Basic Research—Technology

Comparison between the Effect of Plasma and ChemicalTreatments on Fiber Post SurfaceMarta Cl�ea Costa Dantas, DDS, MSc,* Ma�ıra do Prado, DDS, MSc,† Vinicius Silva Costa, DDS,*Mauro G. Gaiotte,* Renata A. Sim~ao, MSc, PhD,* and Fernando Luis Bastian, PhD*

Abstract

Introduction: The aim of the present study was to eval-uate the fiber post surface after plasma and usual treat-ments and the adhesion between treated fiber posts andRely X Unicem resin cement (3M ESPE, St Paul, MN).Methods: Flat fiber posts were divided into 6 groups ac-cording to surface treatment: silane, hydrofluoric acid,hydrofluoric acid plus silane, plasma polymerizationwith argon, ethylenediamine plasma (EDA), and thecontrol group. A goniometer was used to measure thecontact angle between the groups with water or resincement. Scanning electron microscopy and electrondispersive spectroscopy were used to examine thetopography and chemical changes in the post surfacesafter treatment. Push-out tests were performed usinga universal testing machine to evaluate the adhesionstrength between treated fiber posts and resin cement.Results: In the contact angle with water, the mosthydrophilic surface was observed in samples treatedwith argon plasma, followed by treatments with silaneand hydrofluoric acid plus silane. The hydrophobic char-acteristic was observed with EDA and hydrofluoric acid.The contact angle with dual resin cement showed lowervalues with argon and EDA, followed by silane and hy-drofluoric acid plus silane. Electron dispersive spectros-copy analyses showed chemical modifications in thesurface after different treatments although topographicchanges were verified only with EDA plasma comparedwith the control. Push-out results did not show differ-ences between groups compared with the control,except for EDA plasma treatment. Conclusions: Plasmatreatment favored the wettability of the post surface bymodifying it chemically. Adhesion improvementwas only observed after EDA treatment. (J Endod2012;38:215–218)

Key WordsArgon plasma, ethylenediamine plasma, fiber post,hydrofluoric acid, silane, wettability

From the *Department of Metallurgic and Materials EngineerinRestorative Dentistry, Endodontic Division, State University of Camp

Address requests for reprints to Dr Ma�ıra do Prado, Department901, Piracicaba, SP, Brazil 13414-018. E-mail address: mairapr@fop0099-2399/$ - see front matter

Copyright ª 2012 American Association of Endodontists.doi:10.1016/j.joen.2011.10.020

JOE — Volume 38, Number 2, February 2012

Fiber posts are widely used and accepted for the restoration of endodontically treatedteeth as a viable alternative to cast post (1, 2). Fiber post retention depends on the

strength of the chemical and micromechanical interaction between fiber-reinforcedmaterial and composite resin (3). Several surface pretreatments for posts have beenused to optimize the bond between post and resin cement (3–10).

The contact angle technique evaluates the interaction between 2 surfaces: a liquidand a solid. To calculate the contact angle, the following Young’s equation is applied:gifcosq = gsf - gsl, where contact angle qYoung is uniquely determined by the 3 interfacialtensions gif, gsf, and gsl, functioning as an equilibrium property of the system (11).This technique is able to measure wettability and surface free energy (12). Accordingto Asmussen and Peutzfeldt (13), the contact angle between surface and liquids, polarand apolar, with known density are used to calculate the surface free energy, calculatedfrom the equation gs= gs

d+ 2(gs+gs

_)1/2. These authors analyzed both contact angleand surface free energy and showed that the bond strength between polymerizedcomposites and fresh dentin was influenced by the mechanical properties of the formerand by the compatibility between composite and adhesive. Asmussen et al (14) deter-mined the surface energy characteristics of 3 variously treated post materials and 2 resincements and investigated whether previously measured bond strengths betweencements and treated posts could be related to the surface energy characteristics ofboth materials. The authors concluded that factors other than surface energy charac-teristics of adherent and adhesive surfaces play a role in determining the bond strength.

Chemical vapor deposition is a plasma technique. This technique yields neitherwaste product during reaction nor modifies the chemical and physical properties ofthe substrate surface, allowing bond strength between dissimilar materials withoutmodifying their bulk properties. The changes caused by plasma technology are charac-terized by the deposition of ions and molecules resulting from the vaporization ofdifferent substances, which modifies physically and chemically the deep surface depthat micrometric and submicrometric scales (15–22). Yavirach et al (23) evaluated theeffects of treatment on the adhesion between fiber posts and composite core materials,observing that plasma treatment increased the tensile-shear bond strength between postand composite. The aim of the present study was to evaluate the fiber post surface afterplasma and usual treatments as well as the adhesion between treated fiber posts andRely X Unicem resin cement (3M ESPE, St Paul, MN).

Materials and MethodsSample Preparation

Cylindrical fiber epoxy resin posts (FGM, Santa Catarina, Brazil) of 1.6 mm indiameter and 20 mm in length were used. Fiber posts were wet grinded with carbo-rundum sandpapers (400, 600, and 1,200 grits) to obtain a flat surface before being

g, Federal University of Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil; and †Department ofinas, UNICAMP, Piracicaba, S~ao Paulo, Brazil.of Restorative Dentistry, Piracicaba Dental School State University of Campinas, Avenida Limeira,.unicamp.br

Plasma and Chemical Effects on Fiber Post 215

Basic Research—Technology

attached to a metal matrix along their long axis by using beeswax. Next,the posts were polished with aluminum oxide paste and submitted to anultrasonic bath for 15 minutes in distilled water and acetone PA (VetecChemical, Duque de Caxias, Brazil) so that any superficial contaminantcould be removed. The resulting samples were divided into 6 groupsaccording to surface treatment: silane (G1), hydrofluoric acid (G2), hy-drofluoric acid plus silane (G3), argon plasma polymerization (G4),ethylenediamine plasma (G5), and control group (G6).

Surface TreatmentsThe surface modification was performed by using Monobond-S

silane (3-methacryloxypropylmethoxysilane; Vivadent, Barueri, SP,Brazil) and 4% hydrofluoric acid gel (F�ormula & Ac~ao, S~ao Paulo,SP, Brazil). In G1, silane was applied with a microbrush for 60 seconds.In G2, the samples were treated with hydrofluoric acid for 60 secondsand then rinsed with running water for 10 seconds. In G3, the sampleswere treated with hydrofluoric acid for 60 seconds, rinsed with runningwater for 10 seconds, and dried before further silane application for60 seconds.

Surface modification through chemical vapor deposition was per-formed by using a cathode of glow-discharge reactor operating at13.56 MHz. The vacuum chamber was pumped down to 0.1 Pa, andmonomer vapor or gas was allowed to fill the reactor up to 15 Pa.Surfaces were then modified by argon plasma polymerization (G4)(White Martins, Rio de Janeiro, RJ, Brazil) and 99% ethylenediamineplasma polymerization (G5) (Sigma Chemicals by Tedia, Rio de Janeiro,RJ, Brazil) with 280 V self-bias voltage (VB) for 5 minutes. At the end ofthe process, radiofrequency was turned off and the system allowed tocool down before exposure of the samples to air.

Contact Angle AnalysesA Ram�e-Hart goniometer (Ram�e-Hart Instrument Company,

Netcong, NJ) was used to measure the contact angle. A total of 10 anal-yses were made per group: 5 in contact with water (n = 5) and 5 incontact with Rely X Unicem resin cement (n = 5). Twenty measure-ments were obtained for each analysis, totaling 100 measurementsper group. The data were analyzed using one-way analysis of varianceand Fisher post hoc test (P < .05).

To measure the surface free energy of the Rely X Unicem resincement, the material was placed in a rectangular mold (25 mm �2 mm � 2 mm) covered on both sides with transparent matricesand light cured for 40 seconds with a light-emitting diode unit. After1 day, the matrices were removed, and the contact angle was measuredfor each of the 3 test liquids with known surface energy parameters:water, ethylene glycol, and diiodomethane. With these data, the

Figure 1. A graph with the contact angle values between the treated surfaces and

216 Costa Dantas et al.

Ram�e-Hart software calculated the energy parameters and surfaceenergy.

Scanning Electron Microscopic and Electron DispersiveSpectroscopy Analyses

The surface morphology of fiber posts regarding each treatmentand those of the control group was investigated. For this purpose, thesamples were prepared and analyzed by using a scanning electronmicroscope (SEM) (JSM 6460 LV; JEOL, Tokyo, Japan). For eachgroup, 5 samples were used (n = 5), and microphotographs were ob-tained at 100� magnification. Next, electron dispersive spectroscopy(EDS) was used to verify the chemical composition of the samples.

Push-out Test and Failure Pattern AnalysisTreated posts and controls were cut into 2 pieces of 10 mm in

length and cemented within a central hole of 1.8 mm in diametermade in a composite core of a 6-mm height and a 10-mm diameter.Following the manufacturer’s instructions, the encapsulated dual-cured resin cement was manipulated in Amalgam II (3M ESPE) for15 seconds. The resin cement was applied with appropriate syringeinto the hole of the composite core, and the post was properly posi-tioned. Each sample was polymerized for 40 seconds with a light-emitting diode unit (Radi Call, SDI, Australia). After storage for 24hours, each specimen of 6 mm was sectioned perpendicularly to itslong axis by means of a precision saw machine (Isomet 1000; BuehlerLtd, Lake Bluff, IL) to obtain 2 slabs of (2.5 � 0.3) mm in thickness.These slabs were wet grinded with carborundum papers (400, 600,and 1,200 grits) to obtain a flat surface. A total of 8 samples wereprepared for each group (n = 8). Bond strength was analyzed throughthe push-out test by using a universal testing machine (Emic DL 10000,S~ao Jos�e dos Pinhais, PR, Brazil) at a cross-head speed of 1 mm/minand a cylindrical post of a 1.6-mm diameter and a 20-mm lengthwith 200-kgf load cell.

To express the bond strength in megapascals (MPa), the loadvalue recorded in newtons (N) was divided by the area (mm2) of thebonded interface. It was calculated as follows (24): A ¼ 2prh, wherepi is equal to 3.14, r is the post radius, and h is the thickness of the slicein millimeters. Means and standard deviations of bond strength werecalculated, and data were analyzed by using one-way analysis of varianceand the Fisher post hoc test (P < .05).

The fractured specimens were prepared and analyzed by an SEM at50� magnification to classify the failure pattern into 3 types: (1) adhe-siveness between post and composite core with adhered cement, (2)adhesiveness between post and composite core without adheredcement, and (3) cohesiveness in composite core.

water or resin cement.

JOE — Volume 38, Number 2, February 2012

TABLE 1. The Contact Angle (�) between the Treated Surfaces and Water orResin Cement

TreatmentWater contact

angle (�)Resin cement contact

angle (�)

Control 92.3 (5.9)d 75.8 (10.9)b,c

Silane 56.1 (2.4)a,b 66.2 (6.5)b

Hydrofluoric acid 71.2 (5.7)c 76.9 (11.3)b,c

Hydrofluoricacid + silane

59.4 (1.2)b 73.3 (19.1)b

Argon 50 (12.8)a 43.4 (10.0)a

EDA 72.1 (3.5)c 51.0 (15.1)a

*Mean value (standard deviation). The values with the same superscript letter do not differ (P < .05).

Basic Research—Technology

ResultsFigure 1 and Table 1 show the contact angle analyses between

treated surfaces and water or resin cement. As for the contact anglewith water, the most hydrophilic surface was observed in the samplestreated with argon plasma because they showed the lowest contact anglevalues followed by silane-treated samples, which showed no significantdifference compared with the treatment with hydrofluoric acid plussilane. Hydrophobic characteristic was observed in samples submittedto ethylenediamine plasma (EDA) and hydrofluoric acid treatmentsbecause the contact angle obtained was higher than that of controls.As for the contact angle with dual resin cement, lower values were foundfor samples treated with argon and EDA plasma, followed by treatmentswith silane and hydrofluoric acid plus silane. Similarly, treatments withsilane and hydrofluoric acid plus silane showed no differencescompared with the control group. As for the resin cement surface

Figure 2. Topographic images of the different groups and their corresponding E

JOE — Volume 38, Number 2, February 2012

energy parameters, the Rely X Unicem resin cement showed a hydro-phobic characteristic with low surface energy values (6 � 1 mJ/m2).

Figure 2 shows representative topographic images of the differentgroups and their corresponding EDS. EDS analysis showed chemicalmodifications in the surface of the samples after different treatments.Scanning electron microscopic analysis showed topographic changesonly in the EDA plasma group.

Table 2 shows bond strength results and fracture surfacemorphology for all groups. The bond strength value of the EDA plasmagroup (17.3 MPa) was significantly higher compared with all othergroups, ranging from 10.9 to 13.9 MPa (P < .05). Scanning electronmicroscopic images from fracture morphologies showed that fractureoccurred mainly because of adhesive failure, with no resin cementadhered to the post surface. Only EDA group had fractures in compositecore because of cohesive failure.

DiscussionIn the present study, the contact angle between treated surfaces

and water was used to evaluate the hydrophilic characteristic of thesurfaces. In this sense, samples treated with argon plasma showedthe highest hydrophilic characteristic, presenting lower values ofcontact angle, without any topographic changes compared with control.Samples treated with EDA showed a hydrophobic characteristic withhigh values of contact angle. It can be explained by the presence of polargroups after argon treatment and nonpolar groups after EDA treatment.

According to the manufacturer, the Rely X Unicem resin cementpresents hydrophilic characteristics before polymerization andbecomes hydrophobic after polymerization, which was observed in

DS.

Plasma and Chemical Effects on Fiber Post 217

TABLE 2. Bond Strength Values (MPa) and the Failure Pattern of theExperimental Groups and the Control

Treatment Bond strength* Failure pattern

Control 13.9 (1.4)a Adhesive without cementSilane 11.7 (3.1)a Adhesive without cementHydrofluoric acid 10.9 (5.3)a Adhesive without cementHydrofluoric

acid + silane12.3 (5.4)a Adhesive without cement

Argon 12.4 (2.0)a Adhesive without cementEDA 17.3 (2.7)b Cohesive in composite

core

*Mean value (standard deviation). Values with the same superscript letter do not differ (P < .05).

Basic Research—Technology

the present study. Adhesive materials should come into intimate contactwith the substrate to facilitate molecular attraction and allow eitherchemical adhesion or penetration for micromechanical surface attach-ment (12). The wettability contact angle with Rely X Unicem resincement was used to measure the interaction with the treated surface.These analyses showed that plasma treatments with EDA and argonwere better than the use of silane, hydrofluoric acid and its associationto promote the spread of cement. According to de Sousa Menezes et al(3), the use of hydrofluoric acid etching increases the surface rough-ness of fiber posts, but, on the other hand, it causes damage to glassfibers, thus affecting the integrity of the posts. In the present work, topo-graphic changes were not observed. In the case of silane, a chemicalchange was observed. Silane only bridges resins and OH-covered inor-ganic superficially exposed glass fibers (25, 26).

The plasma treatment provides a long-lasting surface modificationand could be easily used by the manufacturer. Regarding plasma treat-ment, Yavirach et al (23) reported that it does not induce any new reac-tive functionalities on the polymer surface. Argon treatment induces freeradical formation on the polymer surface through ion bombardment.Epoxy resin is considered a chemically stable polymer, and, for thisreason, it should be expected to be of little significance for the reactivelayer when it reacts with the methacrylate-based matrix found in Rely XUnicem cement. This fact is evident from the low values of the push-outbond strength.

According to our data, EDA plasma caused a significant chemicalmodification on the surface as well as topographic changes, whichwas indicated by the high roughness observed qualitatively by theSEM. The Rely X Unicem cement showed an affinity with fiber poststreated with EDA plasma, which was observed for the bond strengthof 17.3 MPa. The chemical modifications are associated with nitrogen,carbon and oxygen incorporation, and their high binding energysides, indicating carbon-oxygen and carbon-nitrogen bonding. Inthis case, scanning electron microscopic images showed that allfractures occurred because of cohesive failure in the compositecore. These data are in accordance with C€okeliler et al (16), whoevaluated the effect of plasma-treated E-glass fiber to improvethe mechanical properties of acrylic resin denture base material(polymethylmethacrylate) and observed that this treatment producedchemical and topographic changes, besides increasing the flexuralstrength.

As for the bond strength analysis, the push-out test showed thathydrofluoric acid combined or not with silane did not increase thebond strength or cause modifications in the fracture morphology, aswell as with argon plasma, as compared with the control group. Accord-ing to the findings of the present work, plasma treatment favored thewettability of the post surface bymodifying it chemically when compared

218 Costa Dantas et al.

with usual treatments. Adhesion improvement was only observed afterEDA treatment.

AcknowledgmentsWe would like to thank Jackson Belmiro for technical support.The authors deny any conflicts of interest related to this study.

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