Cytotoxic effects of packable and nonpackable dental composites

Objectives. Advanced dental packable and nonpackable composite materials have been recently introduced onto the market as ‘amalgam alternatives’ for the restoration of posterior teeth. Most established composites are applied in increments of no more than 2 mm and light cured to ensure complete polymerization, whereas new formulations have been claimed to be suitable for application in increments of 4–5 mm. The aims of the present study were to analyze the cytotoxicity of these new composites in comparison to an established nonpackable composite using standardized cell culture systems and to examine the influence of thickness of the light cured increments on the cytotoxicity of these materials. Methods. Specimens were prepared in polyethylene tubes covered with mylar. All materials were light cured in 2.5 or 5 mm increments with a Demetron curing light (light intensity: 550 mW/cm2). Specimens were added to the cultures immediately after production or after preincubation for 1, 2, 7 days or 6 weeks under cell-culture conditions. Specimens were incubated with L-929 fibroblasts for 72 h and cell numbers determined by flow cytometry. In a different series of experiments, dopaminergic cells were incubated with composite supernatants. Results. Results with L-929 fibroblasts demonstrated that all freshly prepared composite materials reduced cell numbers (p<0.05) in comparison to controls. The cytotoxicity of all substances diminished after increasing preincubation times (p<0.0001). In a rank order of cytotoxicity, the established composite and two of the advanced composite materials exhibited least cytotoxicity, whereas the other advanced composites showed moderate or severe cytotoxic effects. The cytotoxicity of each material was much higher when polymerized in 5 mm increments than in 2.5 mm composite increments (p<0.0001). Significance. Our data demonstrate that the advanced composites tested show similar or more severe cytotoxicity than an established nonpackable composite and that cytotoxicity of all materials investigated increases when applied in a 5 mm bulk increment.