Effe

the

cem

Plínio Sciasci, DD

Supported by grant 2011/14461-4 f

aDoctoral student, Department of DbAdjunct Professor, Department of DcProfessor, Department of Dental MdProfessor, Department of Oral ScieeAssociate Professor, Department of

Sciasci et al

ct of surface treatments on

shear bond strength of luting

ents to Y-TZP ceramic

S, MSC,a

Filipe Oliveira Abi-Rached, DDS, MSc, PhD,b

Gelson Luis Adabo, DDS, MSc, PhD,c

Paolo Baldissara, DDS, MSc, PhD,d andRenata Garcia Fonseca, DDS, MSc, PhDe

Araraquara Dental School, São Paulo State University (UNESP),Araraquara, São Paulo, Brazil; School of Dentistry, Alma MaterStudiorum, University of Bologna, Bologna, Italy

Statement of problem. Because zirconia is a glass-free material, alternative surface treatments such as airborne-particleabrasion or silica coating should be used for long-term bonding. However, these surface treatments in combination withdifferent bonding agents and luting cements have not yet been studied.

Purpose. The purpose of the study was to evaluate the effect of surface treatments on the shear bond strength (SBS) ofluting cements to Y-TZP ceramic.

Material and methods. Zirconia disks (N¼240) were airborne-particle abraded with the following particles (n¼48): 50 mmAl2O3; 120 mm Al2O3; 30 mm silica-coated Al2O3 (Rocatec Soft); 120 mm Al2O3þ110 mm silica-coated Al2O3 (Rocatec Plus);and Rocatec Plus. After silanization of the zirconia surface, composite resin disks were bonded with (n¼12) RelyX Luting 2;RelyX ARC; RelyX U100; and Panavia F. The bonded specimens were thermocycled (10 000 cycles) and tested for SBS. Failuremode was determined with a stereomicroscope (�20). The morphology and elemental composition of airborne-particleabraded surfaces were evaluated with scanning electron microscopy (�500) and energy-dispersive x-ray spectroscopy (�50).

Results. Surface treatments, cements, and their interaction were significant (P<.001). For RelyX ARC, Rocatec Soft andRocatec Plus provided the highest SBS. In general, surface treatments did not influence the SBS of RelyX U100 and Panavia F.Regardless of the cement, no significant difference was found between 50 mm and 120 mm Al2O3 particles, between RocatecSoft and Rocatec Plus, or between Rocatec Plus and 120 mm Al2O3 particlesþRocatec Plus. All groups showed adhesivefailures. Different particle sizes provided differences in morphological patterns. The elemental composition comprised Al andAl/Si for alumina and silica-abraded zirconia.

Conclusions. Particle size did not influence the SBS of the groups abraded exclusively with alumina or silica-coated particles.RelyX ARC was more surface-treatment dependent than RelyX U100 and Panavia F. (J Prosthet Dent 2014;-:---)

Clinical Implications

For RelyX U100 and Panavia F, any surface treatment usually providessuitable bonding, while for RelyX ARC, silica coating is better indicated.The size of the alumina and silica-coated particles did not influence SBS.No surface treatment was effective for RelyX Luting 2.

rom the São Paulo State Research Foundation (FAPESP).

iagnosis and Surgery, São Paulo State University (UNESP).ental Materials and Prosthodontics, São Paulo State University (UNESP).aterials and Prosthodontics, São Paulo State University (UNESP).nces, Division of Prosthodontics, University of Bologna.Dental Materials and Prosthodontics, São Paulo State University (UNESP).

2 Volume - Issue -

Because of their excellent mechanical with a silane that is applied subse- (Lava; 3M ESPE AG) were polished with

properties,1 biocompatibility,2 low ther-mal conductivity,3 chemical stability,4

and esthetic potential,5 yttria-stabilizedtetragonal zirconia polycrystal (Y-TZP)ceramics have been used to fabricatedental prostheses. However, the surfacetreatments used for silica ceramics donot promote suitable bonding betweenresin-based materials and zirconia.6,7

This problem deserves special attention,particularly when the prepared tooth haslimited resistance and retention form, asY-TZP ceramic restorations exhibit mini-mal inherent mechanical retention totooth preparations.8 Additionally thezirconia surface is relatively smoothand flat.9 In such a clinical situation,resin-based cements should be the ma-terial of choice8,10,11 because of theirimproved mechanical properties as com-pared with zinc phosphate and conven-tional or resin-modified glass ionomercements12,13 and the possibility ofestablishing chemical interactions withthe zirconia surface.14-17

For a long-term durable bond at thezirconia/cement interface, there shouldbemicromechanical retention and chem-ical bonding.8,16,18 Although there aredifferent methods of promoting micro-mechanical retention on the zirconiasurface, including grinding with diamondrotary instruments,8 surface prepara-tion with an erbium-doped yttrium-aluminum-garnet (Er:YAG) laser,19 theuse of selective infiltration etching,20 anda liner21 or an application of low fusingporcelain glaze application,22 airborne-particle abrasion with Al2O3 particles isone of the most simple, functional, andwidely used.23-25 This procedure cleans26

and roughens the surface to increase thebonding surface area for mechanicalinterlocking between the cement and thezirconia surface27 and the wettability28

of the zirconia surface for bondingagents.18,19,29,30 Airborne-particle abra-sion may be performed with differentsizes of Al2O3 particles, which maybe silica coated or not. When silica-coated alumina particles are used, theprocedure is known as tribochemicalsilica coating, which deposits a silicalayer on the zirconia surface to react

The Journal of Prosthetic Dentis

quently.28,31-37

However, the chemical reactions be-tween silane and abraded (hSi-O-Sih,¼Al-O-Sih)ornonabraded(hZr-O-Sih)zirconia surfaces are susceptible to hy-drothermal effects,38,39 which may de-grade zirconia bonding. Thus, in orderto improve the bond at this substrate/cement interface, the efficacy of dif-ferent compositions of luting agentshas been evaluated. Self-etching resincements, which are composed ofmultifunctional phosphoric acid meth-acrylates, seem to promote suitablebonding to different substrates.30,40-44

Adhesive resin cements, which containfunctional monomers such as 10-methacryloyloxydecyl dihydrogen phos-phate (MDP), 4-methacryloxyethyltrimellitate anhydride (4-META), 11-methacryloyloxundecan 1,1-dicarboxylicacid (MAC-10), and others, are alsoindicated for bonding zirconia restora-tions. These adhesive monomers canestablish a chemical bond with thezirconia surface,21 promoting an in-creased and more durable bondstrength.23,29,30,44-46 Few studies14,15,47

have evaluated the bonding perfor-mance of conventional and resin-modified glass ionomer cements tozirconia or the chemical interactionsbetween their components and thoseof the treated or untreated zirconiasurface.

Because dentists have a wide choiceof surface treatments and luting ce-ments, the effect of these on the zirco-nia/cement interface should beinvestigated. The aim of this in vitrostudy was to evaluate the efficacy ofdifferent surface treatments on theshear bond strength (SBS) betweenzirconia and luting cements. The nullhypothesis was that the use of differentsurface treatments and luting cementswill not influence the SBS at the zirco-nia/cement interface.

MATERIAL AND METHODS

The bonding surfaces of 240 disks(6.25 mm diameter � 2.5 mm thick)prepared from presintered zirconia

try

wet 600- and 1200-grit silicon carbideabrasive paper. After oven sintering(Lava Furnace 200; Dekema Dental-Keramiköfen GmbH) according to themanufacturer’s instructions, the di-mensions of all zirconia disks were 5mm diameter by 2 mm thick due tothe sintering shrinkage of the zirconia(approximately 25%). To simulate theeffect of the veneering porcelain appli-cation, the disks were subjected to 4firing cycles (wash, 950�C; dentin 1,910�C; dentin 2, 900�C; glaze, 900�C)in a porcelain oven (Aluminipress) asrecommended by the manufacturer ofVM9 zirconia veneering porcelain (VitaZahnfabrik).

The specimens (N¼240) weredivided into 5 groups and airborne-particle abraded with the followingparticles (n¼48): 50 mm Al2O3; 120 mmAl2O3; 30 mm silica-coated Al2O3

(Rocatec Soft); 120 mm Al2O3, fol-lowed by 110 mm silica-coated Al2O3

(Rocatec Plus); and Rocatec Plus.Subsequently, the surfaces were treatedwith a silane coupling agent. For eachgroup, 4 luting cements were used(n¼12): RelyX Luting 2 (resin-modifiedglass ionomer cement), RelyX ARC(resin cement), RelyX U100 (self-etching resin cement), or Panavia F(adhesive resin cement). The silaneused was RelyX Ceramic Primer, exceptfor the groups bonded with Panavia F,in which the combination of ClearfilSE Bond Primer/Clearfil PorcelainBond Activator (silane coupling agent)was applied, as recommended by themanufacturer. The materials evaluatedare summarized in Table I.

For the airborne-particle abrasion,the zirconia disks were mounted in aholder at a 90-degree angle and a dis-tance of 10 mm from the tip of theairborne-particle abrasion unit (BasicClassic; Renfert GmbH) and abraded ata pressure of 0.28 MPa for 15 seconds.All specimens were cleaned in 99%isopropanol for 10 minutes in an ul-trasonic bath and left to dry at roomtemperature for 24 hours.

Composite resin disks (Filtek Z350XT; 3M ESPE) were produced from a

Sciasci et al

Table I. Materials evaluated

Material Composition Manufacturer

50 mm Al2O3 particles Al2O3>99% Bio-Art Dental Equipment Ltd

120 mm Al2O3 particles Al2O3>99% Bio-Art Dental Equipment Ltd

Rocatec Soft 30 mm silica-coated Al2O3 particles 3M ESPE AG

Rocatec Plus 110 mm silica-coated Al2O3 particles 3M ESPE AG

RelyX Ceramic Primer MPS, ethanol, water 3M ESPE

Clearfil SE Bond Primer MDP, HEMA, hydrophilic aliphatic dimethacrylate,dl-camphorquinone, water

Kuraray Medical Inc

Clearfil Porcelain Bond Activator MPS, hydrophobic aromatic dimethacrylate Kuraray Medical Inc

RelyX Luting 2 (resin-modifiedglass ionomer cement)

Methacrylated polycarboxylic acid, Bis-GMA, HEMA, silanatedzirconia/silica filler, fluoroaluminosilicate (FAS) glass, water

3M ESPE

RelyX ARC (resin cement) Bis-GMA, TEGDMA, silanated zirconia/silica filler 3M ESPE

RelyX U100 (self-etching resin cement) Glass powder, methacrylated phosphoric acid esters,TEGDMA, silanated silica filler

3M ESPE AG

Panavia F 2.0 (adhesive resin cement) Paste A: MDP, DMA, silanated silica filler, dl-camphorquinonePaste B: DMA, silanated barium glass filler, sodium fluoride

Kuraray Medical Inc

Filtek Z350XT Bis-GMA, UDMA, TEGDMA, Bis-EMA(6), zirconia/silica filler 3M ESPE

MPS, 3-methacryloyloxypropyl trimethoxysilane; MDP, 10-methacryloyloxydecyl dihydrogen phosphate; Bis-GMA, bisphenol A diglycidyl ether dimetha-crylate; HEMA, 2-hydroxyethyl methacrylate; TEGDMA, triethylene glycol dimethacrylate; DMA, dimethacrylates; UDMA, uretane dimethacrylate; Bis-EMA(6), bisphenol A polyethylene glycol diether dimethacrylate.

- 2014 3

custom-made metal split matrix (5 mminternal diameter and 2 mm thick).The top surface and 2 diametricallyopposed sides of the disks were eachlight polymerized (Radii-Cal light-polymerizing unit; SDI Ltd) for 40 sec-onds for a total of 120 seconds14 at aconstant intensity of 800 mW/cm2. Thesilane coupling agents were applied for20 seconds to the airborne-particle-abraded zirconia surface and left todry for 60 seconds at room tempera-ture. The zirconia disk was positionedin an alignment apparatus with thetreated surface facing up. All luting ce-ments were proportioned by weight,mixed according to their manufacturinginstructions, placed onto the bottomsurface of the resin disks, and posi-tioned over the zirconia specimen. Next,a weight of 1000 g was applied on topof the resin disk for 10 minutes14 with acustom-made device. Except for theRelyX Luting 2, after excess removal, thecements were light polymerized in 2different positions (equidistant sides) ofthe cementation line for a total of 80seconds under the conditions described

Sciasci et al

previously. All specimens were thermo-cycled in distilled water between 5�Cand 55�C for 10000 cycles, with a dwelltime of 30 seconds in each bath.

The bonded disks were attached to acustom-made special holder and testedfor SBS in a mechanical testing machine(EMIC DL2000; EMIC Equipment andSystems Testing Ltd) with a 1 kN loadcell (Fig. 1). According to the method ofFawzy and El-Askary,40 a uniaxial tensileforce was applied to the adhesive inter-face at a constant crosshead speed of0.5 mm per minute until failure. SBSvalues were recorded (MPa).

The data were analyzed statisticallyby SPSS software (IBM). The assump-tions of the analysis were satisfied(Shapiro-Wilk, .07�P�.97; Levene,P¼.30), and the data were analyzed by2-way ANOVA to test the effect of sur-face treatment, luting cement type(except for RelyX Luting 2, which failedspontaneously), and their interactionon the SBS. The Tukey honestly signifi-cant difference post hoc test (a¼.05)was applied to determine the differ-ences among means.

Debonded specimens were exam-ined under a stereomicroscope (M80;Leica Microsystems Ltd) at �20 mag-nification by a single trained observer,and failure mode was classified as:adhesive, cohesive within the cementlayer or within the composite resin, oras a combination of both (mixed), ac-cording to the predominant mode offailure in each quadrant of the zirconiasurface.48 Although RelyX Luting 2debonded spontaneously, its groupswere also analyzed concerning failuremode.

To analyze the zirconia surfacemorphology, 2 additional specimensfrom each airborne-particle abrasioncondition were mounted on metallicstubs and analyzed under a field emissionscanning electron microscope (JSM-7500F; JEOL Ltd) at�500 magnificationwith an accelerating voltage of 2.0 kV. Todetermine the elemental composition,these same specimens were mountedon metallic stubs and examined qualita-tively under �50 magnification and 7.0kV accelerating voltage by a field emis-sion scanning electron microscope (JSM-

1 SBS test apparatus.

Table II. Two-way ANOVA

Source of Variation SS df MS F P

Surface treatment 326.873 4 81.718 11.009 <.001

Cement 162.461 2 81.231 10.943 <.001

Surface treatment�Cement 382.256 8 47.782 6.437 <.001

Residual 1224.773 165 7.423

Total 2096.363 179

SS, sum of squares; MS, mean square.

Table III. Mean shear bond strength values (MPa), standard deviations (�),and statistical results of all groups

Surface Treatment

Cement

RelyX ARC RelyX U100 Panavia F

50 mm Al2O3_silane 7.7 �2.6 Ca 11.5 �1.8 ABa 10.8 �2.4 Aa

120 mm Al2O3_silane 8.4 �3.5 Ca 10.8 �3.2 Ba 10.8 �1.8 Aa

Rocatec Softþsilane 14.9 �3.0 Aa 12.0 �3.0 ABab 10.1 �2.5 Ab

Rocatec Plusþsilane 13.8 �2.9 ABab 15.2 �2.5 Aa 11.2 �2.1 Ab

120 mm Al2O3_Rocatec Plusþsilane 10.0 �2.9 BCb 14.9 �2.5 Aa 11.1 �3.3 Aab

For RelyX Luting 2, all groups failed spontaneously. Different lowercase letters indicate significantdifferences among cements (P<.05). Different uppercase letters indicate significant differences amongsurface treatments (P<.05).

4 Volume - Issue -

The Journal of Prosthetic Dentistry

7500F; JEOL Ltd) fitted with an energydispersive x-ray spectrometer.

RESULTS

The results from the 2-wayANOVA (Table II) showed that surfacetreatment (P<.001), cement (P<.001),and their interaction (P<.001) werestatistically significant. Table III showsthe mean SBS values (MPa), standarddeviations, and statistical results fromthe Tukey test.

For RelyX Luting 2, all groups failedspontaneously. For RelyX ARC, RocatecSoft and Rocatec Plus provided thehighest SBS value. For RelyX U100(except for the group 120 mm Al2O3

particlesþsilane) and Panavia F, nosignificant differences were foundamong the surface treatments. Regard-less of the cement, no significant dif-ference was found between 50 mm and120 mm Al2O3 particles (P¼1.0 for eachcement), between Rocatec Soft (30mm) and Rocatec Plus (110 mm)

Sciasci et al

Rocatec Soft1000800600400200

00

1 2 3 4 5

keV

ZrSiAI

O

C

50 µm Al2O31000800600400200

00 1 2

keV

ZrAI

O

C

3 4 5

Zr

AI

O

C

120 µm Al2O31000800600400200

00 1 2

keV

3 4 5

ZrAI Si

O

C

120 µm Al2O3 + Rocatec Plus1000800600400200

00 1 2

keV

3 4 5

ZrAI

Si

O

C

Rocatec Plus1000

800600400200

00 1 2

keV

3 4 5

2 Energy-dispersive x-ray spectra of airborne-particle abrasion conditions evaluated.

- 2014 5

(.21�P�1.0), or between RocatecPlusþsilane and 120 mm Al2O3 parti-clesþRocatec Plusþsilane (.06�P�1.0).

For the groups abraded with 50 mm(.05�P�1.0) and 120 mm Al2O3 par-ticles (.68�P�1.0), no significant dif-ference was found among the cements,while for those abraded with RocatecSoft and Rocatec Plus, Panavia F pro-vided the lowest SBS value. RelyX ARCexhibited the lowest SBS mean valueamong the groups abraded with 120mm Al2O3 particlesþRocatec Plus.

Failure mode was adhesive for allspecimens of all cements (includingRelyX Luting 2). The energy-dispersive x-ray spectra revealed C, O, Al, and Zrpeaks for alumina-abraded surfaces andC, O, Al, Si, and Zr for the silica-coatedzirconia (Fig. 2). The scanning electronmicroscopic analysis indicated that dif-ferent particle sizes provided differencesin the morphological patterns (Fig. 3).

DISCUSSION

The null hypothesis was rejectedbecause surface treatment, cement, and

Sciasci et al

their interaction were significant. ForRelyX ARC, Rocatec Soft and RocatecPlus followed by silane provided thehighest SBS value. Blatz et al14 alsoobserved that Rocatec Soft providedhigher SBS results than 50 mm Al2O3

particles. For the groups bonded withRelyX ARC, besides the micro-mechanical retention provided byairborne-particle abrasion and thechemical reaction between the silane(hydrolyzable alkoxy groups) and theresin monomers of this cement, 2additional reactions occurred, depend-ing on the airborne-particle abrasioncondition. In the groups abraded withAl2O3 particles, a reaction occurredbetween the silane and the alumina38,46

deposited on the zirconia surface,whereas in those abraded with silica-coated Al2O3 particles, a silica layerformed over the zirconia surface, withwhich the silane reacted.34,35,38,46 Thereaction to silica is chemically strongerand more hydrolytically stable than thereaction to alumina,38,46 which explainswhy treatment with the tribochemicalsystems provided the best results for

the RelyX ARC groups. Moreover, unlikeRelyX U100 and Panavia F, RelyXARC does not contain phosphoricacid groups or adhesive functionalmonomers capable of reacting chemi-cally with oxides16,34,42 and hydroxylgroups42,49 on the zirconia surface,which makes the chemical bondingexclusively dependent on the tri-bochemical system. These explanationsmay also justify why, for RelyXARC, abrasion with 120 mm Al2O3

particlesþRocatec Plus holds an inter-mediate position with respect to theother surface treatments. As observedin some studies,31-33 the energy-dispersive x-ray spectra revealed thatwhen airborne-particle abrasion wasperformed exclusively with Al2O3 parti-cles, the zirconia surface contained C,O, Al, and Zr. When zirconia was silicacoated, its surface exhibited C, O, Al,Si, and Zr.

The lack of statistically significantdifferences among the surface treat-ments observed for RelyX U100 (exceptfor 120 mm Al2O3 particlesþsilane) andfor Panavia F may be related to their

3 Scanning electron microscopic images (original magnification, �500) of airborne-particle abrasion conditions. A,50 mm Al2O3. B, 120 mm Al2O3. C, Rocatec Soft. D, 120 mm Al2O3þRocatec Plus. E, Rocatec Plus.

6 Volume - Issue -

formulation. The phosphoric acidmethacrylates of RelyX U100 and theMDP adhesive monomer of Panavia Fseem to have had a more significantrole than the other chemical reactionspreviously discussed for RelyX ARC.Some studies reported that these com-ponents have the ability to establishchemical bonds with metal oxides pre-sent on the zirconia surface and toprovide van der Waals forces orhydrogen bonds at the zirconia/resin

The Journal of Prosthetic Dentis

cement interface.23,30 Subası andInan17 also observed no significantdifference between airborne-particleabrasion with 110 mm Al2O3 particlesand silica coating with Cojet Sandfor Panavia F. Besides the chemicalbonds, the micromechanical retentionpromoted by airborne-particle abra-sion is essential for adequate bondstrength between zirconia and lutingcement. According to Yang et al,26 thesurface activation and cleaning effect of

try

airborne-particle abrasion are neededfor chemical bonding. RegardingRelyX Luting 2, the spontaneous fail-ures indicate its poor bonding capa-bility to zirconia, irrespective of thesurface treatments evaluated in thepresent study. Attia,15 by means of themicrotensile bond strength test, alsoobserved debonding of Ketac CemPlus (resin-modified glass ionomercement) after thermocycling for theairborne-particle abrasion with 50 mm

Sciasci et al

- 2014 7

Al2O3þCojet Sand, followed or not bythe silane ESPE Sil. This behavior wasexplained by the low mechanical prop-erties of Ketac Cem Plus, which makesit less resistant to aging conditions.Moreover, the author15 commentedthat the mismatch between the thermalexpansion coefficient of the materials(zirconia, luting agent, and compositeresin) could result in hoop stress duringthermocycling. Kim et al49 also ob-served that the resin-modified glassionomer cement Ionotite F yielded zeroSBS values after thermocycling. Ac-cording to Kim et al, although theHEMA monomer present in the for-mulation of the resin-modified glassionomer cements may participate inhydrogen bonding with the hydroxylgroups present on the zirconia surface,it is hydrophilic and tends to absorbwater, which may impair the bondof these cements to zirconia. Sabatiniet al43 found that for 50-mm-aluminaabraded zirconia, the resin-modifiedglass ionomer cement FujiCEM Auto-mix provided the lowest SBS value (4.4MPa) when compared with RelyX Uni-cem (16.6 MPa), Maxcem Elite (16.5MPa), and Multilink Automix (8.7MPa). Despite the poor performance ofresin-modified glass ionomer cementsin our study and in other reports,15,43,49

this behavior was observed for geo-metric specimens. In the case ofcrowns, in which there should be fric-tional retention, the bonding capabilityof these cements may be improved.

Regardless of the cement, no sig-nificant difference was found between50 mm and 120 mm Al2O3 particles orbetween Rocatec Soft (30 mm) andRocatec Plus (110 mm). According toOzcan et al,28 airborne-particle abra-sion with a larger particle size wouldproduce higher surface roughness,and hence higher micromechanicalretention. Taking this fact into consid-eration and also the different morpho-logical patterns observed in the presentstudy, SBS value differences were ex-pected but did not happen. However,some studies corroborate our re-sults.9,17,22,46,47 Phark et al9 and Val-entino et al22 found no statistical

Sciasci et al

difference regarding SBS between 50mm and 110 mm Al2O3 particles afterbonding Panavia F or Enforce to zirco-nia disks. Uo et al47 observed similarbehavior between 70 mm Al2O3 parti-cles and 125 mm SiC powder, andSubası and Inan17 between 110 mmAl2O3 particles and Cojet Sand (30mm). Concerning silica-coated Al2O3

particles, Amaral et al46 reported nosignificant difference in microtensilebond strength between Rocatec Soft andRocatec Plus when Panavia F wasbonded to In-Ceram Zirconia disks. Nostudies were found that compared theeffectiveness of Rocatec Plus combinedor not with previous airborne-particleabrasion with 110 mm Al2O3 particles,as recommended by the manufacturer.In the present study, this additional stepwas not necessary, irrespective of thecement used.

Comparison among the cements forthe groups abraded with Al2O3 parti-cles (50 mm and 120 mm) showedno significant difference. As previouslydiscussed, RelyX ARC does not containany adhesive monomer to establishchemical bonds with the zirconia sur-face. Therefore, to justify the lack ofstatistically significant difference of theRelyX ARC in comparison with RelyXU100 and Panavia F, we can highlightthe difference in viscosity of these ce-ments. Some authors reported thatRelyX ARC exhibits lower viscosity thanPanavia F, and consequently, it may bemore able to flow into the micropo-rosities of the abraded substrate.9,50

Another possible explanation is basedon the cohesive strength of these ce-ments. Pace et al10 observed that RelyXARC exhibited a significantly higherflexural strength compared with Pa-navia F. In the study of Piwowarczyket al,12 RelyX ARC presented higherflexural and compressive strengthswhen compared with RelyX Unicem(similar composition to RelyX U100).However, the lack of statistically sig-nificant difference observed betweenRelyX U100 and Panavia F (except forRocatec Plus) is probably due to theperformance of their acid phosphoricgroups/MDP adhesive monomer and to

the nonsignificant difference betweentheir cohesive strengths, as observed byJongsma et al.51 Therefore, despite theadhesive failures observed for the 3 ce-ments, the chemical bonding mecha-nism prevailed for RelyX U100 andPanavia F and the micromechanicalretention for RelyX ARC. Accordingto Attia,15 differences in chemical com-position, wetting capability, viscosity,and mechanical properties among thecements may influence their bondingcapacity to zirconia.

Within the groups abraded with thetribochemical systems, Panavia F per-formed less favorably than the othercements. In the groups bonded withPanavia F, 2 main chemical reactionscan occur: between the silane (ClearfilPorcelain Bond Activator) and sil-ica,16,35 which is as effective as theMDP/alumina reaction,34,42,46 and be-tween the MDP monomer (ClearfilSE Bond Primer and Panavia F) andsilica. Chen et al35 and Qeblawi et al8

observed significantly lower bondstrength at the interface silica-coatedzirconia/MDP monomer than theinterface silica-coated zirconia/silanerespectively when Panavia F and Multi-link resin cements were used. Passoset al41 obtained statistically higher SBSfor the association Cojet Sand (silica)/silane/Variolink II (does not containMDP) than for Cojet Sand/silane/Panavia F. The studies by Baldissaraet al21 and Piwowarczyk et al11 pointedto statistically higher SBS for RelyXUnicem than for Panavia F when Lavazirconia was silica-coated with CojetSand or Rocatec Plus. Another studyindicated a significant decrease in SBSvalues at the nickel-chromium alloy/RelyX ARC interface when tribochem-ical silica coating was followed by MDPinstead of silane.37 In contrast, somestudies show similar14,31 or even betterbehavior,16,27,42 indicating in this lattersituation that the association betweensilica coating and MDP monomercould be an advantageous method ofimproving bond strength. Given thesecontroversial results, this associationshould be used with caution. AlthoughPanavia F exhibited less favorable

8 Volume - Issue -

behavior in comparison with RelyXU100 and RelyX ARC, all cements pre-sented adhesive failures, indicating thatthe cohesive strength of these cementsovercame their adhesive capability.

Among the limitations of thepresent study, besides geometric speci-mens being used instead of crowns, thelong-term influence of water on thechemical reactions that occur at thezirconia/cement interface under cyclicfatigue loading was not evaluated.These aspects are essential to simulatethe clinical environment more closelyand to achieve more realistic resultsand a more accurate recommendationfor the surface treatments/luting ce-ments evaluated.

CONCLUSIONS

Within the limitations of this in vitrostudy, the following conclusions weredrawn:

1. The particle size did not influencethe SBS of the groups abraded exclu-sively with Al2O3 particles or silica-coated ones.

2. Although the cement did not in-fluence the SBS when abrasion wasperformed exclusively with Al2O3 parti-cles, RelyX ARC benefited the mostand Panavia F benefited the leastfrom the tribochemical silica-coatingsystems.

3. The pretreatment with Al2O3 par-ticles before Rocatec Plus, as recom-mended by the manufacturer, was notnecessary.

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Corresponding author:Dr Renata Garcia FonsecaDepartamento de Materiais Odontológicose PróteseFaculdade de Odontologia deAraraquara - UNESPRua Humaitá, n� 1680AraraquaraSão Paulo 14801-903BRAZILE-mail: renata@foar.unesp.br

Copyright ª 2014 by the Editorial Council forThe Journal of Prosthetic Dentistry.