Cumulative effect of disinfection procedures on microhardness and tridimensional stability of a poly(methyl methacrylate) denture base resin.

Microwave irradiation has been used for disinfection of dentures instead of chemical solutions; yet, its effect on resin properties after repeated procedures still is unclear. This study evaluated the cumulative effect of two disinfection methods on Knoop microhardness and tridimensional stability of a poly(methyl methacrylate) denture base resin. For the microhardness measurement, 24-resin discs received mechanical polishing and were submitted to the following treatments: (1) control (no disinfection), (2) chemical disinfection (immersion in 100ppm chloride solution for 24h), or (3) microwave disinfection (irradiation at 690 W for 6 min). Disinfection procedures were performed twice (T1, T2) with a 7-day interval. Knoop microhardness was recorded after polishing (T0) and after T1 and T2. For the dimensional stability test (measured by the adaptation of the denture bases), 36-maxillary denture bases were obtained from type III dental stone casts duplicated from a metallic master model and submitted to the disinfection treatment. Adaptation of denture bases was measured at baseline (T0) and after T1 and T2 by weighing a vinyl polysiloxane film reproducing the gap between resin base and master model. Data were analyzed by ANOVA GLM for repeated measures and Bonferroni's test, alpha = 0.05. Knoop microhardness was not modified by any disinfection procedure but decreased over time. Denture resin bases submitted to microwave disinfection had gradual increase of distortion over time, while bases immersed in chloride solution did not differ from the control group and remained dimensionally stable from T1 to T2. (c) 2007 Wiley Periodicals, Inc.