Passivity of Fit of a Novel Prefabricated Implant-Supported Mandibular Full-Arch Reconstruction: A Comparative In Vitro Study.

PURPOSE: To quantify the strain development of a new prefabricated implant-supported mandibular full-arch reconstruction. MATERIALS AND METHODS: Five resin models reflecting edentulous mandibles were each restored with three interforaminal implants and prefabricated frameworks with a novel compensation mechanism, cast frameworks, and computer-aided design/computer-assisted manufacturing (CAD/CAM)-fabricated frameworks. Strains were recorded during superstructure fixation. Statistical analyses (analysis of variance, t tests; α = .05) were based on level of misfit and distribution of misfit. RESULTS: Cast restorations showed significantly higher levels of misfit and a significantly more uneven distribution of misfit compared to prefabricated and CAD/CAM restorations (P < .05 for all comparisons). Prefabricated and CAD/CAM frameworks showed a similar low level and distribution of misfit (P = .24145 and P = .2837, respectively). CONCLUSION: The compensation mechanism of the prefabricated frameworks provides a level of fit comparable to CAD/CAM superstructures.

Corrigendum to "Prediction of Local Ultimate Strain and Toughness of Trabecular Bone Tissue by Raman Material Composition Analysis".

[This corrects the article DOI: 10.1155/2015/457371.].

Prediction of local ultimate strain and toughness of trabecular bone tissue by Raman material composition analysis.

Clinical studies indicate that bone mineral density correlates with fracture risk at the population level but does not correlate with individual fracture risk well. Current research aims to better understand the failure mechanism of bone and to identify key determinants of bone quality, thus improving fracture risk prediction. To get a better understanding of bone strength, it is important to analyze tissue-level properties not influenced by macro- or microarchitectural factors. The aim of this pilot study was to identify whether and to what extent material properties are correlated with mechanical properties at the tissue level. The influence of macro- or microarchitectural factors was excluded by testing individual trabeculae. Previously reported data of mechanical parameters measured in single trabeculae under tension and bending and its compositional properties measured by Raman spectroscopy was evaluated. Linear and multivariate regressions show that bone matrix quality but not quantity was significantly and independently correlated with the tissue-level ultimate strain and postyield work (r = 0.65-0.94). Principal component analysis extracted three independent components explaining 86% of the total variance, representing elastic, yield, and ultimate components according to the included mechanical parameters. Some matrix parameters were both included in the ultimate component, indicating that the variation in ultimate strain and postyield work could be largely explained by Raman-derived compositional parameters.

Within subject heterogeneity in tissue-level post-yield mechanical and material properties in human trabecular bone.

The ability to determine patient-specific mechanical properties of trabecular bone is needed for a reliable estimation of fracture risks. Tissue mechanics and material composition are important factors that contribute to trabecular bone performance, but only a few studies have investigated the post-yield behaviour of human trabecular bone, and limited knowledge for modelling is available about ultimate properties needed. Aim of this paper was to investigate absolute values and deviation of mechanical and material properties of human trabecular bone at the tissue level, in a healthy and osteoporotic donor. A combination of tensile and bending tests of single trabeculae up to failure, µCT measurement of sample geometry and finite element analysis were incorporated to determine mechanical properties. The samples were analysed with Raman spectroscopy to evaluate the material composition. High within-subject variability was found, for both the healthy and osteoporotic donor. Nevertheless, the two donors could be separated by analysing the ultimate strain and post-yield work, as well as two of the material parameters (B-type carbonate substitution ratio and collagen cross-link ratio). It indicates that tissue level properties seem to be relevant also for macroscopic mechanical behaviour. These findings also suggest that the mechanical variability for the inelastic region at the tissue level may be associated with varying material properties, while until yielding occurs our data does not suggest any connection between the mechanical and the investigated material. Finally, a set of mechanical properties of human bone have been reported that are a relevant reference for computational studies and FE analysis.

Novel method to analyze post-yield mechanical properties at trabecular bone tissue level.

Tissue level mechanics is a key factor to be investigated to improve the knowledge of how the overall trabecular structure reacts to loading and overloading. The aim of this study was to develop a new device for measuring the mechanical competence of single trabeculae in the post-yield region for both tensile and bending tests, characterized by high accuracy and precision, and to assess the effect of testing mode, donor age and material composition. A novel approach for measuring the displacement and deformation was developed (accuracy error of 0.3% and a precision of 2.7%). A total of 30 samples from two bovine femora of different ages (from <3-year-old and 14-year-old cows) were tested in tension or bending, while average material properties have been acquired by means of Raman spectroscopy. A group of trabeculae was tested in bending after treatment for collagen degradation. As a result, a complete set of post-yield properties has been reported. The results highlight significant differences between tensile and bending groups, with higher values for the bending test mode for yield strain, ultimate strain and post-yield work and lower for the elastic modulus. Significant higher values were found for the old donor (differences in the range of 30-60%) for elastic modulus, yield stress and ultimate stress as well as for material properties measured by Raman spectroscopy. We quantified that changes in materials properties induced by collagen degradation corresponded to a substantial decrease (up to 120% for post-yield work) of mechanical competence, both in the elastic and inelastic region.

Towards patient-specific material modeling of trabecular bone post-yield behavior.

Bone diseases such as osteoporosis are one of the main causes of bone fracture and often result in hospitalization and long recovery periods. Researchers are aiming to develop new tools that consider the multiple determinants acting at the different scales of bone, and which can be used to clinically estimate patient-specific fracture risk and also assess the efficacy of new therapies. The main step towards this goal is a deep understanding of the bone organ, and is achieved by modeling the complexity of the structure and the high variability of the mechanical outcome. This review uses a hierarchical approach to evaluate bone mechanics at the macroscale, microscale, and nanoscale levels and the interactions between scales. The first section analyzes the experimental evidence of bone mechanics in the elastic and inelastic regions, microdamage generation, and post-yield toughening mechanisms from the organ level to the ultrastructural level. On the basis of these observations, the second section provides an overview of the constitutive models available to describe bone mechanics and predict patient-specific outcomes. Overall, the role of the hierarchical structure of bone and the interplay between each level is highlighted, and their effect is evaluated in terms of modeling biological variability and patient specificity.

Imaging of cellular spread on a three-dimensional scaffold by means of a novel cell-labeling technique for high-resolution computed tomography.

Computed tomography (CT) represents a truly three-dimensional (3D) imaging technique that can provide high-resolution images on the cellular level. Thus, one approach to detect single cells is X-ray absorption-based CT, where cells are labeled with a dense, opaque material providing the required contrast for CT imaging. Within the present work, a novel cell-labeling method has been developed showing the feasibility of labeling fixed cells with iron oxide (FeO) particles for subsequent CT imaging and quantitative morphometry. A biotin-streptavidin detection system was exploited to bind FeO particles to its target endothelial cells. The binding of the particles was predominantly close to the cell centers on 2D surfaces as shown by light microscopy, scanning electron microscopy, and CT. When cells were cultured on porous, 3D polyurethane surfaces, significantly more FeO particles were detected compared with surfaces without cells and FeO particle labeling using CT. Here, we report on the implementation and evaluation of a novel cell detection method based on high-resolution CT. This system has potential in cell tracking for 3D in vitro imaging in the future.

A new device and method for measuring the elastic modulus of single trabeculae.

The smallest functional unit of cancellous bone is the single trabecula. To investigate its influence at the macroscopic level, a mechanical characterization is required. The aim of this work is to present a new procedure for measuring the elastic behavior of a single trabecula, assumed as an isotropic material, by means of a bending protocol. Our experimental setup permits the measurement of the bending force and deflection of a single trabecula within the natural network. The exact geometry of the trabecula is attained by using a laser scanning microscopy of the labeled sample and subsequently using it as the input for FE simulation. The results between the FE analysis and experimental data are compared in order to determine an isotropic elastic modulus of the trabecula. The system uncertainty has been estimated using the propagation of uncertainty method based on the analytical bending function for a fixed beam. Variables are force, deflection, radius and length and their relative uncertainties. It results in a total uncertainty of 13%, dominated by the influence of radius uncertainty, which is related to the exact determination of the real geometry of the trabecula. The system has been subsequently validated using samples with known geometry and elastic modulus. Finally, the proposed new method consists of sample preparation, a newly designed sample positioning system, an experimental bending test on a single trabecula within the trabecular network, labeling of the bone with a fluorescent marker, 3D imaging of the trabecula and FE analysis of the bending test.