Research Article Mechanical Properties Comparing Composite...

Research ArticleMechanical Properties Comparing CompositeFiber Length to Amalgam

Richard C Petersen1 and Perng-Ru Liu2

1Departments of Biomedical Engineering Biomaterials and Restorative Sciences University of Alabama at BirminghamSDB 539 1919 7th Avenue South Birmingham AL 35294 USA2Department of Restorative Sciences University of Alabama at Birmingham SDB 539 1919 7th Avenue South BirminghamAL 35294 USA

Correspondence should be addressed to Richard C Petersen richbmeuabedu

Received 30 August 2015 Revised 17 January 2016 Accepted 19 January 2016

Academic Editor Francesco Aymerich

Copyright copy 2016 R C Petersen and P-R Liu This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Photocure fiber-reinforced composites (FRCs) with varying chopped quartz-fiber lengths were incorporated into a dentalphotocure zirconia-silicate particulate-filled composite (PFC) for mechanical test comparisons with a popular commercialspherical-particle amalgam FRC lengths included 05-mm 10mm 20mm and 30mmall at a constant 282 volume percent Four-point fully articulated fixtures were used according to American Standards Test Methods with sample dimensions of 2times2times50mm3across a 40mm span to provide sufficient Euler flexural bending and prevent top-load compressive shear error Mechanicalproperties for flexural strength modulus yield strength resilience work of fracture critical strain energy release critical stressintensity factor and strain were obtained for comparison Fiber length subsequently correlated with increasing all mechanicalproperties119901 lt 11times10minus5 Although themodulus was significantly statistically higher for amalgam than all composites all FRCs andeven the PFC had higher values than amalgam for all other mechanical properties Because amalgams provide increased longevityduring clinical use compared to the standard PFCs modulus would appear to be a mechanical property that might sufficientlyreduce margin interlaminar shear stress and strain-related microcracking that could reduce failure rates Also since FRCs weretested with all mechanical properties that statistically significantly increased over the PFC new avenues for future developmentcould be provided toward surpassing amalgam in clinical longevity

1 Introduction

Dental professionalsmust assume responsibility over time forproviding a level of care that is expected to be no less thancontinuous quality improvement above historically relatedstandards Since the late 1960s amalgam has experienced adecline in the United States at over 75 of all restorationsto only about 50 by 1991 [1] and an overall 78 reductionin placement from 157 million in 1977 to just 66 million in1999 [2] Conversely in the United States particulate-filledcomposites (PFCs) have increased use in load-bearingmolarsand surpassed amalgam for the number of fillings placed inthe late 1990s [2] It is known that the critical barrier forboth dental composites and amalgam is primarily bacterialrecurrent decay at the margins but with lower PFC lifetimes

compared to the amalgam [3ndash25] On the other hand futureimprovement is expected for PFCs since instruction forposterior placement was minimal in most dental schoolsbefore 1990 increasing to a level where PFCs account forabout 30 of all posterior fillings in a 2005 survey [26] Inaddition improved materials and clinician experience havesignificantly reduced failures of the posterior PFC [26 27]Regarding the need for continual dental composite researchand development amalgam has further experienced severalproblems related to potential toxicity-related biocompatibil-ity [28] that has resulted in several countries discouraging andeven banning silver-alloy filling placement [27]

Amalgam has been mechanically tested historically bycompressive stress and occasionally by tensile tests thatproduce results on the order of about 6ndash11x lower than

Hindawi Publishing CorporationJournal of CompositesVolume 2016 Article ID 3823952 13 pageshttpdxdoiorg10115520163823952

2 Journal of Composites

compressive values [29ndash32] Conversely the more recentdevelopment of the dental PFC has been historically testedby flexural-test standards developed through the Ameri-can National Standards Institute (ANSI) and InternationalStandards Organization (ISO) [33] that should producevalues very close to tensile tests ideally In addition photo-cure chopped or discontinuous fiber-reinforced composites(FRCs) have demonstrated highly significant mechanicalproperty improvements over similar PFCs during flexuraltesting [34ndash37] Significant statistical differences for FRCmechanical property improvements over PFC included flex-ural strength modulus yield strength resilience work offracture (WOF) critical strain energy release (119878

119868119888) critical

stress intensity factor (119870119868119888) and strain that in turn appear

to be important for future development of restorative dentalmaterials

To better understand general advantages and disad-vantages between amalgams and composites toward futurematerial development equivalent flexural-test results shouldbe available for comparison Therefore a range of choppedquartz-fiber FRCs at different lengths a quality zirconia-sil-icate PFC and a standard commercial amalgam were exten-sively tested by advanced four-point flexuralmethods accord-ing to American Standards Test Methods (ASTM) protocol

2 Materials and Methods

21 Samples Quartz fibers (Saint-Gobain QPC ProductsLexington KY) supplied as yarn at 9999 pure silica werechopped to fiber lengths of 05 10 20 and 30mm andsilanated with 10 wt 3-methacryloxypropyltrimethoxysi-lane (MPTMS) (DOW Chemical Midland MI) in 70 2-propanol dried overnight and heated briefly at 120∘C Thesilanated discontinuous quartz fibers were then impregnatedwith a photocure resin at 70wt fibersThe bisphenyl A vinylester resin consisted of 22-bis[119901-(21015840-hydroxy-31015840-methacry-loxypropoxyphenyl)]propane (BisGMA) resin (Esstech PA)and was combined with 25 wt triethylene glycol dimetha-crylate (TEGDMA) monomer (Esstech Essington PA) toreduce viscosity Resin systems were optimized to photocureby incorporating photooxidants camphorquinone (AldrichMilwaukee WI) 06 wt and Irgacure 819 (Ciba TarrytownNY) 10 wt and photoreductant 2-dimethylaminoethylmethacrylate (Aldrich Milwaukee WI) 10 wt Adhesionpromoter SR9016 diacrylate (SartomerWestChester PA) andMPTMS organosilane were added to the photocure resin aswell at 20 and 10 wt respectively Silanated chopped quartzfibers were preimpregnated using the photocure resin systemThe resultant chopped quartz-fiber-reinforced compoundswere then thickened with 03 wt zirconia-silicate filler from3M Corporation (St Paul MN) The zirconia-silicate partic-ulate had beenmilled into spheres by a proprietary process toprovide a uniform particle distribution from 10 nm to 35 120583mThe zirconia-silicate particulate thus provides a hydrolyticallystable thickener with high atomic numbers for radiographicpurposes BisGMA vinyl ester resin and TEGDMAmonomerwere then combined at a 50 50 ratio in a similar photo-cure system for the addition of 845 wt or 66 vol 3MCorporation zirconia-silicate particulate supplied silanated

by the manufacturer The resultant PFC provided a cleanphotocure system identical to a Z100 commercial prod-uct with full free-radical activity without residual storagefree-radical contaminants The resultant paste with possibleadditional zirconia silicate was then used to incorporate allfiber length groups preimpregnated with photocure resinfor final molding compounds with 30wt (uniform 282119881

119891)

fibersSamples 2times2times50mm3meeting AmericanNational Stan-

dards Institute (ANSI)American Dental Association (ADA)specification number 27 but for a longer span at 40mmrather than 20mm were prepared with a split mold clampedbetween two glass plates Epilar 3000 (3M CorporationSt Paul MN) was used for the photocure initiation andmonitored with a Demetron Radiometer daily to ensureintensities of concentrated light at a wavelength of 470 nmwere above 500mWcm2 The Epilar had a 12mm diameterlight guide to photocure samples Samples were irradiatedby a small overlapping sequence for a total of 20 s on topand bottom through the glass plates 20 s on top and bottomafter removing the glass plates and from the sides for 1mineach with a focused 2mm diameter beam Excess materialwas removed from each sample followed by a sanding processdown to 600-grit silicon carbide Samples were then placed ina 37∘C water bath for 24 h primarily as a control for uniformpostcure before mechanical testing

Tytin Regular 600mg amalgam capsules (Kerr OrangeCA) supplied as spherical particulate and 425 mercury(Hg) were triturated according to the manufacturer instruc-tions and placed by increments in a 2 times 2 times 50mm3mold Further 2 operators were employed with an electric-pneumatic condenser to ensure that all amalgam incrementswere placed under 2 minutes In addition samples wereallowed to set for a 48-hour period before mechanical test-ing as the manufacturer recommended 24-hour-set periodproduced unacceptable highly inferior results for all prop-erties except modulus Conversely modulus was actuallytemporally excessive during a tremendous transformationperiod in mechanical properties between 24-hour and 48-hour amalgam set

22 Flexural-Test Methods Flexural-test methods recom-mended for dental materials by ANSI and ISO are notaccepted ASTM flexural-test methods due to lack ofpure-Euler bending ASTM recommends a span-to-depthratio of at least 16 to prevent compressive top-shear load-ing that reduces mechanical test results whereas currentdental standards recommend a span-to-depth ratio of just10 [36] In fact results for PFCs and FRCs with identicalsample dimensions demonstrated significant improvementsfor flexural quarter-point mechanical properties in modulusflexural strength and WOF when extending 20mm flexurallengths to a 40mm span [36] In the current investigationquarter-point 20mm spaced loading noses with 40mm spanand self-articulating fixtures were used for the mechan-ical testing Four specimens from the PFC group eachFRC length group (05mm 10mm 20mm and 30mm)and the amalgam group were tested An MTS inspec-tion machine (858 MiniBionix) with a crosshead speed of

Journal of Composites 3

05mmminute was used to mechanically test flexural prop-erties by

Flexural Strength (120590) 120590 = 311986511987141198871198892

(1)

Flexural Modulus (119864) 119864 = 0171198713119872

1198871198893 (2)

specifying 119865 as maximum load 119871 as span length 119887 as samplewidth 119889 as sample depth and119872 as slope of the tangent to theinitial straight line on the steepest part of the load-deflectioncurve and

Yield Strength (YS) YS =3119865119910119871

41198871198892 (3)

for 119865119910where plastic deformation yielding starts as deflection

increases rapidly beyond the initial steep load-deflectionslope

Resilience is measured in kJm2 units where energy wasintegrated by numerical methods from the load-deflectioncurve up to the yield point for cross-sectional area toughness[35 36]

WOF is measured in kJm2 units where energy wasintegrated by numerical methods from the load-deflectioncurve out past maximum load until the force dropped backto no more than 5 deflection past critical load for cross-sectional area toughness [35 36]119878119868119888is measured in kJm2 units where crack-propagation

energy was integrated by numerical methods for area duringMode 119868 (119868) Euler-tensile flexural bending under the load-deflection curve from peak or critical load (119888) until the forcedropped back to nomore than 5 deflection past critical load[35 36] 119878

119868119888toughness is then a function of energy relative to

the material cross-sectional area119870119868119888in MPasdotm12 units can be derived by direct numerical

integration methods and (1) for strength and (2) for modulusfrom the load-deflection curve by (4) where correctionfactors (h) are replaced by real-data-calculated values for 120590and the WOF that serve the same purpose [37] whereby

119870119868119888= 120590 (120587119886)

12= h (119864119866

119868119888)12

= h (119864119878119868119888)12 or (120590WOF)12 + (119864119878119868119888)

12

(4)

We further signify 119886 as the crack tip length or half the cracklength and 119866

119868119888as strain energy release rate equivalent to

119878119868119888described in more detail in a previous publication [37]

h is replaced as (120590WOF)12 representing the starter crackup to critical load as an additive correction factor [37] Theconvenience of accurate-real-data values easily calculatedfrom the load-deflection curve is then available withoutsuspect h correction factors greatly criticized by the UnitedStates National Academy of Sciences as not providing bulk-material results [38]

Strain (119903) 119903 = (436 lowast 119863119889)(1198712) (5)

further denoting 119903 without units at maximum strain in theouter fibers at midspan on the tensile surface at maximumload and119863 as sample beam deflection as digitally provided atmaximum bend strength by (5)

23 Failure Analysis Fracture theory was developed througha correlation matrix where mechanical properties were ana-lyzedwith the vertical-crack lengthmeasured from the lower-tensile-failure surface as a ratiowith sample depth of the com-posite samples and further compared to fiber length Imagingwas done by Nikon digital micrographs for crack-depth mea-surements In addition characterization was accomplishedby scanning electron micrographs (SEMs) for compositescomparing amalgamNikonmicrographs for sample fracture

24 Statistics Regression analyses were done using Statisticaand Microsoft Excel 119905-tests were carried out by unequalvariances with Microsoft Excel Marginal level of uncertaintywas set at 120572 = 005

3 Results

31 Mechanical Properties Mechanical flexural-test resultsfor the PFC FRC at 30mm length and amalgam are shownin Figures 1(a)ndash1(h) Further linear regression is calculatedfor composite mechanical properties between the PFCs at00mm to 05mm 10mm 20mm and 30mm quartz-fiberlengths Table 1 further presents group averages and statisticaldifferences by 119901 values between the amalgam and all fiberlength groups with the PFC group for each mechanical testresult

Amalgam was tested at different set periods and flexural-test span conditions presented in Figure 2 and Table 2

32 Correlation Coefficient Fracture Analysis A correlationmatrix Table 3 was developed with both Pearson productcorrelation coefficients and 119901 values to examine relation-ships for improvements with fiber length and many of themechanical properties including failure analysis by the degreeof fracture depth in addition to the examined parameterinterrelationships

33 Imaging Analysis SEM composite images in Figures3(a)ndash3(e) show noticeable lessening in open tensile flexuralfractures from the PFC that continually decrease by increas-ing fiber lengths from 00mm up to 30mm In additionFigure 3(f) at higher SEM magnification provided examplesfrom a crack image where possible fiber fracture fiber pull-out and fiber bridging were occurring Images for amalgamcharacterization by Nikon micrographs further demonstraterepresentative samples for fracture failure in Figures 3(g)-3(h) The sample in Figure 3(g) was chosen as the amalgambottom surface with the least amount of cracking

4 Discussion

Fibers dominate FRC material properties evidenced by theuniformpositive fiber length regressions for the experimentalresults in Figures 1(a)ndash1(h) 119901 lt 11 times 10minus5 and overall


3749

8601176

050

100150200250300350400450

Flex

ural

stre

ngth

(MPa

)

Fiber length Linear regressionR2 = 086 (p lt 10 times 10minus8)

48hr setAmalgamPFC + 30mm

fibersPFC

(no fibers)

(a)

436

315

195

0

10

20

30

40

50

60

Mod

ulus

(GPa

)

Fiber length Linear regressionR2 = 074 (p = 21 times 10minus6)


fibersPFC

(no fibers)

(b)

626

3435

954

050

100150200250300350400

Yiel

d str

engt

h (M

Pa)



fibersPFC

(no fibers)

(c)

067300

2330

0

5

10

15

20

25

30

35Fiber length Linear regressionR2 = 082 (p lt 10 times 10minus7)


fibersPFC

(no fibers)

Resil

ienc

e (kJ

m2)

(d)

450140

3010

0

5

10

15

20

25

30



fibersPFC

(no fibers)

WO

F (k

Jm2)

(e)

24

0036 00130

05

1

15

2

25

3



fibersPFC

(no fibers)

S Ic

(kJm

2)

(f)

091171

1201

02468

10121416 Fiber length

Linear regressionR2 = 084 (p lt 38 times 10minus8)


fibersPFC

(no fibers)

KIc

(MPamiddotm

12)

(g)

00046

00131

00079

00002000400060008

001001200140016

Stra

in



fibersPFC

(no fibers)

(h)

Figure 1 Mechanical properties for PFC PFC with 282 vol 30mm chopped quartz fibers and amalgam with 48 hr set Regression with1198772 variability and 119901 values for chopped quartz-fiber lengths of 00mm 05mm 10mm 20mm and 30mm (a) Flexural strength (b)

modulus (c) yield strength (d) resilience (e) work of fracture (f) critical strain energy release (g) critical stress intensity factor and (h) strainat peak load For comparisons human dentin tensile strength 104MPa and modulus 137 GPa [39] and 119870

119868119888soaked in water approximately

25MPasdotm12 [40] human enamel modulus 48GPa [41] to 94GPa and119870119868119888077plusmn005MPasdotm12 [42] human bone longitudinal cortical and

tensile strength 70ndash150MPa yield strength 30ndash70MPa and modulus 15ndash30GPa [43]


Table 1 Averages and 119905-test (119901 value) comparisons between composites and amalgam

Fiberlength(mm)

Flexuralstrength(MPa)

Modulus(GPa)

Yieldstrength(MPa)

Resilience(kJm2)

WOF(kJm2) 119878

119868119888(kJm2) 119870

119868119888

(MPasdotm12)Strain atpeak load

00 (PFC) 1176(00012)

195(000102)

954(001337)

303(001882)

448(51 times 10minus5)

0036(016055)

171(006584)

00079(09740)

05 1138(01399)

230(00008)

928(00372)

235(00400)

391(00984)

0075(01794)

193(007953)

00062(09189)

10 1736(000318)

262(0001875)

1261(000018)

384(000083)

87(001879)

0097(00584)

277(000797)

00084(02993)

20 3739(52 times 10minus5)

340(000116)

3298(000168)

197(000287)

282(000046)

1882(00338)

1101(000579)

00121(01290)

303749(22 times10minus8)

315(001236)

3435(000014)

233(000348)


24(000296)


00131(00677)

Amalgam 860 436 626 067 140 0013 091 00078

Table 2 Mechanical properties for Tytin alloy at 24 hours and 48 hours (st dev)

Mechanical property 24-hour 3 pt 20mm span 24-hour 4 pt 40mm span 48-hour 4 pt 40mm spanFlexural strength (MPa) 044 (004) 019 (002) 8600 (1064)Modulus (GPa) 27257 (10782) 19764 (5594) 4363 (613)Yield strength (MPa) 044 (004) 019 (002) 6256 (1350)Resilience (kJm2) 0001 (0000) 0001 (0000) 067 (023)WOF (kJm2) 0001 (0000) 0001 (0000) 140 (028)119878119868119888(kJm2) 000015 (000010) 000008 (000001) 0013 (0012)119870119868119888(MPasdotm12) 019 (003) 012 (002) 091 (052)

Strain 00022 (00009) 00021 (00001) 00078 (00050)

019 044

5253

86007193

020406080

100120

Stre

ngth

(MPa

)

48-h

our

3pt

10

mm

span

48-h

our

3pt

20

mm

span

48-h

our

4pt

40

mm

span

24-h

our

3pt

20

mm

span

24-h

our

4pt

40

mm

span

Figure 2 Chart for amalgam flexural-test results at 24 hours and 48hours with both 3-point bend and 4-point bend spans at differentlengths

mechanical test correlations in Table 3 also with unusuallylow 119901 values Although 05mm fibers produced a gen-eral small decrease in many of the mechanical propertieslower than the PFC Table 1 micromechanics predict fiber-related defects due to full debonding of fibers at the sameapproximate critical length [35] All composite mechanicalproperties were better than amalgam except for modulus

that was statistically significantly higher for amalgam thanall composites Correlation between fiber lengths and failureexamined by degree-of-fracture values was extremely statis-tically significant 119901 lt 21 times 10minus9 Regarding failure analysisfiber length had the highest linear relationship with degree-of-fracture depth (119877 = minus0940672) followed by WOF (119877 =minus0928299) and then flexural strength (119877 = minus0924982) and119870119868119888(119877 = minus0896627) In terms of validity for the current

amalgam mechanical test comparisons previous tensile testsfor 16 different amalgams have produced values in a rangefrom 425 to 621MPa [29ndash32] In contrast tensile failureby the existing investigation with ASTM flexural testinggave a much higher amalgam average of 86MPa but at theextended 48-hour set Also a possibility exists that amalgammechanical propertieswould continue to increase over longertimes In fact in a 1949 study amalgam compressive orcrushing strength was shown over a six-month period toslowly continually increase after the initial 6ndash8-hour set [30]

Tested values on modulus were higher for the amalgam(436GPa) over the composites (195ndash340GPa) and closerto approximate values for enamel (48ndash94GPa) [41 42]Conversely FRC moduli with fiber lengths from 05mmto 30mm in a range from 23 to 340GPA and the PFCat 195 GPA could be compared more to dentin (137 GPa)[39] and bone (15ndash30GPa) [43] More importantly although


(a) (b)

(c) (d)

(e) (f)

(g) (h)

Figure 3 Flexural fracture samples (a) SEM 30x no fibers (b) SEM 30x 05mm fibers (c) SEM 30x 10mm fibers (d) SEM 30x 20mmfibers (e) SEM 30x 30mm fibers (f) SEM 200x fiber fracture bridging and pullout Scale bar 100 120583m (g) Nikon micrograph amalgambottom surface scale bar 10mm (h) Nikon micrograph amalgam top surface scale bar 10mm


Table 3 Correlation coefficient matrix fracture analysis (119901 values)

Fiber length Flexuralstrength

Modulus WOF119878119868119888

119870119868119888

Degreefracturedepth

Length 1000000 0928050(10 times 10minus8)

0861638(21 times 10minus6)

0934687(47 times 10minus9)

0869319(14 times 10minus6)

0915848(38 times 10minus8)

minus0940672(21 times 10minus9)

Strength 1000000 0931744(67 times 10minus9)

0996124(22 times 10minus19)

0913242(49 times 10minus8)

0975863(11 times 10minus12)


Modulus 1000000 0908892(72 times 10minus8)

0810965(25 times 10minus5)

0893058(27 times 10minus7)


WOF 1000000 0933409(55 times 10minus9)

0984717(24 times 10minus14)


119878119868119888 1000000 0977671

(59 times 10minus13)minus0844474(54 times 10minus6)

119870119868119888 1000000 minus0896627

(20 times 10minus7)Fracture 1000000

both PFC and FRC mechanical properties were superior toamalgams for strength and toughness the reverse clinical-longevity association between PFCs and amalgam [3ndash25]then might possibly suggest other alternate composite failuremechanisms related to the mechanical property for modulusor approximately stiffness As an example PFC materialwith a lower modulus would resist strain less than amalgammetal and deform through interlaminar shear stress moreinto the cavity as another factor related to breaking themarginal cavity bond with the higher modulus tooth enamelIn addition lower modulus PFC would strain more toinitiate polymer matrix microcracking In fact applied stressaccelerates moisture uptake by opening up polymer voidsand initiating microcracks that will adsorb more water [44]As the PFC filling distorts under a load by shearing againstthe tooth wall and opens the cavity margin with adhesivebond breaking microcracking would be most detrimental atthe enamel and filling marginal interface Subsequent margindefects could then lead to even more moisture ingress withbacterial infiltration further leading to bigger failure rateswith secondary decay On the other hand from test resultsmoduli for the FRCs can significantly statistically increaseover the dental PFC with increasing fiber lengths to reduceproblems related to interlaminar shear stress deformation ofthe filling material at the bond interface with the cavity toothmargin and also strain-related microcracking

In terms of general adhesive bonding to joints polymermatrix adherends are more sensitive to interlaminar shearstress and tensile stresses thanmetals [45] Againmasticatoryloading onto the cavity margin would produce interlaminarshear stress deflections more pronounced in a dental PFCwith lower modulus than a stiff metal alloy filling materialIn effect the lower modulus polymer adherend material willdeflect by interlaminar shear stress to a much greater extentunder masticatory loading than a stiffer metal alloy amalgamto more easily break and open up the marginal cavity bondAs a countermeasure for polymer matrix materials bonddeflections are limited by the presence of high-modulus fibers

[45] Further polymer matrix adherends are susceptible tomoisture that is not the case with metals where moistureis found on the adhesive layer but is confined mostly toexposed edges on the metal [45] As a result chopped fibersin mat carriers for adhesives are commonly used to preventmoisture ingress into the bond [45] Also withmicrocrackingdimensional instability increases moisture adsorption ratesand levels ofmoisture [44 45] Althoughmoisture adsorptionincreases with polarity of the polymer chain moleculesdiffusion is the chief mechanism for moisture ingress wherewater molecules enter the polymer and reside in positionsbetween polymer chains that become forced apart [29] Aswater enters the polymer the chains become less entangledand more mobile so that the polymer plasticizes or softensand also hydrolyzes [29 44ndash46] with loss of compositemechanical properties [45] such as strength andmodulus [4446] Resin hydrophilicity as tendency for a polymer to adsorbmoisture has been shown to reduce polymer strength afterwater storage [47] Also dental PFCs have shown significantreductions in strength when stored in water [48] Possiblestrain-relatedmicrocracking from lowermodulus dental PFCmaterials would then appear to accelerate such moistureingress not only at the adhesive joint but also within theentire PFC The fact that dental PFCs are not recommendedby the American Dental Association in stress bearing areas[49] may be due to loss of mechanical strength particularlyover time from water adsorption Further deeper largerfillings with more surfaces are identified as reasons for usingamalgam instead of composite [20 50 51] In addition asfilling sizes increase cavity margins have a greater possibilityof encountering stresses that would more easily deform alower modulus PFC to break the adhesive bond So althoughmechanical properties with strength and fracture toughnessfor PFCs are better than amalgam in an air environment overtime in an oral moisture environment loss of mechanicalproperties with more applied loading stress at the marginscould be the reason why PFCs are considered unsuitable forlarger posterior fillings


Concerning another major marginal interface problempolymer matrix composites shrink during polymerizationcuring that produces residual stresses along the stationarysurface walls [29 52] One of the most characteristic featuresfor free-radical covalent bonding from a resin to solid poly-mer structure with increasedmodulus and density propertiesbecomesmost apparent inmaterials that polymerize by cova-lent chain-growth polymerization as the linearvolumetriccure shrinkage [29 45 52ndash56] In fact free radicals are engi-neered for specific and accurate polymerization applicationto cross-link molecules with subsequent cure shrinkage andpossibly warpage as two of the most distinguished materialproblems of extensive polymer electron-pair covalent bond-ing [56] Because polymerization shrinkage is not necessarilyperfect with inhomogeneous material nonuniform electron-pairing during curing in addition to increasing the modulusor stiffness can also create residual internal stresses toproduce warpage of materials which weakens parts [45 56]Subsequent residual cure stresses from polymerization cureshrinkage into the bulk of the material are then prone toopening up a defect at the margins of dental PFCs [2952] In fact polymerization cure shrinkage is considered amajor clinical problem with dental PFCs that can producebacterial sensitivity [57]On the other handwith incrementalcuring FRCs shrink during the polymerization cure processby stabilizing the polymer matrix with the high-modulusfibers in a planar fashion onto the floor of the cavity anda wall or margin with reduced shrinkage along the fiberaxis [58] Further 9 120583m diameter fibers in a polymer matrixmolding compound will consolidate by pressure along acavity wall during packing insertion to squeeze unwantedlower molecular weight monomers excess resin and particlefiller toward the cavity surface and away from the marginssealing themargin interfacewith an elevated concentration ofhigh-modulus fibermaterial that is insoluble [34 58] AtomicForce Microscopy (AFM) that provides better visual imagesof FRC molding paste compressed by a flat instrument fromanother study illustrates the top surface layer of PFC pressedup to the surface when compared to the same sample but witha chip exposing an underlying chopped quartz-fiber yarnFigure 4 Another AFM image shows how a 9120583m diameterindividual quartz fiber will mold by bending 90∘ without fullbreakage and PFC paste that fills all space around the fiberduring consolidation Figure 5 Figures 4 and 5 were obtainedwith permission from Dr Petersen [59 Figures 1ndash3]

As a tacky paste without a viable consolidation processthe dental PFC presents another major serious concern forvoids when developing a filling material that more success-fully competes with amalgams in clinical longevity [58] Onthe other hand FRCs increase viscosities as discontinuousfibers are added [60] Consequently common dental PFCvoids [58 61ndash66] Figure 6 can be practically eliminatedby FRCs that mold with consolidating properties [58 61]Problems with voids have been sufficiently notable that theAmerican Dental Association Council of Dental Materialsat the November 1980 meeting suggested specifications beset for X-ray density radiopacification in class II restorationsthat describes cavities with loss of a tooth lateral wallwhich included the requirement to detect ldquomajor voidsrdquo [62]

1

2

3

4

(120583M)

X 1000 120583MdivZ 1000 120583Mdiv

0deg

View angleLight angle

(a)

5

10

(120583M)

X 5000 120583MdivZ 3000 120583Mdiv

0deg


(b)

Figure 4 AFM surface plots of PFC material (a) Portion of samplecovered only by polymer and particulate with aspect ratios (b)Portion of sample with chip defect exposing underlying choppedquartz yarn

Figure 5 AFM 2D laser scan of 90 120583m diameter quartz fiber bentwithout full breakage at about 90-degree angle Molding pressuresqueezed particulate and resin toward the surface covering allfibers in the composite before photocuring Measurement length939 120583m


(a) (b)

Figure 6 X-ray showing occlusal and class II PFC voids from a typodont mock-clinical study [77] (a) and class II photocured PFC gingivaloverhang (b)

Composite voids are most often left unnoticed until an X-rayor radiograph is carried out much later Subsequent marginalmoisture leakage in voids predisposes the filling to commonbacterial ingress with pain often experienced [57] Also den-tal students were found to produce class II failures 10x greaterfor composites than with amalgams with voids charted fromX-rays as one of the common reasons for replacement at nocost [63] Voids generally incorporate into the dentin hybridlayer as porosities at the gingivaladhesive interface as apossible reason for secondary decay acid-based deteriorationadhesive error and loss of bond strength [64] Further voidsin a class II cavity were found to be detrimental clinicallyfor adhesive bond strength [65] Common class II gingivaloverhang [14 67 68] Figure 6 also occurs due to difficult-to-control runny excess PFC that flows under the matrixband as another source for bacterial collection after cure-sethardening By controllable thickened viscosity FRCs can beincrementally placed carefully by wedge sealing and explorercleaned before photocuring to prevent such runny flowoverhangs that may not be seen by X-ray with radiolucentand lower-viscosity photocure bonding agent Also withoutproper consistency dental PFCs cannot condense or packsimilar to the amalgam that often prevents reestablishment ofthe interproximal contact in a class II filling [58 61] In factthe past two most commonly mentioned clinical complaintsregarding class II composites have been frequent poor inter-proximal contacts [69ndash76] and void defects in the proximalbox [69]

Wear concepts for ldquoshelteringrdquo are based on the fact thatwear for dental PFCs increases with wider cavity prepara-tions as the enamel margins shelter the dental composite[78] The sheltering concept was then extended successfullywith micro and hybrid composites and finally heavily fillednanocomposites where smaller particles fit closer together toprotect the polymer matrix to wear less than composites withlarger filler diameters in the low micrometer range [78 79]Without agglomeration theoretically only about 15ndash6 volfiller at about 40 nm diameter is needed for interparticledistances of 100 nm that provide adequate polymer protec-tion but with agglomeration around 35 vol 40 nm diameterfiller is needed [78] Also larger higher modulus particlesshear from applied pressure during wear into the lower-modulus polymer matrix and with polymer microcracking

debond from the polymer and increase wear at a greater ratewithout smaller particle protection [78 80] Conversely wearimproves for FRCs in conjunction with underlying mechan-ical strength properties that support loading particularly asthe reinforcement length extends beyond the average plowinggroove [81 82] Further fibers cannot debond by shearinginto the soft polymer but peel off in worn thin sheets [82] andwear slowly as exceptionally strong materials for a smoothsurface [58] Also fibers above critical lengths with a dentalPFCmatrix have been shown towear even better than enamel[58]

Another practical FRC advantage over amalgam includesbonding with tooth structure Composite bonding allows amore conservative cavity preparation with less tooth weak-ening than amalgam that further requires bulk for strength[26 83] In addition thermoset polymer interfaces have beenextensively studied for cost-effective repair bonding andstructural joining to avoid complete replacement [84] Infact composite bonded repair is instructed by over half ofall United States dental schools to reduce iatrogenic under-mining sound tooth structure [85] Further again FRCs haveshown the ability to pack better than amalgam in restoringthe interproximal contact consolidate well to eliminate voidscommon with PFCs and can provide pressure infiltration ofresin for enhanced adhesive bonding [58 61 66] Currentstandard dental adhesives require acid etching to provideenamel microporosity and open the dentinal tubules formicromechanical interlocking and with a subsequent rinseto remove the acid [86] Alternatively newer types of cementinclude the acid in the primer without rinse to provide amorewettable or hydrophilic and polar surface to help infiltratedentinal tubules with resin adhesive [86] But adhesives thatetch and rinse provide more long-lasting bonds than mostadhesives that incorporate an acid [87] Further adhesivebond tests that etch and rinse have shown nanofillers dissolvein a water rich zone in the adhesive layer so that expertsbelieve removing water from the resin-dentin interface isfurther crucial to bonding [88] Since water diffusion intoan adhesive with soluble release of unpolymerized monomeris associated with polymer softening and hydrolytic damage[89] nonpolar or hydrophobic methods that reduce theamounts of acid in the bond appear to be beneficial Glassionomer cement similarly has residual acids to interact


well for adhesion to moist substrates [90] However whencomparing marginal integrity of glass ionomers to resin-based cement after thermocycling at 5∘C 37∘C and 55∘C for250 cycles and immersion in artificial saliva for 15 days glassionomer cement demonstrated highly significant inferiorbonds with greater marginal gaps than conventional resincement [91] In efforts to correct bond problems polymermatrix FRCmolding compounds have thickened consistencyfor effective placement so that pressure can be applied [58]during adhesive bonding after complete acid elimination andwater removal by solventair drying to apply force and pushresin into the tooth deep for micromechanical interlockingAlong the margins monomer resin and particulate aresqueezed away from the surface to seal the bondwith a higherconcentration of insoluble high-strength pure quartz fibers[34 58] Further 90120583m diameter yarn fibers planarize toapplied forces and surfaces and bend into tight corners foreasy-to-finish margins [34 58]

Amalgam has one more clinical problem overlookedsince premeasured capsules were developed Fracturing onthe lower flexural tensile side of the relatively larger amalgamsample Figure 3(g) combined with reduced 24-hour-setflexural mechanical test results for amalgams that furtherrequired a 48-hour-set period may possibly be relatedAlthough spherical particulate improves bonding comparedto particulate with an aspect ratio [92] poor adaptabilitybetween the initial increment and subsequent incrementsduring the packing phase of spherical particulate Tytin amal-gam is considered According to earlier recommendationsto improve amalgam plasticity and adaptability Hg washistorically removed lightly with a squeeze cloth in the firstincrement for large fillings and then progressively squeezedout harder with each successive increment [93] Howeverwith the premeasured capsules all Hg content is the same Infact during the historical clinical development of amalgamHg content practically controls plasticity and adaptabilityof the amalgam in a relatively narrow range between 48and 62 [94] while strength can be inversely influencedby residual Hg in the set amalgam [31] By comparisonTytin Regular amalgam mix used in the current study issupplied in premeasured capsules with a low 425 Hgcontent for reduced plasticity that might dry on the bottomduring the set of larger incremental placements AlthoughHgtoxicity has been well documented [28] on a positive noteduring the same period of premeasured capsule commercialdevelopment Hg blood levels of dental professionals havedeclined dramatically [95 96] As an explanation for reducedHg blood levels squeeze cloth handling was found to be themost common source of exposure [1 96]

5 Conclusions

FRCs are the original engineering designmaterial and shouldvastly improve dental composites during future developmentResearch strategy includes protecting composites from bac-terial colonization by stabilizing surfaces and interfaces fromall manners of defects with increasingmechanical propertiesAs fiber lengths and volume percentages increase FRCsgreatly increase all mechanical properties significantly over

common dental PFCs and even over the amalgam fillingfor all properties except modulus Subsequent lower PFCmodulus appears to play a role in reduced longevity comparedto the amalgam that better resists interlaminar shear stressdeformation and strain-related microcracking at the highlysusceptible cavity margin with the tooth that could open thebond interface Photocure FRCmolding compounds can alsopack into a cavity better than the amalgam alloy for easyclinician operator success more easily satisfied to further helpovercome multiple serious problems experienced with thedental PFC

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project was supported in part by funding through theNational Institutes of Health Grant no T32DE014300 SEMswere provided by Dr Vladimir M Dusevich Director ofElectron Microscopy Laboratory University of Missouri-Kansas City AFMs were provided by the laboratory of DrYip-Wah Chung Director of Materials Science School ofEngineering Northwestern University

References

[1] ADACouncil on Scientific Affairs ldquoDental amalgam update onsafety concernsrdquo The Journal of the American Dental Associa-tion vol 129 no 4 pp 494ndash503 1998

[2] Council on Scientific Affairs ldquoDirect and indirect restorativematerialsrdquo Journal of the American Dental Association vol 134no 4 pp 463ndash472 2003

[3] P Spencer Q Ye J Park et al ldquoAdhesivedentin interface theweak link in the composite restorationrdquo Annals of BiomedicalEngineering vol 38 no 6 pp 1989ndash2003 2010

[4] K K Skjorland ldquoPlaque accumulation on different dental fillingmaterialsrdquo Scandinavian Journal of Dental Research vol 81 no7 pp 538ndash542 1973

[5] K K Skjorland ldquoBacterial accumulation on silicate and com-posite materialsrdquo Journal de Biologie Buccale vol 4 no 4 pp315ndash322 1976

[6] D Oslashrstavik and A Pettersen ldquoBacterial activity of tooth-colored dental restorativematerialsrdquo Journal of Dental Researchvol 57 pp 141ndash174 1978

[7] K K R Skjoslashrland and T Sonju ldquoEffect of sucrose rinses onbacterial colonization on amalgam and compositerdquo Acta Odon-tologica Scandinavica vol 40 no 4 pp 193ndash196 1982

[8] M Svanberg I A Mjor and D Oslashrstavik ldquoMutans streptococciin plaque from margins of amalgam composite and glass-ionomer restorationsrdquo Journal of Dental Research vol 69 no3 pp 861ndash864 1990

[9] C G Matasa ldquoMicrobial attack of orthodontic adhesivesrdquoAmerican Journal of Orthodontics and Dentofacial Orthopedicsvol 108 no 2 pp 132ndash141 1995

[10] CHansel G LeyhausenU EHMai andWGeurtsen ldquoEffectsof various resin composite (co)monomers and extracts on twocaries-associated micro-organisms in vitrordquo Journal of DentalResearch vol 77 no 1 pp 60ndash67 1998


[11] A Karanika-Kouma P Dionysopoulos E Koliniotou-Koubiaand A Kolokotronis ldquoAntibacterial properties of dentin bond-ing systems polyacid-modified composite resins and compositeresinsrdquo Journal of Oral Rehabilitation vol 28 no 2 pp 157ndash1602001

[12] C Boeckh E Schumacher A Podbielski and B Haller ldquoAnti-bacterial activity of restorative Dental Biomaterials in vitrordquoCaries Research vol 36 no 2 pp 101ndash107 2002

[13] S Imazato ldquoAntibacterial properties of resin composites anddentin bonding systemsrdquo Dental Materials vol 19 no 6 pp449ndash457 2003

[14] L Levin M Coval and S B Geiger ldquoCross-sectional radio-graphic survey of amalgam and resin-based composite poste-rior restorationsrdquo Quintessence International vol 38 no 6 pp511ndash514 2007

[15] J A Soncini N NMaserejian F TrachtenbergM Tavares andC Hayes ldquoThe longevity of amalgam versus compomercom-posite restorations in posterior primary and permanent teethfindings from the New England childrenrsquos Amalgam trialrdquo TheJournal of the American Dental Association vol 138 no 6 pp763ndash772 2007

[16] A Gama-Teixeira M R L Simionato S N Elian M A PSobral and M A A D C Luz ldquoStreptococcus mutans-inducedsecondary caries adjacent to glass ionomer cement compos-ite resin and amalgam restorations in vitrordquo Brazilian OralResearch vol 21 no 4 pp 368ndash374 2007

[17] N Beyth A J Domb and E I Weiss ldquoAn in vitro quantitativeantibacterial analysis of amalgamand composite resinsrdquo Journalof Dentistry vol 35 no 3 pp 201ndash206 2007

[18] M Bernardo H Luis M DMartin et al ldquoSurvival and reasonsfor failure of amalgam versus composite posterior restorationsplaced in a randomized clinical trialrdquo Journal of the AmericanDental Association vol 138 no 6 pp 775ndash783 2007

[19] P Spencer Q Ye J Park et al ldquoDurable bonds at the adhesivedentin interface an impossible mission or simply a movingtargetrdquo Brazilian Dental Science vol 15 no 1 pp 4ndash18 2012

[20] B S Bohaty Q Ye A Misra F Sene and P Spencer ldquoPosteriorcomposite restoration update focus on factors influencing formand functionrdquo Clinical Cosmetic and Investigational Dentistryvol 5 pp 33ndash42 2013

[21] C J Collins RW Bryant and K-L V Hodge ldquoA clinical evalu-ation of posterior composite resin restorations 8-year findingsrdquoJournal of Dentistry vol 26 no 4 pp 311ndash317 1998

[22] A Shenoy ldquoIs it the end of the road for dental amalgam Acritical reviewrdquo Journal of Conservative Dentistry vol 11 no 3pp 99ndash107 2008

[23] K Antony D Genser C Hiebinger and F Widisch ldquoLongevityof dental amalgam in comparison to compositematerialsrdquoGMSHealth Technology Assessment vol 4 Article ID Doc12 2008

[24] M G Rasines Alcaraz A Veitz-Keenan P Sahrmann P RSchmidlin D Davis and Z Iheozor-Ejiofor ldquoDirect compositeresin fillings versus amalgam fillings for permanent or adultposterior teethrdquo Cochrane Database of Systematic Reviews no3 Article ID CD005620 2014

[25] M G Rasines Alcaraz A Veitz-Keenan P Sahrmann P RSchmidlin D Davis and Z Iheozor-Ejiofor ldquoAmalgam or com-posite fillings-which materials lasts longerrdquo Cochran DatabaseSystem Review vol 7 no 3 Article ID CD005620 2014

[26] C D Lynch R J McConnell and N H F Wilson ldquoTrendsin the placement of posterior composites in dental schoolsrdquoJournal of Dental Education vol 71 no 3 pp 430ndash434 2007

[27] G J Christensen ldquoLongevity vs esthetics in restorative den-tistryrdquo Journal of the American Dental Association vol 129 no7 pp 1023ndash1024 1998

[28] M F Ziff ldquoDocumented clinical side-effects to dental amal-gamrdquo Advances in Dental Research vol 6 pp 131ndash134 1992

[29] K J Anusavice Dental Materials Elsevier Saunders St LouisMo USA 11th edition 2003

[30] R W Phillips ldquoCompressive strength of amalgam as related totimerdquo Journal of Dental Research vol 28 no 4 pp 348ndash3551949

[31] M L Swartz and R W Phillips ldquoResidual mercury contentof amalgam restorations and its influence on compressivestrengthrdquo Journal of Dental Research vol 35 no 3 pp 458ndash4661956

[32] E J Sutow D W Jones G C Hall and E L Milne ldquoTheresponse of dental amalgam to dynamic loadingrdquo Journal ofDental Research vol 64 no 1 pp 62ndash66 1985

[33] I A Mjor ldquoProblems and benefits associated with restorativematerials side-effects and long-term costrdquo Advances in DentalResearch vol 6 no 1 pp 7ndash16 1992

[34] R C Petersen ldquoDiscontinuous fiber-reinforced compositesabove critical lengthrdquo Journal of Dental Research vol 84 no 4pp 365ndash370 2003

[35] R C Petersen J E Lemons and M S McCracken ldquoFiberlength micromechanics for fiber-reinforced composites with aphotocure vinyl ester resinrdquo Polymer Composites vol 27 no 2pp 153ndash169 2006

[36] R C Petersen J E Lemons and M S McCracken ldquoFracturetoughness micromechanics by energy methods with a photo-cure fiber-reinforced compositesrdquo Polymer Composites vol 28no 3 pp 311ndash324 2007

[37] R C Petersen ldquoAccurate critical stress intensity factor Griffithcrack theory measurements by numerical techniquesrdquo in Pro-ceedings of the SAMPE pp 737ndash752 Society for AdvancedMate-rials and Process Engineering Long Beach Calif USA May2013 httpwwwncbinlmnihgovpmcarticlesPMC4302413

[38] National Materials Advisory Board ldquoMaterials characteriza-tionrdquo in Reliability of Ceramics for Heat Engine ApplicationsNMAB 35744 chapter 4 National Academy of Sciences Wash-ington DC USA 1980

[39] H Sano B CiucchiWGMatthews andDH Pashley ldquoTensileproperties ofmineralized anddemineralized human andbovinedentinrdquo Journal of Dental Research vol 73 no 6 pp 1205ndash12111994

[40] R K Nalla J H Kinney A P Tomsia and R O Ritchie ldquoRoleof alcohol in the fracture resistance of teethrdquo Journal of DentalResearch vol 85 no 11 pp 1022ndash1026 2006

[41] J B Parks and R S Lakes Biomaterials Plenum Press NewYork NY USA 2nd edition 1992

[42] L Yin X F Song Y L Song T Huang and J Li ldquoAn overviewof in vitro abrasive finishing amp CADCAM of bioceramics inrestorative dentistryrdquo International Journal ofMachine Tools andManufacture vol 46 no 9 pp 1013ndash1026 2006

[43] D R Ratner A S Hoffman F J Shoen and J E LemonsBiomaterials Science Elsevier Boston Mass USA 2nd edition2004

[44] P Robinson E Greenhalgh and S Pinho Failure Mechanismsin Polymer Matrix Composites WP Woodhead PublishingOxford UK 2012

[45] S T PetersHandbook of Composites ChapmanampHall LondonUK 1998


[46] K K Chawla Composite Materials Springer New York NYUSA 2nd edition 1998

[47] C K Y Yiu N M King D H Pashley et al ldquoEffect of resinhydrophilicity and water storage on resin strengthrdquo Biomateri-als vol 25 no 26 pp 5789ndash5796 2004

[48] K-J M Soderholm and M J Roberts ldquoInfluence of waterexposure on the tensile strength of compositesrdquo Journal ofDental Research vol 69 no 12 pp 1812ndash1816 1990

[49] American Dental Association and Council on Scientific AffairsldquoStatement on posterior resin-based compositesrdquo Journal of theAmerican Dental Association vol 129 pp 1627ndash1628 1998

[50] S K Makhija V V Gordan G H Gilbert et al ldquoPractitionerpatient and carious lesion characteristics associated with typeof restorative material findings from the dental practice-basedresearch networkrdquo Journal of the American Dental Associationvol 142 no 6 pp 622ndash632 2011

[51] J L Ferracane ldquoCurrent trends in dental compositesrdquo CriticalReviews in Oral Biology and Medicine vol 6 no 4 pp 302ndash3181995

[52] C L Davidson and A J Feilzer ldquoPolymerization shrinkage andpolymerization shrinkage stress in polymer-based restorativesrdquoJournal of Dentistry vol 25 no 6 pp 435ndash440 1997

[53] X A J Peacock and A Calhoun Polymer Chemistry Propertiesand Applications Hanser Publishers Munich Germany 2006

[54] I Mironi-Harpaz M Narkis and A Siegmann ldquoPeroxidecrosslinking of a styrene-free unsaturated polyesterrdquo Journal ofApplied Polymer Science vol 105 no 2 pp 885ndash892 2007

[55] Y Wang L Woodworth and B Han ldquoSimultaneous measure-ment of effective chemical shrinkage and modulus evolutionsduring polymerizationrdquo Experimental Mechanics vol 51 no 7pp 1155ndash1169 2011

[56] K M B Jansen J de Vreugd and L J Ernst ldquoAnalytical esti-mate for curing-induced stress and warpage in coating layersrdquoJournal of Applied Polymer Science vol 126 no 5 pp 1623ndash16302012

[57] G Bergenholtz ldquoEvidence for bacterial causation of adversepulpal responses in resin-based dental restorationsrdquo CriticalReviews in Oral Biology andMedicine vol 11 no 4 pp 467ndash4802000

[58] R C Petersen MicromechanicsElectron Interactions forAdvanced Biomedical Research LAP LAMBERT AcademicPublishing Saarbrucken Germany 2011

[59] Petersen ldquoAtomic Force Microscopy (AFM) surface roughnessevaluation of discontinuous fiber-reinforced compositesrdquo inMicromechanicsElectron Interactions for Advanced BiomedicalResearch Figures 1ndash3 pp 179ndash187 Lambert Academic Publish-ing (LAP) Saarbrucken Germany 2011

[60] B R Pipes J W S Hearle A J Beaussart A M Sastry andR K Okine ldquoA constitutive relation for the viscous flow of anoriented fiber assemblyrdquo Journal of Composite Materials vol 25pp 1204ndash1217 1991

[61] R C Petersen ldquoUnited States Patent approved chopped fiberreinforced dental material (high purity quartz) assigned UnitedStates application number 09259317 March 1 1999rdquo Patentnumber 6270348 August 2001 httpwwwusptogov

[62] Council onDentalMaterials-Instruments and Equipment ldquoThedesirability of using radiopaque plastics in dentistry a statusreportrdquoThe Journal of the American Dental Association vol 102no 3 pp 347ndash349 1981

[63] J D Overton and D J Sullivan ldquoEarly failure of class II resincomposite versus class II amalgam restorations placed by dentalstudentsrdquo Journal of Dental Education vol 76 no 3 pp 338ndash340 2012

[64] A P Martini R B Anchieta E P Rocha et al ldquoInfluence ofvoids in the hybrid layer based on self-etching adhesive systemsa 3-D FE analysisrdquo Journal of Applied Oral Science vol 17 pp19ndash26 2009

[65] J H Purk V M Dusevich A Glaros and J D Eick ldquoAdhesiveanalysis of voids in class II composite resin restorations at theaxial and gingival cavity walls restored under in vivo versus invitro conditionsrdquo Dental Materials vol 23 no 7 pp 871ndash8772007

[66] R C Petersen and E G Wenski ldquoMechanical testing of aphotocured chopped fiber-reinforced dentalrdquo in Proceedings ofthe 47th International SAMPE Symposium and Exhibition pp380ndash394 Long Beach Calif USA May 2002

[67] A Fabianelli A Sgarr C Goracci A Cantoro S Pollingtonand M Ferrari ldquoMicroleakage in class II restorations open vsclosed centripetal build-up techniquerdquoOperative Dentistry vol35 no 3 pp 308ndash313 2010

[68] B A C Loomans N J M Opdam F J M Roeters E MBronkhorst and M C D N J M Huysmans ldquoRestorationtechniques and marginal overhang in Class II composite resinrestorationsrdquo Journal of Dentistry vol 37 no 9 pp 712ndash7172009

[69] G J Christiansen ldquoOvercoming challenges with resin in class IIsituationsrdquo Journal of the American Dental Association vol 128no 11 pp 1579ndash1580 1997

[70] J F Roulet ldquoTheproblems associatedwith substituting compos-ite resins for amalgam a status report on posterior compositesrdquoJournal of Dentistry vol 16 no 3 pp 101ndash113 1988

[71] J Cunningham L H Mair M A Foster and R S IrelandldquoClinical evaluation of three posterior composite and twoamalgam restorative materials 3-year resultsrdquo British DentalJournal vol 169 no 10 pp 319ndash323 1990

[72] J F Roulet and M J Noack ldquoCriteria for substituting amalgamwith composite resinsrdquo International Dental Journal vol 41 no4 pp 195ndash205 1991

[73] R Wilkie A Lidums and R Smales ldquoClass II glass ionomercermet tunnel resin sandwich and amalgam restorations over 2yearsrdquo American Journal of Dentistry vol 6 no 4 pp 181ndash1841993

[74] K F Leinfelder ldquoPosterior composite resins the materials andtheir clinical performancerdquoThe Journal of the American DentalAssociation vol 126 no 5 pp 663ndash667 1995

[75] G J Kaplowitz ldquoAchieving tight contacts in class II direct resinrestorationsrdquo The Journal of the American Dental Associationvol 128 no 7 pp 1012ndash1013 1997

[76] S-F Chuang K-C Su C-H Wang and C-H Chang ldquoMor-phological analysis of proximal contacts in class II directrestorations with 3D image reconstructionrdquo Journal of Den-tistry vol 39 no 6 pp 448ndash456 2011

[77] R C Petersen ldquoInterproximal contact measurement withhigh viscosity experimental condensable dental compositesrdquoin Proceedings of the 77th General Session of the Interna-tionalAmerican Association for Dental Research p 68 Vancou-ver Canada March 1999

[78] S C Bayne D F Taylor andHOHeymann ldquoProtection hypo-thesis for composite wearrdquo Dental Materials vol 8 no 5 pp305ndash309 1992


[79] S Schultz M Rosentritt M Behr and G Handel ldquoMechanicalproperties and three-body wear of dental restoratives and theircomparative flowable materialsrdquo Quintessence Internationalvol 42 no 1 pp e1ndashe10 2010

[80] K F Leinfelder ldquoComposites current status and future develop-mentsrdquo in Proceedings of the International State-of-the-Art Con-ference on Restorative Dental Materials pp 393ndash408 NationalInstitute of Dental Research Bethesda Md USA September1986

[81] J P Giltrow ldquoFriction and wear of self-lubricating compositematerialsrdquo Composites vol 4 no 2 pp 55ndash64 1973

[82] ldquoWear models for multiphase materials and synergistic effectsin polymeric hybrid compositesrdquo in Advances in CompositeTribology K Friedrich Ed pp 209ndash269 Elsevier AmsterdamThe Netherlands 1993

[83] K F Leinfelder ldquoA conservative approach to placing posteriorcomposite resin restorationsrdquo The Journal of the AmericanDental Association vol 127 no 6 pp 743ndash748 1996

[84] J Raghavan andR PWool ldquoInterfaces in repair recycling join-ing and manufacturing of polymers and polymer compositesrdquoJournal of Applied Polymer Science vol 71 no 5 pp 775ndash7851999

[85] V V Gordan I A Mjor I R Blum and N Wilson ldquoTeachingstudents the repair of resin-based composite restorationsrdquo TheJournal of the American Dental Association vol 134 no 3 pp317ndash339 2003

[86] K J Anusavice ldquoBondingrdquo in Science of Dental Materials pp381ndash398 Saunders St Louis Mo USA 11th edition 2003

[87] D H Pashley F R Tay L Breschi et al ldquoState of the art etch-and-rinse adhesivesrdquo Dental Materials vol 27 no 1 pp 1ndash162011

[88] M G Brackett N Li W W Brackett et al ldquoThe critical barrierto progress in dentine bonding with the etch-and-rinse tech-niquerdquo Journal of Dentistry vol 39 no 3 pp 238ndash248 2011

[89] R Parthasarathy AMisra J Park Q Ye and P Spencer ldquoDiffu-sion coefficients of water and leachables in methacrylate-basedcrosslinked polymers using absorption experimentsrdquo Journal ofMaterials Science Materials in Medicine vol 23 no 5 pp 1157ndash1172 2012

[90] U Lohbauer ldquoDental glass ionomer cements as permanent fill-ing materials-Properties limitations and future trendsrdquoMate-rials vol 3 no 1 pp 76ndash96 2010

[91] S Gunjal L Nagesh and H G Raju ldquoComparative evaluationof marginal integrity of glass ionomer and resin based fissuresealants using invasive and non-invasive techniques an in vitrostudyrdquo Indian Journal of Dental Research vol 23 no 3 pp 320ndash325 2012

[92] R Davis and J D Overton ldquoEfficacy of bonded and nonbondedamalgam in the treatment of teeth with incomplete fracturesrdquoJournal of the American Dental Association vol 131 no 4 pp469ndash478 2000

[93] M L Swartz and RW Phillips ldquoA study of amalgam condensa-tion procedures with emphasis on the residual mercury contentof the incrementsrdquo Journal of Dental Research vol 33 no 1 pp12ndash19 1954

[94] J F Simon Jr and D A Welk ldquoInfluence of mercury-to-alloyratios on line angle adaptation of dental amalgamrdquo Journal ofDental Research vol 49 no 5 pp 1055ndash1059 1970

[95] C Naleway H N Chou T Muller J Dabney D Roxe and FSiddiqui ldquoOn-site screening for urinary Hg concentrations andcorrelationwith glomerular and renal tubular functionrdquo Journalof Public Health Dentistry vol 51 no 1 pp 12ndash17 1991

[96] D Echeverria N J Heyer M D Martin C A Naleway J SWoods and A C Bittner Jr ldquoBehavioral effects of low-levelexposure to Hg∘ among dentistsrdquo Neurotoxicology and Teratol-ogy vol 17 no 2 pp 161ndash168 1995

Submit your manuscripts athttpwwwhindawicom

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compressive values [29ndash32] Conversely the more recentdevelopment of the dental PFC has been historically testedby flexural-test standards developed through the Ameri-can National Standards Institute (ANSI) and InternationalStandards Organization (ISO) [33] that should producevalues very close to tensile tests ideally In addition photo-cure chopped or discontinuous fiber-reinforced composites(FRCs) have demonstrated highly significant mechanicalproperty improvements over similar PFCs during flexuraltesting [34ndash37] Significant statistical differences for FRCmechanical property improvements over PFC included flex-ural strength modulus yield strength resilience work offracture (WOF) critical strain energy release (119878

119868119888) critical

stress intensity factor (119870119868119888) and strain that in turn appear

to be important for future development of restorative dentalmaterials

To better understand general advantages and disad-vantages between amalgams and composites toward futurematerial development equivalent flexural-test results shouldbe available for comparison Therefore a range of choppedquartz-fiber FRCs at different lengths a quality zirconia-sil-icate PFC and a standard commercial amalgam were exten-sively tested by advanced four-point flexuralmethods accord-ing to American Standards Test Methods (ASTM) protocol

2 Materials and Methods

21 Samples Quartz fibers (Saint-Gobain QPC ProductsLexington KY) supplied as yarn at 9999 pure silica werechopped to fiber lengths of 05 10 20 and 30mm andsilanated with 10 wt 3-methacryloxypropyltrimethoxysi-lane (MPTMS) (DOW Chemical Midland MI) in 70 2-propanol dried overnight and heated briefly at 120∘C Thesilanated discontinuous quartz fibers were then impregnatedwith a photocure resin at 70wt fibersThe bisphenyl A vinylester resin consisted of 22-bis[119901-(21015840-hydroxy-31015840-methacry-loxypropoxyphenyl)]propane (BisGMA) resin (Esstech PA)and was combined with 25 wt triethylene glycol dimetha-crylate (TEGDMA) monomer (Esstech Essington PA) toreduce viscosity Resin systems were optimized to photocureby incorporating photooxidants camphorquinone (AldrichMilwaukee WI) 06 wt and Irgacure 819 (Ciba TarrytownNY) 10 wt and photoreductant 2-dimethylaminoethylmethacrylate (Aldrich Milwaukee WI) 10 wt Adhesionpromoter SR9016 diacrylate (SartomerWestChester PA) andMPTMS organosilane were added to the photocure resin aswell at 20 and 10 wt respectively Silanated chopped quartzfibers were preimpregnated using the photocure resin systemThe resultant chopped quartz-fiber-reinforced compoundswere then thickened with 03 wt zirconia-silicate filler from3M Corporation (St Paul MN) The zirconia-silicate partic-ulate had beenmilled into spheres by a proprietary process toprovide a uniform particle distribution from 10 nm to 35 120583mThe zirconia-silicate particulate thus provides a hydrolyticallystable thickener with high atomic numbers for radiographicpurposes BisGMA vinyl ester resin and TEGDMAmonomerwere then combined at a 50 50 ratio in a similar photo-cure system for the addition of 845 wt or 66 vol 3MCorporation zirconia-silicate particulate supplied silanated

by the manufacturer The resultant PFC provided a cleanphotocure system identical to a Z100 commercial prod-uct with full free-radical activity without residual storagefree-radical contaminants The resultant paste with possibleadditional zirconia silicate was then used to incorporate allfiber length groups preimpregnated with photocure resinfor final molding compounds with 30wt (uniform 282119881

119891)

fibersSamples 2times2times50mm3meeting AmericanNational Stan-

dards Institute (ANSI)American Dental Association (ADA)specification number 27 but for a longer span at 40mmrather than 20mm were prepared with a split mold clampedbetween two glass plates Epilar 3000 (3M CorporationSt Paul MN) was used for the photocure initiation andmonitored with a Demetron Radiometer daily to ensureintensities of concentrated light at a wavelength of 470 nmwere above 500mWcm2 The Epilar had a 12mm diameterlight guide to photocure samples Samples were irradiatedby a small overlapping sequence for a total of 20 s on topand bottom through the glass plates 20 s on top and bottomafter removing the glass plates and from the sides for 1mineach with a focused 2mm diameter beam Excess materialwas removed from each sample followed by a sanding processdown to 600-grit silicon carbide Samples were then placed ina 37∘C water bath for 24 h primarily as a control for uniformpostcure before mechanical testing

Tytin Regular 600mg amalgam capsules (Kerr OrangeCA) supplied as spherical particulate and 425 mercury(Hg) were triturated according to the manufacturer instruc-tions and placed by increments in a 2 times 2 times 50mm3mold Further 2 operators were employed with an electric-pneumatic condenser to ensure that all amalgam incrementswere placed under 2 minutes In addition samples wereallowed to set for a 48-hour period before mechanical test-ing as the manufacturer recommended 24-hour-set periodproduced unacceptable highly inferior results for all prop-erties except modulus Conversely modulus was actuallytemporally excessive during a tremendous transformationperiod in mechanical properties between 24-hour and 48-hour amalgam set

22 Flexural-Test Methods Flexural-test methods recom-mended for dental materials by ANSI and ISO are notaccepted ASTM flexural-test methods due to lack ofpure-Euler bending ASTM recommends a span-to-depthratio of at least 16 to prevent compressive top-shear load-ing that reduces mechanical test results whereas currentdental standards recommend a span-to-depth ratio of just10 [36] In fact results for PFCs and FRCs with identicalsample dimensions demonstrated significant improvementsfor flexural quarter-point mechanical properties in modulusflexural strength and WOF when extending 20mm flexurallengths to a 40mm span [36] In the current investigationquarter-point 20mm spaced loading noses with 40mm spanand self-articulating fixtures were used for the mechan-ical testing Four specimens from the PFC group eachFRC length group (05mm 10mm 20mm and 30mm)and the amalgam group were tested An MTS inspec-tion machine (858 MiniBionix) with a crosshead speed of




(1)


1198871198893 (2)



41198871198892 (3)









119870119868119888= 120590 (120587119886)

12= h (119864119866

119868119888)12

= h (119864119878119868119888)12 or (120590WOF)12 + (119864119878119868119888)

12

(4)





Strain (119903) 119903 = (436 lowast 119863119889)(1198712) (5)




3 Results





4 Discussion



3749

8601176

050

100150200250300350400450

Flex

ural

stre

ngth

(MPa

)



fibersPFC

(no fibers)

(a)

436

315

195

0

10

20

30

40

50

60

Mod

ulus

(GPa

)



fibersPFC

(no fibers)

(b)

626

3435

954

050

100150200250300350400

Yiel

d str

engt

h (M

Pa)



fibersPFC

(no fibers)

(c)

067300

2330

0

5

10

15

20

25

30



fibersPFC

(no fibers)

Resil

ienc

e (kJ

m2)

(d)

450140

3010

0

5

10

15

20

25

30



fibersPFC

(no fibers)

WO

F (k

Jm2)

(e)

24

0036 00130

05

1

15

2

25

3



fibersPFC

(no fibers)

S Ic

(kJm

2)

(f)

091171

1201

02468




fibersPFC

(no fibers)

KIc

(MPamiddotm

12)

(g)

00046

00131

00079

00002000400060008

001001200140016

Stra

in



fibersPFC

(no fibers)

(h)








Fiberlength(mm)


Modulus(GPa)

Yieldstrength(MPa)

Resilience(kJm2)

WOF(kJm2) 119878

119868119888(kJm2) 119870

119868119888


00 (PFC) 1176(00012)

195(000102)

954(001337)

303(001882)


0036(016055)

171(006584)

00079(09740)

05 1138(01399)

230(00008)

928(00372)

235(00400)

391(00984)

0075(01794)

193(007953)

00062(09189)

10 1736(000318)

262(0001875)

1261(000018)

384(000083)

87(001879)

0097(00584)

277(000797)

00084(02993)

20 3739(52 times 10minus5)

340(000116)

3298(000168)

197(000287)

282(000046)

1882(00338)

1101(000579)

00121(01290)


315(001236)

3435(000014)

233(000348)


24(000296)


00131(00677)

Amalgam 860 436 626 067 140 0013 091 00078



Strain 00022 (00009) 00021 (00001) 00078 (00050)

019 044

5253

86007193

020406080

100120

Stre

ngth

(MPa

)

48-h

our

3pt

10

mm

span

48-h

our

3pt

20

mm

span

48-h

our

4pt

40

mm

span

24-h

our

3pt

20

mm

span

24-h

our

4pt

40

mm

span







(a) (b)

(c) (d)

(e) (f)

(g) (h)





Modulus WOF119878119868119888

119870119868119888

Degreefracturedepth


0861638(21 times 10minus6)

0934687(47 times 10minus9)

0869319(14 times 10minus6)

0915848(38 times 10minus8)



0996124(22 times 10minus19)

0913242(49 times 10minus8)

0975863(11 times 10minus12)



0810965(25 times 10minus5)

0893058(27 times 10minus7)


WOF 1000000 0933409(55 times 10minus9)

0984717(24 times 10minus14)


119878119868119888 1000000 0977671


119870119868119888 1000000 minus0896627








1

2

3

4

(120583M)

X 1000 120583MdivZ 1000 120583Mdiv

0deg


(a)

5

10

(120583M)

X 5000 120583MdivZ 3000 120583Mdiv

0deg


(b)




(a) (b)









5 Conclusions





Acknowledgments


References











































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






(1)


1198871198893 (2)



41198871198892 (3)









119870119868119888= 120590 (120587119886)

12= h (119864119866

119868119888)12

= h (119864119878119868119888)12 or (120590WOF)12 + (119864119878119868119888)

12

(4)





Strain (119903) 119903 = (436 lowast 119863119889)(1198712) (5)




3 Results





4 Discussion



3749

8601176

050

100150200250300350400450

Flex

ural

stre

ngth

(MPa

)



fibersPFC

(no fibers)

(a)

436

315

195

0

10

20

30

40

50

60

Mod

ulus

(GPa

)



fibersPFC

(no fibers)

(b)

626

3435

954

050

100150200250300350400

Yiel

d str

engt

h (M

Pa)



fibersPFC

(no fibers)

(c)

067300

2330

0

5

10

15

20

25

30



fibersPFC

(no fibers)

Resil

ienc

e (kJ

m2)

(d)

450140

3010

0

5

10

15

20

25

30



fibersPFC

(no fibers)

WO

F (k

Jm2)

(e)

24

0036 00130

05

1

15

2

25

3



fibersPFC

(no fibers)

S Ic

(kJm

2)

(f)

091171

1201

02468




fibersPFC

(no fibers)

KIc

(MPamiddotm

12)

(g)

00046

00131

00079

00002000400060008

001001200140016

Stra

in



fibersPFC

(no fibers)

(h)








Fiberlength(mm)


Modulus(GPa)

Yieldstrength(MPa)

Resilience(kJm2)

WOF(kJm2) 119878

119868119888(kJm2) 119870

119868119888


00 (PFC) 1176(00012)

195(000102)

954(001337)

303(001882)


0036(016055)

171(006584)

00079(09740)

05 1138(01399)

230(00008)

928(00372)

235(00400)

391(00984)

0075(01794)

193(007953)

00062(09189)

10 1736(000318)

262(0001875)

1261(000018)

384(000083)

87(001879)

0097(00584)

277(000797)

00084(02993)

20 3739(52 times 10minus5)

340(000116)

3298(000168)

197(000287)

282(000046)

1882(00338)

1101(000579)

00121(01290)


315(001236)

3435(000014)

233(000348)


24(000296)


00131(00677)

Amalgam 860 436 626 067 140 0013 091 00078



Strain 00022 (00009) 00021 (00001) 00078 (00050)

019 044

5253

86007193

020406080

100120

Stre

ngth

(MPa

)

48-h

our

3pt

10

mm

span

48-h

our

3pt

20

mm

span

48-h

our

4pt

40

mm

span

24-h

our

3pt

20

mm

span

24-h

our

4pt

40

mm

span







(a) (b)

(c) (d)

(e) (f)

(g) (h)





Modulus WOF119878119868119888

119870119868119888

Degreefracturedepth


0861638(21 times 10minus6)

0934687(47 times 10minus9)

0869319(14 times 10minus6)

0915848(38 times 10minus8)



0996124(22 times 10minus19)

0913242(49 times 10minus8)

0975863(11 times 10minus12)



0810965(25 times 10minus5)

0893058(27 times 10minus7)


WOF 1000000 0933409(55 times 10minus9)

0984717(24 times 10minus14)


119878119868119888 1000000 0977671


119870119868119888 1000000 minus0896627








1

2

3

4

(120583M)

X 1000 120583MdivZ 1000 120583Mdiv

0deg


(a)

5

10

(120583M)

X 5000 120583MdivZ 3000 120583Mdiv

0deg


(b)




(a) (b)









5 Conclusions





Acknowledgments


References











































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




3749

8601176

050

100150200250300350400450

Flex

ural

stre

ngth

(MPa

)



fibersPFC

(no fibers)

(a)

436

315

195

0

10

20

30

40

50

60

Mod

ulus

(GPa

)



fibersPFC

(no fibers)

(b)

626

3435

954

050

100150200250300350400

Yiel

d str

engt

h (M

Pa)



fibersPFC

(no fibers)

(c)

067300

2330

0

5

10

15

20

25

30



fibersPFC

(no fibers)

Resil

ienc

e (kJ

m2)

(d)

450140

3010

0

5

10

15

20

25

30



fibersPFC

(no fibers)

WO

F (k

Jm2)

(e)

24

0036 00130

05

1

15

2

25

3



fibersPFC

(no fibers)

S Ic

(kJm

2)

(f)

091171

1201

02468




fibersPFC

(no fibers)

KIc

(MPamiddotm

12)

(g)

00046

00131

00079

00002000400060008

001001200140016

Stra

in



fibersPFC

(no fibers)

(h)








Fiberlength(mm)


Modulus(GPa)

Yieldstrength(MPa)

Resilience(kJm2)

WOF(kJm2) 119878

119868119888(kJm2) 119870

119868119888


00 (PFC) 1176(00012)

195(000102)

954(001337)

303(001882)


0036(016055)

171(006584)

00079(09740)

05 1138(01399)

230(00008)

928(00372)

235(00400)

391(00984)

0075(01794)

193(007953)

00062(09189)

10 1736(000318)

262(0001875)

1261(000018)

384(000083)

87(001879)

0097(00584)

277(000797)

00084(02993)

20 3739(52 times 10minus5)

340(000116)

3298(000168)

197(000287)

282(000046)

1882(00338)

1101(000579)

00121(01290)


315(001236)

3435(000014)

233(000348)


24(000296)


00131(00677)

Amalgam 860 436 626 067 140 0013 091 00078



Strain 00022 (00009) 00021 (00001) 00078 (00050)

019 044

5253

86007193

020406080

100120

Stre

ngth

(MPa

)

48-h

our

3pt

10

mm

span

48-h

our

3pt

20

mm

span

48-h

our

4pt

40

mm

span

24-h

our

3pt

20

mm

span

24-h

our

4pt

40

mm

span







(a) (b)

(c) (d)

(e) (f)

(g) (h)





Modulus WOF119878119868119888

119870119868119888

Degreefracturedepth


0861638(21 times 10minus6)

0934687(47 times 10minus9)

0869319(14 times 10minus6)

0915848(38 times 10minus8)



0996124(22 times 10minus19)

0913242(49 times 10minus8)

0975863(11 times 10minus12)



0810965(25 times 10minus5)

0893058(27 times 10minus7)


WOF 1000000 0933409(55 times 10minus9)

0984717(24 times 10minus14)


119878119868119888 1000000 0977671


119870119868119888 1000000 minus0896627








1

2

3

4

(120583M)

X 1000 120583MdivZ 1000 120583Mdiv

0deg


(a)

5

10

(120583M)

X 5000 120583MdivZ 3000 120583Mdiv

0deg


(b)




(a) (b)









5 Conclusions





Acknowledgments


References











































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





Fiberlength(mm)


Modulus(GPa)

Yieldstrength(MPa)

Resilience(kJm2)

WOF(kJm2) 119878

119868119888(kJm2) 119870

119868119888


00 (PFC) 1176(00012)

195(000102)

954(001337)

303(001882)


0036(016055)

171(006584)

00079(09740)

05 1138(01399)

230(00008)

928(00372)

235(00400)

391(00984)

0075(01794)

193(007953)

00062(09189)

10 1736(000318)

262(0001875)

1261(000018)

384(000083)

87(001879)

0097(00584)

277(000797)

00084(02993)

20 3739(52 times 10minus5)

340(000116)

3298(000168)

197(000287)

282(000046)

1882(00338)

1101(000579)

00121(01290)


315(001236)

3435(000014)

233(000348)


24(000296)


00131(00677)

Amalgam 860 436 626 067 140 0013 091 00078



Strain 00022 (00009) 00021 (00001) 00078 (00050)

019 044

5253

86007193

020406080

100120

Stre

ngth

(MPa

)

48-h

our

3pt

10

mm

span

48-h

our

3pt

20

mm

span

48-h

our

4pt

40

mm

span

24-h

our

3pt

20

mm

span

24-h

our

4pt

40

mm

span







(a) (b)

(c) (d)

(e) (f)

(g) (h)





Modulus WOF119878119868119888

119870119868119888

Degreefracturedepth


0861638(21 times 10minus6)

0934687(47 times 10minus9)

0869319(14 times 10minus6)

0915848(38 times 10minus8)



0996124(22 times 10minus19)

0913242(49 times 10minus8)

0975863(11 times 10minus12)



0810965(25 times 10minus5)

0893058(27 times 10minus7)


WOF 1000000 0933409(55 times 10minus9)

0984717(24 times 10minus14)


119878119868119888 1000000 0977671


119870119868119888 1000000 minus0896627








1

2

3

4

(120583M)

X 1000 120583MdivZ 1000 120583Mdiv

0deg


(a)

5

10

(120583M)

X 5000 120583MdivZ 3000 120583Mdiv

0deg


(b)




(a) (b)









5 Conclusions





Acknowledgments


References











































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c) (d)

(e) (f)

(g) (h)





Modulus WOF119878119868119888

119870119868119888

Degreefracturedepth


0861638(21 times 10minus6)

0934687(47 times 10minus9)

0869319(14 times 10minus6)

0915848(38 times 10minus8)



0996124(22 times 10minus19)

0913242(49 times 10minus8)

0975863(11 times 10minus12)



0810965(25 times 10minus5)

0893058(27 times 10minus7)


WOF 1000000 0933409(55 times 10minus9)

0984717(24 times 10minus14)


119878119868119888 1000000 0977671


119870119868119888 1000000 minus0896627








1

2

3

4

(120583M)

X 1000 120583MdivZ 1000 120583Mdiv

0deg


(a)

5

10

(120583M)

X 5000 120583MdivZ 3000 120583Mdiv

0deg


(b)




(a) (b)









5 Conclusions





Acknowledgments


References











































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Modulus WOF119878119868119888

119870119868119888

Degreefracturedepth


0861638(21 times 10minus6)

0934687(47 times 10minus9)

0869319(14 times 10minus6)

0915848(38 times 10minus8)



0996124(22 times 10minus19)

0913242(49 times 10minus8)

0975863(11 times 10minus12)



0810965(25 times 10minus5)

0893058(27 times 10minus7)


WOF 1000000 0933409(55 times 10minus9)

0984717(24 times 10minus14)


119878119868119888 1000000 0977671


119870119868119888 1000000 minus0896627








1

2

3

4

(120583M)

X 1000 120583MdivZ 1000 120583Mdiv

0deg


(a)

5

10

(120583M)

X 5000 120583MdivZ 3000 120583Mdiv

0deg


(b)




(a) (b)









5 Conclusions





Acknowledgments


References











































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






1

2

3

4

(120583M)

X 1000 120583MdivZ 1000 120583Mdiv

0deg


(a)

5

10

(120583M)

X 5000 120583MdivZ 3000 120583Mdiv

0deg


(b)




(a) (b)









5 Conclusions





Acknowledgments


References











































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)









5 Conclusions





Acknowledgments


References











































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






5 Conclusions





Acknowledgments


References











































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Research Article Mechanical Properties Comparing Composite...

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Transcript of Research Article Mechanical Properties Comparing Composite...