HIGH VISCOSITY BULK-FILL GIOMER AND ORMOCER-BASED RESIN COMPOSITES: AN IN-VITRO COMPARISON OF THEIR MECHANICAL BEHAVIOUR
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Figure 2. Micro-mechanical properties – a) Martens Hardness; b) Vickers Hardness; c) Indentation modulus, YHU; d) Creep
specimens were polished with a grinding system( EXAKT 400 CS, EXAKT, Norderstedt, Germany) using silicon carbide paper P 2500 followed by P 4000. Measurements were done on the top( n = 10) of the slabs with 6 measurements per sample. The test procedure was carried out force-controlled, where the test load increased and decreased with constant speed between 0.4 and 500 mN. The load and the penetration depth of the indenter( Vickers pyramid: diamond right pyramid with a square base and an angle of α = 136 ° between the opposite faces at the vertex) were continuously measured during the load-unload hysteresis. Universal hardness( HM) is defined as the test force divided by the apparent area of indentation under the applied test force. From a multiplicity of measurements stored in a database supplied by the manufacturer, a conversion factor( 0.0945) between HM and HV was calculated by the manufacturer and entered into the software so that the measurement results were also indicated in the more familiar HV units. Y HU was calculated from the slope of the tangent adapted at the beginning( at maximum force) of the nonlinear indentation depth curve upon unloading. By measuring the change in indentation depth with a constant test force, a relative change in the indentation depth can be calculated. This is a value for the creep of the materials.
2.3 Statistical Analysis The Kolmogoroff-Smirnoff test was applied to verify the data were normally distributed. Results were compared using one-way ANOVAs and Tukey’ s HSD post hoc test( α = 0.05). A multivariate analysis( general linear model) assessed the effect
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