Long-term release of monomers from modern dental ... - Dentsply

Eur J Oral Sci 2009; 117: 68–75 

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Long-term release of monomers from 

modern dental-composite materials 

Polydorou O, Ko¨nig A, Hellwig E, Ku¨mmerer K. Long-term release of monomers from 

modern dental-composite materials. Eur J Oral Sci 2009; 117: 68–75. Ó 2009 The 

Authors. Journal compilation Ó 2009 Eur J Oral Sci 

The elution of monomers from composite materials influences the biocompatibility of 

dental restorations. The purpose of the present study was to investigate the elution of 

monomers [bisphenol A glycidyl methacrylate (BisGMA), triethylene glycol dimethacrylate 

(TEGDMA), urethane dimethacrylate (UDMA), and bisphenol A (BPA)] 

from two light-cured materials (nanohybrid and ormocer) and from a chemically cured 

composite material, after different curing times (0, 20, 40 and 80 s) and different 

storage periods (24 h, 7 d, 28 d, and 1 yr after curing). Each specimen was stored in 

1 ml of 75% ethanol. This medium was renewed after 24 h, 7 d, 28 d, and 1 yr. The 

ethanol samples were analyzed using liquid chromatography tandem mass spectrometry 

(LC–MS/MS). The amount of monomers released from the nanohybrid and the 

chemically cured composite was significantly higher than released from the ormocer. 

The curing time exerted a significant effect on the release of monomers. For the 

nanohybrid, less monomer was released after increasing the curing time. For the 

ormocer, 80 s of curing resulted in a higher degree of monomer release. The effect of 

storage differed between the monomers. Although the elution of TEGDMA was significantly 

decreased after storage for 28 d and 1 yr, a similar amount of BisGMA was 

released at each storage time-point analyzed, even after 1 yr. The present study 

showed that ormocer released a very small amount of monomers compared with the 

other materials. 

Ó 2009 The Authors. 

Journal compilation Ó 2009 Eur J Oral Sci 

European Journal of 

Oral Sciences 

Olga Polydorou 1 , Armin Kçnig 2 , 

Elmar Hellwig 1 , Klaus Kümmerer 2 

1 Department of Operative Dentistry and 

Periodontology, Dental School and Hospital, 

University Medical Center Freiburg, Freiburg; 

2 Department of Environmental Health 

Sciences, University Medical Center Freiburg, 

Freiburg, Germany 

Olga Polydorou, Department of Operative 

Dentistry and Periodontology, Dental School 

and Hospital, University Medical Center 

Freiburg, Hugstetter Straße 55, 79106 Freiburg 

i. Br., Germany 

Telefax: +49–761–2704762 

E-mail: olga.polydorou@uniklinik-freiburg.de 

Key words: composite; dental restorative 

material; monomer; photopolymerization 

Accepted for publication November 2008 

The increased demand for esthetic dental restorations 

during the last few years in the general dental practice 

has led to an increased use of composite materials. It has 

been assumed that composite materials have excellent 

mechanical properties, good esthetic quality, are easy to 

handle, and are able to bond with the enamel surface. 

However, a major concern exists about their toxicity and 

consequently their effect on human health. Different 

substances (such as residual monomers, additives, and 

degradation products) may irritate the oral soft tissues, 

stimulate the growth of bacteria, and promote allergic 

reactions (1). 

The cross-linking dimethacrylates bisphenol A glycidyl 

methacrylate (BisGMA), urethane dimethacrylate 

(UDMA), triethylene glycol dimethacrylate (TEG- 

DMA), and bisphenol A ethoxylated dimethacrylate 

(BisEMA) are most widely used for the preparation of 

composite materials. Moreover, resin composites contain 

various additives, such asphotoinitiators (e.g. 

camphoroquinone), co-initiators (e.g. dimethyl-aminobenzoic-acid-ester), 

inhibitors of polymerization (e.g. 

BHT [butylated hydroxytoluene]), and photostabilizers 

(e.g. benzophenone). The differences in composition of 

the monomers used for each composite material impact 

the reactivity, the viscosity and the polymerization 

shrinkage of the monomer as well as the mechanical 

properties of the composite material (2). Therefore, the 

elution of components (residual monomers, oligomers, 

and degradation products) from resin composites may 

influence the biocompatibility of the restorations (3). 

Several factors contribute to the process of elution 

from resin-based dental materials. According to Ferracane 

(4), the first relates to the amount of components 

released, and this should be directly related to the extent 

of the polymerization reaction (i.e. the degree of doublebond 

conversion). Second, the chemistry of the solvent 

has a significant effect on the elution. Third, the size and 

the chemical nature of the released components play a 

role. Additionally, the composition (filler loading) of the 

composite materials directly influences the elution of 

monomers (5). The filler content, the filler size, and the 

distribution of the filler particles influence the physical 

and mechanical properties of the composite resins. It has 

been shown that the filler volume fraction and filler load 

level of the composites correlate with the material 

strength and elastic modulus, as well as the fracture 

toughness of the material (6, 7). Increasing the filler 

content and reducing the average filler size have been one 

approach used to produce composite resins for posterior 

restorations. Advanced, highly filled composite resins 

exhibit excellent material properties and a good clinical 

performance (8).

Monomer release from composite materials 69 

In various studies (4, 9) the degree of monomer– 

polymer conversion in dental-composite resins has been 

found to vary between approximately 35 and 77%. 

Several authors investigated a possible correlation 

between the degree of conversion from the monomer to 

polymer which determine the chemical stability and 

solubility. Pearson & Longman (10) showed that 

reduced irradiation significantly increases the solubility. 

Tanaka et al. (1) found that increasing the irradiation 

time from 30 to 50 s resulted in a significant decrease in 

residual monomer contents and the quantities that were 

released into water. In contrast to the above studies, 

Ferracane (4) found a very poor correlation between 

the degree of conversion and solubility. 

The elution of substances from composite materials 

has been widely studied (11–15). Geurtsen et al. (13) 

evaluated the release of substances from restorative 

materials and also the cytotoxicity of the released 

monomers on fibroblasts. In their study, substances were 

identified that caused severe or minor cytotoxic effects in 

all permanent and primary cell lines. Additionally, their 

results indicate that for most of the severely toxic composite 

components, few cytotoxic alternatives are available. 

Spahl et al. (16) identified (co)monomers, 

additives, and contaminants from the manufacturing 

process to be released from resin composites. Several 

in vitro studies (12, 17) have shown the cytotoxic, genotoxic, 

mutagenic or estrogenic effects and pulpal and 

gingival/oral mucosa reactions of some of the monomers 

released from the composite materials. However, most of 

the in vitro studies (14, 18) have used experimental 

composite materials to investigate the process of monomer 

elution, leading to useful information about commercial 

products. 

Several studies have been conducted in water and in 

oral/food-simulating liquids, among which 75% ethanol/water 

solution has been used. This solution is 

recommended by the Food and Drug Administration 

(FDA) Guidelines of the USA (1976, 1988) as a food 

simulator and might be considered clinically relevant 

(19). It simulates the influence of certain beverages 

(including alcoholic), vegetables, fruits, and syrup. 

Different studies (9, 12) indicate the important role of 

the type of the solvent, and that irreversible processes, 

such as leaching of components, may occur (e.g. in the 

presence of ethanol). A close match in the solubility 

parameter results in maximum softening of the resin 

(20, 21). This phenomenon may contribute to irreversible 

material degradation provoked by ethanol because 

it penetrates the matrix and expands the space between 

polymer chains into which soluble substances, such as 

unreacted monomers, may diffuse. A 75% ethanol 

solution has a solubility parameter which matches that 

of BisGMA (20, 21). 

Another point of concern about the elution process of 

monomers of the resin composites is the method used to 

determine the quality and the quantity of the eluted 

monomers. Analysis is usually performed with highperformance 

liquid chromatography (HPLC) (14, 22). In 

this case, pure components are used as external standards 

for the identification and quantification of the 

eluted components. However, as reported previously 

(12), this method has some disadvantages and it is not 

suitable to give an exact identification of the substances 

eluted. Liquid chromatography–mass spectrometry 

(LC–MS) is an analytical technique that combines the 

advantages of an LC instrument with those of a mass 

spectrometer. High-performance liquid chromatography 

is a means of separating components of mixtures by 

passing them through a chromatographic column so that 

they emerge sequentially. Because LC operates in the 

liquid phase but MS is a gas-phase method, it is not a 

simple matter to connect the two. In order to allow the 

separated components of a mixture to be passed 

sequentially from the LC into the MS, an interface is 

needed. Having interfaced the two, LC–MS is a very 

powerful technique (23). A combination of HPLC (or 

LC) with MS can be used in these cases for a very specific 

identification of the compounds eluted (15). The fact that 

most of the studies made in this field were performed 

without LC–MS highlights the need for further research 

in this field. 

Although the advantages of the light-cured composites 

cannot be questioned, the chemically cured composites 

still have important applications in contemporary 

restorative dentistry, especially in areas that are not 

easily penetrable by light (24). This low conversion rate 

(17–24) of these materials could result in an increased 

release of monomers. Core build-up materials may be in 

contact with the oral cavity for a long period of time 

before crown preparation is performed. No information 

on the elution of monomers from core build-up materials 

exists in the literature. 

Although much literature has been published on the 

release of monomers (3, 11–13, 15, 25), information is 

still lacking with respect to the elution of monomers 

from modern composite materials such as ormocers, 

nanohybrid composite resins, and core build-up materials 

that are used daily in the dental clinical practice. 

Therefore, new studies are necessary to evaluate these 

materials under clinically relevant conditions. Additionally, 

no information is available on the release of 

monomers over a post-cure period of longer than 

3 months. A longer storage time period simulating clinical 

oral conditions would be very useful in order to 

evaluate the composite materials. However, to correspond 

to the period that the composite restorations are 

expected to remain in the mouth, a storage time of 

5–10 yr would be necessary. This would not be particularly 

useful for studying composite materials because 

each year new composite materials become commercially 

available and therefore results concerning 10-yr-old 

composite materials would not be clinically relevant. 

Therefore, the aim of the present in vitro study was to 

identify and quantify the elution of monomers of three 

different resin composites using liquid chromatography 

tandem mass spectrometry (LC–MS/MS), after different 

curing times and storage periods up to 1 yr after curing. 

Additionally, the following hypothesis was examined: 

composite materials with new chemistry, such as ormocers, 

release fewer monomers than materials with traditional 

chemistry.

70 Polydorou et al. 

Table 1 

Composite materials tested 

Material Type Main monomer composition Manufacturer 

Filtek 

Supreme XT 

Ceram X 

Clearfil Core 

Universal restorative, 

nanohybrid 

ÔOrmocerÕ, universal nano-ceramic 

restorative 

Self-curing composite core 

build-up material 

BisGMA, TEGDMA, UDMA, BisEMA 

Methacrylate modified polysiloxane, 

dimethacrylate resin 

TEGDMA, BisGMA 

3M ESPE Dental Products, 

Seefeld, Germany 

Dentsply DeTrey, Konstanz, Germany 

Kuraray Europe, 

Du¨ sseldorf, Germany 

Material and methods 

Three different resin-composite materials were used: a 

nanohybrid (Filtek Supreme XT; 3M ESPE Dental Products, 

Seefeld, Germany), an ormocer (Ceram X; Dentsply 

DeTrey, Konstanz, Germany) and a chemically cured 

(Clearfil Core; Kuraray Europe, Du¨ sseldorf, Germany) 

resin composite. Detailed information about the composition 

of the composite materials and the manufacturers are 

given in Table 1. 

For curing the samples of the two light-cured resin 

composites (Filtek Supreme XT and Ceram X), a halogen 

unit (Elipar Highlight; 3M ESPE) was used. The light 

intensity of this unit was 780–800 mW cm )2 . The spectral 

irradiance was determined using a visible curing light meter 

(Cure Rite; Dentsply, York, USA). 

From each of the two light-cured composite materials 

(Filtek Supreme XT and Ceram X), four groups (n = 10) 

were prepared, one for each curing time tested (0, 20, 40, and 

80 s). From the chemically cured resin composite (Clearfil 

Core) 10 specimens were fabricated. The specimens were 

prepared using forms, given from Dentsply DeTrey, allowing 

the production of standardized cylindrical specimens 

(4.5 mm in diameter and 2 mm thick). The forms were 

positioned on a transparent plastic matrix strip lying on a 

glass plate. Then, they were filled with the composite materials. 

The samples were built up in one increment (2 mm). 

After inserting the materials into the discs, a transparent 

plastic matrix strip (Kerr Hawe, Bioggio, Switzerland) was 

placed on top of them in order to avoid creating an oxygeninhibited 

superficial layer. In addition, a glass slide was used 

in order to flatten the surface. Every sample was then cured 

according to the group to which it belonged. 

Directly after curing, each sample was immediately 

immersed in 1 ml of 75% ethanol. The samples were stored 

in a dark box at room temperature (’21°C) and the storage 

medium (1 ml) was renewed 24 h, 7 d, 28 d, and 1 yr after 

the polymerization. From the storage medium removed, 

ethanol samples were prepared and stored until analysis at 

4°C in the dark. 

Analytical method 

Information about the substances used as standards for the 

analysis are given in Table 2. The reference standards of 

BPA, BisGMA, one UDMA, and TEGDMA were 

purchased from Dentsply DeTrey. A second type of UDMA 

was obtained from Deltamed (Freidberg, Germany). The 

two types of UDMA differ in chemical composition and 

molecular weight. Usually, different types of UDMA are 

used for the production of composite materials. The analysis 

was performed as described in detail by Polydorou et al. 

(15) with the difference being that the limits of quantification 

were improved: 1 lg ml )1 for UDMA, 0.5 lg ml )1 for 

TEGDMA,1 lg ml )1 for BisGMA, and 0.5 lg ml )1 for 

BPA. Values lower than these levels could not be qualified. 

For the analysis, the ethanol samples were investigated 

using LC–MS/MS. A Bruker Esquire 3000 plus (Bruker- 

Franzen Analytik, Bremen, Germany) was used. Separation 

of the monomers was performed using a CC 125/4 Nucleodur 

100-5 C18ec HLC-Column (Machery & Mayiel, 

Du¨ ren, Germany) and a solvent gradient of 0.1% formic 

acid and acetonitrile. For the analysis, external calibrations 

with ethanol standards (up to a 1,000 lg ml )1 ) were carried 

out with the help of the peak areas of the extracted ion 

chromatograms (EICs). Table 3 presents the identification 

masses that were used for the qualification and the quantification 

of the substances during LC–MS/MS. 

Statistical analysis 

The significance level of the statistical analysis was 0.05. 

For the statistical analysis, the repeated-measures analysis 

of variance (anova) was used with two between-factors 

(materials and monomers) and two within-factors (curing 

time and storage time). Because the data were not normally 

distributed, the logarithms were used for the statistical 

analysis. According to the Ôcorrelation procedureÕ, the 

log-transformed data were normally distributed 

(P = 0.27). 

Table 2 

Monomers used as reference standards 

Substances Name Chemical type Mol. weight CAS-number 

BisGMA Bisphenol A glycidyl methacrylate C 29 H 36 O 8 513.0 1565-94-2 

TEGDMA Triethylene glycol dimethacrylate C 14 H 22 O 6 286.32 109-16-0 

UDMA 1 Urethane dimethacrylate Product C 26 H 42 O 8 N 2 498.0 – 

UDMA 2 Urethane dimethacrylate C 23 H 38 N 2 O 8 470.56 41137-60-4 or 72869-86-4 

BPA Bisphenol A C 15 H 16 O 2 228.29 80-05-7


Table 3 

Identification masses of monomers in liquid chromatography 

tandem mass spectrometry (LC–MS/MS) 

Substances Qualification Quantification 

BisGMA 512 495 

TEGDMA 287 113 

UDMA 1 499 499 

UDMA 2 471 471 

Bisphenol A 227 227 

BisGMA, bisphenol A glycidyl methacrylate; TEGDMA, 

triethylene glycol dimethacrylate; UDMA, urethane dimethacrylate. 

Results 

The logarithmic values and the standard deviations of 

the substances released from the three composite materials, 

for each curing time and storage period, are given 

in Tables 4–6. 

All monomers used as reference standards could be 

identified in the ethanol samples of the composite 

materials. However, differences were found in the type of 

monomers released from each material. BisGMA, 

TEGDMA, BPA, and one form of UDMA (UDMA 2) 

could be detected in the ethanol samples of Filtek 

Supreme XT. BisGMA, TEGDMA, and Bisphenol A 

were released from Ceram X; and only BisGMA and 

TEGDMA were detected from samples of Clearfil Core. 

The amount of BisGMA eluted was always significantly 

higher (P < 0.0001) than the amount of TEG- 

DMA eluted, regardless of curing time, type of material, 

and storage period. According to the statistical analysis 

there was a significant difference between the two lightcured 

resin composites (P < 0.0001). More BisGMA 

and TEGDMA were released from Filtek Supreme XT 

compared with Ceram X for each storage time tested. 

For these two monomers, the following results were 

obtained. 

For Filtek Supreme XT, the curing time had a significant 

effect on the elution of monomers (P < 0.0001). A 

smaller amount of monomers was released after 

increasing the polymerization time. However, a curing 

time of 80 s did not seem to reduce the elution of 

monomers compared with a curing time of 40 s. The 

elution of monomers differed significantly during the 

storage periods (24 h until 1 yr) (P < 0.0001). During 

storage, the release of TEGDMA decreased significantly, 

whereas the amount of BisGMA released from the 

polymerized samples remained high, even 1 yr after 

curing. 

For Ceram X, the curing time exerted a significant 

effect on the elution of BisGMA and TEGDMA 

(P = 0.0004). Curing for 80 s resulted in the release of a 

significantly higher amount of monomers. The amount 

of BisGMA and TEGDMA released from Ceram X was 

significantly influenced by the storage time of the composite 

samples (P = 0.01). However, the effect of the 

storage time was significantly different for the two 

Table 4 

Filtek Supreme XT: log values of the concentration ± standard deviation (SD) 

24 h 7 d 28 d 1 yr 

0s 

BisGMA 3.52 ± 0.03 2.22 ± 0.1 1.94 ± 0.26 1.13 ± 0.14 

TEGDMA 2.7 ± 0.025 2.67 ± 0.08 1.12 ± 0.54 0.48 ± 0.15 

UDMA 1 ND ND ND ND 

UDMA 2 2.14 ± 0.03 1.64 ± 0.03 0.7 ± 0.35 1.07 ± 0.18 

Bisphenol A ND ND ND 

20 s 

BisGMA 2.01 ± 0.14 1.59 ± 0.1 1.59 ± 0.07 1.95 ± 0.07 

TEGDMA 1.4 ± 0.25 1.16 ± 0.42 0.75 ± 0.05 0.59 ± 0.07 


UDMA 2 1.3 ± 0.08 0.65 ± 0.06 0.67 ± 0.06 2.16 ± 0.04 

Bisphenol A ND ND ND ND 

40 s 

BisGMA 1.82 ± 0.06 1.36 ± 0.11 1.43 ± 0.08 1.9 ± 0.06 

TEGDMA 1.16 ± 0.42 1.21 ± 0.07 0.66 ± 0.03 0.55 ± 0.09 


UDMA 2 1.14 ± 0.06 0.44 ± 0.1 0.54 ± 0.05 2.12 ± 0.08 


80 s 

BisGMA 1.76 ± 0.06 1.22 ± 0.09 1.16 ± 0.3 1.69 ± 0.28 

TEGDMA 1.1 ± 0.11 1.07 ± 0.13 0.55 ± 0.19 0.41 ± 0.18 


UDMA 2 1.04 ± 0.06 0.29 ± 0.09 0.36 ± 0.02 1.84 ± 0.47 


Logarithmic (log) values of the concentration and SDs of the monomers released from Filtek Supreme XT. 

BisGMA, bisphenol A glycidyl methacrylate; ND, not detected; TEGDMA, triethylene glycol dimethacrylate; UDMA, urethane 

dimethacrylate.


Table 5 

Ceram X: log values of the concentration ± standard deviation (SD) 

24 h 7 d 28 d 1 yr 

0s 

BisGMA 0.59 ± 0.1 0.99 ± 0.05 0.61 ± 0.02 0.51 ± 0.07 

TEGDMA 0.09 ± 0.14 0.38 ± 0.08 0.05 ± 0.1 ND 



Bisphenol A 0.65 ± 0.03 1.37 ± 0.06 0.96 ± 0.08 ND 

20 s 

BisGMA 0.58 ± 0.06 0.66 ± 0.02 0.56 ± 0.02 0.84 ± 0.04 

TEGDMA 0.05 ± 0.1 0.35 ± 0.06 ND ND 



Bisphenol A 0.72 ± 0.03 0.76 ± 0.04 0.85 ± 0.1 ND 

40 s 

BisGMA 0.64 ± 0.14 0.65 ± 0.04 0.54 ± 0.19 0.91 ± 0.1 

TEGDMA 0.13 ± 0.15 0.35 ± 0.09 ND ND 



Bisphenol A 0.71 ± 0.06 0.59 ± 0.31 0.32 ± 0.14 ND 

80 s 

BisGMA 1.28 ± 0.02 0.6 ± 0.01 0.53 ± 0.19 0.84 ± 0.04 

TEGDMA 0.42 ± 0.13 0.24 ± 0.04 ND ND 



Bisphenol A ND 0.5 ± 0.27 0.28 ± 0.16 ND 

Logarithmic (Log) values of the concentration and SDs of the monomers released from Ceram X. 


dimethacrylate. 

monomers (P < 0.0001). No TEGDMA could be 

detected 1 yr after curing, while at the same time-point 

the release of BisGMA remained at detectable levels. 

Bisphenol A was detected only in the polymerized 

samples of Ceram X. The amount of BPA was not 

influenced by the curing time (P > 0.05). The second 

type of UDMA (UDMA 2) was released by the samples 

of Filtek Supreme XT. Its release was influenced by 

curing and storage time (P £ 0.05). Increasing the 

curing time reduced the amount of UDMA 2 eluted, 

whereas storage for 1 yr resulted in a significantly higher 

release. 

The amount of BisGMA released from Clearfil Core 

was higher compared with the amount of TEGDMA 

released. The amount of BisGMA and TEGDMA eluted 

from Clearfil Core was compared with the amount of 

BisGMA and TEGDMA released from Filtek Supreme 

XT and Ceram X cured for 40 s and 80 s. For both 

curing times, a significant difference (P £ 0.05) was 

found between the three composite materials concerning 

the elution of BisGMA and TEGDMA, namely that the 

amounts of BisGMA and TEGDMA released from 

Clearfil Core were higher than the amounts of BisGMA 

and TEGDMA released from Filtek Supreme XT and 

Ceram X. 

Discussion 

In the present study, monomer release from three different 

dental-composite materials was investigated. The 

highest elution of monomers occurred from Filtek 

Table 6 

Clearfil Core: log values of the concentration ± standard deviation (SD) 

24 h 7 d 28 d 1 yr 

BisGMA 2.68 ± 0.06 1.74 ± 0.14 1.29 ± 0.03 2.24 ± 0.09 

TEGDMA 2.39 ± 0.45 1.42 ± 0.29 0.86 ± 0.03 0.96 ± 0.07 




Logarithmic (log) values of the concentration and SDs of the monomers released from Clearfil Core. 


dimethacrylate.


Supreme XT, followed closely by Clearfil Core. Very 

small amounts of monomers were eluted from Ceram X. 

These findings support the results of Franz et al. (26), 

who demonstrated that Filtek Supreme XT exhibits 

higher cytotoxicity on L-929 fibroblasts than the other 

composite materials tested. 

According to the manufacturersÕ information, the filler 

content of these materials is as follows: Ceram X, filler 

content 76% by weight; Clearfil Core, filler content 78% 

by weight; and Filtek Supreme XT, filler content 78.5% 

by weight. These small differences in the filler loading 

between the three materials could not be the reason for 

our findings. It is more likely that the difference in the 

chemistry between the three materials, the filler size, and 

the distribution of the filler particles could have influenced 

our results. 

As far as Clearfil Core is concerned, no published data 

exist concerning the elution of monomers. The decreased 

degree of conversion of the chemically cured composites 

compared with the light-cured materials (27) could 

explain the high degree of elution of monomers from 

Clearfil Core. Storage of the samples in ethanol immediately 

after their manufacture could have influenced the 

release of TEGDMA and BisGMA because of the fact 

that the degree of conversion Clearfil Core at the end of 

mixing is markedly lower than that of photoinitiated 

systems. Although such a comparison of the composite 

materials directly after mixing might be considered to be 

quite unfair for the chemically cured composite, as 

mentioned above, the use of this solution for sample 

storage simulates the situation in the mouth. Chemicallycured 

materials are generally used as core build-up 

materials and therefore they should not come into direct 

contact with saliva or oral soft tissues because they are 

covered with a crown. However, these materials very 

often remain in the oral cavity for a considerable period 

of time before they are covered with the final restoration. 

Additionally, it is possible that monomers can diffuse 

through dentin into the pulp (28, 29). 

In the present study, the ethanol samples were analysed 

using LC–MS/MS. Using this method, substances 

with the same mass and retention time can be identified. 

The use of MS/MS has the benefits of separating different 

molecular ions, generating fragment ions from a 

selected ion, and then mass measuring the fragmented 

ions. The fragmental ions are used for structural determination 

of original molecular ions (23). Therefore, a 

combination of LC and MS in the form of LC–MS/MS 

can be very helpful to identify specific compounds with 

similar structures, which is one of the greatest problems 

encountered in analytical methods. In the present study, 

the identification of specific molecules was studied. 

However, it should be mentioned that beside these 

molecules, other substances and degradation products 

could be released from the composite materials. The use 

of LC–MS/MS could be very helpful in their identification. 

An important finding of the present study was the 

small amount of monomers released from Ceram X. 

Ormocer contains inorganic–organic copolymers in 

addition to the inorganic silanized filler particles. It is 

synthesized through solution and gelation processes (sol– 

gel process) from multifunctional urethane and thioether(meth)acrylate 

alkoxysilanes. By hydrolysis and 

polycondensation reactions, the alkoxysil groups of the 

silane promote the formation of an inorganic Si–O–Si 

network, while the methacrylate groups are still available 

for light-activated organic polymerization. Ormocers are 

characterized by the novel inorganic–organic copolymers 

in the formulation that allow the modification of 

mechanical properties over a wide range (30). Hickel 

et al. (31) suggested that the advantages of ormocer 

include low shrinkage, high abrasion resistance, biocompatibility, 

and caries protection. However, only 

limited information is available on the elution of 

monomers from ormocers and their toxicity. Brackett 

et al. (32) found that materials with traditional compositions, 

such as Filtek Supreme XT, were severely cytotoxic 

throughout an 8-wk interval, but materials with 

newer chemistries or filling strategies, such as Ceram X, 

improved over time of aging in artificial saliva. This 

appears to support the claims of better polymerization 

and lower leaching in newer chemistries (33). The difference 

in the chemical structure of the composite, and 

the variation in the ratio of filler and monomer, have a 

significant effect on the element release and cytotoxicity 

level of the materials (34). 

Regardless of the polymerization time, storage time, 

and material, a greater amount of BisGMA was released 

compared with the other monomers. As mentioned 

above, 75% ethanol has a solubility parameter which 

matches that of BisGMA and this could be the reason for 

the higher amount of BisGMA released. Additionally, 

BisGMA and TEGDMA differ markedly as far as their 

chemical properties and reactive potentials are concerned. 

(35). BisGMA is more reactive than TEGDMA, 

but the fact that it presents a sterically hindered structure 

precludes a higher degree of conversion (36). It has been 

shown that the quantity of unreacted unsaturations in 

the BisGMA/TEGDMA system can be qualitatively 

correlated with the amount of BisGMA in the polymerizing 

system (37, 38) and that neat TEGDMA 

exhibits a degree of conversion that is about 10% higher 

than that of neat BisGMA (37, 38). 

In the present study, BPA was found to be eluted by 

unpolymerized composite samples of Filtek Supreme XT 

and Ceram X and by polymerized samples of Ceram X. 

This is in contrast to previous studies where no BPA was 

detected (15, 16, 25). However, detectable amounts of 

BPA have been mentioned, also by other authors (34, 

39), to be extracted from composite materials. Dental 

composites typically contain monomers [such as 

BisGMA and bisphenol A dimethacrylate (BisDMA)] 

that are derived from BPA, but there is no known use for 

BPA itself in dental composites. As these monomers may 

leach from dental composites, their stability has been 

studied under a variety of conditions to determine whether 

they may hydrolyze to form BPA. BisGMA, the 

base monomer for many resin composites, has been 

found to be stable under various hydrolytic conditions 

(25). However, two researchers have reported that Bis- 

DMA is hydrolyzed to BPA, which probably accounts


for the BPA detected in extracts from certain composites 

(25–40). Further research is necessary to evaluate the 

source of BPA released from the composite materials. 

With respect to the different polymerization times used 

in the present study, it could be shown that an increase in 

the curing time from 20 to 40 s resulted in a decrease in 

the amount of monomers released from Filtek Supreme 

XT. The increased polymerization time of 80 s did 

decrease the monomer release compared with the polymerization 

time of 40 s. For Ceram X, the amount of 

monomers eluted was shown to increase after polymerization 

for 80 s. However, the amount of monomers 

released from this material was very low, especially when 

the samples were polymerized only for 20 s. This result 

suggests that Ceram X can be used with short curing 

times without exposing the patients to high levels of 

monomers. However, further research is necessary to 

evaluate the effect of the increased curing time on the 

chemistry of this material. Although this type of negative 

effect on composite materials after a longer curing time 

has not been previously reported, it may be assumed that 

the longer exposure time could have a negative effect on 

the network of the materials, affecting their polymerization 

and, as a result, making the special chemistry of 

these materials a disadvantage. The results of the present 

experiments did underline the conclusion that for different 

composites, polymerization times of < 80 s are 

not sufficient to prohibit monomer release. 

Within the limitations of the present study, the 

composite materials tested as a result of having marked 

differences in their composition could be considered as a 

model for a wide variety of materials in clinical use. As 

far as the hypothesis made at the start of the study is 

concerned, it can be stated that materials with new 

chemistries, like ormocer, can show, after a short timeperiod 

of curing, a low elution of monomers compared 

to composites with traditional compositions and chemically 

cured materials. However, this hypothesis cannot 

be totally accepted because the behavior of the ormocer 

was not linear and therefore it cannot be considered as 

chemically stable without further research. 

Acknowledgements – This work was supported by the 

Research Commission of the Medical Faculty of the University 

Freiburg (Forschungskommission), Germany; number 

KU¨ M431/05. 

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