Positive Patch Test Reactions to Dental Rubber Dams and Zinc Ethylphenyldithiocarbamate in a Patient Sensitised to Thiurams and Other Carbamates

A 63-year-old atopic man was referred by his dentist to the Department of Occupational and Environmental Dermatology in Malmö, Sweden, before an upcoming dental procedure with intended use of rubber dams, to ascertain his contact allergies. Patch testing in childhood had revealed a contact allergy to rubber chemicals. He had later worked assembling rubber trims but had to stop due to severe hand eczema. Patch testing was performed with the Swedish baseline series, the extended baseline series used in Malmö, rubber series, and dental series with an occlusion time of 48 h. Test readings on day (D)3 and D7 [1] showed strong positive reactions to carba mix, thiuram mix and its components, and doubtful reactions to zinc diethyldithiocarbamate and zinc dibutyldithiocarbamate (Table 1). Additional patch testing was performed with two exemplars of rubber dental dam acquired from the local Swedish Public Dental Service. Positive patch test reactions were found to both dental dams (Table 1), one natural rubber latex (NRL)-based (NRL) and one NRL-free. Skin prick tests with commercial latex extracts (Soluprick, ALK-Abelló, Hørsholm, Denmark) turned out negative. A chemical analysis of both dams with high-performance liquid chromatography (HPLC) as described before [2] identified the presence of diphenylguanidine (0.08 mg/cm2) and zinc diethylthiocarbamate (0.04 mg/cm2) in the NRL-free dam. Zinc ethylphenyldithiocarbamate (ZEPC) (0.01 mg/cm2) was detected in the NRL-dam. The concentration and identity of ZEPC were determined by comparison with reference substances of UV spectrum and area under curve in the chromatogram. Further patch tests were performed with ZEPC (> 98.0%, TCI, Zweindrecht, Belgium) in a dilution series resulting in positive reactions down to 0.01% in petrolatum. Twenty controls were tested negative to 0.1% and 0.01% in petrolatum. The use of rubber dams (Figure 1) during endodontic treatment is recommended to isolate the tooth, prevent microbial contamination, and avoid aspiration or ingestion of dental materials [3, 4]. Source: Wikimedia Commons. Licensed under CC BY-SA 3.0. The potential for NRL gloves and rubber dam used during dental procedures to be the cause of immediate allergic reactions has been acknowledged [5]. Hitherto only one case of delayed reaction following the use of rubber dam has been suspected and described [6]. ZEPC has previously been reported as a cause of allergic contact dermatitis in a patient with exposure to rubber work gloves containing ZEPC [7]. Our patient exhibited a strong (+++) patch test reaction to carba mix, with only doubtful reactions to zinc diethyldithiocarbamate and zinc dibutyldithiocarbamate, and a negative reaction to diphenylguanidine (Table 1). This is likely due to a synergistic, more immunogenic effect of the mixture compared to the individual components. Moreover, the patient reacted to several other carbamates, suggesting cross-reactivity within this chemical group. This is the first report in which a patient with multiple hypersensitivities to rubber chemicals showed positive patch test reactions to two types of rubber dams. A chemical analysis revealed the presence of relevant rubber contact allergens in both samples. Given the type of use, which involves contact with skin and mucous membranes for variable periods, it is advisable in case of a history of rubber hypersensitivity to use dental dams made from alternative materials, such as silicon or vinyl. The authors acknowledge Prof. Camilla Ahlgren for providing the dental dam material and thus enabling us to carry out the patient's investigation. The patients gave the consent for publication. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.