cementos y adhesión al metal okokokokok

8/12/2019 Cementos y Adhesin Al Metal Okokokokok

1/12

Dentists place metal-ceramic crowns withhigh frequency in clin-ical practice today, andthe cements or luting

agents used to retain these cast-ings are critical to the clinicalsuccess and longevity of these res-

torations.1 Several new dentalcements and new forms ofdelivery for these cements havebeen introduced to the dentalmarket; however, high-qualityindependent study resultsregarding the clinical perform-ance of cements often are lacking.Furthermore, many researcherscollect data regarding cement per-formance that do not relatedirectly to potential clinical per-formance. For example, previousinvestigators have used shear-bond strength tests to determinethe ability of commonly usedluting agents to retain simulatedhigh-noble metal-ceramiccrowns.2,3

To better simulate clinical con-ditions, some investigators havetested the retentive strength ofcements by using axial dislodg-ment forces with crownscemented on normally prepared

extracted human teeth.4-7

Severalof these studies have involveduniform conically shaped, circularcrown preparations8,9 that resultin greater removal of tooth struc-

Dr. Johnson is a professor, Department of Restorative Dentistry, School of Dentistry, Box 357456, University of Washington, Seattle, Wash. 98195-7456, e-mail

[email protected]. Address reprint requests to Dr. Johnson.

Dr. Lepe is an associate professor, Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle.

Dr. Zhang is an assistant professor, Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle.

Dr. Wataha is a professor and the chair, Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle.

Retention of metal-ceramic crownswith contemporary dental cementsGlen H. Johnson, DDS, MS; Xavier Lepe, DDS, MS; Hai Zhang, DMD, PhD;John C. Wataha, DMD, PhD

JADA, Vol. 140 http://jada.ada.org September 2009 1125

Background. New types of crown and bridge cementare in use by practitioners, and independent studies areneeded to assess their effectiveness. The authors con-ducted a study in three parts (study A, study B, and studyC) and to determine how well these new cements retainmetal-ceramic crowns.Methods. The authors prepared teeth with a 20-degree taperand a 4-millimeter length. They cast high-noble metal-ceramic copings, thenfitted and cemented them with a force of 196 newtons. The types of cements theyused were zinc phosphate, resin-modified glass ionomer, conventional resin andself-adhesive modified resin. They thermally cycled the cemented copings, thenremoved them. They recorded the removal force and calculated the stress of dis-lodgment by using the surface area of each preparation. They used a single-factoranalysis of variance to analyze the data ( = .05).Results. The mean stresses necessary to remove crowns, in megapascals, were8.0 for RelyX Luting (3M ESPE, St. Paul, Minn.), 7.3 for RelyX Unicem (3MESPE), 5.7 for Panavia F (Kuraray America, New York) and 4.0 for Fuji Plus(GC America, Alsip, Ill.) in study A; 8.1 for RelyX Luting, 2.6 for RelyX LutingPlus (3M ESPE) and 2.8 for Fuji CEM (GC America) in study B; and 4.9 for

Maxcem (Kerr, Orange, Calif.), 4.0 for BisCem (Bisco, Schaumburg, Ill.), 3.7 forRelyX Unicem Clicker (3M ESPE), 2.9 for iCEM (Heraeus Kulzer, Armonk,N.Y.) and 2.3 for Flecks Zinc Cement (Keystone Industries, Cherry Hill, N.J.) instudy C.Conclusions. Powder-liquid versions of new cements were significantly moreretentive than were paste-paste versions of the same cements. The mean valueof crown removal stress for the new self-adhesive modified-resin cements variedappreciably among the four cements tested. All cements retained castings aswell as or better than did zinc phosphate cement.Clinical Implications. Powder-liquid versions of cements, although lessconvenient to mix, may be a better clinical choice when crown retention is anissue. All cements tested will retain castings adequately on ideal preparationsbecause the corresponding removal stresses are comparable with or higher thanthose associated with zinc phosphate. Powder-liquid resin-modified glass

ionomer cement, selected self-adhesive modified-resin cements and conventionalresin cements provide additional retention when desired.Key Words. Dental cements; luting agents; resin-modified glass ionomer; self-adhesive cement; crown retention; prosthodontics.

JADA 2009;140(9):1125-1136.

ARTICLE

3

JA D A

C

O

NT

INU

ING E DU

CAT

ION

ABSTRACT

R E S E A R C H

Copyright 2009 American Dental Association. All rights reserved. Reprinted by permission.


2/12

ture than occurs clinically. Preparations reducedto this extent may result in an atypical dentinsubstrate for bonding because at the surface, 96percent of the dentin is intertubular, comparedwith 12 percent near the pulp.10 In addition, some

researchers have used prepared teeth with min-imal, highly retentive tapers,2,5 which has con-founded the determination of a given cementscontribution to crown retention.11

The most traditional cement used in dentistryis zinc phosphate cement, which clinicians haveused successfully to retain cast restorations since1879.12 Three other cements that clinicians haveused with success during the last 30 years arezinc polycarboxylate,13,14 chemically cured glassionomer15 and conventional resin in combinationwith a dentin adhesive system. Researchers haveconducted extensive evaluations of these cements

ability to retain crowns.4-10,16Resin-modified glass ionomer cements were

developed in the late 1980s. They first were soldas a filling material and liner,17,18 but they laterwere marketed as luting agents.

Self-adhesive modified-resin cement is thenewest type of cement to be introduced for lutingdental restorations. Hecht and Ludstech19 sub-mitted a patent application for this class ofcement in 2002, and Hecht and Richter20 laterdescribed the materials composition and reaction.Since that time, as this type of cement hasincreased in popularity, 21 several other competingself-adhesive modified-resin cements haveappeared in the dental market. The goals for thedevelopment of self-adhesive modified-resincement were simple handling, good mechanicalproperties, favorable esthetics and effective adhe-sion to tooth structure without the need for sepa-rate bonding steps.20 These cements have demon-strated high shear-bond strength to zirconiaceramics under specific conditions3,22 and lowmicroleakage when used on dentin but not whenceramic veneers were cemented on enamel.23

Manufacturers initially supplied, and still

offer, several cements in powder-liquid formula-tions. For convenience, several of these sametypes of cement are available in a paste-pasteconsistency, some with automixing tips. Clini-cians may assume that the two forms of the sameproduct are equivalent in terms of their proper-ties; however, conversion from powder-liquid topaste-paste formulations is not simple, becausethe chemical constituents and the setting reactionof a powder-liquid form may need to be altered to

create a paste version. It is not prudent to extrap-olate study findings regarding powder-liquidcement retention to retention of paste-paste for-mulations; thus, tests of both types are needed.

The purpose of the series of studies we describe

here was to evaluate the ability of new lutingagents to retain high-noble metal-ceramic cast-ings under clinically relevant conditions and tocharacterize the nature of the failure of thecement. The research hypothesis was that withina cement test group, there were no clinicallysignificant differences among cements in terms ofcrown removal stress. Whenever appropriate, wecompared paste-paste formulations with powder-liquid formulations.

METHODS AND MATERIALS

Given the numbers of new cements and varia-

tions in delivery systems, plus a time-consumingresearch methodology, we conducted the study inthree stages, designated as cement study A,cement study B and cement study C. Table 1 liststhe cements used in each of the three groups.

In cement study A, we evaluated three types ofluting agents in common use. Included were aconventional resin cement with dentin adhesiveand an alloy primer (Panavia F, Kuraray

America, New York City), two resin-modifiedglass ionomers (Fuji Plus capsules, GC America,

Alsip, Ill.; RelyX Luting bottle and jar, 3M ESPE,St. Paul, Minn.) and the first self-adhesivemodified-resin cement to be marketed (RelyXUnicem capsules, 3M ESPE). Promotionalmaterials and the dental literature often refer tothis latter cement type as a self-adhesive com-posite resin or self-adhesive resin. To avoidconfusion with traditional resin cements, we pro-pose use of the term self-adhesive modifiedresin for this new type of cement, because itscomposition includes elements from traditionalglass ionomer, resin-modified glass ionomer, com-pomer and conventional resin,1 and its polymer-ization reactions differ from those of traditional

resin.20,24

In cement study B, we evaluated the newpaste-paste versions of two existing resin-modified glass ionomer cements (Fuji CEM withConditioner, GC America; RelyX Luting Plus, 3MESPE) and compared them with an originalpowder-liquid version (RelyX Luting). Beforecementing crowns with Fuji CEM, we applied a

1126 JADA, Vol. 140 http://jada.ada.org September 2009

R E S E A R C H

ABBREVIATION KEY.VPS:Vinyl polysiloxane.



3/12

dilute polyacrylic conditioner (Fuji Plus Condi-tioner, GC America) to the tooth surface for 20seconds and then rinsed the tooth, as recom-mended in the instructions for use when strongeradhesion is desired.

In cement study C, we evaluated three newself-adhesive modified-resin paste-paste products(iCEM, Heraeus Kulzer, Armonk, N.Y.; BisCem,Bisco, Schaumburg, Ill.; Maxcem, Kerr, Orange,Calif.) and the new paste-paste version of anotherself-adhesive modified-resin cement (RelyXUnicem Clicker, 3M ESPE). In addition, wetested zinc phosphate cement (Flecks ZincCement, Keystone Industries, Cherry Hill, N.J.)to help establish the clinical significance of reten-

tion values because zinc phosphate has been usedsuccessfully for a long period without the benefitof the materials having a chemical attraction tometal or dentin.

The laboratory and testing procedures we usedin this series of studies were similar to thosedescribed in reports of previous studies.6,7,22 Oralsurgeons stored recently extracted molars in aliquid sterilant (0.5 percent sodium hypochlorite)immediately after extraction. We cleaned teeth of

surface debris, sterilized them again in 0.5 per-cent sodium hypochlorite and thereafter storedthem in tap water until we mounted them. Asspecimens, we selected noncarious, unrestoredmolars with diverging roots. We roughened andembedded roots in stainless steel mounting ringsby using clear autopolymerizing resin with thebuccal cementoenamel junction positioned 1 mil-limeter above the top of the ring. At all times, themounted specimens were stored in tap water,which we changed frequently.

We sectioned the occlusal surface of eachmounted tooth specimen flat (by using a slow-speed thin sectioning saw [11-4254-blade, Isomet,Buhler, Evanston, Ill.]) and perpendicular to the

long axis of the ring and 5 mm above the top of thestainless steel cylinder. We secured a high-speedhandpiece in an apparatus so that a diamondtapered rotary cutting instrument was oriented ata 10-degree angle from a vertical axis of the toothto create a standardized angle of convergence of 20degrees (Figure 1). We selected a degree of conver-gence higher than the ideal of 12 degrees to betterassess the contribution of the cement in crownretention, as well as on the basis of study results


R E S E A R C H

TABLE 1

Description of cements used in the three crown retention studies.

CEMENT, BY STUDYPORTION

TYPE CONSISTENCY LOT NO. DELIVERY SYSTEM/MIXING

METHOD

MANUFACTURER

Study APanavia F With AlloyPrimer and ED Primer(Liquid A and Liquid B)

Resin-basedcomposite

Paste-paste 488KAalloy: 00122AA-B: 000424

Tubes/hand mixed Kuraray America, New York

Fuji Plus Resin-modifiedglass ionomer

Powder-liquid 0208053 Capsule/machinemixed

GC America, Alsip, Ill.

RelyX Luting Resin-modifiedglass ionomer

Powder-liquid 2PB Jar and bottle/ hand mixed

3M ESPE, St. Paul, Minn.

RelyX Unicem Self-adhesivemodified resin

Powder-liquid 243071 Capsule/machinemixed

3M ESPE

Study B

Fuji CEM With Fuji PlusConditioner

Resin-modifiedglass ionomer

Paste-paste 03100720303121

Tube dispenser/hand mixed

GC America

RelyX Luting Resin-modifiedglass ionomer

Powder-liquid Powder: 4AXLiquid: 4LN

Jar and bottle/hand mixed

3M ESPE

RelyX Luting Plus Resin-modifiedglass ionomer

Paste-paste BE4BA Tube dispenser/ hand mixed

3M ESPE

Study C

Flecks Zinc Cement Zinc phosphate Powder-liquid Powder: Q5LYALiquid: L74

Bottles/hand mixed Keystone Industries, CherryHill, N.J.

iCEM Self-adhesivemodified resin

Paste-paste 071226 Tube dispenser/ automixing tip

Heraeus Kulzer, Armonk,N.Y.

BisCem Self-adhesivemodified resin


Bisco, Schaumburg, Ill.

Maxcem Self-adhesivemodified resin


Kerr, Orange, Calif.

RelyX Unicem Clicker Self-adhesivemodified resin

Paste-paste 274070 Tube dispenser/ hand mixed

3M ESPE



4/12


5/12

digitized all of the occlusal replicas, along withthree circles of a known surface area andperimeter, on a flatbed scanner. We used the digi-tized images of the standard circles and occlusalsurfaces (Figure 2) to determine the length of theperimeter and occlusal area of each specimen byusing specialized software (SCION Image, Scion,Frederick, Md.). (We used the circles to confirmthe accuracy of calculations.) We measured theaxial length of each tooth specimen by using adigital caliper with a measurement accuracy of0.02 mm (CD-6 CS, Mitutoyo, Kawasaki, Kana-gawa Prefecture, Japan). To arrive at the axialsurface area of each preparation, we multipliedeach tooths perimeter by its axial length. Weadded the occlusal and axial surface areas toobtain the total area. We ranked teeth accordingto decreasing surface area and distributed theminto cementation groups equally so that each

group had similar mean surface areas.The sample size for cement studies A and Bwas 12 or 13 teeth, which was similar to thatused in earlier studies6,7,22 and adequate for thedetection of clinically meaningful differences. Weconducted a sample size analysis by using datafrom studies A and B before commencing study C.The results of our analysis indicated that anobservation size of eight specimens would yieldadequate power; thus, we used the smaller

sample size. Table 3 shows sample size, meansurface areas of specimens and standard devia-tions for all three cement studies.

We performed two weeks of provisional cemen-tation to simulate clinical conditions by seatingthe respective stainless steel caps with impres-sion material, lined with a mix of provisionalcement without eugenol (Temp Bond NE, Kerr)


R E S E A R C H

Figure 2. Scans of poly(methylmethacrylate) replicas of theocclusal surface of each prepared tooth. Also shown are circles of aknown circumference and area, used for calibration of software

that would calculate the perimeter and area of each specimen.

TABLE 2

Laboratory materials and procedures used in the productionof the high-noble ceramometal alloy castings.

LABORATORY

ITEM

MATERIAL (MANUFACTURER), ACCORDING TO CEMENT STUDY

A B C

Type IVGypsum

Prima Rock(Whip Mix, Louisville, Ky.)

Prima Rock(Whip Mix)

Resin Rock(Whip Mix)

Die Spacer PDQ Die Spacer(Whip Mix)

PDQ Die Spacer(Whip Mix)

Software controlled(Zeno Tech System,

Wieland Dental+Technik,Pforzheim, Germany)

Burnout CrownForm

Bellewax(Kerr Dental Laboratory Products,

Orange, Calif.)ProArt sculpturing wax, red

(Williams AG, Schaan, Liechtenstein)

Bellewax(Kerr Dental Laboratory Products)

ProArt sculpturing wax, red(Williams AG)

Computer-milled crown form(Zeno PMMA Disk, Zeno Tech

System, Wieland Dental+Technik)

Sprue 10-gauge wax wire spool(Freeman Manufacturing,

Akron, Ohio)

10-gauge wax wire spool(Freeman Manufacturing)

10-gauge wax wire spool(Freeman Manufacturing)

Phosphate-BondedInvestment

Finesse InvestmentPowder and Liquid

(Dentsply Ceramco, York, Pa.)

Finesse InvestmentPowder and Liquid(Dentsply Ceramco)

Finesse InvestmentPowder and Liquid(Dentsply Ceramco)

High-NobleCeramometalCasting Alloy

Special White(45 percent gold, 39.8 percentpalladium, 6.5 percent silver)

(Dentsply Ceramco)

Special White(Dentsply Ceramco)

Special White(Dentsply Ceramco)



6/12

on the respective prepared teeth while the dentallaboratory fabricated the castings. When the cast-ings were ready for cementation, the impressioncaps with the provisional cement were removed,along with gross cement particles. One of theauthors (G.H.J.) cleaned the prepared teeth witha prophylaxis cup containing 2 percent glu-taraldehyde and flour of pumice, then rinsed and

dried them gently, leaving them slightly moist.One clinician (X.L.) mixed all cements,according to manufacturers instructions, andcemented the castings well within designatedworking times. Table 1 provides the consistencies,lot numbers and delivery systems of the cements.For cements that were supplied as two separatepaste tubes or as a powder and liquid (such asPanavia F, RelyX Luting and Flecks ZincCement), one clinician (G.H.J.) weighed the

powder and liquid or catalyst andbase pastes on an electronic micro-balance to ensure proper propor-tioning, then another clinician(X.L.) mixed the cement on a

mixing pad with a plastic spatula.Capsules were mixed in a high-frequency mixing unit (CapMix,3M ESPE) for 10 seconds.

After mixing, the clinician (X.L.)lined two crowns with cement andinitially seated them by usingstrong finger pressure. The secondclinician (G.H.J.) then immediatelyplaced the assembled teeth andcastings in a loading device (RimacSpring Tester, Rimac Tools,Dumont, N.J.). He then subjected

each crown to a total axial seatingforce of 196 newtons (20 kilogramsof force) for twice the specified set-ting time to allow for a slower set-

ting reaction at room temperature. The same clin-ician removed excess cement from the crownmargins and stored the specimens for 24 hours at34C in an atmosphere of 100 percent humidity.

After this storage period, he thermally cycled thecemented castings in water at temperaturesbetween 5C and 55C for 2,500 cycles for speci-mens in cement studies A and B and 5,000 cyclesfor specimens in cement study C. He used a 20-second dwell time in each hot and cold water con-tainer. He increased the number of cycles to 5,000in cement study C because longer cycling timeswere becoming a standard for bond strengthtesting of dentin adhesives.42

After thermal cycling, the clinician subjected thecopings to dislodgment forces along the apico-occlusal axis until they failed by using a universaltesting machine (Model TTMBL, Instron, Nor-wood, Mass.) at a crosshead speed of 0.5 mm perminute (Figure 3). He recorded the force at dislodg-ment and calculated the stress of removal by using

the surface area of each tooth preparation. Aftercasting dislodgment, two examiners (G.H.J. andeither X.L. or H.Z.) examined each crown and toothpreparation to determine the predominant natureof the cement failure on the basis of the criteriapresented in Table 4. When the two examiners haddiffering opinions of a particular specimens classi-fication, they used a forced-consensus approach todetermine the mode of failure.

For each cement study, we analyzed the data to


R E S E A R C H

TABLE 3

Sample size and specimen surface area.MATERIAL, BY CEMENT STUDY* NO. OF

SPECIMENSMEAN SURFACE AREA STANDARD DEVIATION(SQUARE MILLIMETERS)

Study AFuji Plus 12 132 16

Panavia F With Alloy Primer and EDPrimer (Liquid A and Liquid B)

13 132 18

RelyX Unicem 13 132 15

RelyX Luting 13 131 16

Study B

Fuji CEM With Fuji Plus Conditioner 12 119 19

RelyX Luting 12 119 16

RelyX Luting Plus 12 119 15

Study C

Flecks Zinc Cement 8 135 17

iCEM 8 136 18

BisCem 8 133 18

Maxcem 8 133 16RelyX Unicem Clicker 8 130 16

* Manufacturers are listed in Table 1.

TABLE 4

Classification of the natureof failure after crown removal.CLASSIFICATION DESCRIPTION

1 Cement principally on the prepared tooth(greater than three-quarters of the axialsurface)

2 Cement on the internal aspect of thecasting and prepared tooth

3 Cement principally on the internalaspect of the casting (greater than three-quarters of the axial surface)

4 Fracture of tooth



7/12

determine stress of dislodgment with a single-factor analysis of variance (ANOVA). Given sig-nificant main effects, we conducted pairwise com-parison of means by using the Newman-Keulsprocedure. We analyzed the data regarding type

of failure by using a 2

test for associations. Weconducted all hypothesis testing at the 95 percentlevel of confidence.

RESULTS

Figure 4 provides the graphic results for castingremoval stress for each cement and Table 5 pro-vides the corresponding ANOVA statisticalresults. In all three cement studies, we found sig-nificant differences among the cements within thespecific study group. Figure 5 (page 1133) showsthe predominant mode of cement failure; the cor-responding Pearson 2 statistical results for the

analysis of cement failure modes wereP .000,P .000 andP = .342 for cement studies A, B andC, respectively. Thus, we observed significant dif-ferences in failure mode among cements for thefirst two studies, but no significant differences infailure mode among cements in cement study C.

In cement study A, we compared three cementtypes. The resin-modified glass ionomer cement(RelyX Luting, 8.0 megapascals) and the self-adhesive modified-resin cement (RelyX Unicem,7.3 MPa) were most retentive, but notstatistically different (Figure 4).Panavia F (5.7 MPa) and the otherresin-modified glass ionomer, Fuji Plus(4.0 MPa), were less retentive. Themode of cement failure for RelyXLuting was 70 percent mixed, withcement located on both casting anddentin (Figure 5). For RelyX Unicem,62 percent of specimens exhibitedcement primarily on the internal sur-face of the casting (that is, greater thanthree-quarters of the surface area), but31 percent of the specimens failed byreason of tooth fracture without crown

separation. For nearly all of thePanavia F and Fuji Plus specimens, themode of failure was cement located onthe internal surface of the casting.

In cement study B, our focus wascomparing paste-paste and powder-liquid formulations of resin-modified glassionomer cements (Figure 4). The powder-liquidversion of RelyX Luting served as a control. RelyXLuting demonstrated the highest crown removal

stress (8.1 MPa), in which it differed statisticallysignificantly from the paste-paste cements FujiCEM (2.8 MPa) and RelyX Luting Plus (2.6 MPa);the removal stresses of these latter two cements


R E S E A R C H

Figure 3. Testing until dislodgment of crown from preparation.The investigator recorded the force at the time of casting separa-tion and converted it to removal stress by using the cement contactsurface area of each sample.

TABLE 5

Single-factor analysis of variance resultsfor casting removal stress.

CEMENT STUDY SUMS OFSQUARES

df* MEANSQUARE

FRATIO SIGNIFICANCE

A

Between groups 113.648 3 37.883 12.546 .000

Within groups 141.918 47 3.020

TOTAL 255.566 50

B

Between groups 237.995 2 118.997 130.268 .000

Within groups 30.145 33 0.913

TOTAL 268.140 35

C

Between groups 33.504 4 8.376 13.799

.000Within groups 21.276 35 0.608

TOTAL 54.780 39

* df: Degrees of freedom. Fratio: Mean square between groups divided by mean square within groups.



8/12

were not shown to differ statistically signifi-cantly. The mode of cement failure varied for eachcement (Figure 5). For RelyX Luting, 50 percentof the specimens exhibited a mixed failure inwhich cement was located on both the internalaspect of the crown and on the dentin, and 42 per-cent of the specimens failed because of tooth frac-ture without casting separation. All of the fail-ures for the paste-paste RelyX Luting Plus hadcement located on the internal aspect of thecasting, whereas Fuji CEM exhibited 92 percentmixed failures with cement located on the crownand dentin.

We conducted cement study C to evaluate other

self-adhesive modified-resin cements and RelyXUnicem Clicker, which was reformulated as apaste-paste product. We included zinc phosphatecement in this study to provide a clinically rel-evant control with established clinical success.Maxcem (4.9 MPa) was most retentive and dif-fered statistically significantly from the othercements tested. Results for the other cements, indecreasing order of retention, were 4.0 MPa forBisCem, 3.7 MPa for RelyX Unicem Clicker,

2.9 MPa for iCEM and 2.3 MPa forFlecks Zinc Cement. Figure 4shows the cements that did notdiffer statistically significantly.The primary mode of cement

failure was cement located on theinternal aspect of castings in 100percent of the iCEM specimens, 88percent of both the BisCem and theRelyX Unicem Clicker specimens,83 percent of the zinc phosphatespecimens and 62 percent of theMaxcem specimens. The remaining38 percent of the Maxcem speci-mens demonstrated a mixedfailure.

DISCUSSION

The research hypothesis for thisstudy was that there were no dif-ferences of clinical significanceamong cements in their ability toretain high-noble metal-ceramiccrowns. We rejected this hypoth-esis in all three studies because werecorded significant differences,several of which were clinicallyimportant. We discussed each typeof cement separately.

Zinc phosphate cement. In our study, amean stress of 2.3 MPa was required to removecastings cemented with zinc phosphate. The suc-cessful use of this cement for more than 100 yearsstrongly implies that all cements tested shouldretain castings clinically at least as well as zincphosphate does, assuming the properties of thenewer cements remain unchanged in the intra-oral environment across time. Early castingretention studies in which researchers investi-gated the effect of sealing dentin with adhesiveprimers and with 5 percent glutaraldehydedemonstrated retentive stresses for zinc phos-phate in the range of 3 to 6 MPa,6,7 a result com-

parable with what we observed in our study. Inthese two earlier studies, investigators used theaxial surface area alone (without the occlusalarea) as the basis for the calculation of removalstress. Thus, their values would be lower andeven more comparable with those in our study ifhad they included the occlusal area. In anotherstudy involving comparable methods but uniformconical preparations, researchers reported a meancrown removal stress of 1.7 MPa for zinc phos-


R E S E A R C H

Figure 4. Crown removal stress for cement studies A, B and C. Horizontal bars indicatethe mean crown removal stress for each cement; horizontal lines indicate standard devia-tions. Vertical bars indicate the means that did not differ statistically at the 95 percentlevel of confidence. MPa: Megapascals. Manufacturers are listed in Table 1.

Fuji Plus

Panavia F

RelyXUnicem

RelyXLuting

Fuji CEM

RelyXLuting Plus

RelyXLuting

Flecks Zinc Cement

iCEM

RelyXUnicem Clicker

BisCem

Maxcem

0 2 4 6 8 10

CROWN REMOVAL STRESS (MPa)

Cemen

t,StudyA

Cement,StudyB

Cement,StudyC



9/12

phate cement.8 Investi-gators in another studyshowed zinc phosphateto require a low re-moval force compared

with those required forother cements,9 but it isdifficult to make directcomparisons with thisstudys findingsbecause the investiga-tors reported values forcrown removal as aforce rather than as astress.

Conventionalresin, resin-modifiedglass ionomer and

self-adhesivemodified-resincements. Our resultssuggested that all thecements we testedshould retain crownsadequately when toothpreparations have alow angle of conver-gence, adequate axiallength and a well-fitting casting. However, insome clinical circumstancessuch as short crownpreparations, nonideal taper, long-span fixed par-tial dentures, cantilevered restorations and crownrecementationa dentist may wish to use acement with greater retentive properties. In ourstudy, we found greater crown retention with theuse of conventional resin cement with a separatemetal conditioner and dentin adhesive than withzinc phosphate (5.7 MPa versus 2.3 MPa, respec-tively); conventional resin cements often havebeen the cement of choice when the cliniciandesires greater casting retention. However, ourresults show that resin-modified glass ionomercements or self-adhesive modified-resin cements

demonstrated even greater casting retention(7.0-8.0 MPa) than did conventional resincements (5.7 MPa), and use of these newercements does not require metal conditioners anddental adhesives. These retention values (Figure4) are consistent with removal stresses reportedfor three of the same cements investigated in anearlier study by researchers who used the samemethodology but instead evaluated zirconia-basedcrowns.22

Interestingly, castings cemented with conven-tional resin failed with cement located exclusivelyon the internal surface of the crowns (Figure 5).The results suggest that the recommended metalprimer functioned well because the crownretained cement, but that the dentin adhesivepaired with this conventional resin cement didnot promote an effective bond to dentin. Failuremodes indicated that RelyX Luting bonded wellboth to dentin and to the internal surface of thecrown and that the cohesive strength of this setcement was high compared with the strength ofother cements. The bond of the new self-adhesivemodified-resin cement (RelyX Unicem) to dentindid not appear to be as strong as that of RelyX

Luting, because 62 percent of the specimens withRelyX Unicem failed with cement located princi-pally on the internal surfaces of the crown (thatis, greater than three-quarters of the surface).However, more than 30 percent of the specimensexperienced tooth fracture before crown separa-tion, suggesting that the cement had high reten-tive strength.

Yim and colleagues8 reported that Fuji Plusexhibited less crown retention stress than did


R E S E A R C H

Fuji Plus

Panavia F

RelyXUnicem

RelyXLuting

Fuji CEM

RelyXLuting Plus

RelyXLuting

Flecks Zinc Cement

iCEM

RelyXUnicem Clicker

BisCem

Maxcem

0 20 40 60 80 100

CEMENT FAILURE MODE (PERCENTAGE)

Cement

,StudyA

Cement,StudyB

Cement,StudyC

> 3/4on Dentin

Mixed Failure

> 3/4on Casting

Tooth Fracture

Figure 5. Horizontal bars indicate the distribution for modes of failure for each type of cement basedon an examination of the specimens after crown removal. The color code for mode of failure is in thekey, and values represent the percentage frequency of the failure mode for each cement. Cement studiesA, B and C are separated with dotted lines. Manufacturers are listed in Table 1.



10/12

Panavia 21 (Kuraray America) with a dentinadhesive, a result consistent with those of ourstudy, in which we compared Fuji Plus withPanavia F. But when we tested a second resin-modified glass ionomer, we noted differences in

casting retention for cements of the same type:Fuji Plus exhibited one-half the crown retention ofRelyX Luting. We noted a high standard deviationassociated with the mean of Fuji Plus comparedwith those of the other three products we tested.Because the failure analysis showed the cementlocated on the internal aspect of the casting, wedetermined that a weak and variable bond todentin may have been the cause of the highstandard deviation. GC America, the manufac-turer of Fuji Plus, recommends that clinicians usea dilute polyacrylic acid dentin conditioner if theywant to achieve greater adhesion. Because it may

increase the retentive stress, we used this dentinconditioner in cement study B.

Powder-liquid versus paste-paste resin-modified glass ionomer cements. We foundlarge, clinically important differences in theresults of cement study B, in which we comparedpaste-paste formulations of resin-modified glassionomer cements with an original powder-liquidversion. The newer paste-paste products exhib-ited only one-third of the casting retention (withremoval stresses of 2.6-2.8 MPa) of the powder-liquid version (requiring removal stress of 8.1MPa) (Figure 4). Furthermore, the result forRelyX Luting was virtually the same in cementstudies A and B (Figure 4) despite the use ofproducts with different lot numbers, suggestingexcellent reproducibility. The modes of failure(Figure 5) help explain these differences to someextent. All specimens of paste-paste RelyX LutingPlus exhibited cement on the casting at separa-tion, in contrast to specimens of powder-liquidRelyX Luting, for which the failure mode wasmixed or there was tooth fracture. On the basis ofthese results, it appears that the new paste-pasteversion of this particular cement does not pro-

mote the same degree of adhesion to dentin asdoes the powder-liquid version. Retention of cast-ings by Fuji CEM (another paste-paste formula-tion) was 30 percent less than that recorded forthe powder-liquid version (Fuji Plus), despite useof the elective dentin conditioner for the former;the mode of cement failure was mixed. This lowmagnitude of retentive stress suggests that thecohesive strength of Fuji CEM was low overall.The difference between paste-paste and powder-

liquid formulations might have been even greaterhad we used the dentin conditioner for Fuji Plusin study A. Our results strongly suggest that itmay be prudent for clinicians always to use thedentin conditioner with these two cements.

A reason for the differences we observedbetween powder-liquid and paste-paste versionsof these cements may be that the two versions ofthe cement are simply not the same and that cre-ation of a functional paste-paste system requiresdifferent ingredients and chemistry. Becausewater is needed to initiate any glass ionomerreaction in a resin-modified glass ionomerhybrid cement, it is likely that manufacturersformulated a new aqueous base paste to allowthis reaction to take place. Traditional chemicalinitiators are water sensitive; thus, one canassume that new initiators were developed to

create the proper setting times and long-term sta-bility of the paste-paste cement.

Most practitioners likely will assume equiva-lence of paste-paste and powder-liquid formula-tion for cements of the same type and manufac-turer. Our results have significant import forclinical practice because they showed paste-pasteformulations of resin-modified glass ionomercements to have inferior retention. The paste-paste versions of resin-modified glass ionomercements retained castings as well as did zincphosphate cement and, therefore, are reasonablechoices in ideal clinical circumstances. However,when the clinician desires additional retention,we strongly recommend use of the powder-liquidversion of the cement. One potential disadvantageof the powder-liquid system is the deleteriouseffect of moisture contamination of the powder. Ifthe bottle cap is not secured tightly or if thecement is used in a humid environment, thepowder can absorb moisture; this in turn candegrade the catalyst and cause the setting time toincrease appreciably. Thus, dental health carepersonnel always should take precautions afterdispensing powder and liquid to cap the bottles

tightly. If the setting reaction appears to be slow,the clinician should procure a new box of cement.Self-adhesive modified-resin cements.

Soon after the introduction of RelyX Unicem, sev-eral other self-adhesive modified-resin cementsappeared on the dental market, most as paste-paste versions. In cement study C, we evaluatedfour such cements and zinc phosphate cement.The retentive stresses for the self-adhesive groupranged from 2.9 to 4.9 MPa, and the retentive


R E S E A R C H



11/12

stress for zinc phosphate was 2.3 MPa. Similar tothe trend we observed in cement study B, a paste-paste version of a self-adhesive cement yieldedsignificantly lower crown retentive stresses thandid the comparable powder-liquid version tested

in cement study A. Values for RelyX Unicem incement study A and for RelyX Unicem Clicker incement study C were 7.3 MPa and 3.7 MPa,respectively. Because we tested these twocements at different times and in differentgroups, we must exercise care in making directcomparisons. However, we used identical method-ologies for the three sequential studies. Further-more, RelyX Luting cement performed similarlyin two studies, suggesting that at least some com-parisons of RelyX Unicem and RelyX UnicemClicker are appropriate.

In cement study A, the casting retention for

RelyX Unicem was high (7.3 MPa). This retentionstress correlates to a mean removal force of 951 N(97 kg of force) applied to a preparation surfacearea of 132 mm2 and is, under most circum-stances, much greater than ever needed clinically,assuming the bond and cement properties remainunchanged across time. Of significant clinicalnote is that a crown cemented with this level ofretention must be prepared with a coarse dia-mond rather than be sectioned, loosened andlifted off, as is done with a crown cemented withzinc phosphate cement.

The dominant failure mode for self-adhesivemodified-resin cements was cement located on theinternal surface of the crown and not on thedentin. We observed this same result for thepowder-liquid encapsulated RelyX Unicem incement study A, and it is consistent with the find-ings of De Munck and colleagues43 and supportedby the results of a review1 that showed thesetypes of cements to have little infiltration intodentin. We observed no tooth fractures duringdebonding in study C, which suggests that theadhesion to dentin of these self-adhesive cementswas not as great as that of the powder-liquid

cements RelyX Luting and RelyX Unicem. How-ever, the retentive values are comparable with orgreater than those of zinc phosphate, indicatingthat retention would have been adequate for theentire group in many clinical circumstances.

Study limitations.Although we took severalmeasures to ensure the clinical relevance of ourstudy design, the study has limitations. Forexample, the extracted teeth, although hydratedat all times, may not have had the same proper-

ties as those of vital molars. Also, crowns in vivoare bathed in saliva and other media, and theyexperience intraoral stress across long periods.The only means we used to simulate intraoralstresses in this series of studies was thermocy-

cling at 5C and 55C. An improvement would beto subject the cemented crowns to thermomechan-ical cycling not one time for 2,500 to 5,000 cycles,but once per month for six months, to allow thecement and associated bonds to age further.Finally, the high-noble metal-ceramic alloy weused is relevant but not used by all dentists, andother alloys may influence the retention of cast-ings to some extent.

CONCLUSIONS

On the basis of results from this study, and inconsideration of the studys limitations, we can

conclude that all cements tested retained metal-ceramic castings as well as or better than thelong-used standard, zinc phosphate cement.When the clinician sees a need for additionalcrown retention, he or she may prefer to use aconventional resin cement with a dentin adhe-sive, a resin-modified glass ionomer cement or aself-adhesive modified-resin cement. For thelatter two types of cements, we found powder-liquid formulations to be more retentive than thecorresponding paste-paste systems. Our cementfailure data suggested that the cement-dentinbond was more established with the powder-liquid formulations of resin-modified glassionomer cement than with any of the self-adhesive modified-resin cements tested.

Disclosure. The studies described in this article were supported inpart by 3M ESPE, St. Paul, Minn., and Heraeus Kulzer, Armonk, N.Y.

The authors acknowledge the following companies for donation ofcements: 3M ESPE, St. Paul, Minn.; Heraeus Kulzer, Armonk, N.Y.;Kuraray America, New York City; GC America, Alsip, Ill.; and Bisco,Schaumburg, Ill. They acknowledge Whip Mix, Louisville, Ky., fordonation of dental gypsum. Finally, they acknowledge the NakanishiDental Laboratory, Bellevue, Wash., for assistance with crownproduction.

The authors thank emeritus University of Washington School of Den-tistry faculty member Dr. David Bales and former dental students

Drs. Timothy Gatten, David Newell and Andrew Heidergott for theirassistance with tooth preparation, impressions and formation ofworking dies.

Results of these studies were presented at the general sessions of theInternational Association for Dental Research in 2003 (June 28,Gteborg, Sweden), 2005 (March 12, Baltimore, Md.) and 2008 (July 3,Toronto).

1. Radovic I, Monticelli F, Goracci C, Vulicevic ZR, Ferrari M. Self-adhesive resin cements: a literature review. J Adhes Dent 2008;10(4):251-258.

2. Kaufman EG, Coelho DH, Colin L. Factors influencing the reten-tion of cemented gold castings. J Prosthet Dent 1961;11(3):487-502.


R E S E A R C H



12/12

3. Piwowarczyk A, Lauer HC, Sorensen JA. In vitro shear bondstrength of cementing agents to fixed prosthodontic restorativematerials. J Prosthet Dent 2004;92(3):265-273.

4. Mitchell CA, Pintado MR, Geary L, Douglas WH. Retention ofadhesive cement on the tooth surface after crown cementation. J Pros-thet Dent 1999;81(6):668-677.

5. Swift EJ, Lloyd AH, Felton DA. The effect of resin desensitizingagents on crown retention. JADA 1997;128(2):195-200.

6. Johnson GH, Lepe X, Bales DJ. Crown retention with use of a 5percent glutaraldehyde sealer on prepared dentin. J Prosthet Dent1998;79(6):671-676.

7. Johnson GH, Hazelton LR, Bales DJ, Lepe X. The effect of a resin-based sealer on crown retention for three types of cement. J ProsthetDent 2004;91(5):428-435.

8. Yim NH, Rueggeberg FA, Caughman WF, Gardner FM, PashleyDH. Effect of dentin desensitizers and cementing agents on retention offull crowns using standardized crown preparations. J Prosthet Dent2000;83(4):459-465.

9. Ergin S, Gemalmaz D. Retentive properties of five different lutingcements on base and noble metal copings. J Prosthet Dent 2002;88(5):491-497.

10. Garberoglio R, Brnnstrm M. Scanning electron microscopeinvestigation of human dentinal tubules. Arch Oral Biol 1976;21(6):355-362.

11. el-Mowafy OM, Fenton AH, Forrester N, Milenkovic M. Retentionof metal ceramic crowns cemented with resin cements: effects of prepa-ration taper and height. J Prosthet Dent 1996;76(5):524-529.

12. Schulein TM. Significant events in the history of operative den-tistry. J Hist Dent 2005;53(2):63-72.

13. Smith DC. A new dental cement. Brit Dent J 1968;124(9):381-384.14. Crisp S, Prosser J, Wilson AD. An infra-red spectroscopic study of

cement formation between metal oxides and aqueous solutions ofpoly(acrylic) acid. J Mater Sci 1976;11(1):36-48.

15. Wilson AD, Kent BE. A new translucent cement for dentistry: theglass ionomer cement. Brit Dent J 1972;132(4):133-135.

16. Ayad MF, Rosenstiel SF, Salama M. Influence of tooth surfaceroughness and type of cement on retention of complete cast crowns. JProsthet Dent 1997;77(2):116-121.

17. Mathis RS, Ferracane JL. Properties of a glass-ionomer/compositehybrid material. Dent Mater 1989;5(5):355-358.

18. Mitra SB, inventor; 3M Innovative Properties Company (St. Paul,Minn.), assignee. Glass ionomer cement. U.S. patent 6,765,038. July20, 2004.

19. Hecht R, Ludstech M, inventors; 3M ESPE AG (Seefeld, Ger-many), assignee. Initiator system for acid dental formulations. U.S.patent 6,953,535. Oct. 11, 2005.

20. Hecht R, Richter B. Neue Entwicklungen in der adhsivenZementierung [New developments in adhesive cementation].

sthetische Zahnmedizin 2004;7(1):47-55.21. Christensen GJ. Should resin cement be used for every cementa-

tion? JADA 2007;138(6):817-819.22. Palacios RP, Johnson GH, Phillips KM, Raigrodski AJ. Retention

of zirconium oxide ceramic crowns for three types of cement. J ProsthetDent 2006;96(2):104-114.

23. Ibarra G, Johnson GH, Geurtsen W, Vargas MA. Microleakage of

porcelain veneer restorations bonded to enamel and dentin with a newself-adhesive resin-based dental cement. Dent Mater 2007;23(2):218-225.

24. 3M ESPE. Technical data sheet: RelyX Unicem self-adhesive uni-versal resin cement. St. Paul, Minn.: 3M ESPE; 2002.

25. Eames WB, ONeal SJ, Monteiro J, Roan JD, Cohen KS. Tech-niques to improve the seating of castings. JADA 1978;96(3):432-437.

26. Nordlander J, Weir D, Stoffer W, Ochi S. The taper of clinical

preparations for fixed prosthodontics. J Prosthet Dent 1988;60(2):148-151.

27. Steinbock DJ, Tombasco T. Decrease your die preparation timewith the Whip Mix P.D.Q. kit. Trends Tech Contemp Dent Lab1989;6(8):53-56.

28. International Organization for Standardization. ISO 9917-1:2007.Dentistry: water-based cements, part 1powder/liquid acid-basecements. Geneva: International Organization for Standardization;2007.

29. International Organization for Standardization. ISO 4049:2000.Dentistry: polymer-based filling, restorative and luting materials.Geneva: International Organization for Standardization; 2000.

30. Kious AR, Roberts HW, Brackett WW. Film thickness of recentlyintroduced luting cements. J Prosthet Dent 2009;101(3):189-192.

31. American Dental Association Council on Scientific Affairs. Glassionomer-containing cements. ADA Professional Product Rev 2008;3(1):1-6.

32. Worley JL, Hamm RC, von Fraunhofer JA. Effects of cement oncrown retention. J Prosthet Dent 1982;48(3):289-291.

33. Pilo R, Cardash HS, Baharav H, Helft M. Incomplete seating ofcemented crowns: a literature review. J Prosthet Dent 1988;59(4):429-433.

34. Fusayama T, Kimiko I, Hosoda H. Relief of resistance of cementof full cast crowns. J Prosthet Dent 1964;14(1):95-106.

35. Eames WB. The casting misfit: how to cope. J Prosthet Dent1981;45(3):283-285.

36. Campagni WV, Wright W, Martinoff JT. Effect of die spacer onthe seating of complete cast gold crowns with grooves. J Prosthet Dent1986;55(3):324-328

37. Marker VA, Miller AW, Miller BH, Swepston JH. Factorsaffecting the retention and fit of gold castings. J Prosthet Dent 1987;57(4):425-430.

38. Grajower R, Zuberi Y, Lewinstein I. Improving the fit of crownswith die spacers. J Prosthet Dent 1989;61(5):555-563.

39. Passon C, Lambert RH, Lambert RL, Newman S. The effect ofmultiple layers of die-spacer on crown retention. Oper Dent 1992;17(2):42-49.

40. Olivera AB, Saito T. The effect of die spacer on retention and fit-

ting of complete cast crowns. J Prosthodont 2006;15(4):243-249.41. Carter SM, Wilson PR. The effect of die-spacing on crown reten-

tion. Int J Prosthodont 1996;9(1):21-29.42. Yiu CK, King NM, Pashley DH, et al. Effect of resin

hydrophilicity and water storage on resin strength. Biomaterials 2004;25(26):5789-5796.

43. De Munck J, Vargas M, Van Landuyt K, Hikita K, Lambrechts P,Van Meerbeek B. Bonding of an auto-adhesive luting material toenamel and dentin. Dent Mater 2004;20(10):963-971.


R E S E A R C H


cementos y adhesión al metal okokokokok

Documents