Physical Properties of Expired Composite Resins After Air Fryer Thermal Treatment

Abstract

Aims: This study aimed to investigate the Physical properties of two expired composite resins after an experimental air fryer thermal treatment. Methods: Three factors were assessed at two levels each: composite resin (Filtek Z350 XT, 3M ESPE, or Opallis, FGM), polymerization protocol (light only or light + heat), and expiration date (expired or non-expired). Resin bars (n = 6) measuring 2 × 2 × 12 mm were fabricated for three-point micro-flexural testing, and cylindrical specimens (n = 4) measuring 2 mm × 5 mm were prepared for Knoop microhardness testing. Additionally, cylindrical specimens (n = 4) measuring 1 mm × 15 mm were used for water sorption and solubility tests. Data were analyzed by three-way ANOVA and Tukey post-hoc test. Results: Knoop microhardness differed significantly among groups (p = 0.024), with highest values for non-expired Z350 XT activated by light, expired Z350 XT activated by light + heat, and non-expired Opallis activated by light. No significant differences were found for flexural strength (p = 0.423), elastic modulus (p = 0.365), or water sorption and solubility (p = 0.893 and p = 0.193, respectively). Conclusion: Except for microhardness, the physical properties analyzed of the expired composite resins were not affected by expiration date, polymerization protocol, or resin type.