Influence of metals on IL-6 release in vitro

Certain dental alloys have been claimed to cause gingival and periodontal inflammation. However, little information is available on the molecules mediating the mechanism of such an effect. Recently, a three-dimensional cell culture system consisting of human fibroblasts and keratinocytes has been introduced for evaluating the irritancy of cosmetic products, including the analysis of inflammatory mediators. In the present study the influence of pure metals and a high noble dental cast alloy upon cell viability and the synthesis of the proinflammatory mediator interleukin-6 was recorded in this in vitro skin equivalent model. The cultures were exposed to test specimens fabricated from copper, nickel, cobalt, zinc, palladium, tin, indium, a high noble cast alloy and a dental ceramic. Cell vitality was reduced after a 24 h exposure to copper (14-25% of untreated controls), cobalt (60%), zinc (63%), indium (85%), nickel (87%), and the heat treated and not heat treated high noble cast alloy (87%/90%). Dental ceramic, palladium and tin did not influence cell viability. Increased IL-6 levels were observed in cultures exposed to copper (5-19-fold compared to untreated controls), zinc (16-fold), cobalt (12-fold), nickel (10-fold) and palladium (4-fold). Other materials tested produced IL-6 levels comparable to those of untreated controls. Our findings suggest that metal ions are involved in proinflammatory activity at low toxicity and non-toxic levels as assessed by different biological endpoints.