Brandt B, Durst K, Belli R, Göken M, Lohbauer U (2010)
Publication Type: Journal article
Publication year: 2010
Book Volume: 26
Pages Range: e32
DOI: 10.1016/j.dental.2010.08.076
Objectives: To investigate the fracture toughness KIc of a dental glassionomer (GI) cement in terms of terms of different storage intervals and to correlate the development of macroscopic data with findings on the nanoscale.
Materials and methods: Bars with dimensions of 25 mm × 2 mm × 2 mm were produced out of a model GI cement (Schott/Evonik, Germany) and stored for 24 h, 7 d, and 21 d in water of 37 °C. Sharp notches were cut into the bars using a diamond wheel saw blade and a razor blade. Fracture toughness (n = 15) was measured using the SENB (single-edge-notched-bending) method. The actual notch depth for each specimen was measured after fracture under a light microscope. A Nano Indenter (G200, Agilent Tech., USA) was used to observe the elastic modulus and local hardness on the nanoscale. Therefore, flat specimens were produced, surface polished using the lapping technique, and stored as described above. Local mechanical properties were measured on glass particles and matrix of the set cement. Load-control (LCM) and Continuous Stiffness (CSM) measurements were performed.
Results: An increasing fracture toughness was measured with extended storage times. The KIc increased from 0.22 MPa m0.5 after 24 h up to 0.24 MPa m0.5 (7 d) and finally to 0.27 MPa m0.5 after 21 d. The elastic modulus of the GI composite increased from 12.2 GPa (7 d) up to 16.1 GPa after 21 d. Hardness increased from 0.27 GPa (7 d) up to 0.43 GPa after 21 d. The glass particles showed an elastic modulus of 65.5 GPa and a hardness of 0.69 GPa.
Conclusions: Mechanical properties on the nanoscale reflect the macroscopic data without any disturbing influence from material inhomogeneities, porosity, etc. Over time, the elastic modulus showed a higher increase compared to the macroscopic fracture toughness measurements. The material performance was found to be determined by the matrix behaviour. On the nanoscale, a viscoplastic response of the matrix component could be proved. Nanoindentation is a very useful technique for improving the macroscopic behaviour of a GI cement and suitable for localizing the weakest link in the composite structure.
APA:
Brandt, B., Durst, K., Belli, R., Göken, M., & Lohbauer, U. (2010). Fracture toughness of GIC—A mechanistic approach on the nanoscale. Dental Materials, 26, e32. https://doi.org/10.1016/j.dental.2010.08.076
MLA:
Brandt, B, et al. "Fracture toughness of GIC—A mechanistic approach on the nanoscale." Dental Materials 26 (2010): e32.
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