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Vol 15, No 3, 2013 207

Effect of Surface Conditioning Modalities on the

Repair Bond Strength of Resin Composite to the

Zirconia Core / Veneering Ceramic Complex

Mutlu Özcana / Luiz Felipe Valandrob / Sarina Maciel Braga Pereirac / Regina Amaralc /Marco Antonio Bottinod / Gurel Pekkane

Purpose: This study evaluated the effect of different surface conditioning protocols on the repair strength ofresin composite to the zirconia core / veneering ceramic complex, simulating the clinical chipping phenomenon.

Materials and Methods: Forty disk-shaped zirconia core (Lava Zirconia, 3M ESPE) (diameter: 3 mm) specimenswere veneered circumferentially with a feldspathic veneering ceramic (VM7, Vita Zahnfabrik) (thickness: 2 mm)using a split metal mold. They were then embedded in autopolymerizing acrylic with the bonding surfaces ex-

posed. Specimens were randomly assigned to one of the following surface conditioning protocols (n = 10 pergroup): group 1, veneer: 4% hydrofluoric acid (HF) (Porcelain Etch) + core: aluminum trioxide (50-μm Al2O3) +core + veneer: silane (ESPE-Sil); group 2: core: Al2O3 (50 μm) + veneer: HF + core + veneer: silane; group 3: ve-neer: HF + core: 30 μm aluminum trioxide particles coated with silica (30 μm SiO2) + core + veneer: silane; group4: core: 30 μm SiO2 + veneer: HF + core + veneer: silane. Core and veneer ceramic were conditioned individuallybut no attempt was made to avoid cross contamination of conditioning, simulating the clinical intraoral repairsituation. Adhesive resin (VisioBond) was applied to both the core and the veneer ceramic, and resin composite(Quadrant Posterior) was bonded onto both substrates using polyethylene molds and photopolymerized. Afterthermocycling (6000 cycles, 5°C–55ºC), the specimens were subjected to shear bond testing using a universaltesting machine (1 mm/min). Failure modes were identified using an optical microscope, and scanning electronmicroscope images were obtained. Bond strength data (MPa) were analyzed statistically using the non-parametricKruskal-Wallis test followed by the Wilcoxon rank-sum test and the Bonferroni Holm correction ( = 0.05).

Results: Group 3 demonstrated significantly higher values (MPa) (8.6 ± 2.7) than those of the other groups

(3.2 ± 3.1, 3.2 ± 3, and 3.1 ± 3.5 for groups 1, 2, and 4, respectively) (p < 0.001). All groups showed exclu-sively adhesive failure between the repair resin and the core zirconia. The incidence of cohesive failure in theceramic was highest in group 3 (8 out of 10) compared to the other groups (0/10, 2/10, and 2/10, in groups1, 2, and 4, respectively). SEM images showed that air abrasion on the zirconia core only also impinged on theveneering ceramic where the etching pattern was affected.

Conclusion: Etching the veneer ceramic with HF gel and silica coating of the zirconia core followed by silanizationof both substrates could be advised for the repair of the zirconia core / veneering ceramic complex.

Keywords: adhesion, all-ceramics, bond strength, chipping, composite resin, repair, surface conditioning, zirconia.

J Adhes Dent 2013; 15: 207–210. Submitted for publication: 27.12.12; accepted for publication: 19.03.13doi: 10.3290/j.jad.a29717

a Professor, University of Zurich, Dental Materials Unit, Center for Dental andOral Medicine, Clinic for Fixed and Removable Prosthodontics and DentalMaterials Science, Zurich, Switzerland. Designed the study, analyzed data,wrote manuscript, discussed results and commented on manuscript at all

stages.

b Associate Professor, Department of Restorative Dentistry, Division of Prosth-odontics, Federal University of Santa Maria, Santa Maria, Brazil. Performedthe experiments, discussed results and commented on manuscript at all

stages.

c Research Fellow, Department of Dental Materials and Prosthodontics, SãoPaulo State University at São Jose dos Campos, Brazil. Performed the experi-ments, discussed results and commented on manuscript at all stages.

d Professor, Department of Dental Materials and Prosthodontics, São PauloState University at São Jose dos Campos, Brazil. Proofread manuscript, dis-cussed results and commented on manuscript at all stages.

e Associate Professor, Department of Prosthodontics, Faculty of Dentistry,Dumlupinar University, Kutahya, Turkey. Performed the experiments, dis-cussed results and commented on manuscript at all stages.

Correspondence:

Prof. Dr. med. dent. Mutlu Özcan, University of Zürich, Den-tal Materials Unit, Center for Dental and Oral Medicine, Clinic for Fixed andRemovable Prosthodontics and Dental Materials Science, Plattenstrasse 11,CH-8032, Zürich, Switzerland. Tel: +41-44-63-45600, Fax: +41-44-63-44305.e-mail: [email protected]



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Özcan et al

The clinical indication of fixed dental prostheses(FDPs) made of a zirconia framework veneered with

a glassy matrix ceramic has increased over the last de-cade due to the improved implementation of CAD/CAMprocedures in dentistry. However, almost all clinicalstudies to date have reported chipping of veneering ce-ramic at varying rates regardless of the type of veneer-

ing ceramic used.13

Undertaking repair actions in casesof chipping, using surface conditioning methods andadhesion promoters, may prolong the survival of suchfailed FDPs, depending on the size of the defect.11

Etching with hydrofluoric acid gel followed by silaniza-tion is a well-established conditioning method to promoteadhesion of resin-based materials to feldspathic, leucite,and lithium disilicate ceramics.1,3 In contrast, denselysintered all-ceramics such as zirconia and alumina areresistant to acid etching. Etching such ceramics doesnot promote significant topographical changes that wouldachieve proper micromechanical bonding of resin materi-als.14 In order to optimize adhesion, air-borne particleabrasion of acid resistant ceramics with either aluminum

oxide (Al2O3) or tribochemical silica coating methods fol-lowed by silanization are suggested.12 Silane couplingagents improve wettability and promote covalent bonding,enhancing the chemical adhesion between the ceram-ics and resin composite.8 Thus, in a chipping scenarioof a zirconia FDP veneered with glass ceramic, differentconditioning methods are indicated for the two differentceramic substrates. It can be anticipated that especiallywhen the zirconia framework is exposed, achieving dura-ble repair may be more challenging. Furthermore, surfaceconditioning methods employed for each ceramic typemay cross contaminate one another. The question thenarises as to what the best clinical conditioning strategy

for repairing the zirconia core/veneering ceramic complexmay be. A recent review of the intraoral repair of veneeringporcelain chipping of FDPs7 indicated a limited number ofstudies dealing with silicate/oxide/metal alloy combinedsurfaces.2,4,5,9,10 According to this review and the au-thors’ best knowledge, there is one study on the fatigueresistance of repaired zirconia crowns2 and none on therepair bond strength of resin materials on the zirconia /veneer ceramic complex to date.

The objectives of this study were thus to determine themost effective surface conditioning protocol for the repairstrength of a resin composite to the zirconia core / veneer-ing ceramic complex and to identify the failure modes. The

null hypothesis tested was that different surface condi-tioning methods would not affect the repair bond strength.

MATERIALS AND METHODS

Disk-shaped zirconia (Lava Zirconia, 3M ESPE; Seefeld,Germany) (Ø: 3 mm) specimens were veneered circum-ferentially (thickness: 2 mm) with a feldspathic ceramic(VM7, Vita Zahnfabrik; Bad Säckingen, Germany) usinga split metal mold. The mold allowed the zirconia coreceramic disk to be positioned exactly in the middle ofthe mold, leaving circular space around the core for the

veneering ceramic that was applied in two stages dueto the shrinkage after firing. Procedures for firing wereperformed according to the veneering ceramic manufac-turer’s instructions.

The specimens were then embedded in autopolymer-izing acrylic with the bonding surfaces exposed. All speci-mens were wet ground down to 1200-grit silicon carbide

paper (SiC) (Struers; Willich, Germany) for 5 min. Thespecimens were ultrasonically cleaned in distilled waterfor 10 min, dried, and randomly assigned to one of thefollowing surface conditioning protocols (N = 40, n = 10per group).

Group 1: First, the veneering ceramic was etched with4% hydrofluoric acid (HF) (Porcelain Etch, Ultradent Prod-ucts; South Jordan, UT, USA) for 90 s, rinsed with air-wa-ter spray, and dried. Then, the zirconia core was air-borneparticle abraded using an intraoral air-abrasion device(Microetcher, Danville Engineering; San Ramon, CA, USA)with 50-µm Al2O3 (Korox, Bego; Bremen, Germany) per-pendicular to the surface from a distance of approximately10 mm for 20 s in circling motions at 2.8 bar. After air

abrasion, the remnants of the sand particles were gentlyair blown for 20 s.

Group 2: First, the zirconia core was air abraded; thenthe veneering ceramic was HF etched as described ingroup 1. The nozzle of the air-abrasion device was aimedat the zirconia core material. During this process, theveneering ceramic was not protected.

Group 3: First, the veneering ceramic was HF etched;then the zirconia core was air abraded as described ingroup 1. In this group, instead of ordinary alumina par-ticles, 30-µm alumina particles coated with silica (SiO2)were used (CoJet Sand, 3M ESPE).

Group 4: First, the zirconia core and then the veneering

ceramic was conditioned as described in group 3.Core and veneering ceramic were conditioned individu-

ally, but no attempt was made to avoid cross contamina-tion of either conditioning method. This simulates theclinical intraoral situation.

All specimens received one coat of silane couplingagent (ESPE-Sil, 3M ESPE) which was left to sit for 5 minto allow the condensation reaction of the silane. Sub-sequently, one coat of adhesive resin (VisioBond, 3MESPE) was applied to both the core and the veneer with amicrobrush, air thinned, and photopolymerized (800 mW/cm2) for 40 s using a photopolymerization unit (DemetronLC, SDS Kerr; Orange, CA, USA). Resin composite (Quad-

rant Posterior, Cavex Holland BV; Haarlem, Netherlands)was then bonded onto both substrates using polyethylenemolds (inner diameter: 4.9 mm; height: 3 mm) and pho-topolymerized from the top for 40 s.

The specimens were then thermocycled for 6000 cy-cles (5°C–55ºC, dwell time 30 s, transfer time 5 s).6 Spontaneous debondings during thermocycling were as-signed a value of 0 MPa.

Specimens were mounted in the jig of the universaltesting machine (Zwick ROELL Z2.5 MA 18-1-3/7; Ulm,Germany) and a blade applied the shear force to thebonded interface at a crosshead speed of 1 mm/minuntil failure.



Vol 15, No 3, 2013 209

Özcan et al

Failure modes were identified using an optical micro-scope (Stemi 2000-C, Carl Zeiss; Göttingen, Germany)at 100X magnification. SEM (JSM-5500, JEOL; Tokyo,Japan) images (75X) were obtained of representative fail-ure types. Failure types were categorized as follows: a) ad-hesive failure between the repair composite and/or corezirconia or veneering ceramic (ADHES); b) cohesive failure

of the repair composite covering core zirconia and/or ve-neering ceramic only (COHES-com); c) cohesive failure ofcore zirconia and/or veneering ceramic only (COHES-cer);cohesive failure of the veneering ceramic and repair com-posite (MIX).

The data were not normally distributed according tothe Kolmogorov-Smirnov test ( = 0.05). Accordingly,non-parametric analysis (Kruskal-Wallis test) was carriedout to determine the significant differences between thegroups. Multiple pairwise comparisons of the groups weremade using the Wilcoxon rank-sum test for independentsamples. Significance levels were adjusted using the Bon-ferroni Holm correction for multiple testing.

RESULTS

The surface conditioning protocol significantly affectedthe results (p < 0.05). Spontaneous debondings oc-curred in groups 1 (5), 2 (4), and 4 (4). Group 3 dem-onstrated significantly higher values (MPa) (8.6 ± 2.7)than those of other groups (3.2 ± 3.1, 3.2 ± 3,and 3.1 ± 3.5 for groups 1, 2, and 4, respectively)(p < 0.001) (Fig 1). Groups 1, 2, and 4 did not show sig-nificant differences (p > 0.05).

All groups showed exclusively adhesive failure betweenthe repair resin and the core zirconia. The incidence of

cohesive failure in the ceramic was the highest in group 3(8 out of 10) compared to the other groups (0/10, 2/10,2/10, in groups 1, 2, and 4, respectively) (Table 1, Fig 2).

SEM images showed microporosities of veneering cer-amic after HF etching due to glassy matrix dissolution(Fig 3a), but after silica coating of the zirconia core, theveneering ceramic also received silica, and the topogra-phy was affected compared to etching only (Fig 3b).

DISCUSSION

Since hydrofluoric acid etching of the veneering ceramicand silica coating of the zirconia core (group 3) pre-sented significantly higher repair bond strength valuesthat those of the other groups, the null hypotheses wasrejected. Only this group had no spontaneous debond-ings. Similarly, the lack of adhesive failures in theveneering ceramic and a higher incidence of cohesiveveneering ceramic failures indicates more reliable re-sults with this protocol. Hydrolytic degradation of Al-O-Sicompared to Si-O-Si has been previously reported.12

This can explain the spontaneous debondings duringthermocycling (ie, automatic adhesive failures) experi-enced in the alumina-treated groups combined with HFtreatment (groups 1 and 2). SEM findings also revealedthat the favorable etching pattern was influenced whenthe sequence of veneer and core conditioning waschanged so that silica coating was applied after etchingthe veneer. However, it must be noted that polishing the

Repair Bond Strength (MPa)

Group 1A Group 2A Group 3B Group 4A

12

10

8

6

4

2

0

Fig 1 Means and standard deviations of the repair bondstrength (MPa) of resin composite to the zirconia core / ve-neering ceramic core complex after 4 surface conditioning pro-tocols. Same superscript letters indicate statistical similarity.

Table 1 Distribution of the frequencies of failure types for experimental groups (n = 10)

Type of failure*

Zirconia core Veneering ceramic

Group ADHES COHES-com COHES-cer MIX ADHES COHES-com COHES-cer MIX

1 10 0 0 0 5 5 0 0

2 10 0 0 0 4 4 2 3

3 10 0 0 0 0 2 8 5

4 10 0 0 0 4 4 2 0

ADHES: adhesive failure between the repair composite and/or core zirconia or veneering ceramic; COHES-com: cohesive failure of the repair composite cov-ering core zirconia and/or veneering ceramic only; COHES-cer: cohesive failure of core zirconia and/or veneering ceramic only; MIX: cohesive failure of theveneering ceramic and repair composite.



210 The Journal of Adhesive Dentistry

Özcan et al

core / veneer complex prior to any surface conditioning

method was performed simultaneously using SiC paperfor 5 min. Although no surface roughness measure-ments were made on either substrate ceramic, varia-tion in the degree of roughness in both substrates canbe anticipated. But again, this represents the typicalclinical repair situation where the surfaces of both sub-strates are roughened at the same time for the sameduration before a repair resin is applied onto core andveneer ceramics. Thus, baseline roughness of one ofthe substrates may be higher than the other. Whetherbaseline roughness plays a role after HF etching or airabrasion needs to be further investigated.

In this study, 6000 thermocycles were performed in

order to age the resin/ceramic interface, which is slightlyabove the recommended number of cycles (5000) accord-ing to the ISO norm for testing metal-resin adhesion.6 However, a prolonged duration of aging could have moredetrimental effects on the results.

On the whole, the results cannot be considered highfor the zirconia / veneer complex. Consequently, surfaceconditioning methods that yield more reliable adhesion onzirconia core have potential for development, where reli-able adhesion to the zirconia / veneer complex is desired.

CONCLUSIONS

Etching the veneering ceramic with hydrofluoric acid gelfor 90 s, silica coating the zirconia core, followed by si-lane and adhesive resin application on both substratesresulted in the highest repair strength of the resin com-posite to zirconia core / veneering ceramic complex.

Cohesive failure of the veneering ceramic, indicatingreliable adhesion, was observed more frequently whenthe veneering ceramic was etched before the zirconiacore was silica coated. In all groups, exclusively adhe-sive failures between the resin composite and zirconiaindicate the weakest link exists between these two ma-terials.

REFERENCES

1. Aida M, Hayakawa T, Mizukawa K. Adhesion of composite to porcelainwith various surface conditions. J Prosthet Dent 1995;73:464-470.

2. Attia A. Bond strength of three luting agents to zirconia ceramic –influence of surface treatment and thermocycling. J Appl Oral Sci2011;19:388-395.

3. Brentel AS, Özcan M, Valandro LF, Alarça LG, Amaral R, Bottino MA.Microtensile bond strength of a resin cement to feldpathic ceramic afterdifferent etching and silanization regimens in dry and aged conditions.Dent Mater 2007;23:1323-1331.

4. Chung KH, Hwang YC. Bonding strengths of porcelain repair systemswith various surface treatments. J Prosthet Dent 1997;78:267-274.

5. Frankenberger R, Krämer N, Sindel J. Repair strength of etched vssilica-coated metal-ceramic and all-ceramic restorations. Oper Dent2000;25:209-215.

6. International Organization for Standardization. Dentistry- polymer-basedcrown and bridge materials. Amendment; 1996. [ISO 10477].

7. Kimmich M, Stappert CF. Intraoral treatment of veneering porcelainchipping of fixed dental restorations: a review and clinical application. JAm Dent Assoc 2013;144:31-44.

8. Matinlinna JP, Lassila LV, Özcan M, Yli-Urpo A, Vallittu PK. An introduc-tion to silanes and their clinical applications in dentistry. Int J Prostho-dont 2004;17:155-164.

9. Sun R, Suansuwan N, Kilpatrick N, Swain M. Characterisation of tri-bochemically assisted bonding of composite resin to porcelain andmetal. J Dent 2000;28:441-445.

10. Özcan M, Niedermeier W. Clinical study on the reasons for and locationof failures of metal-ceramic restorations and survival of repairs. Int JProsthodont 2002;15:299-302.

11. Özcan M. Evaluation of alternative intra-oral repair techniques forfractured ceramic-fused-to-metal restorations. J Oral Rehabil 2003;30:194-203.

12. Özcan M, Vallittu PK. Effect of surface conditioning methods on the bondstrength of luting cement to ceramics. Dent Mater 2003;19:725-731.

13. Raigrodski AJ, Hillstead MB, Meng GK, Chung KH. Survival and compli-cations of zirconia-based fixed dental prostheses: a systematic review.J Prosthet Dent 2012;107:170-177.

14. Valandro LF, Özcan M, Bottino MC, Bottino MA, Scotti R, Bona AD. Bondstrength of a resin cement to high-alumina and zirconia-reinforced ceram-ics: the effect of surface conditioning. J Adhes Dent 2006;8:175-181.

Fig 2 Representative images of a) adhesive failure betweenthe repair composite and/or core zirconia or veneering ceramic(ADHES). Note that there was no remnant of repair compos-ite on either substrate. b) Cohesive failure of the veneeringceramic and repair composite (MIX). *cohesive failure of thecomposite; cohesive failure of the veneering ceramic. C:zirconia core; V: veneering ceramic.

Fig 3 Typical SEM images (75X) of zirconia core (C) andveneering ceramic (V). a) After hydrofluoric acid etching only.Note the microporosities after glassy matrix dissolution. b)After hydrofluoric acid etching of V and silica coating of C. Notethat the veneering ceramic also received silica, and the topog-raphy changed compared to etching only.

Clinical relevance: Repair of chipping of the zirconiacore / veneering ceramic complex can best be achievedby first conditioning the veneering ceramic with hydroflu-oric acid, followed by silica coating of the zirconia coreceramic. Subsequently, silane and adhesive resin needto be applied on both ceramic substrates.

aa bb

C

V

C

V*

C

V

C

V



C o p y r i g h t o f J o u r n a l o f A d h e s i v e D e n t i s t r y i s t h e p r o p e r t y o f Q u i n t e s s e n c e P u b l i s h i n g

C o m p a n y I n c . a n d i t s c o n t e n t m a y n o t b e c o p i e d o r e m a i l e d t o m u l t i p l e s i t e s o r p o s t e d t o a

l i s t s e r v w i t h o u t t h e c o p y r i g h t h o l d e r ' s e x p r e s s w r i t t e n p e r m i s s i o n . H o w e v e r , u s e r s m a y p r i n t ,

d o w n l o a d , o r e m a i l a r t i c l e s f o r i n d i v i d u a l u s e .

effect of surface conditioning modalities on the

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