Keywords
degree of conversion - light curing units - dental composites - elution of monomer
- high-performance liquid chromatography
Introduction
Dental composites are composed of three major components that are chemically different
from each other. These materials are used for restoration of the loss of tooth structure
due to caries, trauma, or other diseases. These materials include resin matrix of
natural polymerizable structure, inorganic filler for strengthening, and a coupling
agent known as silane coupling agent. The coupling agent enhances the chemical bonds
between the organic matrix and inorganic fillers.[1] Base monomers such as bisphenol A glycidyl methacrylate (Bis-GMA) and urethane dimethacrylate
(UDMA) along with low-viscosity monomer like triethylene glycol dimethacrylate (TEGDMA)
constitute the polymerizable resin matrix. Composites can also be used to elute and
to cement crowns and veneers. They are also indicated for the periodontal splinting,
noncarious lesions, enamel hypoplasia, and repair of old composites.[1] Dental composites are considered among the most adaptable dental filling materials.
It is being extensively used in dentistry since its introduction in the dental market
about 50 years ago.[2]
The common drawbacks of composites include polymerization shrinkage and high residual
monomer content.[3] The elution of residual monomers, oligomers, and other degradation products into
the oral environment has raised concerns regarding composites. It occurs by diffusion
of the resin matrix or by its degradation or erosion over the period.[3] In addition to their effect on mechanical properties such as decreased wear resistance,
hardness, and increased tendency to discoloration, eluted monomers can contribute
to a variety of local or systemic health effects.[4]
[5] They can be released either into the oral cavity or diffuse into the pulp through
dentinal tubules causing local reactions including pulpal irritation, allergenic,
cytotoxic, and genotoxic effects. Eluted TEGDMA has been shown to promote the growth
of cariogenic bacteria. Some eluted substances have been linked to systemic effects.
Bisphenol A (BPA), a hydrolytic degradation product or a contaminant eluted from aromatic-based
systems, has been confirmed to have parahormonal activity and it can imitate hormones
from the estrogen group and thus may contribute to female infertility.[6]
Dentists use incremental placement techniques to reduce polymerization shrinkage.
This technique is time-consuming, and there is risk of contamination while placing,
adapting, and curing each increment. Recently, a new class of resin-based composite,
called “bulk-fill” composites, has been introduced with the purpose of saving clinical
chair side time. Its unique advantage is that it can be placed and cured in an increment
of 4-mm thickness, without undergoing polymerization shrinkage.[7]
The degree of conversion (DC) of a resin composite is crucial in determining its biocompatibility.[8] It has been shown that decrease in DC might lead to a decrease in the physical/mechanical
properties and an increase in the elution of monomers, as well as negatively affecting
the pulp tissue. It has been found in various studies that a significant amount of
organic compound residue remains unbound in the cured material.[9]
As described by Ferracane,[2] several factors can influence the elution of different compounds from resin-based
dental materials. First, the amount of compounds released is directly related to the
DC, which varies between 50 and 70% and reaches a maximum after 24 hours due to a
postcure process.[10]
[11] Second, the type of extraction solution can affect the elution. Third, the size
and chemical nature of the released components play a role. Additionally, the physical
and mechanical characteristics of the composite resins are related to the filler content,
filler size, and distribution of filler particles. Therefore, the composition (filler
content) of composites can directly influence the elution process.[12]
According to Sajnani and Hegde,[3] the DC for dental composites is approximately between 35 and 77%. The storage solutions
and chemistry of the solvent have got a direct impact on the elution of unreacted
monomer. Łagocka et al[13] reported that the type of extraction medium used impacts both the concentration
of the eluted monomer and the elution time. Generally, the degree of monomer elution
is proportional to the hydrophobicity and swelling capacity of the organic solvent
used.
The qualitative and quantitative methods of analyzing unreacted monomers and degradation
products include Gas Chromatography (GC) high-performance liquid chromatography (HPLC),
GC/mass spectrometry, and electrospray ionization/mass spectrometry. HPLC is the technique
used most often.[8] Both HPLC and GC can be coupled to a mass spectrometer (MS) as a detector to increase
the sensitivity and selectivity of the technique. This also allows identification
of unknown substances and degradation products from both uncured resins and extracts
from cured materials.[14]
Despite multiple benefits of resin-based composites, there are few drawbacks associated
with it. This monomer possesses different types of toxic effects; particularly, they
produced genotoxic and cytotoxic effects. As a result of this toxicity, pulp formation
and multiple allergic reactions along with infections have been observed within the
patient's physical, chemical, and mechanical properties of the filling material.[2]
Therefore, the aim of this study was to evaluate different composites and how different
factors including storage time, storage solution, and curing modes affect the monomer
release. Consequently, the study focused on evaluating the release of TEGDMA under
different conditions using HPLC.
Material and Method
Resin-Based Composite's Composition and Preparation
In total, 180 disk-shaped samples were prepared using a stainless steel mold of 4-mm
thickness and 10-mm diameter (ISO 4049). Conventional nanohybrid composite (Filtek
Z350XT 3M ESPE) was used in the plays control group and two bulk-fill composites (Shofu
Beautifil-Bulk and Filtek Bulk fill flowable 3M ESPE) were used by the experimental
groups in the study. The composite materials, their composition, batch numbers, and
manufacturers are given in [Table 1].
Table 1
Composites used in the study
|
Material
|
Type
|
Composition
|
Processing method
|
Manufacturer
|
|
Composite (Filtek Z350XT), control group
|
Conventional nanohybrid composite
|
Resin matrix contains Bis-GMA, DMA, TEGDMA, and PEGDMA
Fillers: agglomerated/nonaggregated 20-nm silica filler, nonagglomerated/nonaggregated
4- to 11-nm zirconia filler, and aggregated zirconia/silica cluster filler
|
Placed in increments of 2 mm and cured[9]
|
3M ESPE
Batch no: N162941
|
|
Filtek Bulk fill flowable (group B2)
|
Bulk fill flowable composite
|
Matrix: Bis-GMA, UDMA, Bis-EMA, and TEGDMA
Zirconia filler, ytterbium trifluoride (YbF3) has been added to increase the radiopacity.
The inorganic filler loading is ∼64.5% by weight (42.5% by volume)
|
Placed in bulks of 4 mm[9]
|
3M ESPE
Batch no: 1506500564
|
|
Beautifil-Bulk (group B1)
|
Bulk fill composite
|
Resin-based matrix: Bis-GMA; UDMA; Bis-MPEPP; TEGDMA
Filler: flouroboroaluminosilicate glass
|
Placed in bulks of 4 mm[9]
|
Shofu
Batch no: PN 2035
|
Light emitting diode (LED) light (Mectron S.p.A carasco GE, Italy) with a wavelength
between 440 and 480 nm with the narrowest peak at 460 nm and an output irradiance
greater than 1,400 mW/cm2 was used. A quartz tungsten halogen (QTH) lamp (DeepBlue Technology Co., Ltd) with
an illumination intensity of 480 mW/cm2 and output voltage of 12 V and output power 75 W was used to cure the samples for
40 seconds from the topmost surface.
The mold was positioned over a cellulose acetate strip on a glass slab. The cellulose
acetate strip resting on top of the composite prevents the formation of an oxygen
inhibition layer. A matrix strip and a glass slab with firm pressure were placed for
removal of excess material. Excess material was removed using a blade to prevent overfill.
Each sample was softly pressed out from the mold after curing and flash of the material
was detached by means of a blade. The disks were then finished and polished to attain
a smooth surface without any voids or irregularities.
After curing of the samples (n = 10), samples from each material were immersed into dissimilar media enclosed in
closed vials. Each sample was stored in 2 mL of storage medium at 37°C in an incubator.
The solutions used in the study are detailed in [Table 2].
Table 2
Solutions used in the study
|
1
|
TEGDMA (triethylene glycol dimethacrylate) standard monomer: 250 mL; Sigma Aldrich,
Germany
|
|
2
|
Ethanol (BDH-analytical grade)
|
|
3
|
Artificial saliva (MERCK) with betel quid extract 250 mL (AKUH Pharmacy); 5 mg of
split beetle nut was added in the bottle of artificial saliva; pH of artificial saliva
was 6.8
|
|
4
|
Distilled water (MERCK Millipore Ultrapure type 1 water)
|
|
5
|
Acetonitrile (MERCK)
|
The ratio between the sample and the medium volume was greater than 1:10. The disks
were entirely immersed in the medium, in line with the requirements of ISO 10993-12.[6]
Sorbitol was not used in artificial saliva as it would result in a more glutinous
solution than natural saliva.[6] Storage samples were collected after 1 day and replaced with a fresh solution. After
7 days of storage, samples were collected again for testing and analyzed for the elution
of unreacted TEGDMA. The storage medium was then refreshed again and analyzed after
30 days for elution of TEGDMA. The same protocol was followed for sample fabrication
of both experimental groups.
All the collected solutions after a specific period of storage were transferred into
HPLC vials and assessed by PerkinElmer USA, series 200 for elution of TEGDMA. The
detector used was series 200 UV/VIS. The wavelength of 205 nm was used. Samples (10
µL) were loaded using a series 200 auto-sampler and the software used for data acquisition
was TotalChrom. The separation of monomer was carried out using SPHERl-5ODS C18 column
(5 µm) 250 × 4.6 mm using a solvent system of 80% acetonitrile (analytical grade,
Merck) and 20% deionized water (Millipore) as solvents. The mobile phase was run at
a flow rate of 1 mL/min. Isocratic program was run for 10 minutes for all the samples.
The reference curve of standard TEGDMA was prepared using the monomer TEGDMA (Sigma,
Aldrich). The TEGDMA monomer concentration was calculated with the variables obtained
from linear regression analysis of the results from the calibration curve. A total
of 10 µL of solution with 1 to 5 µg of TEGDMA was injected into the HPLC system for
obtaining standard chromatogram.([Fig. 1]) The calibration curve was obtained with reference to increasing absorbance relative
to the TEGDMA concentration.
After preparation, the disks were immersed to 2 mL of respective storage solvents
in the Eppendorf tubes. Directly after polymerization, the samples were weighed using
the analytical balance and were placed in the Eppendorf tubes in 2 mL of extraction
solvent: distilled water, 70% ethanol/water solution, and artificial saliva with betel
nut extract. The specimens were then placed in the incubator at a temperature of 37°C.
After 1 day, the sample was removed from the incubator (Heraeus B6 incubator 220 V,
50 Hz, 1.4 A, 320 W) and applied to an HPLC analysis. Ten microliters of the sample
from the Eppendorf tubes was loaded to the column for evaluation of the eluted monomer
TEGDMA. After running the sample of 1 day incubation, the extraction media was refreshed
and the disks were left in the extraction media for 7 days. Similarly, after the 7-day
analysis, the media was refreshed and the samples were then kept in the incubator
at 37°C again. The last analysis was carried out after 30 days, by evaluating the
release of monomer TEGDMA in all samples through HPLC.
Results
The mean and standard deviation values of the three types of composites are described
in [Tables 3]
[4]
[5], according to the storage solutions used and the curing lights applied. The elution
of the monomer TEGDMA has been shown after immersion in ethanol, artificial saliva,
and distilled water in [Figs. 2], [3], and [4], respectively, for the three composites at different time intervals.
Fig. 1 Representative chromatogram obtained after running the standard monomer TEGDMA (3
µg) at 3.1 minutes. The y-axis represents absorbance at 205 nm in mAu and x-axis represents
time in minutes. The arrow indicates the peak of TEGDMA. Inset: Standard curve of concentration versus absorbance
of monomer TEGDMA.
Fig. 2 Representative bar diagram of effect of ethanol on (A) Filtek Z350XT, (B) Beautifil-Bulk Shofu, and (C) Filtek Bulk fill flowable 3M ESPE treated with light emitting diode (LED) or quartz
tungsten halogen (QTH).
Fig. 3 Representative bar diagram of effect of betel quid in artificial saliva on (A) Filtek Z350XT, (B) Beautifil-Bulk Shofu, and (C) Filtek Bulk fill flowable 3M ESPE treated with light emitting diode (LED) or quartz
tungsten halogen (QTH).
Fig. 4 Representative bar diagram of effect of distilled water on (A) Filtek Z350XT, (B) Beautifil-Bulk Shofu, and (C) Filtek Bulk fill flowable 3M ESPE treated with light emitting diode (LED) or quartz
tungsten halogen (QTH).
Table 3
Mean value and standard deviation (± SD) of the concentrations (µg/mL) of TEGDMA released
from Filtek Z350XT 3M ESPE
|
Ethanol
|
Artificial saliva + betel quid extract
|
Distilled water
|
|
Time
|
1 d
|
7 d
|
30 d
|
1 d
|
7 d
|
30 d
|
1 d
|
7 d
|
30 d
|
|
LED cured
|
27.6 ± 6.6
|
200.5 ± 49.6
|
59.3 ± 4.1
|
52.7 ± 17.9
|
47.1 ± 8.1
|
37.6 ± 4.6
|
36.4 ± 5.2
|
20.1 ± 6.8
|
16.1 ± 2.4
|
|
QTH cured
|
462.6 ± 135
|
792.5 ± 76
|
666.2 ± 146.1
|
138 ± 51
|
98.2 ± 18.5
|
44.8 ± 8.3
|
235.8 ± 3.8
|
143.5 ± 32.3
|
47.1 ± 17.8
|
Abbreviations: LED, light emitting diode; QTH, quartz tungsten halogen; TEGDMA, triethylene
glycol dimethacrylate.
Table 4
Mean value and standard deviation (± SD) of the concentrations (µg/mL) TEGDMA released
of Beautifil-Bulk Shofu
|
Ethanol
|
Artificial saliva+ betel quid extract
|
Distilled water
|
|
Time
|
1 d
|
7 d
|
30 d
|
1 d
|
7 d
|
30 d
|
1 d
|
7 d
|
30 d
|
|
LED cured
|
34.0 ± 24.4
|
27.3 ± 4.5
|
88.2 ± 11.8
|
98.4 ± 3.1
|
39.1 ± 8.3
|
56.64 ± 10.2
|
17.0 ± 3.4
|
13.8 ± 3.9
|
29.9 ± 4.8
|
|
QTH cured
|
22.3 ± 3.6
|
27.1 ± 14.9
|
198.12 ± 79.8
|
46.8 ± 2.7
|
100.8 ± 7.9
|
62.21 ± 7.4
|
12.1 ± 1.5
|
17.1 ± 5.6
|
43.89 ± 5.2
|
Abbreviations: LED, light emitting diode; QTH, quartz tungsten halogen; TEGDMA, triethylene
glycol dimethacrylate.
Table 5
Mean value and standard deviation (± SD) of the concentrations (µg/mL) TEGDMA released
of Filtek Bulk fill flowable 3M ESPE
|
Ethanol
|
Artificial saliva + betel quid extract
|
Distilled water
|
|
Time
|
1 d
|
7 d
|
30 d
|
1 d
|
7 d
|
30 d
|
1 d
|
7 d
|
30 d
|
|
LED cured
|
24.0 ± 3.5
|
15.7 ± 2.9
|
32.12 ± 5.8
|
49.7 ± 5.4
|
39.2 ± 2.0
|
1,306.30 ± 65.0
|
22.4 ± 2.3
|
11.8 ± 3.3
|
40.57 ± 6.6
|
|
QTH cured
|
25.8 ± 3.4
|
30.7 ± 5.2
|
68.36 ± 6.3
|
43.7 ± 4.1
|
53.5 ± 5.7
|
1,428.62 ± 57.9
|
15.6 ± 2.6
|
27.6 ± 4.5
|
44.32 ± 10.2
|
Abbreviations: LED, light emitting diode; QTH, quartz tungsten halogen; TEGDMA, triethylene
glycol dimethacrylate.
In the control group, Filtek Z350XT 3M ESPE, the highest elution was observed in the
disks cured with the QTH lamp with the highest value observed in ethanol (666.2 ug/ml ± 146.1)
after 30 days of immersion. For Beautifil-Bulk Shofu, the highest value measured was
of the disks cured with QTH lamp immersed in ethanol after 30 days of storage (198.12 ± 79.8).
In case of Filtek Bulk fill flowable 3M ESPE, the release of TEGDMA was highest in
artificial saliva after 30 days of storage (1,428 ± 57.9) after curing with the QTH
lamp.
Two-way mixed analysis of variance (ANOVA) was conducted to access the difference
in concentration of storage material over time with respect to curing light and storage
material in the control group. There is a significant effect of time on concentration
values (p < 0.001). There are no statistically different values observed with respect to curing
lights in the control group. The storage chemicals have a statistically significant
effect (p < 0.001), where ethanol shows highest concentrations. In case of Beautifil-Bulk Shofu,
the effect of time on concentration is significant (p < 0.001). The effect of curing light and storage material is statistically significant
(p < 0.001). In Filtek Bulk fill flowable 3M ESPE, the effect of time on concentration
is significant (p < 0.001). The effect of curing light and storage material is also statistically significant
(p < 0.001).
When the post hoc test was applied on the data, for a comparison of groups, there
was a statistically significant difference (p < 0.01) in the mean concentrations of Filtek Z350XT 3M ESPE and Beautifil-Bulk Shofu.
On the other hand, the difference in mean concentrations of Filtek Z350XT 3M ESPE
and Filtek Bulk fill flowable 3M ESPE was found to be nonsignificant. While comparing
the two experimental groups, there was a significant difference (p < 0.01) in the mean concentrations. This shows that there is considerable difference
in the properties of the two experimental groups.
Discussion
Different studies have been conducted to check the elution of monomers by immersing
them into different storage solutions.[6]
[15]
[16]
[17] The results from the current studies concluded that the elution of the monomer TEGDMA
depends upon the storage media used and irradiance lamp used for curing of the resin-based
composites. Furthermore, this study limits itself to the effect of artificial saliva,
distilled water, and ethanol, and did not use an acidic environment that is created
by the cariogenic bacteria on the tooth surface.
HPLC was used to evaluate the release of the monomer TEGDMA from one conventional
and two bulk-fill resin-based composites. The disks were immersed for 1, 7, and 30
days and TEGDMA was found in all the solvents when evaluated using HPLC. This is in
agreement with other studies, which found TEGDMA to be the major monomer eluted from
different composites.[2]
[6]
[18]
[19]
Tsitrou et al[15] discovered that low-molecular-weight monomers could be extracted in considerably
higher quantities than high-molecular-weight monomers. Low-molecular-weight monomers
such as TEGDMA have higher mobility and will be eluted faster than large molecules
like Bis-GMA and UDMA.[18]
Durner et al reported that the elution of TEGDMA was high due to its hydrophilic nature
and its low molecular weight, which tends to increase its mobility and thus make the
elution easier.[20] In the present study, TEGDMA was found to be eluted after 24 hours and 7 days. But
the long-term immersion also showed considerable amounts of eluted TEGDMA.[12]
The DC for dental composites is approximately between 35 and 77%. Asmussen and Peutzfeldt[21] reported that a linear polymer structure with a fewer cross-links is significantly
more prone to softening in ethanol. Thus, incomplete polymerization may increase residual
monomer.[1] Maximum elution, that is, 85 to 100% of monomers, was reported to occur within 24 hours
by Ferracane[2] and within 7 days by Örtengren et al.[22]
[23] Hence, the elution of monomers after polymerization was tested at the end of 24 hours
and 7 days in the present study. For long-term release of the monomer TEGDMA, Alshali
et al[6] stated that the elution of monomers Bis-GMA and UDMA usually gets completed after
3 months, whereas monomer TEGDMA elution nearly gets completed after 1 month. An important
factor to be considered in the residual monomer is the molecular weight and the size
of the monomer. TEGDMA, being a smaller molecule, tends to release more and quickly
as compared to large monomers including Bis-GMA.[23]
In the present study, the elution of TEGDMA has been evaluated after a 1-month immersion
and all the three types of composites showed considerable amounts of monomer elusion.
Both LED and QTH lights are used for curing the resin-based composites. The samples
cured with the QTH lamp have shown increased elution of TEGDMA when compared with
the samples cured with LED light. Clinically, the most common strategy to maximize
DC and minimize monomer elution is to provide sufficient energy to the system by increasing
curing time. Several works focusing on commercially available composites have emphasized
the need to apply at least 20 seconds, but more likely 40 seconds, of irradiation
to minimize the amount of eluted substances, even with the use of high-irradiance
LED lights.[3]
[24] As stated by Polydorou et al,[25] 40 seconds of polymerization time with a halogen lamp is indicated by the manufacturers
to achieve adequate polymerization of 2-mm incremental thickness of composite. But
the findings of this study revealed that curing time has no significant effect on
TEGDMA elution. The polymerization time was kept to 40 seconds in our study and monomer
elution has been observed in all storage solutions. According to Polydorou et al,[26] for the elution of TEGDMA, no difference was found between the 20-, 40-, and 80-second
polymerization for all three different storage periods tested. Therefore, it can be
concluded that the 40-second polymerization that is usually used as a polymerization
time, which is thought to have satisfying results in the mechanical properties of
the composite resins, compared to the 20-second polymerization time, does not seem
to be more effective on the release of monomers.
We can distinguish two groups of solvents: water or aqueous mixtures, such as cell
culture media artificial saliva and human saliva, and different organic extraction
media, such as ethanol, methanol, acetone, acetonitrile, tetrahydrofuran, and chloroform.[13] The type of extraction medium used impacts both the concentration of the eluted
monomer and the elution time. In general, the degree of monomer elution is proportional
to the hydrophobicity and swelling capacity of the organic solvent used. In our study,
we have used 70% ethanol/water solution, artificial saliva with betel nut extract,
and distilled water. However, according to the International Organization for Standardization
(ISO) specification, distilled water is an extraction medium for resin-based filling
materials, which simulates a humid, intraoral environment containing both saliva and
water.[27] The U.S. Food and Drug Administration (FDA) has graded a 75% ethanol–water solution
as clinical oral stimulating liquid and it has been used in several studies.[28] In our study, we incorporated a 70% ethanol–water solution as one of our storage
solutions and the elution of TEGDMA was high in ethanol as compared to other solutions.
It can further be justified by the fact that ethanol has the ability to penetrate
within the unreacted monomer and widens the gap within the polymer chains, allowing
the soluble compounds to elute. It can mimic and accelerate the typical degradation
as expected clinically from the food and saliva through continuous exposure.[29] The amount of TEGDMA monomer released according to different authors was 0.005 to
2.424 µg/mL.[12]
[30]
[31]
Several studies have been conducted to check the cytotoxic and genotoxic effects of
these leachable materials from the dental biomaterials. These effects then cause adverse
biological reactions including local and systemic cytotoxicity, and pulpal and allergic
reactions.[32] Studies reporting the leaching of uncured monomers from dental adhesive system through
dentin into the dentinal fluid are scarce. Dentinal fluid is an important component
of the pulp–dentin complex, which is a communication between pulp and other areas
of dentin. In healthy conditions, the composition of dentinal fluid is controlled
by the odontoblasts. However, after stresses such as caries or trauma, the fluid composition
is closer to plasma.[32]
Inflammation then leads to increased capillary permeability and localized vasodilatation
allowing leakage of plasma proteins from the blood flow to dentinal fluid. This transudates
from the exposed dentin and contains proteinlike fibrinogen, immunoglobulin G (IgG),
and albumin.[33] Albumin is a multifunctional, low-molecular-weight taxi protein that has the ability
to bind and transport almost any small molecule. According to Mahdhaoui et al, it
can be stated that albumin can transport unbound monomers released from dental adhesives
through the dentin barrier.[32] It is believed that basic monomers such as Bis-GMA and TEGDMA comonomer have got
a toxic potential. TEGDMA, apart from the modified basic monomers UDMA and bis-EMA,
is the main comonomer of the SDR composite resin. TEGDMA is one of the most frequently
used diluents in the composite materials. Its low molecular mass and the presence
of ethylene oxide groups make this monomer reactive, mobile, and relatively easy to
elute from the composite material matrix.[13] However, the incorporation of nanoparticles and combination of Bis-GMA have been
reported to enhance mechanical as well as biological properties.[34]
[35] Other materials like halloysite nanotubes have also been shown to provide similar
enhancement and antibacterial properties.[36]
[37]
The unreacted TEGDMA is a toxic substance exhibiting cytotoxic, genotoxic, mutagenic,
and allergenic effects. Directly capping the pulp with the use of composite resins
does not lead to dentine bridge formation and may be one of the reasons for the development
of inflammatory reactions in dental pulp cells, their apoptosis, as well as dental
pulp inflammation and necrosis.[38]
[39]
[40] The effective dose (ED50) for TEGDMA, assessed in human dental pulp fibroblasts
cultures, is about 0.08 mg/mL. Therefore, similar or higher monomer concentrations,
without sufficient protection of the bottom of cavity, may lead to dental pulp injuries.
Unreacted TEGDMA monomer may also be a substrate for microorganisms colonizing the
marginal gap. It promotes the proliferation of cariogenic microorganisms.[13]
There are no unequivocal literature data on the time period necessary for total elution
of unreacted TEGDMA monomer from composite material. According to some studies, the
elution process ends after 1 to 7 days, while other authors state that it is longer,
for example, 30 days.[25]
[41]
[42] In the present study, elution of the monomer TEGDMA was the highest after immersion
for 24 hours in a 70% ethanol/water solution, artificial saliva, betel nut extract,
and distilled water. It has been reported previously that the release of TEGDMA from
the composite may stimulate the growth of cariogenic bacteria and could lead toward
secondary caries,[43] a reason not to include the acidic solution for monitoring the elution pattern of
the monomer TEGDMA in this study as mentioned earlier. Ferracane[2] report that 50% of monomers are eluted from material during the first 3 hours after
polymerization and 85 to 100% of monomers are eluted within 24 hours.[44] More recent studies using HPLC have shown that monomer elution continued beyond
24 hours for resin-based composites.[26]
[45] However, despite further potential monomer elution, the majority of soluble substances
are extracted from the material within hours.
Conclusion
Within the limitations of the study, it has been concluded that Filtek Bulk fill flowable
3M ESPE showed a lower release of the TEGDMA monomer into the storage media. The material
cured by the QTH lamp results in increased release of monomer. The distilled water
has been the most stable storage media in which the cured samples were immersed to
check the monomer release.
Recommendations
The use of LED light to cure composite when used in the clinical setup should be preferred
over the QTH lamps. Filtek Bulk fill flowable 3M ESPE is advisable to be used within
the clinical setup as it releases less monomer with the passage of time. There had
been tremendous release of the TEGDMA monomer in artificial saliva with betel quid
when Filtek Bulk fill flowable 3M ESPE was immersed for 1 month, so more studies can
be conducted on this in future.
Limitations
-
Only one type of monomer, TEGDMA, was used to study the elution, due to the lack of
availability of other monomer standards and toxicity, for instance Bis-GMA.
-
The study did not perform any techniques to check the DC of a monomer into a polymer,
for example, the Raman spectroscopy.
