IADR Abstract Archives
Effect of Filler Distribution on Fracture Resistance of Modern Dental Composites
Objectives: Failure of dental composite restorations is closely associated with the fracture processes of the filler-matrix systems. The purpose of this study is to investigate how various filler-matrix systems (i.e., hybrid, nanohybrid, and microfill) with different microstructural characteristics and filler distributions (i.e., unimodal, bimodal, and multimodal) can influence the time-dependent fracture resistance.
Methods: Twenty rectangular, single-edge notch specimens (2.75x5x25mm3) per composite brand (n=20 brands) were made from a stainless steel mold with a razor blade insert, producing a 2.5mm notch depth. Fracture toughness, KIC [MPa m0.5] values were measured using a 3-point bending test (span = 20mm and cross-head speed = 0.5mm/min). Composite microstructural features were analyzed by scanning electron microscopy and laser diffraction particle size analyzer. Filler content was measured by thermogravimetric analysis. All specimens were stored in 37°C distilled water for 24 hours prior to testing. Data were analyzed with ANOVA/Tukey (α=0.01) and regression.
Results: Fracture toughness values were found – rankings in descending order were: Nanohybrids > Hybrids > Microfills. Additionally, composites with multimodal distribution demonstrated significantly less fracture resistance than composites with either unimodal or bimodal distribution. The fracture toughness of composite systems adopted with new polymeric matrix chemistry (i.e., ORMOCER, Giomer, DX-511 Monomer, or Dimer acid derived) are not statistically different than methacrylate-based systems.
Conclusions: Fracture toughness as a function of filler content increased with percent filler weight until a critical value of 75%, after which KIC decreased with increasing percent filler weight. In a similar behavior, fracture toughness as a function of filler size range exhibited the highest fracture resistance at a critical value of 4μm. However, composites containing nano-fillers showed significantly higher fracture resistance than composites containing only micro-fillers.
Methods: Twenty rectangular, single-edge notch specimens (2.75x5x25mm3) per composite brand (n=20 brands) were made from a stainless steel mold with a razor blade insert, producing a 2.5mm notch depth. Fracture toughness, KIC [MPa m0.5] values were measured using a 3-point bending test (span = 20mm and cross-head speed = 0.5mm/min). Composite microstructural features were analyzed by scanning electron microscopy and laser diffraction particle size analyzer. Filler content was measured by thermogravimetric analysis. All specimens were stored in 37°C distilled water for 24 hours prior to testing. Data were analyzed with ANOVA/Tukey (α=0.01) and regression.
Results: Fracture toughness values were found – rankings in descending order were: Nanohybrids > Hybrids > Microfills. Additionally, composites with multimodal distribution demonstrated significantly less fracture resistance than composites with either unimodal or bimodal distribution. The fracture toughness of composite systems adopted with new polymeric matrix chemistry (i.e., ORMOCER, Giomer, DX-511 Monomer, or Dimer acid derived) are not statistically different than methacrylate-based systems.
Conclusions: Fracture toughness as a function of filler content increased with percent filler weight until a critical value of 75%, after which KIC decreased with increasing percent filler weight. In a similar behavior, fracture toughness as a function of filler size range exhibited the highest fracture resistance at a critical value of 4μm. However, composites containing nano-fillers showed significantly higher fracture resistance than composites containing only micro-fillers.
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