Effect of pre-heating on hardness of methacrylate- and silorane-based composites

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CATELAN,)Anderson*) BARRETO,)Bruno)de)Castro)Ferreira**) LIMA,)Adriano)Fonseca***) OLIVEIRA,)Marcelo)Tavares****) MARCHI,)Giselle)Maria*) AGUIAR,)Flávio)Henrique)Baggio*)

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EFFECT'OF'PRE@HEATING'ON'

HARDNESS'OF'METHACRYLATE@'AND'

SILORANE@BASED'COMPOSITES'

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ABSTRACT'

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AIM:) To) evaluate) the) effect) of) composite) preXheating) on) the) microhardness)of)different)monomer)resinXbased.)MATERIALS'AND' METHOD:) Circular) specimens) of) methacrylateX) and) siloraneXbased) composite) resins) preXheated) at) 23,) 39,) and) 55˚) C) were) carried) out,) and)cured)using)a)halogen)lightXcuring)unit)at)650)mW/cm².)After)24) h,)the)specimens)were)polished)and)Knoop)hardness)number)(KHN)) was)measured)using)a)microhardness)tester)with)50Xg)load)for)15)s.) The) data) were) analyzed) with) ANOVA) and) Tukey’s) tests) (α) =) 0.05).)

RESULTS:) Top) surface) presented) higher) KHN) than) bottom,) methacrylateXbased) composite) showed) higher) KHN) compared) to) silorane,) and) preXheating) increased) the) KHN) of) the) composites) tested.) CONCLUSION:) PreXheating) can) be) used) to) improve) the) microhardness)of)methracrylateX)and)siloraneXbased)composites.) )

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KEYWORDS'

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INTRODUCTION

! Light&activated, methacrylate&based, composites,cure,is,characterized,by,volumetric, shrinkage1_,_{and,exhibit,a,signi;icant,percentage,} of, incomplete, C=C, conversion., However,, as, higher,the,conversion,rate,as,higher,shrinkage, strain2_{.,Polymerization,shrinkage,may,result,in,} increase, the, risks, of, cuspal, de;lection, and, i n c r e a s e d, o f, m a r g i n a l, l e a k a g e ,, a n d, subsequently, secondary&caries, formation,, and, pulpal,in;lammation3_.

, Recently,, a, monomer, system, was, development, from,the,reaction,of,oxirane,and, siloxane, molecules,, termed, silorane1_{., Silorane,} exhibits,a,cationic,ring&opening,polymerization, instead,of,radical, cure,of,methacrylate4,5_,,with, lower, polymerization, shrinkage1,4_{, and,} mechanical, properties, similar,to, conventional, composites5_.

, It, has, been, reported, that, pre&heating, composite,prior, to, light,curing,might, enhance, the, curing, degree, of, resin&based, material6_., Temperature, increase, molecular, mobility, due, lower, viscosity6,7_{,, but, this, reaction, is, self&} limited, by, the, rapid, formation, of, a, highly, cross&linked, polymeric, network6_{., Increased,} conversion, rate, results, in, higher, mechanical, properties,,such,as,hardness8_.

, Therefore, the, aim, of, this, study, was, evaluate, the, effect, of, pre&heating, on, the, microhardness, of, methacrylate, and, silorane, resin&based, composites., Two, null, hypotheses, were, tested:, there, would, be, no, difference,

between, the, different, (1),composites, and, (2), temperatures, on, the, mechanical, properties, tested.

MATERIAL-AND-METHODS

! In, this, study,, two, microhybrid, composite, resins, were, evaluated., The, methacrylate, Filtek, Z250, (3M, ESPE,, St., Paul,, MN,, USA),and,silorane,Filtek, LS,(3M,ESPE,, St., Paul,, MN,, USA), resin&based, composites, were, used,(Table,1).

, A, circular, te;lon, mold, (5, mm, in, diameter,and,2,mm, in,thickness),was, used,to, prepare,the,specimens,for,microhardness,(n,=, 10)., Composite, resins, were,pre&heating, at, 23,, 39,, and, 55, ºC, using, a, composite, heating, conditioner,(Ena,Heat;,Micerium,S.p.A,,Avegno,, GE,, Italy),, in, accordance, with, manufacturer´s, instruction,,in,room, with,temperature, (23,ºC), and,humidity, (30%),controlled.,The,mold,was, ;illed, with, only, one, increment, of, composite,, covered, with, a, polyester, strip, and, pressed, with,a,500&g,load.,The,composite,was,cured,for, 40, s, using, a, quartz&tungsten&halogen, light& curing, unit, (Demetron, LC;, Kerr, Corporation,, Middleton,, WI,, USA), at, 650, mW/cm²,, monitored, by, a, radiometer, (model, 100;, Demetron/Kerr,,Danbury,,CT,,USA).

, Specimens, were, removed, of, the, mold, and,dry,stored,in,a,lightproof,vial, at,37,°C,for,

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carbide, (SiC), grinding, paper, (CarbiMet, 2, Abrasive,Discs;,Buehler,,Lake,Bluff,,IL,,USA).

Table,1.,Composite,resins,used,in,the,study.

Composite,resin Composition*

Methacrylate,(Filtek,Z250,,A2,shade)

Lot.,N144001BR

Filler:,60,vol%,,aluminum,oxide,,silica,,and,zirconium, oxide,(0.01&3.5,µm).,Resin:, bisphenol&A, glycidyl, dimethacrylate, (Bis&GMA),, ethoxylated, bisphenol, A, dimetacrylate,(Bis&EMA),,and,urethane,dimethacrylate,(UDMA).

Silorane,(Filtek,LS,,A2,shade)

Lot.,N128528

Filler:, 55, vol%,, silica,, and, yttrium, tri;luoride, (0.04&1.7, µm)., Resin:, Bis&3,4& E p o x y c y c l o h e x y l e t h y l & P h e n y l & M e t h y l s i l a n e, a n d, 3 , 4 & Epoxycyclohexylcyclopolymethylsiloxane.

*According!to!manufacturers.

, Knoop,hardness,number,(KHN),reading,

was,measured,on,the,top,and,bottom,surfaces, of,each,specimen,using,a,microhardness,tester, (HMV&2T, E;, Shimadzu, Corporation,, Tokyo,, Japan),with,a,Knoop,diamond,indenter,under,a, 50&g, load,for,15,s., Three, measurements, were, made,on,the, surface,of,each,specimen:, one, at, the, center, and, other, 2, at, a, distance, of, approximately, 100, μm, from, the, central, location., The, average, of, the, 3, values, was, calculated,as,the,KHN,value,for,each,specimen. The, results, of, KHN, on, the, top, and, bottom, surfaces,were,submitted,to,two&way,split&splot, analysis,of,variance,(ANOVA),and,Tukey’s, test, at, the, pre&set, alpha, of, 0.05., The, factors, composite, resin, and, temperature, were, considered, in, the, parcels, and, the, factor, surface, (top, and, bottom, surfaces), was, considered,in,the,sub&parcels.

RESULTS

! ANOVA, showed, signi;icant, difference, for, the, factors, composite, (p, <, 0.001),, temperature,(p,=,0.0145),,surface,(p,<,0.001),, and, for, interaction, of, factors, composite, and, surface,(p,<,0.0001).

, Top,surface,presented,higher,KHN,than,

bottom, of, the, specimens., The, methacrylate& based, composite, showed, higher, KHN, values, compared, to, silorane., Composite, pre&heating, increased,the,microhardness,,independently,of, the, composite, resin, and, surface, analyzed., These,;indings,are,illustrated,in,the,Table,2.

DISCUSSION

! Since, 1960s, improvements, were,

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ranging, from, 1.9, to, 3.5, vol%1_{., Silorane, has,} lower, polymerization, shrinkage, (less, than, 1, v o l % ), b y, t h e, c a t i o n i c, r i n g & o p e n i n g, polymerization, mechanism, instead, of, radical, cure,of,methacrylate1_{.,According,to, the,results,} of, this, study,, higher, hardness, was, found, for, m e t h a c r y l a t e, c o m p a r e d, t o, s i l o r a n e, composite8,9_{,, so, the, ;irst, null, hypothesis, was,} rejected., The, UDMA, monomer, contained, in, methacrylate, composite, gives, more, mobility, and,has, been,related,to, increase,of, DC10_{;, fact,} that, can, have, contributed, to, this, differences, observed., Another, explanation, can, be, related,

to, the, differences, in, the, mechanism, of, the, polymerization, reaction, between, the, two, composites., Methacrylate, is, cured, by, radical, intermediates, and, cycloaliphatic, oxirane, polymerizes, via, cationic, intermediates.1_, Moreover,, the, onset, of, cationic, ring&opening, polymerization,of,the,silorane,is,slower,due,to, the,necessary,formation,of,suf;icient,cations,to, initiate,the, polymerization,, thus, more,time, of, light&curing, is, required, compared, to, radical, cure,of,methacrylate,monomers,molecules,into, polymer,network9_.

Table,2.,Knoop,microhardness,(Kgf/mm2_{),means,(S.D.),,according,to,pre&heating,temperature,,composite,resin,,and,surface,analyzed.}

Composite Surface Pre&heating,temperaturePre&heating,temperaturePre&heating,temperature

Composite Surface _23,_o_C _35,_o_C _59,_o_C

Methacrylate# Top* 66.41,(2.19) 68.15,(2.34) 68.69,(1.76) Methacrylate#

Bottom 63.56,(2.12) 64.42,(2.46) 65.00,(1.61)

Silorane

Top* 49.36,(4.82) 51.20,(2.21) 51.81,(1.69)

Silorane Bottom 42.28,(5.62) 45.25,(1.94) 45.11,(1.81)

B AB A

*indicates,statistical,difference,between,the,top,and,bottom,surfaces,(p,<,0.001).

#indicates,statistical,difference,between,the,methacrylate,and,silorane,composites,(p,<,0.001). Distinct,capital,letters,indicate,statistical,differences,between,the,temperatures,tested.

, Improvements, of, the, mechanical,

properties,have,been,associated,to,increase,of, the, monomer, conversion11,12_{,, and, also, highly,} correlated,to,the,;iller,fraction,of,composites13_., Low, hardness, usually, results, in, poor, wear, resistance14_{, and, has, been, related, to, ;iller,} fraction15_{., Silorane, exhibits, 55, vol%, and,} methacrylate, 60, vol%, of, inorganic, ;iller., A, linear,correlation,between,the,volume,fraction, of,;iller,and,hardness,was,found,in,a,previous, study15_{., Thus,, the, higher, ;iller, content, of, the,}

methacrylate, can, had, in;luenced, the, highest, KHN, values, compared, to, the, silorane, composite.

, _{The, second, null, hypothesis, was, also,}

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material., Nevertheless,, this, reaction, is, self& limited, by, the, rapid, formation, of, a, highly, c r o s s & l i n k e d, p o l y m e r i c, n e t w o r k6_., Furthermore,, pre&heated, composite, provides, better, marginal, adaptation, by, the, viscosity, reduction7_{,, mainly, for, silorane, that, presents,} higher, viscosity, than, some, packable, composites16_{., The, light, radiant, exposure, that,} reaches, the, material, is, an, important, factor,to, modulates, the, physical, properties, of, the, material,, as, well, as, the, distance, increased, between, the, light, guide, tip, and, material,, the, light, scattering, by, ;iller, particles,, and, the, increment, thickness, of, composite,, facts, that, can, decline, the, irradiance, that, reaches, at, bottom, surface, of, the, restorative, material,, jeopardizing, the,properties, of,this,surface17,18_., Therefore,, the, combination, of, problems, reported, could, be, responsible, by, the, difference, between, the, top, and, bottom, surfaces,observed,in,the,present,investigation.

CONCLUSION

! Based, on, the, results, of, this, study,, it, concludes, that, pre&heated, composite, can, be, used, to, increase, the, microhardness, of, methacrylate&, and, silorane&based, composites,, probably, related, to, higher, monomer, conversion., Consequently, this, fact, provides, improvement, on, the, physical, properties, and, associated,to,better,marginal,adaptation,due,to, composite, viscosity, reduction,, increase, the, clinical,longevity,of,dental,restorations.

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