Dynamic mechanical properties of hard, direct denture reline resins

Statement of problem: Dynamic mechanical properties of hard, direct reline resins are important factors in the clinical success of dentures. However, little information is available on the nature of these properties. Purpose: This study evaluated the dynamic mechanical properties of a variety of hard, direct reline resins: (1) visible light-polymerized, powder-liquid type, (2) visible light-polymerized, paste-type, (3) autopolymerized, powder-liquid type, as classified by component composition and mode of polymerization activation, namely, type of delivery system, and (4) heat-polymerized denture base materials. Material and methods: The dynamic mechanical analysis (DMA) of 8 commercial hard denture reline materials (HDR) (2 visible light-polymerized, powder-liquid type, 4 visible light-polymerized, paste-type, and 2 autopolymerized, powder-liquid type), and 2 heat-polymerized denture base materials was obtained at a frequency of 1 Hz at 37°C. Five specimens of each material, 40.0 × 7.0 × 2.0 mm, were made to measure the elastic (storage) (E′) and inelastic (loss) (E″) moduli, and loss tangent (tan δ). These parameters were compared with MANOVA and Student-Newman-Keuls test (α =.05). Results: The E′ values of 3 visible light-polymerized, paste-type reline resins were significantly higher than those of the other 5 reline resins. However, the E′ values of all reline resins were significantly lower than those of the 2 heat-polymerized denture base resins. Except for 1 autopolymerized reliner, all reline materials had significantly lower E″ than the heat-polymerized denture base resins. The tan δ values of all but 1 visible light- and autopolymerized reliners were significantly higher than those of the heat-polymerized denture base materials. Conclusions: Three visible light-polymerized, paste-type reline resins showed greater stiffness than the visible light- or autopolymerized, powder-liquid type reline resins. However, all of the hard, direct reline resins, including the 3 paste-type materials, exhibited greater flexibility compared to the heat-polymerized denture base resins.