Asthma and methacrylates – gluing together the evidence

Acrylates are a group of reactive compounds frequently handled in many different occupations. They cure rapidly without separate addition of hardener; polymerization is catalyzed by light, heat, or oxygen. There are two important groups of acrylates, methacrylates, and cyanoacrylates; both are used as glues. Exposure to cyanoacrylates has been linked to asthma in several case reports and one epidemiological study (1–4). Methacrylates are also used as plastic filling material leading to exposure among dental and surgical personnel and workers in different biotechnical and pharmaceutical industries. In Scandinavia, work with methacrylates has been common among dental personnel for some decades now. The use of composite resin materials for dental restoration has increased because of the replacement of mercury based materials, such as amalgam. Although these newer plastic fillings (composite resins) are made from different varieties of less volatile methacrylates, the bondings consist of more volatile acrylates, such as 2hydroxyethyl-metahcrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA). Studies conducted in Finland and Sweden to measure exposure to HEMA among dental nurses have shown rather low median levels, around 3 lg/m (5, 6). However, higher levels were found when working around the patient s mouth, during mixing of the components and when removing old fillings. The highest short-term concentrations of HEMA were 68 lg/m in the Finnish study (5) and 20 lg/m in the Swedish study (6). The only European Union country which has an occupational exposure limit for HEMA is the Netherlands, where the limit is 270 lg/m, for 8 h work. It has not previously been clear whether exposure to methacrylates increases the risk for asthma. One early publication describes a dental assistant who developed asthma after manufacturing prosthetic dental trays, probably because of exposure to methyl methacrylates (1). There is also one early case report from Poland about a dental technician who developed asthma after working with methyl methacrylate (7) and more recent case reports among Finnish dental personnel (8, 9). Methacrylates are already well known as inducers of contact dermatitis. In the current issue of Allergy, Jaakkola et al. (10) from UK and Finland present an important study showing that exposure to methacrylates is associated with adult-onset asthma. Within a cohort of dental assistants/nurses they observed that the use of methacrylates increased the risk for asthma; and in a dose-dependent manner, the risk for rhinitis. Both exposure and outcome were based on selfreporting. Exposure was based on reporting of jobspecific tasks, a method that has rather high validity (11). The main outcome, physician-diagnosed asthma, is considered to have a high validity, albeit with a bias towards severe disease, as subjects with mild disease tend to underreport their asthma (12). However, as the authors also point out, the most problematic bias occurs if the dental assistants using methacrylates falsely over-report a diagnosis of asthma, a phenomenon known to epidemiologists as dependent misclassification. This is always a problem in studies where both the outcome (disease) and exposure are based on self-reporting. The authors argue against this possibility by pointing out that there was no increased risk associated with the use of latex gloves. If K. Tor n Department of Occupational and Environmental Medicine, Sahlgrenska University Hospital, Gçteborg, Sweden