A model culture system with human gingival fibroblasts for evaluating the cytotoxicity of dental materials

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Abstract
A model experimental culture system and protocol are described to screen polymerized dental materials for diffusible toxic products. The system employs cultures of human gingival fibroblasts grown in plates containing immobilized samples of polymerized resins. Comparative cytotoxicity is evaluated by counting viable cells with the aid of phase optics at several time periods up to 48 h. To achieve adequate statistical sampling, multiple counts are made in four different zones at 90° angles from each sample and at three distances from the centers of samples. The most significant data were generated during a 24 to 48 h test period in culture. This cytotoxicity test measured cell death as a function of time of exposure and distance from the sample (24 h, 0 to 3 mm; 48 h, 3 to 6 mm) and permitted a calculation of the relative cytotoxicity for each material, which is termed the viability index (VI). This can be expressed as a percentage related to the control, which is called the time-distance cytotoxicity index (TDCI). This method is simple to carry out because it uses basic laboratory equipment, is rapid, and has a sound scientific basis. It focuses on times and distances when or where, or both, the greatest cellular changes are taking place. Some data illustrated are based on the screening of eight different restorative resins. The literature of cell culture testing of dental materials is reviewed. It is concluded that biotoxicity studies ideally should employ diploid human target cells from the oral cavity because the cells retain specialized features. Secondary cultures or strains of human diploid gingival fibroblasts, which are relatively easy to obtain and maintain, are recommended as cells of choice for screening dental restorative materials in vitro.