Qualitative analysis of dental material ingredients, composite resins and sealants using liquid chromatography coupled to quadrupole time of flight mass spectrometry

Surface alterations and compound release from aligner attachments in vitro

AIM

The aim of the present study was to assess the alterations in morphology, roughness, and composition of the surfaces of a conventional and a flowable composite attachment engaged with aligners, and to evaluate the release of resin monomers and their derivatives in an aqueous environment.

METHODS

Zirconia tooth-arch frames (n = 20) and corresponding thermoformed PET-G aligners with bonded attachments comprising two composite materials (universal-C and flowable-F) were fabricated. The morphological features (stereomicroscopy), roughness (optical profilometry), and surface composition (ATR-FTIR) of the attachments were examined before and after immersion in water. To simulate intraoral use, the aligners were removed and re-seated to the frames four times per day for a 7-day immersion period. After testing, the eluents were analyzed by LC-MS/MS targeting the compounds Bis-GMA, UDMA, 2-HEMA, TEGDMA and BPA and by LC-HRMS for suspect screening of the leached dental material compounds and their degradation products.

RESULTS

After testing, abrasion-induced defects were found on attachment surfaces such as scratches, marginal cracks, loss of surface texturing, and fractures. The morphological changes and debonding rate were greater in F. Comparisons (before-after testing) revealed a significantly lower Sc roughness parameter in F. The surface composition of the aligners after testing showed minor changes from the control, with insignificant differences in the degree of C = C conversion, except for few cases with strong evidence of hydrolytic degradation. Targeted analysis results revealed a significant difference in the compounds released between Days 1 and 7 in both materials. Insignificant differences were found when C was compared with F in both timeframes. Several degradation products were detected on Day 7, with a strong reduction in the concentration of the targeted compounds.

CONCLUSIONS

The use of aligners affects the surface characteristics and degradation rate of composite attachments in an aqueous environment, releasing monomers, and monomer hydrolysates within 1-week simulated use.

Level of BPA contamination in resin composites determines BPA release

OBJECTIVES

Resin composites may release bisphenol A (BPA) due to impurities present in the monomers. However, there is a lack of knowledge regarding the leaching characteristics of BPA from resin composites. Therefore, experimental resin composites were prepared with known amounts of BPA. The objective of this study was (1) to determine which amount of BPA initially present in the material leaches out in the short term and, (2) how this release is influenced by the resin composition.

METHODS

BPA (0, 0.001, 0.01, or 0.1 wt%) was added to experimental resin composites containing 60 mol% BisGMA, BisEMA(3), or UDMA, respectively, as base monomer and 40 mol% TEGDMA as diluent monomer. Polymerized samples (n = 5) were immersed at 37 °C for 7 days in 1 mL of water, which was collected and refreshed daily. BPA release was quantified with UPLC-MS/MS after derivatization with pyridine-3-sulfonyl chloride.

RESULTS

Between 0.47 to 0.67 mol% of the originally added BPA eluted from the resin composites after 7 days. Similar elution trends were observed irrespective of the base monomer. Two-way ANOVA showed a significant effect of the base monomer on BPA release, but the differences were small and not consistent.

SIGNIFICANCE

The released amount of BPA was directly proportional to the quantity of BPA present in the resin composite as an impurity. BPA release was mainly diffusion-based, while polymer composition seemed to play a minor role. Our results underscore the importance for manufacturers only to use monomers of the highest purity in dental resin composites to avoid unnecessary BPA exposure in patients.

Salivary levels of eluents during Invisalign™ treatment with attachments: an in vivo investigation

BACKGROUND

The aim of the present study was to investigate qualitatively and quantitatively the elution of substances from polyester-urethane (Invisalign™) aligners and resin composite attachments (Tetric EvoFlow) in vivo.

METHODS

Patients (n = 11) treated with the aligners and attachments (16 per patient, without other composite restorations) for an average of 20 months, who were planned for attachment removed were enrolled in the study. Patients were instructed to rinse with 50 mL of distilled water upon entry and the rinsing solution was collected (before removal). Then, the attachments were removed with low-speed tungsten carbide burs for adhesive residue removal, a thorough water rinsing was performed immediately after the grinding process to discard grinding particle residues, and subsequently, after a second water-rinsing the solution was collected for analysis (after removal). The rinsing solutions were analyzed for targeted (LC-MS/MS: Bis-GMA, DCDMA, UDMA, BPA) and untargeted (LC-HRMS: screening of leached species and their degradation products) compounds.

RESULTS

Targeted analysis revealed a significant reduction in BPA after attachment removal (4 times lower). Bis-GMA, DCDMA, UDMA were below the detection limit before removal but were all detectable after removal with Bis-GMA and UDMA at quantifiable levels. Untargeted analysis reviled the presence of mono-methacrylate transformation products of Bis-GMA (Bis-GMA-M1) and UDMA (UDMA-M1), UDMA without methacrylate moieties (UDMA-M2), and 4-(dimethylamino) benzoic acid (DMAB), the degradation product of the photo-initiator ethyl-4-(dimethylamino) benzoate (EDMAB), all after attachment removal. Several amino acids and endogenous metabolites were also found both before and after removal.

CONCLUSIONS

Elevated levels of BPA were traced instantaneously in patients treated with Invisalign™ and flowable resin composite attachments for the testing period. BPA was reduced after attachment removal, but residual monomers and resin degradation products were found after removal. Alternative resin formulations and attachment materials may be utilized to reduce eluents.

Degradation products of resin-based materials detected in saliva in vivo

OBJECTIVES

Dental composites remain under scrutiny regarding their (long-term) safety. In spite of numerous studies on the release of monomers both in vitro and in vivo, only limited quantitative data exist on the in vivo leaching of degradation products from monomers and additives. The aim of this observational study was for the first time to quantitatively and qualitatively monitor the release of parent compounds and their degradation products in saliva from patients undergoing multiple restorations.

MATERIALS AND METHODS

Five patients in need of multiple large composite restorations (minimally 5 up to 28 restorations) due to wear (attrition, abrasion, and erosion) were included in the study, and they received adhesive restorative treatment according to the standard procedures in the university clinic for Restorative Dentistry. Saliva was collected at different time points, starting before the restoration up until 24 h after the treatment with composite restorations. Saliva extracts were analyzed by liquid chromatography-mass spectrometry.

RESULTS

Leaching of monomers and degradation products was highest within 30 min after the placement of the restorations. The highest median concentrations of monomers were recorded for UDMA, BisEMA-3, and TEGDMA; yet, besides BisEMA-3 and TEGDMA, no monomers could be detected after 24 h. Mono- and demethacrylated degradation products remained present up to 24 h and concentrations were generally higher than those of monomers. In patients with multiple restorations, degradation products were still present in the sample taken before the next operation, several weeks after the previous operation.

CONCLUSIONS

Exposure to residual monomers and degradation products occurs in the first hours after restoration. Monomers are present in saliva shortly after restoration, but degradation products can be detected weeks after the restoration confirming a long-term release.

CLINICAL SIGNIFICANCE

Future research should focus more on the release of degradation products from monomers and additives from resin-based materials given their prolonged presence in saliva after restoration.

Logistic Regression Analysis of LC-MS/MS Data of Monomers Eluted from Aged Dental Composites: A Supervised Machine-Learning Approach

Compound identification by database searching that matches experimental with library mass spectra is commonly used in mass spectrometric (MS) data analysis. Vendor software often outputs scores that represent the quality of each spectral match for the identified compounds. However, software-generated identification results can differ drastically depending on the initial search parameters. Machine learning is applied here to provide a statistical evaluation of software-generated compound identification results from experimental tandem MS data. This task was accomplished using the logistic regression algorithm to assign an identification probability value to each identified compound. Logistic regression is usually used for classification, but here it is used to generate identification probabilities without setting a threshold for classification. Liquid chromatography coupled with quadrupole-time-of-flight tandem MS was used to analyze the organic monomers leached from resin-based dental composites in a simulated oral environment. The collected tandem MS data were processed with vendor software, followed by statistical evaluation of these results using logistic regression. The assigned identification probability to each compound provides more confidence in identification beyond solely by database matching. A total of 21 distinct monomers were identified among all samples, including five intact monomers and chemical degradation products of bisphenol A glycidyl methacrylate (BisGMA), oligomers of bisphenol-A ethoxylate methacrylate (BisEMA), triethylene glycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA). The logistic regression model can be used to evaluate any database-matched liquid chromatography-tandem MS result by training a new model using analytical standards of compounds present in a chosen database and then generating identification probabilities for candidates from unknown data using the new model.

TMT-based quantitative proteomic analysis reveals the underlying mechanisms of glycidyl methacrylate-induced 16HBE cell malignant transformation

Glycidyl methacrylate (GMA) has been widely used as tackifying/crosslinking copolymer monomer in the industrial section. Occupational and environmental exposure to GMA is inevitable. GMA is classified as a Group 2 A carcinogen. However, it still lacks a sufficient understanding of its carcinogenicity at the protein level. The major pathways and players during the malignant transformation process remain unknown. In this study, we first established and characterized a malignant transformation model using human bronchial epithelial (16HBE) cells exposed to 8 μg/mL GMA. Then the proteomics approach, western-blot analysis as well as quantitative PCR (qPCR) analysis were employed to investigate its underlying mechanisms of carcinogenicity. Our results showed that the 16HBE cells exposed to GMA and passaged to the 40th generation had undergone a malignant transformation. Proteomic analysis revealed that 123 proteins were significantly up-regulated while 160 proteins were down-regulated during the process of malignant transformation. Importantly, further pathway analysis identified the extracellular matrix-receptor (ECM-receptor) interaction pathway to be one of the major players mediating the process and most of the differentially expressed proteins (DEPs) were up-regulated, including two vital proteins, CD44 and MMP14, as well as members from integrin family. These results provide direct proteomic evidence that DEPs related to the ECM-receptor interaction pathway play an active role in reinforcing the carcinogenicity of GMA. The findings of this study might deepen our understanding of the underlying mechanisms of GMA carcinogenicity and thus facilitate the risk assessment of GMA.

A Pilot Study on Monomer and Bisphenol A (BPA) Release from UDMA-Based and Conventional Indirect Veneering Composites

This study aimed to investigate the release of common monomers from conventional (Dialog Vario, Enamel Plus HFO) and UDMA-based indirect veneering composites (VITA VM LC, GC Gradia). Ten cylindrical samples of each material were prepared (n = 40), immersed in HPLC grade water, and incubated for 24 h in an incubation shaker at 37 °C and 112 rpm. Extraction was performed following ISO 10993-12 and monomers were detected and quantified by HPLC-MS/MS. In all the samples, urethane dimethacrylate (UDMA) and bisphenol A (BPA) were quantifiable. Compared to water blanks, BPA levels were only elevated in the eluates from conventional composites. In all other samples, concentrations were in the range of extraneous BPA and were therefore clinically irrelevant. Low concentrations of Bisphenol A-glycidyl methacrylate (BisGMA) were found in one BPA-free composite and in both conventional materials. Statistical analyses showed that BPA-free materials released significantly less BisGMA and no BPA, while UDMA elution was comparable to elution from conventional materials. All measured concentrations were below reported effective cytotoxic concentrations. Considering these results, the substitution of BPA-derivatives with UDMA might be beneficial since BPA-associated adverse effects are ruled out. Further studies should be enrolled to test the biocompatibility of UDMA on cells of the oral environment.

Analytical Methods for Determination of BPA Released from Dental Resin Composites and Related Materials: A Systematic Review

Knowing the impacts of bisphenol A (BPA) on human health, this systematic review aimed to gather the analytical methods for the quantification of BPA release of BPA in dental materials in in vitro and in vivo (biological fluids) studies. A brief critical discussion of the impacts of BPA on human health and the possible association with BPA in dental materials was also presented. The research was carried out by three independent researchers, (according to PRISMA guidelines) in PUBMED and SCOPUS databases, by searching for specific keywords and articles published between January 2011 and February 2022. Seventeen articles met the eligibility criteria and were included in this systematic review: 10 in vitro and 7 in vivo. In in vitro studies, the highest amounts of BPA released were from flowable to conventional resins, followed by resin-modified glass ionomer. In contrast, the smallest amount was released from "BPA-free" composites and CAD-CAM blocks. Regarding in vivo studies, a higher concentration of BPA were found in saliva than urine or blood. The best analytical method for trace quantifying BPA is LC-MS/MS (Liquid Chromatography with Tandem Mass Spectrometry) due to its selectivity, low quantification limits, and the unequivocal identification. However, further studies are required to develop faster and more sensitive methods, in order to obtain more reliable results.

Metabolic profiling of bisphenol A diglycidyl ether in vitro and in vivo

Bisphenol A diglycidyl ethers (BADGE) is one class of human-made chemicals, and it is one of the most widely used raw materials for epoxy resins. As an active compound, BADGE undergoes biotransformation in vitro and in vivo. However, there is a limited understanding of the biotransformation of BADGE and toxicity studies on transformation products. We conducted comprehensive research on the metabolic transformation of BADGE in vitro and in vivo. The results showed that 12 metabolites and 7 metabolites were identified in vitro and in vivo, respectively. Four biotransformation products, including M1 (hydrolysis), M3 (dehydroxylation), M10 (carboxylation), and M11 (glucose conjugation), can be found in both in vitro and in vivo samples. The main metabolic pathways were hydroxylation, carboxylation, cysteine (Cys) conjugation, and glucose conjugation. Besides, our results suggested the existence of metabolic differences in BADGE between species and gender. Further, we investigated toxicities of BADGE metabolites in-silico. Importantly, some hydrolysis (M1, M2), hydroxylation (M7), and oxidation (M8) products showed similar or even higher potential toxicity than BADGE depending on the endpoint. These results enrich the biotransformation profiles of BADGE and provide useful information for understanding its biotransformation in humans and a reference for the comprehensive assessment for human health risk.

Monomer release from dental restorative materials containing dimethacrylate resin after bleaching

OBJECTIVE

The aim of this study is to determine the type and amount of monomer released over time after bleaching was applied to dental restorative materials containing dimethacrylate resin.

MATERIALS AND METHODS

Thirteen different restorative materials containing dimethacrylate resin were used in this study. Twenty samples were prepared from each material and the samples were randomly divided into 4 subgroups, namely, office bleaching, home bleaching, and separate control group for each of the bleaching methods. After bleaching, the samples were stored in 75% ethanol solution for 1, 14, and 28 days. Analysis of the samples collected to determine the type and amount of residual monomer released from the materials was performed using a liquid chromatography-tandem mass/mass spectrometer (LC-MS/MS). Data were analyzed using Friedman and Kruskal-Wallis tests. Statistical significance level was taken as p < 0.05.

RESULTS

In terms of bleaching groups, mostly no significant difference was found between the groups in each time period in restorative materials (p > 0.05). In terms of time periods, it was determined that the amount of release of all monomers was decreased over time. In terms of restorative materials, the highest monomer release was detected in composite resin groups and the least monomer release was detected in CAD/CAM blocks.

CONCLUSION

Although monomers were released from all materials, bleaching did not affect the amount of released monomer. Amounts of released monomers were generally below toxic limits.

CLINICAL RELEVANCE

Within the limits of this study, bleaching does not significantly affect monomer release in restorative materials containing dimethacrylate resin.

Utilizing a degradation prediction pathway system to understand how a novel methacrylate derivative polymer with flipped external ester groups retains physico-mechanical properties following esterase exposure

OBJECTIVE

The region of failure for current methacrylates (i.e. derivatives of acrylates) are ester bond linkages that hydrolyze in the presence of salivary and bacterial esterases that break the polymer network backbone. This effect decreases the mechanical properties of methacrylate-based materials.

METHODS

The ethylene glycol dimethacrylate (EGDMA) or novel ethylene glycol ethyl methacrylate (EGEMA) discs were prepared using 40 µL of the curing mixture containing photo/co-initiators for 40 s in a PTFE mold at 1000 mW/cm². The degree of conversion was used as a quality control measure for the prepared discs, followed by physical, mechanical, and chemical characterization of discs properties before and after cholesterol esterase treatment.

RESULTS

After 9 weeks of standardized cholesterol esterase (CEase) exposure, EGDMA discs showed exponential loss of material (p = 0.0296), strength (p = 0.0014) and increased water sorption (p = 0.0002) compared to EGEMA discs. We integrated a degradation prediction pathway system to LC/MS and GC/MS analyses to elucidate the degradation by-products of both EGEMA and EGDMA polymers. GC/MS analysis demonstrated that the esterase catalysis was directed to central polymer backbone breakage, producing ethylene glycol, for EGDMA, and to side chain breakage, producing ethanol, for EGEMA. The flipped external ester group linkage design is attributed to EGEMA showing higher resistance to esterase biodegradation and changes in mechanical and physical properties than EGDMA.

SIGNIFICANCE

EGEMA is a potential substitute for common macromer diluents, such as EGDMA, based on its resistance to biodegradation effects. This work inspires the flipped external group design to be applied to analogs of current larger, hydrophobic strength bearing macromers used in future dental material formulations.

A comparative in vitro study on monomer release from bisphenol A-free and conventional temporary crown and bridge materials

This study aimed to investigate the release of common monomers from two conventional and two bisphenol A (BPA)-free temporary crown and bridge materials. Cylindrical samples of all materials were prepared (N = 90; five samples for each material and cycle of analysis). All samples were immersed in high-performance liquid chromatography (HPLC)-grade water and incubated for 1 h, 12 h, 24 h, and 7 days in an incubation shaker at 37°C and 112 rpm. Extraction was performed in accordance with ISO 10993-12. Eluted monomers were detected and quantified by HPLC coupled with ultraviolet-visible spectroscopy and mass spectrometry (HPLC-UV/Vis-MS). Analysis of BPA was performed by HPLC coupled with ultraviolet-visible spectroscopy (HPLC-UV/Vis) and positive results were verified by HPLC-tandem mass spectrometry (HPLC-MS/MS). Neither bisphenol A-glycidyl methacrylate (Bis-GMA) nor BPA was quantifiable in any of the crown and bridge samples investigated in the present study. However, all samples contained triethylene glycol dimethacrylate (TEGDMA) and/or urethane dimethacrylate (UDMA) after 24 h of incubation. Statistical analysis showed that significantly more UDMA was released from the BPA-free materials than from the conventional materials. All concentrations of UDMA measured were below the effective cytotoxic concentrations previously reported. However, for a few materials, especially BPA-free temporary crown and bridge materials, the levels of UDMA were above previously reported potentially harmful concentrations for local cells. As BPA-free materials were introduced as being more biocompatible than materials containing BPA, substitution of Bis-GMA with UDMA should be further investigated.

A novel methacrylate derivative polymer that resists bacterial cell-mediated biodegradation

This study tests biodegradation resistance of a custom synthesized novel ethylene glycol ethyl methacrylate (EGEMA) with ester bond linkages that are external to the central polymer backbone when polymerized. Ethylene glycol dimethacrylate (EGDMA) with internal ester bond linkages and EGEMA discs were prepared in a polytetrafluoroethylene (PTFE) mold using 40 μl macromer and photo/co-initiator mixture cured for 40 s at 1000 mW/cm² . The discs were stored in the constant presence of Streptococcus mutans (S. mutans) in Todd Hewitt Yeast + Glucose (THYE+G) media up to 9 weeks (n = 8 for each macromer type) and physical/mechanical properties were assessed. Initial measurements EGEMA versus EGDMA polymer discs showed equivalent degree of conversion (45.69% ± 2.38 vs. 46.79% ± 4.64), diametral tensile stress (DTS; 8.12± 2.92 MPa vs. 6.02 ± 1.48 MPa), and low subsurface optical defects (0.41% ± 0.254% vs. 0.11% ± 0.074%). The initial surface wettability (contact angle) was slightly higher (p ≤ .012) for EGEMA (62.02° ± 3.56) than EGDMA (53.86° ± 5.61°). EGDMA showed higher initial Vicker's hardness than EGEMA (8.03 ± 0.88 HV vs. 5.93 ± 0.69 HV; p ≤ .001). After 9 weeks of S. mutans exposure, EGEMA (ΔDTS-1.30 MPa) showed higher resistance to biodegradation effects with a superior DTS than EGDMA (ΔDTS-6.39 MPa) (p = .0039). Visible and scanning electron microscopy images of EGEMA show less surface cracking and defects than EGDMA. EGDMA had higher loss of material (18.9% vs. 8.5%, p = .0009), relative changes to fracture toughness (92.5% vs. 49.2%, p = .0022) and increased water sorption (6.1% vs. 1.9%, p = .0022) compared to EGEMA discs. The flipped external ester group linkage design is attributed to EGEMA showing higher resistance to bacterial degradation effects than an internal ester group linkage design methacrylate.

Bisphenol A release from short-term degraded resin-based dental materials

OBJECTIVES

There is still much debate about the release of bisphenol A (BPA) from resin-based dental materials. Therefore, this study aimed to quantify BPA present as an impurity and to evaluate whether their degradation by salivary, bacterial, and chemical challenges could increase its release.

METHODS

BPA was determined in three different amounts (300, 400, and 500 µg) of eight unpolymerized resin-based materials (four composites, one fissure sealant, two adhesives and one root canal sealer). Next, polymerized samples (n = 5) of each material were immersed in 1 mL of whole human pooled saliva collected from adults, Streptococcus mutans (2 × 10⁷ CFU/mL), and acidic (0.1 M HCl), alkaline (0.1 M NaOH), and control media, respectively. The amount of BPA was quantified using an UPLC-MS/MS method including derivatization of BPA by pyridine-3-sulfonyl chloride.

RESULTS

Only the composites contained trace amounts of BPA above the limit of quantification (ranging from 301±32 pg PBA/mg to 1534±62 pg BPA/mg), most likely as impurity from the synthesis of the monomers. The amounts of BPA released from polymerized materials upon salivary and bacterial degradation were too low for accurate quantification, but in water, quantifiable amounts of BPA were released from all materials. In alkaline media, the BPA release from two composites was significantly decreased, while the release from one adhesive was significantly increased, compared to water.

CONCLUSIONS

BPA already present in unpolymerized resin-based materials may account for the release of BPA after polymerization. There was no clear indication that short-term material degradation leads to increased release of BPA.

Identification of chemicals leaching from dental resin-based materials after in vitro chemical and salivary degradation

OBJECTIVES

Only little is known about degradation of methacrylate monomers. Therefore, using in vitro chemical and saliva degradation this study aimed to identify the degradation products of organic compounds present in resin-based dental materials.

METHODS

Ten dental monomers and nine polymerized dental resin-based materials were immersed for 24 h in chemical media (0.1 M HCl, 0.1 M NaOH) and human pooled saliva in order to identify leached monomers and degradation products from chemical and saliva degradation. Samples were analyzed using liquid chromatography coupled to high-resolution mass spectrometry to identify previously unknown degradation products.

RESULTS

During in vitro chemical degradation, uncured monomers were rapidly hydrolyzed into mono- and demethacrylated degradation products. During chemical degradation in alkaline conditions of polymerized materials, considered the worst-case scenario, only degradation products could be detected. In acidic conditions, monomers and their degradation products were detected. In addition, different additives such as EDMAB, DMPA and HMBP were present in acidic degradation samples. Degradation in human pooled saliva for 24 h to mimic the in vivo situation, resulted in the identification of both monomers and their degradation products.

CLINICAL SIGNIFICANCE

Using state-of-the-art high-resolution mass spectrometry previously unknown degradation products of commonly used monomers were identified for the first time. Results show that patients may be exposed to monomers and their degradation products in the first 24 h after restorative procedures. The results provide a base for further research on the degradation of resin-based dental composites in order to assess their safety using elution and toxicity studies.

Identification of chemicals of emerging concern in urine of Flemish adolescents using a new suspect screening workflow for LC-QTOF-MS

An essential step in human biomonitoring or molecular epidemiology programs is to estimate human exposure to environmental chemicals. Despite significant progress in the capabilities of analytical methods, the number of pollutants and their metabolites keeps increasing continuously. Some of these relatively unknown chemicals of emerging concern (CECs) may pose significant health risks to humans and biota, but remain virtually undetected in traditional HBM-studies. Non-target and suspect screening techniques based on high-resolution mass spectrometry (HRMS) perform the detection and identification of compounds without any a priori compound selection or chemical information and provide a more holistic overview of human exposure. In this study, 50 urine samples (25 female and 25 male) from a larger cohort of the Flemish Environment and Health Study (FLEHS IV, 2016-2020) have been submitted to suspect screening analysis, with the aim of detecting and identifying new CECs. For this purpose, an analytical method has been developed, optimised and evaluated in terms of analytical performance. Satisfactory results were obtained in terms of reproducibility, sensitivity and quality control. Data-mining was performed through the combination of two different workflows. The use of two complementary workflows enhanced the number of identified compounds. As a result, 45 CECs have been identified with a level of confidence ranged between 3 and 1. Most of the identified compounds were metabolisation products, many of which were currently not included in the targeted measurements of FLEHS IV. The identified chemicals and metabolites could be used as candidate biomarkers of exposure in future studies. Overall, the newly developed suspect screening workflow of this pilot study provided complementary and promising results for future HBM-programs.

Long-term elution of bisphenol A from dental composites

OBJECTIVES

BPA release from composites on the short term has been reported in several in-vitro and in-vivo studies. However, it remains unclear whether these materials also leach BPA on the long term. Even though composites may release various (BPA-based) methacrylate monomers up to one year, quantitative data about BPA have not been reported due to the lack of a sensitive method to accurately quantify low levels of BPA. In this context, the aim of the study was to quantify the one-year release of BPA with an optimized analytical method.

METHODS

Composite disks (n = 6, 6 mm diameter and 2 mm height) from four commercial materials (G-ӕnial Posterior, Venus, Ceram.x mono and Filtek Supreme XTE) were immersed in 1 mL of water or ethanol as extraction solvent and stored in the dark at 37 °C. The extraction solvent was renewed weekly for a period of 52 weeks. Samples were derivatized with pyridine-3-sulfonyl chloride before analysis with ultra-pressure liquid chromatography tandem mass spectrometry (UPLC-MS/MS).

RESULTS

Derivatizing BPA increased the sensitivity of the analytical method and allowed accurate quantification of very low levels of BPA (i.e. 0.78 pmol BPA). BPA eluted continuously in ethanol from all four tested composites over a period of one year. BPA elution was clearly higher when ethanol was used as extraction solution. In water, BPA eluted could be detected up to one year, but levels could not be accurately quantified anymore after several weeks.

SIGNIFICANCE

Composites can be considered as a potential long-term source of BPA, and thus should not be neglected when assessing the overall exposure to endocrine disrupting chemicals.

Bisphenol A as degradation product of monomers used in resin-based dental materials

OBJECTIVE

There is still much debate about the release of bisphenol-A (BPA) from dental materials. Therefore, this study aimed to quantify BPA present as an impurity in both BPA-based and non-BPA-based monomers and to evaluate whether these monomers may degrade to BPA upon salivary, bacterial, and chemical challenges.

METHODS

BPA was determined in three different amounts (1, 2, and 3 μmol) of each monomer (TEGDMA, UDMA, mUDMA, BisGMA, BisEMA-3, -6, -10, -30, BisPMA, EBPADMA urethane, BADGE, and BisDMA). Next, the monomers (3 μmol) were immersed in whole human pooled saliva collected from adults, Streptococcus mutans (2 × 10⁷ CFU/mL), and acidic (0.1 M HCl), alkaline (0.1 M NaOH), and control media. The amount of BPA was quantified using a specific and highly sensitive UPLC-MS/MS method including derivatization of BPA by pyridine-3-sulfonyl chloride.

RESULTS

The monomers BisGMA and BisEMA-3 contained trace amounts (0.0006% and 0.0025%, respectively) of BPA as impurities of their synthesis process. BPA concentrations increased when the monomers BisGMA, BisEMA-3, BisEMA-6, BisEMA-10, BisPMA and BADGE were exposed to saliva and S. mutans, indicating degradation of a small amount of monomer into BPA. In addition, BisPMA and BADGE degraded into BPA under alkaline conditions. The conversion rate of the monomers into BPA ranged between 0.0003% and 0.0025%.

SIGNIFICANCE

Impurities and degradation of BPA-based monomers may account for the release of BPA from resin-based dental materials. Even though the detected amounts of BPA due to monomer impurity were small, manufacturers of dental materials can reduce the BPA content by using only monomers of the highest purity. Considering the overall current trend towards BPA-free materials, it may be recommendable to investigate whether non-BPA based monomers can be used in dental resin-based materials.

Determinants of exposure levels of bisphenols in flemish adolescents

The broadly used industrial chemical bisphenol A (BPA), applied in numerous consumer products, has been under scrutiny in the past 20 years due to its widespread detection in humans and the environment and potential detrimental effects on human health. Following implemented restrictions and phase-out initiatives, BPA is replaced by alternative bisphenols, which have not received the same amount of research attention. As a part of the fourth cycle of the Flemish Environment and Health Study (FLEHS IV, 2016-2020), we monitored the internal exposure to six bisphenols in urine samples of 423 adolescents (14-15 years old) from Flanders, Belgium. All measured bisphenols were detected in the study population, with BPA and its alternatives bisphenol F (BPF) and bisphenol S (BPS) showing detection frequencies > 50%. The reference values show that exposure to these compounds is extensive. However, the urinary BPA level decreased significantly in Flemish adolescents compared to a previous cycle of the FLEHS (2008-2009). This suggests that the replacement of BPA with its analogues is ongoing. Concentrations of bisphenols measured in the Flemish adolescents were generally in the same order of magnitude compared to recent studies worldwide. Multiple regression models were used to identify determinants of exposure based on information on demographic and lifestyle characteristics of participants, acquired through questionnaires. Some significant determinants could be identified: sex, season, smoking behavior, educational level of the parents, recent consumption of certain foods and use of certain products were found to be significantly associated with levels of bisphenols. Preliminary risk assessment showed that none of the estimated daily intakes (EDIs) of BPA exceeded the tolerable daily intake, even in a high exposure scenario. For alternative bisphenols, no health-based guidance values are available, but in line with the measured urinary levels, their EDIs were lower than that of BPA. This study is, to the best of our knowledge, the first to determine internal exposure levels of other bisphenols than BPA in a European adolescent population.

Effects of Environment and Lifestyle Factors on Premature Ovarian Failure

Premature ovarian insufficiency (POI) or primary ovarian failure is defined as a cessation of the menstrual cycle in women younger than 40 years old. It is strictly defined as more than 4 months of oligomenorrhea or amenorrhea in a woman <40 years old, associated with at least two follicle-stimulating hormone (FSH) levels >25 U/L in the menopausal range, detected more than 4 weeks apart. It is estimated that POI was affected 1 and 2% of women. Although 80% of POI cases are of unknown etiology, it is suggested that genetic disorder, autoimmune origin, toxins, and environmental factors, as well as personal lifestyles, may be risk factors of developing POI. In this section, we will discuss the influences of environmental and lifestyle factors on POI. Moreover updated basic research findings regarding how these environmental factors affect female ovarian function via epigenetic regulations will also be discussed.

Short-term variability of bisphenols in spot, morning void and 24-hour urine samples

Due to worldwide regulations on the application of the high production volume industrial chemical bisphenol A (BPA) in various consumer products, alternative bisphenols such as bisphenol F (BPF) and bisphenol S (BPS) are increasingly used. To assess human exposure to these chemicals, biomonitoring of urinary concentrations is frequently used. However, the short-term variability of alternative bisphenols has not been evaluated thoroughly yet, which is essential to achieve a correct estimation of exposure. In this study, we collected all spot urine samples from ten healthy adults for five consecutive days, and an additional 24 h pooled sample. We measured the concentrations of seven bisphenols (BPAF, BPF, BPA, BPB, BPZ, BPS and BPAP) in these samples using gas chromatography coupled to tandem mass spectrometry. BPA, BPF and BPS were frequently found in spot samples (>80%), while bisphenol AP (BPAP) was detected in 43% of spot samples. Calculations of intra-class correlation coefficients (ICCs) showed that reproducibility of these four bisphenols was relatively poor (<0.01-0.200) but improved when concentrations were corrected for urine dilution using creatinine levels (0.128-0.401). Of these four bisphenols, BPF showed the best reproducibility (ICC 0.200-0.439) and BPS the most variability (ICC <0.01-0.128). In general, the within-participant variability of bisphenol levels was the largest contributor to the total variance (47-100%). We compared repeated first morning voids to 24 h pooled urine and found no significantly different concentrations for BPA, BPF, BPS, or BPAP. Levels of BPA and BPF differed significantly depending on the sampling time throughout the day. The findings in this study suggest that collecting multiple samples per participant over a few days, in predefined time windows throughout the day, could result in a more reliable estimation of internal exposure to bisphenols.

A Novel Dental Polymer with a Flipped External Ester Group Design that Resists Degradation via Polymer Backbone Preservation

Current dental sealants with methacrylate based chemistry are prone to hydrolytic degradation. A conventional ethylene glycol dimethacrylate (EGDMA) was compared to a novel methacrylate monomer with a flipped external ester group (ethylene glycol ethyl methacrylate - EGEMA) that was designed to resist polymer degradation effects. Fourier transform infrared spectroscopy and water contact angle confirmed a comparable degree of initial conversion and surface wettability for EGDMA and EGEMA. EGDMA disks initially performed better compared to EGEMA as suggested by higher surface hardness and 1.5 times higher diametral tensile strength (DTS). After 15 weeks of hydrolytic and accelerated aging, EGDMA and EGEMA DTS was reduced by 88% and 44% respectively. This accelerated aging model resulted in 3.3 times higher water sorption for EDGMA than EGEMA disks. EGDMA had an increase in grain boundary defects and visible erosion sites with accelerated aging, while for EGEMA the changes were not significant.

Human phase I in vitro liver metabolism of two bisphenolic diglycidyl ethers BADGE and BFDGE

Root canal sealers are commonly used to endodontically treat teeth with periapical infections. Some root canal sealers based on epoxy resin contain bisphenol A diglycidyl ether (BADGE) and bisphenol F diglycidyl ether (BFDGE). The presence of these chemicals is of concern due to the close contact to the blood stream at the apex and the long setting times of up to 24 h. These chemicals, or any of their degradation products or metabolites, can then exert their toxic effects before being excreted. This study aimed to identify the phase I in vitro biotransformation products of BADGE and BFDGE using human liver microsomes. During incubation with microsomal fractions, the epoxides were rapidly hydrolysed in a NADPH independent manner resulting in the formation of BADGE.2H₂O and BFDGE.2H₂O. Further, oxidative reactions, such as hydroxylation and carboxylation, generated other BADGE metabolites, such as BADGE.2H₂O-OH and BADGE.H₂O.COOH, respectively. For BFDGE, further oxidation of BFDGE.2H₂O led to the newly reported carboxylic acid, BFDGE.H₂O.COOH. In total, three specific metabolites have been identified which can serve in future human biomonitoring studies of BADGE and BFDGE.

Do resin-based composite CAD/CAM blocks release monomers?

OBJECTIVE

The present study aimed to identify and quantify the elution of monomers of five different resin-based CAD/CAM blocks (RCBs) using HPLC.

METHODS

Five different RCBs were used in the study: GC Cerasmart (CS), Voco Grandio blocs (GR), 3M Lava Ultimate (LU), Shofu Block (SB), and Vita Enamic (VE). Fifteen samples from each material were prepared using a low-speed precision diamond saw (ISOMET Buehler, Lake Bluff, IL, USA) at 5 × 5 × 4 mm size. After the preparation of samples, an extraction solution was mixed with %75/%25 ethanol/water. The samples were stored in the amber-colored bottles during three different immersed periods as 1 h, 24 h, and 90 days (n = 5). After immersion, 0.5 ml solutions were taken from each bottle and analyzed using HPLC.

RESULTS

A total of 16.7 μg/ml of monomers from SB, 13.4 μg/ml of monomers from GR, 13.2 μg/ml of monomers from CS, and 6.7 μg/ml of monomers from LU were found after 3-m immersion. TEGDMA after 3-m of immersion was only released from the SB group, and also BisEMA was released from the CS group. Among the specimens immersed for 1 h, UDMA was released the least from the LU group and the most from the GR group (p < 0.05). Correspondingly, 24 h and 3 m after immersion, the highest release of monomers was found in the GR (p < 0.05).

CONCLUSIONS

When the monomer release from RCBs was evaluated, it was shown that these materials released methacrylate-based monomers except VE, especially if they were kept in a solvent solution for a long time such as 3 m.

CLINICAL SIGNIFICANCE

The novel resin-based CAD/CAM blocks might monomer release, which may cause cytotoxic effects. But, the detected amount of monomer release is below the estimated daily limit.

Validation of a Simple HPLC-UV Method for the Determination of Monomers Released from Dental Resin Composites in Artificial Saliva

Bisphenol-A (BPA), bisphenol A glycerolate dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA) are organic monomers that can be released from dental composites into the oral cavity. Over specific concentrations, they can act as endocrine disruptors or cause toxic effects. The purpose of this work is to develop and validate an analytical method to determine BPA, Bis-GMA, TEGDMA, and UDMA monomers released from synthetic dental resins in artificial saliva. The method was validated before its application to new hybrid ceramic materials used in computer-aided design and computer-aided manufacturing (CAD/CAM) restorations to determine the release of monomers in various time intervals (e.g., 24 h, and 7, 14, 30, and 60 days), both in methanolic solutions, as well as in artificial saliva. Chromatographic analysis was performed isocratically on a Perfect Sil Target ODS-3 analytical column (250 mm × 4.6 mm, 5 µm) with CH₃CN/H₂O, 58/42% v/v as mobile phase within 23 min. The developed method was validated in terms of selectivity, linearity, accuracy, and precision.

Airborne exposure to gaseous and particle-associated organic substances in resin-based dental materials during restorative procedures

Dental composite dust has been shown to act as a vehicle for methacrylates in vivo/in vitro. The objective of this study was to assess airborne exposure of dental personnel to gaseous and particle-associated organic constituents from resin-based dental materials in a simulated clinic. Sampling of total aerosol fractions and gaseous substances was performed by dental students carrying particle filters and gas sorbents attached to a personal pump during preclinical restorative procedures in phantom models (n = 13). Water from the phantoms was sampled. Organic substances were extracted from the sampled water, particle filters, and gas sorbents. Qualitative and quantitative analyses were performed by gas chromatography-mass spectrometry (GC-MS) and ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS). The methacrylates 2-hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA) and the additives camphorquinone (CQ), butylated hydroxytoluene (BHT), and ethyl 4-(dimethylamino)benzoate (DMABEE), were quantified in the gas and particle fractions sampled. A positive-control experiment was conducted. No methacrylates were detected in the gas or particle fractions sampled, whereas strong signals for methacrylates were detected in the positive controls, matching the analysis of the uncured material. In addition, TEGDMA and DMABEE were quantified in the sampled water. Airborne exposure to constituents in resin-based dental materials was below the detection limit. However, the extent of exposure is probably dependent on the procedure, preventive measures, and type of materials used.