Next Article in Journal
Polyvinyl Alcohol/Polyaniline/Carboxylated Graphene Oxide Nanocomposites for Coating Protection of Cast Iron in Simulated Seawater
Next Article in Special Issue
Development of a Highly Efficient Environmentally Friendly Plasticizer
Previous Article in Journal
Advanced Machine Learning Modeling Approach for Prediction of Compressive Strength of FRP Confined Concrete Using Multiphysics Genetic Expression Programming
Previous Article in Special Issue
Impact of Bis-O-dihydroferuloyl-1,4-butanediol Content on the Chemical, Enzymatic and Fungal Degradation Processes of Poly(3-hydroxybutyrate)
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Polymers
Volume 14
Issue 9
10.3390/polym14091790
polymers-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Monomer Release from Dental Resins: The Current Status on Study Setup, Detection and Quantification for In Vitro Testing

by
Tristan Hampe
1,*,
Andreas Wiessner
1,
Holm Frauendorf
2,
Mohammad Alhussein
3,
Petr Karlovsky
3,
Ralf Bürgers
1 and
Sebastian Krohn
1
1
Department of Prosthodontics, University Medical Center Göttingen, 37075 Göttingen, Germany
2
Institute for Organic and Biomolecular Chemistry, University of Göttingen, 37077 Göttingen, Germany
3
Molecular Phytopathology and Mycotoxin Research, University of Göttingen, 37077 Göttingen, Germany
*
Author to whom correspondence should be addressed.
Polymers 2022, 14(9), 1790; https://doi.org/10.3390/polym14091790
Submission received: 6 April 2022 / Revised: 23 April 2022 / Accepted: 25 April 2022 / Published: 27 April 2022
(This article belongs to the Special Issue Advances in Biocompatible and Biodegradable Polymers)
Browse Figures
Versions Notes

Abstract

:
Improvements in mechanical properties and a shift of focus towards esthetic dentistry led to the application of dental resins in various areas of dentistry. However, dental resins are not inert in the oral environment and may release monomers and other substances such as Bisphenol-A (BPA) due to incomplete polymerization and intraoral degradation. Current research shows that various monomers present cytotoxic, genotoxic, proinflammatory, and even mutagenic effects. Of these eluting substances, the elution of BPA in the oral environment is of particular interest due to its role as an endocrine disruptor. For this reason, the release of residual monomers and especially BPA from dental resins has been a cause for public concern. The assessment of patient exposure and potential health risks of dental monomers require a reliable experimental and analytical setup. However, the heterogeneous study design applied in current research hinders biocompatibility testing by impeding comparative analysis of different studies and transfer to the clinical situation. Therefore, this review aims to provide information on each step of a robust experimental and analytical in vitro setup that allows the collection of clinically relevant data and future meta-analytical evaluations.

1. Introduction

Direct dental restorations of posterior teeth have been carried out with various materials, such as dental amalgam or composite resin [1]. Despite the successful application due to the high functional durability of dental amalgam for more than 150 years with a small number of reports on adverse effects [2,3], amalgam is being phased out due to the rise of safety concerns and the restriction of amalgam in some regions of the world [4,5,6]. Improvements in mechanical properties and a shift of focus towards esthetic dentistry led to the application of dental resins in various areas of dentistry [7,8], e.g., as restorative composites, bonding agents, resin-based cements, fissure, and root canal sealers as well as temporary crowns and bridges [9,10,11,12]. The specific monomer composition of dental resins is tailored to the particular area of application [13] and generally consists of one or more monomers, mostly bisphenol A diglycidyl methacrylate (Bis-GMA) and/or urethane dimethacrylate (UDMA) in addition to co-monomers, which are predominantly triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxylethyl methacrylate (HEMA) [14]. Typical Bis-GMA/TEGDMA mixtures have a ratio between 60 and 80 wt.% Bis-GMA and 20 and 40 wt.% TEGDMA [15,16,17]. In combination with UDMA, less TEGDMA is required and most ratios between UDMA and Bis-GMA are possible, even complete replacement [15,17].
Bis-GMA is either the reaction product of bisphenol A (BPA) and glycidyl methacrylate or methacrylic acid and diglycidyl ether of bisphenol A (BADGE or DGEBA) [18]. Due to its low shrinkage, good mechanical properties, and excellent adhesion to enamel [19], Bis-GMA is the base monomer of most dental resins [20]. The central core of Bis-GMA is formed by a phenyl ring and two pendant hydroxyl groups, which are responsible for its extremely high viscosity and low mobility [21].
UDMA is the reaction product of 2-hydroxyethyl methacrylate and 2, 4, 4- trimethyl-hexamethylenediisocyanate and was developed by Foster and Walter in 1974 [22]. Instead of a phenol ring UDMA has an aliphatic urethane chain, which leads to higher flexibility and lower viscosity and results in higher mobility and a greater degree of conversion [23,24]. Due to these advantageous properties and health concerns regarding the release of bisphenol A (BPA) and its derivatives, more and more manufacturers substitute Bis-GMA with UDMA and introduced BPA-free composites to avoid the release of BPA and its derivatives [25,26,27].
Bis-GMA and UDMA are combined with a low-viscosity monomer such as TEGDMA, which improves the degree of conversion, filler loadings, and clinical handling [28]. TEGDMA is the reaction product of two molecules of methacrylic acid and triethylene glycol [18]. Its weaker polar hydrogen bonds lead to greater flexibility and its small size and its high number of double bonds increase conversion [29,30]. TEGDMA is only used as a co-monomer because its hydrophilicity amplifies undesirable properties like water sorption and polymerization shrinkage [31].
HEMA is a common co-monomer in dental adhesives and is characterized by its small dimensions and polar properties [28]. The major advantage of HEMA, especially in dental adhesives, is its ability to improve the miscibility between hydrophilic and hydrophobic monomers and thus dentine adhesion [32].
However, as of today, studies on the short-term release of compounds from the polymer network of composite resins are poorly comparable, studies on the long-term release are still rare, and degradation products are often not measured [33,34,35,36]. Due to its role as an endocrine disrupter of different metabolic pathways even in low concentrations [37], the release of bisphenol A (BPA) is of great interest in recent literature [38]. BPA interacts with the estrogen receptor and mimics the behavior of the natural hormone estradiol [39,40,41]. Furthermore, it is known that BPA exhibits potential cancerogenic, embryotoxic, and metabolic effects [40,42,43]. However, pure BPA is not being used as a monomer in dentistry, but rather as a reagent for the synthesis of derivates like Bis-GMA, and thus only small amounts are leachable due to possible contaminations from the use of BPA derivatives [38,44]. Even though BPA is at the center of current research, cytotoxic, genotoxic, proinflammatory, and even mutagenic effects have been shown for various compounds used in dental resins [45,46,47,48,49,50,51,52]. Considering the advancements and changes in the composition of resin composites [53], monomers, as well as further compounds, e.g., additives eluting from dental resins, should be investigated. The biocompatibility of dental materials may be evaluated by using various in vivo or in vitro techniques [54] and the collection of reliable data depends on the application of adequate detection and quantification methods [55]. As a result of varying clinical situations occurring in vivo, these studies show a large spread width of released monomer concentrations [56,57,58,59]. Therefore, it has been established in biocompatibility testing to verify the results of standardized in vitro studies by in vivo trials [60]. The general setup of in vitro studies on the leachability of monomers from dental resins consists of an experimental part to produce an eluate by incubating resin samples in an extraction medium, and an analytical part to identify and quantify monomers within the eluate. However, as of today, comparative analysis of current in vitro studies is limited due to heterogeneous sample design as well as the diverse application of analytical methods with various extraction media and not standardized observation periods [34]. However, without a systematic meta-analysis, the impact of monomer release from dental resins on patient health remains unclear. The present review aims to provide information on each step of the experimental and analytical setup regarding the in vitro identification and quantification of eluting compounds from dental resins to develop a basis for future meta-analytical evaluations.

2. Sample Design

In current literature, samples are commonly disc-shaped and of various sizes, while the removal of the oxygen inhibition layer is either not performed or not mentioned [17,61,62,63,64,65]. However, the surface area and the oxygen inhibition layer influence the amount of eluting monomers heavily, and therefore sample design is a limiting factor in current research. ISO 4049 specifies the requirements for dental polymer-based restorative materials, and many authors recommend complying with ISO 10993-12 for the sample design [62,66,67,68,69]. ISO 10993-12 regulates sample preparation and reference materials for the biological evaluation of medical devices and recommends regular-shaped samples with a defined surface area [70]. Additionally, ISO 10993-12 specifies in dependency of the surface area the corresponding solvent volume and as a consequence the extraction ratio (Table 1) [70]. To our knowledge, there are no studies on the effects of different extraction ratios on the release of specific monomers, but it is known that the extraction ratio affects the amount of released monomers from the polymer matrix strongly [34,71,72]. The lack of studies with a uniform extraction ratio hinders meta-analytical analysis and limits the comparison to common restoration sizes [34]. Therefore, future studies should comply with ISO 10993-12.
Besides the extraction ratio, the oxygen inhibition layer needs to be considered when evaluating the release of monomers from the polymer network. The oxygen inhibition layer contains unpolymerized monomers [73,74], which can be eluted, and especially TEGDMA concentrations seem to be elevated [71]. Therefore, the removal of the oxygen inhibition layer leads to fewer eluted monomers as well as reduced cytotoxicity, and thus the removal of the oxygen inhibition layer or prevention of its formation is recommended in clinical practice [75,76]. However, in many studies on the leachability from dental resins, the oxygen inhibition layer was either not or ineffectively removed [61,62,63,64,65]. Recent literature shows that water-spray or ethanol treatments are ineffective methods to remove the oxygen inhibition layer [77]. For research purposes, nitrogen [78,79,80], argon [81,82], or carbon dioxide [83] atmospheres have been used to produce samples without an oxygen inhibition layer. Even though these methods are effective, they are costly and not applicable in clinical practice. Effective methods that are applicable in vitro and in vivo include methods that prevent oxygen contact, e.g., glycerin gel or mylar strips, and mechanical methods, e.g., specimen polishing with a defined removal of 0.2 mm [84,85,86]. Recent studies show that these methods are well suited for the in vitro investigation of the release of monomers from dental resins [35,66,87,88,89]. Consequently, the removal or prevention of the oxygen inhibition layer should be included in the sample preparation process and based on the clinical workflow. Besides the oxygen inhibition layer, the surface roughness may influence monomer and BPA elution, but to our knowledge, there are no studies on the effect of surface roughness on the monomer release. Therefore, we recommend polishing procedures corresponding to the standard clinical workflow.

3. Selection of the Extraction Medium

Various solvents, such as water, ethanol-water mixtures, methanol, acetonitrile, tetrahydrofuran, cell culture media, artificial saliva, and collected saliva, have been used as extraction media in studies investigating the in vitro release of monomers from the polymer matrix [9,17,61,64,90,91,92,93]. However, interactions with the extraction medium due to substance-specific properties, such as molecular size and other chemical characteristics, significantly alter elution [94]. Literature assumes that in vivo conditions are somewhere between the less aggressive water solvent and the more potent ethanol solvent [65]. Hence, the US Food and Drug Administration (FDA) recommends a 75 vol. % ethanol/water solution which is supposed to be a good food simulator (alcoholic beverages, fruits, and syrup) and therefore clinically relevant [9]. Due to this recommendation, many studies investigating the leachability of monomers from dental resins used a 75% vol. ethanol/water solution [9,33,95,96,97,98]. However, the solubility parameter of ethanol and Bis-GMA is almost equal, which leads to the softening of resins, with maximum softening reached at 75% vol. ethanol/water [99,100,101]. Ethanol/water solutions penetrate the polymer matrix, especially of Bis-GMA-based resins, and degenerate it irreversibly by expanding the space around the polymers and creating soluble units [94,101]. Considering these findings, it is questionable whether using a 75 vol. % ethanol/water solution results in clinically relevant data [71]. Supporting this hypothesis, many studies found significantly elevated Bis-GMA, TEGDMA, and UDMA levels in 75% vol. ethanol/water solutions compared to artificial saliva [36,72,102,103]. BPA was only detected in samples immersed in a 75% vol. ethanol/water solution [72,102,103]. In addition to elevated monomer concentrations, monomer elution is prolonged in 75 vol. % ethanol/water solutions [35]. Considering these findings, 75 vol. % ethanol/water solutions cannot be recommended to simulate the intraoral environment for the investigation of the leachability of dental monomers. Similarly, immersion in methanol leads to an increased monomer release compared to water or artificial saliva and should be therefore also avoided [92]. Besides alcohol-based solutions, cell culture media were used as extraction solvents, but it was shown that they may lead to false-negative results especially regarding TEGDMA detection due to the binding of albumin to it [17]. Instead, water, artificial saliva, or human saliva should be favored as extraction media. Literature shows similar concentrations of released compounds when comparing distilled water to artificial saliva [17,103,104]. In aqueous environments, mainly hydrophilic molecules of small sizes, such as TEGDMA, elute, while long-chain hydrophobic molecules, such as BisGMA, are hardly released [105,106]. Comparing the eluates from samples incubated in distilled water, artificial saliva, and collected salvia, the latter contains lower monomer levels, as proteins contained in collected salvia bind eluting monomers [104]. When using collected human saliva, the probands must not have restorations [107] and blank samples for the analytical procedure are needed to avoid false positives [91]. In conclusion, the most comparable results can be achieved with collected saliva, but blank samples and a robust analytical procedure are required. Moreover, water and artificial saliva are an option, but in contrast to former assumptions, they may even present slightly increased concentrations of eluted monomers. Further studies on the impact of the composition of human saliva on the elution from dental resins and the effect of protein-bound monomers on the metabolism are necessary.

4. Incubation Parameters

The amount of eluted compounds highly depends on incubation parameters, such as the incubation time, buffering systems, solvent, monomer saturation, and pH value [71,108,109,110]. Under extreme temperature (100 °C) and an alkaline (pH 13) or acid (pH 1) environment, BPA is released due to hydrolytic degradation of Bis-GMA or bisphenol A diglycidylether (BADGE) [111]. Particularly very alkaline conditions seem to promote BPA elution [25]. A long-term study on the leakage of composite resins found that the effect of pH varied among monomers: more BPA was eluted at pH 8 than at pH 4 and 6, while the elution of TEGDMA followed the opposite trend [112]. Considering these findings, future studies on the elution from dental resins should report incubation parameters, especially the pH and temperature of incubation, whereas incubation at 37 °C is recommended to simulate in vivo conditions [34].
In some studies, samples are incubated after a post-irradiation cure, usually 24 h in the dark [61,113,114,115]. Incubation after the post-irradiation cure leads to lower concentrations of released substances [105]. Since direct incubation corresponds to the clinical workflow, it is recommended [114,116].
Studies on the long-term release from dental resins need to take salivation of the oral environment into account and must refresh the extraction medium to avoid saturation, which might lead to the underrepresentation of in vivo conditions [97,117]. This solvent refresh is usually performed once per week [33,35,94]. Furthermore, the stability of dental monomers in water, artificial salvia, or collected saliva must be considered, especially in long-term studies. Presumably, passive hydrolysis reactions lead to the degradation of monomers in water [118]. As a consequence, many studies showed decreasing monomer concentrations when successive incubation periods were analyzed [17,61,103,119,120]. This was not observed or observed to a lesser extent in other extraction media, such as ethanol/water mixtures or lactic acid [103,119]. Passive and/or enzyme-catalyzed hydrolysis, such as in collected saliva, cleaves the ester bonds of the methacrylate groups of BisGMA, TEGDMA, and UDMA [52,121,122,123]. Initial decreases in concentrations were observed after only six hours of incubation [103]. Due to the incomplete hydrolysis of dental monomers, molecules with different numbers of cleaved methacrylate groups may be present simultaneously [122,124]. These hydrolysis products each have different chemical properties as well as molecular masses, and thus detection requires adjustments to the analytical method [124,125]. In conclusion, the analysis of long incubation intervals could lead to the underrepresentation of the in vivo monomer release. Therefore, degradation products should be measured additionally [124,126,127]. Regular refreshment of the extraction medium and the cumulative determination of monomer concentrations are recommended. Cumulative analysis has already been performed in several studies [35,102,128].
In summary, the objective of in vitro incubation is the simulation of in vivo conditions. Therefore, incubation parameters should be based on the intraoral environment, the extraction medium should be refreshed regularly, and samples should be incubated directly. For future meta-analytical evaluation and comparability between studies, a 24-h incubation period should be included in every study on the elution from dental resins [34].

5. Analytical Setup

A wide range of techniques has been used to detect and quantify substances eluting from dental resins [118]. Many older methods such as infrared spectroscopy are nowadays regarded as outdated since the signals are not molecule-specific, the interpretation of spectra is difficult, and quantification unreliable [34]. Nowadays, the analytical setup consists of the separation of the eluate by chromatography followed by subsequent detection of the eluted compounds by optical methods or mass spectrometry. The FDA and recent literature recommend high-performance liquid chromatography (HPLC) and gas chromatography (GC) as separation methods [34,66,129]. Despite the recommendation of GC [66,129] and its application in various studies [107,109,112,130], recent literature showed that the high operating temperatures of GC lead to the overestimation of the leakage of BPA due to thermal degradation of Bis-GMA [64]. Bannach et al. [131] investigated the thermal stability of Bis-GMA, ethoxylated bisphenol A dimethacrylate (Bis-EMA), UDMA, and TEGDMA and found that thermal decomposition starts between 178 and 297 °C, which corresponds to the temperatures between 280 and 400 °C occurring during GC [109,130]. Consequently, GC is not capable of detecting Bis-GMA, Bis-EMA, or UDMA, but only corresponding thermal degradation products [56,132,133,134]. Due to the thermal degradation of BPA derivatives, BPA was found by GC in all samples regardless of the solvent, but HPLC-MS detected BPA only in samples immersed in methanol [64]. HEMA is a potential degradation product of UDMA, and therefore detection and differentiation between them are hindered [109]. Additionally, GC analysis of analytes from aqueous samples requires time-consuming sample preparation [135]. In conclusion, GC should be avoided for the separation of monomers with a high molecular weight in eluates from dental resins due to their thermal instability [136]. Instead, HPLC is the recommended separation method for the analysis of eluting monomers from dental resins. However, GC can be applied for low molecular weight, volatile, and thermally stable substances, e.g., additives contained in dental resins [133,136], as it allows accurate quantitative determination within complex mixtures, including trace amounts of compounds down to parts per trillion in some cases [137].
Most light absorption spectroscopy (UV/Vis) and mass spectrometry (MS) detectors coupled with HPLC are suitable for the identification and quantification of compounds in the eluate [138]. UV/Vis detectors are available in many analytical laboratories due to their easy use, low cost, and near-universal field of application [138]. It is known from other scientific fields that the sole use of UV/Vis can lead to the overestimation of analyte concentrations due to the presence of coeluting substances [139,140,141]. Hope et al. found that the wrong identification of a coeluting substance, probably a photoinitiator, in eluates from an experimental dental resin led to the overestimation of BPA levels by 30-fold when comparing UV/Vis to MS detection [66]. This discrepancy between UV/Vis and MS detection was also found in a recent study on the monomer elution from temporary crown and bridge materials [120]. Therefore, the sole identification and quantification by UV/Vis are not recommended and more sensitive and specific methods like MS should be used. MS is a very sensitive and selective method for the detection of unknown substances and degradation products in eluates from cured as well as uncured resins [67]. In this context, electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI) are available for the ionization of nonvolatile and thermally unstable analytes [142]. Advanced MS detectors coupled with HPLC (HPLC-MS) allow tandem mass spectrometric analysis (HPLC-MS/MS), which increases the specificity of the analysis by the fragmentation of a pre-selected ion and specific detection of selected fragmentation products [143]. In recent years, high-resolution mass spectrometry (HRMS) following HPLC separation has proven to be a viable alternative due to high mass accuracy and sensitivity even in full-scan mode [144]. Even more information about the molecular structure can be obtained by the combination of HRMS and MS fragmentation [145]. Accordingly, HPLC coupled with MS, preferably HRMS and/or tandem MS, is the recommended analytical method for the analysis of monomers eluting from dental resins.

6. Detection/Qualitative Analysis

An essential part of a reliable study design for the detection of monomers is a clear definition of the analyte and the estimation of the limit of detection (LOD), which should be as low as technically achievable. In a typical HPLC-MS analysis with electrospray ionization, the retention time together with the mass of the molecular ion and in tandem MS as well as the fragmentation spectrum of the molecular ion are used to identify the analyte (Figure 1 and Figure 2).
The fragmentation spectrum of a tandem MS analysis contains fragmentation ions, each of which has a separate peak in the mass spectrum [146]. The most abundant, unique fragmentation ion of an analyte is used for quantification (quantifier ion), and less abundant, unique ions are used for detection (qualifier ions) [147,148,149]. By analyzing more than one qualifier ion, confidence in detection can be increased [150]. For the analysis of unknown compounds, mass spectrometry allows the use of libraries with mass spectra collected from literature, like the NIST mass spectral library (National Institute of Science and Technology, Gaithersburg, MD, USA), which contains among other substances dental compounds [56,151,152]. Commercially available and open-source libraries help to identify unknown substances [153]. However, these libraries mostly contain spectra from GC-MS obtained after ionization with “hard” ionization techniques [154]. Due to the lower reproducibility of retention properties in HPLC instruments, the availability of libraries with spectra obtained by HPLC-MS with soft ionization techniques is limited [154,155,156]. Therefore, older studies on the release of dental monomers using libraries, e.g., the NIST applied GC-MS analysis [56,151,152]. However, the identification of an unknown compound should not solely rely on the comparison between a library and an experimental mass spectrum because co-eluting compounds may compromise the fragmentation spectra of the analyte, and library spectra do not reflect experimental conditions [144]. Therefore, the regulation 2002/657/EC issued by the European Union recommends the use of calibration solutions and an internal standard to validate the qualitative analysis [157]. For a clear definition of the reference substances, it is best practice to report their molecular masses and unique Chemical Abstract Service Registry Numbers (CAS Registry Number). This is especially important in dental research, as recent research shows that the trivial name UDMA is used for a variety of molecules, and Bis-EMA is used for molecules of different degrees of ethoxylation [55,130].
Furthermore, the LOD is essential for the assessment of the reliability of detection because compounds present at concentrations below the LOD cannot be detected though may be released and have a toxicological impact [158]. According to the International Union of the Pure and Applied Chemistry (IUPAC), LOD is defined as the lowest reliably detectable concentration of an analyte [159]. Various methods for determining the LOD can be found in the literature. The most common approach is the calculation based on the signal-to-noise ratio, but an experimental determination by a dilution series is also possible [160]. If the analyte is available, the Joint Research Centre of the European Commission recommends using 3.9 times the quotient of the standard deviation of the blank (pseudo-blank) signals and the slope of the calibration curve for the determination of a reliable LOD [161]. Therefore, LOD can be improved either by the reduction of noise or by the increase of signal strength [162]. Common ways to reduce noise are sample clean-up, temperature control of the column, and purity of the reagents and solvents [162]. Consequently, lower LODs are achievable with HPLC grade extraction media than with other media such as collected saliva. The signal strength can be increased by the injection of larger quantities of the sample, a more sensitive detector, and the choice of the mobile phase and column to change peak width [162]. Another way to improve the LOD might be derivatization. Recently, it was shown that the derivatization of BPA in composite eluates allows mass spectrometric detection in the more sensitive positive ESI mode and therefore leads to lower LODs [120,163].
As most studies on the leachability from dental resins do not report the LOD, only the positive and not the negative results can be interpreted [34]. The LODs in the current literature for Bis-GMA range from 0.07 µg/mL to 1.18 μg/mL [86,89,164,165] and for BPA from 0.003 µg/mL to 0.075 µg/mL [66,165,166]. The LODs for UDMA are reported between 0.075 μg/mL and 0.63 µg/mL [86,89,164,165]. Respective values for TEGDMA vary between 0.022 μg/mL and 0.808 µg/mL [86,89,164,165,167] and for HEMA between 0.022 μg/mL and 2.43 μg/mL [86,87,164,165,167].

7. Quantitative Analysis

For reliable quantitative analysis, precise calibration is vital. Calibration methods reconstruct the dependence between the analytical signal and the concentration of internal and/or external standards, which correspond to the relationship between the signal and the concentration of the analyte in the sample [168,169]. This relation is used to prepare a calibration curve and the data are fitted by a mathematical function, which usually is linear regression [170]. Calibration can be performed using single-point, double-point, or multi-point calibration, whereas today only multi-point calibration is considered acceptable [169]. For multi-point calibration, 5–10 concentrations of each standard in the range of 0–150% or 50–150% of the concentration likely to be encountered are analyzed in duplicates or triplicates [171,172,173]. Depending on the expected eluted concentrations, most studies analyzed a series of uniformly distributed standard solutions with concentrations between 0.005 ng/mL and 1000 µg/mL [64,89,107,120,164,171,172,173,174,175,176]. When linear regression is used, the linearity of the calibration curve is often assessed by the correlation coefficient r or the determination coefficient r2 [177]. The latest guideline by the clinical and laboratory standards institute (CLSI) considers a correlation coefficient r ≥ 0.975 or r2 ≥ 0.95 as sufficient evidence for linearity [178]. However, it was shown that even in some cases with r > 0.99 linearity is not always fulfilled and thereby a plot of residuals and possibly a lack of fit or Mandel’s fitting test can be performed to verify a normal distribution of calibration points around the line, which is expected in cases of a true linear fit [172,179,180]. Any curvature of this plot is an indication of a lack of fit and therefore suggests the need for a non-linear regression model [179]. However, linear calibration is preferred over non-linear calibration models because of easy calculation and statistical assessment [180]. The lowest calibration standard used is considered the limit of quantification (LOQ) and the signal corresponding to this calibration standard should be at least five times higher than the blank signal [181]. In order to evaluate the strength of the study, both the LOQ and the calibration curve, including its plot of residuals, the correlation or determination coefficient, and the slope of the curve, should be reported (Figure 3).
The LOQs in the current literature for Bis-GMA range from 0.01 µg/mL to 3.51 μg/mL [35,86,89,164] and for BPA from 0.00003 µg/mL to 0.2 µg/mL [64,120,182,183,184]. The LOQs for UDMA are reported between 0.005 μg/mL and 1.90 µg/mL [35,86,89,164]. Respective values for TEGDMA vary between 0.005 μg/mL and 2.424 µg/mL [35,86,89,164,167] and for HEMA between 0.2 μg/mL and 7.36 μg/mL [35,86,164,167].

8. Calibration Techniques

The most common calibration technique is known as external calibration and consists of the separate preparation and analysis of standards and samples [185]. External calibration is prone to matrix effects and does not consider losses in sample preparation or analysis [185,186]. Therefore, ISO Guide 33:2015 recommends using this technique only for matrix-free samples [187]. This source of error is reduced by calibration methods that use standards present in the sample during preparation and analysis [188]. These methods are known as internal calibration and standard addition calibration [186]. For internal calibration, a constant amount of an internal standard similar to the analyte of interest is added to the samples and calibration standards to obtain a calibration factor that is applied to the analyte signal (Figure 1) [185,186]. Most commonly, a set of standards containing the range of expected concentrations of analyte and a single concentration of internal standard is analyzed to obtain the corresponding calibration curve (Figure 3) [189]. Internal calibration requires substances with similar retention times—ideally, isotope-labeled standards of the analyte—and multiple standards may be required when analyzing multiple analytes [190]. Using standard addition, the signal change by adding increasing amounts of a standard to aliquots of the sample is measured and thereby the original concentration is calculated by applying a linear function fitting all experimental points [191]. Consequently, standard addition leads to long-lasting calibration procedures because the individual calibration of each sample is required [168]. However, in contrast to other methods, this is the only technique not affected by systematic matrix errors and is recommended for complex matrices [185].
Most studies on the release of residual monomers from dental resins are limited by the inaccuracy of external calibration [107]. However, the use of internal standards, especially in complex matrices, such as urine and artificial or collected saliva, is recommended [190]. In the literature, caffeine [64,134,192], diethyl phthalate [109,193,194], or standards labeled with stable isotopes [57,62,66,163] have been used as internal standards. Due to its omnipresence, caffeine should not be used in studies using collected human saliva as the solvent [107]. Special caution is required when using diethyl phthalate, as diethyl phthalate is used in dental materials and has already been detected in different composites [192,195]. However, the internal standard must not be present in the sample. Otherwise, quantification will be falsified [196]. In order to avoid this, deuterated diethyl phthalate has been used in more recent studies [197,198]. When adding internal standards or other compounds to the sample, it is important to rule out the introduction of matrix effects by coeluting substances because they may lead to decreased accuracy and sensitivity [199]. Recent studies added an antibiotic–antimycotic mixture to the solvent to avoid microbial colonialization [61,63], but a recent trial for a study of our working group showed that the peaks corresponding to the mixture overlapped the peaks of relevant dental monomers heavily and may have introduced matrix effects to the analytical procedure (Figure 4).
For this reason, every added compound needs to be evaluated for the introduction of matrix effects. Because of similar properties to the analyte and close elution to the analyte, while being well separable, analytical standards labeled with stable isotopes, such as deuterium or 13C, are the most appropriate internal standards [190]. Future studies should use internal standards, preferably labeled with stable isotopes, for calibration.

9. Method Validation

Method validation is mandatory before routine analysis for all analytical methods. International guidelines, by the FDA [177], European Medicines Agency (EMA) [181], and the International Union of the Pure and Applied Chemistry (IUPAC) [200] provide information on the validation of analytical methods. According to these guidelines, the main parameters which need to be validated are linearity, accuracy, precision, specificity, selectivity, matrix effects, and stability [201]. Key parameters of validation, especially the limits of detection (LOD) and quantification (LOQ) [34,66] as well as the slope of the calibration curve [201], should be stated in the method validation section, so readers can evaluate the strength of the study. Very few studies on the elution from dental resins reported these validation parameters [107,163,174].

10. Conclusions

Due to the diverse application of dental resins in various areas of dentistry, it is necessary to develop reliable, evidence-based analytical methods for the detection and quantification of eluting compounds. Analytical and experimental methods used in recent literature vary widely and validation parameters are reported rarely. We propose a consistent study design to collect reliable data that allows consistent meta-analytical evaluation. When researching the in vitro elution from dental resins, the following criteria should be met:
  • The surface area of the sample and the corresponding solvent volume should be standardized according to ISO 10993-12 and following the clinical workflow, the oxygen inhibition layer of the samples should be removed.
  • In order to achieve results comparable to in vivo conditions, solvents, such as water, artificial saliva, or preferably collected saliva, should be used.
  • Incubation parameters should mimic in vivo conditions. Therefore, immediate incubation at 37 °C and a frequent solvent refresh is recommended. For later meta-analysis, a 24-h incubation period should be included in all studies.
  • HPLC-MS, preferably with HRMS and/or tandem mass spectrometry, calibrated by internal standards is the recommended analytical method for detection and quantification.
  • CAS Registry numbers and molecular weights of standards and detected substances must be reported.
  • The analytical method should be validated properly. Key validation parameters, e.g., the LOD, LOQ, and the calibration curve, including its interception, slope, and the plot of residuals, need to be reported for interpretation of study results.

Author Contributions

Conceptualization: T.H., S.K., R.B.; Methodology: T.H., A.W., R.B., S.K.; Investigation: T.H., S.K., R.B., A.W., H.F., M.A., P.K.; Writing—review and editing: T.H., A.W., R.B., S.K., H.F., M.A., P.K.; Visualization: T.H., M.A., P.K.; H.F. Supervision: T.H., S.K.; Project administration: S.K., R.B. All authors have read and agreed to the published version of the manuscript.

Funding

We acknowledge support by the Open Access Publication Funds of the Göttingen University.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors would like to thank Ultradent, South Jordan, USA and DMG Chemisch-Pharmazeutische Fabrik, Hamburg, Germany for supplying the materials which have been analyzed for the figures.

Conflicts of Interest

The authors would like to thank Ultradent, South Jordan, USA and DMG Chemisch-Pharmazeutische Fabrik, Hamburg, Germany for supplying the materials which have been analyzed for the figures. Besides this the authors of this manuscript certify that they have no proprietary, financial, or other interest of any nature or kind in any product, service, and/or company that is presented in this article.

Abbreviations

Many different abbreviations are used in the scientific literature on the leachability of compounds from the polymer matrix of dental resins. This section provides an overview of the most commonly used abbreviations:
APCIAtmospheric pressure chemical ionization
APPIAtmospheric Pressure Photoionisation
BADGEBisphenol A diglycidyl ether
Bis-EMAEthoxylated bisphenol A dimethacrylate
Bis-GMABisphenol A diglycidyl methacrylate
Bis-HPPPBis-hydroxy-propoxy-phenyl-propane
BPABisphenol A
CASChemical Abstracts Service
ESIElectrospray ionization
GCGas chromatography
HEMA2-hydroxylethyl methacrylate
HPLCHigh-performance liquid chromatography
HRMSHigh-resolution mass spectrometry
LCLiquid chromatography
LODLimit of detection
LOQLimit of quantification
MSMass spectrometry
PDAPhotodiode array,
TEGDMATriethylene glycol dimethacrylate
UDMAUrethane dimethacrylate
UV/VisUltraviolet/visible

References

  1. Schwendicke, F.; Göstemeyer, G.; Blunck, U.; Paris, S.; Hsu, L.Y.; Tu, Y.K. Directly Placed Restorative Materials: Review and Network Meta-analysis. J. Dent. Res. 2016, 95, 613–622. [Google Scholar] [CrossRef] [PubMed]
  2. ADA Council on Scientific Affairs. Dental amalgam: Update on safety concerns. J. Am. Dent. Assoc. 1998, 129, 494–503. [Google Scholar] [CrossRef] [PubMed]
  3. Sjögren, P.; Halling, A. Survival time of Class II molar restorations in relation to patient and dental health insurance costs for treatment. Swed. Dent. J. 2002, 26, 59–66. [Google Scholar] [PubMed]
  4. Jones, D.W. Has Dental Amalgam Been Torpedoed and Sunk? J. Dent. Res. 2008, 87, 101–102. [Google Scholar] [CrossRef] [PubMed]
  5. Mutter, J. Is dental amalgam safe for humans? The opinion of the scientific committee of the European Commission. J. Occup. Med. Toxicol. 2011, 6, 2. [Google Scholar] [CrossRef] [Green Version]
  6. Clarkson, T.W.; Magos, L. The Toxicology of Mercury and Its Chemical Compounds. Crit. Rev. Toxicol. 2006, 36, 609–662. [Google Scholar] [CrossRef]
  7. Cramer, N.; Stansbury, J.; Bowman, C. Recent advances and developments in composite dental restorative materials. J. Dent. Res. 2011, 90, 402–416. [Google Scholar] [CrossRef] [Green Version]
  8. Pegoraro, T.A.; da Silva, N.R.F.A.; Carvalho, R.M. Cements for use in esthetic dentistry. Dent. Clin. N. Am. 2007, 51, 453–471. [Google Scholar] [CrossRef]
  9. Sideridou, I.D.; Achilias, D.S.; Karabela, M.M. Sorption kinetics of ethanol/water solution by dimethacrylate-based dental resins and resin composites. J. Biomed. Mater. Res. B Appl. Biomater. 2007, 81, 207–218. [Google Scholar] [CrossRef]
  10. Nakamura, T.; Wakabayashi, K.; Kinuta, S.; Nishida, H.; Miyamae, M.; Yatani, H. Mechanical properties of new self-adhesive resin-based cement. J. Prosthodont. Res. 2010, 54, 59–64. [Google Scholar] [CrossRef]
  11. Leonardo, M.R.; Da Silva, L.; Almeida, W.; Utrilla, L.S. Tissue response to an epoxy resin-based root canal sealer. Dent. Traumatol. 1999, 15, 28–32. [Google Scholar] [CrossRef]
  12. Kim, S.H.; Watts, D.C. Polymerization shrinkage-strain kinetics of temporary crown and bridge materials. Dent. Mater. 2004, 20, 88–95. [Google Scholar] [CrossRef]
  13. Tiu, J.; Belli, R.; Lohbauer, U. Characterization of Heat-Polymerized Monomer Formulations for Dental Infiltrated Ceramic Networks. Appl. Sci. 2021, 11, 7370. [Google Scholar] [CrossRef]
  14. Dressano, D.; Salvador, M.V.; Oliveira, M.T.; Marchi, G.M.; Fronza, B.M.; Hadis, M.; Palin, W.M.; Lima, A.F. Chemistry of novel and contemporary resin-based dental adhesives. J. Mech. Behav. Biomed. Mater. 2020, 110, 103875. [Google Scholar] [CrossRef]
  15. Szczesio-Wlodarczyk, A.; Domarecka, M.; Kopacz, K.; Sokolowski, J.; Bociong, K. An Evaluation of the Properties of Urethane Dimethacrylate-Based Dental Resins. Materials 2021, 14, 2727. [Google Scholar] [CrossRef]
  16. Barszczewska-Rybarek, I.M.; Chrószcz, M.W.; Chladek, G. Physicochemical and Mechanical Properties of Bis-GMA/TEGDMA Dental Composite Resins Enriched with Quaternary Ammonium Polyethylenimine Nanoparticles. Materials 2021, 14, 2037. [Google Scholar] [CrossRef]
  17. Moharamzadeh, K.; Van Noort, R.; Brook, I.M.; Scutt, A.M. HPLC analysis of components released from dental composites with different resin compositions using different extraction media. J. Mater. Sci. Mater. Med. 2007, 18, 133–137. [Google Scholar] [CrossRef]
  18. Pratap, B.; Gupta, R.K.; Bhardwaj, B.; Nag, M. Resin based restorative dental materials: Characteristics and future perspectives. Jpn. Dent. Sci. Rev. 2019, 55, 126–138. [Google Scholar] [CrossRef]
  19. Barszczewska-Rybarek, I.M.; Chrószcz, M.W.; Chladek, G. Novel Urethane-Dimethacrylate Monomers and Compositions for Use as Matrices in Dental Restorative Materials. Int. J. Mol. Sci. 2020, 21, 2644. [Google Scholar] [CrossRef] [Green Version]
  20. De Nys, S.; Duca, R.C.; Vervliet, P.; Covaci, A.; Boonen, I.; Elskens, M.; Vanoirbeek, J.; Godderis, L.; Van Meerbeek, B.; Van Landuyt, K.L. Bisphenol A as degradation product of monomers used in resin-based dental materials. Dent. Mater. 2021, 37, 1020–1029. [Google Scholar] [CrossRef]
  21. Catalán, A.; Martínez, A.; Muñoz, C.; Medina, C.; Marzialetti, T.; Montaño, M.; Jaramillo, A.F.; Meléndrez, M.F. The effect of preheating of nano-filler composite resins on their degree of conversion and microfiltration in dental fillings. Polym. Bull. 2022. [Google Scholar] [CrossRef]
  22. Canceill, T.; Pages, P.; Garnier, S.; Dandurand, J.; Joniot, S. Thermogravimetric study of the behaviour of organic and inorganic polymers contained in four dental resin-based composites. Polym. Polym. Compos. 2021, 29, 1251–1258. [Google Scholar] [CrossRef]
  23. Fonseca, A.S.; Labruna Moreira, A.D.; de Albuquerque, P.P.; de Menezes, L.R.; Pfeifer, C.S.; Schneider, L.F. Effect of monomer type on the CC degree of conversion, water sorption and solubility, and color stability of model dental composites. Dent. Mater. 2017, 33, 394–401. [Google Scholar] [CrossRef]
  24. Par, M.; Spanovic, N.; Tauböck, T.T.; Attin, T.; Tarle, Z. Degree of conversion of experimental resin composites containing bioactive glass 45S5: The effect of post-cure heating. Sci. Rep. 2019, 9, 17245. [Google Scholar] [CrossRef]
  25. Pulgar, R.; Olea-Serrano, M.F.; Novillo-Fertrell, A.; Rivas, A.; Pazos, P.; Pedraza, V.; Navajas, J.M.; Olea, N. Determination of bisphenol A and related aromatic compounds released from bis-GMA-based composites and sealants by high performance liquid chromatography. Environ. Health Perspect. 2000, 108, 21–27. [Google Scholar] [CrossRef] [PubMed]
  26. Luo, S.; Zhu, W.; Liu, F.; He, J. Preparation of a Bis-GMA-free dental resin system with synthesized fluorinated dimethacrylate monomers. Int. J. Mol. Sci. 2016, 17, 2014. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  27. Mourouzis, P.; Andreasidou, E.; Samanidou, V.; Tolidis, K. Short-term and long-term release of monomers from newly developed resin-modified ceramics and composite resin CAD-CAM blocks. J. Prosthet. Dent. 2020, 123, 339–348. [Google Scholar] [CrossRef] [PubMed]
  28. Szczesio-Wlodarczyk, A.; Polikowski, A.; Krasowski, M.; Fronczek, M.; Sokolowski, J.; Bociong, K. The Influence of Low-Molecular-Weight Monomers (TEGDMA, HDDMA, HEMA) on the Properties of Selected Matrices and Composites Based on Bis-GMA and UDMA. Materials 2022, 15, 2649. [Google Scholar] [CrossRef] [PubMed]
  29. Barszczewska-Rybarek, I.M. Structure-property relationships in dimethacrylate networks based on Bis-GMA, UDMA and TEGDMA. Dent. Mater. 2009, 25, 1082–1089. [Google Scholar] [CrossRef] [PubMed]
  30. Araújo, G.S.; Sfalcin, R.A.; Araújo, T.G.; Alonso, R.C.; Puppin-Rontani, R.M. Evaluation of polymerization characteristics and penetration into enamel caries lesions of experimental infiltrants. J. Dent. 2013, 41, 1014–1019. [Google Scholar] [CrossRef] [Green Version]
  31. Alrahlah, A.; Al-Odayni, A.B.; Al-Mutairi, H.F.; Almousa, B.M.; Alsubaie, F.S.; Khan, R.; Saeed, W.S. A Low-Viscosity BisGMA Derivative for Resin Composites: Synthesis, Characterization, and Evaluation of Its Rheological Properties. Materials 2021, 14, 338. [Google Scholar] [CrossRef]
  32. Tauscher, S.; Angermann, J.; Catel, Y.; Moszner, N. Evaluation of alternative monomers to HEMA for dental applications. Dent. Mater. 2017, 33, 857–865. [Google Scholar] [CrossRef]
  33. Polydorou, O.; König, A.; Hellwig, E.; Kümmerer, K. Long-term release of monomers from modern dental-composite materials. Eur. J. Oral Sci. 2009, 117, 68–75. [Google Scholar] [CrossRef]
  34. Van Landuyt, K.L.; Nawrot, T.; Geebelen, B.; De Munck, J.; Snauwaert, J.; Yoshihara, K.; Scheers, H.; Godderis, L.; Hoet, P.; Van Meerbeek, B. How much do resin-based dental materials release? A meta-analytical approach. Dent. Mater. 2011, 27, 723–747. [Google Scholar] [CrossRef]
  35. Putzeys, E.; Nys, S.D.; Cokic, S.M.; Duca, R.C.; Vanoirbeek, J.; Godderis, L.; Meerbeek, B.V.; Van Landuyt, K.L. Long-term elution of monomers from resin-based dental composites. Dent. Mater. 2019, 35, 477–485. [Google Scholar] [CrossRef]
  36. De Nys, S.; Putzeys, E.; Duca, R.C.; Vervliet, P.; Covaci, A.; Boonen, I.; Elskens, M.; Vanoirbeek, J.; Godderis, L.; Van Meerbeek, B.; et al. Long-term elution of bisphenol A from dental composites. Dent. Mater. 2021, 37, 1561–1568. [Google Scholar] [CrossRef]
  37. Colborn, T.; vom Saal, F.S.; Soto, A.M. Developmental effects of endocrine-disrupting chemicals in wildlife and humans. Environ. Health Perspect. 1993, 101, 378–384. [Google Scholar] [CrossRef]
  38. Fleisch, A.F.; Sheffield, P.E.; Chinn, C.; Edelstein, B.L.; Landrigan, P.J. Bisphenol A and related compounds in dental materials. Pediatrics 2010, 126, 760–768. [Google Scholar] [CrossRef] [Green Version]
  39. Gould, J.C.; Leonard, L.S.; Maness, S.C.; Wagner, B.L.; Conner, K.; Zacharewski, T.; Safe, S.; McDonnell, D.P.; Gaido, K.W. Bisphenol A interacts with the estrogen receptor alpha in a distinct manner from estradiol. Mol. Cell. Endocrinol. 1998, 142, 203–214. [Google Scholar] [CrossRef]
  40. Li, L.; Wang, Q.; Zhang, Y.; Niu, Y.; Yao, X.; Liu, H. The molecular mechanism of bisphenol A (BPA) as an endocrine disruptor by interacting with nuclear receptors: Insights from molecular dynamics (MD) simulations. PLoS ONE 2015, 10, e012033. [Google Scholar] [CrossRef]
  41. Takayanagi, S.; Tokunaga, T.; Liu, X.; Okada, H.; Matsushima, A.; Shimohigashi, Y. Endocrine disruptor bisphenol A strongly binds to human estrogen-related receptor gamma (ERRgamma) with high constitutive activity. Toxicol. Lett. 2006, 167, 95–105. [Google Scholar] [CrossRef]
  42. Alonso-Magdalena, P.; Laribi, O.; Ropero, A.B.; Fuentes, E.; Ripoll, C.; Soria, B.; Nadal, A. Low doses of bisphenol A and diethylstilbestrol impair Ca2+ signals in pancreatic alpha-cells through a nonclassical membrane estrogen receptor within intact islets of Langerhans. Environ. Health Perspect. 2005, 113, 969–977. [Google Scholar] [CrossRef] [Green Version]
  43. Xing, L.; Xu, Y.; Xiao, Y.; Shang, L.; Liu, R.; Wei, X.; Jiang, J.; Hao, W. Embryotoxic and teratogenic effects of the combination of bisphenol A and genistein on in vitro cultured postimplantation rat embryos. Toxicol. Sci. 2010, 115, 577–588. [Google Scholar] [CrossRef] [Green Version]
  44. Söderholm, K.J.; Mariotti, A. BIS-GMA—Based resins in dentistry: Are they safe? J. Am. Dent. Assoc. 1999, 130, 201–209. [Google Scholar] [CrossRef] [PubMed]
  45. Geurtsen, W.; Lehmann, F.; Spahl, W.; Leyhausen, G. Cytotoxicity of 35 dental resin composite monomers/additives in permanent 3T3 and three human primary fibroblast cultures. J. Biomed. Mater. Res. 1998, 41, 474–480. [Google Scholar] [CrossRef]
  46. Kuan, Y.H.; Li, Y.C.; Huang, F.M.; Chang, Y.C. The upregulation of tumour necrosis factor-α and surface antigens expression on macrophages by bisphenol A-glycidyl-methacrylate. Int. Endod. J. 2012, 45, 619–626. [Google Scholar] [CrossRef]
  47. Styllou, M.; Reichl, F.X.; Styllou, P.; Urcan, E.; Rothmund, L.; Hickel, R.; Högg, C.; Scherthan, H. Dental composite components induce DNA-damage and altered nuclear morphology in gingiva fibroblasts. Dent. Mater. 2015, 31, 1335–1344. [Google Scholar] [CrossRef]
  48. Arossi, G.A.; Lehmann, M.; Dihl, R.R.; Reguly, M.L.; De Andrade, H.H.R. Induced DNA damage by dental resin monomers in somatic cells. Basic Clin. Pharmacol. Toxicol. 2010, 106, 124–129. [Google Scholar] [CrossRef]
  49. Kleinsasser, N.H.; Schmid, K.; Sassen, A.W.; Harréus, U.A.; Staudenmaier, R.; Folwaczny, M.; Glas, J.; Reichl, F.X. Cytotoxic and genotoxic effects of resin monomers in human salivary gland tissue and lymphocytes as assessed by the single cell microgel electrophoresis (Comet) assay. Biomaterials 2006, 27, 1762–1770. [Google Scholar] [CrossRef]
  50. Kurt, A.; Altintas, S.H.; Kiziltas, M.V.; Tekkeli, S.E.; Guler, E.M.; Kocyigit, A.; Usumez, A. Evaluation of residual monomer release and toxicity of self-adhesive resin cements. Dent. Mater. J. 2018, 37, 40–48. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  51. Reichl, F.X.; Esters, M.; Simon, S.; Seiss, M.; Kehe, K.; Kleinsasser, N.; Folwaczny, M.; Glas, J.; Hickel, R. Cell death effects of resin-based dental material compounds and mercurials in human gingival fibroblasts. Arch. Toxicol. 2006, 80, 370–377. [Google Scholar] [CrossRef] [PubMed]
  52. Emmler, J.; Seiss, M.; Kreppel, H.; Reichl, F.X.; Hickel, R.; Kehe, K. Cytotoxicity of the dental composite component TEGDMA and selected metabolic by-products in human pulmonary cells. Dent. Mater. 2008, 24, 1670–1675. [Google Scholar] [CrossRef] [PubMed]
  53. Ferracane, J.L. Resin composite—State of the art. Dent. Mater. 2011, 27, 29–38. [Google Scholar] [CrossRef] [PubMed]
  54. Goldberg, M.; Lasfargues, J.J.; Legrand, J.M. Clinical testing of dental Materials—Histological considerations. J. Dent. 1994, 22, 25–28. [Google Scholar] [CrossRef]
  55. Polydorou, O.; König, A.; Hellwig, E.; Kümmerer, K. Urethane dimethacrylate: A molecule that may cause confusion in dental research. J. Biomed. Mater. Res. B Appl. Biomater. 2009, 91, 1–4. [Google Scholar] [CrossRef]
  56. Michelsen, V.B.; Kopperud, H.B.M.; Lygre, G.B.; Björkman, L.; Jensen, E.; Kleven, I.S.; Svahn, J.; Lygre, H. Detection and quantification of monomers in unstimulated whole saliva after treatment with resin-based composite fillings in vivo. Eur. J. Oral Sci. 2012, 120, 89–95. [Google Scholar] [CrossRef]
  57. Berge, T.L.L.; Lygre, G.B.; Lie, S.A.; Lindh, C.H.; Björkman, L. Bisphenol A in human saliva and urine before and after treatment with dental polymer-based restorative materials. Eur. J. Oral Sci. 2019, 127, 435–444. [Google Scholar] [CrossRef] [Green Version]
  58. Sasaki, N.; Okuda, K.; Kato, T.; Kakishima, H.; Okuma, H.; Abe, K.; Tachino, H.; Tuchida, K.; Kubono, K. Salivary bisphenol-A levels detected by ELISA after restoration with composite resin. J. Mater. Sci. Mater. Med. 2005, 16, 297–300. [Google Scholar] [CrossRef]
  59. Moreira, M.R.; Matos, L.G.; de Souza, I.D.; Brigante, T.A.; Queiroz, M.E.; Romano, F.L.; Nelson-Filho, P.; Matsumoto, M.A. Bisphenol A release from orthodontic adhesives measured in vitro and in vivo with gas chromatography. Am. J. Orthod. Dentofac. Orthop. 2017, 151, 477–483. [Google Scholar] [CrossRef]
  60. Anderson, J.M. Future challenges in the in vitro and in vivo evaluation of biomaterial biocompatibility. Regen. Biomater. 2016, 3, 73–77. [Google Scholar] [CrossRef] [Green Version]
  61. Małkiewicz, K.; Owoc, A.; Kluska, M.; Grzech-Leśniak, K.; Turło, J. HPLC analysis of potentially harmful substances released from dental filing materials available on the EU market. Ann. Agric. Environ. Med. 2014, 21, 86–90. [Google Scholar]
  62. Becher, R.; Wellendorf, H.; Sakhi, A.K.; Samuelsen, J.T.; Thomsen, C.; Bølling, A.K.; Kopperud, H.M. Presence and leaching of bisphenol a (BPA) from dental materials. Acta Biomater. Odontol. Scand. 2018, 4, 56–62. [Google Scholar] [CrossRef]
  63. Małkiewicz, K.; Turło, J.; Marciniuk-Kluska, A.; Grzech-Leśniak, K.; Gąsior, M.; Kluska, M. Release of bisphenol A and its derivatives from orthodontic adhesive systems available on the European market as a potential health risk factor. Ann. Agric. Environ. Med. 2015, 22, 172–177. [Google Scholar] [CrossRef] [Green Version]
  64. Deviot, M.; Lachaise, I.; Högg, C.; Durner, J.; Reichl, F.X.; Attal, J.-P.; Dursun, E. Bisphenol A release from an orthodontic resin composite: A GC/MS and LC/MS study. Dent. Mater. 2018, 34, 341–354. [Google Scholar] [CrossRef]
  65. Ferracane, J.L. Elution of leachable components from composites. J. Oral Rehabil. 1994, 21, 441–452. [Google Scholar] [CrossRef]
  66. Hope, E.; Reed, D.R.; Moilanen, L.H. Potential confounders of bisphenol-a analysis in dental materials. Dent. Mater. 2016, 32, 961–967. [Google Scholar] [CrossRef]
  67. Alshali, R.Z.; Salim, N.A.; Sung, R.; Satterthwaite, J.D.; Silikas, N. Qualitative and quantitative characterization of monomers of uncured bulk-fill and conventional resin-composites using liquid chromatography/mass spectrometry. Dent. Mater. 2015, 31, 711–720. [Google Scholar] [CrossRef]
  68. Schmalz, G. Concepts in biocompatibility testing of dental restorative materials. Clin. Oral Investig. 1998, 1, 154–162. [Google Scholar] [CrossRef]
  69. ISO 4049:2019; Dentistry—Polymer-Based Restorative Materials. International Organization for Standardization (ISO): Geneva, Switzerland, 2019.
  70. ISO 10993-12:2012; Biological Evaluation of Medical Devices—Part 12: Sample Preparation and Reference Materials. International Organization for Standardization (ISO): Geneva, Switzerland, 2012.
  71. Pelka, M.; Distler, W.; Petschelt, A. Elution parameters and HPLC-detection of single components from resin composite. Clin. Oral Investig. 1999, 3, 194–200. [Google Scholar] [CrossRef]
  72. Polydorou, O.; Huberty, C.; Wolkewitz, M.; Bolek, R.; Hellwig, E.; Kümmerer, K. The effect of storage medium on the elution of monomers from composite materials. J. Biomed. Mater. Res. B Appl. Biomater. 2012, 100, 68–74. [Google Scholar] [CrossRef]
  73. Ruyter, I.E. Unpolymerized surface layers on sealants. Acta Odontol. Scand. 1981, 39, 27–32. [Google Scholar] [CrossRef] [PubMed]
  74. Kim, J.S.; Choi, Y.H.; Cho, B.H.; Son, H.H.; Lee, I.B.; Um, C.M.; Kim, C.K. Effect of light-cure time of adhesive resin on the thickness of the oxygen-inhibited layer and the microtensile bond strength to dentin. J. Biomed. Mater. Res. B Appl. Biomater. 2006, 78, 115–123. [Google Scholar] [CrossRef] [PubMed]
  75. Komurcuoglu, E.; Olmez, S.; Vural, N. Evaluation of residual monomer elimination methods in three different fissure sealants in vitro. J. Oral Rehabil. 2005, 32, 116–121. [Google Scholar] [CrossRef] [PubMed]
  76. Tang, A.T.H.; Li, J.; Ekstrand, J.; Liu, Y. Cytotoxicity tests of in situ polymerized resins: Methodological comparisons and introduction of a tissue culture insert as a testing device. J. Biomed. Mater. Res. 1999, 45, 214–222. [Google Scholar] [CrossRef]
  77. Bijelic-Donova, J.; Garoushi, S.; Lassila, L.V.J.; Vallittu, P.K. Oxygen inhibition layer of composite resins: Effects of layer thickness and surface layer treatment on the interlayer bond strength. Eur. J. Oral Sci. 2015, 123, 53–60. [Google Scholar] [CrossRef]
  78. Shawkat, E.S.; Shortall, A.C.; Addison, O.; Palin, W.M. Oxygen inhibition and incremental layer bond strengths of resin composites. Dent. Mater. 2009, 25, 1338–1346. [Google Scholar] [CrossRef]
  79. Dall’Oca, S.; Papacchini, F.; Goracci, C.; Cury, A.H.; Suh, B.I.; Tay, F.R.; Polimeni, A.; Ferrari, M. Effect of oxygen inhibition on composite repair strength over time. J. Biomed. Mater. Res. B Appl. Biomater. 2007, 81, 493–498. [Google Scholar] [CrossRef]
  80. Mayinger, F.; Reymus, M.; Liebermann, A.; Richter, M.; Kubryk, P.; Großekappenberg, H.; Stawarczyk, B. Impact of polymerization and storage on the degree of conversion and mechanical properties of veneering resin composites. Dent. Mater. J. 2021, 40, 487–497. [Google Scholar] [CrossRef]
  81. Sehgal, A.; Rao, Y.M.; Joshua, M.; Narayanan, L.L. Evaluation of the effects of the oxygen-inhibited layer on shear bond strength of two resin composites. J. Conserv. Dent. 2008, 11, 159–161. [Google Scholar] [CrossRef] [Green Version]
  82. Rueggeberg, F.A.; Margeson, D.H. The effect of oxygen inhibition on an unfilled/filled composite system. J. Dent. Res. 1990, 69, 1652–1658. [Google Scholar] [CrossRef]
  83. Studer, K.; Decker, C.; Beck, E.; Schwalm, R. Overcoming oxygen inhibition in UV-curing of acrylate coatings by carbon dioxide inerting, Part I. Prog. Org. Coat. 2003, 48, 92–100. [Google Scholar] [CrossRef]
  84. Bergmann, P.; Noack, M.J.; Roulet, J.F. Marginal adaptation with glass-ceramic inlays adhesively luted with glycerine gel. Quintessence Int. 1991, 22, 739–744. [Google Scholar]
  85. Park, H.-H.; Lee, I.-B. Effect of glycerin on the surface hardness of composites after curing. J. Korean Acad. Conserv. Dent. 2011, 36, 483–489. [Google Scholar] [CrossRef]
  86. Bezgin, T.; Cimen, C.; Ozalp, N. Evaluation of Residual Monomers Eluted from Pediatric Dental Restorative Materials. Biomed. Res. Int. 2021, 2021, 6316171. [Google Scholar] [CrossRef]
  87. Manojlovic, D.; Radisic, M.; Vasiljevic, T.; Zivkovic, S.; Lausevic, M.; Miletic, V. Monomer elution from nanohybrid and ormocer-based composites cured with different light sources. Dent. Mater. 2011, 27, 371–378. [Google Scholar] [CrossRef]
  88. Meyer-Lückel, H.; Hartwig, C.; Börner, H.G.; Lausch, J. Elution of Monomers from an Infiltrant Compared with Different Resin-Based Dental Materials. Oral Health Prev. Dent. 2020, 18, 337–341. [Google Scholar]
  89. Saleem, M.; Zahid, S.; Ghafoor, S.; Khalid, H.; Iqbal, H.; Zeeshan, R.; Ahmad, S.; Asif, A.; Khan, A.S. Physical, mechanical, and in vitro biological analysis of bioactive fibers-based dental composite. J. Appl. Polym. Sci. 2021, 138, 50336. [Google Scholar] [CrossRef]
  90. Inoue, K.; Hayashi, I. Residual monomer (Bis-GMA) of composite resins. J. Oral Rehabil. 1982, 9, 493–497. [Google Scholar] [CrossRef]
  91. Yang, S.H.; Morgan, A.A.; Nguyen, H.P.; Moore, H.; Figard, B.J.; Schug, K.A. Quantitative determination of Bisphenol A from human saliva using bulk derivatization and trap-and-elute liquid chromatography coupled to electrospray ionization mass spectrometry. Environ. Toxicol. Chem. 2011, 30, 1243–1251. [Google Scholar] [CrossRef]
  92. Reichl, F.X.; Löhle, J.; Seiss, M.; Furche, S.; Shehata, M.M.; Hickel, R.; Müller, M.; Dränert, M.; Durner, J. Elution of TEGDMA and HEMA from polymerized resin-based bonding systems. Dent. Mater. 2012, 28, 1120–1125. [Google Scholar] [CrossRef]
  93. Kessler, A.; Reichl, F.X.; Folwaczny, M.; Högg, C. Monomer release from surgical guide resins manufactured with different 3D printing devices. Dent. Mater. 2020, 36, 1486–1492. [Google Scholar] [CrossRef]
  94. Polydorou, O.; Trittler, R.; Hellwig, E.; Kümmerer, K. Elution of monomers from two conventional dental composite materials. Dent. Mater. 2007, 23, 1535–1541. [Google Scholar] [CrossRef]
  95. Cebe, M.A.; Cebe, F.; Cengiz, M.F.; Cetin, A.R.; Arpag, O.F.; Ozturk, B. Elution of monomer from different bulk fill dental composite resins. Dent. Mater. 2015, 31, 141–149. [Google Scholar] [CrossRef]
  96. Altintas, S.H.; Usumez, A. Evaluation of TEGDMA leaching from four resin cements by HPLC. Eur. J. Dent. 2012, 6, 255–262. [Google Scholar] [CrossRef] [Green Version]
  97. Shahabi, S.; Sayyari, M.; Sadrai, S.; Valizadeh, S.; Hajizamani, H.; Sadr, A. Effect of Volume and Renewal of the Storage Media on the Release of Monomer from Dental Composites. Int. J. Dent. 2021, 2021, 9769947. [Google Scholar] [CrossRef]
  98. Durner, J.; Schrickel, K.; Watts, D.C.; Becker, M.; Draenert, M.E. Direct and indirect eluates from bulk fill resin-based-composites. Dent. Mater. 2022, 38, 489–507. [Google Scholar] [CrossRef]
  99. McKinney, J.E.; Wu, W. Chemical softening and wear of dental composites. J. Dent. Res. 1985, 64, 1326–1331. [Google Scholar] [CrossRef]
  100. Wu, W.; McKinney, J.E. Influence of chemicals on wear of dental composites. J. Dent. Res. 1982, 61, 1180–1183. [Google Scholar] [CrossRef]
  101. Szczesio-Wlodarczyk, A.; Sokolowski, J.; Kleczewska, J.; Bociong, K. Ageing of Dental Composites Based on Methacrylate Resins-A Critical Review of the Causes and Method of Assessment. Polymers 2020, 12, 882. [Google Scholar] [CrossRef]
  102. Tsitrou, E.; Kelogrigoris, S.; Koulaouzidou, E.; Antoniades-Halvatjoglou, M.; Koliniotou-Koumpia, E.; van Noort, R. Effect of extraction media and storage time on the elution of monomers from four contemporary resin composite materials. Toxicol. Int. 2014, 21, 89–95. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  103. Zhang, Y.; Xu, J. Effect of immersion in various media on the sorption, solubility, elution of unreacted monomers, and flexural properties of two model dental composite compositions. J. Mater. Sci. Mater. Med. 2008, 19, 2477–2483. [Google Scholar] [CrossRef] [PubMed]
  104. Rothmund, L.; Shehata, M.; Van Landuyt, K.L.; Schweikl, H.; Carell, T.; Geurtsen, W.; Hellwig, E.; Hickel, R.; Reichl, F.X.; Högg, C. Release and protein binding of components from resin based composites in native saliva and other extraction media. Dent. Mater. 2015, 31, 496–504. [Google Scholar] [CrossRef] [PubMed]
  105. Tanaka, K.; Taira, M.; Shintani, H.; Wakasa, K.; Yamaki, M. Residual monomers (TEGDMA and Bis-GMA) of a set visible-light-cured dental composite resin when immersed in water. J. Oral Rehabil. 1991, 18, 353–362. [Google Scholar] [CrossRef] [PubMed]
  106. Floyd, C.J.; Dickens, S.H. Network structure of Bis-GMA- and UDMA-based resin systems. Dent. Mater. 2006, 22, 1143–1149. [Google Scholar] [CrossRef]
  107. Michelsen, V.B.; Moe, G.; Strøm, M.B.; Jensen, E.; Lygre, H. Quantitative analysis of TEGDMA and HEMA eluted into saliva from two dental composites by use of GC/MS and tailor-made internal standards. Dent. Mater. 2008, 24, 724–731. [Google Scholar] [CrossRef]
  108. Gregson, K.; Beiswanger, A.; Platt, J. The impact of sorption, buffering, and proteins on leaching of organic and inorganic substances from dental resin core material. J. Biomed. Mater. Res. A 2008, 84, 256–264. [Google Scholar] [CrossRef]
  109. Michelsen, V.B.; Moe, G.; Skålevik, R.; Jensen, E.; Lygre, H. Quantification of organic eluates from polymerized resin-based dental restorative materials by use of GC/MS. J. Chromatogr. B 2007, 850, 83–91. [Google Scholar] [CrossRef]
  110. De Nys, S.; Duca, R.C.; Vervliet, P.; Covaci, A.; Boonen, I.; Elskens, M.; Vanoirbeek, J.; Godderis, L.; Van Meerbeek, B.; Van Landuyt, K.L. Bisphenol A release from short-term degraded resin-based dental materials. J. Dent. 2022, 116, 103894. [Google Scholar] [CrossRef]
  111. Olea, N.; Pulgar, R.; Pérez, P.; Olea-Serrano, F.; Rivas, A.; Novillo-Fertrell, A.; Pedraza, V.; Soto, A.M.; Sonnenschein, C. Estrogenicity of resin-based composites and sealants used in dentistry. Environ. Health Perspect. 1996, 104, 298–305. [Google Scholar] [CrossRef]
  112. Örtengren, U.; Langer, S.; Göransson, A.; Lundgren, T. Influence of pH and time on organic substance release from a model dental composite: A fluorescence spectrophotometry and gas chromatography/mass spectrometry analysis. Eur. J. Oral Sci. 2004, 112, 530–537. [Google Scholar] [CrossRef]
  113. Al-Hiyasat, A.S.; Darmani, H.; Milhem, M.M. Cytotoxicity evaluation of dental resin composites and their flowable derivatives. Clin. Oral Investig. 2005, 9, 21–25. [Google Scholar] [CrossRef]
  114. Hofmann, N.; Renner, J.; Hugo, B.; Klaiber, B. Elution of leachable components from resin composites after plasma arc vs. standard or soft-start halogen light irradiation. J. Dent. 2002, 30, 223–232. [Google Scholar] [CrossRef]
  115. Yap, A.; Han, V.; Soh, M.; Siow, K. Elution of leachable components from composites after LED and halogen light irradiation. Oper. Dent. 2004, 29, 448–453. [Google Scholar]
  116. Ferracane, J.L.; Condon, J.R. Rate of elution of leachable components from composite. Dent. Mater. 1990, 6, 282–287. [Google Scholar] [CrossRef]
  117. Cokic, S.M.; Duca, R.C.; De Munck, J.; Hoet, P.; Van Meerbeek, B.; Smet, M.; Godderis, L.; Van Landuyt, K.L. Saturation reduces in-vitro leakage of monomers from composites. Dent. Mater. 2018, 34, 579–586. [Google Scholar] [CrossRef]
  118. Ferracane, J.L. Hygroscopic and hydrolytic effects in dental polymer networks. Dent. Mater. 2006, 22, 211–222. [Google Scholar] [CrossRef]
  119. Tabatabaei, M.H.; Sadrai, S.; Bassir, S.H.; Veisy, N.; Dehghan, S. Effect of food stimulated liquids and thermocycling on the monomer elution from a nanofilled composite. Open Dent. J. 2013, 7, 62–67. [Google Scholar] [CrossRef] [Green Version]
  120. Hampe, T.; Wiessner, A.; Frauendorf, H.; Alhussein, M.; Karlovsky, P.; Bürgers, R.; Krohn, S. A comparative in vitro study on monomer release from bisphenol A-free and conventional temporary crown and bridge materials. Eur. J. Oral Sci. 2021, 6, e12826. [Google Scholar] [CrossRef]
  121. Sanglar, C.; Defay, M.; Waton, H.; Bonhomme, A.; Alamercery, S.; Baudot, R.; Païsse, O.; Grenier-Loustalot, M.F. Commercial dental composite: Determination of reaction advancement and study of the migration of organic compounds. Polym. Polym. Compos. 2005, 13, 223–234. [Google Scholar] [CrossRef]
  122. Koin, P.J.; Kilislioglu, A.; Zhou, M.; Drummond, J.L.; Hanley, L. Analysis of the degradation of a model dental composite. J. Dent. Res. 2008, 87, 661–665. [Google Scholar] [CrossRef] [Green Version]
  123. de Brito, O.; de Oliveira, I.; Monteiro, G. Hydrolytic and biological degradation of bulk-fill and self-adhering resin composites. Oper. Dent. 2019, 44, 223–233. [Google Scholar] [CrossRef]
  124. Vervliet, P.; Den Plas, J.V.; De Nys, S.; Duca, R.C.; Boonen, I.; Elskens, M.; Van Landuyt, K.L.; Covaci, A. Investigating the in vitro metabolism of the dental resin monomers BisGMA, BisPMA, TCD-DI-HEA and UDMA using human liver microsomes and quadrupole time of flight mass spectrometry. Toxicology 2019, 420, 1–10. [Google Scholar] [CrossRef] [PubMed]
  125. Hsu, W.Y.; Wang, V.S.; Lai, C.C.; Tsai, F.J. Simultaneous determination of components released from dental composite resins in human saliva by liquid chromatography/multiple-stage ion trap mass spectrometry. Electrophoresis 2012, 33, 719–725. [Google Scholar] [CrossRef]
  126. Finer, Y.; Jaffer, F.; Santerre, J.P. Mutual influence of cholesterol esterase and pseudocholinesterase on the biodegradation of dental composites. Biomaterials 2004, 25, 1787–1793. [Google Scholar] [CrossRef] [PubMed]
  127. Finer, Y.; Santerre, J.P. Salivary esterase activity and its association with the biodegradation of dental composites. J. Dent. Res. 2004, 83, 22–26. [Google Scholar] [CrossRef] [PubMed]
  128. Alshali, R.Z.; Salim, N.A.; Sung, R.; Satterthwaite, J.D.; Silikas, N. Analysis of long-term monomer elution from bulk-fill and conventional resin-composites using high performance liquid chromatography. Dent. Mater. 2015, 31, 1587–1598. [Google Scholar] [CrossRef] [PubMed]
  129. Shelby, M.D. NTP-CERHR monograph on the potential human reproductive and developmental effects of bisphenol A. NTP CERHR MON 2008, 22, v–vii, 1–64 passim. [Google Scholar]
  130. Durner, J.; Schrickel, K.; Watts, D.C.; Ilie, N. Determination of homologous distributions of bisEMA dimethacrylates in bulk-fill resin-composites by GC–MS. Dent. Mater. 2015, 31, 473–480. [Google Scholar] [CrossRef] [PubMed]
  131. Bannach, G.; Cavalheiro, C.C.; Calixto, L.; Cavalheiro, É.T.G. Thermoanalytical study of monomers: BisGMA, BisEMA, TEGDMA, UDMA and their mixture. Braz. J. Therm. Anal. 2015, 4, 28–34. [Google Scholar]
  132. Rogalewicz, R.; Batko, K.; Voelkel, A. Identification of organic extractables from commercial resin-modified glass-ionomers using HPLC-MS. J. Environ. Monit. 2006, 8, 750–758. [Google Scholar] [CrossRef]
  133. Spahl, W.; Budzikiewicz, H. Qualitative analysis of dental resin composites by gas and liquid chromatography/mass spectrometry. Fresenius’ J. Anal. Chem. 1994, 350, 684–691. [Google Scholar] [CrossRef]
  134. Geurtsen, W.; Spahl, W.; Leyhausen, G. Variability of cytotoxicity and leaching of substances from four light-curing pit and fissure sealants. J. Biomed. Mater. Res. 1999, 44, 73–77. [Google Scholar] [CrossRef]
  135. Ternes, T.A. Analytical methods for the determination of pharmaceuticals in aqueous environmental samples. Trends Anal. Chem. 2001, 20, 419–434. [Google Scholar] [CrossRef]
  136. Gul, P.; Senol, O.; Yaman, M.E.; Kadıoglu, Y. Quantification and identification of components released from dental composites using different chromatographic techniques. J. Liq. Chromatogr. Relat. Technol. 2016, 39, 581–586. [Google Scholar] [CrossRef]
  137. Siddiqui, M.R.; Alothman, Z.A.; Rahman, N. Analytical techniques in pharmaceutical analysis: A review. Arab. J. Chem. 2017, 10, S1409–S1421. [Google Scholar] [CrossRef] [Green Version]
  138. Swartz, M. HPLC detectors: A brief review. J. Liq. Chromatogr. Relat. Technol. 2010, 33, 1130–1150. [Google Scholar] [CrossRef]
  139. Mariappan, T.T.; Jindal, K.C.; Singh, S. Overestimation of rifampicin during colorimetric analysis of anti-tuberculosis products containing isoniazid due to formation of isonicotinyl hydrazone. J. Pharm. Biomed. Anal. 2004, 36, 905–908. [Google Scholar] [CrossRef]
  140. Barba, A.I.O.; Hurtado, M.C.; Mata, M.C.S.; Ruiz, V.F.; Tejada, M.L.S.d. Application of a UV–vis detection-HPLC method for a rapid determination of lycopene and β-carotene in vegetables. Food Chem. 2006, 95, 328–336. [Google Scholar] [CrossRef]
  141. Babic, N.; Larson, T.S.; Grebe, S.K.; Turner, S.T.; Kumar, R.; Singh, R.J. Application of liquid chromatography-mass spectrometry technology for early detection of microalbuminuria in patients with kidney disease. Clin. Chem. 2006, 52, 2155–2157. [Google Scholar] [CrossRef] [Green Version]
  142. Fagiola, M. Current and future directions of high resolution and tandem mass spectrometry in postmortem and human performance toxicology. Leg. Med. 2019, 37, 86–94. [Google Scholar] [CrossRef]
  143. Picó, Y.; Blasco, C.; Font, G. Environmental and food applications of LC–tandem mass spectrometry in pesticide-residue analysis: An overview. Mass Spectrom. Rev. 2004, 23, 45–85. [Google Scholar] [CrossRef]
  144. Hernández, F.; Sancho, J.V.; Ibáñez, M.; Abad, E.; Portolés, T.; Mattioli, L. Current use of high-resolution mass spectrometry in the environmental sciences. Anal. Bioanal. Chem. 2012, 403, 1251–1264. [Google Scholar] [CrossRef]
  145. Schollée, J.E.; Schymanski, E.L.; Stravs, M.A.; Gulde, R.; Thomaidis, N.S.; Hollender, J. Similarity of High-Resolution Tandem Mass Spectrometry Spectra of Structurally Related Micropollutants and Transformation Products. J. Am. Soc. Mass Spectrom. 2017, 28, 2692–2704. [Google Scholar] [CrossRef]
  146. De Vijlder, T.; Valkenborg, D.; Lemière, F.; Romijn, E.P.; Laukens, K.; Cuyckens, F. A tutorial in small molecule identification via electrospray ionization-mass spectrometry: The practical art of structural elucidation. Mass Spectrom. Rev. 2018, 37, 607–629. [Google Scholar] [CrossRef] [PubMed]
  147. Zhang, S.; Zhang, Q.; Darisaw, S.; Ehie, O.; Wang, G. Simultaneous quantification of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and pharmaceuticals and personal care products (PPCPs) in Mississippi river water, in New Orleans, Louisiana, USA. Chemosphere 2007, 66, 1057–1069. [Google Scholar] [CrossRef] [PubMed]
  148. Devosa, C.; Vliegen, M.; Willaert, B.; David, F.; Moens, L.; Sandra, P. Automated headspace-solid-phase micro extraction-retention time locked-isotope dilution gas chromatography-mass spectrometry for the analysis of organotin compounds in water and sediment samples. J. Chromatogr. A 2005, 1079, 408–414. [Google Scholar] [CrossRef] [PubMed]
  149. Schütze, A.; Pälmke, C.; Angerer, J.; Weiss, T.; Brüning, T.; Koch, H.M. Quantification of biomarkers of environmental exposure to di(isononyl)cyclohexane-1,2-dicarboxylate (DINCH) in urine via HPLC-MS/MS. J. Chromatogr. B Analyt. Technol. Biomed. Life Sci. 2012, 895–896, 123–130. [Google Scholar] [CrossRef]
  150. Kushnir, M.M.; Rockwood, A.L.; Nelson, G.J.; Yue, B.; Urry, F.M. Assessing analytical specificity in quantitative analysis using tandem mass spectrometry. Clin. Biochem. 2005, 38, 319–327. [Google Scholar] [CrossRef]
  151. Michelsen, V.B.; Lygre, H.; Skålevik, R.; Tveit, A.B.; Solheim, E. Identification of organic eluates from four polymer-based dental filling materials. Eur. J. Clin. Investig. 2003, 111, 263–271. [Google Scholar] [CrossRef]
  152. Lygre, H.; Høl, P.J.; Solheim, E.; Moe, G. Organic leachables from polymer-based dental filling materials. Eur. J. Clin. Investig. 1999, 107, 378–383. [Google Scholar] [CrossRef]
  153. Rivier, L. Criteria for the identification of compounds by liquid chromatography–mass spectrometry and liquid chromatography–multiple mass spectrometry in forensic toxicology and doping analysis. Anal. Chim. Acta 2003, 492, 69–82. [Google Scholar] [CrossRef]
  154. Mesihää, S.; Ketola, R.A.; Pelander, A.; Rasanen, I.; Ojanperä, I. Development of a GC-APCI-QTOFMS library for new psychoactive substances and comparison to a commercial ESI library. Anal. Bioanal. Chem. 2017, 409, 2007–2013. [Google Scholar] [CrossRef]
  155. Reinstadler, V.; Lierheimer, S.; Boettcher, M.; Oberacher, H. A validated workflow for drug detection in oral fluid by non-targeted liquid chromatography-tandem mass spectrometry. Anal. Bioanal. Chem. 2019, 411, 867–876. [Google Scholar] [CrossRef] [Green Version]
  156. Stein, S. Mass spectral reference libraries: An ever-expanding resource for chemical identification. Anal. Chem. 2012, 84, 7274–7282. [Google Scholar] [CrossRef]
  157. European Commission. 2002/657/EC: Commission Decision of 12 August 2002 Implementing Council Directive 96/23/EC Concerning the Performance of Analytical Methods and the Interpretation of Results (Text with EEA Relevance) (Notified under Document Number C(2002) 3044); European Commission: Maastricht, The Netherlands, 2002. [Google Scholar]
  158. Wataha, J.; Rueggeberg, F.; Lapp, C.; Lewis, J.; Lockwood, P.; Ergle, J.; Mettenburg, D.J. In vitro cytotoxicity of resin-containing restorative materials after aging in artificial saliva. Clin. Oral Investig. 1999, 3, 144–149. [Google Scholar] [CrossRef]
  159. Mocak, J.; Bond, A.M.; Mitchell, S.; Scollary, G. A statistical overview of standard (IUPAC and ACS) and new procedures for determining the limits of detection and quantification: Application to voltammetric and stripping techniques (Technical Report). Pure Appl. Chem. 1997, 69, 297–328. [Google Scholar] [CrossRef]
  160. Kruve, A.; Rebane, R.; Kipper, K.; Oldekop, M.L.; Evard, H.; Herodes, K.; Ravio, P.; Leito, I. Tutorial review on validation of liquid chromatography-mass spectrometry methods: Part I. Anal. Chim. Acta 2015, 870, 29–44. [Google Scholar] [CrossRef]
  161. Wenzl, T.; Haedrich, J.; Schaechtele, A.; Robouch, P.; Stroka, J. Guidance Document on the Estimation of LOD and LOQ for Measurements in the Field of Contaminants in Food and Feed; Publications Office of the European Union: Luxembourg, 2016. [Google Scholar]
  162. Dolan, J.W. The Role of the Signal-to-Noise Ratio in Precision and Accuracy. LCGC Eur. 2006, 19, 12–16. [Google Scholar]
  163. De Nys, S.; Putzeys, E.; Vervliet, P.; Covaci, A.; Boonen, I.; Elskens, M.; Vanoirbeek, J.; Godderis, L.; Van Meerbeek, B.; Van Landuyt, K.L.; et al. A novel high sensitivity UPLC-MS/MS method for the evaluation of bisphenol A leaching from dental materials. Sci. Rep. 2018, 8, 6981. [Google Scholar] [CrossRef]
  164. Barutcigil, K.; Dündar, A.; Batmaz, S.G.; Yıldırım, K.; Barutçugil, Ç. Do resin-based composite CAD/CAM blocks release monomers? Clin. Oral Investig. 2021, 25, 329–336. [Google Scholar] [CrossRef]
  165. Kakonyi, G.; Mulligan, S.; Fairburn, A.W.; Moharamzadeh, K.; Thornton, S.F.; Walker, H.J.; Burrell, M.M.; Martin, N. Simultaneous detection of monomers associated with resin-based dental composites using SPME and HPLC. Dent. Mater. J. 2021, 40, 1007–1013. [Google Scholar] [CrossRef] [PubMed]
  166. Kang, Y.-G.; Kim, J.-Y.; Kim, J.; Won, P.-J.; Nam, J.-H. Release of bisphenol A from resin composite used to bond orthodontic lingual retainers. Am. J. Orthod. Dentofac. Orthop. 2011, 140, 779–789. [Google Scholar] [CrossRef] [PubMed]
  167. Bielicka-Daszkiewicz, K.; Poniedziałek, K. Extraction of organic compounds released from dental materials. Microchem. J. 2021, 169, 106594. [Google Scholar] [CrossRef]
  168. Kościelniak, P.; Kozak, J. Review of univariate standard addition calibration procedures in flow analysis. Crit. Rev. Anal. Chem. 2006, 36, 27–40. [Google Scholar] [CrossRef]
  169. Cuadros-Rodríguez, L.; Gámiz-Gracia, L.; Almansa-López, E.M.; Bosque-Sendra, J.M. Calibration in chemical measurement processes. II. A methodological approach. Trends Anal. Chem. 2001, 20, 620–636. [Google Scholar] [CrossRef]
  170. Zhao, Y.; Liu, G.; Shen, J.X.; Aubry, A.F. Reasons for calibration standard curve slope variation in LC-MS assays and how to address it. Bioanalysis 2014, 6, 1439–1443. [Google Scholar] [CrossRef]
  171. Bisphenol A Analytical Research Task Group. Analytical Method Criteria for the Determination of Bisphenol A in Various Matrices; American Plastics Council (APC), the Association of Plastics Manufacturers in Europe (APME), and the Japan Chemical Industry Association (JCIA): Arlington, VA, USA, 2002. [Google Scholar]
  172. Thompson, M.; Ellison Stephen, L.R.; Wood, R. Harmonized guidelines for single-laboratory validation of methods of analysis (IUPAC Technical Report). Pure Appl. Chem. 2002, 74, 835–855. [Google Scholar] [CrossRef]
  173. ISO 11095:1996; Linear Calibration Using Reference Materials. International Organization for Standardization (ISO): Geneva, Switzerland, 1996.
  174. Samanidou, V.; Hadjicharalampous, M.; Palaghias, G.; Papadoyannis, I. Development and validation of an isocratic HPLC method for the simultaneous determination of residual monomers released from dental polymeric materials in artificial saliva. J. Liq. Chromatogr. Relat. Technol. 2012, 35, 511–523. [Google Scholar] [CrossRef]
  175. Aldhafyan, M.; Silikas, N.; Watts, D.C. Influence of curing modes on monomer elution, sorption and solubility of dual-cure resin-cements. Dent. Mater. 2022. Epub ahead of print. [Google Scholar] [CrossRef]
  176. Sarosi, C.; Moldovan, M.; Soanca, A.; Roman, A.; Gherman, T.; Trifoi, A.; Chisnoiu, A.M.; Cuc, S.; Filip, M.; Gheorghe, G.F.; et al. Effects of Monomer Composition of Urethane Methacrylate Based Resins on the C=C Degree of Conversion, Residual Monomer Content and Mechanical Properties. Polymers 2021, 13, 4415. [Google Scholar] [CrossRef]
  177. Food and Drug Administration. Analytical Procedures and Methods Validation for Drugs and Biologics; Food and Drug Administration: Silver Spring, MD, USA, 2015. [Google Scholar]
  178. Clinical and Laboratory Standards Institute. Measurement Procedure Comparison and Bias Estimation Using Patient Samples; Approved Guideline—Third Edition; Clinical and Laboratory Standards Institute: Malvern, PA, USA, 2013. [Google Scholar]
  179. González, A.G.; Herrador, M.Á. A practical guide to analytical method validation, including measurement uncertainty and accuracy profiles. Trends Anal. Chem. 2007, 26, 227–238. [Google Scholar] [CrossRef]
  180. Van Loco, J.; Elskens, M.; Croux, C.; Beernaert, H. Linearity of calibration curves: Use and misuse of the correlation coefficient. Accredit. Qual. Assur. 2002, 7, 281–285. [Google Scholar] [CrossRef]
  181. European Medicines Agency. Guideline on Bioanalytical Method Validation; European Medicines Agency: Amsterdam, The Netherlands, 2011. [Google Scholar]
  182. Šimková, M.; Tichý, A.; Dušková, M.; Bradna, P. Dental composites—A low-dose source of bisphenol A? Physiol. Res. 2020, 69, S295–S304. [Google Scholar] [CrossRef]
  183. Bationo, R.; Rouamba, A.; Diarra, A.; Beugré-Kouassi, M.L.A.; Beugré, J.B.; Jordana, F. Cytotoxicity evaluation of dental and orthodontic light-cured composite resins. Clin. Exp. Dent. Res. 2021, 7, 40–48. [Google Scholar] [CrossRef]
  184. Diamantopoulou, E.I.; Plastiras, O.E.; Mourouzis, P.; Samanidou, V. Validation of a Simple HPLC-UV Method for the Determination of Monomers Released from Dental Resin Composites in Artificial Saliva. Methods Protoc. 2020, 3, 35. [Google Scholar] [CrossRef]
  185. Cuadros-Rodríguez, L.; Bagur-González, M.G.; Sánchez-Vinas, M.; González-Casado, A.; Gómez-Sáez, A.M. Principles of analytical calibration/quantification for the separation sciences. J. Chromatogr. A 2007, 1158, 33–46. [Google Scholar] [CrossRef]
  186. Oliveira, E.D.C.; Muller, E.I.; Abad, F.; Dallarosa, J.; Adriano, C. Internal standard versus external standard calibration: An uncertainty case study of a liquid chromatography analysis. Química Nova 2010, 33, 984–987. [Google Scholar] [CrossRef] [Green Version]
  187. ISO Guide 33:2015; Reference Materials—Good Practice in Using Reference Materials. International Organization for Standardization (ISO): Geneva, Switzerland, 2015.
  188. Hajslova, J.; Zrostlikova, J. Matrix effects in (ultra)trace analysis of pesticide residues in food and biotic matrices. J. Chromatogr. A 2003, 1000, 181–197. [Google Scholar] [CrossRef]
  189. Hewavitharana, A.K. Internal Standard—Friend or Foe? Crit. Rev. Anal. Chem. 2009, 39, 272–275. [Google Scholar] [CrossRef]
  190. Hu, Y.L.; Chen, Z.P.; Chen, Y.; Shi, C.X.; Yu, R.Q. Generalized multiple internal standard method for quantitative liquid chromatography mass spectrometry. J. Chromatogr. A 2016, 1445, 112–117. [Google Scholar] [CrossRef]
  191. Bader, M. A systematic approach to standard addition methods in instrumental analysis. J. Chem. Educ. 1980, 57, 703–706. [Google Scholar] [CrossRef]
  192. Durner, J.; Spahl, W.; Zaspel, J.; Schweikl, H.; Hickel, R.; Reichl, F.X. Eluted substances from unpolymerized and polymerized dental restorative materials and their Nernst partition coefficient. Dent. Mater. 2010, 26, 91–99. [Google Scholar] [CrossRef]
  193. Pongprueksa, P.; De Munck, J.; Duca, R.C.; Poels, K.; Covaci, A.; Hoet, P.; Godderis, L.; Van Meerbeek, B.; Van Landuyt, K.L. Monomer elution in relation to degree of conversion for different types of composite. J. Dent. 2015, 43, 1448–1455. [Google Scholar] [CrossRef]
  194. Nilsen, B.W.; Jensen, E.; Örtengren, U.; Bang, B.; Michelsen, V.B. Airborne exposure to gaseous and particle-associated organic substances in resin-based dental materials during restorative procedures. Eur. J. Oral Sci. 2019, 127, 425–434. [Google Scholar] [CrossRef] [Green Version]
  195. Bationo, R.; Jordana, F.; Boileau, M.J.; Colat-Parros, J. Release of monomers from orthodontic adhesives. Am. J. Orthod. Dentofac. Orthop. 2016, 150, 491–498. [Google Scholar] [CrossRef]
  196. Finley-Jones, H.J.; Holcombe, J.A. Evaluation of internal standard predictions across instrumental platforms in inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom. 2009, 24, 837–841. [Google Scholar] [CrossRef]
  197. Putzeys, E.; Duca, R.C.; Coppens, L.; Vanoirbeek, J.; Godderis, L.; Van Meerbeek, B.; Van Landuyt, K.L. In-Vitro transdentinal diffusion of monomers from adhesives. J. Dent. 2018, 75, 91–97. [Google Scholar] [CrossRef]
  198. Putzeys, E.; Vercruyssen, C.; Duca, R.C.; Saha, P.S.; Godderis, L.; Vanoirbeek, J.; Peumans, M.; Van Meerbeek, B.; Van Landuyt, K.L. Monomer release from direct and indirect adhesive restorations: A comparative in vitro study. Dent. Mater. 2020, 36, 1275–1281. [Google Scholar] [CrossRef] [PubMed]
  199. Taylor, P.J. Matrix effects: The Achilles heel of quantitative high-performance liquid chromatography–electrospray–tandem mass spectrometry. Clin. Biochem. 2005, 38, 328–334. [Google Scholar] [CrossRef] [PubMed]
  200. Danzer, K.; Currie, L.A. Guidelines for calibration in analytical chemistry. Part I. Fundamentals and single component calibration (IUPAC Recommendations 1998). Pure Appl. Chem. 1998, 70, 993–1014. [Google Scholar] [CrossRef]
  201. Moosavi, S.M.; Ghassabian, S. Linearity of Calibration Curves for Analytical Methods: A Review of Criteria for Assessment of Method Reliability. In Calibration and Validation of Analytical Methods: A Sampling of Current Approaches; InTech: London, UK, 2018; pp. 109–128. [Google Scholar]
Polymers 14 01790 g001 550
Figure 1. HPLC-MS Chromatogram of a Luxatemp Automix Plus (DMG Chemisch-Pharmazeutische Fabrik, Hamburg, Germany) sample immersed in HPLC grade water with diethyl phthalate (DEP) as an internal standard. At the top, the chromatogram and then, from top to bottom, the extracted ion chromatograms of TEGDMA, UDMA, and the internal standard DEP, respectively. Definitive peak identification is accomplished by the relative abundance of the corresponding molecular mass. This chromatogram was prepared for a study on the monomer elution from resin-based temporary crown and bridge materials [120].
Figure 1. HPLC-MS Chromatogram of a Luxatemp Automix Plus (DMG Chemisch-Pharmazeutische Fabrik, Hamburg, Germany) sample immersed in HPLC grade water with diethyl phthalate (DEP) as an internal standard. At the top, the chromatogram and then, from top to bottom, the extracted ion chromatograms of TEGDMA, UDMA, and the internal standard DEP, respectively. Definitive peak identification is accomplished by the relative abundance of the corresponding molecular mass. This chromatogram was prepared for a study on the monomer elution from resin-based temporary crown and bridge materials [120].
Polymers 14 01790 g001
Polymers 14 01790 g002 550
Figure 2. Tandem mass spectrometry fragmentation spectra of derivatized isotope-labeled BPA (top), derivatized unlabeled BPA (middle), and underivatized BPA (bottom). The spectra were obtained by HPLC-MS/MS with negative ionization for native BPA and positive ionization for BPA derivatized with pyridine-3-sulfonyl chloride. The unique and most abundant product ion is highlighted by a blue square. This mass spectrum was prepared for a study on the monomer elution from resin-based temporary crown and bridge materials [120].
Figure 2. Tandem mass spectrometry fragmentation spectra of derivatized isotope-labeled BPA (top), derivatized unlabeled BPA (middle), and underivatized BPA (bottom). The spectra were obtained by HPLC-MS/MS with negative ionization for native BPA and positive ionization for BPA derivatized with pyridine-3-sulfonyl chloride. The unique and most abundant product ion is highlighted by a blue square. This mass spectrum was prepared for a study on the monomer elution from resin-based temporary crown and bridge materials [120].
Polymers 14 01790 g002
Polymers 14 01790 g003 550
Figure 3. Calibration curve of TEGDMA in relation to the internal standard diethyl phthalate (DEP) including the plot of residuals. The data are fitted by a linear regression model and assessed by the determination coefficient r2. This calibration curve was prepared for a study on the monomer elution from resin-based temporary crown and bridge materials [120].
Figure 3. Calibration curve of TEGDMA in relation to the internal standard diethyl phthalate (DEP) including the plot of residuals. The data are fitted by a linear regression model and assessed by the determination coefficient r2. This calibration curve was prepared for a study on the monomer elution from resin-based temporary crown and bridge materials [120].
Polymers 14 01790 g003
Polymers 14 01790 g004 550
Figure 4. (a) HPLC-MS Chromatogram of an ExperTemp sample (Ultradent, South Jordan, USA) immersed in HPLC grade water and Gibco Antibiotic-Antimycotic solution. Due to the overlapping peaks of the antibiotic-antimycotic solution, the peaks corresponding to the masses of TEGDMA and UDMA are not identifiable. (b) Chromatogram of an ExperTemp sample (Ultradent, South Jordan, USA) immersed in pure HPLC grade water. The peaks corresponding to TEGDMA and UDMA are highlighted. This figure was taken from preliminary tests made by our working group for a study on the elution of monomers from resin-based temporary crown and bridge materials [120].
Figure 4. (a) HPLC-MS Chromatogram of an ExperTemp sample (Ultradent, South Jordan, USA) immersed in HPLC grade water and Gibco Antibiotic-Antimycotic solution. Due to the overlapping peaks of the antibiotic-antimycotic solution, the peaks corresponding to the masses of TEGDMA and UDMA are not identifiable. (b) Chromatogram of an ExperTemp sample (Ultradent, South Jordan, USA) immersed in pure HPLC grade water. The peaks corresponding to TEGDMA and UDMA are highlighted. This figure was taken from preliminary tests made by our working group for a study on the elution of monomers from resin-based temporary crown and bridge materials [120].
Polymers 14 01790 g004
Table
Table 1. Recommended extraction ratios according to ISO 10993-12.
Table 1. Recommended extraction ratios according to ISO 10993-12.
Thickness (mm)Extraction ratio ± 10%
≤0.56 cm2/mL
>0.53 cm2/mL
Irregular shaped sample0.1–0.2 g/mL, 6 cm2/mL
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Hampe, T.; Wiessner, A.; Frauendorf, H.; Alhussein, M.; Karlovsky, P.; Bürgers, R.; Krohn, S. Monomer Release from Dental Resins: The Current Status on Study Setup, Detection and Quantification for In Vitro Testing. Polymers 2022, 14, 1790. https://doi.org/10.3390/polym14091790

AMA Style

Hampe T, Wiessner A, Frauendorf H, Alhussein M, Karlovsky P, Bürgers R, Krohn S. Monomer Release from Dental Resins: The Current Status on Study Setup, Detection and Quantification for In Vitro Testing. Polymers. 2022; 14(9):1790. https://doi.org/10.3390/polym14091790

Chicago/Turabian Style

Hampe, Tristan, Andreas Wiessner, Holm Frauendorf, Mohammad Alhussein, Petr Karlovsky, Ralf Bürgers, and Sebastian Krohn. 2022. "Monomer Release from Dental Resins: The Current Status on Study Setup, Detection and Quantification for In Vitro Testing" Polymers 14, no. 9: 1790. https://doi.org/10.3390/polym14091790

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop