Physical properties of current dental nanohybrid and nanofill light-cured resin composites

Journal Identification = DENTAL Article Identification = 1805 Date: April 21, 2011 Time: 2:53 pm

d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 598–607

avai lab le at www.sc iencedi rec t .com

journa l homepage: www. int l .e lsev ierhea l th .com/ journa ls /dema

Physical properties of current dental nanohybrid andnanofill light-cured resin composites

Irini D. Sideridou ∗, Maria M. Karabela, Evangelia Ch. VouvoudiLaboratory of Organic Chemical Technology, Department of Chemistry, Aristotle University of Thessaloniki,Thessaloniki GR-54124, Greece

a r t i c l e i n f o

Article history:

Received 12 March 2010

Received in revised form

3 February 2011

Accepted 4 February 2011

Keywords:

Dental nanohybrid

Dental nanofill

Sorption-solubility-volumetric

change

Volumetric shrinkage

Flexural strength and modulus

Thermogravimetric analysis

a b s t r a c t

Objectives. The purpose of this work was the detailed study of sorption characteristics of

water or artificial saliva, the determination of flexural strength and the flexural modu-

lus, and the study of the thermal stability of some current commercial dental light-cured

nanocomposites containing nano-sized filler particles.

Methods. Three nanohydrid dental composites (Tetric EvoCeram (TEC), Grandio (GR) and

Protofill-nano (PR)) and two nanofill composites (Filtek Supreme Body (FSB) and the Filtek

Supreme Translucent (FST)) were used in this work. The volumetric shrinkage due to poly-

merization was first determined. Also the sorption, solubility and volumetric increase were

measured after storage of composites in water or artificial saliva for 30 days. The flexural

strength and flexural modulus were measured using a three-point bending set-up according

to the ISO-4049 specification, after immersion of samples in water or artificial saliva for 1

day or 30 days. Thermal analysis technique TGA method was used to investigate the thermal

stability of composites.

Results. GR and TEC composites showed statistically no difference in volumetric shrinkage

(%) which is lower than the other composites, which follow the order PR < FSB < FST. The

amount of sorbed water and solubility is not statistically different than those in artificial

saliva. In all the composites studied the amount of water, which is sorbed (% on composite) is

not statistically different than the amount of water, which is desorbed and follows the order:

GR < TEC < PR < FSB < FST. After immersion in water for 1 day the highest flexural strength

showed the FSB and the lowest TEC. GR, PR and FST showed no statistically different flexural

strength. The flexural modulus of composites after immersion for one day follows the order

TEC < PR≤FST < FSB < GR.

Significance. Among the composites studied, Grandio had the lowest polymer matrix content,

consisting mainly of Bis-GMA. It showed the lowest polymerization shrinkage and water

sorption and the highest flexural strength and flexural modulus after immersion in water or

artificial saliva for 30 days. The water and artificial saliva generally showed the same effect

on physical properties of the studied composites. Thermogravimetric analysis gave good

information about the structure and the amount of organic polymer matrix of composites.

© 2011 Academy

∗ Corresponding author. Fax: +30 210 2310 997769.E-mail address: [email protected] (I.D. Sideridou).

0109-5641/$ – see front matter © 2011 Academy of Dental Materials. Pudoi:10.1016/j.dental.2011.02.015

of Dental Materials. Published by Elsevier Ltd. All rights reserved.

blished by Elsevier Ltd. All rights reserved.

dx.doi.org/10.1016/j.dental.2011.02.015

mailto:[email protected]



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. Introduction

he term “nanotechnology” has evolved over the years viaerminology drift to mean “anything smaller than microtech-ology” such as nano powders and other things that areanoscale in size, but not referring to mechanisms thatave been purposefully built from nanoscale components.his evolved version of the term is more properly labelednanoscale bulk technology” while the original meaning is

ore properly labeled “molecular nanotechnology [1].The most traditional dental composites for restorative

urposes are hybrid and microfill types. Hybrids offer interme-iate esthetic properties but excellent mechanical propertiesy the incorporation of fillers with different average particleizes (15–20 �m and 0.01–0.05 �m). Microfill composites wereaunched in the market to overcome the problems of poorsthetic properties. These materials are usually formulatedith colloidal silica (around 50% in volume) with an averagearticle size of 0.02 �m and a range of 0.01–0.05 �m. Unfor-unately the mechanical properties are considered low forpplication in regions of high occlusal force [2].

Based on the definition “nanoscale bulk technology” newlasses of dental composites, so-called nanocomposites, haveeen developed and marketed during recent years. Nanocom-osites are claimed to combine the good mechanical strengthf the hybrids [3–5] and the superior polish of the microfills [6].ther positive features reported are high wear resistance [7–9]

mproved optical characteristics [4] and reduced polymeriza-ion shrinkage [3,10].

Nanocomposites are available as nanohybrid types con-aining milled glass fillers and discrete nanoparticles40–50 nm) and as nanofill types, containing both nano-sizedller particles, called nanomers and agglomerations of thesearticles described as “nanoclusters” [4]. The nanoclustersrovide a distinct reinforcing mechanism compared withhe microfill or nanohybrid systems resulting in significantmprovements to the strength and reliability [11].

This work is concerned first with the determination of theolumetric shrinkage after polymerization of three currentommercial nanohybrids – Tetric EvoCeram (TEC), GrandioGR) and Protofill-nano (PR) – and two nanofill composites –iltek Supreme Body (FSB) and Filtek Supreme TranslucentFST). The composites were then immersed in water or artifi-ial saliva 37 ◦C for 30 days for the determination of the sorbediquid and volume increase. After that the composites wereut into a desiccator at 37 ◦C for 30-days and desorption of thebsorbed water or artificial saliva was determined. Based onhis experimental data the amount of unreacted monomersxtracted by water or artificial saliva during immersion for 30ays, known as “solubility” of the composites in these liquids,as calculated.

In an aqueous oral environment, polymer compositesbsorb water and release unreacted monomers. The releasef unpolymerized monomers from polymer composites maytimulate the growth of bacteria around the restoration and
romote allergic reactions in some patients. Also the water
ngress into dental composites in the oral cavity can, over time,ead to deterioration of the physical/mechanical propertiesue to hydrolytic breakdown of the bond between the silane-

( 2 0 1 1 ) 598–607 599

filler particles, filler matrix debonding or even hydrolyticdegradation of the fillers. However, some water ingress mayhave a positive side effect, such as the expansion of the com-posite compensating for polymerization shrinkage leading toimproved marginal sealing. Thus the solvent uptake by dentalcomposite is generally a very important property which mustbe investigated. In the authors’ previous work the sorption ofwater [12–15] or ethanol/water solution [14] or ethanol [15] bylight-cured dental resins and commercial polymer compos-ites, was studied. Also the sorption kinetics of ethanol/watersolution by dental resins and composites, was investigated[16].

In the present study the flexural strength and moduluswere also determined, using a three-point bending set-upaccording to the ISO-4049 specification, after immersion ofsamples in water or artificial saliva for 1 day or 30 days. Theweight changes of the above composites were also measuredas a function of temperature by Thermogravimetric Analysis(TGA). TGA is a technique in which the mass of the sample ismonitored as a function of temperature, while the sample issubjected to a controlled program. TGA has been used for thestudy of the thermal stability of dental composites [17–19].

2. Materials and methods

2.1. Materials

Five commercially available dental light-cured compositeswere studied; Tetric EvoCeram (TEC; Ivoclar-Vivadent, Schaan,Liechtenstein), Grandio (GR; VOCO, Cuxhaven, Germany),Protofill-nano (PR; Germany), Filtek Supreme Body (FSB; 3M-ESPE, St. Paul, MN, USA) and Filtek Supreme Translucent (FST;3M-ESPE, St. Paul, MN, USA). Their specifications are listed inTable 1.

2.2. Artificial saliva

The SAGF medium used as artificial saliva in this work andits composition is given in Table 2 [20]. The pH of the SAGFmedium was adjusted to 6.8, because this value was closer tothat of saliva in the mouth after its emission from the canals.The artificial saliva and the samples were sterilized together(0.5 atm/120 ◦C/20 min) to avoid colonization of microorgan-isms. The use of the SAGF medium required special care,because the solution was supersaturated in carbon dioxidewith regard to the air. As a result it tended to lose CO2 gas,which led to an increase in pH, so before each experiment,the pH of solution was controlled.

2.3. Volumetric shrinkage

The volumetric shrinkage was measured based onArchimedes’ Principle, as described in Refs. [21,22]. Thedensities of uncured composites were first measured, usinga Mettler-Toledo AG64 balance. From each test material,
uncured sphere-shaped specimens were carefully formed insuch a way that trapped air bubbles were avoided. Since theuncured materials were rather sticky, a thin polyester film(thickness 0.05 mm) was fixed on the special holder of the


600 d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 598–607

Table 1 – Summary of the constituents and quantities/ratios of components contained in the five compositesinvestigated.a

Composite Classification Lot no. Shade Matrix Filler Total filler content

TetricEvoCeram(TEC)

Nanohybrid K34042 A1 Bis-GMA,UDMA

Barium glass, ytterbiumtrifluoride, mixed oxide andprepolymer; 40–3000 nm,550 nm

82–83 wt% 82.5 vol%

Grandio (GR) Nanohybrid 780610 A2 Bis-GMA,TEGDMA

Silica: 20–60 nm; barium-aluminaborosilicate:0.1–2.5 �m

87.0 wt% 71.4 vol%

Protofill-nano(PR)

Nanohybrid 8W603A A1 Bis-GMA,TEGDMA,UDMA

Strontium aluminumborosilicate: 0.6 �m;nanoparticles 20 nm

81.9%

FiltekSupremeBody (FSB)

Nanofill 5AM A2D Bis-GMA,TEGDMA,UDMA,Bis-EMA

Silica: 5–20 nm nanoparticle(8 wt%); zirconia/silica:0.6–1.4 �m nanocluster(71 wt%)

79 wt% 59.5 vol%

FiltekSupremeTranslucent(FST)

Nanofill 7BN GT Bis-GMA,TEGDMA,UDMA,Bis-EMA

Silica: 75 nm nanoparticle(40 wt%); silica: 0.6–1.4 �mnanocluster (30 wt%)

70 wt% 57.5 vol%

sphen
Bis-GMA, bisphenol A diglycidyl ether dimethacrylate; Bis-EMA, bidimethacrylate; TEGDMA, triethyleneglycol dimethacrylate.a These are the data provided by the manufacturers.
balance and its mass measured in air and in water. Next,the respective material samples were carefully placed onthe polyester film and the mass of the whole assembly wasmeasured again in air and in water. Slight deformations ofthe materials during the test were of no importance sincethey do not influence density. The mass of each materialwas calculated by subtracting the mass of the polyester filmfrom the mass of the whole assembly. Now the density ofthe uncured material (�uncured) was computed. The volumetricshrinkage (�V) was calculated using the following equation:

�V% = 100 ×(

1 − �uncured

�cured

)(1)

where �uncured is the density of the uncured composite and�cured (�d) is the density of the cured composite.

2.4. Sorption and desorption of water or artificialsaliva – solubility – volumetric change

Sorption and solubility tests were determined according tothe method described in ANSI/ADA Specification No. 27-1993(ISO 4049) regarding filling materials. Specimen discs were pre-

Table 2 – Composition of the artificial saliva (SAGFmedium) [20].

Components Concentration (mg l−1)

NaCl 125.6KCl 963.9KSCN 189.2KH2PO4 654.5Urea 200.0NaSO4.10H2O 763.2NH4Cl 178.0CaCl2.2H2O 227.8NaHCO3 630.8

ol A polyethylene glycol diether dimethacrylate; UDMA, urethane

pared by filling a Teflon mold (15 mm in diameter and 1 mmin thickness) with the unpolymerized material. Samples wereirradiated for 60 s on each side, using the XL3000 (3M-ESPE,St. Paul, MN, USA) dental photocuring source. The unit wasused without the light guide in contact with the sample. Fourspecimen discs were prepared for each composite material.

The percentage amount of water or artificial saliva sorbed(WS (%) or ASS (%)) and desorbed (WD (%) or ASD (%)), the sol-ubility (SL (%)) of these liquids, the volumetric change (VI (%))were determined according to the method described in detailin our previous works [14,15].

All the specimens were placed in a desiccator and trans-ferred to a pre-conditioning oven at 37 ◦C. After 24 h they wereremoved, stored in the desiccator for 1 h and weighed to anaccuracy of ±0.00001 g using a Mettler H54AR balance. Thiscycle was repeated until a constant mass (mi) was obtained.

The densities of all samples were measured in dry (�d) orsaturated conditions (�s) using a Mettler-Toledo AG64 balanceand they were calculated based on Archimedes’ principle.

Subsequently, the discs were immersed in water or artificialsaliva at 37 ± 1 ◦C. At fixed time intervals they were removed,blotted dry to remove excess liquid, weighed and returnedto the liquid. The uptake of the liquid was recorded for 30days. The percentage weight increase in specimens, WI (%),was calculated using the following formula:

WI(%) = 100ms − mi

mi(2)

where ms represents the weight of the saturated specimenafter 30 days of immersion. This is an apparent value for theliquid sorbed, because unreacted monomer is simultaneously
extracted resulting in a decrease of specimen weight.
For the determination of monomer extracted, the sampleswere transferred to a drying oven maintained at 37 ◦C and asimilar process to that of sorption repeated during desorption.



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he percentage amount of water or artificial saliva desorbedrom specimens, WD (%) or ASD (%), was calculated using theollowing formula:

D(%) or ASD(%) = 100ms − md

ms(3)

n which md represents the weight of the specimen after0-days desorption. The amount of unreacted monomerxtracted by water or artificial saliva, during immersion for0 days, known as “solubility” (SL) of the composite in theseolvents, was calculated from the equation:

L(%) = 100mi − md

mi(4)

The percentage amount of water or artificial salivabsorbed is then given by the formula:

S(%) or ASS(%) = WI(%) + SL(W or AS)(%) (5)

The percentage amount of water or artificial salivabsorbed was also calculated as % sorption on polymer matrixWSR(%) or AASR(%)) using the equation:

SR(%) = WS(%)a

or AASR(%) = AASR(%)a

(5a)

here a is the %-wt amount of polymer matrix in the compos-te. Also the absorbed amount of water or artificial saliva wasalculated in �g/mm3 using the equation:

S(�g/mm3) = WI(�g/mm3) + SL(�g/mm3) (5b)

here WI(�g/mm3) = 106((ms − mi)/V), SL(�g/mm3) =06((mi − md)/V) and V the volume of discs in cubic millimetersas determined from the diameter and the thickness of the

pecimen disc measured at five points.Furthermore, the % volume increase VI (%) is calculated

sing the available data of densities for the dry (�d) and satu-ated (�s) specimens:

I(%) = 100 (�d − �s) + w�d

�s(6)

here w represents the % sorbed water (WS%) or artificialaliva (ASS%).

.5. Flexural properties

lexural properties were determined according to the methodescribed in ANSI/ADA Specification No. 27-1993 for resinased filling materials or ISO 4049. Specimens were pre-ared by filling a Teflon mold (2 mm × 2 mm × 25 mm) withhe unpolymerized composite, taking care to minimize thentrapped air. The upper and ower surfaces of the mold wereverlaid with glass slides covered by a Mylar sheet to avoiddhesion with the unpolymerized material. The completed
ssembly was held together with spring clips and irradiatedy overlapping, using a XL 3000 dental photocuring unit (3M-SPE, St. Paul, MN, USA). This source consisted of a 75 Wungsten halogen lamp, which emits radiation between 420
( 2 0 1 1 ) 598–607 601

and 500 nm and has the maximum peak at 470 nm. The unitwas used without the light guide at a contact point on theglass slides. The samples were irradiated for 60 s on each side.Then the mold was dismantled and the composite carefullyremoved by flexing the Teflon mold. Twenty five specimen barswere prepared for each composite.

The specimens were divided into five groups of five sam-ples each. The first group consisted of dry samples measuredimmediately after preparation. The second and third groupconsisted of samples, which had been stored in distilled waterat (37 ± 1) ◦C in dark for periods 1 and 30 days, correspond-ingly. The fourth and fifth group consisted of samples, whichhad been stored in artificial saliva at (37 ± 1) ◦C in the dark forperiods 1 and 30 days, correspondingly. The samples of groupsII–V were immersed in their solution immediately after prepa-ration. The specimens were bent in a three-point transversetesting rig with 20 mm between the two supports (3-pointbending). The rig was fitted to a mechanical testing machine(Instron, model 3344). All bend tests were carried out with aconstant cross-head speed of 0.75 ± 0.25 mm/min until frac-ture occurred. The load and the corresponding deflection wererecorded. The flexural modulus (E), in MPa, and the flexu-ral strength (�), in MPa, were calculated using the followingequations:

E = F1l3

4bdh3and � = 3Fl

2bh2

where F1 represents the load in Newtons exerted on thespecimen, F the maximum load in Newtons exerted on thespecimen at the point of fracture, l the distance in mmbetween the supports, h the height of specimen in mmmeasured immediately prior to testing, b the width of thespecimen in mm measured immediately prior to testing andd is the deflection corresponding to the load F1.

2.6. Thermogravimetic analysis

Thermogravimetric Analysis was performed on a Pyris 1 TGA(Perkin Elmer) Thermal Analyzer using about 5 mg of eachsample. It evaluated weight changes as a function of temper-ature during a thermal program ranging from 30 to 700 ◦C atthe heating rate of 10 ◦C min−1 in nitrogen atmosphere (flow20 ml/min) followed by cooling to room temperature.

2.7. Statistical analysis

The values reported in tables and figures represent mean val-ues ± standard deviation of replicates. One-way analysis ofvariance (ANOVA) test, followed by Tukey’s test, for multiplecomparisons between means to determine significant differ-ences was used at a significance level set at p ≤ 0.05.

3. Results

The determined mean values and standard deviations of the
percentage of volumetric shrinkage of the studied compositesare shown in Fig. 1.
In Table 3 the sorption of water (37 ± 1 ◦C) by the studiedcomposites after immersion in water for 30 days is shown.




Table 3 – Sorption/desorption of water (37 ± 1 ◦C) by the studied composites after immersion in water for 30 days [means(S.D.)]*, n = 4.

Composite Sorption oncomposite (%)

Desorption oncomposite (%)

Sorption onpolymermatrix (%)

Sorption oncomposite(�g/mm3)

TEC 1.10 (0.02)A 1.13 (0.02)A 6.29 (0.11)a 23.00 (0.40)GR 0.68 (0.01)B 0.72 (0.02)B 5.21 (0.11) 14.65 (0.38)PR 1.30 (0.02)C 1.28 (0.02)C 7.17 (0.08) 24.90 (0.99)FSB 1.59 (0.01)D 1.63 (0.04)D 7.41 (0.03) 31.13 (0.44)FST 1.66 (0.04)E 1.68 (0.04)E 6.05 (0.16)a 29.00 (1.51)

∗ Common corresponding uppercase letters in a given row and lowercase letters in a given column indicate no significant difference (p ≤ 0.05).

Table 4 – Solubility and volume increase of the studied composites after immersion in water for 30 days [means (S.D.)]*,n = 4.

Composite Solubility (%) Solubility (�g/mm3) % Volume increase

TEC 0.09 (0.02)a 1.84 (0.31)d 0.41 (0.62)g,h

GR 0.09 (0.02)a 2.03 (0.38)d 0.00 (0.00)h

PR 0.28 (0.03)b 5.43 (0.63)e 1.12 (0.64)gb,c 4.90 (0.82)e,f 0.82 (0.17)g

3.78 (0.32)f 1.00 (0.12)g

te no significant difference (p ≤ 0.05).

TEC GR PR FSB FST0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0a

% s

orp

tion

water artificial saliva

FSB 0.25 (0.05)FST 0.22 (0.02)c

∗ Common corresponding lowercase letters in a given column indica

The solubility in water and the volume increase is shown inTable 4.

Analogously, the results obtained for the sorption of artifi-cial saliva (37 ± 1 ◦C) are shown in Tables 5 and 6.

In Fig. 2a the sorption (%) is compared, in Fig. 2b the solu-bility (%) is compared and finally in Fig. 3 the volume increase(%) of studied composites after immersion in water or artificialsaliva (37 ± 1 ◦C) is compared.

The results obtained for the flexural strength and flexuralmodulus of the studied composites after immersion in water37 ± 1 ◦C for 1 day or 30 days are shown in Table 7. Correspond-ingly the results obtained after immersion of composites inartificial saliva 37 ± 1 ◦C for 1 day or 30 days are shown inTable 8.

The effect of the aging in liquid medium on flexuralstrength of the studied composites is shown in Fig. 4. Cor-respondingly the effect of the aging in liquid medium on theflexural modulus is shown in Fig. 5.

TEC

GR

PR

FSB

FST

0,0 0,5 1,0 1,5 2,0 2,5

volumetric shrinkage (%)

Fig. 1 – Means values and standard deviations of thepercentage of volumetric shrinkage of the studiedcomposites.

b


0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

So

lubi

lity

(%)

water artificial saliva

Fig. 2 – (a) Sorption of water or artificial saliva 37 ◦C by thestudied composites after immersion in the liquid for 30days. (b) Effect of the liquid medium aging on solubility ofstudied composites after immersion in water or artificialsaliva for 30 days.



d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 598–607 603

Table 5 – Sorption of artificial saliva (37 ± 1 ◦C) by the studied composites after immersion in artificial saliva for 30 days[means (S.D.)]*, n = 4.

Composite Sorption oncomposite (%)

Desorption oncomposite (%)

Sorption onpolymermatrix (%)

Sorption oncomposite(�g/mm3)

TEC 1.11 (0.02)A 1.08 (0.01)A 6.37 (0.10) 23.30 (0.80)a

GR 0.63 (0.01)B 0.63 (0.03)B 4.82 (0.06) 13.60 (0.69)PR 1.29 (0.02)C 1.26 (0.01)C 7.15 (0.11) 24.58 (0.85)a

FSB 1.58 (0.02)D 1.55 (0.02)D 7.33 (0.09) 30.84 (0.63)FST 1.67 (0.03)E 1.64 (0.03)E 6.07 (0.12) 29.42 (0.09)

∗ Common corresponding uppercase letters in a given row and lowercase letters in a given column indicate no significant difference (p ≤ 0.05).

Table 6 – Solubility and volume increase of the studied composites after immersion in artificial saliva for 30 days [means(S.D.)]*, n = 4.

Composite Solubility (%) Solubility (�g/mm3) % Volume increase

TEC 0.09 (0.01)a 1.98 (0.11)b 1.26 (0.40)c

GR 0.06 (0.02)a 1.25 (0.40)b −0.22 (0.67)d

PR 0.36 (0.04) 6.24 (0.42) 0.71 (0.38)c,d

FSB 0.28 (0.01) 5.48 (0.15) 0.75 (0.74)c,d

FST 0.22 (0.04) 3.33 (0.74) 0.92 (0.71)c,d

*Common corresponding lowercase letters in a given column indicate no significant difference (p ≤ 0.05).

Table 7 – Flexural strength, �, and flexural modulus, E, of studied composites after immersion in water (37 ± 1 ◦C) for 1day or 30 days [means (S.D.)]*, n = 5.

Composite Flexural strength [MPa] Flexural modulus [GPa]

1 day 30 days 1 day 30 days

TEC 98.88 (5.94)a 79.49 (8.11) 7.72 (0.20) 6.94 (0.33)GR 116.37 (3.70)b,A 116.13 (5.28)A 14.81 (0.07)B 14.44 (0.76)B

PR 107.47 (7.47)a,b 98.04 (2.69)c 8.36 (0.24)d,C 8.24 (0.33)C

FSB 144.36 (9.84) 95.57 (4.87)c 10.14 (0.21) 9.21 (0.26)FST 103.69 (11.14)a,b 94.23 (11.19)c 8.42 (0.22)d 7.58 (0.12)

*Common corresponding lowercase letters in a given column and uppercase letters in a given row indicate no significant difference (p ≤ 0.05).

Table 8 – Flexural strength, �, and flexural modulus, E, of studied composites after immersion in artificial saliva(37 ± 1 ◦C) for 1 day or 30 days [means (S.D.)]*, n = 5.

Composite Flexural strength [MPa] Flexural modulus [GPa]

1 day 30 days 1 day 30 days

TEC 105.39 (3.20)a 76.94 (6.55)c 8.03 (0.14) 7.33 (0.23)GR 112.24 (0.86)b 101.49 (3.91) 14.92 (0.32)A 14.91 (0.32)A

PR 115.97 (10.39)a,b 79.91 (6.08)c 8.76 (0.10)e,C 8.46 (0.17)C

FSB 147.93 (5.65) 86.36 (8.20)c 10.49 (0.20) 9.75 (0.24)FST 127.19 (26.45)a,b 80.46 (12.81)c 8.54 (0.22)e 8.03 (0.22)

*Common corresponding lowercase letters in a given column and uppercase letters in a given row indicate no significant difference (p ≤ 0.05).

Table 9 – Temperatures (◦C) with the maximum degradation rate of each step of thermal degradation of studiedcomposites.

Composite 1st weight loss 2nd weight loss Weight loss at800 ◦C (%)

Organicmatrixa

Weight loss at2 steps (%)

T1 (◦C) Weight loss (%) T2 (◦C) Weight loss (%)

TEC 340.1 4.43 425.4 19.06 28.52 17.50 23.49GR — — 424.3 12.23 14.54 13.00 12.23PR 322.8 11.0 415.2 10.87 25.40 18.10 21.83FSB 319.4 3.57 412.9 16.64 26.20 21.50 20.21FST 344.8 6.66 419.9 16.92 29.79 27.50 23.59

aThese are the data provided by the manufacturers.





0,4

0,8

1,2

1,6

2,0V

olum

e In

crea

se (

%)

water saliva

Fig. 3 – Volume increase (%) of studied composites afterimmersion in water or artificial saliva for 30 days.

TEC GR PR FSB FST0

2

4

6

8

10

12

14

16

Fle

xura

l mo

dulu

s [G

Pa

]

water saliva

immersion for 1 daya

2

4

6

8

10

12

14

16

Fle

xura

l mod

ulus

[GP

a]

water saliva

immersion for 30 daysb

In Fig. 6 the thermograms of the TGA and the thermogramsof the first derivative (dTGA) are shown. In Table 9 the temper-atures with the maximum degradation rate of each step ofthermal degradation of the studied composites and the corre-sponding weight loss are shown.

TEC GR PR FSB FST0

30

60

90

120

150

180

Fle

xura

l str

eng

th [M

Pa

]

water saliva

immersion for 1 daya

TEC GR PR FSB FST0

20

40

60

80

100

120

140immersion for 30 days

Fle

xura

l str

eng

th [

MP

a]

water salivab

Fig. 4 – Effect of the liquid medium aging on flexuralstrength of studied composites after storage in water orartificial saliva for (a) 1 day and (b) 30 days.

TEC GR PR FSB FST0

Fig. 5 – Effect of the liquid medium aging on flexuralmodulus of studied composites after storage in water or
artificial saliva for (a) 1 day and (b) 30 days.
4. Discussion

The volumetric shrinkage (%) of studied composites followsthe order Grandio (GR) < Tetric EvoCeram (TEC) < Protofill-nano(PR) < Filtek Supreme Body (FSB) < Filtek Supreme Translucent(FST) (Fig. 1). This order seems to depend on the total contentof organic matrix of composites. GR contains the least amountof organic matrix (13.0 wt-%) and FST the most (30.0 wt-%)(Table 1). However, PR showed higher shrinkage than TEC,although they both contain about the same amount of organicmatrix (∼18.0 wt-%). This is attributed to the different chem-istry of their organic matrix. The organic matrix of PR consistsof Bis-GMA, UDMA and TEGDMA, while that of TEC consistsof Bis-GMA and UDMA. It is known that the polymerizationshrinkage of composites depends on the degree of conversionof monomers during polymerization; the greater the degreeof polymerization the greater the shrinkage. It is well knownalso from literature [23] that TEGDMA shows a much greaterdegree of conversion than both Bis-GMA and UDMA.

After polymerization the composites were immersed inwater or artificial saliva. Water or artificial saliva uptake in
the polymeric phase of polymer composites causes generallytwo opposing processes. The solvent will extract unreactedcomponents, mainly monomer resulting in shrinkage, loss ofweight and reduction in mechanical properties. Conversely


d e n t a l m a t e r i a l s 2 7 ( 2 0 1 1 ) 598–607 605

80070060050040030020010070

75

80

85

90

95

100

Temperature (C)o

wei

ght l

oss

(%)

-3,5

-3,0

-2,5

-2,0

-1,5

-1,0

-0,5

0,0

deri. weight loss (%

/min)

TEC

80070060050040030020010084

86

88

90

92

94

96

98

100

Temperature (oC)

wei

ght l

oss

(%)

GR

-1,8

-1,6

-1,4

-1,2

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

der.weight loss (%

/min)

80070060050040030020010070

75

80

85

90

95

100

Temperature (C)o

wei

ght l

oss

(%)

-2,5

-2,0

-1,5

-1,0

-0,5

0,0der. w

eight loss (%/m

in)FSB

80070060050040030020010065

70

75

80

85

90

95

100

Temperature (oC)

wei

ght l

oss

(%)

-2,5

-2,0

-1,5

-1,0

-0,5

0,0

der. weight loss (%

/min)

FST

80070060050040030020010070

75

80

85

90

95

100

Temperature (oC)

wei

ght l

oss

(%)

-1,6

-1,4

-1,2

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

der. weiht loss (%

/min)

PR

of st

siwsioipdTmitlwt

Fig. 6 – TGA and dTGA curves

olvent uptake leads to a swelling of the composite and anncrease in weight. The solvent diffuses into the polymer net-ork and separates the chains creating expansion. However

ince the polymer network contains microvoids created dur-ng polymerization and free volume between chains, a partf the solvent is accommodated without creating a change

n volume. Thus the dimensional change of a polymer com-osite in a solvent is complex and difficult to predict andepends on the chemical structure of the polymer matrix.he hydrophilicity of the polymer needs to be of sufficientagnitude to distend the polymer. In all the composites stud-

ed the amount of water sorbed is not statistically different
o the amount of water which is desorbed (Table 3) and fol-ows the order: GR < TEC < PR < FSB < FST. This order shows thatater sorption seems to depend on the polymer matrix con-
ent. However PR, which has the same matrix content as TEC,

udied composites in nitrogen.

showed statistically higher water sorption. This shows thatthe water sorption of composites depends also on the matrixchemistry. PR contains TEGDMA, which is known to be ofgreater hydrophilicity than Bis-GMA and UDMA [12]. Whenthe amount of sorbed water was calculated on the basis ofthe content of composite in polymer matrix (Table 3) then theorder was different GR < FST≤TEC < PR < FSB.

The GR and TEC with lower polymer matrix content showedalso lower solubility than that of PR, FSB and FST (Table 4).Analogous behavior was observed in artificial saliva (Table 6).

The amount of sorbed water (Fig. 2a), the solubility (Fig. 2b)and the volume increase (Fig. 3) is not statistically different
from the corresponding quantities observed in the case ofartificial saliva.
After immersion in water for 1 day FSB (79 wt% fillercontent) showed the greatest flexural strength and TEC



l s 2

r

606 d e n t a l m a t e r i a

(82–83 wt%) the lowest. GR (87 wt%), PR (81.9 wt%) and FST(70 wt%) showed no statistically different flexural strength(Table 3). This result shows that the flexural strengthdepends not only on the filler content but also on the fillerchemistry.

After immersion in water for 30 days the flexural strengthof TEC remained constant while that of all other compositesdecreased. It is worthy of note that after immersion in waterfor 30 days GR showed the greatest flexural strength and TECthe lowest. FSB, FST and PR showed no statistically differentflexural strength, which was less than that of GR but higherthan that of TEC.

The flexural modulus of composites after immersion forone day follows the order TEC < PR≤FST < FSB < GR and afterimmersion for 30 days the order TEC < FST < PR < FSB < GR(Table 3). It is interesting to note that the flexural mod-ulus of GR and PR remained constant after immersionin water for 30 days, while that of FSB, PR and TECdecreased.

Comparison of flexural strength after immersion for 1 dayin water or artificial saliva showed the values obtained arecomparable. When the composites remained in water or arti-ficial saliva for 30 days, the saliva had a stronger effect onthe flexural strength for GR and PR and no significant differ-ence was observed for the other composites. Comparison offlexural modulus after immersion in water or artificial salivadid not show any significant difference ( p < 0.05) for 1 day or30 days.

Thermogravimetric analysis of dental composites gavegood information about the structure and the amount of theorganic matrix. In the authors’ previous work [24] the ther-mal degradation mechanism of neat dental resins Bis-GMA,Bis-EMA, UDMA and TEGDMA was studied. Differences inthe chemical structure of the resins considerably influencethe degradation behavior of the resins. Bis-GMA and Bis-EMAshowed one-step degradation mechanism with a maximumrate corresponding to 415 and 424 ◦C respectively [24]. Onthe contrary TEGDMA and UDMA showed two degradationsteps with maximum rate at 306 and 403 ◦C for TEGDMA and357 and 444 ◦C for UDMA. GR showed only a strong peakat 424 ◦C (19.06%, wt/wt) revealing that the organic matrixconsists mainly of Bis-GMA rather than TEGDMA (Table 1).FSB showed a shoulder at 319 ◦C (3.6%, wt/wt) and a strongpeak at 413 ◦C (16.6%, wt/wt). Also FST showed a shoulderat 345 ◦C (6.7%, wt/wt) and a strong peak at 420 ◦C (16.9%,wt/wt). These results confirm that these composites containboth aromatic and aliphatic dimethacrylate resins, and showthat the aromatic content (Bis-GMA and Bis-EMA) is higherthan that of the aliphatic (TEGDMA and UDMA). They alsoconfirm that FST contains more organic matrix than FSB. TECshowed a small peak at 340 ◦C (4.4%, wt/wt) which must beattributed to the UDMA it contains, and a strong peak at 424 ◦C(19.06%, wt/wt) due to the Bis-GMA content. PR showed twostrong peaks at 323 ◦C (11.0%, wt/wt) and at 415 ◦C (10.9%,wt/wt) which show that this composite contains about equal
quantities of aromatic (Bis-GMA) and aliphatic (TEGDMA andUDMA) resins. All composites showed a weight loss higherthan their organic matrix content at 800 ◦C, which must be dueto the condensation reactions of surface hydroxyl groups ofthe filler.
7 ( 2 0 1 1 ) 598–607

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Documents

Physical properties of current dental nanohybrid and nanofill light-cured resin composites