Preparation Of Novel Acrylic Resin Denture Base Enhanced With Nanocomposites And Study On Its Flexural Properties

Acrylic (PMMA) resin is the most commonly used denture base material in clinical fabrication. Acrylic resin denture base has a combination of virtues rather than one excellent aspect that accounts for its wide usage, including its popularity in satisfying aesthetic demands, fairly good physical property and clearly defined processing method. However, this material is not ideal in every respect. Fracture of acrylic resin happens quite frequently because of the fatigue and chemical degradation of base material and its low toughness. Many attempts have been made to repair fractures of denture base for decades in order to improve its usability.Organic and inorganic materials have different features, when combined together the composites may get better and more comprehensive properties. Still some problems might be caused when mixing these two materials, such as compatibility between organic/inorganic phase and dispersion of inorganic particles. In this research, silica nano-particle (SiO2) and hydroxy apatite nano-whisker (HA) were chosen as inorganic fillers to reinforce acrylic denture base. Through "Grafting To" and "Grafting From", two different surface modification route, modified silica and HA composites were prepared to be incorporated into denture base, which had similar polymeric coating and good adhesion with PMMA matrix. The modification made inorganic filler as an effective reinforcement for denture base and mechanical properties of the denture base samples prepared were enhanced greatly. The size, morphology and surface property of the inorganic fillers and its effect on the mechanical properties of the denture base prepared were discussed in the present study:(1) Novel acrylic denture base enhanced with SiO2:Thermal gravimetric analysis (TGA), fourier transform infrared spectroscopy (FT-IR) and transmission electron microscope (TEM) all show that PMMA chains were coated on the surface of prepared SiO2through "Grafting To" route. This PMMA-SiO2nanocomposites displays core-shell structure and the grafting ratio reaches17.8wt%. The mechanical properties of prepared denture base were enhanced clearly with the incorporation of PMMA-SiO2nanocomposites and the optimal inorganic content was1.5wt%. PMMA-SiO2with40nm diameter as filler in the denture base sample played better mechanical performance than those with80nm and150nm diameter, due to itsvhigh specific surface area and interface boundary. Cross-section picture from scanning electron microscope (SEM) shows the silica had better compatibility with PMMA matrix and dispersed well after surface modification.(2) Novel acrylic denture base enhanced with SiO2:TGA, FT-IR and SEM manifest that PMMA-SiO2cluster were synthesized through "Grafting From" route using atom transfer radical polymerization, which had higher grafting density up to44.6wt%. Contact angle (CA) shows surface modification of silica turned its surface from hydrophilic to hydrophobic. The composites with more polymer content got bigger CA and reveals better reinforcing capacity from their machanical performance. Denture base enhanced with PMMA-SiO2nano cluster had the best mechanical properties compared to the "Grafting To" route silica sample and coupling agent modified silica sample. This can also be confirmed through cross-section picture from SEM, which showed good coherence between organic/inorganic interface. The optimal inorganic content of those three acrylic sample was1.5wt%. On the contrast, the mechanical properties of acrylic resin decreased when incorporated with unmodified silica.(3) Novel acrylic denture base enhanced with HA:TGA, FT-IR, XRD and SEM manifest that HA whiskers were prepared by hydrothermal homogeneous precipitation process. PMMA-HA nano whisker with15.2wt%grafting ratio were synthesized through "Grafting To" route after that. The mechanical properties of prepared denture base were also enhanced when incorporated with modified HA whisker, but failed when added with unmodified HA whisker. The optimal organic incorporation content is0.6wt%to flexural properties and0.4wt%to impact strength. Different modification steps lead to similar mechanical performance of enhanced acrylic resin, which is different from silica fillers. Cross-section view from SEM shows that the modified HA cohered with acylic resin tightly, while the unmodified HA whisker had some cavity around.