IADR Abstract Archives
Nanoindentation Analysis of Modern Dental Composites
Objectives: All modern dental composites are designed with two phases, filler and matrix, which their load-bearing capacity is an attribute of the filler. However, most would agree the link between filler-matrix features, microstructures, and physical properties for these materials are not well understood. The purpose of this study is to characterize various commercial composites in accordance with their micromechanical properties and microstructural features with a specific focus on the filler-matrix relationship.
Methods: Twenty composite brands were tested to determine their microstructural features and micromechanical properties such as elastic modulus (EM), stiffness (S), and hardness (H). EM, S, and H were measured using a nanoindenter with a Berkovich diamond indenter. Five rectangular samples (2.75x5x12mm3) per composite brand were prepared, fixed in epoxy resin, and underwent multiple iterations of polishing, ultimately finishing with 0.25μm polished surfaces. All specimens were stored in 37°C distilled water for 24 hours prior to testing. An indentation load of 10mN was applied (Poisson’s ratio = 0.3), and 2000 indents per composite brand were measured. Microstructural features were analyzed by scanning electron microscopy and laser diffraction particle size analyzer. Data were analyzed with ANOVA/Tukey (α=0.01) and regression.
Results: Composite filler sizes exhibited unimodal, bimodal, and multimodal distributions. Bimodal filler distribution responded with significantly higher modulus, hardness, and stiffness than unimodal and multimodal distributions. Additionally, the twenty brands were classified based on current terminology, and significant differences (p<0.01) in modulus and stiffness were found – rankings in descending order were: Nanohybrids > Hybrids > Microfills. However, hardness rankings showed: Hybrids > Nanohybrids > Microfills. Bivariate regression analyses demonstrated filler weight correlated with modulus with the highest r2 (0.634), followed by stiffness (r2=0.625), and then hardness (r2=0.522).
Conclusions: Composite systems adopted with new polymeric matrix chemistry behaved differently than methacrylate-based systems (p<0.01). In general, filler weight values directly correlated with elastic modulus, hardness, and stiffness.
Methods: Twenty composite brands were tested to determine their microstructural features and micromechanical properties such as elastic modulus (EM), stiffness (S), and hardness (H). EM, S, and H were measured using a nanoindenter with a Berkovich diamond indenter. Five rectangular samples (2.75x5x12mm3) per composite brand were prepared, fixed in epoxy resin, and underwent multiple iterations of polishing, ultimately finishing with 0.25μm polished surfaces. All specimens were stored in 37°C distilled water for 24 hours prior to testing. An indentation load of 10mN was applied (Poisson’s ratio = 0.3), and 2000 indents per composite brand were measured. Microstructural features were analyzed by scanning electron microscopy and laser diffraction particle size analyzer. Data were analyzed with ANOVA/Tukey (α=0.01) and regression.
Results: Composite filler sizes exhibited unimodal, bimodal, and multimodal distributions. Bimodal filler distribution responded with significantly higher modulus, hardness, and stiffness than unimodal and multimodal distributions. Additionally, the twenty brands were classified based on current terminology, and significant differences (p<0.01) in modulus and stiffness were found – rankings in descending order were: Nanohybrids > Hybrids > Microfills. However, hardness rankings showed: Hybrids > Nanohybrids > Microfills. Bivariate regression analyses demonstrated filler weight correlated with modulus with the highest r2 (0.634), followed by stiffness (r2=0.625), and then hardness (r2=0.522).
Conclusions: Composite systems adopted with new polymeric matrix chemistry behaved differently than methacrylate-based systems (p<0.01). In general, filler weight values directly correlated with elastic modulus, hardness, and stiffness.
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