Heat-cured acrylic resin reinforcement with aluminum oxide: Degree of conversion, monomer release and flexural strength

Background : Degree of monomer conversion during processing of acrylic resin denture base materials is very critical in determination of monomer release and mechanical properties of acrylic resin in service. Objectives : The purpose of this research project was to investigate the effect of aluminum oxide powder reinforcement on the degree of monomer conversion, residual monomer, deflection at fracture and flexural strength after processing of heat-cured acrylic resin denture base materials. Also, the correlation between these properties was statistically tested. Materials and methods : The materials used were conventional heat-cured and aluminum oxide powder-reinforced acrylic resin denture base materials (2.5 % and 5% aluminum powder). Samples were prepared according to the manufacturer’s instructions, ADA Specifications no. 12 and the International Organization for Standardization Recommendation. Acrylic resin samples of specific dimensions were prepared from unreinforced and reinforced acrylic resin materials using stainless steel plates. The degree of conversion was determined using FTIR Spectrometer. The concentrations of released methyl methacrylate monomer was measured using isocratic high-performance liquid chromatography. Flexural strength was tested using three point-bending test with a universal testing machine. Results : Aluminum oxide powder reinforcement showed slight increased degree of conversion than that of the unreinforced denture base resins. The released monomer in deionized water from the reinforced acrylic resins was significantly lower than that of the unreinforced specimens. The deflection at fracture of the reinforced specimens was significantly lower than that of the unreinforced acrylic resin. The flexural strength was significantly increased by addition of 2.5 % and 5 % aluminum oxide powder when compared to the unreinforced group. There was high positive correlation between the degree of conversion and flexural strength. On the other hand, there was negative correlation between degree of conversion and monomer release. Conclusions : Aluminum oxide powder reinforcement was slightly increased the degree of conversion of the heat-cured acrylic resin. Aluminum oxide powder reinforcement was significantly reduced the amount of monomer released and the deflection at fracture heat-cured specimens. The reinforced specimens showed significantly increased flexural strength than that of the unreinforced specimens. There was high positive correlation between the degree of conversion and flexural strength. There was negative correlation between degree of conversion and monomer release.