Cultured pulp fibroblasts: are they suitable for in vitro cytotoxicity testing?

The use of cell cultures to test the biocompatibility of dental materials i s gaining in importance. Any cytotoxic effects that restorative materials m ay have will be on the dental pulp and for that reason cultured pulp cells should be the model of choice for biocompatibility testing. The aim of this investigation was to study the growth and morphologic characteristics and toxic response of human pulp lines and to compare these parameters to those of human buccal mucosa fibroblasts. Twenty-one specimens of pulp tissue an d six from buccal mucosa were cultured using standard techniques. Six pulp cell lines were cultured successfully as were all six from the buccal mucos a specimens. From these specimens, 12 growth curves were computed. To study the morphology of the cultured cells, they were observed microscopically a nd classified into three morphological types: slender elongated cells (type I), epithelioid shaped cells (type II) and large stellate cells (type III) . Their numbers and proportions were determined for each cell line and comp ared statistically. To gauge sensitivity to toxic materials, cells were exp osed to concentrations of arecoline. An analysis of the growth curves showe d no statistical difference between pulp cells and buccal mucosa cells; the slopes of the curves, however, differed significantly between individual c ell lines, and these individual differences were greater among pulp cell li nes, The morphology of the pulp and mucosa fibroblasts was similar microsco pically. There was no significant difference between the number and proport ion of the cell types in the two groups, but there were significant differe nces between the individual cell lines. Pulp cells showed a greater inhibit ion of growth when exposed to arecoline. Because pulp fibroblasts are diffi cult to culture, their reported survival rate is poor; due to the differenc es that exist between individual cell lines, we conclude that pulp cells wh en used as single cell lines or even pooled may not be ideal for testing bi ocompatibility, especially if reproducibility is a prerequisite. Any evalua tion will require tests on not one, but several cell lines in order to mini mize the effect of inter-cell-line differences. Their greater sensitivity t o toxic substances, on the other hand, may show that pulp cells could be mo re sensitive indicators of cytotoxicity.