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The fracture or dislodgement of an interim prosthesis may result in additional appointments and could negatively affect the outcome of a fixed prosthodontic procedure.The purpose of this study was to evaluate the flexural strength (FS), flexural modulus (FM), work-of-fracture (WOF), and Weibull parameters of 4 bis-acryl (Protemp Plus, Integrity, Turbo Temp 2, Temphase Fast-set) and 2 urethane (NuForm and Tuff-Temp) interim resins after being stored in distilled water for 1 hour and 24 hours.Rectangular beam specimens (25 × 2 × 2 mm) of each resin (n=23) were prepared and stored in distilled water at 37°C. Then 3-point bending tests were performed on 1-hour and 24-hour (wet) and 24-hour (dry and wet) specimens in a universal testing machine at a cross-head speed of 1.0 mm/min. Stress/strain curves were generated and flexural strength, flexural modulus, and WOF values were calculated. Data were subjected to 3-way ANOVA and the Tukey-Kramer pairwise comparison test (α=.05). FS data were also subjected to a 2-parameter Weibull analysis.The 24-hour (wet) mean flexural strength and flexural modulus values were significantly higher than 1-hour values. The urethane Tuff-Temp, chemically and dual-polymerized, showed significantly higher (P<.05) 1-hour FS and FM, while the bis-acryl Protemp Plus showed significantly greater flexural strength and work-of-fracture than the other resins after 24 hours of wet storage. Protemp Plus, NuForm, and Turbo Temp 2 did not decrease in flexural strength and flexural modulus after 24 hours in dry and wet storage conditions. The Weibull modulus values of the flexural strengths of the interim resins at 1 hour and 24 hours ranged from 8.4 to 26.8.Postgelation polymerization plays an important role in the substantial increase in the flexural strength and flexural moduli of the interim resins between 1 and 24 hours. A wide variation in the mechanical properties of the interim resin materials was noted but was, for the most part, not category specific.