The blood flow and transportation of molecules in the cardiovascular system plays crucial role in the genesis and progression of atherosclerosis. Atherosclerosis shows predilection in regions of the arterial tree with hemodynamic particularities, as local disturbances of wall shear stress in space, and locally high concentrations of lipoprotein. A semi-permeable nature of the arterial wall computational model is incorporated with hydraulic conductivity and permeability treated as wall shear stress dependent. Six image-based human diseased right coronary arteries (RCA) are used to elucidate the low-density lipoprotein (LDL) transport. The 3D reconstruction technique is a combination of angiography and IVUS. The numerical simulation couples the flow equations with the transport equation applying realistic boundary conditions at the wall. The coupling of fluid dynamics and solute dynamics at the endothelium is achieved by the Kedem-Katchalsky equation (water infiltration). The luminal surface LDL concentration at the arterial wall is flow-dependent with local variations due to geometric features. The relationship between WSS and luminal surface concentration of LDL indicates that LDL is elevated at locations where WSS is low. There is medium correlation (Pearson) between low WSS and high LDL. The degree of elevation in luminal surface LDL concentration is mostly affected by the water infiltration velocity at the vessel wall. Under constant water infiltration the shear dependent endothelial permeability effects, in comparison to those using constant value, are marginal. Area-averaged normalized LDL concentration over the RCAs, using constant water infiltration and endothelial permeability is 3.6% higher than that at the entrance. Area-averaged normalized LDL concentration over the RCAs, using shear dependent water infiltration and endothelial permeability is 9.6%. Perspective computational fluid dynamics users, incorporating mass transfer (LDL) within the blood flow, are forced to treat the problem using shear dependent endothelial values.

Four molecular Non-Newtonian viscosity models plus the Newtonian one were analyzed for the normal human aorta under oscillating flow via: molecular viscosity, time Average Wall Shear Stress (AWSS), Oscillatory Shear Index (OSI) and Relative Residence Time (RRT). The capabilities of the applied non-Newtonian law models appear at low strain rates. The Newtonian blood flow treatment is considered to be a good approximation at mid-and high-strain rates. All blood flow models yield a consistent aorta pattern. High RRT values develop in the concave part of the aortic arch downstream to left subclavian artery. In this region the molecular viscosity is elevated, the WSS is low and the OSI is high. Concave aorta parts are prone to exhibit elevated RRT. The non-Newtonian Power Law blood flow model approximates the molecular viscosity, WSS, OSI and particularly the RRT in a more satisfactory way. High RRT distribution is emerging as an appropriate tool for identifying the possible regions of atheromatic concentrations.

Alexander Tsouknidas, Dr Eng/Dimitrios Giannopoulos, DDS/Savvas Savvakis, PhD/Nikolaos Michailidis, Dr Eng/Evdokia Lympoudi, DDS, MS/Dimitrios Fytanidis, BSc, MSc/Argirios Pissiotis, DDS, MS, PhD/Konstantinos Michalakis, DDS, MSc, PhD: Purpose: The purpose of this study was to evaluate whether or not bone quality has an effect on the biomechanical behavior of a tooth connected to an implant, when a rigid and a nonrigid attachment are used. Materials and Methods: Models of fixed partial dentures supported by a tooth and an implant were developed. These models were then imported into finite element analysis software to study the impact of forces on different types of attachments (rigid vs nonrigid) and bones (types 1 to 4). Each fixed partial denture was subjected to a vertical load of 200 N on the premolars and 230 N on the molar. The materials were considered linear, isotropic, and homogenous. Eight different scenarios were tested. The von Mises criterion was used to display the stress in five structures: fastening screw, implant, attachment, cortical, and trabecular bone. The displacements of the tooth and the implant were also examined. Results: The calculated maximum observed stress values differed among the simulated scenarios. The biggest values of stress concentrations were observed at the lingual cervical areas, the implant-cortical bone interface, the implant-crown interface, the butt-joint contact of the implant-abutment screw, and the apical parts of the tooth and implant. The main difference between the rigid and nonrigid connection was observed between the natural tooth retainer and the pontic. In the rigid connection, the movement of the natural tooth retainer was smooth. In the nonrigid connection, the attachment exhibited a partial buccal displacement. Von Mises stresses among the different tested structures ranged between 24 and 840 MPa. Conclusion: The quality of the bone and the rigidity of the connection between a natural tooth and an implant influence both the generated stresses and the displacement of the tooth and the implant. The highest stresses for the implant-trabecular bone interface, the neck of the implant, and the fastening screw were observed in type 3 bone when a rigid connection was used. The lowest stresses for the implant-cortical bone interface, the neck of the implant, and the connector were registered in type 1 bone, when a rigid connection was used. The smallest tooth and implant displacement was observed in type 1 bone, when a rigid connection was used, while the biggest tooth and implant displacement was registered in type 4 bone when a nonrigid connection was used.