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Int Chin J Dent 2005; 5: 1-6.

Long-term water sorption of three resin-based restorative
materials
Ma’an M. Nayif, BDS, MSc,a Abdul-Haq A. Suliman, BDS, MSc, PhD,b Toru Nikaido,
DDS, PhD,a Masaomi Ikeda, BSc, RDT,a Richard M. Foxton, BDS, PhD,c and Junji
Tagami, DDS, PhDa,da

Cariology and Operative Dentistry, Department of Restorative Sciences, Graduate School, Tokyob
Medical and Dental University, Tokyo, Japan, Department of Conservative Dentistry, College ofc
Dentistry, Mosul University, Mosul, Iraq, Division of Conservative Dentistry, Guy’s, King’s and St.
dThomas’ Dental Institute, Kings College of London, London, UK, and Center of Excellence Program for
Frontier Research on Molecular Destruction and Reconstruction of Tooth and Bone, Tokyo Medical and
Dental University, Tokyo, Japan
Purpose: To evaluate water sorption of three resin-based restorative materials over 180 days of storage inde-ionized water.
Materials and Methods: Three disks (12.0 mm in diameter and 1.25 mm in thickness) were prepared for eachlight-cured resin-based material; a polyacid-modified resin composite (élan), an organically modified ceramic(Definite), and a hybrid resin composite (Prodigy). The disks were immersed in de-ionized water at 37˚C for
180 days. The weight of the disks was measured at intervals of 1, 7, 14, 60, and 180 days. The results wereanalyzed using two–way ANOVA followed by the Bonferroni comparison test at 95% level of confidence.
Results: Significant differences (p<0.05) were found among the materials and the storage time. Over 180 days,élan showed earlier and higher water sorption compared with the other materials. Prodigy exhibited the least
water sorption over the test period.
Conclusion: Water sorption of the resin-based restorative materials was material and storage time dependent.
Prodigy resin composite was the most stable material with the lowest water sorption.
(Int Chin J Dent 2005; 5: 1-6.)
Clinical Significance: The polyacid-modified resin composite (élan) showed earlier and higher water sorption
behavior than the other materials. It was suggested that undesirable properties might appear subsequent to water
sorption.
Key Words: polyacid-modified resin composite, resin composite, water sorption.

Introduction
Resin composite was introduced more than 40 years ago, and at that time its use was routinely for anterior
teeth. Improvements in mechanical properties, biocompatibility, handling and color matching have lead to its
wide acceptance for virtually all types of cavities. An attempt to combine the desirable properties of resin
composite and those of glass ionomer cement (GIC) led to the development of polyacid modified resin
composite (PAMRC). Resin-based materials demonstrate water sorption in the oral cavity, which is the amountof the water absorbed by the material on the surface and into the body while the restoration is in service.1 The
most popular method for measurement of the water sorption of restorative materials is the gravimetricmethodology that involves weighing at different periods.2-11
Water sorption affects the physical and mechanical properties of resin composite, such as dimensionalchange,12,13 decrease in surface hardness and wear resistance,14 filler leaching and change in color stability,15
reduction in elastic modulus,16 an increase in creep and a reduction in ultimate strength,2 fracture strength,
fracture toughness, and flexural strength.17 Water sorption increases as the amount of resin matrix increases andfiller content decreases, since the filler particles do not absorb water.2-4,12,16,18,19 Factors, such as type of resin
composite material, chemical composition, storage time, type and pH of storage solution, and degree ofpolymerization, strongly affect the water sorption and leachability behavior of the material.5-7,20,21

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penetration into the material has been shown to be directly related to the degradation of the filler-matrix
interface.3,22
The purpose of this study was to evaluate the water sorption of three resin-based restorative materials over
180 days. The tested hypothesis was that the material type and storage time have an influence on water sorption.

Materials and Methods
The tested materials, their batch numbers, compositions and their manufacturers are listed in Table 1. Threetypes of resin-based restorative materials were used; a polyacid-modified resin-based composite (élan, Kerr
Corp., Orange, CA, USA), an organically modified ceramic material (Definite, Degussa, Hanau, Germany), anda microhybrid composite (Prodigy, Kerr Corp.). The élan material has 76wt% inorganic filler particles with anaverage particle size of 1.4 µm. Definite has 77wt% inorganic filler particles with an average particle size of
1-1.5 µm. Prodigy has 79wt% filler particles with an average particle size of 0.6 µm.
Table 1. Resin-based restorative materials used in the study.
Material

Lot number

Composition

élan
Definite
Prodigy80729480170525897

Polymerizable poly-carboxylic acid, ETMPTA, EBis-GMA, TEGDMA, Al-F-silicate, BPO
Poly-DMA-polysiloxane, Various DMA, Glass polymerizable SiO2, Bis-GMA, TEGDMA
EBis-GMA, Barium aluminum borosilicate, SiO2, TiO2

ETMPTA, Ethoxylated trimethylolpropane triacrylate; EBis-GMA, Ethoxylated bisphenol-A diglycidyl methacrylate; TEGDMA,
Triethyleneglycol dimethacrylate; BPO, Benzoyl peroxide; DMA, Dimethacrylate; Bis-GMA, Bisphenol-A diglycidyl methacrylate.

Three specimens of each material were prepared following the manufacturer’s recommendations.

A

stainless-steel mold with a 12.0 mm in diameter and 1.25 mm in thickness was placed on a celluloid matrix strip
on a glass slide, and one of the three materials was packed into the mold. A second strip with a glass slide wasplaced onto the resin-based material. Sufficient finger pressure was applied until the two strips contacted withthe mold.

The resin materials were light-cured with a halogen light-curing unit (DE 19963-0359,

Dentsply/Caulk, Milford, DE, USA) from both top and bottom sides for a total of 120 s (Fig. 1).

Fig. 1. Assembly used for specimen preparation.
The disks were dried in desiccators with calcium sulfate desiccant until a constant weight was achieved
throughout daily weighing of the samples for 14 days. An electronic balance (PC 400, Mettler, Mettler Weagen
GmbH, Switzerland) was used for weight determination to an accuracy of 0.1 mg. Each disk was stored in a2

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tightly capped polypropylene container with 10 mL of de-ionized water at 37˚C over 180 days. The weights ofthe disks were measured at intervals of 1, 7, 14, 60, and 180 days. Water evaporation during the storage period
was completed from a blank solution in order to keep the specimens continuously immersed in 10 mL of
de-ionized water.
The specimens were dried with filter papers and weighed within one minute. The dry weight (the weight ofthe specimens after desiccation and before immersion in water) was subtracted from their wet weight (the weightof the specimens after their immersion in water) to determine water gain. The average water gain of thematerials at each storage interval was recorded and divided by the total surface area of the disk to calculate water
sorption.
A two-way analysis of variance (ANOVA) and Bonferroni test was used to observe differences in water
sorption among the specimens as a function of time (paired comparison) and among the materials (non-paired
comparison) as main effects at a 95% level of confidence.

Results
The amounts of water sorption of the three resin-based restorative materials accumulated over 180 days are
summarized in Table 2 and Fig. 2. The amount of water sorption was influenced by the restorative material(F=59.949, p<0.001) and storage time (F=11.939, p<0.001).
The water sorption of the three materials was initially high during the first day of storage; however élanabsorbed approximately 56% of its total water sorption (over 180 days) in the first day of storage, while Definite
and Prodigy absorbed approximately 47% and 40%, respectively.
Table 2.

2

Accumulated water sorption (mg/cm ) of the resin-based restorative materials (n=3).

Storage period 1 day
Material
Mean SD

7 daysMean SD

14 days
Mean SD

60 days
Mean SD

180 days
Mean SDélan

0.58 0.25 a

1.31 0.28
A

1.26 0.27
A

1.26 0.25
A

1.02 0.13 f
ADefinite

0.33 0.00 a, b
B

0.59 0.05 c
B, C

0.79 0.15 dC

0.72 0.10 e
B, C

0.70 0.13 f, g
B, C

Prodigy

0.19 0.04 b
D

0.44 0.20 c
D

0.58 0.14 dD

0.39 0.10 e
D

0.47 0.17 g
D

There were no significant differences within the horizontal columns and vertical rows labeled with the same large and small
superscript letters, respectively (p>0.05).

The amount of accumulated water sorption of élan at the first day of storage was significantly lower than theamount at subsequent storage periods. However, Definite showed no difference in water sorption among thestorage periods except between 1 day and 14 days, while Prodigy showed no difference in water sorption among
the storage periods.
As expected, over 180 days of the storage, the water sorption of élan was significantly higher than that ofDefinite and Prodigy except for 1 and 180 days, in which there were no significant differences between élan andDefinite. Meanwhile, no significant difference was recorded between Definite and Prodigy through the storage
periods.

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mg/cm

Int Chin J Dent 2005; 5: 1-6.

2

Storage time period (days)
2

Fig. 2. Accumulated water sorption (mg/cm ) of three resin materials.

Discussion
Nowadays, hybrid resin composite is recommended for use in a wide range of clinical situations. It contains
fine and microfine filler particles that occupy around 80wt% of the resin material.23 This formula provides
mechanical properties superior to other classes of resin composites. Prodigy is a light-cured micro-hybrid
composite for anterior and posterior applications. Its average particle size of 0.6 µm ensures an excellent andlasting finish together with ease of handling and placement.
Definite is a new class of highly filled hybrid resin composite with a different filler distribution that changes
their consistency to being less sticky and stiffer in comparison with a conventional hybrid. Definite is based on
Ormocer technology characterized by a novel inorganic-organic copolymer in its formulation instead of a
traditional monomer system. A multifunctional urethane and thioether methacrylate aloxysilanes have beendeveloped for synthesis of an inorganic-organic copolymer.24
The élan material is a polyacid-modified resin composite, so-called “compomer” which has two main
constitutes; a dimethacrylate monomer with two carboxylic groups and filler similar to ion-leachable glass
present in glass-ionomer cement (GIC). The ion-leachable glasses are mostly calcium-aluminum fluorosilicate
to ensure direct bonding with the matrix through partial silanization.9

New bifunctional monomers react

simultaneously with methacrylates by a process of polymerization and with the glass particles in the presence ofwater to initiate an acid-base neutralization reaction.10 The élan material was selected for evaluation because thisresinous material contains elements of GIC, that have hydrophilic properties and would be anticipated to show
more water sorption as is case with resin-modified GIC when compared to the composites.8
The three resin-based materials exhibited high water sorption at the initial time of storage. Under all time
conditions, the equilibrium water content of élan was greater than those for Definite and Prodigy. These results
agreed with the results of previous studies.9,11
The early and high water sorption of élan might be attributed to less resistant to crack propagation compared4

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with the resin composites,25 which might be a factor for acceleration of water sorption. Also, polyacid-modified
resin composite has a high fluoride content with no water in its composition. The initial setting of the material isdue to photo-polymerization and subsequently an acid-base reaction after exposure of the material to water as asecond stage mechanism.9

The polyacid-modified resin composite contains bifunctional monomers withhydrophilic functional groups and two double bonds. Water uptake would take place preferentially at thehydrophilic site of the resin matrix after polymerization.
Definite composite showed a significant difference in water sorption between 1 day and 14 days intervals.
Diaz-Arnold et al.26 measured the water sorption of resin composite adhesives with near-infrared spectroscopy.
They also reported that the most rapid water sorption occurred within the first 14 days of storage in the following
370 days water storage period. The minimal amount of water sorption was obtained in Prodigy through thewhole time frame, which may be due to the highly filled resin with a hydrophobic monomer of Bis-GMA.
Polishing was not carried out during specimen preparation in this study. Therefore, the surface layer of thespecimen was resin rich, and totally different from the inside of the specimen.27 If the resin rich surfaces of thespecimens were removed before, the amount of water sorption is expected to be lower. Water sorption of a resin
composite is a diffusion- controlled process.28 Long-term water penetration into 2.5 mm block of dental
composites was evaluated using silver nitrate staining.29 The staining material continued to penetrate up to three
years with a proportional behavior. Therefore, specimen size is one of the critical factors affecting the timerequired to be saturated. A large portion of the water was reversibly absorbed by the resin composite materials.26
However, Ferracane and Condon (1990)30 have described the inability to remove 100% of absorbed water by
short-term desiccation.
It was reported that high water sorption at the first day was responsible for the large hygroscopic expansion,
which continued up to 180 days.31 In contrast, other researchers reported that hygroscopic expansion following
water sorption equilibrates after 7 days.12 Since direct composite restorations are widely accepted, further
characterization of the effects of water on the resin composite materials is warranted.

Conclusion
The resin-based materials investigated in this study demonstrated different levels of water sorption. The
polyacid-modified resin composite showed higher water sorption than composite resin.

Prodigy (hybrid

composite) was a stable material with the least water sorption. The water sorption of élan and Definite tended toincrease up to 7th day and 14th day, respectively.
Acknowledgment
This research was supported by grant for Center of Excellence Program for Frontier Research on Molecular Destruction
and Reconstruction of Tooth and Bone in Tokyo Medical and Dental University.

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Reprint request to:
Dr. Ma’an M. Nayif
Cariology and Operative Dentistry, Department of Restorative Sciences
Graduate School, Tokyo Medical and Dental University
1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, Japan
Fax: +81-3-5803-0195 E-mail: mmnayif@yahoo.com
Received September 27, 2004. Revised December 6, 2004. Accepted December 11, 2004.
Copyright ©2005 by the Editorial Council of the International Chinese Journal of Dentistry.

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