In vitro biological response to core and flowable dental restorative materials

In vitro cytotoxicities of commercially available core and flowable dental restorative materials were assessed and compared to traditional resin composites. Our hypothesis was that the increased resin diluents added to achieve higher flow in flowables would increase cytotoxicities, whereas the higher filler content of core materials would decrease cytotoxicities relative to traditional resin composites.

Specimens were made under aseptic conditions, then extracted into an artificial saliva solution for 0-4 weeks, to assess the effect of aging on cytotoxicity. After extraction, specimens were tested for cytotoxicity in vitro using Balb/c fibroblasts in direct contact format. Cells were exposed to the materials for 48h, after which the mitochondrial activity of the cells was measured (MTT method). Cellular activity was normalized to Teflon negative controls.

Core materials were uniformly and severely (<50% of Teflon cellular activity) cytotoxic initially, but several materials (Corepaste, Definite core) improved somewhat with aging in artificial saliva. Flowable materials were uniformly and severely cytotoxic with no trend toward improvement with aging. The Definite-flow was the least cytotoxic of the flowable materials, but it too was severely cytotoxic.

Commercially available core and flowable restorative materials showed severe in vitro cytotoxicities that are worse than some traditional composites and most dental casting alloys and amalgams used today. Of particular note was the persistent cytotoxicity of these materials after 4 weeks of extraction with artificial saliva. These cytotoxicities indicate a continuing release of mass from these materials at levels that have biological relevance in vitro. In vivo relevance of these cytotoxicities is less clear, but these results indicate a higher biological risk for these materials compared to traditional materials that exhibit less initial toxicity and improve with aging time.