Effect of Additional PMMA Fillers in Composites on Compressive Strength

Objectives: The aim of this study was to evaluate the effect of additional poly(methyl methacrylate) (PMMA) fillers on compressive strengths of experimental resin composites. Methods: PMMA particles (d=30 ƒÝm, MH-101-12, Fujikura Kasei, Japan) (0, 0.1, 0.3. 0.5. 1.0. 2.0, 3.0, 4.0, 5.0, 10.0 and 30.0 parts by weight) were incorporated with an experimental resin composite, ingredients of which were multi-functional monomer, photo-initiator, and micro-filler (PM0, PM0.1, PM0.3, PM0.5, PM1, PM2, PM3, PM4, PM5, PM10 and PM30). The experimental resin composite was inserted into a mold (d=4 mm, h=6 mm), and light-cured from the top and bottom sides for 40s each. The specimens were then stored in desiccators (DRY) or in distilled water (WET). Following this, compressive strengths were measured at a crosshead speed of 1.0 mm/min using a universal testing machine (Autograph AGS-1000A, Shimadzu, Japan). The fractured specimens were then observed using a SEM (JSM-5310LV, Jeol, Japan). The data were analyzed with two-way ANOVA and Bonferroni test (p=0.05). Results: Two-way Anova indicated that the compressive strengths of the composites were influenced by concentration of PMMA fillers (F=33.107, p<0.0001) and storage condition (F=22.970, p<0.0001). The compressive strengths of the composites were significantly higher in DRY than in WET (p<0.05). The highest value was obtained in PM0.1 in both DRY and WET conditions. The compressive strengths of the materials were gradually reduced from PM0.1 to PM30. SEM observations of the fracture surfaces suggested that the fracture mode was influenced by the filler contents in the composites. In PM0.1, the crack progression due to compressive stress was centered at the PMMA filler particles. Conclusion: A small amounts of additional PMMA fillers enhanced compressive strengths of the resin composites.