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 degrees C. Five specimens of each material, 40.0 x 7.0 x 2.0 mm, were made to measure the elastic (storage) (E') and inelastic (loss) (E'') moduli, and loss tangent (tan delta). These parameters were compared with MANOVA and Student-Newman-Keuls test (alpha =.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 delta 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.