Tomasz Topoliński

Microarchitecture Parameters Describe Bone Structure and Its Strength Better Than BMD

Introduction and Hypothesis. Some papers have shown that bone mineral density (BMD) may not be accurate in predicting fracture risk. Recently microarchitecture parameters have been reported to give information on bone characteristics. The aim of this study was to find out if the values of volume, fractal dimension, and bone mineral density are correlated with bone strength. Methods. Forty-two human bone samples harvested during total hip replacement surgery were cut to cylindrical samples. The geometrical mesh of layers of bone mass obtained from microCT investigation and the volumes of each layer and fractal dimension were calculated. The finite element method was applied to calculate the compression force F causing ε = 0.8% strain. Results. There were stronger correlations for microarchitecture parameters with strength than those for bone mineral density. The values of determination coefficient R 2 for mean volume and force were 0.88 and 0.90 for mean fractal dimension and force, while for BMD and force the value was 0.53. The samples with bigger mean bone volume of layers and bigger mean fractal dimension of layers (more complex structure) presented higher strength. Conclusion. The volumetric and fractal dimension parameters better describe bone structure and strength than BMD.

Study of the behavior of the trabecular bone under cyclic compression with stepwise increasing amplitude

This paper presents the results of a study of 61 trabecular bone samples exposed to a cyclic (1 Hz) compression load. The load was increased stepwise. Characteristic patterns of the hysteresis loop for the middle cycles of successive steps of load and for respective steps of load are presented. Characteristic patterns of secant modulus were also determined. The fatigue life results recorded were compared with the indices of bone architecture determined using micro-CT. Using Pearsons correlation, the best relationship between fatigue life and bone volume ratio (BV/TV) and the maximum load for which there was also reported a maximal value secant stiffness were identified. Based on these findings, it was determined that it is possible to use stepwise increasing load for analysis of the fatigue behavior of trabecular bone.

The Relationship between Trabecular Bone Structure Modeling Methods and the Elastic Modulus as Calculated by FEM

Trabecular bone cores were collected from the femoral head at the time of surgery (hip arthroplasty). Investigated were 42 specimens, from patients with osteoporosis and coxarthrosis. The cores were scanned used computer microtomography (microCT) system at an isotropic spatial resolution of 36 microns. Image stacks were converted to finite element models via a bone voxel-to-element algorithm. The apparent modulus was calculated based on the assumptions that for the elastic properties, E = 10 MPa and ν = 0.3. The compressive deformation as calculated by finite elements (FE) analysis was 0.8%. The models were coarsened to effectively change the resolution or voxel size (from 72 microns to 288 microns or from 72 microns to 1080 microns). The aim of our study is to determine how an increase in the distance between scans changes the elastic properties as calculated by FE models. We tried to find a border value voxel size at which the module values were possible to calculate. As the voxel size increased, the mean voxel volume increased and the FEA-derived apparent modulus decreased. The slope of voxel size versus modulus relationship correlated with several architectural indices of trabecular bone.

Fatigue Energy Dissipation in Trabecular Bone Samples with Stepwise-Increasing Amplitude Loading*

Abstract The research method proposed in the paper assumes multi-level loads of trabecular bone, which are similar to the real ones and demonstrate a step-wise amplitude increase. Throughout the study, such loadings were applied to bone structures sampled from 61 donors. The samples were obtained after hip arthroplasty from the neck fragment of femur heads. All the samples were scanned with a desktop microtomographer. The fatigue damage of the sample structures throughout the experiments was seen in changes in the form of the hysteresis loop recorded in the stress-strain system. The dissipation energy, which is calculated based on the hysteresis loop, is present in the fatigue life function. A three-stage sample fatigue damage pattern was demonstrated. The sum of the dissipation energies was calculated for all the hysteresis loops, and thus we obtain the accumulated dissipation energy, which is referred to as the total fatigue life for all the samples. The calculation results were determined to have an exponential-like curve and reported a high value of the coefficient of determinacy. The accumulated dissipation energy is also related to the value of the compressive stress levels applied. Referring the calculated results of the accumulated energy to the structure index BV/TV, we identified the existence of a strong relationship between the quantities.

Verification of selected hypotheses attempting to explain the effect of fatigue damage build-up in trabecular bones

This paper presents results of verification computations done for selected hypotheses attempting to explain the effect of fatigue damage buildup, performed for loads with gradually increasing amplitude applied to trabecular bone samples. The study tested 42 trabecular bone samples of 10 mm diameter and 8.5 mm height cut out from human femoral heads along the axis of symmetry of the bone’s neck. A value for the damage function D was determined for each sample based on the Palmgren-Miner hypothesis and a non-linear variant of the hypothesis. The two hypotheses were based on a fatigue diagram parameterized in accordance with literature references and on an area exposed to fatigue proposed by the authors: σ-BV/TV-log10Nf. The outcomes are insufficient for making a recommendation on application of fatigue damage buildup hypotheses. Instead, the results suggest that the hypotheses should be used very carefully.

Shear Strength Testing of Bonded Joints of Dental Materials

Zirconium dioxide is a material more and more used by technicians and dental surgeons due to its chemical composition and excellent mechanical strength. It features high biocompatibility and may be used even in 6-unit fixed dental bridges. Adhesive bonding is one of the methods used in dental applications. New generation bonding agents featuring high mechanical strength are widely available on the market. This article presents the equipment designed and manufactured to European Standards for bonded joint testing as well as specimen geometry and bonding method. Monotonic and fatigue tests of bonded joints were performed, the results were presented and Weibull analysis was performed.

Performance of Bone Modelling Techniques in the Assessment of Bone Fragility

This paper describes the effect of different radiation-reducing methods of bone modelling on the volume of bone models and structural differences between individual models. Careful analysis of data has enabled to determine which of these methods are the best from a structural point of view. The next step is to compare different methods of bone modelling with regard to potential similarities in strength behaviours of bone models.

Analysis of P-M Damage Accumulation in Zirconium Dioxide; Testing through Gradually Increasing Load Method

Zirconium dioxide has been known since the 90s. The Zirconium dioxide that has been used in the research was supplied by 3M ESPE under trade name Zirconium Lava. The trabecular rectangular shaped samples with dimensions of 1.5 mm x 1.5 mm x 12 mm has been put under three-point bending process in accordance to PN-EN 843-1:2006 standards. The tests were performed using the servohydraulic strength o R=0,1 at maximum compressive stress 700 and 710MPa, and a gradually increasing load for the two groups of samples. Aim of this study was to analyze the process of strengthening the quality of Zrconium dioxide by testing under variable loads including studies with gradually increasing load using linear fatigue damage accumulation hypothesis.

Determining the S-N Fatigue Curve for Lava Zirconium Dioxide

Zirconium dioxide is a material which over the recent years has been winning support among dental technicians and dentists. Due to its chemical composition and mechanical properties is can replace non-aesthetic caps or metal crowns. In their paper the authors have focused on the analysis of the material itself; zirconium dioxide under the trade name LAVA and assumed a single treatment technology developed together with dentists. The main objective of the study was to determine the S-N curve for the material that is zirconium dioxide. The next step for the authors was to perform a static three-point bending. Fatigue testing covered a group of 30 specimens which were then used to determine the S-N curve for zirconium dioxide. The authors determined the S-N curve thanks to which the dentists are able to predict the destruction of the construction element which presents all-ceramic substructure. In the lecture review and according to authors it is said that in the aqueous environment the values of stress are similar with the dry environment and are within 850 MPa.

Applying a Stepwise Load for Calculation of the S-N Curve for Trabecular Bone Based on the Linear Hypothesis for Fatigue Damage Accumulation

In this work were presented calculated fatigue curves based on fatigue tests of trabecular bone under stepwise load with the application of a linear hypothesis accumulation of fatigue damage. The investigation was performed on 61 cylindrical bone samples obtained from the neck of different femur heads. The bone sample fatigue tests were carried out under compression with stepwise increases of the applied load. The fatigue calculation assumed the Palmgren-Miner (P-M) linear hypothesis accumulation of fatigue damage and the associated modified formulae. The obtained mean fatigue curves were based on the modified stress σ/E0 (E0 – initial stiffnes) for the assumed rule-determined slope or y-intercept. The highest agreement with the literature was obtained for Σn/N=10.