '' The increasedtlexural strength (about 820 MPa) and fracture tough-ness {about 8 MPa • m''^) of the commercially avail-able zirconia posts,''' and their use with the adhesiveluting teehnique,^" makes failures more unlikely tooccur. The smaller zirconia posts (ISO 050, 090)might he used for an all-ceramic post-and-core con-struction for narrower root canals, where the othertechniques are contraindieated.

The heat-pressed technique is advantageous becausea uniform all-ceramic post-and-core restoration is fab-ricated with a fatniliar technique that is also followedfor metal posts and cores, ie, with prefabricated high-precious metal posts. * The combination of the glass-ceratnic and the zirconia ceramic materials is possiblebecause of the similarity of their thermal expansion co-efficients (9.5 ± 0.5 lOVK and 10.0 ± 1.0 lOVK,

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respectively), which results in a corresponding shrink-age and a good fit after the heat-pressing procedure.However, it is not known whether the heat-pressingprocedure has a negative effect on the strength of thezirconia post because the crystalhne structure of zirco-nia is influenced by larger temperature changes,'"'

Finally, when a zirconia post is used with a directresin composite buildup, large stress-bearing compositebuildups in combination with suhgingival marginsshould be avoided. Composite cores exhibit relativelyhigh polymerization shrinkage and have a higher ther-mal expansion coefficient than the tooth, which maycontribute to microleakage and, under functional forces,allow deformation,' ' ' ' ^ This disadvantage of a compos-ite buildup becomes less critical when more than 60% ofthe tooth structure remains to support the buildup,'- s- '

CONCLUSIONS

1, All-ceramic posts and cores cemented with ad-hesive technology can be used in combinationwith all-ceramic crowns because they contributeto better hght transmission and reflectance, pro-vide natural translucency to the all-ceramic res-toration, and offer excellent biocompatibility,

2, The 2-piece technique appears to be the mostpromising method for post-and-core fabrication. Inaddition to improved esthetics, it provides a postand core with improved mechanical properties,

3, All-ceramic posts and cores made of alumina ce-ramic in 1 piece, for root canals with a width lessthan an ISO 110, should he avoided.

4 Long-term clinical data are required to validatethe potential of all-ceramic post-and-core restor-ations hefore they can be recommended for gen-eral dental use.

ACKNOWLEDGMENTS

This review was supported by grant No, T1Û4630092 for DenialTechnology by the Sale Scholarships Foundation of [he Republic ofGreece.

REFERENCES

1. Albers HF Core build-ups and posts, ADEPT Report 1993;4:25-35,

2. Pissis P, Fabrication of a metal-free ceramic restoration uti-lizing the monobloc teehnique, Pract Periodont AesthetDent iy95;7(5):83-94,

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