The Experimental Study Of Denture Base Polymers Reinforced By Different Content Fiber

Polymethyl methacrylate (PMMA) has been the most frequently used material in oral clinical field for its low cost, good biocompatibility and good plasticity, but its low abrasion durability and easily stained restrained its usage, especially the fracture of upper complete denture was an un-resolved problem for many years. Fiber reinforcement composite(FRC) has low density, high strength, high hardness and high elastic modulus, which has been widely used in each part of dentistry such as bridge without metal, post-core system without metal, periodontal splints, space maintainers et al. Since 1930s', it has showed us the uncomparable characters with PMMA. To evaulate and develop better materials for denture use and explore the mechanism of the change of physical and chemical properties, we used ultra-high-modulus polyethylene fiber (UHMPE) and Kevlar fiber to strengthen the resin matrix, and investigated flexural strength, elastic modulus, solubility, residual methyl monomer mount. To detect the mechanism, we compared and analyzed the properties of UHMPE and Kevlar fiber under different weight content, and investigated the characters on the interface between fiber and resin matrix by SEM. To explore the mechanism further, the difference between self-cured resin and heat-cured resin was examined. Considering the complexity in material knowledge, the method for sample manufacturing and analyzing in this experiment was based on ISO 1567 international standard for dentistry-denture base polymer.Part Ⅰ The mechanical properties study of denture base polymers reinforced by different content UHMPEF and Kevlar fibers.The ultrahigh-modulus polyethylene fiber and Kevlar fiber were cut into 0.6±0.1 cm, 0.5wt%, 2.0wt%, 3.5wt%, 5.0wt% fiber mixed with heat- polymerizable powder and auto polymerizable powder respectively, and then added liquid, the ratio of powder liquid was 2:1(g/ml). All specimens were made. Mixed the resin and packed the mixture into the mould with polyester film against the steel cover of the mould. Processed the mixture, but retained the polyester film during the processing cycle. Forheat-polymerizable polymers, the specimens were kept in 74 °C water bath lh, and then rising the temperature to 100°C, keep lh again. After samples were cured, seperating the mould and taking out specimens. Machine the strips in a milling machine on the edges and equally from both moulded surfaces so that the dimensions remain slightly oversized. Take care to avoid overheating the specimens wet-grind all faces and edges smooth and flat with the metallographic grinding papers to the required width and height. Flexural strength and flexural modulus were tested, and fractured test specimens were examined by scanning electron microscope (SEM).The results showed that UHMPEF and Kevlar fiber could enhance the flexural strength and flexural modulus; compared with self-cured resin, the FRC polymers could get strengthened in characters under heat-cured condition. SEM observation showed that there was better bonding effect between fiber and resin matrix.Part II The physical properties study of denture base polymers reinforced by different content UHMPEF and Kevlar fiber.The preparation of test specimens was the same as part I, but the mould and procession of test specimens were different from part I . The water sorption and solubility were tested. The specimens were "conditioned" (mi), "wet" (m2) and "reconditioned" (ni3), and the value of water sorption and solubility were calculated according to special equation. The results showed that UHMPEF and Kevlar fiber had no significant impact on the water sorption and solubility.Part m The chemical property study of denture base polymers reinforced by different content UHMPEF and Kevlar fiber. The residual methyl methacrylate monomer was tested.Heat-cured denture base polymer reinforced by 3.5% and 5.0% UHMPEF and Kevlar fiber.The preparation of test specimens was the same as part II, but the residual methyl methacrylate monomer was analyzed using gas chromatographic method.The results showed that the residul methyl methacrylate monomer decreased compared with no fiber polymers, and the value of every tested group was weet the requirement of ISO 1567.ConclusionsWithin the scope of this research, the following conclusions were made:1. Compared with self-cured resin, FRC could get strengthened in characters under heat-cured condition.2. For self-cured resin, UHMPE and Kevlar fiber had more change in elastic modulus than flexural strength. When the weight content is 5.0% for UHMPE and 3.5% for Kevlar, they had the ideal elastic modulus.3. Both UHMPE and Kevlar fiber could enhance the flexural strength when they were heat-cured, but it was related with the fiber weight content. The best content for UHMPE was 3.5% and 5.0% for Kevlar.5.0% was the best content for the two fibers under the condition of heat-cured.4. UHMPE and Kevlar fiber had no significant impact on the water sorption. The water sorption decreased slightly when the resin was self-cured, and when heat-cured, the water sorption of Kevlar FRC increased. So it indicated that the way of polymerizing may have influence on the adhesive strength of fiber and resin matrix and had an effect on water sorption, but the sort and the content of fiber had no obvious influence on it.5. UHMPE and Kevlar fiber had no significant effect on the water solubility either when the resin was heat-cured, but the water solubility changed a lot when the resin was self-cured. So the way of curing was very important to the solubility.6. UHMPE and Kevlar fiber decreased the residual methyl methacrylate monomer compared with resin without fiber. So UHMPE and Kevlar FRC may meet the requirement of ISO 1567-1999, MOD.7. SEM showed that the short fibers distributed randomly and homogeneously. There were some resin matrix particles on the surface of fibers. It illustrated that there was better adhesive strength between fibers and resin matrix.