Embryonic-fetal toxicity and teratogenic effects of a group of methacrylate esters in rats

Suicide by Ethyl Methacrylate Ingestion

ABSTRACT

This case report characterizes a unique way in which suicide was accomplished through ingestion of chemicals typically used to create acrylic fingernails that resulted in death. Ethyl methacrylate and acrylic powder are commonly combined to form acrylic nails in nail salons. The process of applying acrylic nails utilizes each substance by mixing both before it typically solidifies within seconds of combining the two compounds. Ingestion of these compounds has not been previously described within the medical literature. The decedent was a nail technician at a local salon. He was found unresponsive in his yard which led to a 911 call. At the scene, a mostly empty 16-oz bottle of ethyl methacrylate, a chemical used at the salon where he worked, was found. At autopsy, the decedent's body had a strong chemical odor consistent with odors present at nail salons. Significant gastrointestinal tract damage was seen including discoloration within the esophagus, and the stomach contained a molded, hardened nail compound. The cause of death was ruled as complications of nail acrylic powder and liquid ethyl methacrylate ingestion. This case shows the unusual findings seen at autopsy from a decedent who committed suicide by ingestion of ethyl methacrylate with acrylic powder.

A Roadmap for Navigating Occupational Exposures for Surgeons: A Special Consideration for the Pregnant Surgeon

SUMMARY

Surgeons are exposed to occupational hazards daily. Risks include chemical, biological, and physical hazards that place providers at risk of serious harm. Departmental policies or written guides to help pregnant surgeons navigate the hospital are lacking. In response to the scarcity in the literature, the authors have summarized current guidelines and recommendations to aid surgeons in making an informed decision. In addition, the authors present a brief narrative of the impact of these exposures during pregnancy and methods of transmission and, where relevant, include specialties that are at risk of these exposures.

Clinical Issues-July 2021

Debris in sterilized instrument sets Key words: organic debris, inorganic debris, instrument sets, sterile processing, sterilizing agent. Preventing debris in sterilized instrument sets Key words: debris, instrument sets, sterile processing equipment, instructions for use (IFU), quality assurance. Bone cement precautions during pregnancy Key words: bone cement, exposure, methyl methacrylate (MMA), pregnant. Using a bed sheet or blanket for positioning Key words: patient positioning devices, improvised positioning device, pressure distribution, skin shear, pressure injury. Laundering of cloth head coverings Key words: laundering, head covering, reusable cloth hat, surgical attire, disposable bouffant.

Is methylmethacrylate toxic during pregnancy and breastfeeding?--- a systematic review

Introduction

Methyl methacrylate (MMA) is commonly used in the fields of dentistry and orthopaedic surgery. However, there remain concerns for the occupational hazards of MMA, particularly during pregnancy and breastfeeding.

Methods

We performed a systematic review of studies on effects that MMA may have in pregnancy in the context of exposure during orthopaedic surgery and dentistry. Review articles, studies lacking statistical data, single case reports and other evidence level V studies were excluded.

Results

Nine studies were included. One basic science study demonstrated an increase in neuronal cell lysis and shrunken cell bodies when neocortical neurons were exposed to MMA monomer. Three animal studies exposed pregnant rodents to MMA via intraperitoneal injection or inhalation. Exposed fetuses in two studies had an increase in gross abnormalities such as hemangiomas, while there was no increase in teratologic effects in the third study. In dental workers exposed to MMA, two retrospective cohort studies did not find a statistically significant increase in birth defects or miscarriage. After exposure to MMA during total joint arthroplasty, two studies found that MMA levels were undetectable in the mothers’ serum or breast milk. One study measuring the airborne levels of MMA during simulated joint arthroplasty found that concentrations never exceeded 1% of the recommended limit set forth by the Occupational Safety and Health Administration (OSHA).

Conclusions

Potential teratologic effects of MMA cannot be excluded by existing evidence. However, the typical MMA exposure levels for dental and orthopaedic personnel appear to be substantially less than currently proposed exposure limits.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42836-020-00059-z.

Mechanistic insight into 3-methylmercaptopropionate metabolism and kinetical regulation of demethylation pathway in marine dimethylsulfoniopropionate-catabolizing bacteria

The vast majority of oceanic dimethylsulfoniopropionate (DMSP) is thought to be catabolized by bacteria via the DMSP demethylation pathway. This pathway contains four enzymes termed DmdA, DmdB, DmdC and DmdD/AcuH, which together catabolize DMSP to acetylaldehyde and methanethiol as carbon and sulfur sources respectively. While molecular mechanisms for DmdA and DmdD have been proposed, little is known of the catalytic mechanisms of DmdB and DmdC, which are central to this pathway. Here, we undertake physiological, structural and biochemical analyses to elucidate the catalytic mechanisms of DmdB and DmdC. DmdB, a 3-methylmercaptopropionate (MMPA)-coenzyme A (CoA) ligase, undergoes two sequential conformational changes to catalyze the ligation of MMPA and CoA. DmdC, a MMPA-CoA dehydrogenase, catalyzes the dehydrogenation of MMPA-CoA to generate MTA-CoA with Glu435 as the catalytic base. Sequence alignment suggests that the proposed catalytic mechanisms of DmdB and DmdC are likely widely adopted by bacteria using the DMSP demethylation pathway. Analysis of the substrate affinities of involved enzymes indicates that Roseobacters kinetically regulate the DMSP demethylation pathway to ensure DMSP functioning and catabolism in their cells. Altogether, this study sheds novel lights on the catalytic and regulative mechanisms of bacterial DMSP demethylation, leading to a better understanding of bacterial DMSP catabolism.

Final Report on Ethyl Methacrylate

Ethyl Methacrylate is the ester of ethyl alcohol and methacrylic acid used as the major structural monomer of artificial fingernail formulations that are cross-linked with one or more multifunctional methacrylates. Ethyl methacrylate monomer is polymerized rapidly and very little free monomer is available even during filing of the fingernails. The oral LD50 for rats ranged from 12.7 to 18.14 g/kg, with lesions in the respiratory system and hemoglobinuria observed in treated animals. Ocular, nasal, and respiratory tract irritation was observed in acute inhalation tests using rats. Very little toxicity was seen in subchronic studies using rabbits. Ethyl Methacrylate caused irritation and vehicle dependent sensitization in animals, but no photosensitization. Evidence of embryotoxic and teratogenic effects were observed in pregnant rats after intraperitoneal injection of Ethyl Methacrylate at a range of concentrations. Both positive and negative mutagenicity test data were found. Clinical testing showed little evidence of irritation, although case studies report allergic contact dermatitis as a result of exposure to Ethyl Methacrylate and related methacrylates with application of artificial fingernails. Occupational contact dermatitis from acrylates and methacrylates are also reported, with some evidence for cross-reactivity between the two chemical classes. Based on the sensitizing potential of this ingredient the CIR Expert Panel recommended that fingernail enhancement formulations with Ethyl Methacrylate be applied only by trained individuals and that the ingredient not be used in products intended for retail sale (currently, these products are believed to be sold only for application by a trained individual). Because of the low likelihood of significant exposure if such formulations are applied properly, the Expert Panel concluded that the ingredient is safe as used, with the caveat that skin contact should be avoided.

Airborne Exposure of Methyl Methacrylate During Simulated Total Hip Arthroplasty and Fabrication of Antibiotic Beads

As the use of cement remains prevalent in orthopedic surgery, so do concerns over the safety of its active ingredient, methyl methacrylate (MMA). The Occupational Health and Safety Agency (OSHA) limits the airborne exposure to 100 parts per million (ppm) averaged over an 8 hour period. We measured MMA exposure to operating room personnel during simulated total hip arthroplasty (THA), antibiotic bead fabrication and simulated spill of MMA. Cumulative and peak exposures during simulated THA and antibiotic bead fabrication did not exceed OSHA limits of 100ppm. Vacuum mixing and greater distance from the vapor source reduced measured MMA exposure. Spilled MMA led to prolonged and elevated MMA levels. MMA levels returned to a negligible level in all scenarios by 20 minutes after mixing.

Theoretical investigation of an atmospherically important reaction between methyl methacrylate and Cl atom: A mechanistic and kinetic approach

A theoretical investigation of the mechanism, kinetics and probable product analysis of the Cl -initiated oxidation reaction of methyl methacrylate (MMA) is presented in this paper. The major degradation pathway of MMA is the Cl -addition to the terminal carbon of the olefinic bond. Beside this, energetic and mechanism of other possible reaction pathways are discussed in detail. In addition, the mechanism for the secondary reactions in presence of O 2 and NO has also been presented. Cl -addition to the double bond takes place via formation of the pre-reactive complex as these reaction channel passes through negative activation barrier. Energetics and thermochemical analysis have been studied at the MP2=Full/6-311++g(d,p) level of theory. The rate constant of the Cl -addition reaction has been calculated using conventional transition state theory (CTST) at 1 atm pressure and 250–350 K temperature range.

Occupational hazards for pregnant or lactating women in the orthopaedic operating room

Pregnant or lactating staff working in the orthopaedic operating room may be at risk of occupational exposure to several hazards, including blood-borne pathogens, anesthetic gases, methylmethacrylate, physical stress, and radiation. Because the use of proper personal protective equipment is mandatory, the risk of contamination with blood-borne pathogens such as hepatitis B, hepatitis C, and HIV is low. Moreover, effective postexposure prophylactic regimens are available for hepatitis B and HIV. In the 1960s, concerns were raised about occupational exposure to harmful chemicals in the operating room such as anesthetic gases and methylmethacrylate. Guidelines on safe levels of exposure to these chemicals and the use of personal protective equipment have helped to minimize the risks to pregnant or lactating staff. Short periods of moderate physical activity are beneficial for pregnant women, but prolonged strenuous activity can lead to increased pregnancy complications. The risk of prenatal radiation exposure during orthopaedic procedures is of concern, as well. However, proper lead protection and contamination control can minimize the risk of occupational exposure to radiation.

Atmospheric oxidation mechanism and kinetic studies for OH and NO3 radical-initiated reaction of methyl methacrylate

The mechanism for OH and NO₃ radical-initiated oxidation reactions of methyl methacrylate (MMA) was investigated by using density functional theory (DFT) molecular orbital theory. Geometrical parameters of the reactants, intermediates, transition states, and products were fully optimized at the B3LYP/6-31G(d,p) level. Detailed oxidation pathways were presented and discussed. The rate constants were deduced by the canonical variational transition-state (CVT) theory with the small-curvature tunneling (SCT) correction and the multichannel Rice-Ramspergere-Kassele-Marcus (RRKM) theory, based on the potential energy surface profiles over the general atmospheric temperature range of 180–370 K. The calculated results were in reasonable agreement with experimental measurement.

Serum levels of methyl methacrylate following inhalational exposure to polymethylmethacrylate bone cement

Teratogenic effects of polymethylmethacrylate cement at levels used during routine orthopaedic procedures have never been reported, however the hypothetical risk remains a major concern among female surgeons. Our aim was to determine if methyl methacrylate is detectible in the serum during routine cement exposure.

METHODS

Twenty healthy volunteers were exposed during the mixing of polymethylmethacrylate cement in a simulated operating room environment. Forty serum samples were obtained during the expected peak inhalational exposure and levels of methyl methacrylate were assessed utilizing headspace gas chromatography mass spectrometry.

RESULTS

Methyl methacrylate was not detected in any of the forty experimental specimens.

CONCLUSIONS

With a detection level of 0.5 ppm, methyl methacrylate is undetectable in the serum during routine mixing of polymethylmethacrylate cement.

Occupational hazards to the pregnant orthopaedic surgeon

The number of female orthopaedic residents and orthopaedic surgeons has increased substantially. Concerns have been raised regarding the effect of the work environment on the health of the female orthopaedic surgeon and her fetus or neonate. Occupational risks, and specifically risks to the pregnant orthopaedic surgeon, are becoming an important issue in medicine. Such risks include exposure to methylmethacrylate (MMA), anesthetic gases, blood-borne pathogens, radiation, emotional stress, and physical stress. Awareness of and knowledge about such exposures are needed for the pregnant orthopaedic surgeon to make informed decisions about her occupational exposures and to be proactive about her own and her child's health.

Occupational exposure in dentistry and miscarriage

BACKGROUND

Information on the reproductive effects of chemical exposures in dental work is sparse or inconsistent.

AIM

To investigate whether dental workers exposed to acrylate compounds, mercury amalgam, solvents or disinfectants are at an increased risk of miscarriage.

METHODS

The study was conducted among women dental workers and a comparison group of workers occupationally unexposed to dental restorative materials. Information on pregnancies was obtained from national registers and outpatient units of hospitals. Data on occupational exposure were obtained using postal questionnaires. The final study population included 222 cases of miscarriage and 498 controls (births). An occupational hygienist assessed exposure to acrylate compounds, disinfectants and solvents. Exposure to other agents was assessed on the basis of the questionnaire data. Odds ratios (ORs) and confidence intervals (CIs) were estimated using conditional logistic regression.

RESULTS

The ORs adjusted for confounding factors were increased for moderate-exposure and high-exposure categories of mercury amalgam (OR 2.0, 95% CI 1.0 to 4.1 and OR 1.3, 95% CI 0.6 to 2.5, respectively). The risk was slightly increased for the highest-exposure category of 2-hydroxyethylmethacrylate (OR 1.4, 95% CI 0.7 to 2.6) and polymethylmethacrylate dust (OR 1.4, 95% CI 0.8 to 2.4). A slightly increased risk was also detected for likely exposure to organic solvents (OR 1.4, 95% CI 0.8 to 2.3) and disinfectants (OR 1.5, 95% CI 0.9 to 2.7).

CONCLUSIONS

No strong association or consistent dose-response relationship was observed between exposure to chemical agents in dental work and the risk of miscarriage. A slightly increased risk was found for exposure to mercury amalgam, some acrylate compounds, solvents and disinfectants. These findings indicate that the possibility of a weak association between exposure to these agents and an increased risk of miscarriage cannot be excluded.

In vitro cytotoxicity of a low-shrinkage polymerizable liquid crystal resin monomer

The objective of this study was to determine the in vitro cytotoxicity of novel, polymerizable liquid crystal resin monomers when placed in direct contact with dental and nondental cell lines. One common dimethacrylate and three liquid crystal compounds, Bis-glycidyl methacrylate (Bis-GMA), 2-(t-butyl)-1,4-bis-{4-(6-acryloxy-hexane-1-oxy)-benzoyloxy}-benzene (C6), 2-(t-butyl), 1-[6-(3-acryloxy-propionoxy)-hexane-1-oxy-benzoyloxy], 4-[4-(6-acryloxy-hexane-1-oxy)-benzoyloxy]-benxene (by-product), and a 3:2 mixture of C6 and by-product, respectively, were tested for relative cytotoxicity in vitro. Cultured dental and nondental cells were treated for 24 h with test compound dissolved in media over a fourfold range of concentration (10(-4) -10(-7) mol/L). Cytotoxicity was measured using the WST-1 reagent as an indicator of remaining cell numbers based on the reduction of WST-1 substrate by mitochondrial dehydrogenases in viable cells. Bis-GMA ID(50) was found to be consistent with ID(50) values reported in the literature. A small but significant difference in the sensitivity of the dental and nondental cells in regard to their response to this dimethacrylate was noted. The liquid crystal resin monomers were significantly less cytotoxic to all cell lines tested. ID(50) values of >1 x 10(-4) mol/L were registered for the C6 and by-product monomers alone. The 3:2 mixture of C6 and by-product had a slightly higher cytotoxicity (ID(50) = 1 x 10(-4) mol/L); however, this remained significantly less than that of Bis-GMA. The results demonstrate that the newly synthesized low-shrinkage, polymerizable liquid crystal resin monomers demonstrate a minimal cytotoxic effect on both dental and nondental cells. These data suggest that the low-shrinkage liquid crystal resin monomers will not elicit a response by oral tissues (pulp tissue) when used to repair carious lesions in posterior teeth.

Final report of the safety assessment of methacrylate ester monomers used in nail enhancement products

Methacrylate ester monomers are used in as artificial nail builders in nail enhancement products. They undergo rapid polymerization to form a hard material on the nail that is then shaped. While Ethyl Methacrylate is the primary monomer used in nail enhancement products, other methacrylate esters are also used. This safety assessment addresses 22 other methacrylate esters reported by industry to be present in small percentages as artificial nail builders in cosmetic products. They function to speed up polymerization and/or form cross-links. Only Tetrahydrofurfuryl Methacrylate was reported to the FDA to be in current use. The polymerization rates of these methacrylate esters are within the same range as Ethyl Methacrylate. While data are not available on all of these methacrylate esters, the available data demonstrated little acute oral, dermal, or i.p. toxicity. In a 28-day inhalation study on rats, Butyl Methacrylate caused upper airway irritation; the NOAEL was 1801 mg/m3. In a 28-day oral toxicity study on rats, t-Butyl Methacrylate had a NOAEL of 20 mg/kg/day. Beagle dogs dosed with 0.2 to 2.0 g/kg/day of C12 to C18 methacrylate monomers for 13 weeks exhibited effects only in the highest dose group: weight loss, emesis, diarrhea, mucoid feces, or salivation were observed. Butyl Methacrylate (0.1 M) and Isobutyl Methacrylate (0.1 M) are mildly irritating to the rabbit eye. HEMA is corrosive when instilled in the rabbit eye, while PEG-4 Dimethacrylate and Trimethylolpropane Trimethacrylate are minimally irritating to the eye. Dermal irritation caused by methacrylates is documented in guinea pigs and rabbits. In guinea pigs, HEMA, Isopropylidenediphenyl Bisglycidyl Methacrylate, Lauryl Methacrylate, and Trimethylolpropane Trimethacrylate are strong sensitizers; Butyl Methacrylate, Cyclohexyl Methacrylate, Hexyl Methacrylate, and Urethane Methacrylate are moderate sensitizers; Hydroxypropyl Methacrylate is a weak sensitizer; and PEG-4 Dimethacrylate and Triethylene Glycol Dimethacrylate are not sensitizers. Ethylene Glycol Dimethacrylate was not a sensitizer in one guinea pig study, but was a strong sensitizer in another. There is cross-reactivity between various methacrylate esters in some sensitization tests. Inhaled Butyl Methacrylate, HEMA, Hydroxypropyl Methacrylate, and Trimethylolpropane Trimethacrylate can be developmental toxicants at high exposure levels (1000 mg/kg/day). None of the methacrylate ester monomers that were tested were shown to have any endocrine disrupting activity. These methacrylate esters are mostly non-mutagenic in bacterial test systems, but weak mutagenic responses were seen in mammalian cell test systems. Chronic dermal exposure of mice to PEG-4 Dimethacrylate (25 mg, 2 x weekly for 80 weeks) or Trimethylolpropane Trimethacrylate (25 mg, 2 x weekly for 80 weeks) did not result in increased incidence of skin or visceral tumors. The carcinogenicity of Triethylene Glycol Dimethacrylate (5, 25, or 50%) was assessed in a mouse skin painting study (50 microl for 5 days/week for 78 weeks), but was not carcinogenic at any dose level tested. The Expert Panel was concerned about the strong sensitization and crossor co-reactivity potential of the methacrylate esters reviewed in this report. However, data demonstrated the rates of polymerization of these Methacrylates were similar to that of Ethyl Methacrylate and there would be little monomer available exposure to the skin. In consideration of the animal toxicity data, the CIR Expert Panel decided that these methacrylate esters should be restricted to the nail and must not be in contact with the skin. Accordingly, these methacrylate esters are safe as used in nail enhancement products when skin contact is avoided.

Final report on the safety assessment of Acrylates Copolymer and 33 related cosmetic ingredients

Ingredients in the Acrylates Copolymer group all contain the monomers acrylic acid or methacrylic acid or one of their salts or esters. These ingredients are considered similar in that they are uniformly produced in chemical reactions that leave very little residual monomer. Although residual acrylic acid may be as high as 1500 ppm, typical levels are 10 to 1000 ppm. There is sufficient odor if residual monomers are present to cause producers to keep levels as low as possible. These ingredients function in cosmetics as binders, film formers, hair fixatives, suspending agents, viscosity-increasing agents, and emulsion stabilizers. Concentrations may be as high as 25% if used as a binder, film former, or fixative; or as low as 0.5% if used as a viscosity-increasing agent, suspending agent, or emulsion stabilizer. These very large polymers exhibit little toxicity. In rabbits and guinea pigs, Acrylates Copolymer did produce irritation, but no evidence of sensitization was found. The principle concern regarding the use of these polymer ingredients is the presence of toxic residual monomers. In particular, although 2-ethylhexyl acrylate was not genotoxic, it was carcinogenic when applied at a concentration of 21% to the skin of C3H mice. Lower concentrations (2.5%) and stop-dose studies at high concentrations (43%) were not carcinogenic. 2-Ethylhexyl acrylate was not carcinogenic in studies using NMRI mice. Whether an increase in carcinogenesis was seen or not, there was evidence of severe dermal irritation in these 2-ethylhexyl acrylate studies. Another concern regarding residual monomers was inhalation toxicity. Although the acrylic acid monomer is a nasal irritant, exposure to the monomer from use of these polymers in cosmetic formulations would always be less than the established occupational exposure limits for nasal irritation. Although there appears to be a huge variation in the mix of monomers used in the synthesis of these polymers, they are similar in that the polymers, except for dermal irritation, are not significantly toxic, and residual monomer levels are kept as low as possible. Although the monomers may be toxic, the levels that would be found in cosmetic formulations are not considered to present a safety risk. Accordingly, these Acrylate Copolymers are considered safe for use in cosmetic formulations when formulated to avoid irritation.

Biocompatibility of dental materials used in contemporary endodontic therapy: a review. Part 2. Root-canal-filling materials

Root-canal-filling materials are either placed directly onto vital periapical tissues or may leach through dentine. The tissue response to these materials therefore becomes important and may influence the outcome of endodontic treatment. This paper is a review of the biocompatibility of contemporary orthograde and retrograde root-canal-filling materials.

Amended final report on the safety assessment of ethyl methacrylate

Ethyl Methacrylate is a methacrylate ester used as a chemical additive in artificial fingernail enhancement products. These products may be applied by trained professionals or be provided directly to consumers with instructions for use. Ethyl Methacrylate readily polymerizes and rapidly reacts with multifunction methacrylates to form a highly cross-linked polymer. The oral LD(50) of Ethyl Methacrylate for rats ranged from 12.7 to 18.14 g/kg. In acute studies with rats, hemoglobinuria and respiratory tract lesions were observed. Animal studies indicate that Ethyl Methacrylate is a skin irritant and sensitizer. In some cases the results were dependent on the vehicle. Evidence of embryotoxicity and teratogenicity were observed in rats injected intraperitoneally with 0.1223 to 0.4076 ml/kg Ethyl Methacrylate. Positive evidence of mutagenicity was observed in the L5178Y mouse lymphoma cell assay, but not in two Ames tests. Case reports cite examples of individuals suffering allergic contact dermatitis from exposure to Ethyl Methacrylate and related methacrylates, and some degree of cross-reactivity appears to exist between widely used acrylates and methacrylates. Information from several clinical registries of sensitization reactions to various agents reported that Ethyl Methacrylate is a sensitizer, but not a potent one. Because Ethyl Methacrylate monomer is short-lived in the normal course of using artificial fingernail-enhancement products, the primary hazard is expected to be inadvertant skin contact. In order to avoid sensitization, it is necessary to avoid skin contact. It is recommended that fingernail-enhancement products containing Ethyl Methacrylate include directions to avoid skin contact because of the sensitizing potential. Based on the available data on the formulation of nail products containing this ingredient, it is concluded that Ethyl Methacrylate is safe as used, when application is accompanied by directions for use as above.

Human liver disease decreases methacrylyl-CoA hydratase and beta-hydroxyisobutyryl-CoA hydrolase activities in valine catabolism

BACKGROUND

Methacrylyl-coenzyme A (MC-CoA) hydratase and beta-hydroxyisobutyryl-coenzyme A (HIB-CoA) hydrolase are key enzymes regulating the toxic concentration of MC-CoA generated in valine catabolism.

MATERIALS AND METHODS

We studied the activities and mRNA expression levels of these enzymes in normal human livers and in human livers with chronic hepatitis, cirrhosis, or hepatocellular carcinoma.

RESULTS

The activities of both enzymes were significantly lower by 36% to 46% in livers with cirrhosis or hepatocellular carcinoma compared with normals, suggesting a decrease in the capability of detoxifying MC-CoA with these diseases. The mRNA levels for both enzymes measured by quantitative polymerase chain reaction were significantly increased in livers with cirrhosis, but were not altered in those with chronic hepatitis or hepatocellular carcinoma when compared with normal livers.

CONCLUSION

Our results suggest that low levels of these enzyme activities in livers with cirrhosis or hepatocellular carcinoma are the result of posttranscriptional regulation in the damaged liver.

Biocompatibility of resin-modified filling materials

Increasing numbers of resin-based dental restorations have been placed over the past decade. During this same period, the public interest in the local and especially systemic adverse effects caused by dental materials has increased significantly. It has been found that each resin-based material releases several components into the oral environment. In particular, the comonomer, triethyleneglycol di-methacrylate (TEGDMA), and the 'hydrophilic' monomer, 2-hydroxy-ethyl-methacrylate (HEMA), are leached out from various composite resins and 'adhesive' materials (e.g., resin-modified glass-ionomer cements [GICs] and dentin adhesives) in considerable amounts during the first 24 hours after polymerization. Numerous unbound resin components may leach into saliva during the initial phase after polymerization, and later, due to degradation or erosion of the resinous restoration. Those substances may be systemically distributed and could potentially cause adverse systemic effects in patients. In addition, absorption of organic substances from unpolymerized material, through unprotected skin, due to manual contact may pose a special risk for dental personnel. This is borne out by the increasing numbers of dental nurses, technicians, and dentists who present with allergic reactions to one or more resin components, like HEMA, glutaraldehyde, ethyleneglycol di-methacrylate (EGDMA), and dibenzoyl peroxide (DPO). However, it must be emphasized that, except for conventional composite resins, data reported on the release of substances from resin-based materials are scarce. There is very little reliable information with respect to the biological interactions between resin components and various tissues. Those interactions may be either protective, like absorption to dentin, or detrimental, e.g., inflammatory reactions of soft tissues. Microbial effects have also been observed which may contribute indirectly to caries and irritation of the pulp. Therefore, it is critical, both for our patients and for the profession, that the biological effects of resin-based filling materials be clarified in the near future.

Cytotoxic effects of acrylates and methacrylates: relationships of monomer structures and cytotoxicity

Thirty-nine acrylates and methacrylates that had been used in dental resin materials were evaluated by a cytotoxicity test, and the relationships between their structures and cytotoxicity were studied to predict cytotoxic levels of dental resin materials in order to develop new low-toxic resin materials. All the acrylates evaluated were more toxic than corresponding methacrylates. In both the acrylates and methacrylates, a hydroxyl group seemed to enhance cytotoxicity. Dimethacrylates with 14 or fewer oxyethylene chains showed similar cytotoxicity while dimethacrylates with 23 oxyethylene chains showed lower cytotoxicity. The cytotoxicity ranking of monomers widely used in dental resin materials was bisphenol A bis 2-hydroxypropyl methacrylate (bisGMA) > urethane dimethacrylate (UDMA) > triethyleneglycol dimethacrylate (3G) > 2-hydroxyethyl methacrylate (HEMA) > methyl methacrylate (MMA). In acrylates, methacrylates, and ethylmethacrylates with either substituents, the lipophilicity of substituents affected their cytotoxicity, and an inverse correlation between IC50 and logP was observed. These results will be useful in developing new resin materials with low toxic monomer compositions.

Acrylic acid: two-generation reproduction toxicity study in Wistar rats with continuous administration in the drinking water

In a two-generation reproduction toxicity study, groups of 25 male and 25 female Wistar rats (for both F0 and F1 generations) received acrylic acid (AA) in the drinking water at concentrations of 0 (control), 500, 2500 and 5000 ppm for at least 70 days prior to mating, through mating, gestation, lactation and to weaning. The study continued through to weaning of the F2 offspring at 21 days of age. Achieved intakes of AA for the F0 and F1 parents during premating ranged from 46 (500 ppm) to 502 (5000 ppm) mg/kg/day. AA had no adverse effects on fertility and reproductive performance of the parent rats at doses up to 5000 ppm. General systemic toxicity was apparent with reduced body weights, food and water consumption in F0 parents at 5000 ppm and in F1 parents at 2500 and 5000 ppm; the only treatment-related pathological finding was a minimal hyperkeratosis of the limiting ridge of the forestomach with a minimal oedema of the submucosa of the glandular stomach in both parental generations at 5000 ppm. Dose-related signs of developmental toxicity were detected in F1 and F2 pups at 2500 and 5000 ppm in the form of retarded growth and some delay in the eye/auditory canal opening in F2 pups, but there was no evidence that AA had an adverse influence on pup morphology. Thus, the no-observed-adverse-effect level (NOAEL) is 5000 ppm for fertility and reproductive performance of the parents, 2500 ppm (F0 parents) or 500 ppm (F1 parents) for general systemic toxicity and 500 ppm for developmental toxicity.

Developmental toxicity study of inhaled acrylic acid in New Zealand White rabbits

In range-finding and definitive developmental toxicity studies, timed pregnant New Zealand White rabbits were exposed to acrylic acid (CAS No. 79-10-7) vapour for 13 consecutive days during pregnancy. In the range-finding study, eight pregnant does/group were exposed to 30, 60, 125 or 250 ppm acrylic acid vapour on gestation days (gd) 10-22 of pregnancy. Monitors of toxicity included body weight measurements, daily food consumption measurements and clinical observations. Three of the eight does/group were killed on the day following the last exposure (gd 23), and the remaining does were killed and autopsied on gd 29. At autopsy, special attention was given to gross observation of maternal nasal turbinates, and nasal turbinates from all does were evaluated histologically. No evaluation of foetuses was performed in the range-finding study. In the definitive study, 16 does/group were exposed to concentrations of 25, 75 or 225 ppm acrylic acid vapour from gd 6 to 18, the major period of organogenesis. Monitors of maternal toxicity included clinical observations and measurements of body weight and daily food consumption measurements. Does were killed and autopsied on gd 29. Maternal liver and kidney weights were measured and external, visceral and skeletal evaluations of foetuses were conducted. Maternal nasal turbinates were not evaluated histologically in the definitive study. Effects in does from both studies included consistent concentration-related reductions in food consumption and body weight gains throughout the exposure period at concentrations of acrylic acid vapour above 60 ppm. Characteristic clinical signs of sensory irritation, including perinasal and perioral wetness and severe nasal congestion, were noted in does from both studies at or above vapour concentrations of 75 ppm. Gross observation of nasal turbinates immediately following exposures in the range-finding study indicated colour changes in the nasal turbinates of does in the 60 and 250 ppm groups. Colour changes in the nasal turbinates were noted in one doe from the 250 ppm exposure group killed on gd 29. Pertinent autopsy findings in the does from the definitive study included ulceration of the nasal turbinates of a single doe in the 225 ppm group. Histological evaluation of turbinates from does killed the day following exposures in the range-finding study revealed lesions in the nasal epithelium in all acrylic acid-exposed groups. The severity of the lesions was concentration related. Microscopic evaluation of turbinates from does killed on gd 29 showed the presence of nasal lesions in the 60, 125 and 250 ppm groups. However, the nasal tissues had recovered considerably during the post-exposure interval. Despite the severe effects on the nasal mucosa of does in both studies, there was no evidence of developmental toxicity including teratogenicity at any exposure concentration used in the definitive study.

Regulation of valine catabolism in canine tissues: tissue distributions of branched-chain aminotransferase and 2-oxo acid dehydrogenase complex, methacrylyl-CoA hydratase and 3-hydroxyisobutyryl-CoA hydrolase

To clarify the valine catabolism, the activities of principal enzymes in its catabolic pathway, branched-chain aminotransferase, branched-chain 2-oxo acid dehydrogenase complex, methacrylyl-CoA hydratase and 3-hydroxyisobutyryl-CoA hydrolase, were measured using canine tissues. After killing of beagle dogs, tissues (liver, pancreas, kidney, heart, skeletal muscle and mucosae of digestive organs such as stomach, small intestine and colon) were removed and immediately frozen. Branched-chain aminotransferase activity in liver was the lowest among the tissues measured. In contrast, the activities of branched-chain 2-oxo acid dehydrogenase complex in liver as well as in kidney were relatively high and the enzyme complex activities were markedly low in small intestine and skeletal muscle. The activities of methacrylyl-CoA hydratase and 3-hydroxyisobutyryl-CoA hydrolase were relatively high in all tissues, suggesting that a cytotoxic intermediate, methacrylyl-CoA, is immediately degraded to non-toxic compounds, 3-hydroxyisobutyrate and free CoA. These findings suggest that the consumption of branched-chain amino acids in the absorption site (small intestine) is suppressed in order to supply them to the whole body, in particular to skeletal muscle and that skeletal muscle might act as a storage of gluconeogenic amino acids. The high capacity to dispose methacrylyl-CoA produced in the valine catabolism is suggested to play an important role in protecting cells against the toxic effects of methacrylyl-CoA.

Metabolic disorders of embryogenesis

Prevention of major physical malformations would represent a significant reduction in the burden of mortality and morbidity in infants and young children. However, preventive and therapeutic approaches must be based on a clear understanding of underlying pathogenic mechanisms. While it is estimated that single gene defects account for up to 10% of cases of major malformation, relatively few of these have been identified and analysed in detail. The recognition of characteristic patterns of developmental anomalies associated with specific enzyme defects has highlighted the important role of the metabolic environment in normal development and offers the possibility of correlating biochemical abnormalities with particular teratogenic effects. Once it is generally appreciated that some forms of structural malformation have a specific biochemical basis, metabolic studies should be performed more often in patients with major developmental anomalies. This should lead to identification of other examples of diseases of this type and the elucidation of molecular mechanisms of human teratogenesis.

Methyl methacrylate: inhalation developmental toxicity study in rats

Methyl methacrylate (99.9% pure) was administered by vapor inhalation exposure to five groups (27 rats/group) of presumed pregnant rats (Crl:CD) at concentrations of 0 (control), 99, 304, 1,178, and 2,028 ppm for 6 hr/day on days 6-15 of gestation (G). Maternal body weight, feed consumption, and clinical signs were recorded throughout gestation. Dams were euthanized on day 20 G. Each uterus was weighed and corpora lutea, implantation sites and resorptions were counted. The number of fetuses per litter were counted and their location within the uterus recorded. All fetuses were weighed, sexed and examined for external and skeletal alterations. One half of the fetuses from each litter were examined for visceral alterations. No treatment-related deaths were noted at any concentration tested. Treatment-related effects on maternal body weight and feed consumption were noted at all exposure levels. The decreases in maternal body weight at 99 and 304 ppm were minimal and transient since they returned to control values by the next weighing period. When exposure was discontinued, body weight gain and feed consumption in all exposure groups returned to control values. There were no treatment-related changes in the number of litters produced or in the mean number per litter of corpora lutea, implantations, resorptions, live or dead fetuses, or sex ratio. Fetal body weights were similar between the control and treated groups. There were no treatment-related increases in the type or incidence of external, visceral, or skeletal malformations, developmental variations, or variations indicative of retarded development. Exposure to methyl methacrylate concentrations up to 2,028 ppm resulted in no embryo or fetal toxicity or malformations even at exposure levels that resulted in maternal toxicity.

Dysmorphic syndromes with demonstrable biochemical abnormalities

Many inborn errors of metabolism are associated with dysmorphic manifestations. In this review, we have attempted to correlate the dysmorphic features with the underlying metabolic defect or its consequences. Most of the defects which we have discussed affect the synthesis or degradation of macromolecules (for example, collagen, elastin, bone mineral, proteoglycans, glycoproteins, and triglycerides). Such defects may affect either a single enzyme or multiple enzymes in specific organelles, such as lysosomes or peroxisomes, or they may affect hormonal control of synthesis and degradation. Examples are also included of defects affecting the catabolism of simple molecules when accumulating metabolites have a secondary effect on macromolecules, as in homocystinuria. In a number of instances, however, the correlation between the biochemical abnormality and the dysmorphic features are not understood. Ultimately, all dysmorphic syndromes will be attributable to a biochemical defect or its effects. The aim of this overview is to provide an insight into the relationship between the two at the present time.

The isolation and characterization of 2-carboxyethyl adducts following in vitro reaction of acrylic acid with calf thymus DNA and bioassay of acrylic acid in female Hsd:(ICR)Br mice

Reaction of acrylic acid (AA) at pH 7.0 and 37 degrees C for 40 days with 2'-deoxyadenosine (dAdo), 2'-deoxycytidine (dCyd), 2'-deoxyguanosine (dGuo) and thymidine (dThd) resulted in the formation of 2-carboxyethyl (CE) adducts via Michael addition. The alkylated 2'-deoxynucleoside adducts isolated (percent yield after 40 days) were 1-CE-dAdo (5%), N6-CE-dAdo (11%) (via Dimroth rearrangement of 1-CE-dAdo), 3-CE-dCyd (7.5%), 7-CE-Gua (4%), 7,9-bis-CE-Gua (0.9%) (formed by reaction of AA with depurinated 7-CE-Gua during the course of the reaction) and 3-CE-dThd (0.5%). The products isolated following in vitro reaction of AA with calf thymus DNA at pH 7.0 and 37 degrees C for 40 days were (nmol/mg DNA) 1-CE-Ade (9.9), N6-CE-Ade (8.2), 7-CE-Gua (7.2) and 3-CE-Thy (1.9). Compound 3-CE-Cyt was not detected. Thus the adducts formed following in vitro reaction of AA with DNA are identical to those formed by in vitro reaction of the carcinogen beta-propiolactone (BPL) with DNA as reported in an earlier paper. Structures were assigned on the basis of identical UV spectra, Rf values on paper chromatograms and Rt values on HPLC as marker compounds prepared from reactions of BPL with 2'-deoxynucleosides and 2'-deoxynucleotides-5'-monophosphoric acids. AA was assayed for carcinogenic activity by s.c. injection (20 mumol, once a week for 52 weeks) in female Hsd: (ICR)Br mice. Two mice with sarcomas at the site of application were observed out of 30 mice. Malignancies were not observed in solvent and no-treatment controls. The bioassay results reported in this paper and elsewhere in the same strain of mice suggest that AA is a weak carcinogen in female Hsd:(ICR)Br mice.

Methacrylic acid as a teratogen in rat embryo culture

Using day 10 rat embryos cultured in vitro, we have shown that methacrylic acid is teratogenic at concentrations ranging from 1.2 to 2.1 mM. At these concentrations, methacrylic acid produced concentration-dependent decreases in growth parameters, i.e., crown-rump length, number of somites, and embryo protein content. In addition, methacrylic acid exposure produced malformed embryos characterized primarily by abnormal neurulation. Less frequent abnormalities included hypoplasia of the prosencephalon, edema, malpositioned heart, abnormal flexion, and dilated otic vesicles. Accompanying these abnormalities was an underlying increase in methacrylic acid-induced cell death.

Teratogenic inborn errors of metabolism

Most children with inborn errors of metabolism are born healthy without malformations as the fetus is protected by the metabolic activity of the placenta. However, certain inborn errors of the fetus have teratogenic effects although the mechanisms responsible for the malformations are not generally understood. Inborn errors in the mother may also be teratogenic. The adverse effects of these may be reduced by improved metabolic control of the biochemical disorder.

A critical review of the literature on acrolein toxicity

A detailed literature review of human and animal toxicity studies of acrolein is presented, and information gaps identified that call for further investigation. Specific recommendations are suggested for additional short-/long-term studies, including chemical disposition and cytogenetic investigations. Two bibliographies are provided indicating the scope of the review: (1) literature actually cited and (2) literature examined but not included.

Dermal oncogenicity bioassays of monofunctional and multifunctional acrylates and acrylate-based oligomers

Several important components of photocurable coatings were studied for dermal tumorigenic activity by repeated application to the skin of mice. The substances tested were 2-ethylhexyl acrylate (EHA) and methylcarbamoyloxyethyl acrylate (MCEA) (monomers); neopentyl glycol diacrylate (NPGDA), esterdiol-204-diacrylate (EDDA), and pentaerythritol tri(tetra)acrylate (PETA) (cross-linkers); and three acrylated urethane oligomers. For each bioassay, 40 C3H/HeJ male mice were dosed 3 times weekly on the dorsal skin for their lifetime with the highest dose of the test agent that caused no local irritation or reduction in body weight gain. Two negative control groups received acetone (diluent) only. A positive control group received 0.2% methylcholanthrene (MC). NPGDA and EHA had significant tumorigenic activity with tumor yields of eight and six tumor-bearing mice (three and two malignancies), respectively. The MC group had 34 mice with carcinomas and 1 additional mouse with a papilloma. MCEA had no dermal tumorigenic activity but resulted in early mortality. No skin tumors in the treatment area were observed in the other groups. Additional studies will be necessary to elucidate possible relationships between structure and tumorigenic activity for the acrylates.

Dermal oncogenicity bioassays of acrylic acid, ethyl acrylate, and butyl acrylate

Male C3H/HeJ mice (40 per group) were treated with 25-microliter applications of undiluted ethyl acrylate, 1% acrylic acid, or 1% butyl acrylate on the dorsal skin 3 times weekly for their lifetime. A negative control group received acetone (diluent) only, and a positive control group received 0.1% 3-methylcholanthrene (MC). No epidermal tumors were observed in the animals that received any of the three test substances. In the positive control group, 39 animals had skin tumors, including 33 with confirmed squamous-cell carcinomas. Nonneoplastic skin changes such as dermatitis, dermal fibrosis, epidermal necrosis, and hyperkeratosis were observed in several mice that received ethyl acrylate. No statistically significant effects on survival were seen. Therefore, there was no evidence for local carcinogenic activity of acrylic acid, ethyl acrylate, or butyl acrylate under the conditions of these studies.

Acrylate and methacrylate esters: relationship of hemolytic activity and in vivo toxicity

Quantitative hemolysis assays of acrylate and methacrylate esters provided estimates of the intrinsic hemolytic activity (Hi, the slope of the concentration-response curve) and the concentrations effecting 5% (H5) and 50% (H50) hemolysis. The dependence of hemolytic activity and LD50 (mice) on physical properties (lipophilicity, molar refraction, and molecular volume) of the esters was determined by multiple regression analysis. The observed correlations were: Hi, R2 = 0.94; H5, R2 = 0.95; H50, R2 = 0.94; and LD50, R2 (all compounds) = 0.80, R2 (all compounds less the methyl esters) = 0.94. The difference of the methyl esters was associated with the smaller steric volume of the methyl ester substituent and the presence (methacrylates) or absence (acrylates) of the branched methyl group. Associative steric contributions of the branched methyl group and the ester substituents were probably responsible for greater variability in the methyacrylate series. The results were consistent with the conclusion that the mechanism of the action of the esters is membrane mediated and relatively nonspecific and that in vivo biotransformation was not a significant factor. Also, long-term toxic liability of the esters may be more closely related to intrinsic toxicity than acute toxicity.

Embryotoxic effects of acrolein, methacrylates, guanidines and resorcinol on three day chicken embryos

Acrolein, four methacrylates, two guanidine compounds and resorcinol were tested for embryotoxicity on three day chicken embryos. The most potent chemical was acrolein, with the ED50 0.05 mumol per egg for the total effect, including deaths and malformations. The substances next in potency were N,N'-di-o-tolyl-guanidine and N,N-diphenylguanidine, with ED50 values 0.17 and 0.20 mumol per egg, respectively. Resorcinol and the methacrylates had ED50 values ranging from 2.4 to 22.0 mumol per egg. Acrolein, diphenylguanidine, tetrahydrofururylmethacrylate and trimethylolpropanetrimethacrylate caused the largest amounts of malformed embryos.

Subchronic and reproductive toxicology studies on acrylic acid in the drinking water of the rat

In the subchronic study acrylic acid was incorporated in the drinking water of Fischer 344 rats (15 per group) for three months at dosage levels of 0.75, 0.25, 0.083 or 0 g/kg/day. No deaths occurred during the study but several treatment-related effects were observed. At 0.75 g/kg/day dosage level, body weight gain was reduced as were food and water consumption. Changes in organ weights and clinical chemistry parameters were observed along with increases in urine specific gravity and protein concentration. Similar, though less profound, changes occurred at 0.25 g/kg/day. At 0.083 g/kg/day, the only effect was a reduction of water consumption by male rats. There were no significant treatment-related histopathologic changes. Many of the effects observed may have been the result of decreased water and food consumption rather than specific toxic effects of acrylic acid. In the reproduction study, the same dosages of acrylic acid were given to groups of 10 males and 20 females for 90 days after which the animals were mated. Treatment was continued throughout gestation and lactation. Treatment-related effects included decreased body weight gain, and reduced food and water consumption in F0 rats at the 2 highest dosage levels. Organ weight changes occurred in both F0 and F1 animals and reduced body weight gain was seen in the F1 pups at the highest level. No statistically significant changes in reproductive indices were observed, perhaps because of an atypical control group.

Identification or urinary mercapturic acids formed from acrylate, methacrylate and crotonate in the rat

1. After administration to rats of methyl acrylate (I), methyl methacrylate (II) and methyl crotonate (III), urinary mercapturic acids were isolated and identified as the dicarboxylic acids N-acetyl-S-(2-carboxyethyl)cysteine (IV, R = H), N-acetyl-S-(2-carboxypropyl)cysteine (V, R = H) and N-acetyl-S-(1-methyl-2-carboxyethyl)cysteine (VI, R = H) and for a minor part as their monomethyl esters IV (R = CH3) and VI (R = CH3). 2. After a single dose of the acrylates (I), (II) and (III) (0.14 mmol/kg), the excretion of the thioethers amounted to 6.6 +/- 0.6, 0.0, and 2.0 +/- 0.6% dose respectively. 3. After 18 h previous administration of the carboxylesterase inhibitor tri-o-tolyl phosphate (0.34 mmol/kg) the excretion of the thioethers amounted to 40.6 +/- 2.1, 11.0 +/- 3.3, and 16.0 +/- 2.0% dose. 4. For methyl acrylate (I) the ratio of the excreted dicarboxylic acid and monomethyl ester was 20:1. After previous administration of tri-o-tolyl phosphate this ratio was 1:2.

Occupational chemicals tested for teratogenicity

Literature was surveyed concerning the teratological testing of chemicals, to which large numbers of workers are occupationally exposed. They include metals, plastics monomers and additives, solvents, and other organic chemicals. The effective doses used in the studies were compared to the potential exposures in the occupational environment as regulated by hygienic standards. In light of the animal experiments, the TLVs for some organic chemicals, particularly for acrylonitrile, methacrylate esters, styrene, carbon disulfide, chloroform, methylene chloride, toluene and xylene, appeared too high to provide absolute safety for pregnant workers. The mechanisms of teratogenesis and the validity of the animal experiments were also considered.