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d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 207–213

avai lab le at www.sc iencedi rec t .com

journa l homepage: www. int l .e lsev ierhea l th .com/ journa ls /dema

nfluence of surface conditioning and cleaning methods onesin bonding to zirconia ceramic�

hmed Attiaa,∗, Frank Lehmannb, Matthias Kernb

Department of Conservative Dentistry and Fixed Prosthodontics, Faculty of Dentistry, Mansoura University, Mansoura, EgyptDepartment of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts University at Kiel, Germany

r t i c l e i n f o

rticle history:

eceived 8 August 2009

eceived in revised form 1 June 2010

ccepted 14 October 2010

eywords:

irconia ceramic

eramic primer

leaning method

ensile bond strength

a b s t r a c t

Objectives. The purpose of this laboratory study was to evaluate the influence of different

surface conditioning, new ceramic primers and cleaning methods on the bond strength of

luting resin to zirconia ceramic (e.max ZirCAD).

Methods. A total of 96 zirconia ceramic discs were divided into six groups (n = 16) according to

surface conditioning, cleaning methods and ceramic primers. Zirconia ceramic discs were

either air-abraded with 110 �m alumina particles or tribochemically silica-coated (Rocatec).

Visible dust resulting from air-borne particle abrasion or silica coating was removed either

by oil-free air stream or by ultrasonic cleaning in alcohol. Then either a conventional silane

(Espe Sil) or a universal primer containing a silane and a phosphate monomer (Monobond

Plus) were applied to the conditioned surface. Transparent plastic tubes filled with composite

resin were bonded to the zirconia ceramic discs using a luting resin (MultiLink Automix). The

bonded specimens were stored in water at 37 ◦C for 3 days and for 30 days with 7500 thermal

cycles between 5 ◦C and 55 ◦C prior to tensile test. Statistical analyses were conducted with

three-, two- and one-way ANOVAs followed by comparison of means with Tukey’s HSD test.

Results. Tensile bond strength ranged from 31.5 to 45.2 MPa after 3 days and from 10.6

to 38.8 MPa after 30 days storage in water with thermal cycling. After artificial aging the

decrease in bond strength was significant when the conventional silane was applied after

silica coating or when the universal primer was used after air-borne particle abrasion with-

out ultrasonic cleaning (P < .05). However after artificial aging, the decrease in bond strength

was not significant (P > .05) when the universal primer was used after air-borne particle

abrasion with ultrasonic cleaning or after silica coating.

Significance. A new universal primer improved bonding to zirconia ceramic while the cleaning

no ef

emy

method had little or

© 2010 Acad

. Introduction

irconia ceramic is an attractive core material for fabricationf all-ceramic restorations due to its outstanding mechan-

� This work was undertaken at the Department of Prosthodontics, Prlbrechts University at Kiel, Arnold-Heller Str. 16, 24105 Kiel, Germany∗ Corresponding author. Tel.: +20 50 2211440; fax: +20 50 2260173.

E-mail address: aattia@mans.edu.eg (A. Attia).109-5641/$ – see front matter © 2010 Academy of Dental Materials. Puoi:10.1016/j.dental.2010.10.004

fect.

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

ical properties [1–3]. However compared to silica ceramics,

opaedeutics and Dental Materials, School of Dentistry, Christian-. Tel.: +49 431 597 2874; fax: +49 431 597 2860.

which can be bonded using hydrofluoric acid etching andsilanation, zirconia ceramic requires alternative techniquesfor long-term durable resin bonding [4–13]. Various surfacetreatments such as air-borne particle abrasion, silica coating

blished by Elsevier Ltd. All rights reserved.

l s 2

208 d e n t a l m a t e r i a

and selective infiltration etching technique have been usedto improve bonding to zirconia [14–29]. However, the resultswere conflicting especially regarding long-term bond dura-bility. Indeed, the maintenance of a durable bond under theinfluence of fatigue conditions, in presence of saliva, and tem-perature changes is of outermost importance [20], so silanesand ceramic primers are used to enhance chemical bondingto these ceramics [5,7,15,19,20,30].

However the most often used silane couplingagent for silica-based ceramics, 3-methacryloxy-propyltrimethoxysilane (MPS), might help in surface wettingof oxide ceramics [20] but it does not promote adequate bond-ing to zirconia ceramics [6,9,12]. Recently several new ceramicprimers have been introduced into the dental market toenhance chemical bonding to zirconia ceramic [19,15,20,30],e.g., primers containing organophosphates, carboxylic acids,silanes, other adhesive monomers and combinations ofmonomers. A newly developed universal primer (MonobondPlus, Ivoclar Vivadent, Schaan, Liechtenstein) containing analcohol solution of 3-methacryloxypropyl-trimethoxysilane,phosphoric acid methacrylate and sulphide methacrylate isclaimed by its manufacturer to bond effectively to zirconiaceramic. However, no independent data whether this primerpromotes durable bonding to zirconia ceramic has beenpublished yet.

Moreover after surface conditioning and prior to primerapplication the bonding surfaces are cleaned from dust result-ing from air-borne particle abrasion either by cleaning with astream of oil-free air or by ultrasonic cleaning. Some studies[6,9,10,27] reported long-term bond durability to alumina andzirconia ceramics after silica coating and ultrasonic cleaning,while Nishigawa et al. [18] reported a decreased bond strengthafter ultrasonic cleaning of silica-coated zirconia ceramic.

Therefore the purpose of this laboratory study was toinvestigate the influence of different surface conditioning andcleaning methods on the tensile bond strength of luting resinto zirconia ceramic. In addition, the effect of the applicationof a silane or a universal primer containing a silane and aphosphate monomer was tested.

The hypotheses of the study were that (1) using a newuniversal primer will increase resin bond strength to zirco-nia ceramic regardless of surface conditioning, (2) ultrasoniccleaning in alcohol will improve bonding durability to zirconiaceramic regardless of surface conditioning.

2. Material and methods

A total of 96 disc-shaped specimens were fabricated fromzirconia ceramic (e.max ZirCAD, Ivoclar Vivadent, Schaan,Liechtenstein). Specimens were divided into 6 test groups(n = 16) according to surface conditioning, cleaning methodsand ceramic primers used as follows (materials and manufac-turers are listed in Table 1):

Group ROC-A-S: air-borne particle abrasion with 110 �malumina particles according to manufacturer instructions for

15 s at 0.28 MPa (Rocatec Pre), followed by air-borne particleabrasion with 110-�m grain sized aluminum trioxide parti-cles surface-modified with silica (tribochemical silica coating,Rocatec Plus), at 0.28 MPa, from a perpendicular distance of

7 ( 2 0 1 1 ) 207–213

10 mm for 15 s [25], cleaning with oil-free air stream [7] for 15 sin the Rocatec device and application of one coat of a silane(Espe Sil) with a clean disposable brush (Ivoclar Vivadent)[6,9,27].

Group ROC-U-S: as group ROC-A-S but 3 min ultrasoniccleaning in 99% isopropanol after tribochemical silica coating.Then specimens were dried using oil-free air stream for 15 s.

Group ROC-A-P: as group ROC-A-S but a universal primercontaining a silane and a phosphate monomer (MonobondPlus) was used instead of the silane. The primer was appliedin excess to the pre-treated ceramic with a disposable brushand was allowed to react for 60 s, and then it was dispersedwith oil-free air stream for 5 s.

Group ROC-U-P: as group ROC-U-S but the universal primerwas used instead of the silane.

Group ABR-A-P: air-borne particle abrasion with 110 �malumina particles (Rocatec Pre) for 15 s at 0.28 MPa, followed bycleaning with oil-free air stream for 15 s in the Rocatec deviceand application of the universal primer.

Group ABR-U-P: as group ABR-A-P but 3 min ultrasoniccleaning in 99% isopropanol after air-borne particle abrasion.Then specimens were dried using oil-free air stream for 15 s.

Transparent plastic tubes (Plexiglas, Rohn, Darmstadt,Germany) with 3.2 mm inner diameter were filled withfreshly mixed composite resin (Multicore flow) and allowedto autopolymerize for 6 min before bonding [9–11,15]. Then,a dual curing adhesive luting resin (MultiLink Automix) wasused according to the manufacturer’s instructions for bond-ing the filled plastic tubes to the zirconia ceramic discs usingan alignment apparatus under a load of 750 g. Bonded spec-imens were light-cured from two opposite sides for 20 s at5 mm distance and light intensity of 650 mW/cm2 with a hand-held light-curing device (UniXS, Heraeus Kulzer, Wehrheim,Germany). Furthermore specimens were light-cured in light-curing device (Dentacolor XS, Heraeus Kulzer) for 90 s andkept in an oven at 37 ◦C for 5 min. Each main group wasdivided into 2 subgroups (n = 8). Eight specimens were storedin distilled water bath at 37 ◦C for 3 days without thermalcycling, while the other 8 specimens were stored for 30 daysin the same water bath at 37 ◦C interrupted by thermal cyclingbetween 5 ◦C and 55 ◦C in distilled water with a dwell timeof 30 s (Willytec, Munich, Germany) for 7500 cycles. Tensilebond strength (TBS) was measured in a universal testingmachine (Zwick Z010, Zwick, Ulm, Germany) at a crossheadspeed of 2 mm/min using a chain loop alignment which pro-vided a moment-free axial application [9–11,15]. Statisticalanalyses were performed with three-way analyses of variance(ANOVA) followed by serial two-way ANOVAs and serial one-way (ANOVAs) at each level of the study followed by Post HocTukey-HSD test at (˛ = 0.05).

The fractured interfaces of the zirconia ceramic specimenswere examined with a light microscope (Wild Makroskop M420; Heerbrug, Germany) at 20× magnification to assess thefailure modes. Debonded surfaces were assigned to cohesivefailure within luting resin or composite resin, adhesive atceramic/cement interface or mixed adhesive/cohesive modes

[10]. Representative specimens for each failure mode wereexamined using a scanning electron microscope (SEM; XL 30CP; Philips, Eindhoven, Netherlands) with an acceleration volt-age of 15 kV and a working distance of 10 mm.

d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 207–213 209

Table 1 – Materials used in the study.

Materials Composition Lot/batch no manufacturer

e.max ZirCAD Zirconia ceramic containing 87.0–95.0% ZrO2, 4.0–6.0%Y2O3, 0.0–1.0% Al2O3, 1.0–5.0% HfO2, <0.2% other oxides

54299; Ivoclar Vivadent, Schaan,Liechtenstein

Multilink Automix Transparent, two paste, dual curing adhesive lutingresin containing dimethacrylates and HEMA withbarium glass silica and fillers

04084; Ivoclar Vivadent

Multi core flow Autopolymerised flowable composite resin in base andcatalyst form containing dimethacrylates, barium glassfillers, Ba-Al-fluorosilicate glass, highly dispersedsilicon dioxide, ytterbium trifluoride and catalysts,stabilizers and pigments

9792; Ivoclar Vivadent

Monobond Plus Alcohol solution of3-methacryloxyprophyl-trimethoxysilane, phosphoricacid methacrylate and sulphide methacrylate

MM 0022 Ivoclar Vivadent

Espe Sil 3-methacryloxyprophyl-trimethoxysilane in ethanol 352539; 3M Espe, Seefeld, Germany

rticle

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other specimens showed cohesive failure pattern with 6 spec-imens in group ROC-A-P, 4 specimens in group ABR-U-P and 3specimens in group ROC-U-P.

Rocatec Pre 110 �m alumina particlesRocatec Silica 110 �m silica containg alumina pa

. Results

eans TBS were compared across test groups at two timesith a three-factor ANOVA model, including the following

actors: ceramic primer, cleaning methods, storage conditionnd their interactions. The overall ANOVA F-test (Table 2) wasighly significant (P < .0001), indicating differences in meanBS across at least one of the factors. Ceramic primers and

ime factors were both significant (P < .0001), while the clean-ng factor was not significant (P = .343). However, significantnteractions between ceramic primers and the other factorsere detected (P < .01).

Therefore, further analyses with serial 2-way ANOVAsTable 2) were performed including the following fac-ors: ceramic primers × cleaning methods, ceramicrimers × storage time and cleaning methods × storageime. Interactions of ceramic primers and cleaning methodsP = .06) and storage time and cleaning methods (P = .64) wereot significant. However the interaction of storage time anderamic primers was significant (P = .001).

A significant interaction between ceramic primers andtorage time (P = .001), and tendency to significant differenceetween ceramic primers and cleaning methods (P = .06) com-licated the interpretation of bond strength results. Therefore,o determine which factor had the main effect on bondtrength, further analyses with serial one-way ANOVA modelere used to test the effect of each factor independently

Table 3).Results of the Tukey HSD test for comparison of means

re presented in (Table 4). Thermal cycling significantlyecreased mean tensile bond strength TBS of group ROC-A-Srom 38.3 ± 9.7 to 16.5 ± 6.2 MPa (P < .001), of group ROC-U-

from 31.5 ± 8.5 to 10.6 ± 5.3 MPa (P < .001) and of groupBR-A-P from 42.5 ± 7 to 27.8 ± 12 MPa (P = .03). Although ther-al cycling decreased mean TBS for group ROC-A-P from

4.0 ± 6.4 to 39.7 ± 7.0 MPa, for group ROC-U-P from 45.2 ± 4.7

o 37.2 ± 7.2 MPa and for group ABR-U-P from 44.1 ± 8.9 to8.8 ± 12 MPa, these decreases were not significant (P > .05).

After 3 days storage in water (Table 4), there were notatistically significant differences in the mean TBS of all

329474; 3M Espes 347302; 3M Espe

groups (P > .05). After 30 days storage in water and thermalcycling (Table 4), there were statistically significant differencesbetween the following groups (ROC-A-S vs ROC-A-P, ROC-U-Svs ROC-U-P and ROC-U-S vs ABR-U-P) (P < .05). However therewere no statistically significant differences between the othergroups (P > .05).

Considering the failure pattern of debonded specimens,after 3 days storage in water debonded specimens showeda cohesive failure within the luting resin and the compositeresin (Fig. 1) for all groups except groups ROC-A-S and ROC-U-S where 2 specimens of each group showed mixed (adhesiveand cohesive) failure pattern (Fig. 2). After 30 days storagein water and thermal cycling debonded specimens showedmainly mixed failure pattern (cohesive and adhesive) with8 specimens in group ROC-A-S and ABR-A-P, 6 specimens ingroup ROC-U-S, 5 specimens in group ROC-U-P, 4 specimensin group ABR-U-P, and 1 specimen in group ROC-A-P. Only 2specimens showed adhesive failure in group ROC-U-S. The

Fig. 1 – Representative SEM micrograph showing a cohesivefailure within the adhesive luting resin and the compositeresin.

210 d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 207–213

Table 2 – Summary of overall 3-way ANOVA and serial 2-way ANOVAs.

By level Sum of squares Df Mean square F P-Values

OverallCleaning 65.3 1 65.3 .911 .343Priming 5237.5 1 5237.5 73 <.0001Storage time 54,607.96 1 54,607.96 64.2 <.0001Cleaning × Priming 453.9 1 453.9 6.3 .01Priming × Time 937.2 1 937.2 13 .001Cleaning × Time 19.4 1 19.4 0.27 .605Cleaning × Priming × Time 5.1 1 5.14 0.72 .790Error 6313.7 88 71.75Total 132,202.6 96Total (Corr.) 16,720.95 95

Priming 5237.5 1 5237.5 70.8 <.0001Storage time 4608 1 4608 62.3 <.0001Time × Priming 937.2 1 937.2 12.7 .001Error 6803.7 92 73.953Total 132,202.6 96Total (Corr.) 16721 95

Priming 5237.5 1 5237.5 43.7 <.0001Cleaning 65.3 1 65.3 .545 .462Cleaning × Priming 453.9 1 453.9 3.8 .06Error 11,028.5 92 119.9Total 132,202.6 96Total (Corr.) 16721 95

Cleaning 1 1 1 .008 .9Storage time 3742.5 1 3742.5 26.6 <.0001Cleaning × time 30 1 30 .2 .646Error 12947.5 92 140.7Total 132202.6 96Total (Corr.) 16721 95

Table 3 – Summary of serial 1-way ANOVAs conducted at each level of interacting factor.

By level Sum of squares Df Mean square F P-Values

3 days storageBetween groups 1087.8 5 217.561 3.64 0.0079Within groups 2508 42 59.715Total (Corr.) 3595.8 47

30 daysBetween groups 6168.7 5 1233.74 16.12 <.0001Within groups 3213.9 42 76.5212Total (Corr.) 9382.6 47

Silane at 3 days/30 daysBetween groups 3963.6 3 1321.2 22.76 <.0001Within groups 1625.5 28 58Total (Corr.) 5589.1 31

Universal primer at 3 d/30 daysBetween groups 1797.88 7 256.8 3.51 0.0034Within groups 4096.43 56 73.2Total (Corr.) 5894.32 63

Cleaning with oil-free air stream at 3/30 daysBetween groups 4503.36 5 900.7 12.95 <.0001Within groups 2920.12 42 69.5Total (Corr.) 7423.5 47

Ultrasonic cleaning at 3/30 daysBetween groups 6494.6 5 1298.92 19.47 <.0001Within groups 2801.8 42 66.7Total (Corr.) 9296.4 47

d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 207–213 211

Fig. 2 – Representative SEM micrograph showing mixedfai

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Table 4 – Statistical significant differences between testgroups after 3 days and 30 days storage in water.

Control andtest groups

P-Values

3 daysNo thermalcycling

30 daysThermalcycling

ROC-A-S/ROC-U-S NS NSROC-A-P/ROC-U-P NS NSABR-A-P/ABR-U-P NS NSROC-A-S/ROC-A-P NS *

ROC-A-S/ABR-A-P NS NSROC-A-P/ABR-A-P NS NSROC-U-S/ROC-U-P NS *

ROC-U-S/ABR-U-P NS *

ROC-U-P/ABR-U-P NS NS

NS, not statistically significant (P < 0.05); ROC, silica coating; ABR,air-borne particle abrasion; A, cleaning with oil-free air stream; U,

ailure pattern, cohesive within the adhesive luting resinnd the composite resin, adhesive at ceramic/luting resinnterface.

. Discussion

ond strengths after 3 days storage in water were high andithin the range of bond strength values reported in previous

tudies [6,9,27]. There were no significant differences betweenested groups independent of surface conditioning, clean-ng methods and ceramic primers used. Air-borne particlebrasion (Rocatec Pre alumina) produced an activated micro-oughened zirconia surface, increased the bonding area and

odifying the surface energy and wettability, thus enhancedhe formation of resin-ceramic micromechanical interlocking6,9,10,24,26,27]. These factors plus the use of ceramic primers,

hich could create a chemical bond with metal oxides at theirconia ceramic surface, provided initial high bond strengtho zirconia ceramic as reported before [6,9,27].

In case of tribochemical silica coating, alumina particlesodified with silica were used for air-abrasion at 0.28 MPa

mbedding silica particles in the ceramic surface [9,17,25,27].hese silica particles formed a base for micromechanical

nterlocking and a reactive silica layer which enabled chemicaldhesion after silane application [4,5,19,25].

Silane coupling agents lower the surface tension of a sub-trate, wet it and make its surface energy higher, and henceccessible for effective bonding [25]. Thus, the hydrophobicatrix of a luting resin can adhere to hydrophilic surfaces,

uch as silica, glass, and glass-ceramics [25]. Moreover silanes a hybrid inorganic–organic bifunctional coupling agent

hich is capable of forming covalent bonds to the silica-oated zirconia ceramic through formation of silanol groups5,12,14,17,22].

For durability testing of resin bonding, aging and thermalycling are two important factors which decreased the bondtrength as reported in several studies [8,9,14,27,28]. There-ore one month storage in water and thermal cycling for 7500ycles was used as aging regime to simulate clinical condi-

ions. After 30 days storage in water and thermal cycling TBSas significantly decreased for groups ROC-A-S, ROC-U-S andBR-A-P. This decrease might be due to the hydrolytic effectf water at the luting resin/ceramic interface as reported in

ultrasonic cleaning; S, silane; P, universal primer.∗ P > 0.001

several previous studies [6,9,28]. Moreover mismatch betweencoefficients of thermal expansion of the bonded substrates(zirconia ceramic, luting resin and the Multicore flow com-posite resin) results in stressing the bonded interfaces duringthermal cycling [27]. Therefore, the combined negative effectof water ingress and thermal cycling might be responsible forthe decrease of bond strength of all test groups although thedecrease was significant only for some groups.

Wegner et al. [27] reported that relatively small numberof thermal cycles with no further water storage resulted in adecrease of bond strength. Friederich and Kern [6] reportedthat initial bond strength values to densely sintered alu-mina ceramic after air-borne particle abrasion followed byapplication of a silane was 18.0 MPa, and after tribochemi-cally silica-coating followed by application of a silane was20.3 MPa. However, after 150-days storage in water with 37,500thermal cycles all specimens had debonded spontaneously.Although in the current study initial results of groups (ROC-A-S = 38.3 MPa and ROC-U-S = 31.5 MPa) were higher than resultsof Friederich and Kern [6] (18.0 and 20.3 MPa) after 30 days stor-age in water and thermal cycling bond strength values weredecreased (ROC-A-S = 16.5 MPa and ROC-U-S = 10.6 MPa) andcame into the same range of the initial results of Friederichand Kern [6].

Air-borne particle abrasion and silica coating are effectiveto improve resin bonding to zirconia and alumina ceram-ics [6,9,26]. However, loose alumina particles might be lefton the bonding surfaces [20] which might affect long-termbond durability. Therefore cleaning the conditioned surfacesonly with oil-free air stream (groups ROC-A-S, ROC-A-P andABR-A-P) might not be sufficient, because loose surface parti-cles might negatively influence both chemical adhesion andmicromechanical interlocking. However the current resultsshow that ultrasonic cleaning of the conditioned surfaces didnot improve TBS of groups ROC-U-S, ROC-U-P and ABR-U-Pafter 3 days or after 30 days storage in water and thermal

cycling.

However, Nishigawa et al. [18] reported a negative effectof ultrasonic cleaning in distilled water on bonding to silica-coated zirconia ceramic compared to groups bonded without

l s 2

r

212 d e n t a l m a t e r i a

prior ultrasonic cleaning. They attributed this decrease inbond strength to the fact that ultrasonic cleaning removedloose silica particles plus a significant amount of silica coat-ing layer from the ceramic surface. In the current studya negative effect of ultrasonic cleaning in alcohol was notfound. Therefore, the negative effect of ultrasonic clean-ing in distilled water in the study of Nishigawa et al. [18]might be related more to the effect of water on the highlyreactive silica-coated surface than to the ultrasonic cleaningitself.

The bond strength of groups ROC-A-P, ROC-U-P and ABR-U-P did not decrease significantly after 30 days storage in waterwith thermal cycling. Therefore the new universal primer(Monobond Plus) which contains a silane and a phosphatemonomer was able to promote durable resin bonding to zirco-nia ceramic in these groups which is in agreement with recentresults of Kern et al. [15]. A possible explanation might be thatthe phosphate monomer promoted bonding in groups ABR-A-P and ABR-U-P, while in groups ROC-A-P and ROC-U-P bondingwas promoted by reaction of the silane to the silica coating.However, as silica may have not covered the zirconia ceramiccompletely, the phosphate monomer in the universal ceramicprimer might have bonded to the non-silica coated areas ofthe ziconia ceramic. This might explain the highest and mostdurable bonding results which were achieved after using thenew universal primer.

The initial high bond strength results was reflected on thefailure pattern of debonded specimens as examined by opti-cal reflection microscope and confirmed by SEM. All groupsshowed cohesive failure within the adhesive luting resinand composite resin except groups ROC-U-P and ROC-A-Swhere 2 specimens from each group showed mixed (adhe-sive and cohesive) failure pattern. After 30 days storage inwater and thermal cycling failure pattern was mainly mixedadhesive/cohesive indicating a decrease in the bond strengthdue to the hydrolytic effect of water, hoop stress due tothermal cycling and degradation of the luting resin itself. Clin-ically restorations are subjected to repeated thermal stressand mechanical fatigue due to masticatory forces. Thereforelimitations of this study could be that the specimens were sub-jected only to thermal stress in water instead of artificial salivawithout mechanical fatigue.

5. Conclusions

Within the limitation of this laboratory study, the followingconclusions can be drawn:

1. The cleaning method after surface conditioning had nosignificant effect on the resin bond strength to zirconiaceramic after up to 30 days storage time.

2. After artificial aging a universal primer showed improvedresin bonding to silica coated zirconia ceramic comparedto using a conventional silane.

Acknowledgments

The authors thank Prof. Dr. Hassan Soltan Faculty of Engineer-ing, Mansoura University for his help with statistical analysis

7 ( 2 0 1 1 ) 207–213

of the results. The authors also thank Ivoclar Vivadent forsupplying all materials free of charge.

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