Effect of rigid rod polymer filler on mechanical properties of poly-methyl methacrylate denture base material

Objectives The aim of this study was to evaluate the mechanical properties of denture base material with rigid rod polymer (RRP) particulate fillers. Methods Specimens were fabricated from autopolymerized polymethylmethacrylate denture base resin (Palapress Heraus-Kulzer) and RRP particles were used as fillers (Parmax Mississippi Polymer Technologies, Inc.). Five groups were tested: 0 wt% RRP, 10 wt% RRP, 20 wt% RRP, 30 wt% RRP, and 100 wt% RRP. Specimens were stored dry at room temperature for 2 days or in water at 37 °C for 44 days before testing until failure at a three point bending test (ISO 1567) for measuring flexural properties. The surface microhardness, water sorption, and solubility were also measured. Existence of interpenetrating polymer network (IPN) between filler and denture resin was examined using solvent treatment and scanning electron microscopy (SEM). Results Specimens with RRP filler revealed higher flexural modulus, but the flexural strength decreased. Specimens with 30% RRP filler showed flexural strength of 67.4 MPa, whereas specimens without fillers gave strength of 93.9 MPa. The 100% RRP group revealed the highest flexural strength (305 MPa). Flexural strength of water-stored test specimens decreased in most groups when compared to dry specimens. Microhardness increased as a function of RRP filler. SEM micrographs revealed no IPN-network on the surface of RRP fillers. Addition of RRP fillers decreased the water sorption, whereas solubility was not affected. Significance This study revealed that although RRP polymer has good mechanical properties, addition of RRP to denture base resin as fillers did not increase mechanical properties. This was explained by lack of IPN-formation between RRP fillers and polymer matrix.