Microtensile bond strength of a resin cement toglass infiltrated zirconia-reinforced ceramic:The effect of surface conditioning

Regina Amarala, Mutlu Ozcanc,*, Marco Antonio Bottinoa,Luiz Felipe Valandrob

aSao Paulo State University, Department of Dental Materials and Prosthodontics,Sao Jose dos Campos, BrazilbFederal University of Santa Maria, Department of Restorative Dentistry, Santa Maria, BrazilcFaculty of Medical Sciences, Department of Dentistry and Dental Hygiene,Antonius Deusinglaan, University of Groningen, Groningen, The Netherlands

Received 6 January 2005; accepted 7 April 2005

01do

KEYWORDSBond strength;Microtensile test;Silane coupling agent;Silica coating;Surface conditioningmethods;Zirconia ceramics

09-5641/$ - see front matter Q 200i:10.1016/j.dental.2005.04.021

* Corresponding author. Tel.:C31 50E-mail address: mutluozcan@hotm

Summary Objectives. This study evaluated the effect of three surface condition-ing methods on the microtensile bond strength of resin cement to a glass-infiltratedzirconia-reinforced alumina-based core ceramic.

Methods. Thirty blocks (5!5!4 mm) of In-Ceram Zirconia ceramics (In-CeramZirconia-INC-ZR, VITA) were fabricated according to the manufacturer’s instructionsand duplicated in resin composite. The specimens were polished and assigned to oneof the following three treatment conditions (nZ10): (1) Airborne particle abrasionwith 110 mm Al2O3 particles C silanization, (2) Silica coating with 110 mm SiOx

particles (Rocatec Pre and Plus, 3M ESPE) C silanization, (3) Silica coating with30 mm SiOx particles (CoJet, 3M ESPE) C silanization. The ceramic-composite blockswere cemented with the resin cement (Panavia F) and stored at 37 8C in distilledwater for 7 days prior to bond tests. The blocks were cut under coolant water toproduce bar specimens with a bonding area of approximately 0.6 mm2. The bondstrength tests were performed in a universal testing machine (cross-head speed:1 mm/min). The mean bond strengths of the specimens of each block werestatistically analyzed using ANOVA and Tukey’s test (a%0.05).

Results. Silica coating with silanization either using 110 mm SiOx or 30 mm SiOx

particles increased the bond strength of the resin cement (24.6G2.7 MPa and 26.7G2.4 MPa, respectively) to the zirconia-based ceramic significantly compared to thatof airborne particle abrasion with 110-mm Al2O3 (20.5G3.8 MPa) (ANOVA, P!0.05).

Dental Materials (2006) 22, 283–290

www.intl.elsevierhealth.com/journals/dema

5 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

363 8528; fax: C31 50 363 2696.ail.com (M. Ozcan).

R. Amaral et al.284

Significance. Conditioning the INC-ZR ceramic surfaces with silica coating andsilanization using either chairside or laboratory devices provided higher bondstrengths of the resin cement than with airborne particle abrasion using 110 mmAl2O3.Q 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Introduction

Etching the inner surfaces of ceramics with glassymatrix using hydrofluoric acid followed by theapplication of a silane coupling agent is an efficientconditioning method for bonding resin composite[1–6]. However neither etching with this agent noradding silane resulted in an adequate resin bond tosome new high-strength ceramics [7,8]. Particularlyhigh-alumina [9–12] or zirconia-reinforced ceramics[13,14] cannot be roughened by hydrofluoric acidetching since such ceramics do not contain a silicondioxide (silica) phase. Similarly, cement adhesionto glass-infiltrated zirconia–alumina ceramic(In-Ceram Zirconia-INC-ZR) is also not favorablesince this ceramic presents the same character-istics due to its high crystal content (aluminumoxide: G67 wt%; zirconium oxide: G13 wt%) andlimited vitreous phase (lanthanum aluminum sili-cate: G20 wt%) [15]. For this reason, specialconditioning systems are indicated for these typesof ceramics [16].

Previous investigations revealed that most clini-cal failures have initiated from the cementation orinternal surfaces. Failure rates due to high-strengthceramic fractures have been reported to rangebetween 2.3 and 8% [17–19]. Therefore, theintegrity of the luting cement to ceramic surfacesplays a major role in the longevity of the restorationand the failures originated from cementationsurfaces identified the need for a reliable con-ditioning method to strengthen this critical area.

Modern surface conditioning methods requireairborne particle abrasion of the surface beforebonding in order to achieve high bond strength. Onesuch system is silica coating. In this technique,the surfaces are air-abraded with aluminum oxideparticles modified with silisic acid [20,21]. Theblasting pressure results in the embedding of silicaparticles on the ceramic surface, rendering thesilica-modified surface chemically more reactive tothe resin through silane coupling agents. Silanemolecules, after being hydrolized to silanol, canform polysiloxane network or hyroxyl groups coverthe silica surface. Monomeric ends of the silanemolecules react with the methacrylate groups ofthe adhesive resins by free radical polymerization

process. When a ceramic exhibits chemical states ofsilicon and oxygen, then siloxane bond will beachieved as these represent the binding sites for thecoupling agent to the ceramic surface. Since silanecoupling agents do not bond well to alumina, thebond strengths of resin composite to such ceramicscould be affected [10].

Air-particle abrasion is a prerequisite for achiev-ing sufficient bond strength between the resins andhigh-strength ceramics that are reinforced eitherwith alumina or zirconia [22]. The air abrasionsystems rely on air-particle abrasion with differentparticle sizes ranging from 30 to 250 mm [16,23].The abrasive process removes loose contaminatedlayers and the roughened surface provides somedegree of mechanical interlocking or ‘keying’ withthe adhesive. It can be argued that the increasedroughness also forms a larger surface area for thebond. While these mechanisms explain some of thegeneral characteristics of adhesion to roughenedsurfaces, it may also introduce physico-chemicalchanges that affect surface energy and wettability.Such conditioning systems could be applied eitherat the laboratory or chairside, using large or smallsize particles. However, there is limited knowledgeas to whether micromechanical retention usinglarge or small particle size increase resin bond tohigh-strength ceramics of different microstructuresand chemical compositions.

A high and reliable resin bond to alumina andzirconia ceramics was also achieved with airborneparticle abrasion and by using a phosphate mono-mer (MDP) containing resin composite lutingcement. Although there are some studies on bondstrength of resin cements to the zirconium-basedceramics [24–26], to the authors’ knowledge, nostudy has investigated the bond strength ofphosphate-monomer based resin cement to zirco-nium-reinforced ceramics in combination withconditioning methods that rely on chairside con-ditioning systems.

The aim of this study, therefore, was to evaluatethe effect of three surface conditioning methodsbased on airborne particle abrasion, employingthree types of sand particles, on the microtensilebond strength of the resin cement to a glass-infiltrated zirconia-reinforced ceramic.

Bond strength of a resin cement to zirconia ceramic 285

Material and methods

Thirty blocks (5!5!4 mm) of zirconia-reinforcedalumina-based ceramics [In-Ceram Zirconia-INC-ZR(VITA Zahnfabrik, Bad Sackingen, Germany)] werefabricated according to the manufacturer’sinstructions. Ceramic surfaces were ground finishedup to 1200-grit silicon carbide abrasive (3M, St.Paul, USA) in a polishing machine (Labpol 8–12,Extec, USA) and cleaned for 10 min in an ultrasonicbath (Quantrex 90, L&R Ultrasonics, Kearny, NJ,USA) containing ethylacetate and air-dried. Eachceramic block was duplicated in composite resin(W3D-Master, Wilcos, Petropolis, RJ, Brazil) using amold made out of silicon impression material(Express, 3M/ESPE, St. Paul, USA). Compositeresin layers were incrementally condensed intothe mold to fill up the mold and each layer was lightpolymerized for 40 s (XL 3000-3M/ESPE, St. Paul,USA; light output: 500 mW/cm2). One compositeresin block was fabricated for each ceramic block.

Surface conditioning methods

Table 1 summarizes the three surface conditioningmethods, silane, ceramic and cement used for theexperiments. The ceramic blocks (10 blocks perconditioning) were assigned to one of the threefollowing treatment conditions:

Chairside Gritblasting (CGB): In this group, air-borne particle abrasion was performed using110 mm grain sized Al2O3 particles using an intraoralair abrasion device (Micro–Etcher, Danville Inc.,

Table 1 Characteristics of surface conditioning methodswith codes and manufacturing company names.

Conditioning principles,silane, ceramic, cement

Abbreviation Characteris

Chairside Gritblasting CGB 110 mm Al2O

Laboratory Silica CoatingGermany

LSC Rocatec Pretec Plus (11bars, 10 mm

Chairside Silica Coating CSC CoJetw-San10 mm, 20 s

Silane coupling agentGermany

3-methacrysilane in eth

CeramicIn-Ceram Zirconia INC-ZR Glass-infiltr

CementPanavia F Filler (78%),

cyldihydrogdimethacrylphotoinitiat

San Ramon, CA, USA) at a pressure of 2.8 bars froma distance of approx. 10 mm, for 20 s in circlingmovements.

Laboratory Silica Coating (LSC): Silica coatingprocess was conducted using a laboratory type ofair abrasion device (Rocatector Delta device, 3MESPE) in which the specimens were first conditionedby air-abrasion with 110 mm grain sized Al2O3

particles at a pressure of 2.8 bars with RocatecPre abrasive. Then the specimens were air-abradedwith Rocatec Plus abrasive, which was 110 mm grainsized SiOx, at 2.8 bars under the same conditionswith CGB.

Chairside Silica Coating (CSC): Silica coatingprocess was achieved using an intraoral air abrasiondevice (Micro–Etcher, Danville Inc., San Ramon, CA,USA) filled with CoJetw-Sand (30 mm SiOx particles)(3M-ESPE, Minnesota, USA) under the same con-ditions with CGB.

Following all three surface conditioningmethods, the remnants of sand particles weregently air blown, silane coupling agent (ESPEw-Sil,3M ESPE AG, Seefeld, Germany) was applied andwaited for its evaporation for 5 min.

Topographic analyses of conditionedceramic surface

Additional ceramic specimens were conditionedusing the three surface conditioning methods inorder to observe the topographic surface changesunder the Scanning Electron Microscope (SEM)(JEOL-JSM-T330A, Jeol Ltd, Tokyo, Japan).

, silane, ceramic and cement used for the experiments

tics Manufacturer

3, (2.8 bars, 10 mm, 20 s) Korox, Bego, Bremen,Germany

(110 mm Al2O3)C Roca-0 mm SiOx) (both at 2.8, 20 s)

3M ESPE AG, Seefeld,

d (30 mm SiOx) (2.8 bars,)

3M-ESPE, Minnesota, USA

loxyprophyltrimethoxyanol (ESPEw-Sil) (5 min)

3M ESPE AG, Seefeld,

ated zirconia Vita Zahnfabrik, BadSaeckingen, Germany

10-Methacryloyloxyde-enphosphate (MDP),ates, chemical andors

Kuraray, Okayama, Japan

Figure 1 (a) Cutting procedure to obtain slices ofcemented ceramic and composite blocks with ca 0.8 mmthickness (3 slices per block); (b) The slices rotated 908and bonded onto the metal base again for further cuttingprocedures (0.8 mm-thickness) in order to obtain non-trimmed bar specimens with ca 8 mm in length and0.6 mm2 adhesive surface area.

R. Amaral et al.286

Bonding procedure and specimenpreparation

Each conditioned ceramic block was bonded to acomposite block under the load of 750 g using aresin cement system (Panavia F, Kuraray CO.,Okayama, Japan). The excess resin cement wasremoved by means of a brush. The resin cement wasthen light polymerized (XL 3000) for 40 s from eachdirection. Oxyguard was applied on the cementlayer for 10 min. The blocks were washed with air-water spray and stored in distilled water at 37 8C for7 days prior to bond tests.

The blocks were then bonded with cyanoacrylateglue (Super Bonder Gel, Loctite Ltd, Sao Paulo,Brazil) to a metal base that was coupled to a cuttingmachine. Slices were obtained using a slow-speeddiamond wheel saw (KG Sorensen, Barueri, Brazil)under cooling. The peripheral slices were disre-garded in case the results could be influenced byeither the excess or insufficient amount of resincement at the interface. Three slices (0.8G0.1 mmin thickness) were obtained per block initially. Theslices were rotated 908 and bonded onto the metalbase again. The peripheral bar specimens were alsodisregarded for the same reasons described above.Other 3 sectioning were carried out. (Fig. 1(a)-(b)).Twelve non-trimmed bar specimens (withapproximately 8 mm in length and 0.6G0.1 mm2

adhesive surface area) were obtained per block(Fig. 2(a)-(c)).

Microtensile bond strength test

The bar specimens were glued parallel to the longaxis of an adapted caliper using cyanoacrylateglue. This apparatus was coupled to the universaltesting machine (EMIC DL-1000, EMIC, Sao Josedos Pinhais, Brazil) and the specimens wereloaded in tension to failure at a crosshead speedof 1 mm minK1.

Bond strength values were calculated using theformula, sZL/A, where ‘L’ is the load at failure(Kgf) and ‘A’ is the adhesive area (mm2) measuredusing a digital caliper (Mitutoyo, Tokyo, Japan)prior to the tests.

Statistical analysis

Statistical analysis was performed using Statistics8.0 for Windows (Analytical Software Inc, Talla-hassee, FL, USA). The means of the specimens ofeach blocks were obtained and these values(nZ10) were analyzed by 1-way analysis ofvariance (ANOVA) and Tukey’s test (aZ05) in

order to determine the significant differencesbetween surface conditioning methods. P valuesless than 0.05 are considered to be statisticallysignificant in all tests.

Results

The results of the microtensile bond strength testsfor three surface conditioning methods are pre-sented in Table 2.

Silica coating with silanization either with110 mm SiOx particles or 30 mm SiOx revealedsignificantly higher bond strengths of the resincement (24.6G2.6 MPa and 26.7G2.4 MPa,respectively) to the INC-ZR ceramic compared tothat of airborne particle abrasion with 110-mmAl2O3 (20.5G3.8 MPa) (ANOVA, PZ0.0004). Therewere no significant differences between both silicacoating groups (PO0.05)

SEM analysis at !2000 magnification, comp-lementary to the bond strength tests, revealedthat all three types of sand particles penetrated thesubstrate surfaces and the ceramic surfaces werecovered with abundant sand particles even after airblowing (Fig. 3(a)–(c)).

tested

not tested

(c)

*Adhesive zone

*

(b)

Resincomposite

ResinCement

Ceramic

(a)

Figure 2 (a) Protocol of specimen choice according to cutting procedure (tested-and non-tested regions); (b) Barspecimens with ca 8 mm in length and 0.6G0.1 mm2 bonded surface area; (c) Bonded zone (*) between the ceramic andcomposite block at the bar specimen.

Table 2 Microtensile bond strength (MPa) of theresin luting cement, and statistical differences con-sidering the surface conditioning factor after (a)Airborne particle abrasion with 110 mm Al2O3 particles,(b) Silica coating with 110 mm Al2O3 and 110-mm SiOx

particles, (c) Silica coating with 30 mm SiOx particles.

Groups s* (MPa) (SD)

1-INC ZIRC-CGB 20.5a (3.8)2-INC ZIRC-LSC 24.6b (2.7)3-INC ZIRC-CSC 26.7b (2,4)

For abbreviations, see Table 1. Different superscriptedletters indicate significant differences between the cer-amic-surface conditioning combinations (P!0.05). SD, stan-dard deviation.

Bond strength of a resin cement to zirconia ceramic 287

Discussion

In this study, roughening the zirconia-reinforcedceramic surfaces with air particle abrasion andapplying silane prior to cementation provided highbond strengths and silica coating followed bysilanization evidently enhanced the bond betweenthe luting cement and the ceramic surfaces. Thesilica layer left by silica coating on the ceramicsurface provides a basis for silane to react. In theceramic-resin bond, silane functions as a couplingagent, which adsorbs onto and alters the surface ofthe ceramic, thereby facilitating chemical inter-action [11,23].

When alumina or zirconia ceramics are glassinfiltrated, they are melted together at hightemperatures to form a ceramic composite. Thechemical components of the ceramics (traces suchas Li2O, Na2O, K2O, CaO, MgO) are then bonded toeach other by strong covalent bonds with hydroxylgroups at the surface of the ceramic material [27].When the surface is air abraded, this wouldgenerate more hydroxyl groups on the surface andalso enhance the micro-mechanical retention.Furthermore, the methoxy groups of silane wouldreact with water to form silanol groups that in turn,will react with the surface hydroxyl groups to formsiloxane network. Amphoteric alumina in theceramic matrix could form chemical adhesion,covalent bridges, through its surface hydroxylgroups with hydrolyzed silanol groups of the silane:–Al–O–Si–[10].

In principle, the presence of the glassy phase inceramics favors better siloxane bonds. The silanolgroups could then react further to form a siloxane(–Si–O–Si–O–) network with the silica on the surface.The In-Ceram ceramic system tested in this study,In-Ceram Zirconia (INC-ZR), is glass infiltrated. Mostprobably the glass infiltration facilitated better

silane bonding and therefore increased bondstrength values were obtained for this ceramic.These findings are in compliance with the study ofOzcan and Vallittu [10], even though a differentexperimental set up was used where a bis-GMAbased resin cement and shear bond test wereemployed.

Material selection and clinical recommendationson resin bonding are based on mechanical labora-tory tests that show great variability in materialsand methods. One of the most common testing-method is the shear bond test. However the specificfracture pattern in shear testing may causecohesive failure in the substrate that may lead toerraneous interpretation of the data while inmicrotensile tests, stress distribution was reportedto be more homogeneous [28–31]. Although, for thisreason, microtensile test was employed in thisstudy, similar ceramic-cement performance wasobserved in dry conditions in the study of Ozcan andVallittu [10].

Some studies, on the other hand, have evaluatedceramics with different microstructures, reporting

Figure 3 (a) Typical SEM micrographs (!2000) of conditioned ceramic surfaces for a-Airborne particle abrasion with110 mm Al2O3 particles, (b) Silica coating with 110 mm SiOx particles, c-Silica coating with 30 mm SiOx particles. Note thatafter all three conditioning methods, ceramic surfaces were covered with abundant sand particles.

R. Amaral et al.288

that high-strength ceramics are compact materialsmaking them difficult to gritblast [13,22]. Interest-ingly, the results of this study indicate that thesilica coating system with small particle size of30 mm SiOx particles as well as large particle size of110 mm SiOx produced statistically higher meanbond strength values than with chairside gritblasting using 110-mm grain sized Al2O3 particles.One can expect higher surface roughness createdusing bigger particle size thereby higher micro-mechanical retention but this was not achieved inthis study. One reason for this could be associatedwith the phenomenon of less wettability andcontact angle [13,32] between the silane couplingagent and the deep grooves on the ceramic surfacesoccurred after grit blasting. However thisassumption could not be verified for the applicationof 110 mm SiOx. The reason for this can beexplained on the grounds that particle depositionmechanisms differ depending on the substratecharacteristics, particle composition, sizedistribution, quantity and morphology. AlthoughSEM images demonstrated comparable views withagglomerates of sand particles, it is difficult todeduce whether the sand is in contact with thealumina or the glass phase of the ceramic testedin this study. Nevertheless, the results of thisstudy together with some other studies revealgood adhesion of silica particles in the vitreousphases of the glass-infiltrated zirconia ceramics

[33–36]. In a previous study, a significant increaseof silica on the surface of the In-Ceram ceramic(15.8–19.7 wt%) was detected after blasting withRocatec-Plus (SiOx) when compared with thesamples blasted only with Rocatec-Pre (Al2O3

particles) suggesting better bond strength betweenthe In-Ceram ceramic and the resin cements due tothe increase of silica content and the interactionwith the silane agent. Our ongoing studies involveEnergy Dispersive X-ray Spectroscopy (EDS) analysisto gain more insight on the interaction betweenthese three sand particles and the ceramiccomposites [37].

The other reason for lower results obtained after110 mm grain sized Al2O3 particle deposition couldbe due to the weak bond between Al–Si–O asreported earlier elsewhere [10].

Although satisfactory bond strength values ofresin cement to high-strength ceramics are yet tobe determined for clinically successfulperformance, the bond values obtained for theceramic tested in this study could be consideredsufficient with both conditioning methods. Inclinical applications however, when air abrasionwill be contemplated by chairside, cliniciansshould also consider the possible material loss[9] especially at the margins of the restorationsthat may lead to ditching when bigger grain sizeparticles are used during airborne particleabrasion.

Bond strength of a resin cement to zirconia ceramic 289

Bonding of ceramic to tooth substance is basedon the adhesion of luting cement and its bondingresin to the ceramic substrate together with theadhesion of luting cement to enamel and dentine.Future studies should also concentrate on theinvolvement of the tooth tissues in the testcomplex.

The cement–ceramic adhesion is susceptible tochemical, thermal and mechanical influences underintraoral conditions. One limitation of this studycould be the lack of thermocycling although thereare controversial reports on the effect of thermo-cycling in the literature [16].

Some earlier studies reported high and stablebond strength to the zirconia reinforced ceramicafter airborne particle abrasion using Al2O3

particles in combination with phosphate monomerbased resin cement [24–26]. Comparing the resultsof these studies with this present study, it can besuggested that the silica coating and silanizationmay allow a better bond strength to the zirconiumwith this resin cement.

The general outcome of this study suggeststhat relatively recent surface conditioning tech-niques based on the combination of micromecha-nical and chemical conditioning should beconsidered for improved adhesion of resincements to glass-infiltrated zirconia ceramics.More importantly, these methods seem to offsetthe importance of the varieties of the substratesand therefore could be applicable to a widerange of high-strength ceramics [31]. The equip-ments to apply these techniques were sophisti-cated and expensive during the last two decadesbut they are recently simplified and brought tothe chairside. By employing chairside devices forairborne particle abrasion, contamination duringdelivery of the restoration from the laboratory tochairside could also be avoided. As long as theavailable conditioning methods will not beoptimized, the development in the high-strengthceramic field is expected to continue experien-cing failures.

Conclusions

Silica coating either with 110 mm SiOx particles or30 mm SiOx followed by silanization increased thebond strength of the phosphate monomer-basedresin cement to glass infiltrated zirconia-reinforced ceramic when compared with airborneparticle abrasion using 110 mm Al2O3 andsilanization.

Acknowledgements

We express our appreciation to the Wilcos Ltd inBrazil (Petropolis/RJ, Brazil) and VITA Zahnfabrik(Bad Sackingen, Germany) for providing some ofthe materials used in this study. We also thankProf. Dr. Ivan Balducci, School of Dentistry, SaoPaulo State University at Sao Jose dos Campos,Brazil, for his assistance with statistical analysis.

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