Exposure to volatile methacrylates in dental personnel

Investigation of biological effects of HEMA in 3D-organotypic co-culture models of normal and malignant oral keratinocytes

Several in vitro studies utilizing 2-dimensional (2D) cell culture systems have linked 2-hydroxyethyl methacrylate (HEMA) with cytotoxic effects in oral mucosa and dental pulp cells. Although such studies are invaluable in dissecting the cellular and molecular effects of HEMA, there is a growing interest in the utilization of appropriate 3-dimensional (3D) models that mimic the structure of oral mucosa. Using a previously characterized 3D-organotypic co-culture model, this study aimed to investigate the cellular and molecular effects of HEMA on a 3D-co-culture model consisting of primary normal oral keratinocyte (NOK) grown directly on top of collagen I gel containing primary oral fibroblasts (NOF). The second aim was to examine the suitability of a 3D-co-culture system consisting of oral squamous cell carcinoma (OSCC) cells as a model system to investigate the biological effects of HEMA. We demonstrated that HEMA treatment led to reduced viability of NOK, NOF and OSCC-cell lines in 2D-culture. The keratinocytes in 3D-co-cultures of NOK and OSCC-cells reacted similarly with respect to cell proliferation and activation of autophagy flux, to HEMA treatment. Nevertheless, NOK was found to be more susceptible to apoptosis following HEMA treatment than OSCC in 3D-co-cultures. These results indicate that 3D-organotypic co-cultures of NOK might represent an appropriate model system for the investigation of the biological effects of HEMA and other dental biomaterials. Given the challenges in obtaining primary cultures of NOK and issues associated with their rapid differentiation in culture, the possible use of OSCC cells as an alternative to NOK for 3D models represents an area for future research.

N-acetyl cysteine inhibits IL-1α release from murine keratinocytes induced by 2-hydroxyethyl methacrylate

The hydrophilic compound 2-hydroxyethyl methacrylate (HEMA) is a major component of dental bonding materials, and it enhances the binding of resin-composites to biomolecules. However, HEMA is a well-known contact sensitizer. We reported previously that intradermal injection of HEMA induces the production of IL-1 locally in the skin. Keratinocytes are the first barrier against chemical insults and constitutively express IL-1α. In this study, we analyzed whether HEMA induces the production of inflammatory cytokines from murine keratinocyte cell line Pam212 cells. We demonstrated that HEMA induced the release of 17-kDa mature IL-1α and caused cytotoxicity. The activity of calpain, an IL-1α processing enzyme, was significantly higher in HEMA-treated cells. The thiol-containing antioxidant N-acetyl cysteine (NAC) inhibited HEMA-induced IL-1α release but not cytotoxicity. NAC inhibited intracellular calpain activity and reactive oxygen species (ROS) production induced by HEMA. NAC post-treatment also inhibited IL-1α release and intracellular ROS production induced by HEMA. Furthermore, HEMA-induced in vivo inflammation also inhibited by NAC. NAC inhibited polymerization of HEMA through adduct formation via sulfide bonds between the thiol group of NAC and the reactive double bond of HEMA. HEMA-induced IL-1α release and cytotoxicity were also inhibited if HEMA and NAC were pre-incubated before adding to the cells. These results suggested that NAC inhibited IL-1α release through decreases in intracellular ROS and the adduct formation with HEMA. We concluded that HEMA induces IL-1α release from skin keratinocytes, and NAC may be a promising candidate as a therapeutic agent against inflammation induced by HEMA.

Methyl methacrylate and respiratory sensitisation: a comprehensive review

Methyl methacrylate (MMA) is classified under GHS as a weak skin sensitiser and a skin and respiratory irritant. It has recently been proposed that MMA be classified as a respiratory sensitiser (a designation that in a regulatory context embraces both true respiratory allergens, as well as chemicals that cause asthma through non-immunological mechanisms). This proposal was based primarily upon the interpretation of human data. This review, and a detailed weight of evidence analysis, has led to another interpretation of these data. The conclusion drawn is that persuasive evidence consistent with the designation of MMA as a respiratory sensitiser is lacking. It is suggested that one reason for different interpretations of these data is that occupational asthma poses several challenges with respect to establishing causation. Among these is that it is difficult to distinguish between allergic asthma, non-allergic asthma, and work-related exacerbation of pre-existing asthma. Moreover, there is a lack of methods for the identification of true chemical respiratory allergens. The characterisation and causation of occupational asthma is consequently largely dependent upon interpretation of human data of various types. Recommendations are made that are designed to improve the utility and interpretation of human data for establishing causation in occupational asthma.

Identifying a reference list of respiratory sensitizers for the evaluation of novel approaches to study respiratory sensitization

The induction of immunological responses that trigger bio-physiological symptoms in the respiratory tract following repeated exposure to a substance, is known as respiratory sensitization. The inducing compound is known as a respiratory sensitizer. While respiratory sensitization by high molecular weight (HMW) materials is recognized and extensively studied, much less information is available regarding low molecular weight (LMW) materials as respiratory sensitizers. Variability of symptoms presented in humans from such exposures, limited availability of (and access to) documented reports, and the absence of standardized and validated test models, hinders the identification of true respiratory sensitizers. This review aims to sort suspected LMW respiratory sensitizers based on available compelling, reasonable, inadequate, or questionable evidence in humans from occupational exposures and use this information to compose a reference list of reported chemical respiratory sensitizers for scientific research purposes. A list of 97 reported respiratory sensitizers was generated from six sources, and 52 LMW organic chemicals were identified, reviewed, and assigned to the four evidence categories. Less than 10 chemicals were confirmed with compelling evidence for induction of respiratory sensitization in humans from occupational exposures. Here, we propose the reference list for developing novel research on respiratory sensitization.

Application of Antimicrobial Polymers in the Development of Dental Resin Composite

Dental resin composites have been widely used in a variety of direct and indirect dental restorations due to their aesthetic properties compared to amalgams and similar metals. Despite the fact that dental resin composites can contribute similar mechanical properties, they are more likely to have microbial accumulations leading to secondary caries. Therefore, the effective and long-lasting antimicrobial properties of dental resin composites are of great significance to their clinical applications. The approaches of ascribing antimicrobial properties to the resin composites may be divided into two types: The filler-type and the resin-type. In this review, the resin-type approaches were highlighted. Focusing on the antimicrobial polymers used in dental resin composites, their chemical structures, mechanical properties, antimicrobial effectiveness, releasing profile, and biocompatibility were included, and challenges, as well as future perspectives, were also discussed.

Methacrylate perspective in current dental practice

OBJECTIVE

To provide a current perspective concerning dental personnel sensitivity to methacrylate materials.

OVERVIEW

Methacrylate related sensitivity and allergies are currently beyond traditional thoughts concerning denture base resins and methyl methacrylate provisional materials. Methacrylates are now ubiquitous in current dental practice and dental personnel should be aware that dental adhesives contain potent sensitizers that may also cross-sensitize individuals to other methacrylates not experienced. The growing sensitivity to 2-hydroxyethyl methacrylate (HEMA) has been described to be epidemic in nature due to the artificial nail industry with dental patients and dental personnel may be more susceptible to dental methacrylate sensitization. While contact dermatitis remains the most prevalent methacrylate-related clinical presentation, respiratory complications and asthma are increasing associated with methacrylate exposure. While additional personal protective equipment (PPE) is thought to be first protective choice, the National Institute for Occupational Safety and Health (NIOSH) considers PPE overall largely ineffective and should be considered only as a last resort.

CONCLUSION

Dental personnel need to be more aware of methacrylate sources and use workplace control measures to limit methacrylate exposures to both dental personnel and patients.

CLINICAL SIGNIFICANCE

Sensitivity to methacrylate materials is a growing dental workplace major concern and dental personnel should be aware of both the methacrylate content of current materials and the products that contain ingredients with the most sensitization potential.

In vitro effects of dental monomer exposure - Dependence on the cell culture model

Methacrylate monomers are major components of resin-based biomaterials. The polymerization of these materials is never complete, and methacrylates leaking from cured materials cause exposure of patients. Only some selected methacrylates have thoroughly been tested for possible interaction with living cells. In the current study, we compared the effects of 2-hydroxyethyl-methacrylate (HEMA; a carefully studied methacrylate) and hydroxypropyl-methacrylate (HPMA; a scarcely investigated methacrylate). Five cell lines differing in both source and cell type were used. The cells were exposed to methacrylates (1-8 mM). Cell viability, cell death, glutathione levels, reactive oxygen species (ROS), and cell growth pattern were measured. Both methacrylates reduced cell viability, and glutathione depletion was observed in all cell lines. The cell death pattern varied among the cell lines. The ROS levels and cell growth pattern also differed between the cell lines after exposure to methacrylate monomers. No difference between HEMA and HPMA exposures were observed in any of the cell lines. The variation between cell lines shows that the measured methacrylate toxicity depends heavily on the test system chosen. Further, the conformity between HEMA and HPMA effects suggests that the two methacrylates similarly affect living cells.

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.

Nanoparticle release from dental composites

Dental composites typically contain high amounts (up to 60 vol.%) of nanosized filler particles. There is a current concern that dental personnel (and patients) may inhale nanosized dust particles (<100 nm) during abrasive procedures to shape, finish or remove restorations but, so far, whether airborne nanoparticles are released has never been investigated. In this study, composite dust was analyzed in real work conditions. Exposure measurements of dust in a dental clinic revealed high peak concentrations of nanoparticles in the breathing zone of both dentist and patient, especially during aesthetic treatments or treatments of worn teeth with composite build-ups. Further laboratory assessment confirmed that all tested composites released very high concentrations of airborne particles in the nanorange (>10(6)cm(-3)). The median diameter of airborne composite dust varied between 38 and 70 nm. Electron microscopic and energy dispersive X-ray analysis confirmed that the airborne particles originated from the composite, and revealed that the dust particles consisted of filler particles or resin or both. Though composite dust exhibited no significant oxidative reactivity, more toxicological research is needed. To conclude, on manipulation with the bur, dental composites release high concentrations of nanoparticles that may enter deeply into the lungs.

Risk factors associated with asthma phenotypes in dental healthcare workers

BACKGROUND

Exposure in the dental environment can increase the risk of respiratory disease in dental healthcare workers (HCWs). This study investigated the prevalence of asthma phenotypes in dental HCWs and associated risk factors.

METHODS

A cross-sectional study of 454 dental HCWs in five dental institutions in South Africa was conducted. A self-administered questionnaire elicited the health and employment history of subjects. Sera was analyzed for atopic status and latex sensitization. Pre- and post-bronchodilator spirometry was performed.

RESULTS

The prevalence of atopic asthma was 6.9%, non-atopic asthma 5.9% and work-exacerbated asthma (WEA) 4.0%. Atopy and work-related ocular-nasal symptoms were strong predictors of WEA (OR: 3.4; 95% CI: 1.07-10.8; OR: 6.7, 95% CI: 2.4-19.1), respectively. Regular use of personal protective equipment (PPE) was associated with a protective affect (OR: 0.23, 95% CI: 0.1-0.7) among non-atopic asthmatics, while glove use and respiratory protection was protective among atopic asthmatics (OR: 0.39, 95% CI: 0.17-0.89).

CONCLUSION

Identification of risk factors associated with specific asthma phenotypes in dental HCWs can be used to focus preventive strategies for asthmatics.

Air pollution/working activity correlation: a case study in a dental hospital

The paper deals with a multidimensional approach demonstrating a direct link between the entity of ongoing dentistry activity (number and kind of interventions) and specific pollution components. Simultaneously indoor/outdoor air concentrations of a set of volatile organic compounds (VOCs) and activity variables, describing the amount and nature of ongoing dentistry activities, were monitored over a year at a dental hospital located in an urban area. Principal Component Analysis (PCA) was used to single out mutually orthogonal pollution components which were then correlated to "pathology" factors arising from the analysis of dentistry activity indexes. The use of a multidimensional perspective allowed us to obtain a statistically significant model of the link between level of pollution and dentistry activity. In particular, the correlation approach linking pollution results to pathological variables allows us to establish a causative link even in the presence of sub-threshold concentrations of pollutants.

Identification of covalent binding sites of ethyl 2-cyanoacrylate, methyl methacrylate and 2-hydroxyethyl methacrylate in human hemoglobin using LC/MS/MS techniques

Acrylates are used in vast quantities, for instance in paints, adhesive glues, molding. They are potent contact allergens and known to cause respiratory hypersensitivity and asthma. Here we study ethyl 2-cyanoacrylate (ECA), methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA). There are only limited possibilities to measure the exposure to acrylates, especially for biological monitoring. The aim of the present study was to investigate the chemical structures of adducts formed after reaction of hemoglobin (Hb) with ECA, MMA, and HEMA. This information may be used to identify adducted Hb peptides for biological monitoring of exposure to acrylates. Hb-conjugates with ECA, MMA, and HEMA were synthesized in vitro. The conjugates were digested by trypsin and pronase E. Adducted peptides were characterized and analyzed by liquid chromatography and nano electro spray/hybrid quadrupole time-of-flight mass spectrometry (MS) as well as tandem quadrupole MS. The search for the adducted peptides was facilitated by visualizing the MS data by different computer programs. The results showed that ECA binds covalently to cysteines at the 104 position in the α and the position 112 in the β-chains in Hb. MMA and HEMA bound to all the cysteines in both chains, Cys(104) in the α-chain and Cys(93) and 112 in the β-chain. The full-length spectra of in un-digested Hb confirmed this binding pattern. There was no reaction with N-acetyl-L-lysine at physiological pH. The adducted peptides were possible to measure using LC/MS/MS in selected reaction monitoring mode. These peptides may be used for biological monitoring of exposure to ECA, MMA and HEMA.

A cross-industry assessment of personal exposures to methyl methacrylate

This study investigated personal exposures to methyl methacrylate (MMA) monomer during monomer production and use within the chemical manufacturing industry. The aim was to include multiple companies and sites to provide information regarding differences and similarities among exposure subgroups within the industry during the time period of 1998-2000. To this end, personal exposure data for MMA monomer from three chemical corporations was combined into a single data set. The data was stratified by sample type (full shift or short term), job classification (monomer production, monomer use, maintenance, distribution, and laboratory operations), company, and facility. Only classifications with three samples or more were included in the final data set, yielding 376 samples for analysis (334 full-shift and 42 short-term samples). Results compare well with previously published data on MMA monomer exposures. Although there was significant variability in several exposure subgroups (particularly among companies and facilities), MMA monomer use in the manufacture of other products resulted in the highest exposure distributions, with lower exposures associated with monomer production, maintenance, and distribution operations. The usefulness of these findings is related to the provision of information for discussion of current needs in the industry regarding data sampling, exposure assessment, and standards development.

Do adverse effects of dental materials exist? What are the consequences, and how can they be diagnosed and treated?

OBJECTIVES

All dental biomaterials release substances into the oral environment to a varying degree. Various preclinical biocompatibility test systems have been introduced, aiming at an evaluation of the potential risks of dental materials. Potential pathogenic effects of released substances from dental materials have been demonstrated. For the biocompatibility of a biomaterial, it is not only important that minimal diffusable substances are released when it is in body contact--the material must also fulfill the function for which it has been designed. This is also very much dependent on the material properties and its handling properties. The aim of this review was to generate an overview of the present status concerning adverse reactions among patients and personnel.

MATERIALS AND METHODS

A systematic review was performed using a defined search strategy in order to evaluate all MEDLINE-literature published between 1996 and 2006.

RESULTS

The compilation of the literature available has revealed that the majority of studies have been carried out on patients compared with personnel. Adverse reactions towards dental materials do occur, but the prevalence and incidence are difficult to obtain. The results were essentially based on cohort studies. Clinical trials, especially randomized-controlled trials, are in the minority of all studies investigated, with the exception of composite and bonding studies, where clinical trials, but not randomized-controlled trials, represent the majority of studies. Patients and personnel were treated separately in the manuscript. Amalgam studies show the lowest degree of verified material-related diagnosis. Even if objective symptoms related to adverse reactions with polymer resin-based materials have been reported, postoperative sensitivity dominates reports concerning composites/bondings. Verified occupational effects among dental personnel show a low frequency of allergy/toxic reactions. Irritative hand eczema seemed to be more common than in the general population.

CONCLUSIONS

Patient- and personnel-related studies are of variable quality and can be improved. There is a need for a better description of the content of materials. A registry for adverse effects of dental materials would be useful to detect the occurrence of low-incidence events.

Respiratory effects of exposure to methacrylates among dental assistants

BACKGROUND

Case reports of occupational asthma in dental personnel have been published, but there is little data on the risk of respiratory disorders related to occupational exposure to methacrylates in dental assistants. The objective of this study was to investigate the relation of exposure to methacrylates to occurrence of respiratory symptoms and diseases among dental assistants.

METHODS

A cross-sectional study of female dental assistants from the membership register of the Finnish Association of Dental Hygienists and Assistants was conducted in the Helsinki metropolitan area. A CATI was carried out to collect information on health and exposures. A total of 799 dental assistants participated (response rate 87%).

RESULTS

Daily use of methacrylates was related to a significantly increased risk of adult-onset asthma (adjusted OR 2.65, 95% CI 1.14-7.24), nasal symptoms (1.37, 1.02-1.84), and work-related cough or phlegm (1.69, 1.08-2.71). Nasal symptoms showed a dose-response relation with increasing years of exposure to methacrylates, and those with >10 years of exposure had also increased risk of hoarseness, dyspnoea, and wheezing with dyspnoea. Dental assistants with a history of atopic diseases were particularly susceptible to exposure to methacrylates, the adjusted OR for adult asthma being in this group 4.18 (95% CI 1.02-28.55) and for nasal symptoms 2.11 (1.08-4.19).

CONCLUSIONS

This study provides new evidence that the risk of adult-onset asthma, nasal symptoms and other respiratory symptoms increase significantly with daily use of methacrylates in dental assistants' work. The results suggest that exposure to methacrylates poses an important occupational hazard for dental assistants.