The effect of different cooling procedures on mechanical properties of denture base materials measured by instrumented indentation testing

PURPOSE To evaluate the different cooling procedures on the mechanical properties of five heat-cured polymethyl methacrylate (PMMA) denture materials. METHODS 250 specimens were made equally from Meliodent (ME), Paladon 65 (PA), Probase Hot (PB), Stellon QC-20 (QC) and Vertex Rapid Simplified (VE) implementing five different cooling procedures (n=10/procedure): A) removal from water bath, bench-cooling (10min) and cooling under water (15min), B) remain in water bath till room temperature, C) removal from water bath and cooling in water for 15min, D) removal from water bath and bench cooling till room temperature and E) removal from water bath, bench cooling for 30min and cooling under water for 15min. The specimens were immersed in distilled water (15 days/37ºC) and then subjected to Instrumented Indentation Testing for Martens Hardness (HM), indentation modulus (E$_{IT}$) and elastic index (η$_{ΙΤ}$). Results were statistically analyzed by two- and one-way Analysis of variance (ANOVA) plus Tukey post hoc tests (α=0.05). RESULTS The highest values for HM were recorded for QC, PA, VE with B cooling procedure, PB with A and ME with E, for E$_{ΙΤ}$ for QC, PB with A, for PA, VE with B and ME with E, and for η$_{IT}$ for QC, PB with B, PB with E, ME with C and VE with D. CONCLUSIONS The cooling procedures recommended for PB resulted in the lowest mechanical properties. A and B may be considered as universal short- and long-cooling procedures respectively providing the highest mechanical properties for the materials tested