Mehmet Zor

Analysis of Dentinal Stress Distribution of Maxillary Central Incisors Subjected to Various Post-and-core Applications

This study evaluated the stress distribution on an endodontically treated maxillary central incisor restored with different post-and-core systems by using a three-dimensional finite element analysis model. Seven three-dimensional finite element models were created. Each model contained cortical bone, cancelous bone, periodontal ligament, 3 mm apical root canal filling, post-and-core and all-ceramic crowns. Two different pre-fabricated zirconia ceramic post systems, a glass fiber-reinforced post system and a titanium post system were modeled. As a control, an all-ceramic crown on an endodontically treated maxillary central incisor without a post-and-core was modeled. Each model received a 45 degrees oblique occlusal load at a constant intensity of 100 N. In each model, the ratio of Von Mises stress distribution was compared. The greatest stresses were observed in the coronal third of the roots on facial surfaces. The ratio of Von Mises stress distribution in dentin for the zirconia ceramic post (CosmoPost) and ceramic core (Cosmo Ingot), zirconia ceramic post (CosmoPost) and composite core (Tetric Ceram), glass fiber-reinforced post (FRC Postec) and composite core (Tetric Ceram), titanium post (Er post) and composite core (Tetric Ceram), zirconia ceramic post (Cerapost) and ceramic core (Cosmo Ingot), zirconia ceramic post (Cerapost) and composite core (Tetric Ceram) and the control group were 0.886, 0.889, 0.988, 0.924, 0.889, 0.893 and 1, respectively. The stress concentrations in dentin created by two different zirconia ceramic post systems were nearly the same. The zirconia ceramic post systems created slightly less stress concentration in dentin than the glass fiber-reinforced and titanium posts.

AN INVESTIGATION OF SQUARE DELAMINATION EFFECTS ON THE BUCKLING BEHAVIOR OF LAMINATED COMPOSITE PLATES WITH A SQUARE HOLE BY USING THREE-DIMENSIONAL FEM ANALYSIS

In the present study, the effects of the square delamination, around a square hole, on the buckling loads of the simply supported and clamped woven steel-reinforced thermoplastic (LDPE, F.2.12) laminated composite plates have been investigated. Three-dimensional finite element models of laminated plates with four layers have been established. The square delaminations exist between second/third layers. The stacking sequences are chosen as [0]4, [15 / 15]s, [15 / 15]2, [30 / 30]s, [30 / 30]2, [45]4. Firstly the harmony between theoretical and finite element solution results of the plate without hole and delamination has been shown. Then, the buckling loads have been determined for each of the models having different square delamination dimensions. Significant decreases in the buckling loads occur after a certain value of delamination dimension. It is seen, for clamped plates that the changing ratios of the results of the symmetric or antisymmetric cases are approximately the same and there is a linear relationship between the values of the fiber angles and buckling loads.

Elastic-Plastic Stress Analysis and Residual Stresses in a Woven Steel Fiber Reinforced Thermoplastic Composite Cantilever Beam Loaded Uniformly

In this study an elastic-plastic stress analysis is carried out in a woven steel fiber reinforced thermoplastic (LDFE, F.2.12) composite cantilever beam loaded uniformly at the upper surface. The intensity of the uniform force is chosen as a small value; therefore the normal stress component of ay is neglected during the elastic-plastic solution. An analytical solution is found, satisfying both equations of equilibrium and boundary conditions for a plane stress case. The orientation angle of the fibers is chosen as 00, 150, 300 and 45. The intensity of the residual stress component of ox is maximum at the upper or lower surfaces of the beam. Yielding begins earlier at the upper surface of the beam for 150 and 300 orientation angles. The intensity of the residual stress component of the shear stress is maximum on or around the longitudinal axis of the beam.

Residual stress effects on fracture energies of cement-bone and cement-implant interfaces.

The effects of residual stresses, which are caused by the temperature difference arising after polymerisation of bone cement, on the fracture energies of cement bone and cement-implant interfaces have been examined by using both experimental and numerical works. Only fracture loads of the test specimen having interfacial cracks have been measured in the experimental stage. The values of fracture loads and temperature difference after polymerisation have been applied to finite element models of the test specimens to calculate critical J-integral values of these both interfaces in the numerical stage. In addition, fracture energies of bone and cement, have been obtained by experimentally, using three-point bending test method The results have shown that residual stresses can produce changes in the fracture energies of these bimaterial systems, especially in cement implant interface and J(Ic) values of interfaces are considerably smaller than the experimentally determined J(Ic) values of cement and bone.

An analytical elastic–plastic stress analysis in a woven steel reinforced thermoplastic cantilever beam loaded uniformly

Abstract In this investigation, an elastic–plastic stress analysis is carried out in a woven steel fiber reinforced thermoplastic (LDFE, F.2.12) composite cantilever beam loaded uniformly at the upper surface. Closed form solution is found satisfying both the governing differential equation and boundary conditions. The beam is loaded by a small uniform force at the upper surface, therefore during the solution of the problem for the elastic–plastic case, the normal stress σ y is neglected in comparison with other stress components. The orientation angle of the fibers are chosen as 0, 15, 30 and 45°. The intensity of the residual stress component of σ x is maximum at the upper and/or lower surfaces of the beam. The intensity of the residual stress component of the shear stress τ xy is maximum on or around the x axis.

The three-dimensional finite element analysis of fixed bridge restoration supported by the combination of teeth and osseointegrated implants.

This study investigated the designs of osseointegrated prostheses in cases of free-end partial edentulism using comparative stress interpreted with the three-dimensional finite element method. Three free-end fixed osseointegrated prostheses models with various connection designs (ie, rigidly connected to an abutment tooth and an implant, rigidly connected to an implant and two abutment teeth, and rigidly connected to an implant and three abut- ment teeth) were studied. The stress values of the three models loaded with vertical, buccolingual, and linguobuccal directions at 30° angled to vertical axis forces were analyzed. When the fixed partial denture was connected to the three natural abutment teeth and an implant, the lowest levels of stress in the bone were noted.

Delamination Width Effect on Buckling Loads of Simply Supported Woven-Fabric Laminated Composite Plates Made of Carbon/Epoxy

The effects of the strip delamination width on the buckling loads of the simply supported carbon/epoxy woven laminated composite plates have been investigated. For this purpose, 3D finite elements models of the square carbon/epoxy laminated plates have been established. Each of these models possesses four layers and different delamination width between second and third layers. Firstly, the harmony between theoretical and finite element solutions results of the plate without delamination has been shown. Then, the buckling loads have been determined for each model and different fiber orientation angles. The results show that important decrease in the buckling loads occur after a certain value of the delamination width. The changing ratios of the results of the symmetric or antisymmetric cases are approximately the same for each angle. For the high values of orientation angles, the values and changing ratios of the buckling loads are also higher than those of the low angles.

Three-dimensional Buckling Analysis of Thermoplastic Composite Laminated Plates with Single Vertical or Horizontal Strip Delamination

In this study, the effects of the strip vertical or horizontal delamination width on the buckling loads of the simply supported woven steel-reinforced thermoplastic (LDFE, F.2.12) laminated composite plates of four layers have been investigated. Three-dimensional finite element models of the square laminated plates have been established. There are two different delamination shapes, between second and third layers in each of these models. The stacking sequences are chosen as [0]4, [15°/-15°]s, [15°/-15°]2, [30°/-30°]s, [30°/-30°]2, [45°]4, and [45°/-45°]s. Firstly the harmony between theoretical and finite element solutions’ results of the plate without delamination has been shown. Then, the buckling loads have been determined for each models having different delamination width. The results show that important decreases in the buckling loads occur after a certain value of the delamination width. The changing ratios of the results of the symmetric or antisymmetric cases are approximately the same for each angle. For the high values of orientation angles, the values and changing ratios of the buckling loads are also higher than those of the low angles.

Elastic-plastic finite elements analysis of transient and residual stresses in ceramo-metal restorations

Transient and residual stresses occurring in partially fixed dental prostheses after the firing process can be calculated with elastic or elastic-plastic finite element analyses (FEA). In this study, firstly, the mechanical and thermal properties at various temperatures of the materials used in a porcelain fused metal (PFM) system were obtained by experimental and literature studies. The effects of viscoelastic and viscoplastic behaviours of the dental porcelain at the elevated temperatures were reflected onto its elastic properties. The equivalent heat transfer coefficients were determined experimentally by measuring temperatures and the results were supplied as input to the 3D finite elements analysis. It has been observed that the maximum stresses occur within a short time period after cooling begins and that stresses decrease during the cooling process and remain at a constant value at the end of cooling; these are the thermal residual stresses.

Elastic-Plastic Stress Analysis of Simply Supported and Clamped Thermoplastic Composite Laminated Plates Loaded Transversely

In this study, an elastic-plastic stress analysis is carried out on simply supported and clamped cross-ply and angle-ply steel fiber reinforced thermoplastic composite laminated plates under transverse loading. Classical lamination theory with first order shear deformation theory are used for small plasticde formations. The orientation angles are chosen as [0 / 90]2, [30 / 30]2, [45 / 45]2, [60 / 60]2 for symmetric and antisymmetric cases. Loading is gradually increased in sequence of 100, 300 and 500. The expansion of the plastic region and the residual stress components are obtained by using the finite element technique.