Graded Nano Glass-Zirconia Material for Dental Applications-Part II Biocompatibility Evaluation

A graded glass/graded zirconia (G/Z) system was previously synthesized via the infiltration of a low modulus nanosized glass into a zirconia surface. The bond strength of G/Z to veneering porcelains was demonstrated to be 3-fold higher than in zirconia-based systems. Nevertheless, biocompatibility testing prior to the possible clinical application of G/Z systems is essential. Herein, such biocompatibility testing was performed with L-929 fibroblasts seeded onto G/Z and yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) for 2-72 h. Assessments included an oral mucous membrane irritation test in conjunction with analyses of cell viability, cell morphology, cell cycle, cell apoptosis, oxidative stress responses, inflammatory cytokine expression, and cellular toxicity. Cell viability tests showed no significant decrease in G/Z- and Y-TZP-treated cells over 72 h. Fluorescence and SEM images demonstrated that cell spreading on Y-TZP and G/Z was similar; cells were flattened and well-spread. Oxidative stress data for G/Z- and Y-TZP-treated cells showed no significant difference in ROS production. Cellular toxicity results for G/Z did not elicit significant differences in LDH release compared with Y-TZP over 72 h. G/Z and Y-TZP had no significant differences in IL-1α, IL-8, PGE2, and TNF-α expression and elicited significantly increased IL-8 expression compared with that of the untreated control group. Cells that were cultured with G/Z showed no significant changes in cell cycle distribution compared with Y-TZP or the untreated control group. Cells that were cultured with Y-TZP and G/Z showed no apoptosis compared to untreated controls at 24 and 48 h. According to the oral mucous membrane irritation test, scores for the macroscopic and microscopic observations for both G/Z and Y-TZP sides were 0, demonstrating no consequent irritation. Therefore, the excellent biocompatibility of G/Z indicates that it has potential for future clinical applications.