PSI - Issue 43

Apolena Šustková et al. / Procedia Structural Integrity 43 (2023) 276–281 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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segmented datasets). Nine geometries were then created in STL Model Creator (Marcián et al. 2011 programmed in Matlab 2011b (Math Works, Natick MA, USA). Figure 2c) shows geometries with thresholds 0.25 and 0.65 g/cm 3 . The effect of the threshold is evident in the detail of the figure – as the value of the threshold increases, the amount of bone tissue decreases. The difference between the volumes of these two geometries yields 38%.

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Figure 2: Considered ROI: a) Selected micro-CT image with highlighted ROI; b) Comparison of one image segmented with different threshold values (0.25 g/cm 3 up vs 0.65g/cm 3 down); c) Comparison of different threshold values for ROI (0.25 g/cm 3 on the left vs 0.65g/cm 3 on the right). The circles indicate in more detail how threshold value affects the amount of bone tissue. Orientation of coordinate system: x-labiolingual, y-mesiodistal, z-occlusal. 2.2. FE mesh ANSYS® Academic esearch Mechanical, elease 1 .0 (Swanson Analysis, Inc., Houston, PA, USA was used to create the micro FEM models as well as FE calculation. Each geometry model was discretized using volume quadratic element SOLID 187 with the global element size 0.03 mm. The number of nodes ranged from 5467559 to 8453260. 2.3. Material model Two variants of material models were used. The first material model was assumed as linear, isotropic, and homogeneous with material properties of Young's modulus 5000 MPa (Costa et al. 2017; Rahmoun et al. 2014) and Poisson's ratio 0.3 (Kayabaşı et al. 200 ; Natali et al. 200 . It is the linear homogeneous model that is most often used and sufficient for most analyzes (Viceconti 2011). The second material model was assumed as nonhomogeneous based on micro CT data (Marcián et al. 2021 . Local values of the Young's modulus are determined based on the density obtained from the pixel gray value according to the following relationship (1) (Inagawa et al. 2018): = 17486 ∙ 1.596 (1) where E is Young's modulus MPa and ρ is density g cm 3 ] given by the following equation: = 1.5570 ∙ 10 −4 ∙ − 1.4519 (2)