Corrigendum to "The impact of horizontal eye movements versus intraocular pressure on optic nerve head biomechanics: A tridimensional finite element analysis study" .

[This corrects the article DOI: 10.1016/j.heliyon.2023.e13634.].

The impact of horizontal eye movements versus intraocular pressure on optic nerve head biomechanics: A tridimensional finite element analysis study.

It has been proposed that eye movements could be related to glaucoma development. This research aimed to compare the impact of intraocular pressure (IOP) versus horizontal duction on optic nerve head (ONH) strains. Thus, a tridimensional finite element model of the eye including the three tunics of the eye, all of the meninges, and the subarachnoid space (SAS) was developed using a series of medical tests and anatomical data. The ONH was divided into 22 subregions, and the model was subjected to 21 different eye pressures, as well as 24 different degrees of adduction and abduction ranging from 0.5° to 12°. Mean deformations were documented along anatomical axes and in principal directions. Additionally, the impact of tissue stiffness was assessed. The results show no statistically significant differences between the lamina cribrosa (LC) strains due to eye rotation and IOP variation. However, when assessing LC regions some experienced a reduction in principal strains following a 12° duction, while after the IOP reached 12 mmHg, all LC subzones showed an increase in strains. From an anatomical perspective, the effect on the ONH following 12° duction was opposite to that observed after a rise in IOP. Moreover, high strain dispersion inside the ONH subregions was obtained with lateral eye movements, which was not observed with increased IOP and variation. Finally, SAS and orbital fat stiffness strongly influenced ONH strains during eye movements, while SAS stiffness was also influential under ocular hypertension. Even if horizontal eye movements cause large ONH deformations, their biomechanical effect would be markedly distinct from that induced by IOP. It could be predicted that, at least in physiological conditions, their potential to cause axonal injury would not be so relevant. Thus, a causative role in glaucoma does not appear likely. By contrast, an important role of SAS would be expectable.

Comparison of Mechanical and Structural Properties of Nickel-titanium Alloy with Titanium-molybdenum Alloy and Titanium-niobium Alloy as Potential Metals for Endodontic Files.

Introduction: The objective of this study was to compare the mechanical and structural properties of the nickel-titanium (Ni-Ti) alloy already used in endodontics with titanium-molybdenum (Ti-Mo) and titanium-niobium (Ti-Nb) alloys to determine if these can be suggested in the manufacture of endodontic files. Methods and Materials: Orthodontic wires made of the different alloys were used. The previously mentioned alloys were characterized by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and torsion tests. Cyclic fatigue tests were performed on a simulated canal with a curvature of 86° to 375 rpm. The fractured surfaces of the wires were observed by means of scanning electron microscopy (SEM). A Kruskal-Wallis test and U Mann Whitney test were used to determine significant differences in cyclic fatigue between groups. Results: In the mechanical tests, similar values of torsion were found for the three alloys. In XRD, the Ti-Nb showed less structural changes. In the cyclic fatigue test, Ti-Nb was found to be significantly more resistant with respect to Ni-Ti and Ti-Mo. Conclusion: Based on our in vitro study, Ti-Nb is suggested as a possible alloy for the manufacture of rotary files due to its impressive properties.

An Algorithm to Optimize the Micro-Geometrical Dimensions of Scaffolds with Spherical Pores.

Despite the wide use of scaffolds with spherical pores in the clinical context, no studies are reported in the literature that optimize the micro-architecture dimensions of such scaffolds to maximize the amounts of neo-formed bone. In this study, a mechanobiology-based optimization algorithm was implemented to determine the optimal geometry of scaffolds with spherical pores subjected to both compression and shear loading. We found that these scaffolds are particularly suited to bear shear loads; the amounts of bone predicted to form for this load type are, in fact, larger than those predicted in other scaffold geometries. Knowing the anthropometric characteristics of the patient, one can hypothesize the possible value of load acting on the scaffold that will be implanted and, through the proposed algorithm, determine the optimal dimensions of the scaffold that favor the formation of the largest amounts of bone. The proposed algorithm can guide and support the surgeon in the choice of a "personalized" scaffold that better suits the anthropometric characteristics of the patient, thus allowing to achieve a successful follow-up in the shortest possible time.

Irregular Load Adapted Scaffold Optimization: A Computational Framework Based on Mechanobiological Criteria.

By combining load adaptive algorithms with mechanobiological algorithms, a computational framework was developed to design and optimize the microarchitecture of irregular load adapted scaffolds for bone tissue engineering. Skeletonized cancellous bone-inspired lattice structures were built including linear fibers oriented along the internal flux of forces induced by the hypothesized boundary conditions. These structures were then converted into solid finite element models, which were optimized with mechanobiology-based optimization algorithms. The design variable was the diameter of the beams included in the scaffold, while the design objective was the maximization of the fraction of the scaffold volume predicted to be occupied by neo-formed bony tissue. The performance of the designed irregular scaffolds, intended as the capability to favor the formation of bone, was compared with that of the regular ones based on different unit cell geometries. Three different boundary and loading conditions were hypothesized, and for all of them, it was found that the irregular load adapted scaffolds perform better than the regular ones. Interestingly, the numerical predictions of the proposed framework are consistent with the results of experimental studies reported in the literature. The proposed framework appears to be a powerful tool that can be utilized to design high-performance irregular load adapted scaffolds capable of bearing complex load distributions.

Comparison of the mechanobiological performance of bone tissue scaffolds based on different unit cell geometries.

Enhancing the performance of scaffolds for bone regeneration requires a multidisciplinary approach involving competences in the fields of Biology, Medicine and Engineering. A number of studies have been conducted to investigate the influence of scaffolds design parameters on their mechanical and biological response. The possibilities offered by the additive manufacturing techniques to fabricate sophisticated and very complex microgeometries that until few years ago were just a geometrical abstraction, led many researchers to design scaffolds made from different unit cell geometries. The aim of this work is to find, based on mechanobiological criteria and for different load regimes, the optimal geometrical parameters of scaffolds made from beam-based repeating unit cells, namely, truncated cuboctahedron, truncated cube, rhombic dodecahedron and diamond. The performance, -expressed in terms of percentage of the scaffold volume occupied by bone-, of the scaffolds based on these unit cells was compared with that of scaffolds based on other unit cell geometries such as: hexahedron and rhombicuboctahedron. A very intriguing behavior was predicted for the truncated cube unit cell that allows the formation of large amounts of bone for low load values and of very small amounts for the medium-high ones. For high values of load, scaffolds made from hexahedron unit cells were predicted to favor the formation of the largest amounts of bone. In a clinical context where medical solutions become more and more customized, this study offers a support to the surgeon in the choice of the best scaffold to be implanted in a patient-specific anatomic region.

An intramembranous ossification model for the in silico analysis of bone tissue formation in tooth extraction sites.

The accurate modeling of biological processes allows us to predict the spatiotemporal behavior of living tissues by computer-aided (in silico) testing, a useful tool for the development of medical strategies, avoiding the expenses and potential ethical implications of in vivo experimentation. A model for bone healing in mouth would be useful for selecting proper surgical techniques in dental procedures. In this paper, the formulation and implementation of a model for Intramembranous Ossification is presented aiming to describe the complex process of bone tissue formation in tooth extraction sites. The model consists in a mathematical description of the mechanisms in which different types of cells interact, synthesize and degrade extracellular matrices under the influence of biochemical factors. Special attention is given to angiogenesis, oxygen-dependent effects and growth factor-induced apoptosis of fibroblasts. Furthermore, considering the depth-dependent vascularization of mandibular bone and its influence on bone healing, a functional description of the cell distribution on the severed periodontal ligament (PDL) is proposed. The developed model was implemented using the finite element method (FEM) and successfully validated by simulating an animal in vivo experiment on dogs reported in the literature. A good fit between model outcome and experimental data was obtained with a mean absolute error of 3.04%. The mathematical framework presented here may represent an important tool for the design of future in vitro and in vivo tests, as well as a precedent for future in silico studies on osseointegration and mechanobiology.

Utilidad de la conformación del túnel liso antes de usar limas rotatorias endodónticas de níquel-titanio / Usefulness of shaping the glide path before using rotary nickel-titanium endodontic files

Introducción: para prevenir la fractura de instrumentos endodonticos actualmente se siguen investigando materiales, técnicas y diseños los cuales buscan reducir su incidencia. La conformación de túnel liso (Glide Path) se ha propuesto con este fin, sin embargo su utilidad ha sido controvertida. Objetivo: comprobar teóricamente mediante la utilización de un análisis de elementos finitos, la utilidad de la conformación de túnel liso, antes de la utilización de limas rotatorias endodonticas de níquel-titanio. Métodos: se realizó una simulación numérica mediante un análisis de elementos finitos, para lo cual se construyeron modelos matemáticos de las limas rotatorias de níquel-titanio S1 y S2 de la serie Protaper®. Con el software Simulation multyphisics de Autodesk® se programaron las propiedades mecánicas de las limas y un límite de falla por fractura de 1270,588 MPa. Posteriormente se aplicó el torque recomendado por el fabricante y se fijo la punta del instrumento (sin conformación de túnel liso) aplicando allí restricciones en todos los grados de libertad.Para simular la realización de la conformación de túnel liso, se aplicaron restricciones en todos los grados de libertad a una determinada distancia de la punta del instrumento, simulando de esta forma que la punta del instrumento permanecía libre. Resultados: al fijar la punta de las limas, los esfuerzos máximos fueron 1545,77 MPa para la S1 y 1306,47 MPa para la S2, observando fractura de los instrumentos. Al fijar las limas a distancia de la punta no se observó fractura. Conclusiones: se demostró teóricamente que al impedir que se atrapen la punta de las limas, se previene su fractura y que dicho atrapamiento se evita con una conformación de túnel liso, por lo que se concluye que este procedimiento es útil para prevenir la fractura de los instrumentos rotatorios de níquel-titanio(AU)

Introduction: materials, techniques and designs continue to be studied with the purpose of reducing the incidence of fracture in endodontic instruments. Shaping of the glide path has been proposed for this end; however, its usefulness has been a matter of controversy. Objective: based on the finite element method, carry out a theoretical analysis of the usefulness of shaping the glide path before using rotary nickel-titanium endodontic files. Methods: numerical simulation was performed based on finite element analysis, to achieve which mathematical models were built of rotary nickel-titanium files S1 and S2 of the Protaper™ series. Autodesk™ Simulation Multiphysics software was used to program the mechanical properties of the files, as well as a fracture failure limit of 1270.588 MPa. The torque recommended by the manufacturer was then applied and the instrument tip fixed into place (without shaping the glide path) with restrictions on all degrees of freedom. In order to simulate glide path shaping, restrictions were applied to all degrees of freedom at a certain distance from the instrument tip, thus simulating that the instrument tip remained free. Results: on fixing the file tips, maximum efforts were 1545.77 Mpa for S1 and 1306.47 Mpa for S2. Instrument fracture was observed. When files were fixed at a distance from the tip, no fracture was observed. Conclusions: it was theoretically demonstrated that when file tips are prevented from being caught, fracture is prevented as well, and such catch is avoided by shaping the glide path. It is therefore concluded that the procedure is useful to prevent the fracture of rotary nickel-titanium instruments(AU)

Comparación de esfuerzos pre y post quirúrgicos sobre articulación de cadera con secuelas de displasia / Comparison of pre- and postsurgical stress over a hip joint with dysplastic sequels

Introducción: la displasia residual de cadera en jóvenes y adultos requiere un procedimiento quirúrgico para su tratamiento; tener en cuenta el comportamiento biomecánico futuro de la articulación podría ser una útil herramienta en la planeación y evaluacióndel procedimiento quirúrgico más adecuado para el paciente. Objetivo: realizar una comparación entre la distribución de esfuerzos pre y post quirúrgicos sobre una articulación de cadera con secuelas de displasia utilizando el método de elementos finitos para su resolución. Métodos: se usó un modelo de elementos finitos de la articulación de un paciente con secuelas de displasia, reconstruido a partir de imágenes obtenidas por TAC, y un modelo de la reubicación articular simulando elprocedimiento quirúrgico realizado. El máximo esfuerzo generado y el área de soporte de peso fueron calculados durante la etapa de apoyo de un ciclo de marcha. Resultados: hay una excesiva carga sobre la articulación patológica debido a la reducida cobertura articular. Las simulaciones sobre el modelo post-quirúrgico revelaron una reducción del 20,20 % en elesfuerzo máximo generado sobre la cabeza femoral en el punto de mayor carga en la marcha (20 % de la fase de apoyo), además de una reducción del 49 % en la presión de contacto sobre el cartílago articular y un incremento del 64 % en el área de soporte de peso en el mismo punto. Conclusiones: este estudio revela una mejora biomecánica post-quirúrgica muy considerableen el nivel de la carga que soporta la articulación; por otra parte, permite tener un mayor acercamiento a la realidad del paciente y contribuye a la toma de una óptima decisión para el tratamiento de la patología.

Introduction: The treatment of residual hip dysplasia in young persons and adults requires surgery. Bearing in mind the future biomechanical behavior of the joint could be a useful tool in the planning and evaluation of the most appropriate surgical procedure. Objective: Compare the distribution of pre- and postsurgical stress over a hip joint with dysplastic sequels using the finite element method for its resolution. Methods: Use was made of a finite element model of a patient's hip joint with dysplastic sequels reconstructed from CT scan images, and a model of the joint relocation that simulated the surgical procedure performed. The maximum stress generated and the weight bearing area were estimated during the stance phase of the gait cycle. Results: The load on the treated joint is excessive due to the reduced joint coverage. Simulations on the postsurgical model showed a 20.20% reduction in the maximum stress exerted on the femoral head at the point of greatest load during the gait (20% of the stance phase), a 49% reduction in the contact pressure over the joint cartilage, and a 64% increase in the weight bearing area at the same point. Conclusions: The study revealed very considerable postsurgical biomechanical improvement in the amount of load borne by the joint. On the other hand, it allows a better view of the patient's reality and contributes to taking the best treatment decision.