CYTOTOXICITY TESTING OF MATERIALS WITH LIMITED IN-VIVO EXPOSURE IS AFFECTED BY THE DURATION OF CELL-MATERIAL CONTACT

Silicones for dental impression largely are used to record the geometr y of hard and soft dental tissues. They are considered to be medical d evices, and the assessment of cytotoxicity is a necessary step in the evaluation of their biocompatibility. Extracts of six addition-type an d six condensation-type silicones have been tested with L929 cells acc ording to the ISO 10993-Part 5 standard. The cytotoxicity was evaluate d by three different methods: neutral red uptake, propidium iodide (PI ) staining, and amido black staining. According to the selected specif ic assay, contact between cells and material extracts was maintained f or 24 h in the first series of experiments; then, considering that in vivo application of these materials is restricted to a few minutes, ad ditional experiments were performed after 1 h of cell/extract contact. Analysis of the results showed that the addition-type silicones are n ontoxic even when tested after prolonged exposure of the cells to the materials while the condensation-type silicones were cytotoxic at 24 h of incubation. Nevertheless, harm to the patient actually could be ne gligible, considering its very short time of exposure in vivo. This is supported by our finding that most are not toxic after 1 h. We sugges t that the experimental conditions of cytotoxicity testing have to be relevant to the in vivo situation; accordingly, the time of exposure s hould be designed carefully. (C) 1998 John Wiley & Sons, Inc.