Effect of microwave disinfection on the flexural strength of hard chairside reline resins

Objectives This study investigated the effect of microwave disinfection (650 W/6 min) on the flexural strength of five hard chairside reline resins (Kooliner, Duraliner II, Tokuso Rebase Fast, Ufi Gel Hard, New Truliner) and one denture base resin (Lucitone 550). Methods Thirty-two specimens (3.3×10×64 mm) from each acrylic resin were produced and divided into four groups of eight specimens each. The flexural test was performed after polymerization (G1), after two cycles of microwave disinfection (G2), after 7 days storage in water at 37 °C (G3) and after seven cycles of microwave disinfection (G4). Specimens from group G4 were microwaved daily being stored in water at 37 °C between exposures. The specimens were placed in three-point bend fixture in a MTS machine and loaded until failure. The flexural values (MPa) were submitted to ANOVA and Tukeyʹs test (p=0.05). Results Two cycles of microwave disinfection promoted a significant increase in flexural strength for materials Kooliner and Lucitone 550. After seven cycles of microwave disinfection, materials Kooliner and New Truliner showed a significant increase (p<0.05) in flexural values. The flexural strength of the material Tokuso Rebase was not significantly affected by microwave irradiation. Seven cycles of microwave disinfection resulted in a significant decrease in the flexural strength of material Duraliner II. Material Ufi Gel Hard was the only resin detrimentally affected by microwave disinfection after two and seven cycles. Conclusions Microwave disinfection did not adversely affect the flexural strength of all tested materials with the exception of material Ufi Gel Hard.