Since early 1940’s, PMMA became the most widely preferred and used denture base material by prosthodontists and other dentists[1, 2]. Features such as aesthetic appearance, easy processing and low cost have made PMMA a widely used base material in prosthetic dentistry[3–5]. Besides these, PMMA is biocompatible, safe, dimensionally stable, non-taste and odor, non-irritant, non-toxic, stable in the oral environment, insoluble with saliva and color stable. Despite these excellent properties PMMA has unfavorable weakness in some mechanical and physical properties such as impact resistance, flexural strength and fatigue fracture[7, 8]. 63–68% of the dentures become useless because of the fracture as a result of fatigue fracture due to chewing forces while in mouth or breaking due to accidental fall on hard surfaces while out of mouth[9, 10]. In order to avoid fractures, strategies like enhancing PMMA denture base by metal wire were used but poor adhesion between the metal wire and the PMMA matrix was the main problem with this strategy[8, 10–13]. Another application for this purpose was forming a graft copolymer of PMMA and butadiene styrene but it was found to be weaker than PMMA because of the low bending strength compared to conventional acrylic resin despite its high impact resistance[14, 15].
Carbon fibers, aramid fibers, high molecular weight polyethylene fibers and similar fibers were used as denture base enhancing materials and it was reported that these fibers increased the bending and impact strength of the denture base resin[5, 8, 16–18]. Due to their biocompatibility, aesthetic compatibility and mechanical properties, nylon fiber, polyethylene fibers, polyamide fibers and especially glass fibers were used in several studies[16, 17, 19, 20]. Enhancing effect of glass fibers on bending properties and fatigue resistance of PMMA denture base resin was previously reported[8, 16, 19, 21, 22]. Polypropylene is suitable material for PMMA base resin reinforcement because of its properties such as high-level resilience, elasticity and tensile strength, durable in acid and similar medium, low density (0.91 g/cm3) and low cost[23, 24]. Carbon fiber was shown to increase the bending strength of the PMMA denture base resin.
In this study it was aimed to comparatively investigate the effect of fiber reinforcement using fibers with different characteristics, namely different materials [glass, polypropylene (PP), and carbon], three fiber lengths (3, 6 and 12 mm), and three different concentrations (0.25, 0.50 and 1.0% v/v), on mechanical properties of PMMA denture base resin. As described above, various fibers were used in order to enhance the mechanical properties of the PMMA denture base resin, but none of these studies reported a comparative investigation about effects of fiber materials, fiber lengths and fiber concentrations on mechanical properties. In order to eliminate the effect of differences in densities of each fiber material, volumetric ratios for fiber reinforcement was used instead of weight ratios using appropriate calculations.