Dermal uptake study with 4,4'-diphenylmethane diisocyanate led to active sensitization

In vitro cytotoxicity of different thermoplastic materials for clear aligners

OBJECTIVES

To investigate the in vitro cytotoxicity of different thermoplastic materials for clear aligners on human primary gingival fibroblasts (HGFs).

MATERIALS AND METHODS

Four materials for clear aligners were considered in this study: Duran (Scheu-Dental GmbH, Iserlohn, Germany), Biolon (Dreve Dentamid GmbH, Unna, Germany), Zendura (Bay Materials LLC, Fremont, CA, USA), and SmartTrack (Align Technology, San Jose, CA, USA). Three out of four materials (Duran, Biolon, Zendura) were assessed as thermoformed and nonthermoformed, whereas the SmartTrack was assessed only as thermoformed. The samples were placed at 37°C in airtight test tubes containing Dulbecco's Modified Eagle's Medium (DMEM; 0.1 mg/mL) for 14 days. The cell viability of HGFs cultured with this medium was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Data were analyzed by means of one-way and two-way analysis of variance and post hoc tests (α = 0.05).

RESULTS

Each material exhibited a slight cytotoxic effect after 14 days. The highest cytotoxicity level on HGFs was achieved by Biolon (64.6% ± 3.3 of cell viability), followed by Zendura (74.4% ± 2.3 of cell viability), SmartTrack (78.8% ± 6.3 of cell viability), and finally Duran (84.6% ± 4 of cell viability), which was the least cytotoxic. In the comparison between nonthermoformed and thermoformed materials for Duran, Biolon, and Zendura, the thermoformed materials showed the highest level of cytotoxicity (P < .001).

CONCLUSIONS

Under the experimental conditions of this study, all the materials for clear aligners presented a slight cytotoxicity. Biolon was the most cytotoxic and the thermoforming process increased the cytotoxicity of the materials.

Residual Isocyanates in Medical Devices and Products: A Qualitative and Quantitative Assessment

We conducted a pilot qualitative and quantitative assessment of residual isocyanates and their potential initial exposures in neonates, as little is known about their contact effect. After a neonatal intensive care unit (NICU) stockroom inventory, polyurethane (PU) and PU foam (PUF) devices and products were qualitatively evaluated for residual isocyanates using Surface SWYPE™. Those containing isocyanates were quantitatively tested for methylene diphenyl diisocyanate (MDI) species, using UPLC-UV-MS/MS method. Ten of 37 products and devices tested, indicated both free and bound residual surface isocyanates; PU/PUF pieces contained aromatic isocyanates; one product contained aliphatic isocyanates. Overall, quantified mean MDI concentrations were low (4,4'-MDI = 0.52 to 140.1 pg/mg) and (2,4'-MDI = 0.01 to 4.48 pg/mg). The 4,4'-MDI species had the highest measured concentration (280 pg/mg). Commonly used medical devices/products contain low, but measurable concentrations of residual isocyanates. Quantifying other isocyanate species and neonatal skin exposure to isocyanates from these devices and products requires further investigation.

Role of dermal exposure in systemic intake of methylenediphenyl diisocyanate (MDI) among construction and boat building workers

The causal relationship between inhalation exposure to methylenediphenyl diisocyanate (MDI) and the risk of occupational asthma is well known, but the role of dermal exposure and dermal uptake of MDI in this process is still unclear. The aims of this study were to measure dermal exposure to and the dermal uptake of MDI among workers (n=24) who regularly handle MDI-urethanes. Dermal exposure was measured by the tape-strip technique from four sites on the dominant hand and arm. The workers with the highest exposure (n=5) were biomonitored immediately after their work shift, in the evening and the next morning, using urinary 4,4´methylenedianiline (MDA) as a marker. Dermal uptake was evaluated by comparing workers' MDA excretions both when they were equipped with respiratory protective devices (RPDs) and when they did not use them. The measured amounts of MDI on their hands varied from below 0.1 to 17 μg/10 cm(2) during the test. MDI concentrations were in the range of 0.08 to 27 μg m(-3) in the breathing zone outside the RPDs. MDA concentrations varied from 0.1 to 0.2 μmol mol(-1) creatinine during the test period. The decreasing effect of RPDs on inhalation exposure was absent in the next morning urine samples; this excretion pattern might be an indication of dermal uptake of MDI.

Permeation tests of glove and clothing materials against sensitizing chemicals using diphenylmethane diisocyanate as an example

Diphenylmethane diisocyanate (MDI) is a sensitizing chemical that can cause allergic contact dermatitis and asthma. Protective gloves and clothing are necessary to prevent skin exposure. Breakthrough times are used for the selection of chemical protective gloves and clothing. In the EN 374-3:2003 European standard, breakthrough time is defined as the time in which the permeation reaches the rate of 1.0 µg min(-1) cm(-2) through the material. Such breakthrough times do not necessarily represent safe limits for sensitizing chemicals. We studied the permeation of 4,4'-MDI through eight glove materials and one clothing material. The test method was derived from the EN 374-3 and ASTM F 739 standards. All measured permeation rates were below 0.1 µg min(-1) cm(-2), and thus, the breakthrough times for all the tested materials were over 480min, when the definitions of EN 374-3 and ASTM F 739 for the breakthrough time were used. Based on the sensitizing capacity of MDI, we concluded that a cumulative permeation of 1.0 µg cm(-2) should be used as the end point of the breakthrough time determination for materials used for protection against direct contact with MDI. Using this criterion for the breakthrough time, seven tested materials were permeated in <480min (range: 23-406min). Affordable chemical protective glove materials that had a breakthrough time of over 75min were natural rubber, thick polyvinylchloride, neoprene-natural rubber, and thin and thick nitrile rubber. We suggest that the current definitions of breakthrough times in the standard requirements for protective materials should be critically evaluated as regards MDI and other sensitizing chemicals, or chemicals highly toxic via the skin.

Oral epithelial cell reaction after exposure to Invisalign plastic material

INTRODUCTION

Invisalign plastic aligners (Align Technology, Santa Clara, Calif) are used to correct malocclusions. The aligners wrap around the teeth and are in contact with gingival epithelium during treatment. The purpose of this study was to evaluate the cellular responses of oral epithelium exposed to Invisalign plastic in vitro.

METHODS

Oral epithelial cells were exposed to eluate obtained by soaking Invisalign plastic in either saline solution or artificial saliva for 2, 4, and 8 weeks. Cells grown in media containing saline solution or saliva served as controls. Morphologic changes were assessed by light microscopy. The 3-[4, 5-dimethythiazol- 2-yl]-2, 5-diphenyl tetrazolium bromide assay and flow cytometry were used to determine cell viability and membrane integrity, respectively. Cellular adhesion and micromotion of epithelial cells were measured in real time by electrical cell-substrate impedance sensing.

RESULTS

Cells exposed to saline-solution eluate appeared rounded, were lifted from the culture plates, and demonstrated significantly increased metabolic inactivity or cell death (P <0.05). Saliva eluates did not induce significant changes in cell viability compared with untreated cells. Flow cytometry and electric cell-substrate impedance sensing showed that cells treated with saline-solution eluate exhibited compromised membrane integrity, and reduced cell-to-cell contact and mobility when compared with saliva-eluate treatment.

CONCLUSIONS

Exposure to Invisalign plastic caused changes in viability, membrane permeability, and adhesion of epithelial cells in a saline-solution environment. Microleakage and hapten formation secondary to compromised epithelial integrity might lead to isocyanate allergy, which could be systemic or localized to gingiva. However, these results suggest that saliva might offer protection.