Development of a discriminatory biocompatibility testing model for non-precious dental casting alloys

ObjectivesTo develop an enhanced, reproducible and discriminatory biocompatibility testing model for non-precious dental casting alloys, prepared to a clinically relevant surface finishing condition, using TR146 oral keratinocyte cells.MethodsComparative biocompatibility was determined following direct and indirect exposure of TR146 cells to two nickel–chromium (Ni–Cr) and a cobalt–chromium (Co–Cr) alloy-discs. The surface roughness of the discs was determined using a contact stylus profilometer and the elemental ion release by inductively coupled plasma mass spectrometry (ICP-MS). Subsequent biocompatibility analysis included cell morphology, cell density measurements with Trypan blue exclusion assay, inflammatory cytokine expression with ELISAs, cellular metabolic activity using XTT and cellular toxicity using lactate dehydrogenase (LDH) release assay.ResultsTR146 cell morphology was altered following direct and indirect exposure to the Ni–Cr alloys but not the Co–Cr alloy. Significant reductions (all P < 0.001) in viable cell density measurements, cellular metabolic activity, significant increases inflammatory cytokine expression and cellular toxicity were observed when TR146 cells were exposed to the Ni–Cr alloys. Significant decreases in cell density measurements, cellular metabolic activity, significant increases inflammatory cytokine expression and cellular toxicity for the Ni–Cr d.Sign®15 alloy compared with d.Sign®10 alloy were identifiable (all P < 0.001). Cellular toxicity was attributed to nickel ion release levels in solution detected by ICP-MS analysis.DiscussionNickel ions from the Ni–Cr alloys permeated the epithelial cells and activated a proinflammatory response, namely IL-1a, IL-8 and PGE2 expression. Further evidence of nickel ioninduced cell death was supported by the decreased biocompatibility of the highest nickel ion releasing alloy (d.Sign®15 compared with d.Sign®10) and the increased biocompatibility of the Co–Cr (d.Sign®30) alloy where nickel ions were absent.