Static and Dynamic Mechanical Properties of Acrylic Denture-Base Resins Cross-Linked with Polyvinylchloride

Static mechanical data (creep, at room temperature and at different loading levels) using a three-point bending test method and the viscoelastic characteristics (using the Dynamic Mechanical Thermal Analyser, DMTA) at a temperature range of between 40 °C and 155 °C and a frequency of 1 Hz), of acrylic denture-base resins that incorporate polyvinyl chloride (PVC) power were studied. Characteristic creep curves obeying an exponential growth as a function of time represented by: J(t) = A + Blog(t), where J(t) is the time-dependent deformation in time, t with A and B as constants, which depend on the materials properties, applied load and temperature, were obtained. There is a gradual decrease in storage modulus, E ' with increasing temperature until a critical temperature is reached which depends on the resin type. For the commercial Perspex, a rapid decrease in modulus occurred above 110 °C, which is just above the normally accepted Tg for polymethyl methacrylate, PMMA. For the heat-cured dental resin, QC-20, the critical temperature is higher, at about 120 °C. For the cold-cured dental resin, Pour-n-cure, it softens at about 70 °C and the Maxum, the softening occurs at about 80 °C. The low softening temperatures for the cold-cured are attributed to the presence of residual monomer. However, it is important to recognize the fact that the moduli of the dental resins are somewhat higher than that of the commercial Perspex at ≈40 °C, which is just above the mouth temperature, 37 °C. This is attributed to the possibility of cross-linking, as demonstrated by the limited swelling in acetone. Static Young's Modulus decreases, marginally for all samples tested, with increasing nominal loading times (1, 15.85 and 1,000 seconds).