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Brazilian Oral ResearchPrint version ISSN 1806-8324

Braz. oral res. vol.26 no.6 So Paulo Nov./Dec. 2012

http://dx.doi.org/10.1590/S1806-83242012000600004

DENTAL MATERIALS

Addition of silver nanoparticles reduces the wettabilityof methacrylate and silorane-based composites

Shahin KasraeiI; Mohadese AzarsinaII

IDepartment of Operative Dentistry, Dental Research Center, Dental School,Hamadan Univ of Medical Sciences, Hamadan, IranII

Department of Operative Dentistry, Dental School, International Branch of ShahidBeheshti Univ of Medical Sciences, Tehran, Iran

Corresponding Author

ABSTRACT

Incorporation of silver nanoparticles into composite resins is recommended for theirreported antibacterial properties, but this incorporation can affect the wettability ofsuch materials. Therefore, this study evaluated the effect of nano-silver addition tosilorane-based and methacrylate-based composites on their contact angle. Nano-silver particles were added to Z250 (methacrylate-based) and P90 (silorane-based)composites at 0.5% and 1% by weight. The control group had no additions. SEM-EDX analysis was performed to confirm the homogeneity of the nano-silverdistribution. Seventy-two composite discs were prepared and standardized to theidentical surface roughness values, and then distributed randomly into 6 groupscontaining 12 samples each (N = 12). Two random samples from each group wereobserved by atomic force microscopy. Distilled water contact angle measurementswere performed for the wettability measurement. Two-way ANOVA, followed by theTukey-HSD test, with a significance level of 5%, were used for data analysis. It was
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observed that wettability was significantly different between the composites(p = 0.0001), and that the addition of nano-silver caused a significant reduction inthe contact angle (p = 0.0001). Wettability varied depending on the concentrationof the nano silver (p = 0.008). Silorane-based composites have a higher contactangle than methacrylate-based composites. Within the limitations of this study, itcan be concluded that the addition of 0.5% nano-silver particles to the composites

caused a decrease in the contact angle of water.

Descriptors: Nanotechnology; Silver; Composite Resins; Hydrophobic andHydrophilic Interactions.

Introduction

Silorane composites are a new generation of restoratives with a ring-openingcationic polymerization mechanism.1-3 These restorative materials have beenintroduced in an attempt to overcome the polymerization shrinkage of conventionalmethacrylate-based composites. A low potential to absorb the dyes from dailynutrition is considered to be an advantage of silorane-based restoratives because oftheir siloxane backbone, which is responsible for the hydrophobic nature of therestorative material.3,4

Measurement of the contact angle at the solid-air-liquid meeting point is a widelyknown technique used to investigate wettability of solid substrates. Lower

wettability of the composite resin surface and less water sorption contribute to thereduction of staining, and is an effective factor affecting plaqueaccumulation.5,6Silorane-based composites are claimed to have a higher contactangle and a lower amount of plaque adhesion compared to methacrylate-basedcomposites.7

In operative dentistry, secondary caries is the main reason for restorationreplacement.8 Therefore, dental materials with low wettability properties arepreferable to limit the adhesion and proliferation of pathogens and, consequently,to prevent secondary caries. Although the presence of silver in restorative materialshas proved to be effective against streptococci of the human oral cavity, and itmight also be useful as an antibacterial additive to dental restorations,9 it is not

known whether the addition of silver at the nano scale could interfere with thewettability of dental restorative materials.

Furthermore, considering that the incorporation of nanoparticles can affectrestoration contact angle measurements,10,11 the aim of the present study was toevaluate the effect of the addition of nano silver particles to silorane-based andmethacrylate-based composites on this surface property.

Methodology

Experimental design


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This experimental study was performed on 72 resin composite discs. Nano silverparticles (TopNano Tech Co., Taipei, Taiwan) with an average size of 50 nm wereadded mechanically to Z250 (3M ESPE, St. Paul, USA) and P90 (3M ESPE)composites at 0.5% and 1% by weight. The control group did not contain anysilver. One sample from each test group was prepared for SEM-EDX analysis. Eachsample was observed with a scanning electron microscope (Tescan, VegaII, XMU,

Brno, Czech Republic) at 350. To assess the wettability of the samples distilledwater contact angles on composite resins were measured using a contact anglemeasuring system. Two-way ANOVA, followed by Tukey-HSD, were used for dataanalysis. The significance level was set at 5%.

Specimen preparation

Nano silver particles (TopNano Tech Co., Taipei, Taiwan) with an average size of50 nm were added mechanically to Z250 (3M ESPE) and P90 (3M ESPE) compositesat 0.5% and 1% by weight. Unloaded composite resins were used as controls. Thenano particles were mixed continuously with the composites using a plastic spatulafor 30 min in a dark room. The samples were prepared in PVC molds of 10 mm

diameter and 1.5 mm height. The composite was inserted into the mold andimmediately covered with two glass slides from the top and the bottom. Thespecimen was polymerized by light, using an LED (Demi LED Light Curing System,Kerr Corp., Orange, USA) light-curing unit with a light intensity of 800 mW/cm2,measured with a radiometer for 60 s from both sides. All of the samples werepolished with 600, 800, and 1200 grit SiC papers (991A Softlex, Berlin, Germany)to obtain highly polished samples with identical surface roughness (Ra) values. Toconfirm the Ra was homogenous, two samples from each group were observedrandomly by atomic force microscopy (AFM) (Dualscope/Rasterscope C26, DME,Herlev, Denmark) under a load of 0.2 nN and a probe motion speed of 10 m/s.

Silver distribution

SEM-EDX (Scanning electron microscopy with an energy dispersive X-ray analyticalsystem) analysis was performed to confirm the homogeneity of the distribution ofthe nano particles in the composite resins. Therefore, one disc-shaped sample fromeach test group was prepared for SEM-EDX analysis. Samples were broken into twopieces with a chisel-like blade, and the broken surfaces were gold sputter coated(Sputter Coater, Emitech, K45OX Ashford, Kent, England) in a thin 15-nm layer toprevent the sample surfaces from burning during SEM observation. The elementalgold was finally eliminated from the diagram by the system software. The brokensurfaces of each sample were observed with a scanning electron microscope.

Wettability

The wettability of the samples was assessed by measuring the contact angles ofdistilled water on composite resins with a contact angle measuring system (SessileDrop, Kruss G10, Hamburg, Germany). The contact angle was defined as the angleat which the liquid interface met the solid surface of the composite disc at fourpoints on each sample, and the mean of the points was reported as the contactangle of each sample. The surface of the drop was monitored constantly, and thecontact angle was measured just after 20 s, when the droplet was stabilized.

All data were analyzed by SPSS Software (Version 11, SPSS Inc., Chicago, USA)using two-way ANOVA and Tukey HSD multiple comparison tests. The level ofsignificance was set at 0.05.


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Results

Figures 1and2indicate the distribution of nano silver particles in compositeresins.Figures 3and4are the topographic images of the surface of compositeresins taken by atomic force microscopy (AFM).
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The means and standard deviations of the contact angles of the studied groups are

summerized inTable 1.

Analysis of factorial variance was performed in control and test groups for watercontact angles. The contact angle was significantly different between the P90 andZ250 composites. The contact angle of the P90 composite was significantly higherthan that of Z250 (p = 0.0001). The addition of nano silver particles reducedsignificantly the contact angle (p = 0.0001). The interaction of the type of the

composite and the concentration of the nano silver was significant (p = 0.006).
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Therefore, exclusive of the type of composite, incorporation of differentconcentrations of nano silver reduced the contact angle significantly (p = 0.008).

In the Z250 composite, increasing the concentration of nano silver particles from0.5 to 1% caused an increase in the contact angle (p = 0.0001), whereas in theP90 composite the difference between the samples with 0.5% and 1% nano silver

particles was not statistically significant (p > 0.05).

Discussion

Considering the higher level of sorption of microorganisms by the composite resinscompared to other restorative materials,12 some previous studies have suggestedthe addition of silver as an antibacterial material to the composite resinrestorations.10,11 Silver is a safe bactericidal metal, because it is not toxic for animalcells, while it is severely toxic and lethal to bacterial cells.13,14

Concerns have been raised about the adverse effect of nano particle additives onthe mechanical properties of composite resins. Previous studies have reported silvercompounds added at 10% or greater to dental materials would significantly reducecompressive strength, elastic modulus, and tensile strength.11,15 Therefore, it seemsthat nano particles added in low concentrations, as in the present study, would notadversely affect the mechanical properties of composite resins. Discoloration and achange in color to a tone of gray are common problems in all materials containingsilver, especially composite resins.16,17 Using low concentrations of metal nanoparticles can prevent severe discoloration of composite resins.16 It has beenreported in a previous study that the incorporation of silver microparticulates atconcentrations of 0.3% and 0.6% into the composite resin imparted antibacterial

properties to the material. Therefore, according to previous studies, we choseconcentrations of 0.5% and 1% silver nano particles to impart both theantibacterial properties of silver and the less detrimental effect of these nanoparticles on the color of composite resins.

In the present study, the influence of surface roughness was eliminated bypolishing all specimens to a level of clinically acceptable surfacesmoothness18 (about 1 m), which was confirmed by AFM observations.

The contact angle of the silorane-based composite (P90) was significantly higherthan that of the Z250 composite, which is indicative of the higher hydrophobicity ofP90. This is in accordance with the study of Buergers et al.10 Addition of silver nano

particles to P90 and Z250 composites caused a reduction in water contact angle ofthese composites. Both composites exhibited higher contact angles when theconcentration of nano silver was increased from 0.5 to 1% by weight but thecontact angles were still lower than that in the control groups. Therefore,depending on the type of the composite, addition of nano particles couldsignificantly change (reduce) the water contact angle of the composites.

Contrary to the results of the present study, Brgers et al.11 reported greaterhydrophobicity upon the addition of silver to composite resins. They used a flowablecomposite in their study. Filler characteristics of composites have been considered asignificant factor in their water sorption. The amount of water sorption bycomposite resin depends on the hydrophilicity of the polymeric matrices and the

composition of the filler. There is also a correlation between filler load and watersorption.19 The flowable composite used in the study of Brgers et al.(X-flow)contains 38% by volume silicon dioxide filler particles, whereas the Z250 composite


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is filled to 60% by volume with zirconia/silica particles, and Filtek Silorane contains76% by volume quartz and yttrium fluoride filler particles. The contact angle of theflowable composite used in the study of Brgers et al.11 was 66, which increasedupon the addition of silver particles. In addition, they used microparticulates ofsilver with sizes ranging from 3.5 to 18 m. Metallic particles of silver have a largesurface energy. The smaller the silver particles, the higher their energy and surface

activity. Addition of nanometer sized silver particles, as done in the present study(50 nm) could result in an increase in the surface energy of composite resin,consequently decreasing the water contact angle. It is reported in previous studiesthat the addition of these particles to hydrophobic materials, such as compositeresins, causes an increase in surface energy and a reduction of the contact angle,which is in accordance with the results of the present study.20

The results of our study indicated that the addition of nano silver could reduce thecontact angle of the composite resins in comparison to the control groups;however, the water contact angle increased by increasing the nano silverconcentration from 0.5 to 1% by weight. It is possible that the addition of morethan 0.5% nano particles caused the accumulation of these particles, creating

clusters of silver resembling microparticulate silver, and therefore resulting in anincrease in hydrophobicity and contact angle in comparison with compositescontaining 0.5% nano silver.

Although the contact angle was reduced by the addition of nano silver to compositeresins, numerous other factors affect bacterial adherence. The anti-adherence andbactericidal properties of nano silver-containing composites against mutansstreptococci are reported in some previous studies.5,6,11,16,17

Although nano silver particles might be useful as an antibacterial agentincorporated into dental composites, this metal influences the color of the estheticrestorative materials and reduces water contact angles of the heavily filled

composite resins. Therefore, addition of silver nano particles into composite resinrestorations may not be clinically advantageous.

Conclusions

Within the limitations of the present study, it was concluded that addition of 0.5%and 1% silver nano particles increased the wettability of the methacrylate andsilorane-based restorative composites.

Acknowledgements

The authors thank the Dental Research Center and Vice Chancellor of Research,Hamadan University of Medical Sciences, for supporting this study.

References

1. Leprince J, Palin WM, Mullier T, Devaux J, Vreven J, Leloup G. Investigating fillermorphology and mechanical properties of new low-shrinkage resin composite types.J Oral Rehabil. 2010 May;37(5):364-76. [Links]


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2. Klautau EB, Carneiro KK, Lobato MF, Machado SM, Silva e Souza Jr MH. Lowshrinkage composite resins: influence on sealing ability in unfavorable C-factorcavities. Braz Oral Res. 2011 Jan-Feb;25(1):5-12. [Links]

3. Ilie N, Jelen E, Clementino-Luedemann T, Hickel R. Low-shrinkage composite fordental application. Dent Mater J. 2007 Mar;26(2):149-55. [Links]

4. Weinmann W, Thalacker C, Guggenberger R. Siloranes in dental composites.Dent Mater. 2005 Jan;21(5):68-74. [Links]

5. Kondo Y, Takagaki T, Okuda M, Ikeda M, Kadoma Y, Yamauchi J, et al. Effect ofPMMA filler particles addition on the physical properties of resin composite. DentMater J. 2010 Oct;29(5):596-601. [Links]

6. Namen FM, Galan Jr J, Oliveira JF, Cabreira RD, Costa E, Silva-Filho F, et al.Surface properties of dental polymers: measurements of contact angles, roughnessand fluoride release. Mater Res. 2008 Jul-Sep;11(3):239-43. [Links]

7. Beyth N, Domb AJ, Weiss EI. An in vitro quantitative antibacterial analysis ofamalgam and composite resins. J Dent. 2007 Mar;35(3):201-6. [Links]

8. Sarrett DC. Prediction of clinical outcomes of a restoration based on in vivomarginal quality evaluation. J Adhes Dent. 2007;9(Suppl. 1):117-20. [Links]

9. Spacciapoli P, Buxton D, Rothstein D, Friden P. Antimicrobial activity of silvernitrate against periodontal pathogens. J Periodontol Res. 2001;36(2):108-13. [Links]

10. Buergers R, Schneider-Brachert W, Hahnel S, Rosentritt M, Handel G.

Streptococcal adhesion to novel low-shrink silorane-based restorative. Dent Mater.2009 Feb;25(2):269-75. [Links]

11. Brgers R, Eidt A, Frankenberger R, Rosentritt M, Schweikl H, Handel G, et al.The anti-adherence activity and bactericidal effect of microparticulate silveradditives in composite resin materials. Arch Oral Biol. 2009 Jun;54(6):595-601. [Links]

12. Papagiannoulis L, Kakaboura A, Eliades G. In vivo vs in vitro anticariogenicbehavior of glass-ionomer and resin composite restorative materials. Dent Mater.2002 Dec;18(8):561-9. [Links]

13. Janardhanan R, Karuppaiah M, Hebalkar N, Narsinga Rao T. Synthesis andsurface chemistry of nano silver particles. Polyhedron. 2009 Aug;28(12):2522-30. [Links]

14. Fondevila M, Herrer R, Casallas MC, Abecia L, Ducha JJ. Silver nanoparticles asa potential antimicrobial additive for weaned pigs. Anim Feed Sci Technol. 2009Apr;150(3):259-69. [Links]

15. Yoshida K, Tanagawa M, Atsuta M. Characterization and inhibitory effect ofantibacterial dental resin composites incorporating silver-supported materials. JBiomed Mater Res. 1999 Dec;15(4):516-22. [Links]

16. Hernndez-Sierra JF, Ruiz F, Pena DC, Martnez-Gutirrez F, Martnez AE,Guilln Ade J, et al. The antimicrobial sensitivity of Streptococcus mutans to


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nanoparticles of silver, zinc oxide, and gold. Nanomedicine. 2008 Sep;4(3):237-40. [Links]

17. Li L, Deng J, Deng H, Liu Z, Li X. Preparation, characterization and antimicrobialactivities of chitosan/Ag/ZnO blend films. Chem Eng J. 2010 May;160(1):378-82. [Links]

18. Sidhu SK, Henderson LJ. The surface finish of light-cured composite resinmaterials. Clin Mater. 1993;12(1):11-5. [Links]

19. Berger SB, Palialol AR, Cavalli V, Giannini M. Characterization of water sorption,solubility and filler particles of light-cured composite resins. Braz Dent J.2009;20(4):314-8. [Links]

20. Torchinsky I, Rosenman G. Wettability modification of nanomaterials by low-energy electron flux. Nanoscale Res Lett. 2009 Jul;4(10):1209-17. [Links]

Corresponding Author:

Mohadese AzarsinaE-mail:[email protected]

Submitted: May 16, 2012Accepted for publication: Aug 18, 2012Last revision: Sep 20, 2012

Declaration of Interests: The authors certify that they have no commercial orassociative interest that represents a conflict of interest in connection with themanuscript.
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Eur J Dent. 2012 April; 6(2): 198205.

PMCID: PMC3327495

The effect of one-step and multi-step polishing

systems on the surface roughness and

microhardness of novel resin composites

Ugur Erdemir,1Hande Sar Sancakli,1 andEsra Yildiz1

Author information Copyright and License information

Go to:Abstract

Objectives:

The objective of this in vitro study was to evaluate the surface roughnessand micro-hardness of three novel resin composites containing

nanoparticles after polishing with one-step and conventional multi-steppolishing systems.

Methods:

A total of 126 specimens (10 X 2 mm) were prepared in a metal mold usingthree nano-composites (Filtek Supreme XT, Ceram-X, and Grandio), 21specimens of each resin composite for both tests (n=63 for each test).Following light curing, seven specimens from each group received no

polishing treatment and served as controls for both tests. The specimens

were randomly polished using PoGo and Sof-Lex systems for 30 secondsafter being wet-ground with 1200-grit silicon carbide paper. The meansurface roughness of each polished specimen was determined with a

profilometer. The microhardness was determined using a Vickers hardnessmeasuring instrument with a 200-g load and 15 seconds dwell time. Thedata were analyzed using the Kruskal-Wallis test and the post hoc Dunn'smultiple comparison tests at a significance level of .05.

Results:
http://www.ncbi.nlm.nih.gov/pubmed/?term=Erdemir%20U%5Bauth%5Dhttp://www.ncbi.nlm.nih.gov/pubmed/?term=Erdemir%20U%5Bauth%5Dhttp://www.ncbi.nlm.nih.gov/pubmed/?term=Sancakli%20HS%5Bauth%5Dhttp://www.ncbi.nlm.nih.gov/pubmed/?term=Sancakli%20HS%5Bauth%5Dhttp://www.ncbi.nlm.nih.gov/pubmed/?term=Sancakli%20HS%5Bauth%5Dhttp://www.ncbi.nlm.nih.gov/pubmed/?term=Yildiz%20E%5Bauth%5Dhttp://www.ncbi.nlm.nih.gov/pubmed/?term=Yildiz%20E%5Bauth%5Dhttp://www.ncbi.nlm.nih.gov/pubmed/?term=Yildiz%20E%5Bauth%5Dhttp://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3327495/#ui-ncbiinpagenav-2http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3327495/#ui-ncbiinpagenav-2http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3327495/#ui-ncbiinpagenav-2http://void%280%29/http://void%280%29/http://www.ncbi.nlm.nih.gov/pubmed/?term=Yildiz%20E%5Bauth%5Dhttp://www.ncbi.nlm.nih.gov/pubmed/?term=Sancakli%20HS%5Bauth%5Dhttp://www.ncbi.nlm.nih.gov/pubmed/?term=Erdemir%20U%5Bauth%5D


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Among all materials, the smoothest surfaces were obtained under a matrixstrip (control) (P.05). The lowest hardness values for the three resin composites were

obtained with a matrix strip, and there was a statistically significantdifference compared with other polishing systems (P.05).

Conclusion:

The current one-step polishing system appears to be as effective as multi-step systems and may be preferable for polishing resin compositerestorations.

Keywords: Polishing systems, surface roughness, microhardness,nanocomposites

Go to:INTRODUCTIONResin composites are widely used for the direct restoration of both anteriorand posterior teeth because of the simple bonding procedures, estheticdemands by the patients, and improved physical and mechanical properties

of these materials.1One of the most significant advances in the last fewyears is the application of nanotechnology to resin composites.

Nanotechnology produces functional materials and structures in the rangeof 1 to 100 nanometers using various physical and chemical methods.These novel resin composites, which contain nanoparticles, have improvedfiller technology, modified organic matrixes, and offer a greater degree of

polymerization that improves their mechanical and physical properties.2,3Regardless of the cavity class and location, a smooth surface finish isclinically important, as it determines the esthetics and longevity of

composite restoration.1A rough surface has a major impact on the aestheticappearance and discoloration of a restoration,46plaque accumulation,secondary caries, gingival irritation,7,8and wear of opposing and adjacentteeth.9Furthermore, a smooth surface adds to the patients comfort, as achange in surface roughness of 0.3 m can be detected by the tip of thetongue.10The intrinsic characteristics of resin-based composite materials, such ashardness and strength, are crucial mechanical properties that provide aclinically successful restorative material.11Hardness, defined as theresistance of a material to indentation, is an important mechanical propertythat predicts the degree of cure of restorative materials.11,12Restorations
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that are not properly polymerized may result in a softer surface that willretain the scratches created by the finishing procedures. These scratchescan compromise fatigue strength and lead to the premature failure of arestoration.13

The smoothest composite surface is obtained under a polyester matrixfilm.1417However, the removal of this surface by the usually requiredfinishing procedures will produce a harder, more resistant, and estheticallyacceptable surface.17Finishing is defined as the gross contouring or reduction of a restoration toobtain ideal anatomy. Polishing refers to the reduction of roughness andscratches created by finishing instruments. A variety of instruments, suchas carbide and diamond burs, abrasive finish strips, and polishing pastes arefrequently used to finish tooth-colored restorative materials.9,14Clinicianscan choose among a wide range of finishing and polishing instruments.Several studies have demonstrated that multi-step aluminum oxide, graded,abrasive, flexible finishing and polishing discs produce the best surfacesmoothness.9,18,19Many attempts have been made to develop compositefinishing instruments and one-step polishing systems for resin composites.Contouring, finishing, and polishing procedures can be completed using asingle instrument, and it appears to be as effective as multi-step systems for

polishing dental composites.5,20

The purpose of the present study was to investigate the surface roughness

and microhardness of three novel resin composites containing nanoparticlesafter polishing with one-step and conventional multi-step polishingsystems. The null hypotheses tested were that there would be no differencein surface roughness or microhardness (1) among the polished resincomposites or (2) among the different polishing systems when used on thesame resin composites.

Go to:MATERIALS AND METHODS

Materials and Preparation of the Specimens

Three nanocomposites were used in this study: Filtek Supreme XT (3MESPE, St. Paul, MN, USA), Ceram X (Dentsply, DeTrey, Konstanz,Germany), and Grandio (Voco, Cuxhaven, Germany). The properties ofthese materials are shown inTable 1. The finishing and polishing systemsevaluated were PoGo (Dentsply/Caulk, Milford, DE, USA) and Sof-Lexdiscs (3M ESPE, St Paul, MN, USA).Table 2shows the composition andmanufacturers of the polishing systems tested.
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Table 1.

Descriptive table of the resin composites used in the study according to the

manufacturers data.

Table 2.

The composition and manufacturers of the polishing systems investigated.

A total of 126 specimens were fabricated for both tests (n=63 for each test)using a cylindrical metallic mold (10 mm in diameter and 2 mm thick).Each material was inserted into a cylindrical metal mold and confined

between two opposing transparent matrix strips. A glass microscope slide(1 mm in thickness) was then placed on the mold, and a constant pressurewas applied to extrude the excess material. All the restorative materialswere polymerized according to the manufacturers recommended

polymerization times (20 s) with a halogen light-curing unit (VIP; BiscoInc., Schaumburg, IL, USA) operating in standard mode and emitting noless than 600 mW/cm2 as measured with a light meter placed on the curingunit before beginning the polymerization. The guide of the light-curing unitwas placed perpendicular to the specimens surface at a distance of 1 mm.Immediately after the light curing, the specimens were removed from themold and immersed in distilled water at 37C for 7 days prior to thefinishing procedures.

To reduce variability, all specimen preparations and finishing and polishingprocedures were performed by the same investigator. The specimens wererandomly divided into three treatment groups (n=7). The matrix stripgroups were selected, and others were wet-ground with 1200-grit siliconcarbide abrasive paper (SiC) on a rotary polisher (Buehler Metaserv,Buehler, Germany) to provide a baseline before using the polishing

systems.
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Group I (control group) was made up of specimens that received nofinishing or polishing treatment.

Group II (PoGo group), the specimens were polished with diamondmicropolisher discs under dry conditions with light hand pressure using a

planar motion for 30 seconds at 15,000 rpm using a slow-speed hand piece.

Group III (Sof-Lex group), the specimens were sequentially polished withmedium, fine, and super-fine aluminum oxide-impregnated discs under dryconditions with light hand pressure for 30 seconds. After each polishingstep, the specimens were thoroughly rinsed with water for 10 seconds toremove debris, air-dried for 5 seconds, and then polished with another discof lower grit for the same period of time until final polishing. For eachspecimen, a new polishing disc and a new polisher were used and discardedafter each use.

Surface Roughness Test

Following polishing, the specimens were washed, allowed to dry, andstored in distilled water for 7 days before measuring the mean surfaceroughness (Ra) values. The Ra value of each specimen was measured 5times, and the mean Ra values were determined with a cut-off value of 0.8mm, a transverse length of 0.8 mm, and a stylus speed of 0.1 mm/secondsnear the center of each specimen using a surface profilometer (Taylor

Hobson Surtronic 3

+

, Taylor Hobson Ltd., Leicester, England), which wascalibrated to meet the standards before each new measuring session.

Microhardness Test

The microhardness was determined using a Vickers hardness measuringinstrument (Micromet 5114; Buehler, Lake Bluff, IL, USA). Threeindentations were recorded at different points on each specimen no closerthan 1 mm to the adjacent indentations with a 200-g load for a 15-s dwelltime, and the average value was converted into a Vickers hardness number

(VHN).

Statistical Analysis

Statistical analysis was performed using the 2007 version of the NCSS-PASS statistical software package (Kaysville, Utah, USA). As the averageroughness and microhardness values were not normally distributed(Kolmogorov-Smirnov test), a non-parametric Kruskal-Wallis analysis ofvariance was applied to assess significant differences among theexperimental groups. Dunns multiple comparison was applied for post-hoc

comparisons. The statistical significance level was established at P


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Go to:RESULTS

Surface Roughness Test Results

The mean surface roughness (Ra) values and standard deviation producedby the matrix strips, PoGo, and Sof-Lex discs on three resin-basedcomposites are listed inTable 3andFigure 1. For all materials, the smoothestsurfaces were obtained under matrix strip (control) rather than the polishingsystems tested (P.05). In the Filtek Supreme XT and Ceram-X groups,Sof-Lex produced higher roughness values than the PoGo with no

statistically significant difference. On the other hand, in the Grandio group,PoGo produced higher roughness values than the Sof-Lex, but thedifference was statistically insignificant.

Figure 1.

Surface roughness of the resin composites tested. Polishing systems with

the same black bar are not statistically different.

Table 3.Mean surface roughness values (Ra, m) and standard deviations (SD) for

the tested resin composite materials and polishing systems.

For the matrix strip groups, Filtek Supreme XT had the smoothest surface,which was significantly different from the Ceram-X and Grandio groups(P.05).

For the PoGo groups, Grandio showed a significantly higher surfaceroughness compared to the other composites (P


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no statistically significant differences among Filtek Supreme XT andCeram-X groups (P>.05). For the Sof-Lex group, Grandio showed asignificantly higher surface roughness compared to the other composites(P.05).Microhardness Test Results

The mean microhardness values and standard deviations produced bymatrix strips, PoGo, and Sof-Lex discs on three resin-based composites aredisplayed inTable 4andFigure 2. The lowest hardness values were recordedfor the three resin composites under matrix strips, which showed astatistically significant difference compared with other polishing systemstested (P.05). For all the polishing systems, the ranking formicrohardness values from least to greatest were as follows: Ceram-X

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