Eval

mor

tetr

afte

pro

Filipe Oliveira Ab

Supported by the National CouncilSão Paulo Research Foundation (FA

aAdjunct Professor, Department of DbPostgraduate student, DepartmentcAssociate Professor, Department ofdAssociate Professor, Department of

Abi-Rached et al

uation of roughness, wettability, and

phology of an yttria-stabilized

agonal zirconia polycrystal ceramic

r different airborne-particle abrasion

tocols

i-Rached, DDS, MSc, PhD,a

Samira Branco Martins, DDS, MSc,b

Juliana Alvares Campos, DDS, MSc, PhD,c andRenata Garcia Fonseca, DDS, MSC, PhDd

Araraquara Dental School, Univ Estadual Paulista (UNESP),Araraquara, São Paulo, Brazil

Statement of problem. Airborne-particle abrasion is an effective method of roughening a zirconia surface and promotingmicromechanical interlocks with luting cements. However, the effect of different airborne-particle abrasion protocols on themicromechanical retention mechanism has been poorly investigated.

Purpose. The purpose of the study was to evaluate the effect of airborne-particle abrasion protocols on the surfaceroughness, wettability, and morphology of an yttria-stabilized tetragonal zirconia polycrystal ceramic.

Material and methods. A total of 140 zirconia specimens (14�14�1.4 mm) were made from Lava and divided into 7 groups.Their surfaces were treated as follows (n¼20): as-sintered (control); airborne-particle abraded with 50-mm Al2O3 particles;120-mm Al2O3 particles; 250-mm Al2O3 particles; 30-mm silica-coated Al2O3 particles (Rocatec Soft); 110-mm silica-coatedAl2O3 particles (Rocatec Plus); and 120-mm Al2O3 particles followed by Rocatec Plus. The surface roughness (Ra) andwettability analyses were performed on the same specimens of each group. The test liquid used for the wettability analysis wasthe silane RelyX Ceramic Primer. Two additional specimens (6.0�6.0�1.0 mm) per group were prepared to evaluate thesurface morphology with scanning electron microscopy. The roughness (Ra) data were analyzed by 1-way ANOVA and theDunnett C test (a¼.05), and the wettability data with 1-way ANOVA (a¼.05). The Spearman correlation analysis was appliedto test for a possible correlation between roughness and wettability.

Results. The control group (0.35 mm) exhibited the lowest mean roughness value (Ra), which was followed by Rocatec Soft(0.40 mm), 50-mm Al2O3 particles (0.52 mm), Rocatec Plus (0.69 mm), 120-mm Al2O3 particles (0.80 mm) / 120-mm Al2O3

particles þ Rocatec Plus (0.79 mm), and 250-mm Al2O3 particles (1.13 mm). No significant difference was found among thegroups concerning wettability. No correlation (rs¼�0.09; P¼.27) was found between the 2 dependent variables. The scanningelectron microscopy analysis indicated that the different airborne-particle abrasion protocols produced differences in themorphologic patterns.

Conclusions. Although roughness and morphology of the zirconia surface varied according to the airborne-particle abrasionprotocol, no close relationship was found between them. The roughness increase seemed to have followed the size of theparticles. (J Prosthet Dent 2014;112:1385-1391)

for Scientific and Technological Development (CNPq) (Grant 143251/2011-2) and by thePESP) (Grants 2011/11893-0 and 2011/05984-3).

ental Materials and Prosthodontics.of Dental Materials and Prosthodontics.Social Dentistry.Dental Materials and Prosthodontics.

Table I. Materia

Material

50-mm Al2O3 parti

120-mm Al2O3 par

250-mm Al2O3 par

Rocatec Soft (30 m

Rocatec Plus (110

RelyX Ceramic Prim

MPS, 3-methacryloylo

1386 Volume 112 Issue 6

The Journal of

Clinical Implications

Although airborne-particle abrasion with larger particles providesrougher surfaces, when considering roughness, wettability, andmorphology together, abrasion with 120-mm Al2O3 particles seems to bethe most promising for mechanical bonding. The wettability of thezirconia surface by the RelyX Ceramic Primer silane is not influenced byparticle size and surface roughness. Rocatec Plus is not necessary afterabrasion with 120-mm Al2O3 particles.

For a long-term durable bond atthe zirconia/luting cement interface,the surface of yttria-stabilized tetragonalzirconia polycrystal (Y-TZP) ceramicrestorations should promote micro-mechanical interlocking and establishchemical reactions with luting resins.1,2

Some authors3,4 highlight the essentialrole of micromechanical retention inthe improvement of the bonding withluting resins. Others claim that con-tamination of the intaglio of the zirconiaframeworks during handling can affectchemical bonding5,6 or that the mate-rials at the bonding interface are sus-ceptible to hydrolytic degradation.7,8

The micromechanical bonding mech-anism is a result of luting cement infil-tration into the micro-irregularities on theinner surface of the restoration. Althoughsome alternative surface treatments pro-vide mechanical bond, airborne-particleabrasion is one of the most used andstudied methods for zirconia.3,9-16 Be-sides roughening the surface, this proce-dure cleans and increases the availablesurface area for bonding, favoring themechanical interlocking between theluting cement and the airborne-particle-abraded zirconia surface,3,10,17 and also

ls evaluated

cles

ticles

ticles

m) aluminum o

mm) aluminum ox

er

xypropyl trimethoxysilane; w

Prosthetic Dentis

increases the surface free energy, whichmay enhance the wettability of thesubstrate.18,19

For airborne-particle abrasion, a va-riety of particle sizes (25 mm to 250 mm)and compositions (conventional alu-mina or silica-coated particles) exist.20,21

Airborne-particle abrasion with silica-coated Al2O3 particles, besides favoringthe micromechanical retention at thezirconia/luting cement interface, de-posits a silica layer on the zirconia sur-face,22,23 preparing it to react with thesilane (hydrolyzable alkoxy groups)applied afterward.24,25 However, in spiteof the importance of the airborne-particle abrasion and the wide rangeof particle options used in thisprocedure, information about theeffects of particle size on roughness,19,26-30 morphology,26,27,29,30 and wetta-bility31 of the zirconia surface is contro-versial or scarce.

Thus, the purpose of this in vitro studywas to evaluate the effect of airborne-particle abrasion protocols on the sur-face roughness, wettability (dependentvariables), and morphology of a Y-TZPceramic. The null hypothesis was that theairborne-particle abrasion protocol

Composition

Al2O3>99 wt%

Al2O3>99 wt%

Al2O3>99 wt%

xide>97 wt% amorphous silica<3 wt%

ide>95 wt% amorphous silica 1-5 wt%

MPS, ethanol, water

t%, percentage by weight.

try

would not influence the dependent vari-ables and that no correlation wouldbe found between them.

MATERIAL AND METHODS

Preparation and surface treatmentof zirconia specimens

The materials evaluated in this studyare summarized in Table I. A calculationof sample size was made from dataobtained from the pilot study. Forroughness, a minimum difference of 0.05among the means obtained among thetreatments (D) was considered, with ageneral SD (s) of 0.04, number oftreatments (k) equal to 7, power (b) of.80, and level of significance (a) of .05,resulting in n¼19. For contact angle, itwas D¼0.17, s¼0.14, k¼7, b¼.80, anda¼.05, resulting in n¼20. Thus, n¼20was used in the present study.

A total of 140 presintered zirconiaspecimens were obtained from Lavaframes (3M ESPE AG), which were cutwith a saw (IsoMet 1000; Buehler Ltd)under water irrigation. The specimenswere washed in tap water to remove thecutting debris and finished manually

Manufacturer

Bio-Art Equipamentos Odontológicos Ltda

Bio-Art Equipamentos Odontológicos Ltda

Polidental Indústria e Comércio Ltda

3M ESPE AG

3M ESPE AG

3M ESPE

Abi-Rached et al

Table II. Mean �SD of Ra (mm) and contact angle (degrees) values

Group Ra Contact Angle

As-sintered (control) 0.35 �0.05f 1.66 �0.72*

50-mm Al2O3 0.52 �0.03d 1.60 �0.72*

120-mm Al2O3 0.80 �0.04b 1.50 �0.59*

250-mm Al2O3 1.13 �0.14a 1.56 �0.65*

Rocatec Soft (30 mm) 0.40 �0.03e 1.51 �0.49*

Rocatec Plus (110 mm) 0.69 �0.04c 1.45 �0.31*

120-mm Al2O3 þ Rocatec Plus 0.79 �0.03b 1.32 �0.53*

Different letters indicate significant differences (P<.05).*No significant differences (P>.05).

December 2014 1387

with a ceramic polisher (Exa Cerapol0361HP; Edenta AG) in a slow-speedhandpiece. One surface of each spec-imen was polished with 600- and 1200-grit silicon carbide abrasive papersunder wet conditions.

Specimens were sintered in an oven(Lava Furnace 200; Dekema Dental-Ker-amiköfen GmbH) according to themanufacturer’s instructions (heatingrate¼20�C/min for 0�C-1000�C and10�C/min for 1000�C-1500�C; holdingtime¼2 hours; and cooling rate¼15�C/min for 1500�C-800�C and 20�C/minfor 800�C-250�C; the oven was openedat 250�C). Afterward, all zirconia spec-imens (14�14�1.4 mm) were subjectedto one of the following surface treatmentconditions (n¼20): as-sintered (control);airborne-particle abraded with 50-mmAl2O3 particles; 120-mm Al2O3 particles;250-mm Al2O3 particles; 30-mm silica-coated Al2O3 particles (Rocatec Soft);110-mm silica-coated Al2O3 particles(Rocatec Plus); and 120-mm Al2O3 par-ticles followed by Rocatec Plus similar tothe manufacturer’s recommendation touse 110-mm Al2O3 particles previous toRocatec Plus.

For the airborne-particle abrasionprocedure, the specimens were moun-ted on a special holder and airborne-particle abraded for 15 seconds withan airborne-particle abrasion unit (BasicClassic; Renfert GmbH) at a pressure of0.28 MPa and a perpendicular distanceof 10 mm from the zirconia surface.24

All specimens were cleaned in 99%isopropanol for 10 minutes in an ul-trasonic bath and left to dry at roomtemperature for 24 hours.

Surface roughness measurements

The average surface roughness (Rain mm) of all specimens was determinedwith a profilometer (Surftest SJ-400;Mitutoyo Corp) with a cutoff value(lc) of 0.8 mm12,16,19 before contactangle measurements. Resolution was0.01 mm; the transverse length (lengthof the surface examined by the instru-ment) was 4.0 mm; and the speed ofthe diamond stylus with a 5-mm tipradius was 0.5 mm/s. Three equidistant

Abi-Rached et al

parallel measurements were made witha perpendicular stylus on different areasof the specimen. All measurements wereperformed perpendicular to the direc-tion of the airborne-particle abrasion.The average reading was designated asthe Ra value of each specimen. Onecalibrated operator (intraclass correla-tion coefficient [ICC]¼0.89) recordedall measurements.

Contact angle measurements

Contact angle is defined as theangle at the intercept of a plane tangentto a drop and the plane containingthe substrate-liquid interface. Thewettability of the zirconia surface by thesilane RelyX Ceramic Primer was char-acterized by means of the contactangle formed between the silane andthe airborne-particle-abraded zirconiasurface. For the measurements, anautomated goniometer (model 200-00;Ramé-Hart Instrument Co) with acharge-coupled device camera was usedto record the image of a liquid dropplaced onto the surface by a micro-syringe while image processing softwaredetermined the contact angle. Onecalibrated operator (ICC¼0.67) ob-tained 2 measurements for each spec-imen, and the average was determined.

Statistical analysis

For roughness, because the homoge-neity assumption was violated (Levene,P<.001), the data were analyzed by 1-way ANOVA and the Dunnett C test

(a¼.05). For wettability, the assump-tions of the analysis were satisfied (Sha-piro-Wilk, .18�P�.87; Levene, P¼.08),and the data were submitted to 1-wayANOVA (a¼.05) (IBM SPSS Statisticsv20; IBM Corp). To estimate the signifi-cance of the correlation between rough-ness and wettability, the Spearman rankcorrelation test was used.

Scanning electron microscopyanalysis

The morphologic patterns of thezirconia surface after the differentairborne-particle abrasion protocolswere characterized with scanning elec-tron microscopy (SEM). Two addi-tional specimens (6.0�6.0�1.0 mm)from each experimental group wereprepared, mounted on metallic stubs,and analyzed under a high-resolutionfield emission scanning electron micro-scope (model JSM-7500F; JEOL Ltd)at �500 magnification and an acceler-ating voltage of 2.0 kV.

RESULTS

The 1-way ANOVA found thatthe airborne-particle abrasion protocolwas significant for roughness (df¼6;F¼348.1; P<.001) and did not influ-ence the wettability (df¼6; F¼0.7;P¼.66).

Table II shows the mean Ra values(mm), SDs, and statistical analysis re-sults identified with the Dunnett C testand the contact angle mean values(degrees) and SDs. The control group

1388 Volume 112 Issue 6

(0.35 mm) exhibited the lowest meanroughness value (Ra), which was fol-lowed by Rocatec Soft (0.40 mm), 50-mm Al2O3 particles (0.52 mm), RocatecPlus (0.69 mm), 120-mm Al2O3 particles(0.80 mm) and 120-mm Al2O3

particles þ Rocatec Plus (0.79 mm),and finally by 250-mm Al2O3 particles(1.13 mm), which provided the highestroughness. No significant difference inwettability was found among thegroups.

The Spearman correlation testfound no correlation (rs¼�0.09; P¼.27)between roughness and wettability. Therepresentative SEM images (Fig. 1) indi-cated that different airborne-particleabrasion protocols produced differ-ences in the morphologic patterns of thezirconia surface.

DISCUSSION

The results of this study did notsupport the null hypothesis, as the

1 Representative scanning electron micr(control). B, 50-mm Al2O3. C, 120-mm A

The Journal of Prosthetic Dentis

particle size affected the zirconia sur-face roughness and the morphology.The influence of the particles on theroughness and/or morphology ofmetal32,33 and zirconia19,26-30 has beenobserved in previous studies.

In the present study, airborne-particle abrasion with 30-mm silica-coated Al2O3 particles (Rocatec Soft)provided significantly higher roughnessthan the as-sintered group (control), asobserved in other studies.15,16,19,22,27

Although the particles of Rocatec Soft(30 mm) were smaller than the others,SEM analysis found that they were ableto roughen the zirconia surface morein comparison with the control group;the control group presented a surfacethat was less favorable to micro-mechanical retention and that abradedwith Rocatec Soft was more favorable.This difference in morphology was alsoobserved by Subası and _Inan.15,16 Themean roughness value (Ra) found inthe present study for the as-sintered

oscope images (�500) of airborne-particlel2O3. D, 250-mm Al2O3.

try

group is consistent with the studies ofMonaco et al27 and Cavalcanti et al,11

and the roughness of the Rocatec Softgroup is corroborated by the study ofCattani Lorente et al.22

The significantly higher roughnessprovided by 50-mm Al2O3 particles incomparison with the control group andthe group abraded with 30-mm silica-coated Al2O3 particles was also foundin the literature.11,14,27-30 Concerningthe morphologic analysis, it was ob-served that, unlike in the control group(which exhibited a smooth surface),abrasion with Rocatec Soft and 50-mmAl2O3 particles resulted in a change insurface texture, forming more evidentmicroretentive grooves with the 50-mmAl2O3 particles. Monaco et al27 re-ported the same behavior when these3 conditions were evaluated (controlgroup, Rocatec Soft, and 50-mm Al2O3

particles), and Oguri et al14 and Cav-alcanti et al11 when airborne-particleabrasion was performed with Al2O3

abrasion protocols. A, as-sintered

Abi-Rached et al

1 (continued) Representative scanning electron microscope images (�500) of airborne-particle abrasion protocols.E, Rocatec Soft. F, Rocatec Plus. G, 120-mm Al2O3 þ Rocatec Plus.

December 2014 1389

particles of approximately 50 mm incomparison with the control group.Contrary to these findings, Foxtonet al13 reported that airborne-particleabrasion with 53-mm Al2O3 particlesdid not appear to significantly changethe zirconia surface appearance incomparison with the control group.

The Rocatec Plus group exhibitedthe third highest roughness. When thisgroup was compared with that abradedwith Rocatec Soft (30 mm) or 50-mmAl2O3 particles, a significant increasewas observed in the surface roughnessmean value. This behavior may beattributed to the higher grain size (110mm) of the Rocatec Plus particles. Evenwith airborne-particle abrasion param-eters different from those used in thepresent study, Monaco et al27 (10 sec-onds, 0.2 MPa, and 15 mm) and Turpet al29 (15 seconds, 0.2 MPa, and10 mm) also observed that the largerAl2O3 particles (110 mm) providedmore roughness than the smaller silica-

Abi-Rached et al

coated (30 mm) and alumina (50 mm)particles. Monaco et al27 also reportedmore marked deformations with thelarger Al2O3 particles (110 mm). Con-cerning the silica-coated Al2O3 parti-cles, Yamaguchi et al19 observed thatthe 110-mm particles provided moreroughness than the 30-mm particles.

The groups abraded with 120-mmAl2O3 particles and 120-mm Al2O3

particles þ Rocatec Plus providedthe second highest roughness value.Regarding the superiority of thesegroups over the 50-mm Al2O3 particles,Monaco et al,27 Turp et al,29 and Wanget al30 also reported significantly higherroughness after abrasion with 110-mmand 120-mm Al2O3 particles in com-parison with that of the group abradedwith 50-mm particles. Only Curtiset al26 observed statistically similarroughness values between the groupsabraded with 50-mm and 110-mmAl2O3 particles. The higher roughnessprovided by the larger particles

(110 mm/120 mm) with respect to the50-mm particles was corroboratedby the SEM performed in this study.The SEM analysis indicated differentmorphologic patterns, with advantagesfor the 110-mm and 120-mm Al2O3

particles, which promoted a surfacemore favorable for micromechanicalretention at the zirconia/luting cementinterface.

The finding that the 120-mm Al2O3

particles (0.80 mm) and 120-mm Al2O3

particles þ Rocatec Plus (0.79 mm) hadgreater roughness than Rocatec Plus(0.69 mm) has not been previouslyreported. Although the Rocatec Plusparticles are coated by silica, the alu-mina particles are probably identical tothe 120-mm noncoated ones. Therefore,although the difference between theparticle sizes is quite small (10 mm),this appears to be the decisive factor indetermining the higher roughness ach-ieved by the 120-mm Al2O3 particlescompared with that of the group

1390 Volume 112 Issue 6

abraded with the 110-mm silica-coatedparticles. This fact also explains whythe double airborne-particle abrasion,as recommended by the manufacturerof the Rocatec Plus, provided no sig-nificant difference in roughnesscompared with the group abraded withonly 120-mm Al2O3 particles.Comparing the morphology in these 3groups, the group abraded with only120-mm Al2O3 particles seems to pro-vide a surface with more edge-shapedmicro-irregularities than the other 2groups, which exhibited a flatterpattern. Therefore, both roughness andmorphology analyses indicate that, inthose 3 groups, abrasion with 120-mmAl2O3 particles seems to be moreeffective in terms of micromechanicalretention.

With respect to the higher rough-ness (1.13 mm) provided by abrasionwith 250-mm Al2O3 particles, somestudies27,30,34 also reported an increasein this property when the particle sizefor the airborne-particle abrasion waslarger. In addition, these authors27,30,34

also observed that the use of largerparticles provided a clearly rougherprofile than the smaller particles.However, these studies27,30,34 did notevaluate abrasion with 250-mm Al2O3

particles. Although this particle size ledto the highest roughness in the presentstudy, the morphologic analysis founda flatter and broader pattern than thatobserved for 110-mm/120-mm particles.Another concern was that airborne-particle abrasion with this particle sizemay result in severe surface damageand material loss, which could com-promise the mechanical properties ofzirconia. A study by Fonseca et al20

found a decrease in flexural strengthwhen zirconia was abraded with 250-mm Al2O3 particles, and, in contrast, anincrease in this property with 50-mmand 110-/120-mm Al2O3 particles.However, in that study,20 the flexuralstrength was assessed under monotonicloading conditions. Zhang et al,35 whosimulated the equivalent of 1 yearof occlusal contacts, observed thatairborne-particle abrasion with 50-mmAl2O3 particles provided a reduction in

The Journal of Prosthetic Dentis

the zirconia strength of 20% to 30%compared with when this material wasjust polished.

Regarding the contact angle anal-ysis, although the optimal wettability ofthe zirconia by the adhesive agent isessential for achieving strong adhesionat the zirconia/luting resin interface,the effects of different factors capableof modifying the wettability of thezirconia surface were poorly investi-gated.14,19,31,36,37 Among the studies,only that by Noro et al31 evaluatedthe effect of the Al2O3 particle size onzirconia wettability by distilled water.Although those authors31 used a testliquid different from the present study,their results corroborate the presentresults, because the particle size en-largement seemed not to influence thewettability of the abraded zirconia sur-face. Yamaguchi et al19 investigated theeffect of the particle size on the surfacefree energy of Lava zirconia, which isclosely related to wettability. Changesin the surface energy of a substratealter its wetting capability by a certainliquid.37 Yamaguchi et al19 observedthe following descending order of meansurface free energy values: Rocatec Soft(30 mm), Rocatec Plus (110 mm),70-mm Al2O3 particles, and finally thecontrol group. This result indicatesthat, regarding surface free energy,airborne-particle abrasion with silica-coated Al2O3 particles is more favor-able. However, in terms of wettability,this behavior was not observed in thepresent study, because there was nosignificant difference in the contactangle among the groups. The novelty ofthe present research, besides the effectof different particle sizes on wettability,is that the test liquid used for contactangle analysis was a silane, which is abonding agent recommended mainlyafter abrasion with silica-coated Al2O3

particles. According to Silva et al,37 arough surface will exhibit better wetta-bility by increasing the surface area.However, in the present study, thesilane was able to spread over the zir-conia surface regardless of the surfaceroughness. This may explain the weakcorrelation between roughness and

try

wettability observed in the presentstudy. In the study of Yamaguchi et al,19

the same behavior was observedbetween roughness and surface freeenergy.

Although this study indicated thatsome groups seem to present bettermicromechanical retention than others,the investigation of the effect of theseairborne-particle abrasion conditionson adhesive bonding, as well as on theelemental composition, phase trans-formation, and mechanical propertiesof zirconia is necessary to confirm theirefficacy.

CONCLUSIONS

Within the limitations of this invitro study, the following conclusionswere drawn. Although roughness andmorphology of the zirconia surface var-ied according to the airborne-particleabrasion protocol, no close relationwas found between them. The roughnessincrease seemed to have followed theparticle size. Double airborne-particleabrasion as recommended by themanufacturer of the Rocatec Plus couldbe replaced by abrasion with only120-mm Al2O3 particles to achievesimilar micromechanical retention. Thedifferent airborne-particle abrasionprotocols did not influence the wetta-bility of the zirconia surface by thesilane coupling agent. No correlationbetween roughness and wettabilitywas observed.

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Corresponding author:Dr Renata Garcia FonsecaRua Humaitá, No. 1680Araraquara, SP 14801-903BRAZILE-mail: renata@foar.unesp.br

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