Development of novel dental nanocomposites reinforced with polyhedral oligomeric silsesquioxane (POSS)

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<ul><li><p>dental mater ials 2 6 ( 2 0 1 0 ) 456462</p><p>avai lab le at www.sc iencedi rec t .com</p><p>journa l homepage: www. int l .e lsev ierhea l th .com/ journa ls /dema</p><p>Development of novel dental nanocomposites reinforcedwith polyhedral oligomeric silsesquioxane (POSS)</p><p>Xiaorona Departmb Departm</p><p>a r t i c</p><p>Article histo</p><p>Received 1</p><p>Received i</p><p>18 July 200</p><p>Accepted 1</p><p>Keywords:</p><p>Dental com</p><p>Nanocomp</p><p>Shrinkage</p><p>Polyhedral</p><p>silsesquiox</p><p>Mechanica</p><p> CorrespE-mail</p><p>0109-5641/doi:10.1016g Wua,, Yi Suna, Weili Xieb, Yanju Liua, Xueyu Songa</p><p>ent of Astronautic Science and Mechanics, Harbin Institute of Technology, Chinaent of Stomatology, Harbin Medical University, China</p><p>l e i n f o</p><p>ry:</p><p>4 April 2009</p><p>n revised form</p><p>9</p><p>6 November 2009</p><p>posite resins</p><p>osites</p><p>oligomeric</p><p>ane (POSS)</p><p>l properties</p><p>a b s t r a c t</p><p>Objectives. It has been the focus to develop low shrinkage dental composite resins in recent</p><p>ten years. A major difculty in developing low shrinkage dental materials is that their</p><p>deciency in mechanical properties cannot satisfy the clinical purpose. The aim of this</p><p>study is to develop novel dental nanocomposites incorporated with polyhedral oligomeric</p><p>silsesquioxane (POSS). It is especially interesting to evaluate the volumetric shrinkage and</p><p>mechanical properties, improve the shrinkage, working performances and service life of</p><p>dental composite resins.</p><p>Methods. The effect of added POSS on the composites mechanical properties has been</p><p>evaluated. The weight percentages of added POSS are 0, 2, 5, 10 and 15wt% respectively.</p><p>Fourier-transform infra-red spectroscopy and X-ray diffraction were used to characterize</p><p>their microstructures. Physico-mechanical properties that were investigated included vol-</p><p>umetric shrinkage, exural strength, exural modulus, compressive strength, compressive</p><p>modulus, Vikers hardness and fracture energy. Furthermore, the possible reinforced mech-</p><p>anism has been discussed.</p><p>Results. The shrinkage of novel nanocomposites decreased from 3.53% to 2.18%. The</p><p>nanocomposites incorporated with POSS showed greatly improved mechanical properties,</p><p>for example, with only 2wt% POSS added, the nanocompsites exural strength increased</p><p>15%, compressive strength increased 12%, hardness increased 15% and uncommonly, even</p><p>the toughness of resins was obviously increased. With 5wt% POSS polymerized, compres-</p><p>sive strength increased from 192MPa to 251MPa and compressive modulus increased from</p><p>3.93GPa to 6.62GPa, but exure strength began to decline from 87MPa to 75MPa. This nd-</p><p>ing indicated that the reinforcing mechanism of exure state maybe different from that of</p><p>compressive state.</p><p>Conclusions. Themechanical properties and volumetric shrinkage of dental composite resins</p><p>polymerized with POSS can be improved signicantly. In current study, the nanocomposite</p><p>with 2wt% POSS incorporated is observed to achieve the best improved effects.</p><p> 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.</p><p>onding author. Tel.: +86 0451 86414825.addresses: wuxr2230@163.com, atanackovic@uns.ns.ac.yu (X. Wu).$ see front matter 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved./j.dental.2009.11.161</p></li><li><p>dental mater ials 2 6 ( 2 0 1 0 ) 456462 457</p><p>1. Introduction</p><p>The develolar direct rthe eld ofment has bdiscovery,tailor-madeposite) or aphoto initisome probtal restorareduction oimprovemeties [912],[16,17].</p><p>Polyhedcal organicdevelopednanostructin structureformula (Rsurrounded</p><p>It has bmodied pthe organicand low coin mechanAt present,good perfor</p><p>SellingePOSS beingstudy, theevaluated t(without lthe POSS coplayed a veformulated</p><p>Based on[22], Fong erestorativetially (or comonly a smain the resinof the comdistinct impressive str</p><p>Dodiuk-functional gnanotailoriIt showed thand adhesirated by oc</p><p>Many otstructural dcess of modBut we havniques of sneeded for</p><p>Molecular anatomy of multifunctional methacryl</p><p>imits thedevelopment andapplicationof POSS indentaltions.his paper, multifunctional methacryl POSS cage mix-= 8, 10, 12) (from Hybrid Plastics) was explored to beinto dental composite resins to develop novel dentalomposites with improved properties. Multifunctionalcryl POSS molecules anatomy (showed by Fig. 1) con-f an inorganic cage built with silicon and oxygen, andi isy, theaimwith</p><p>age,ces</p><p>Ma</p><p>For</p><p>cryl PCA).EGDMereers</p><p>Molecular structures of the monomers andinitiation system.pment of dental restorative materials, in particu-esin-based lling composites, has revolutionizeddentistry over the past 30 years. This develop-een achieved mainly through organic monomermodications in formulation, the use of newllers (e.g. nanollers or clusters for the com-</p><p>dvances in light curing equipment and efcientators [1]. Despite these developmental advances,lems still limit the use of composites in den-tion. Most improvements are focused on thef polymerization shrinkage [25], as well as thent of wear resistance [68], mechanical proper-biocompatibility [1315], and processing properties</p><p>ral oligomeric silsesquixanes (POSS) is one typi-inorganic hybrid nanocomposite, which has beensince the end of last century. POSS is really aural chemical whose molecule is 1.5nm isotropic. POSS monomer is represented by the empirical</p><p>SiO1.5)n with an inorganic silica-like core (SiO1.5)by organic corner groups R.een revealed that the performances of POSS-</p><p>olymers are usually attractive. They not only havecharacters such as good processability, toughnessst, but also hold excellent inorganic performancesics, thermodynamics, anti-oxidation, etc. [1820].it is a very important way to get functional andmance materials modied by POSS.r and Laine [21] rst mentioned the possibility ofused in dental restorative materials. In a latter</p><p>research group of Culbertson and co-workers [22]he systems of POSS incorporated with neat resinsler). The results showed that miscibility betweenmponent and the matrix, especially the diluents,</p><p>ry important role in improving the properties of thethermosets.the research of Culbertson and co-workers groupt al.s team [23] explored novel polymeric dentalcomposites, in which POSS-MA was used to par-pletely) replaceBis-GMA.The results showed that</p><p>ll percentage of POSS-MA substitution of Bis-GMAsystems could improve the mechanical propertiesposites. However, it was a pity that there was noprovement in such important properties as com-ength, hardness and toughness.Kenig et al. [24] believed that the type of the graftedroup of the caged silicawas the dominant factor inng of improved dental composites and adhesives.at themechanical properties of dental composites</p><p>ves were improved by acrylated POSS but deterio-taphenyl grafted POSS.her research works [2527] have been done on theesign of the POSS molecule, synthesizing the pro-ied resins, as well as properties characterization.e to admit that considerably complicated tech-ynthesis and rigorous conditions of reaction aremost new POSS monomers. Therefore, this seri-</p><p>Fig. 1 POSS.</p><p>ously lrestora</p><p>In tture (naddednanocmethasists oeach Stionall</p><p>Thepositesshrinkforman</p><p>2.</p><p>2.1.</p><p>MethaValley,and T98%) wmonom</p><p>Fig. 2 photo-attached by amethacrylate functional group. Addi-methacryl POSS is soluble in the composite resins.of the studywas to develop novel dental nanocom-POSS incorporated, evaluate their polymerization</p><p>mechanical properties, and improve working per-and service life.</p><p>terials and methods</p><p>mulation of nanocomposites</p><p>OSS was obtained from Hybrid Plastics (FountainBis-GMA (Bisphenol A glycerolate dimethacrylate)A (Tri(ethylenglycol) dimethacrylate, TEGDMA,</p><p>from Aldrich Chemical Co. (shown in Fig. 2). Allwere used as receivedwithout further purication.</p></li><li><p>458 dental mater ials 2 6 ( 2 0 1 0 ) 456462</p><p>Table 1 Weight percentage of the components used indental nanocomposites (wt%).</p><p>Composit</p><p>P00P02P05P10P15</p><p>The commphorquinonmethacrylaBoth CQ anThe ller uium oxide0.8m, proStomatolog</p><p>2.2. Syn</p><p>A solution0.5wt% CQsufcientlyfunctionalsolution ofuniformly.stirred in thbles. In thiat room temmens werein distilledless steel mdirection unal dimenrately and</p><p>2.3. FTI</p><p>Fourier-tranto evaluatewere collecequipped wwas used fsamples inwithout ll</p><p>2.4. X-r</p><p>Wide-angleD/max-B rCu Ka irradThe X-rayspoints werevals. The saresins with</p><p>2.5. Sh</p><p>According tdensity ()</p><p>metric shrinkage was calculated using the formula:</p><p>age( )</p><p>samundemplehe viniti</p><p>Fle</p><p>ecimnsioth. Fre ob9: 20medne, Gws:</p><p>3PLWT2</p><p>P</p><p>d</p><p>)(</p><p>P isrts (wen,ion a</p><p>Co</p><p>essivere mof 103mmmedne, Gws:</p><p>4PD2</p><p>L0(FHD2(L</p><p>D iseciming lof lo</p><p>Haes code Resin matrix wt% POSS wt% BG wt%</p><p>40 0 6038 2 6035 5 6030 10 6025 15 60</p><p>only used visible light photo-initiator CQ (cam-e, 97%) and co-initiator (2-(dimethylamino) ethylte, DMAEMA, 98%) were selected for this research.d DMAEMA were also from Aldrich Chemical Co.sed in this study was nely milled silanized bar-glass powder (BG) with an average particle size ofvided by the materials laboratory of the School ofy at Peking University.</p><p>thesis of materials</p><p>containing 49.5wt% Bis-GMA, 49.5wt% TEGDMA,and 0.5wt% DMAEMA was prepared by mixingin a container kept away from light. Then multi-methacryl POSS was proportionately added to theneat resins as Table 1 and magnetically blendedFinally, BG was slowly put into the mixture ande vacuummixer allowing for the escape of air bub-s study the curing time of each sample was 40 sperature, except special explanation. Five speci-</p><p>prepared for each type of material and immersedwater at 37 C for 24h after taking out of the stain-olds, followed by a careful polish in a longitudinal</p><p>nder water with 2400 grit silicon carbide paper. Thesions of the specimens were then measured accu-recorded immediately before testing.</p><p>R characterization</p><p>sform infra-red spectroscopy (FTIR) was utilizedthe degree of conversion. The mid-IR spectra</p><p>ted with an AVATAR360 (Nicolet, USA) instrumentith 4000400 cm1 wave speed. A blank KBr pellet</p><p>or the collection of the background spectrum. Thevolved in this part of the study were neat resinser.</p><p>ay characterization</p><p>X-ray diffraction (WAXD) was performed using aotational anode X-ray diffractometer (Japan) withiation (wavelength of 1.54) using a nickel lter.were collimated with a pinhole collimator. Datacollected over the 2 range of 1090 at 0.02 inter-</p><p>Shrink</p><p>Theparedthe sathen tphoto-</p><p>2.6.</p><p>The spa dimein leng(Ef) weISO404perforMachias follo</p><p>FS =2</p><p>Ef =(</p><p>wheresuppospecimdeect</p><p>2.7.</p><p>Compr(EC) wspeedsionsperforMachias follo</p><p>CS =</p><p>EC = 4</p><p>wherethe spspondphase</p><p>2.8.</p><p>mples involved in this part of the study were neatout ller.</p><p>rinkage</p><p>o ISO3521, a pycnometer was used to measure theof uncured and cured resin specimens. The volu-</p><p>Vickers hamicroindenness Testinindented wwas in righVickers haV% = 1 uncuredcured</p><p> 100% (1)</p><p>ples involved in this part of the study were pre-r a two-step photo-initiated curing process. First,s were exposed to visible light and cured for 60 s,isible light switched off, 60min later, the secondated curing began and lasted for another 30 s.</p><p>xural strength and exural modulus</p><p>ens were prepared in stainless steel molds withn of 2mm in width by 2mm in depth by 25mmlexural strength (FS) and exural elastic modulustained by three-point exure testing (according to00) at a crosshead speed 0.5mm/min. The test wason a T1-FR010TH A50 (ZWICK Materials Testingermany). Calculations were made using formulas</p><p>(2)</p><p>L3</p><p>4WT3</p><p>)(3)</p><p>the load at fracture, L is the distance between twohich was set to be 20mm), W is the width of theT is the thickness of the specimen and d is thet load P.</p><p>mpressive strength and compressive modulus</p><p>e strength (CS) and compressive elastic moduluseasured by compressive testing at a crosshead</p><p>mm/minwith cylindrical sampleswith the dimen-in diameter by 7mm in length. The test was</p><p>on a T1-FR010TH A50 (ZWICK Materials Testingermany). Calculations were made using formulas</p><p>(4)</p><p> FL)H LL)</p><p>(5)</p><p>the diameter of the specimen, L0 is the length ofen, FH(FL) and LH(LL) is the end(start) of the corre-oad and distortion of the specimen in the elasticaddistortion curve.</p><p>rdness</p><p>rdness (HV) was determined using a depth-sensingtation technique on BZ2.5/TSIS (Universal Hard-g Instrument, Germany). The specimens wereith a Vickers indenter, whose diamond press headt square pyramid shape with 136 relatively angle.rdness (HV) data was obtained by dividing the peak</p></li><li><p>dental mater ials 2 6 ( 2 0 1 0 ) 456462 459</p><p>F Wposs=0wt%) and (b) P02 (Wposs=2wt%).</p><p>load (Pmax)as follows:</p><p>HV = PmaxAmax</p><p>where d is t</p><p>2.9. Fra</p><p>Fracture ening fracturestressstraitest. In theenergy relesurement ogreater the</p><p>3. Re</p><p>In this papmatrix/inornot only haing, but albe processposites witthe polymeinvestigate</p><p>3.1. De</p><p>The FTIR sments of thresins wereples and d(Fig. 3) it ca1635 cm1</p><p>the methacresins had p</p><p>d Fiof Ctedat othelly, tn inc</p><p>WA</p><p>angleer POWAXta (Fhousono</p><p>rystaultifuig. 3 FTIR spectra of the resins irradiated for 40 s. (a) P00 (</p><p>over the maximum projected contact area (Amax)</p><p>= 1.8544 Pmaxd2</p><p>(6)</p><p>he average length of two indented diagonals.</p><p>cture energy</p><p>ergy (Nmm) is the dissipative outside energy dur-, which can be calculated by the enclosed area ofn fracture curve obtained from three-point exurephysics, the square of toughness is namely the</p><p>ase rate. Therefore, fracture energy can be themea-f the toughness of the materials, and usually, thefracture energy, the tougher the material.</p><p>sults and discussion</p><p>P00 andegreeaccounthan thone ofGenerawith apaper.</p><p>3.2.</p><p>Widewhethof thetion daamorpPOSS mPOSS cthe mer, 40/60 (wt%) was chosen as the ratio of resinganic ller. The composite resins with such ratiod proper viscosity to keep the ller from deposit-so had sufcient uidity to make resins easy toed. In this paper, the effects of dental nanocom-h different weight percentage (015wt%) POSS onrization shrinkage andmechanical propertieswered.</p><p>gree of conversion</p><p>pectra shown in Fig. 3 were the mid-IR measure-e C C absorption at 1635 cm1. Uncured and curedevaluated, which deadline stood for uncured sam-ashed stood for cured ones. From FTIR spectran be seen that the intensity of C C absorption atwas obviously weaker after curing. It proved thatrylate double bonds had partly conversed and theolymerized during curing. Comparedwith Fig. 3(a)</p><p>matrix.</p><p>Fig.g. 3(b) P02, it could be seen that the weakenedC absorption of P02was greater than that of P00. It</p><p>for why the degree of conversion of P02 was greaterf P00. The methacrylate double bond conversion isimportant properties in dental composite resins.he mechanical property of resins can be improvedrease in conversion. It was also proved later in this</p><p>XD</p><p>X-ray diffraction was employed to investigateSS crystal peaks appear in the nanocompositesD proles. In this study, wide-angle X-ray diffrac-ig. 4) indicated that all POSS nanocomposites were, even when the mass fraction of the methacrylmers in the resin mixture was as high as 15%, nol peaks could be identied, which conrmed thatnctional POSS had polymerized within the resin4 WAXD proles of the nanocomposites.</p></li><li><p>460 dental mater ials 2 6 ( 2 0 1 0 ) 456462</p><p>3.3. Shrinkage</p><p>Most dental composite resins are free-radical initiation pho-topolymers, and volumetric shrinkage during polymeriza...</p></li></ul>