The aim of this study is to compare the stress distribution in porous scaffolds with different structures with similar geometric parameters to study a new approach in dental implantation. Three-dimensional finite element models of the fully porous and dense-core porous scaffolds with defined porosity parameters including space diameter and thickness with two porosity patterns were embedded in the jaw bone model with cortical and cancellous bone. The cylindrical shape was considered as the main shape of the scaffolds. To evaluate the mechanical performance, the Von Mises stress was compared in the models under static and dynamic masticatory loading. Incidentally, to validate the modeling results, experimental strain gauge tests were performed on four specimens fabricated from Ti6Al4V. Finally, the stress distribution in the models was compared with the results of previous studies on commercial implants. The results of the finite element analysis show that there are considerable differences in the magnitude of the equivalent stress in the models in static and dynamic phases. Also, changes in the defined geometric parameters have significant effects on the stress distribution in terms of Von Mises stress in the overall models. The experimental results indicated good agreement with those of the modeling. It can be concluded that some porous structures with optimal geometries can be proposed as a new structure for dental implants. However, considering the physiology of bone when confronted with porous structures, further studies such as in vivo experiments are needed in this field.

Background The cornea plays a role in the refractive power of the eye, and when its natural curvature and thickness are compromised by diseases such as keratoconus or high myopia, this results in loss of visual acuity. Intracorneal rings (ICRs) were developed as a treatment option to restore the natural corneal curvature by implanting rings into tunnels cut within the corneal stroma. However, selecting and placing the appropriate ring can be difficult, and predicting refractive outcomes is challenging. Objective The purpose of this study was to better understand the design parameters of the rings that determine postoperative refractive and mechanical outcomes. Methods We developed an automated finite element simulation pipeline for ICR implantation and tested 300 variations of 20 ICRs. Results The outcome of ICR was dominated by the vertical size of the ring; 84% of the change in corneal curvature can be attributed to the vertical size of the ring, while only 13% were attributed to the detailed cross-sectional shape of the ring. However, the cross-sectional shape of the ring is limited to the change in axial length and contact pressure between the ring and the cornea. The horizontal dimension of the ring plays only a minor role in the postoperative outcome. Conclusion These results support Keraring’s approach to ring scaling, in which only the vertical dimension of the ring is changed, while the horizontal dimension remains constant. Numerical models help to understand ICR outcomes, design implants, and personalize empirical nomograms to achieve more successful postoperative outcomes.

The mandibular bone may be damaged for a variety of reasons. One of the methods used to facilitate and stimulate the bone to improve hard tissue formation is the use of bone grafts. In this study, a novel methodology was introduced to take a step towards making a custom xenograft for a patient with a mandibular bone defect. The application of the finite element method and evaluation of the graft simulation results was proposed, then the customized xenograft was provided using micro-milling. Also, 3D printing technology was used as a preoperative assessment of bone-graft interface conformity. Afterward, the graft was implemented for mandibular augmentation and the patient was prepared for further dental implantation. Finally, cone-based computer tomography images in different time intervals were taken for clinical assessment. Results showed that six months after the graft placement, the vertical distance from the alveolar ridge to the incisive canal and the mandibular canal was increased by 261% and 250%, respectively. Furthermore, the images taken after the insertion of dental implants and frequent observations by the dental surgeon approved the success of the treatment. Additionally, several quantitative parameters were compared to and established with the previous literature. Combining the conventional clinical examination method with an initial computational simulation by the criteria proposed in this study aided in predicting the success of mandibular augmentation and the subsequent dental implantation. More numerical analysis criteria can be added and assessed in future studies to improve the proposed method.

Although corneal biomechanics plays an important role in ophthalmology, its characterization remains limited due to tissue availability. This problem is particularly critical when studying specific pathologic conditions such as keratoconus. A preservation method that maintains the mechanical response of the tissue over time allows the collection, transport, and storage of tissue samples from different, distant clinical sites and increases the number of samples available for testing. Therefore, the aim of this study was to quantify the change in mechanical response of porcine corneas after 6 days of storage either at -20 degrees C or in standard culture medium. The viscoelastic response of porcine corneas was measured at different loading rates by nano-indentation. While the loading rate had a significant effect on the mechanical response (p < .0001), the results showed that the mechanical response were not altered by any of the preservation methods (p > .270). However, the standard deviation was up to 4.9 times larger when the samples were stored in the culture medium compared to the fresh and frozen samples. In addition, storage in culture medium resulted in significant swelling (+38%). In conclusion, although both preservation techniques provide equivalent mechanical response measured by nano-indentation, freezing the samples prevents swelling and provides more stable measurements.

PURPOSE The aim of this study is to summarize various biomechanical aspects in evaluating the long-term stability of dental implants based on finite element method (FEM). MATERIALS AND METHODS A comprehensive search was performed among published studies over the last 20 years in three databases; PubMed, Scopus, and Google Scholar. The studies are arranged in a comparative table based on their publication date. Also, the variety of modeling is shown in the form of graphs and tables. Various aspects of the studies conducted were discussed here. RESULTS By reviewing the titles and abstracts, 9 main categories were extracted and discussed as follows: implant materials, the focus of the study on bone or implant as well as the interface area, type of loading, element shape, parts of the model, boundary conditions, failure criteria, statistical analysis, and experimental tests performed to validate the results. It was found that most of the studied articles contain a model of the jaw bone (cortical and cancellous bone). The material properties were generally derived from the literature. Approximately 43% of the studies attempted to examine the implant and surrounding bone simultaneously. Almost 42% of the studies performed experimental tests to validate the modeling. CONCLUSION Based on the results of the studies reviewed, there is no "optimal" design guideline, but more reliable design of implant is possible. This review study can be a starting point for more detailed investigations of dental implant longevity.

This comparative study simulates bone remodeling outcome around titanium dental implants and compares the final bone configuration with the one around novel implants composed of radial functionally graded materials (FGMs) and the titanium implants with hydroxyapatite (HA) coating. A dental implant system embedded in 3D mandibular bone with masticatory loading was simulated by the finite element method. A bone remodeling algorithm was applied to cancellous and cortical bones. Young's modulus and von Mises stress were obtained to ensure bone homeostasis and evaluate the final bone configuration. Local stress distribution in the bone-implant interface was analyzed before and after bone remodeling. The average final Young's modulus of cancellous bone reached 2.68, 2.49, and 2.32 GPa for the FGM, HA-coated, and the titanium models, respectively. These values for cortical bone were 17.75, 16.86, and 17.20 GPa in the same order. Radial FGM implants generated the highest remodeling stimulus and bone density. Their superiority over the HA-coated models was confirmed by four implant surface stiffness values (10, 20, 30, and 40 GPa). Remodeling increased bone density around the implant, consistent with clinical data and reduced stress concentration in the cortical neck. The stress values were in the safe zone regarding overload-induced bone resorption. The findings of this study were substantiated by clinical images and bone density values from previous literature.

Fractal dimension (FD) together with advances in imaging technologies has provided an increasing application of digital images to interpret biological phenomena. In ophthalmology, topography-based images are increasingly used in common practices of clinical settings. They provide detailed information about corneal surfaces. Few-micron alterations of the corneal geometry to the elevation and curvature cause a highly multifocal surface, change the corneal optical power up to several diopters, and therefore adversely affect the individual’s vision. Keratoconus (KCN) is a corneal disease characterized by a local alteration of the corneal anatomical and mechanical features. The formation of cone-shaped regions accompanied by thinning and weakening of the cornea are the major manifestations of KCN. The implantation of tiny arc-like polymeric sections, known as intracorneal implants, is considered to be effective in restoring the corneal curvature. This study investigated the FD nature of healthy corneas (n = 7) and compared it to the corresponding values before and after intracorneal implant surgery in KCN patients (n = 7). The generalized Hurst exponent, Higuchi, and Katz FDs were computed for topography-based parameters of corneal surfaces: front elevation (ELE-front), back elevation (ELE-back), and corneal curvature (CURV). The Katz FD showed better discriminating ability for the diseased group. It could reveal a significant difference between the healthy corneas and both pre- and post-implantation topographies (p < 0.001). Moreover, the Katz dimension varied between the topographic features of KCN patients before and after the treatment (p < 0.036). We propose to describe the curvature feature of corneal topography as a “strange attractor” with a self-similar (i.e., fractal) structure according to the Katz algorithm.

Background: Center of pressure (CoP) trajectory is one of the gait parameters that is widely used for clinical assessments. Moreover, the CoP trajectory could be adversely affected by anatomic and mechanical factors that involve foot function, which was shown to be correlated with musculoskeletal diseases. The aim of this study is to compare angle-associated parameters of gait in patients with different lumbar spinal disorders. Methods: The subjects suffered from the same levels of spine impairment, including patients with lumbar spinal stenosis (LSS) and lumbar intervertebral disc degeneration (LIDD) were recruited in this study. The spatio-temporal angular parameters associated with the CoP of the subjects during their gait were collected and examined. The measurements were used to calculate the CoP angle and symmetry angle (SA). Then the butterfly diagram (BD) intersection angle was introduced as a new potential parameter in gait assessment. Results: The results of the current study showed that CoPs and SAs did not vary between the two groups (P > 0.05). The BD intersection angle, however, indicated some variations between patients with LSS and LIDD (P < 0.05). Conclusion: While the results showed that CoP angles and SAs did not differ between the LSS and LIDD groups, it is hypothesized that such disorders that affect the gait could be reflected in the BD intersection angle. Therefore, the BD intersection angle is suggested as a clinical indicator in clarifying patients with lumbar spinal disorders.

BACKGROUND:Ground reaction forces are biomechanical data, providing information to investigate pathological gait. The vertical component of ground reaction force introduces the upward thrust force within gait progression. Although alterations in the vertical component in patients with spinal disorders were addressed in the literature, still the corresponding effect on spinal disorders is a major issue to scrutiny. In this study, the effects of two different anatomical spinal disorders on the vertical component pattern were investigated. METHODS:Two groups of patients with lumbar spine stenosis and lumbar intervertebral disc degeneration with lesions at L4-L5 and/or L5-S1 levels, were recruited. The vertical component of ground reaction force and spatio-temporal parameters were obtained and analyzed using one-way analysis of variance. FINDINGS:The results indicated that all spatio-temporal parameters differed significantly (P < 0.05) except step lengths and stride times (P > 0.05). In a similar test, the Fz2 in patients with lumbar stenosis was higher than that of those with disc degeneration (P < 0.05). Besides, the vertical ground reaction force pattern showed lower slopes in stenosis patients. INTERPRETATION:This study showed that the vertical component of ground reaction force alterations and spatio-temporal parameters could be employed as indicators for certain spinal lesions. The results of this study could implement as an adjunct diagnostic method to help clinicians to differentiate between stenosis and disc degeneration patients and plan for their rehabilitation purposes.

Varus misalignment of the hip-knee-ankle angle causes greater loads on the medial compartment of the knee and increases the risk of developing knee osteoarthritis. High tibial osteotomy is a surgical method where the load-bearing axis is shifted laterally. The purpose of this study is to define a subject-specific three-dimensional multibody model of the knee to investigate the effect of osteotomy on cartilages and menisci during the stance phase of gait. It is assumed that osteotomy transfers load-bearing to the lateral parts of the knee. Magnetic resonance images of a patient with varus alignment were used to generate the geometries of the bones, cartilages, and menisci. Then, an experimental approach was used to determine the parameters for the stiffness matrices and compliant contact models of the tibio-menisco-femoral articulations with the use of finite element solutions. As indicated by the research findings, the contact force at the medial cartilage decreased as the load-bearing axis was transferred to the lateral parts. This subject-specific noninvasive analysis of contact force can be considered as a preoperative assessment tool for the surgeon. to predict the effects of high tibial osteotomy and the shifting of the load-bearing axis to the soft tissues of the knee.

Keratoconus (KC) is a progressive corneal disease. It is mostly characterized by corneal thinning and irregular steepening as well as formation of cone-shaped regions on the cornea. Amongst treatment modalities, implantation of Intrastromal Corneal Ring Segments (ICRSs) could decrease corneal surface irregularities. However, controversy exists over the selection of proper ICRSs. Here, the aim was to compare the effects of two sets of ICRSs. The ICRSs were identical both in cross-section and total arc length. The results showed that under normal physiological range of intraocular pressures (IOPs), the two selected ICRSs caused slightly different deformations in the same in-silico keratoconic eye model.

The varus knee has been defined as a Hip-Knee-Ankle alignment of less than 180 degrees. Varus knee alignment increases the load on the medial knee and also the risk of osteoarthritis. High tibial osteotomy has been designed to modify the malalignment of varus knee. The aim of this study was to investigate the osteotomy effects on knee adduction moment (KAM) and contact forces using a musculoskeletal and subject-specific knee model. A patient with varus knee and no symptoms of any other disease or disability participated in this study. The geometry of the multibody knee model has been modified using MR images. The solutions of its finite element model have been used to determine the parameters of the multibody model. The motion data, ground reaction force and kinetic data have been applied to run the subject-specific musculoskeletal model during the stance phase of gait. After osteotomy, the adduction moment decreased, where the maximum values are comparable to other studies. The pattern of KAM did not witness any significant changes. The total and medial contact forces reduced considerably after surgery, but the lateral contact force did not significantly change. The changes in total and medial contact forces and lack of change in lateral contact force could be explained by modification of the gait pattern after surgery.

BACKGROUND:The finite element method (FEM) has been used to analyze stress and strain distributions around 3 suggested dental implants with newly-designed thread parameters and the optimal shape of the implant was introduced considering the response surface optimization method sensitivity analysis. Experimental tests seemed necessary to confirm the results of the FEM.OBJECTIVES:The aim of this study was to use experimental tests to prove the results of a finite element analysis of 3 dental implants with different thread designs under axial loads. Photoelastic stress analysis was chosen due to the similarity of analysis with FEM.MATERIAL AND METHODS:Two-dimensional models of 3 dental implants were built of grade 4 titanium to be tested in the polariscope. Model 1: A tapered implant with V-shaped threads; Model 2: A tapered implant with micro-threads in the upper area and V-shaped threads in the rest of the body; Model 3: A tapered implant with reverse buttress threads in all areas. Axial loading of 100 N was applied to the top of the implants and stress patterns and the maximum stress were evaluated for each implant.RESULTS:The minimum Huber-Mises-Hencky stresses of cortical bone were recorded in model 2, a tapered implant with micro-threads in the upper area and V-shaped threads in the rest of the body. The value for 100 N loading was 15.25 MPa, which was in agreement with the FEM.CONCLUSIONS:Considering the stress patterns and values obtained from experimental tests of photoelasticity, the tapered implant with micro-threads in the upper area and V-shaped threads in the rest of the body has the most uniform and desirable stress distribution in the surrounding cortical bone and is preferred to be used in future applications.

OBJECTIVES:This study aimed to optimize the thread depth and pitch of a recently designed dental implant to provide uniform stress distribution by means of a response surface optimization method available in finite element (FE) software. The sensitivity of simulation to different mechanical parameters was also evaluated.MATERIALS AND METHODS:A three-dimensional model of a tapered dental implant with micro-threads in the upper area and V-shaped threads in the rest of the body was modeled and analyzed using finite element analysis (FEA). An axial load of 100 N was applied to the top of the implants. The model was optimized for thread depth and pitch to determine the optimal stress distribution. In this analysis, micro-threads had 0.25 to 0.3 mm depth and 0.27 to 0.33 mm pitch, and V-shaped threads had 0.405 to 0.495 mm depth and 0.66 to 0.8 mm pitch.RESULTS:The optimized depth and pitch were 0.307 and 0.286 mm for micro-threads and 0.405 and 0.808 mm for V-shaped threads, respectively. In this design, the most effective parameters on stress distribution were the depth and pitch of the micro-threads based on sensitivity analysis results.CONCLUSION:Based on the results of this study, the optimal implant design has micro-threads with 0.307 and 0.286 mm depth and pitch, respectively, in the upper area and V-shaped threads with 0.405 and 0.808 mm depth and pitch in the rest of the body. These results indicate that micro-thread parameters have a greater effect on stress and strain values.

The aim of this study was to assess stress and strain patterns in cortical and cancellous bones surrounding newly designed dental implants with different thread patterns. Static loading of dental implants has been well studied, but studies on dynamic loading and fatigue analysis of dental implants are scarce. This study analyzed the static, dynamic, and fatigue behaviors of dental implants using finite element analysis (FEA). Two models of dental implants were analyzed in this study. Model A was a tapered implant with V-shaped threads and model B was a tapered implant with microthreads in the uppermost region and V-shaped threads in the rest of the body. Two types of loading conditions were simulated in an FEA model and stress and strain patterns in the surrounding bone were analyzed. Dynamic loading increased the level of stress by 5-10% compared with static loading. Both implants showed acceptable results under static and dynamic loadings, but the second implant with microthreads caused lower stress and strain in cortical and cancellous bones. Dynamic and fatigue analyses can provide a more realistic understanding of the function of dental implants. Replacing the uppermost threads with microthreads can lead to more desirable stress patterns in bone, as well as a higher safety factor and longevity.

In this study, we aimed to design an ideal dental implant with respect to stress and strain patterns on the surrounding cortical and cancellous bones. The effects of static loading on dental implants have been previously assessed, but the impact of dynamic loading and fatigue analysis has not been well studied. We evaluated static, dynamic, and fatigue behaviors of dental implants to fully understand the mechanism and acquire a more realistic perspective of the process. In this study, we analyzed three models of a tapered dental implant: model 1 had V-shaped threads; model 2 had microthreads in the upper area and V-shaped threads in the rest of the body; model 3 had reverse buttress threads in all areas. Two types of loading conditions were simulated in a finite element model, and stress and strain patterns in the surrounding bone were evaluated. Minimum von Mises stresses of cortical bone were recorded in model 2. The values for a 100-N load with a 25° angle were 44.5 and 47.4 MPa for static and dynamic analyses, respectively. Considering the obtained stress and strain patterns, we conclude that a tapered implant with microthreads in the upper area and V-shaped threads in the rest of the body is preferred for best uniform stress distribution in both static and dynamic analyses.

Understanding cardiac blood flow patterns has many applications in analysing haemodynamics and for the clinical assessment of heart function. In this study, numerical simulations of blood flow in a patient-specific anatomical model of the left ventricle (LV) and the aortic sinus are presented. The realistic 3D geometry of both LV and aortic sinus is extracted from the processing of magnetic resonance imaging (MRI). Furthermore, motion of inner walls of LV and aortic sinus is obtained from cine-MR image analysis and is used as a constraint to a numerical computational fluid dynamics (CFD) model based on the moving boundary approach. Arbitrary Lagrangian-Eulerian finite element method formulation is used for the numerical solution of the transient dynamic equations of the fluid domain. Simulation results include detailed flow characteristics such as velocity, pressure and wall shear stress for the whole domain. The aortic outflow is compared with data obtained by phase-contrast MRI. Good agreement was found between simulation results and these measurements.

The trabecular bone fracture healing differs from diaphyseal fracture healing, in which trabecular bone heals based on intramembraneous ossification. The process includes a small callus formation, then woven bone forms, it follows by remodeling process to form regular trabecular bone. The objective of this study was to present an energy based model to simulate bone formation and remodeling during trabecular bone fracture healing. This modeling mainly focused on the mechanical factors. The model distinguishes three basic type of tissue: bone, cartilage and soft tissue. In order to determine tissue differentiation a fuzzy controller was proposed. An algorithm was developed to link the fuzzy logic controller to a finite element model (FEM) of trabecular bone. In general, finite element analysis provides input for fuzzy controller. Based on the input data, the fuzzy system selects the type of tissue to build. Strain energy density was used as the mechanical stimulus and a new parameter was incorporated in to the healing process as the remodeling index.

Integrative modeling of cardiac system is important for understanding the complex biophysical function of the heart]. To this end, multimodal cardiovascular imaging plays an important role in providing the computational domain, the boundary/initial conditions, and tissue function and properties. In particular, the incorporation of blood flow in the physiological models can help to simulate the hemodynamic properties and their effects on cardiac function. In this paper, we present a multimodal framework for quantitative and subject-specific analysis of blood flow in the cardiac chambers, including the left ventricle (LV). The 3D geometries of the LV at different time steps are extracted from medical images using an atlas of LV shape. The motion of the myocardium wall is used to extract the moving boundary data of the computational geometry. The data is used as a constraint for the computational fluid dynamics (CFD). An arbitrary Lagrangian–Eulerian (ALE) finite element method (FEM) formulation is used to derive a numerical solution of the transient dynamic equation of the fluid domain. With this method, simulation results describe detailed flow characteristics (such as velocity, pressure and wall shear stress) in the computational domain. The personalized hemodynamic characteristics obtained with the proposed approach can provide clinical value for diagnosis and treatment of abnormalities related to disturbed blood flow such as in myocardial remodeling and aortic sinus lesion formation.