Affiliations: Department of Restorative Dentistry, Indiana University School of Dentistry, Indianapolis, IN 46202, USA | Department of Operative Dentistry, Nihon University School of Dentistry, Tokyo, Japan
Note: [] Correspondence should be addressed to Dr. Yoshiki Oshida, Dental Materials Laboratory, Department of Restorative Dentistry, Indiana University School of Dentistry, 1121 West Michigan Street, Indianapolis, IN 46202-5186, USA.
Abstract: In Part I, it was found that (i) 2 vol.% admixture of reinforcing elements in PMMA (Jet) resin matrix had a significant beneficial effects on the mechanical properties, and (ii) among these, zirconia exhibited the greatest improvements in modulus of elasticity, transverse strength, toughness, and hardness number. Using the best combination (i.e., PMMA resin matrix and 2 vol.% ZrO2), exothermic temperature raise and polymerization shrinkage were further investigated. Deterioration in mechanical properties due to prolonged water sorption were also studied for 5 weeks. The following can be concluded: (1) By increasing liquid/powder ratio for PMMA control samples, the peak temperature occurrence was retarded by 3 min and raised by 8°C. (2) The effect of admixed oxide particles to PMMA resin matrix on the heat generated during polymerization was not significant. (3) The polymerization volumetric shrinkage was influenced by the admixture of particles, with increases as large as 0.9% (or 0.3% in linear shrinkage). (4) PMMA resin admixed with 2 vol.% of zirconia particles showed a continuous weight gain due to water sorption, mechanical properties appears to be increasing up to 1-week sorption, followed by rapid drop of all properties. (5) Autopolymerizing acrylic resins are a resin-resin composite material of pre-polymerized beads embedded in a newly formed acrylic matrix. The main fracture modality appears to occur through the matrix and at the interface, although some trans-beads fractures were identified. (6) It was suggested that incorporating certain type of oxide particles into the pre-polymerized beads would provide stronger resin matrix.
Keywords: Polymerization shrinkage, exothermic temperature raise, PMMA, oxide-reinforced polymers, water deterioration
