Effects of Aging and Denture Cleansers on the Flexural Strength and Surface Microhardness of Two Flexible Denture Materials

Clinical observations of flexible partial removable dental prostheses (FPRDP) indicate deteriorating physical properties often requiring replacement. Patients are advised to cleanse FPRDPs daily with denture cleansers. The purpose of this study was to investigate aging and denture cleansing effects on flexural strength and surface microhardness of FPRDPs. Methods: Rectangular shaped (2.0 mm × 10.0 mm × 35.0 mm) specimens were prepared by a dental laboratory as clinical FPRDPs from DuraFlex™ and Valplast®. Specimens were divided into fourteen groups (n=8 per group) by respective group treatments and storage methods. Treatments were artificial aging (thermal cycled), no artificial aging, and physiological body temperature. Storage methods were reverse osmosis water (22°C and 37°C) and denture cleansers. Flexural strength was measured using three-point bending test in a universal testing machine. Microhardness determinations were made using a Vickers microhardness tester. Data were analyzed with three-way ANOVA and SNK post-hoc test (α=0.05) between baseline and 5,000 cycles. Results: Significant differences in flexibility between DuraFlex™ and Valplast® occurred at baseline (p=0.027). Valplast® specimens became significantly more flexible in all treatments groups (p<0.001). DuraFlex™ experienced no significant change for flexural strength among any groups. Significant differences occurred between DuraFlex™ and Valplast® for Efferdent thermocycled (p=0.015), Polident thermocycled (p<0.001), and specimens stored at 37°C. Conclusion: Decreased flexural strength in Valplast ® is perhaps related to water absorption. Thermocycling and elevated temperature storage had a minimalistic effect on microhardness in FPRDP materials. DuraFlex™ maintained its flexural strength and surface hardness, and Valplast® did not. In regards to surface hardness and flexural strength, Polident® appeared to be less deleterious to both DuraFlex™ and Valplast®. This study may help improve clinical recommendation for home cleansing advice to patients, FPRDP performance, and appearance.