IADR Abstract Archives
Quantitative Fractography to Measure Fracture Toughness of Direct Resin Composites
Objectives: To test the hypothesis that conventional (C), bulkfill (BF), flowable (F) and bulkfill flowable (BFF) dental resin composites have the same value of fracture toughness and to determine the effect of microstructure on the mechanical properties.
Methods: Microtensile (hour glass) specimens (n=30) of Tetric Evoceram using four groups of dental composites C, BF, F and BFF with average dimensions of 1.76 mm by 1.51 mm and gauge length of 3 mm were produced using a prefabricated PVS mold. They were cured for 10 seconds (~1000 mW/cm2). The polished specimens were broken in tension using a universal machine. The strength σ, was calculated from the load and the cross-sectional area; and the toughness KIC was calculated from the strength and the size of the critical flaws (using solutions of Newman and Raju) at the surface or internal and compared to the SEVNB method. The hardness was measured using a Vickers’ diamond indenter at 500g/30s. The elastic modulus was measured using indentation and ultrasonic methods.
Results: The greatest value of toughness is for BFF which has KIC of 0.86 MPa.m1/2, while the C group was the lowest KIC value of 0.49 MPa.m1/2. The results of KIC using SEVNB were higher without measuring the original cracks. C and BF exhibited greater elastic modulus E 16.2 and 17.8 GPa and VH 519 and 568 MPa respectively.
Conclusions: The combination of low fillers percentage and using particles with refractive index similar to the matrix is the best method for increasing the toughness as in BFF. The SENVB method requires a re-measurement of the original crack for the failed samples. Indentation is a simple and accurate method after including the viscoelasticity factor.
Methods: Microtensile (hour glass) specimens (n=30) of Tetric Evoceram using four groups of dental composites C, BF, F and BFF with average dimensions of 1.76 mm by 1.51 mm and gauge length of 3 mm were produced using a prefabricated PVS mold. They were cured for 10 seconds (~1000 mW/cm2). The polished specimens were broken in tension using a universal machine. The strength σ, was calculated from the load and the cross-sectional area; and the toughness KIC was calculated from the strength and the size of the critical flaws (using solutions of Newman and Raju) at the surface or internal and compared to the SEVNB method. The hardness was measured using a Vickers’ diamond indenter at 500g/30s. The elastic modulus was measured using indentation and ultrasonic methods.
Results: The greatest value of toughness is for BFF which has KIC of 0.86 MPa.m1/2, while the C group was the lowest KIC value of 0.49 MPa.m1/2. The results of KIC using SEVNB were higher without measuring the original cracks. C and BF exhibited greater elastic modulus E 16.2 and 17.8 GPa and VH 519 and 568 MPa respectively.
Conclusions: The combination of low fillers percentage and using particles with refractive index similar to the matrix is the best method for increasing the toughness as in BFF. The SENVB method requires a re-measurement of the original crack for the failed samples. Indentation is a simple and accurate method after including the viscoelasticity factor.
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