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Objective: The aim of this study was evaluating the cytotoxicity of resilient relining materials used in Brazil, according tothe time of water storage and heat treatment. Material and Methods: The specimens were made measuring 14 mm in diameter and 1.2 mm thick. Twelve samples ofeach material were prepared and divided into four groups (n = 3): Group 1: assessment of cytotoxicity immediately after the samples making; Group 2: assessment of cytotoxicity after storage of the samples in distilled water at 37° C for 24hours; Group 3: assessment of cytotoxicity after storage of the samples in distilled water at 37° C for 48 hours; Group 4:cytotoxicity after soaking the samples in water at 55° C for 10 minutes. To prepare the extracts, 3 samples of each groupwere placed into vials containing 3 mL of culture medium and stored at 37° C for 24 hours. L929 cells were used and theMTT test was performed. The results were subjected to two-factor factorial analysis of variance (ANOVA) at the level of5% significance. In addition, the materials were classified according to the cytotoxic effect: non-cytotoxic, slightly cytotoxic,moderately cytotoxic, and strongly cytotoxic. Results: The Dentuflex reliner was considered slightly cytotoxic. The other resins, compared to the control group, wereclassified as non-cytotoxic. Storage in water for 24 or 48 hours did not affect the cytotoxicity of lining materials tested. Conclusion: The heat-treatment reduced the number of viable cells, and Soft Comfort and Dentuflex resins were classifiedas slightly and moderately cytotoxic, respectively.

Objective: The purpose of this study was to evaluate the effectiveness of complementary heat treatment and water storagein reducing cytotoxicity of acrylic resins denture bases used in Brazil by the MTT assay. Material and Methods: First, nine specimens were fabricated from metal matrix in the form of discs with 14 mm indiameter and 1.2 mm of thick. Immediately after making, 24 or 48 hours after storage in distilled water, the samples of heat-polymerized resins were divided into 3 groups (n = 3) according to the type of thermal treatment: Group 1: sampleswere individually exposed to microwave energy (500 W for 3 minutes); Group 2: samples were immersed in water at 550C for 60 minutes; Group 3: samples did not receive heat treatment. To prepare the extracts, 3 samples of each group wereplaced into vials containing 3 mL of culture medium and stored at 37°C for 24 hours. L929 cells were used and the MTTassay was performed to analyze the cellular metabolism. Two-factor analysis of variance was used to detect significantamong groups at 5% significance. Results: After statistical analysis, the materials were classified according to the cytotoxic effect: non-cytotoxic, slightly cytotoxic;moderately cytotoxic; and strongly cytotoxic. The results showed that the resins ranged from moderately cytotoxicto non-cytotoxic, but no statistically significant difference among experimental groups. Furthermore, the water storage andthermal treatments reduced the cytotoxicity of the resins. Conclusions: It was concluded that the resins studied are potentially toxic and that treatments can decrease their cytotoxicity.