Figure 5. The effect of grade 4 and grade 5 implant particles on human gingival fibroblast viability in vitro. Viability was determined using an MTT metabolic activity assay. Cells were exposed to either a dissolution products (ions and nanoparticles) or b culture medium containing suspended implant particles throughout the duration of the culture period. Cells were exposed to various concentrations of particles (0.75, 1.5 or 3 mg ml−1). Basal medium and basal medium containing unprocessed dental implants were used as controls. All results were normalized against the value of basal medium at day 3. Results presented as mean ± standard deviation, n = 3. The asterisk indicates p < 0.05, and + indicates 0.05 < p < 0.1 when compared to basal medium control at each time point.