Comparative Cytotoxicity of Commercially Pure Titanium, Silver–Palladium and Nickel–Chromium Alloys on Human Gingival Fibroblasts: An In Vitro Study

Background/Objectives: This study aimed to evaluate the direct effect of elements released from dental casting alloys on human gingival fibroblasts (HGF). Methods: Ten discs each of commercially pure titanium (Ti), silver-palladium (Ag-Pd), and nickel-chromium (Ni-Cr) alloys, measuring 4 mm in diameter and 3 mm in thickness, were fabricated and placed directly on HGF cultures for 72 h. Five discs from each alloy group were incubated in DMEM, whereas the remaining five discs were incubated in artificial saliva. Cytotoxicity was assessed using three in vitro methods: morphological evaluation of HGF, the dye exclusion test (DET), and the methyl-thiazolyl-tetrazolium (MTT) colorimetric assay. Results: HGF directly exposed to cpTi, Ag-Pd, and Ni-Cr discs demonstrated reduced cell density around the alloy specimens compared with untreated control cells after 72 h of incubation in both DMEM and artificial saliva. cpTi alloy exhibited no detectable cytotoxic effects, whereas Ag-Pd and Ni-Cr alloys demonstrated cytotoxicity in both DMEM and artificial saliva under the experimental conditions. Among the tested alloys, Ni-Cr exhibited the highest cytotoxicity. Artificial saliva enhanced the cytotoxic effects of the tested alloys, as evidenced by increased morphological alterations, reduced cell viability, and lower MTT activity compared with DMEM. Conclusions: cpTi alloy exhibited the lowest direct cytotoxic effect on HGF in both DMEM and artificial saliva. In contrast, Ag-Pd and Ni-Cr alloys demonstrated greater cytotoxicity, particularly in the presence of artificial saliva, suggesting that both alloy composition and the surrounding environment influence the biological response of oral soft tissues.