Papers by Keyword: Cortical Bone

Abstract: The relationship between implant thread design and dental bone arguably has an influence on the distribution of bone stresses. However, the existing data on the influence of the thread profiles on bone stresses is considerably conflicting. For example, some studies concluded that thread shape has a substantial effect on the intensity of bone stresses, while others revealed that thread shape has no effect on the intensity of bone stresses. Accordingly, this study aims to computationally investigate and compare the effect of dental implant thread design on bone stresses under axial loading using a finite element analysis (FEA) approach. A geometrical model of V-thread and square thread implants, with a fixed thread pitch of 0.8 mm and a depth of 42 mm, and the surrounding bone was developed to assess the stresses generated within the implant components and bone structure under a 114 N axial load. The simulation is primarily concerned with the von Mises stresses within the implant components and the surrounding bone. The results demonstrate that the V-thread implant causes extremely high stress on the cortical and cancellous bones compared to the square thread implant. For example, the maximum stresses induced in the cortical bone are 195.3 MPa and 68.8 MPa, while the maximum stresses created in the cancellous bone are 19.7 Mpa and 2.2 Mpa in both designs, respectively. In addition, the cortical bone stresses substantially exceed the implant body stresses in both designs, with maximum stresses of 93.18 Mpa and 41 Mpa for V-thread and square-thread implants, respectively. However, the implant thread shape doesn’t affect the stress distribution in the abutment and screw. In general, the results show that implant thread design can result in featured mechanical stresses in the implant body and bone structure.

Abstract: Fiber orientation is essential when we want to predict the behavior of a composite material, also for determining the mechanical properties of such materials. Many researches in this field showed that the orientation of fibers has a major role, for example, in increasing some properties, or decreasing others. Some of these studies are experimental, some are made using only the Finite Element Method (FEM).In this work, we present a numerical approach in order to estimate the influence of the collagen fibers orientation on the mechanical properties of the natural composite, which is human cortical bone. Based on the mathematical theory of homogenization, allowing computing all the elastic (but also piezo and dielectric) properties of a composite material, this study quantifies the main influence of the fibers orientation and its effect on the mechanical properties, but also on the influence of the cortical architecture on mechanical properties.

Abstract: The purpose of this study was to develop a new three-dimensional model of an osseointegrated molar dental prosthesis and to carry out finite element analysis to evaluate stress distributions and intensities in the bone and in the components of dental prosthesis under three loads (corono-apical, distal-mesial and buccal-lingual) were applied to the top of the occlusal face of the prosthesis crown. The interfacial stresses were also determined inside and outside of the threading when the dental prosthesis system was subjected to one of three masticatory loads. All materials used in the models were considered to be isotropic, homogeneous and linearly elastic. The elastic properties, loads and constraints used in the model were taken from published data. In this study, the stress concentration occurred around the threaded dental implant neck. Thus, this area should be preserved clinically in order to maintain the bone–implant interface structurally and functionally.

Abstract: This paper presents some results of the experimental investigations that were aimed at assessing the primary stability of orthodontic mini-implant anchorage by measuring the tensile force with a special device adapted for traction in the axial direction and at a 45 degree angle, taking as variables bone characteristics (thickness and cortical bone density, thickness and density of the medulla). We used samples (pork ribs) whose characteristics were measured at computer tomography with a specialized software, in which there have been inserted orthodontic mini-implants with spherical head, round thread having different characteristics of shape and dimensions of the thread (length diameter, pitch). Experiments have provided information on the relationship between bone characteristics of samples and maximum traction force in the axial direction and at 45degree angle, as well as mini-implant primary stability.

Abstract: Cutting force and temperature are the two chief factors affecting bone rehabilitation during bone cutting in many orthopedic surgeries. To reveal new knowledge of thermal and force when milling cortical bone, slotting experiments were carried on high-speed milling platform. Cutting force and temperature were measured during the milling process. The effects of cutting inputs on cutting thermal and force were researched in detail. The results showed that: feed rate and spindle speed had a great impact on the milling temperature, while the milling force was mainly influenced by spindle speed. A feed rate of 1.0-1.4 mm/s is recommended to obtain preferable milling force and temperature, and a larger feed rate of 1.2-1.4 mm/s is advised to use with a lower spindle speed (8000-20000 r/min), while a smaller feed rate of 1.0-1.2 mm/s should be chosen when spindle speed was between 20000-40000 r/min. Feeding parallel to the growth direction of the cortical bone can significantly reduce the milling temperature, but there was no obvious change in milling force. The lowest cutting temperature obtained during the experiment was around 50 °C without coolant, which was acceptable for orthopedic surgeries.

Abstract: The elastic properties of cortical bone tissue and other types of bone have been determined by the classical methods such as tensile stress and shearing stress. In recent years, by nanoindentation method, it has developed techniques for measuring the viscoelastic properties of bone tissues. In the same time, they show effects the dependent on time due to loading. The time dependent behavior of such viscoelastic materials may be described by constitutive equations whose variables are stress, deformation and time. These equations may be expressed by means of rheological models. Furthermore, bone tissues present both the phenomenon of creep and relaxation, indicating that they have a rheological behavior. In this paper viscoelastic behavior of bone is simulated numerically, and analyzed in Simulink, using Burgers rheological model.

Abstract: The stress distribution in cortical bone and dental implant has been modeled by finite element method (FEM) using linear static analysis in the case of monocortical and bicortical fixation of a real dental implant for three cortical bone thicknesses: 2 mm, 2.5 mm, 4 mm. The analysis revealed that the highest stresses in the cortical bone and in the implant after three-axial loading are localized at the edge of the cortical bone near the implant neck where bending moment is the highest. An increase of the maximum stresses has been observed with the decrease of the intraosseal length of the implant and cortical bone thickness.

Abstract: This study was aimed at investigating the effect of the bone compositions on the fracture toughness of bovine cortical bone. A series of the SENB bovine cortical bone specimens were tested to assess the fracture toughness. Dual energy X-ray absorptiometry (DEXA) was applied to determine the mineral content of each bovine cortical specimen and hence the porosity and bone mineral fraction were measured. Current results indicate that the mean value fracture toughness is 9.37 MNm^3/2. Moreover, the fracture toughness was found to be significantly correlated with the apparent wet bone density and porosity of bone structure. No apparent correlations are found among clinical BMD and mechanical properties, implying that the BMD is an invalid indicator of the bone properties. Additionally, the tested data were fitted to the relationship, based on power law model, that the fracture toughness increase as a power (1.526) of increasing volume fraction and as a power of increasing bone mineral fraction (0.8195). These data indicate that small changes in the amount or density of compact bone tissue exert a more pronounced influence on fracture property.

Abstract: Linear elastic response of the bovine cortical bone has been examined under compression load. Experimental and computational methods were used to observe and predict the response of cortical bone. In computational method, two mechanical behaviors of isotropic and orthotropic were considered to simulate the cortical bone deformation. In experimental process, the specimens were designed to show maximum stiffness and strength by specifying osteon direction along loading axis during tests. The tests were controlled by displacement rate of 0.5 mm/minute and the overall stiffness responses of the structures were recorded to extract mechanical properties and also for validation aims. Finite Element Method (FEM) was used to model the linear response of the structure by using ABAQUS6.9EF. The FE results using orthotropic definition shows a good correlation with experimental data. A discussion was given based on overall stiffness and effective stress variation for both mechanical behaviors. In order to design the optimal implant structure, the presented study was proposed for prediction of bone structure deformation that attached to the orthopedic implants.

Abstract: The present paper is concerned with an experimental research and numerical modelling of the viscoelastic-viscoplastic-damage behaviour of bovine cortical bone. A one-dimensional constitutive model is proposed to predict the experimental behaviour under creep-recovery load conditions. The material parameters are determined by fitting experimental results. The derived algorithm for the integration of the proposed constitutive model is implemented into finite element formulation. The computational algorithm shows an excellent capability to describe the tensile behaviour of bovine cortical bone for the specific mechanical conditions analyzed.