DYNAMIC VISCOELASTIC PROPERTIES OF HEAT CURED AND INJECTION MOLDED THERMOPLASTIC DENTURE RESINS

Background: Poly methyl methacrylate (PMMA) resin is still the most commonly used material for denture bases despite of their known disadvantages. Attempts to overcome these problems were approached through the introduction of new denture base materials including the injection molded thermoplastic resins. Objective: The purpose of this study was to evaluate and compare the viscoelastic behavior of conventional heat cured and injection molded thermoplastic resins over wide range of thermal variation. Materials and Methods: A total number of 90 Specimens were prepared. 45 specimens for conventional heat cured resin (Vertex regular, Zeist, Netherlands) and 45 specimens for thermoplastic injection molding denture base materials (Bre-Crystal, Bredent, Germany) were polymerized according to their manufacturer instructions. The Dynamic mechanical thermal analysis at a frequency of 1 Hz under shearing mode and over a temperature range of 5 to 50 0C was carried out using a dynamic viscoelastometer. The shear storage modulus (G′), the loss modulus (G″), and damping factor (tan δ) were obtained. Results: Significant differences were detected between the two tested materials regarding storage and loss moduli. Higher mean storage and loss moduli and damping factors were recorded for the heat cured resin compared to thermoplastic injection molded resin. Conclusion: Within the limitations of this study it could be concluded that different types of denture base materials and processing techniques affect the dynamic viscoelastic properties and consequently could influence their clinical performance in the oral environment. The regular clinical use of thermoplastic resin should be considered in special cases.