CYTOTOXICITY OF URETHANE DIMETHACRYLATE COMPOSITES BEFORE AND AFTER AGING AND LEACHING

The in vitro cytotoxicity of urethane dimethacrylate composites cured at different times by visible light and after different aging times an d extraction treatments was evaluated using succinic dehydrogenase act ivity in the mitochondria of a fibroblastic cell line to reflect cell viability. In addition, extractable chemicals associated with cell res ponse were identified. The composite samples were tested untreated, po lished, or extracted with water or 75% ethanol-water. Balb/c 3T3 fibro blasts were used as the cell culture system while MTT-formazan product ion was used as the toxicity parameter. Cell viability was calculated as a percentage of Teflon controls. Identification of the chemicals wa s measured by extracting the composites with 75% ethanol-water, separa ting the extract by HPLC, and identifying the fractions with mass spec troscopy. In general, cell viability increased continuously with curin g time for differently treated samples at high aging times (288 h) whi le it decreased when the composites were not aged (0 h). In addition, for 75% ethanol or water-extracted composites, cell viability increase d within the first 24 h of aging and reached a plateau after 72 h. Low est cytotoxicity occurred when the samples were extracted with the 75% ethanol solution. The highest cytotoxic effects were found when the s amples were untreated. Slightly reduced cytotoxic effects were seen wi th polished composites. The results suggest that curing the light-acti vated composites for a minimum of 150 s and post-curing for 24 h is re quired to attain comparable biocompatibility with the Teflon control. Removing the oxygen-inhibited layer from these composites decreased th e cytotoxicity by 33% while extracting the composites with 75% ethanol -water decreased it by 77%. Chemicals released from the surface accoun ted for approximately 40% of cellular response while about 60% of the response was due to chemical components released from the bulk. The pr imary leachable component from the composites was UDMA monomer. Small quantities of 1,6 hexane diol methacrylate, camphoro-quinone, and 2,4, 6-tritertiarybutyl phenol also were found. (C) 1998 John Wiley & Sons, Inc.