Polymerization shrinkage and contraction stress of dental resin ...

Dental Materials (2005) 21, 1150–1157 

Polymerization shrinkage and contraction stress 

of dental resin composites 

Cornelis J. Kleverlaan*, Albert J. Feilzer 

Department of Dental Materials Science, Academic Centre for Dentistry Amsterdam (ACTA), Universiteit 

van Amsterdam and Vrije Universiteit, Louwesweg 1, 1066 EA Amsterdam, The Netherlands 

Received 2 September 2004; accepted 8 February 2005 

KEYWORDS 

Polymerization; 

Strain rate; 

Composite; 

Dental restorative 

material 

* Corresponding author. Tel.: C31 20 5188257; fax: C31 20 

6692726. 

E-mail address: dental.materials@acta.nl (C.J. Kleverlaan). 

Summary Objective: The aim of this study was to evaluate the shrinkage, 

contraction stress, tensile modulus, and the flow factor of 17 commercially available 

dental resin composites. 

Method: The volumetric shrinkage measurements were performed by mercury 

dilatometry, and the contraction stress and tensile modulus were determined by 

means of stress–strain analysis. The statistical analysis was conducted by ANOVA and 

Tukey’s post hoc test, and linear regression. 

Results: Strong linear correlation for most resin composites were found for 

(i) contraction stress and shrinkage (ii) contraction stress and tensile modulus, and 

(iii) shrinkage and tensile modules. For most of the materials the unpolymerized resin 

content determines the amount of shrinkage, contraction stress and tensile modules. 

The pre-polymerized clusters in Heliomolar results in improved shrinkage/contraction 

stress properties. The shrinkage/contraction stress for Filtek Z100, Aelite Flo, 

and Flow-it was too high for the amount of resin in the resin composite. This was 

rationalized by high polymerization rates, a flow factor, and the nature of the resin. 

Significance: High shrinkage and/or high contraction stress may lead to failure of the 

bond between the resin composites and the tooth structure. This study shows that 

the unpolymerized resin content determines the amount of shrinkage, contraction 

stress and tensile modules. Therefore, using pre-polymerized clusters will improve 

shrinkage/contraction stress properties, as was shown in Heliomolar, while high 

polymerization rates, and low flow factors have a deteriorative effect on the 

shrinkage/contraction stress properties. 

Q 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. 

Introduction 

www.intl.elsevierhealth.com/journals/dema 

Polymerization shrinkage of dental resin composites 

is due to the fact that monomer molecules are 

converted into a polymer network and, therefore, 

exchanging van der Waals spaces in covalent bond 

0109-5641/$ - see front matter Q 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. 

doi:10.1016/j.dental.2005.02.004

Polymerization shrinkage and contraction stress 1151 

spaces [1]. This polymerization shrinkage creates 

contraction stresses in the resin composite 

restoration and internal stress and deformation in 

the surrounding tooth structure [2–4]. Despite 

considerable effort none of the contemporary 

bonding systems are able to maintain a reliable 

bonding between the resin composite and the tooth 

structure, resulting in poor marginal adaptation, 

postoperative pain, and recurrent carries. 

Reduction of the polymerization shrinkage has 

been an important issue, since the use of dental 

resin composites. Non-shrinking resins and modified 

filler particles have been developed to tackle 

this problem, but are not commercially available 

yet [5]. Factors that can affect the shrinkage are 

inorganic filler content, the molecular weight of 

monomer system, and the degree of conversion 

of the monomer system [1]. Previous studies 

proved that ca 90% of the shrinkage occurs within 

the first hours [6,7]. During setting of the resin 

composites the polymerization shrinkage induces 

contraction stress. The magnitude contraction 

stress has been found to be dependent on the 

cavity configuration (C-factor), which is the ratio 

of the bonded to unbonded surface area of the 

restoration [8], the nature of the matrix material 

[5], the filler load [9,10], and the viscous–elastic 

properties [4,9]. Layering techniques or applying 

a low elastic modulus liners between the tooth 

structure and the resin composite have been 

proposed to minimize the internal stress and 

deformation of the tooth structure [11,12]. Also 

the polymerization rate influences the amount of 

stress, i.e. higher contraction stress was observed 

with high polymerization rates [13,14]. The 

elastic modulus of the resin composite has been 

found to be an important factor for both the 

shrinkage and the contraction stress. In vitro test 

has shown that the setting shrinkage increases 

with the rigidity of the resin composite [9]. It has 

also shown that the elastic modulus of the resin 

composite increases with the volume fraction of 

the inorganic filler content [15]. During curing 

not all the shrinkage is converted to contraction 

stress because the polymer can rearrange and 

relieve stress. This flow is in principle composed 

of a macroscopic and microscopic component. 

The macroscopic flow occurs at the free surfaces 

during the polymerization reaction. The physical 

evidence is the development of a meniscus on 

the latter surfaces [16]. Microscopic flow is due 

to possible polymer rearrangement within the 

resin composite. Structure of the molecules, 

crosslink density of the network, the interaction 

of the matrix and filler particles and reaction 

kinetics may play a role in this type of flow. 

Furthermore, it is most likely that most of flow 

takes place before the gel point and that after 

the gel point most of the contraction stress is 

being developed. 

Polymerization shrinkage, contraction stress, 

elastic modulus, and flow are important factors 

determining the final properties of the resin 

composite. However, so far, only polymerization 

shrinkage in relation to elastic modulus [9], and 

polymerization contraction stress in relation to 

elastic modulus [17], and filler load [18] and type of 

resin composite [19,20] have been evaluated. The 

present study is focused on the relation shrinkage, 

contraction stress, elastic modulus, and the flow of 

a range of resin composites; microfilled, (micro)hybride, 

condensable, and flowable resin composites. 

It was expected that highly filled resin 

composites have low shrinkage values, high contraction 

stress values and are relatively ridged, and 

the low-viscosity or flowable resin composites have 

high shrinkage values, low contraction stress values 

and are relatively flexible. 

Materials and methods 

Table 1 describes the materials tested. 

Volumetric shrinkage 

Volumetric shrinkage measurements were performed 

by mercury dilatometry at 23.0G0.1 8C 

similar as reported previously [21]. The standard 

procedure and operation of the dilatometer was as 

follows: (i) A layer of high vacuum grease (Dow 

Corning Corporation, Midland, MI, USA) was applied 

on the flat surface of the glass stopper for 

separation. (ii) An amount of approximately 

300 mg of a resin composite paste was applied on 

the greased surface of the stopper and flattened to 

a thickness of approximately 1.5 mm. The flowable 

resin composites were vacuum sealed in a PE 

plastic sheet. (iii) After the stopper was inserted 

into the dilatometer the sample was light activated 

with an Elipar Highlight or Elipar Trilight (3M-ESPE, 

Seefeld, G) for 40 s in standard mode (ca 750 mW/ 

cm 2 ), ensuring complete curing. Recording was 

started at the moment that the light source was 

switched on. (iv) After the samples were removed 

from the dilatometer, the grease was washed off 

with ether and the density measured by means of 

pycnometry with a Mettler AT261 DeltaRange 

(Mettler-Toledo, Tiel, NL). From each material six 

samples (nZ6) were measured over a period of 

30 min.

1152 

Table 1 Material properties according to manufacturers data. 

Material Matrix a 

Filler size Filler Manufacturer 

(mm) (vol.%) 

b 

Batch no. 

HelioMolar Bis-GMA, UDMA, decandiol 

dimethacrylate 

0.04–0.2 46 Ivoclar Vivadent E50807 

Filtek A110 Bis-GMA, TEGDMA 0.01–0.09 40 3M ESPE 20020404 

Filtek Z250 Bis-GMA, UDMA, Bis-EMA 0.01–3.5 60 3M ESPE 20021227 

Filtek P60 Bis-GMA, UDMA, Bis-EMA 0.01–3.5 61 3M ESPE 20030122 

Filtek Surpreme Bis-GMA, UDMA, 

TEGDMA, Bis-EMA 

0.6–1.4 58 3M ESPE 20030326 

Filtek Z100 Bis-GMA, TEGDMA 0.01–3.5 66 3M ESPE 20030625 

Prodigy condensable Methacrylate ester 

monomers 

Kerr 208365 

Tetric Ceram Bis-GMA, UDMA, 

TEGDMA 


Herculite XRV Methacrylate ester 

monomers 

0.6 59 Kerr 204828 

Spectrum TPH Bis-GMA, UDMA, Bis-EMA 0.04–5.0 57 Densply deTrey 0204001130 

Point4 Methacrylate ester 

monomers 

0.4 57 Kerr 301614 

Heliomolar flow Bis-GMA, UDMA, decandiol 

dimethacrylate 


Tetric flow Bis-GMA, TEGDMA, 

UDMA 


Aelite Flo Bis-GMA, TEGDMA 36 Bisco 0200006428 

Revolution Formula 2 Methacrylate ester 

monomers 

35 Kerr 2-1147 

Flow-it Bis-GMA, TEGDMA, 

EBPADMA 

40 Jeneric/Pentron 62249 

UltraSeal XT Plus Bis-GMA 36 Ultradent YL5C 

a 

Bis-GMA, bisphenyl glycidylmethacrylate; UDMA, urethane dimethacrylate; TEGDMA, triethylene glycol dimethacrylate; Bis- 

EMA, ethoxylated bisphenol A dimethacrylate; EBPADMA, ethoxylated bisphenol A dimethacrylate. 

b 

Ivoclar Vivadent, Schaan, Liechtenstein; 3M ESPE, St. Paul, MN, USA; Kerr, Orange, CA, USA; Densply deTrey, Konstanz, 

Germany; Jeneric/Pentron, Wallingford, CT, USA; Ultradent, South South Jordan, UT, USA. 

Contraction stress 

The test setup shown in Figure 1 was placed in an 

Instron 6022 Tensilometer (Instron Ltd., Wycombe, 

UK). The resin composite paste was inserted 

between the glass plate and the flat surface of the 

steel bolt head and adhered to both these surfaces. 

During light curing and a period of 30 min following, 

the contraction stress development was measured, 

while the distance between the glass and the steel 

bolt head was kept constant. This simulated a 

restoration in a fully rigid situation, where the 

cavity walls do not yield to the contraction forces. 

The glass plate (4 mm thick) was sandblasted 

with Al2O3 (50 mm) and remaining Al2O3 was 

removed by compressed air. The surface was 

treated with Ceramic Primer (3M, St. Paul, MN, 

USA) and Scotch Bond MP (3M, St. Paul, MN, USA) 

according to the manufacturer’s procedures. The 

bolt head (3.2 mm diameter) was wet-ground on 

600 grit SiC sandpaper and then sandblasted with 

C.J. Kleverlaan, A.J. Feilzer 

Al2O3 (50 mm), rinsed with acetone and treated in a 

Silicoater (Heraeus Kulzer, Wehrheim, G) to deposit 

a thin silica layer. A drop of fresh Silicoup (Heraeus 

Kulzer, Wehrheim, G) was applied to silanize the 

surface. After drying, a thin layer of Scotch Bond MP 

Figure 1 Schematic representation of the tensilometer. 

The resin composite was bonded to the surface 

of the bold head and the surface of the silanated glass 

plate.


was applied and light cured for 20 s. The composite 

was applied between the glass plate and bolt head, 

and the cross-head was moved to set the distance 

between the glass plate and bolt head to 0.8 mm. 

This configuration resulted in C-value of 2 

(CZd/2hZ3.2/1.6) [8]. The samples were light 

cured through the glass with an Elipar Highlight or 

Elipar Trilight (ESPE, Seefeld, Germany) for 40 s in 

standard mode, ensuring complete curing. From the 

start of light curing the contraction stress development 

was measured during 30 min. The axial 

contraction of the samples was continuously 

counteracted by a feedback displacement of the 

cross-head to keep the height of the specimen 

constant. The tensile modulus was measured after 

30 min after the initial curing with a cross-head 

speed of 0.025 mm min K1 . 

The tensile modulus, was calculated using the 

following formula: EZs/3, where s is the stress 

(F/A) and 3, the strain (Dl/l0). The contraction 

stress and the tensile modulus of each of the resin 

composites in Table 1 was determined from six 

measurements (nZ6). 

Stress relief in axial direction, further denoted as 

flow of the resin composite for a predefined 

configuration at a selected time is calculated as 

follows [22]. sth is the theoretical stress, which 

would have been developed if the flow was zero, 

can be calculated accordingly: sthZE3CZ0. In this 

formula 3 CZ0 represents the linear shrinkage (Dl/l 0) 

during free shrinkage or approximately 1/3 of the 

volumetric shrinkage. The flow factor can be 

expressed by: fCZ2Z(sthKsCZ2)/sth, where sCZ2 

is the contraction stress observed for a configuration 

factor of 2. 

Statistical analysis 

One-way analysis of variance (ANOVA) and Tukey’s 

post hoc test were used to analyze the volumetric 

shrinkage, contraction stress and tensile modulus 

results obtained at 30 min. The volumetric shrinkage 

and contraction stress data measured at 5, 15 

and 30 min, respectively, were analyzed with a 

paired t-test. A P-value of !0.05 was considered 

significant. The software used was SPSS 10.0 (SPSS 

inc., Chicago, USA). Origin 5.0 (Microcal Software 

Inc, Northampton, USA) was used for the regression 

analysis. 

Results 

The volumetric shrinkage, contraction stress and 

the tensile modulus are graphically depicted in 

Figure 2 Shrinkage (vol.%), contraction stress (MPa), 

and tensile modulus (GPa) of 17 different resin 

composites. 

Figure 2. The shrinkage, contraction stress, and the 

tensile modulus were measured during 30 min and 

the values at 5, 15, and 30 min are reported in 

Table 2. Paired t-test showed that there was a 

significant increase for the shrinkage and contraction 

stress for all resin composites at both time 

intervals (5 vs 15 min, and 15 vs 30 min). One-way 

ANOVA and Tukey’s post hoc tests were used for 

evaluation of the resin composites and the results 

are summarized in Table 2. 

The shrinkage of the studied resin composites 

ranged from 2.00 to 5.63 vol.% at 30 min. The 

shrinkage of the non-flowable resin composites was 

from 2.00 to 3.42 vol.%, where Heliomolar showed 

the lowest shrinkage and Point 4 the highest. For 

the flowable resin composites the shrinkage ranged 

from 4.17 vol.% (Heliomolar Flow) to 5.63 vol.% 

(UltraSeal XT Plus). The contraction stress of the 

studied resin composites was from 3.3 to 23.5 MPa 

at 30 min. The contraction stress of the nonflowable 

resin composites was from 8.4 MPa 

(Heliomolar) to 23.5 MPa (Filtek Z100). In the 

flowable resin composites the contraction stress

1154 

Table 2 

materials. 

Shrinkage (vol.%), contraction stress (MPa) and tensile modulus (GPa) of 17 commercial available 

Material Shrinkage (vol.%) 

5 min 15 min 30 min 

Contraction stress (MPa) 

5 min 15 min 30 min 

Tensile 

modulus 

(GPa) 

Heliomolar 1.76 (0.11) 1.90 (0.12) 2.00 (0.11) a 

7.2 (0.7) 8.0 (0.8) 8.4 (0.8) a 

2.7 (0.3) defg 

Filtek A110 1.95 (0.06) 2.08 (0.09) 2.17 (0.09) b 

15.7 (0.7) 16.8 (0.7) 17.4 (0.8) b 

3.3 (0.4) fghi 

Filtek Z250 2.07 (0.05) 2.22 (0.03) 2.33 (0.04) bc 

12.2 (0.9) 13.3 (1.0) 13.9 (1.0) cde 

3.8 (0.4) i 

Filtek P60 2.07 (0.07) 2.22 (0.07) 2.34 (0.07) c 

12.7 (1.1) 13.9 (1.1) 14.6 (1.1) def 

3.3 (0.3) ghi 

Filtek Supreme 2.19 (0.05) 2.38 (0.03) 2.51 (0.04) d 

12.8 (1.1) 14.3 (1.3) 15.1 (1.3) ef 

3.7 (0.4) i 

Filtek Z100 2.32 (0.02) 2.48 (0.02) 2.56 (0.06) d 

21.4 (0.3) 22.8 (0.3) 23.5 (0.4) 3.5 (0.2) hi 

Prodigy Condensable 

2.79 (0.02) 2.96 (0.02) 3.07 (0.02) e 

14.5 (1.0) 15.5 (1.0) 16.1 (1.1) bf 

3.2 (0.1) fghi 

Tetric Ceram 2.84 (0.12) 3.02 (0.12) 3.15 (0.11) e 

10.8 (0.7) 12.1 (0.7) 12.8 (0.7) cd 

2.9 (0.4) defgh 

XR Herculite 2.86 (0.09) 3.05 (0.10) 3.16 (0.09) e 

13.0 (0.9) 14.2 (1.0) 14.9 (1.0) ef 

3.4 (0.3) hi 

Spectrum TPH 2.87 (0.10) 3.04 (0.09) 3.16 (0.10) e 

13.7 (0.6) 15.0 (0.6) 15.6 (0.7) bef 

3.0 (0.5) efgh 

Point 4 3.12 (0.04) 3.30 (0.02) 3.42 (0.03) 10.3 (1.9) 11.3 (2.0) 11.9 (2.1) c 

2.7 (0.3) def 

Heliomolar 

Flow 

3.81 (0.08) 3.98 (0.03) 4.17 (0.10) 7.4 (0.9) 8.0 (1.0) 8.4 (1.0) a 

1.9 (0.5) bc 

Tetric Flow 3.98 (0.02) 4.21 (0.03) 4.39 (0.04) 6.7 (1.2) 7.3 (1.3) 7.6 (1.3) a 

1.9 (0.3) bc 

Aelite Flo 4.38 (0.09) 4.66 (0.07) 4.84 (0.07) f 

14.0 (1.3) 15.3 (1.2) 16.0 (1.2) bef 

2.3 (0.3) cd 

Revolution 

Formula 2 

4.56 (0.06) 4.82 (0.07) 4.99 (0.06) f 

5.9 (0.6) 6.5 (0.6) 6.8 (0.7) a 

1.2 (0.1) a 

Flow-it 4.89 (0.04) 5.13 (0.04) 5.30 (0.05) 13.8 (0.8) 14.8 (0.8) 15.4 (0.8) bef 

2.4 (0.2) cde 

UltraSeal XT 

Plus 

5.07 (0.06) 5.48 (0.11) 5.63 (0.11) 2.7 (0.2) 3.1 (0.3) 3.3 (0.3) 1.3 (0.2) ab 

No significant differences were observed if mean is quoted with the same letter. 

was the lowest for UltraSeal XT Plus 3.3 MPa, but 

Aelite Flo (16.0 MPa) and Flow-it (15.4 MPa) showed 

remarkable high contraction stress values. The 

tensile modulus, measured after 30 min, varied 

from 1.2 GPa (Revolution Formula 2) to 3.8 GPa 

(Filtek Z250). 

Regression curves between the tensile modulus 

and shrinkage (Figure 3 top), the tensile modulus 

and contraction stress (Figure 3, bottom) and the 

shrinkage and contraction stress (Figure 4) showed 

a very good fit with linear functions (Table 3). For 

the regression curve between the tensile modulus 

and shrinkage Heliomolar, Flow-it, and Aelite Flo 

were omitted for the analysis. Heliomolar, Filtek 

Z100, Flow-it, and Aelite Flo were omitted for the 

regression analysis between the tensile modulus 

and contraction stress, and the shrinkage and 

contraction stress. The regression curves between 

the shrinkage and inorganic filler load (Figure 5, 

Table 3) showed a very good fit with a linear 

function except for Heliomolar, Heliomolar flow, 

and Filtek A110. 

The theoretical stress (sth) is the stress that 

would have been developed if the flow was 

zero. The theoretical stress for Filtek Z250 was 

29.5 MPa, while the observed stress was only 

13.9 MPa. The flow of resin composite was, 

under the circumstances measured, 53%. The 

flow of all resin composites are graphically 

depicted in Figure 6. 

Discussion 


The magnitude of the shrinkage and the accompanying 

stress generated by the polymerization 

reaction of the resin composite material are the 

main factors for in vivo problems like poor marginal 

adaptation, postoperative pain, and recurrent 

carries. Furthermore, the elastic properties (i.e. 

E-modulus or tensile modulus) and the ability of the 

polymer to rearrange and relieve stress, i.e. flow, 

has been shown to influence the final contraction 

stress. These four parameters, shrinkage, contraction 

stress, tensile modulus, and flow, show an 

interesting interplay which depends on many 

factors such as filler load, type of filler particles, 

monomer system, pre-polymerized particles, etc. 

In this study the shrinkage, contraction stress, and 

tensile modulus of 17 commercially available resin 

composites were investigated, representing resin 

composites from different groups like microfilled, 

(micro)hybride, condensable, and flowable resin 

composites. This study was not focused on


Shrinkag e (vol%) 

Contraction Stress (MPa) 

6 

5 

4 

3 

2 

1 

0 

20 

15 

10 

5 

Aelite Flo 

Flow-it 

Heliomolar 

Filtek Z100 

Flow-it 

Aelite Flo 

Heliomolar 

0 

0 1 2 3 4 5 

Tensile Modulus (GPa) 

Figure 3 Linear regression analysis of shrinkage vs 

tensile modulus (top) and contraction stress vs tensile 

modulus (bottom) of 17 different resin composites. 

comparing the properties of the different resin 

composite groups, but on general properties within 

the whole group. In general, linear regression 

analysis between (i) shrinkage and tensile 

modulus (ii) contraction stress and tensile 

modulus (iii) shrinkage and contraction stress, and 

Contraction Stress (MPa) 

25 

20 

15 

10 

5 

Heliomolar 

Filtek Z100 

Aelite Flo 

Flow-it 

0 

1 2 3 4 5 6 

Shrinkage (vol%) 

Figure 4 Linear regression analysis of contraction 

stress vs shrinkage of 17 different resin composites. 

(iv) shrinkage and filler load (as reported by the 

manufacturer) yielded strong correlations 

(Table 3), where some of the resin composites 

deviated from. This strong correlation is rather 

surprising, since there are many differences in filler 

size and load, resin type, and photoinitiator 

systems present among these materials. 

The contraction stress is determined by characteristic 

of the resin composite. The filler content 

and resin matrix composition dictate the amount of 

volumetric shrinkage and the elastic modulus of the 

resin composite. According to Figure 3 (top) an 

inverse relation between the tensile modulus and 

shrinkage exists, which confirms the findings of 

Labella et al. [9]. Flowable resin composites 

produce high volumetric shrinkage and low tensile 

modulus compared with non-flowable resin composites, 

which show low volumetric shrinkage and high 

tensile modulus. Braem et al. [15] showed a strong 

correlation between filler load of commercial resin 

composites and their tensile modulus. Thus, 

increasing the filler load (e.g. flowable resin 

composites/non-flowable resin composites) 

results in an increase of the tensile modulus. On 

the other hand, a higher filler load decreases the 

amount of resin in the resin composite and, 

therefore, a decrease in shrinkage is observed, 

explaining the inverse relation between tensile 

modulus and shrinkage. Furthermore, Condon 

et al. [18] showed a strong correlation between 

filler volume of commercial resin composites and 

contraction stress. Increasing filler load resulted in 

higher stresses. Combining this result with the 

increasing filler load (e.g. flowable resin composites/non-flowable 

resin composites) resulted in 

an increase of the tensile modulus, explaining the 

positive correlation between tensile modulus and 

contraction stress (Figure 3 (bottom)). In short, 

increasing the filler load results in less shrinkage, 

more stress and a higher tensile modulus. 

The relation between the contraction stress and 

shrinkage is shown in Figure 4, which clearly shows 

that low shrinkage is accompanied with high 

contraction stress, and that high shrinkage shows 

lower contraction stress values. This implies that 

using low shrinking resin composite in the clinical 

situation is not always favorable! Low shrinking 

resin composites will give high stress if the tooth 

structure is not able to comply, eventually resulting 

in poor marginal adaptation, postoperative pain or 

fracture. So, in rigid surroundings, e.g. Class V 

restorations, a low contraction stress resin composite 

is advised. Furthermore, Figure 4 shows that 

Heliomolar, Filtek Z100, Aelite Flo and Flow-it 

differ from the other resin composites. Materials 

below the regression line, e.g. Heliomolar, show

1156 

Table 3 The results of the regression analysis of shrinkage (vol.%), contraction stress (MPa), tensile modulus (GPa) 

and filler load (vol.%). 

Variables Equation r 2 

Contraction stress vs tensile modulus s (MPa)ZK0.10C4.49E (GPa) 0.84 

Contraction stress vs shrinkage s (MPa)Z25.00K3.743 (vol.%) 0.88 

Shrinkage vs tensile modulus 3 (vol.%)Z6.62K1.17E (GPa) 0.90 

Shrinkage vs filler load 3(vol.%)Z8.65K0.097 filler% (vol.%) 0.89 

superior shrinkage/contraction stress properties, 

compared to the materials on the regression line. 

Thus, the materials above the regression line, e.g. 

Filtek Z100, Aelite Flo and Flow-it show inferior 

shrinkage/contraction stress properties, compared 

to the materials on the regression line. It should be 

noted that these resin composites did also not 

follow the regression line for tensile modules/ 

contraction stress and tensile modules/shrinkage 

(Figure 3). 

In agreement with our findings, low shrinkage 

and low contraction stress has been reported for 

Heliomolar [9,17]. Heliomolar is microfilled resin 

composite, which contain lower filler levels (ca 

40 vol.%) compared to hybrid resin composites 

(ca 60 vol.%). Therefore, the contraction stress 

and tensile modules should be low, but the 

shrinkage should be high. However, much of the 

filler is added to the resin matrix in pre-polymerized 

clusters, and therefore, the shrinkage levels of 

Heliomolar is similar to the more heavily filled 

hybrid resin composites [17,23]. In order to 

determine the level of pre-polymerized clusters 

the inorganic filler load against the shrinkage has 

been plotted and assumed that the shrinkage of the 

monomer system is similar. An increase in inorganic 

filler load gives a decrease in resin and 

Shrinkage (vol%) 

6 

4 

2 

0 

Heliomolar Flow 

Filtek A110 

Heliomolar 

30 40 50 60 70 

Filler Load (vol%) 


consequently a reduction in shrinkage. If any prepolymerized 

clusters were added the shrinkage it 

should decrease. Figure 5 shows that Heliomolar, 

Filtek A110, and Heliomolar Flow shrink less due to 

pre-polymerized clusters. From this plot it can be 

estimated that these resin composites contain ca 

23, 25, 17 vol.% pre-polymerized resin, respectively. 

Interestingly, Heliomolar showed improved 

shrinkage/contraction stress properties, while Filtek 

A110, and Heliomolar Flow showed relative high 

shrinkage values for the amount of pre-polymerized 

resin added. Apparently the flow characteristics of 

Filtek A110, and Heliomolar Flow were also 

important (see below). Using pre-polymerized 

clusters in resin composites can decrease the 

shrinkage, and contraction stress, but has one 

major drawback; the wear of these resin composites 

is much higher compared to more heavily filled 

hybrid resin composites [23]. 

The materials above the regression line of 

Figure 4, e.g. Filtek Z100, Aelite Flo and Flow-it 

show inferior shrinkage/contraction stress properties, 

compared to the materials on the regression 

line. Filtek Z100 is a heavily filled hybrid resin 

composite, which is rather transparent. Due to the 

transparent character and the choice of photoinitiator 

system the kinetics of the polymerizing 

reaction are affected in such a way that Filtek Z100 

is among one of the fastest curing resin composites 

[9]. Faster polymerization rates imply that the resin 

composite reaches more quickly the gel point and 

Figure 5 Linear regression analysis of shrinkage vs filler 

load of 16 different resin composites (filler load was 

according to manufacturer’s data). Figure 6 Flow factor of 17 different resin composites.


rapidly giving rise to stiffness instead of giving it 

time to let the resin composite flow. The fast 

reaction rate is, therefore, associated with fast 

growth of the elastic modulus and as a result also 

higher contraction stress is obtained. 

High shrinkage and high stress has been reported 

for Aelite Flo [9,17], which is in agreement with the 

inferior shrinkage/contraction stress properties of 

this material. To our knowledge no shrinkage or 

contraction stress data for Flow-it are reported. 

The origin for the high contraction stress for Flow-it 

and Aelite Flo is not straightforward. One possible 

explanation is that TEGDMA is added to improve the 

viscosity of the resin composite. It has been shown 

that increase in the concentration of TEGDMA leads 

to higher shrinkage and higher contraction stress, 

due to the fact that the double bond conversion 

increases [24]. 

The flow factor as shown in Figure 6 can only be 

used as relative number for a predefined set of 

conditions. Since, the conditions were identical of 

all resin composites it is possible to compare the 

obtained values. Figure 6 shows that the nonflowable 

resin composites have a flow factor of ca 

50%, except for Filtek A110 (27%) and Filtek Z100 

(21%). The low flow factor for Filtek Z100 is most 

probably due to the fast setting kinetics of this resin 

composite. The pre-polymerized clusters in Filtek 

A110 may contribute to the low flow factor, 

although this effect was not observed for 

Heliomolar. The flow factor of the flowable resin 

composites is higher than the flow factor of the nonflowable 

resin composites. Apparently, the 

viscosity and/or the filler load are important 

factors. To get a better inside in the mechanisms 

involved in the flow more standardized resin 

composites are necessary, which was beyond the 

scope of this paper. It should be noted that the flow 

is an important factor and has a strong influence on 

the contraction stress. 

Acknowledgements 

Mrs J. Rezende is gratefully acknowledged for 

performing the experiments. 

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