Initial Cytotoxicity of Additively and Subtractively Manufactured Resin‐Based Materials for Interim Fixed Dental Prostheses: An In Vitro Study

OBJECTIVES: To compare the initial cytotoxic response of additively manufactured (AM) and subtractively manufactured (SM) resin-based materials for interim fixed dental prostheses (FDPs) under indirect and direct in vitro exposure conditions. MATERIAL AND METHODS: A total of 216 standardized resin discs were fabricated from AM resins (Group P, n = 108) and SM polymethyl methacrylate (PMMA)-based resins (Group M, n = 108). L929 mouse fibroblasts were used as the biological model, with a negative control group (Group C, n = 36). After 24 h of cell attachment, cell viability was assessed after 72 h under two conditions: indirect exposure to resin eluates and direct contact with resin discs. Viability was quantified by crystal violet staining. Data were analyzed using Kruskal-Wallis tests followed by Dunn's pairwise post hoc comparisons (α = 0.05). RESULTS: In the indirect assay, Group M showed 87% cell survival relative to the control, whereas Group P showed 65%; in the direct assay, values were 89% and 48%, respectively. Significant differences were observed among pooled groups in both assays (p < 0.001). Based on ISO 10993-5 thresholds, Group P was classified as slightly cytotoxic in the indirect assay and moderately cytotoxic in the direct assay, whereas Group M remained within the non-cytotoxic to slightly cytotoxic range. Group P showed significantly lower cell viability than Group M in both assays (adjusted p < 0.001), while no statistically significant differences were detected within each manufacturing category (adjusted p > 0.05). CONCLUSIONS: At 72 h, the tested AM resins showed significantly lower cell viability than the tested SM PMMA-based resins under the present in vitro conditions. CLINICAL SIGNIFICANCE: The lower cell viability observed for the tested 3D-printed interim materials under short-term in vitro conditions highlights the need for caution when extrapolating 72-h cell-viability findings to clinical performance and supports further standardized long-term in vitro and in vivo investigations.