A hybrid finite-discrete element method for modelling cracking processes in sandy mudstone containing a single edge-flaw under cyclic dynamic loading.

Rock mass deformation and failure are macroscopic manifestations of crack initiation, propagation, and coalescence. However, simulating the transition of rocks from continuous to discontinuous media under cyclic dynamic loading remains challenging. This study proposes a hybrid finite-discrete element method (HFDEM) to model crack propagation, incorporating a frequency-dependent cohesive-zone model. The mechanical properties of standard sandy mudstone under quasi-static and cyclic dynamic loading were simulated using HFDEM, and the method's reliability was verified through experimental comparison. The comparative analysis demonstrates that HFDEM successfully captures crack interaction mechanisms and accurately simulates the overall failure behavior of specimens. Additionally, the effects of pre-existing flaw inclination angle and dynamic loading frequency on rock failure mechanisms were investigated. The numerical results reveal that rock samples exhibit significantly higher compressive strength under dynamic loading compared to quasi-static loading, with compressive strength increasing with higher cyclic dynamic load frequencies. Furthermore, by analyzing the strength characteristics, crack propagation, and failure modes of the samples, insights into the failure mechanisms of rocks under different frequency loads were obtained. This study provides valuable insights into crack development and failure of rocks under seismic loads, offering guidance for engineering practices.

Fracture Resistance of Posterior Milled Nanoceramic Crowns after Thermomechanical Aging.

Fracture resistance is an important parameter used to predict the performance of indirect dental restorations. The purpose of this in vitro study was to assess the fracture load of posterior milled nanoceramic crowns, in comparison with the lithium disilicate crowns, after fatigue loading, for two different restoration occlusal thicknesses. Forty test metal dies were fabricated by duplicating a master metal model consisting of an anatomic abutment preparation of the maxillary first premolar for a single crown. The dies were divided into two groups of 20 each for the fabrication of nanoceramic (Lava Ultimate) and lithium disilicate (IPS e.max CAD) single crowns. Each material group was further divided into two sub-groups of 10 dies each, based on crown occlusal thickness, of 0.5-mm and 0.75-mm (n = 10). Dental Type V stone dies poured from polyvinyl siloxane impressions of the test metal dies were laboratory scanned in order to design and mill 40 ceramic crowns. The crowns were cemented on to the test metal dies with a self-adhesive resin luting cement. All crowns were thermocycled (2500 cycles) and mechanically loaded (250,000 cycles) in a chewing simulator followed by static loading until failure, and the values noted. The data were statistically analyzed by 2-way ANOVA and Tukey HSD post-hoc multiple comparison tests (α = 0.05). The mean fracture loads ranged from 1022 to 1322 N for nanoceramic crowns and from 1145 to 1441 N for the lithium disilicate crowns. Two-way ANOVA revealed insignificant differences between the nanoceramic and lithium disilicate crowns (p > 0.05) in terms of fracture load. Significant differences were noted in the fracture resistance of crowns based on occlusal thickness (303 N; p = 0.013) regardless of the material used. Multiple comparisons by Tukey HSD post-hoc test showed insignificant differences between the four material-occlusal thickness groups (p > 0.05). The nanoceramic crowns were found to be comparable with lithium disilicate crowns in terms of fracture load. The mean fracture loads of all of the tested crowns were within the normal physiological masticatory load limits. Based on the fracture-resistance results, nanoceramic crowns seem to be suitable for clinical use for the tested occlusal thicknesses.

Sensitivity of cartilage mechanical behaviour to spatial variations in material properties.

Articular cartilage tissue exhibits a spatial dependence in material properties that govern mechanical behaviour. A mathematical model of cartilage tissue under one dimensional confined compression testing is developed for normal tissue that takes account of these variations in material properties. Modifications to the model representative of a selection of mechanisms driving osteoarthritic cartilage are proposed, allowing application of the model to both physiological and pathophysiological, osteoarthritic tissue. Incorporating spatial variations into the model requires the specification of more parameters than are required in the absence of these variations. A global sensitivity analysis of these parameters is implemented to identify the dominant mechanisms of mechanical response, in normal and osteoarthritic cartilage tissue, to both static and dynamic loading. The most sensitive parameters differ between dynamic and static mechanics of the cartilage, and also differ between physiological and osteoarthritic pathophysiological cartilage. As a consequence changes in cartilage mechanics in response to alterations in cartilage structure are predicted to be contingent on the nature of loading and the health, or otherwise, of the cartilage. In particular the mechanical response of cartilage, especially deformation, is predicted to be much more sensitive to cartilage stiffness in the superficial zone given the onset of osteoarthritic changes to material properties, such as superficial zone increases in permeability and reductions in fixed charge. In turn this indicates that any degenerative changes in the stiffness associated with the superficial cartilage collagen mesh are amplified if other elements of osteoarthritic disease are present, which provides a suggested mechanism-based explanation for observations that the range of mechanical parameters representative of normal and osteoarthritic tissue can overlap substantially.

Simulation of Orbital Fractures Using Experimental and Mathematical Approaches: A Pilot Study.

This contribution gives basic information about the mechanical behavior of the facial part of the human skull cranium, i.e., the splanchnocranium, associated with external loads and injuries caused mainly by brachial violence. The main areas suffering from such violence include the orbit, frontal, and zygomatic bones. In this paper, as a first approach, brachial violence was simulated via quasi-static compression laboratory tests, in which cadaveric skulls were subjected to a load in a testing machine, increasing till fractures occurred. The test skulls were also used for research into the dynamic behavior, in which experimental and numerical analyses were performed. A relatively high variability in forces inducing the fractures has been observed (143-1403 N). The results lay the basis for applications mainly in forensic science, surgery, and ophthalmology.

Study of hydrothermal processes in ice-layers subgrade under constant temperature and dynamic loading.

The presence of ice-layers in the subgrade soils makes the hydrothermal state of road subgrade built in island permafrost regions more susceptible to external environmental influences. In order to deepen the study of the ice-layers subgrade, a hydrothermal study of subgrade under constant temperature and dynamic loading was carried out. It was found that dynamic loading can change the temperature, moisture and pore water pressure distribution. Under dynamic loading, the hydrothermal and pore water pressure state of the soil in the upper part of the ice layer changed significantly at the beginning of the test. The application of dynamic loads alters the spatial distribution of pore water pressure in the soil, resulting in pressure differences between different areas, which affects the migration of moisture and ultimately leads to the formation of areas with higher moisture content in the area below the load. However, the reduction in soil temperature will weaken the effect of the load, therefore, the temperature of the soil should be controlled for frozen subgrade with ice-layers to prevent the accumulation of moisture in the soil.

Transformer hot spot temperature estimation through adaptive neuro fuzzy inference system approach.

Transformer performance and efficiency can be enhanced by effectively address the properties of its insulation system. The power transformer insulation system weakens as a result of operational thermal stresses brought on by dynamic loading and shifting environmental patterns. Winding hot spot temperature is a crucial metric that must be maintained below the prescribed limit while power transformers are operating so as to maintained power system reliability. This is due to the fact that, among other variables, the time-dependent aging effect of insulation depends on transitions in hot spot temperatures. Due to the non-linear nature of the conventional mathematical models used to determine these temperatures, and complexity of thermal phenomena, investigations still need to be exercised to fully understand the variables that associate with hot spot temperature computation with minimum error. This paper explores the possibilities of enhancing top oil and hot spot temperature estimation accuracy through the use of an adaptive neuro-fuzzy inference (ANFIS) technique. The paper presents an adaptive neuro fuzzy model to approximate the hot spot temperature of a mineral oil-filled power transformer based on loading, and established top oil temperature. Initially, a sub-ANFIS top oil temperature estimation model based on loading and ambient temperature as inputs is established. Using a hybrid optimization technique, the ANFIS membership functions were fine-tuned throughout the training process to reduce the difference between the actual and anticipated outcomes. The correctness and reliability of the created adaptive neural fuzzy model have been verified using real-world field data from a 60/90MVA, 132 kV power transformers under dynamic operating regimes. The ANFIS model results were validated against field measured values and literature-based electrical-thermal analogous models, establishing a precise input-output correlation. The developed ANFIS model achieves the highest coefficient of determination for both TOT and HST (0.98 and 0.96) and the lowest mean square error (7.8 and 10.3) among the compared thermal models. Correct determination of HST can help asset managers in thermal analysis trending of the in-service transformers, helping them to make proper loading recommendations for safeguarding the asset.

The effect of contaminating media on the static and dynamic mechanical resilience of dental implant abutments' screws: In vitro study.

INTRODUCTION: This in vitro study aims to biomechanically evaluate the influence of medium contamination for example, saliva, blood, chlorhexidine (liquid and gel), and fluoride mouthwash on the biomechanical behavior of implant abutments' screws under static and dynamic loading. METHODS: Forty five Ti6Al4V commercial dental implants and abutments were tested in this study. Two main mechanical tests were carried out in the selected media. The first, static, aimed to evaluate the torque loss after the first tightening. The second, dynamic, involved a random cyclic load range between 0 and 200 N to evaluate torque loss due to mastication. In addition, metallographic longitudinal and cross-sections of the abutment-implant apparatus were examined to evaluate the abutment screw-abutment-implant interface. RESULTS: The static torque test showed that irrespective of the media, no statistical difference in static torque loss was found prior to dynamic loading. For the dynamic tests, torque-angle evolution analysis during tightening to 30 Ncm and after the spectrum loading, showed the same global mechanical behavior for all media, but the statistical analysis indicated a difference between the groups in reverse torque values (RTV) and in the torque loss due to dynamic loading. The medium groups CHX, CHX-gel, and Fluoride mouthwash, showed a meaningful torque loss due to loading, but the medium groups, control (no medium), blood and saliva showed an opposite trend and required a higher torque to open the abutment screws. The microstructural analysis revealed clear signs of cold-welding/galling, post-dynamic loading in these latter groups. CONCLUSIONS: The presence of lubrication/contamination media (CHX mouthwash/CHX-gel/Fluoride mouthwash) reduces the preload generated due to tightening but prevents damage due to galling. The observed reduction of RTV clearly emphasizes the need for frequent abutment screw retightening for implant-supported prosthetic long-term stability.

Talon cannulated compression device as an alternative in the fixation of acetabulum posterior column fractures: A biomechanical study.

To compare the amount of displacement and rigidity at the fracture line under static & dynamic axial loading and torsional stress of conventional cannulated screw (CS), plate screw fixation including inter-fragmentary screw (PL), and talon cannulated compression device or talon screw in other words (TS) in posterior column fracture models. Synthetic hemipelvis bone models presenting a posterior column fracture were used in this study. Group PL, CS, and TS were created with ten bone models prepared for each group for dynamic and static loading tests and another ten for torsional tests. Rigidity and displacement amounts before and after loading were measured at the reference points AL, BL, and CL, located at the acetabulum's top, middle, and bottom, respectively. Torsional tests for each group were used to calculate torsional rigidity and maximum torque values. In dynamic axial loading tests, Group CS showed more displacement than PL at the BL point (p = 0,032) and Group TS at AL (p = 0,032) and CL (p = 0,004) points. In static axial loading tests, Group CS significantly displaced more than TS at AL and CL points (p = 0,05 and p = 0,014, respectively). Group PL and Group TS exhibited similar behavior in dynamic, static axial loading tests and torsional rigidity. The maximum torque that Group PL could withstand was statistically significantly higher than the other two groups (p <0,001). Talon cannulated screws had promising results in posterior column fractures of the acetabulum, which may decline the need for open surgery for stable fixation.

Mechanical behaviour of reconstructed defected skull with custom PEEK implant and Titanium fixture plates under dynamic loading conditions using FEM.

Skull reconstruction using cranial implants is often required for repairing skull defects caused due to trauma, diseases, or malignancy to protect intracranial structures. For relieving Intracranial Pressure (ICP) surgeons restore cranial defects either using natural bones or fabricated custom cranial implants. With the increase in Traumatic Brain Injuries (TBI) and challenges faced by TBI patients to regain normalcy, it is imperative to analyse the mechanical behaviour of skull-implant assemblies under some Head Injury Criteria (HIC). Medical grade materials including Titanium Alloys (Ti-6Al-4V) and Polyether-ether-ketone (PEEK) are used by fabricating Patient-Specific Implants (PSI) manufactured using 3D imaging, modelling and printing techniques. 3D technologies are preferred over conventional manufacturing methods, as they enable fabrication of custom shapes, sizes and properties for these PSI. For an effective attachment of PSI with a defective skull, a stable joint and plate arrangement as fixture plates is necessary at their interface. These fixtures can have variable numbers, design shapes, materials and location arrangements. This paper presents the Finite Element Method/Analysis (FEM/FEA) study of PSI attached to a defected skull for reconstruction, with linear shaped fixture configuration, when subjected to an external dynamic loading at 5 m/s, strain rate of 10s-1 to 243s-1 and ICP of 15mm Hg from three sides of the skull faces. Three different materials as Neoprene (soft), Concrete (medium rigid) and E-Glass (highly rigid) have been used, in the form of a rectangular thin cuboidal wall structure, at an angle of 45° with the skull face. Four linear shaped fixture plates which were simplest to design, were used to attach the PSI-skull assembly, to ensure that weight of the PSI-fixation assembly on the patient remains minimal, overall assembly has symmetrical fixations and efforts required by a surgeon for fitment of these plates remain minimal. Placement of these fixture plates has been optimized to encompass the complete PSI-skull interface section, due to which the stresses within all the assembly components (PSI, fixture plate and skull) reduced by nearly 2.5 times than the initial design and remained within yielding limits, thereby, averting any failure under heavy external dynamic loading.

An Ex-Vivo Model for Investigating Bacterial Extrusion from Infected Root Canals during Masticatory Function.

INTRODUCTION: The extrusion of bacteria from infected root canals may lead to increase in symptoms, expansion of periapical lesions, and contribution to systemic diseases. The aim of this study is to investigate a potential proof-of-concept model to study the extent to which bacteria can escape from infected root canals under dynamic loading (simulated chewing). METHODS: The study was completed in 2 experiments performed at 2 institutions. Biofilms of Streptococcus intermedius in the first experiment and S. intermedius and Actinomyces naeslundii were allowed to grow in root canals of single-rooted extracted teeth for 3 weeks. The roots of the teeth were suspended in a small chamber containing dental transport medium and were mounted on a lower sample holder of a chewing simulator. In the experimental group, simulated chewing cycles equivalent to 1 year of function were conducted, and then bacterial migration was quantified and compared with stationary teeth. RESULTS: All experimental samples of the loading group revealed bacterial penetration in both experiments. Several of the unloaded samples revealed no bacterial penetration. In the first experiment, a significantly higher number of bacteria were able to escape into the periapex of the loaded group compared with the unloaded group (P = .017). In the second experiment, there was no significant difference between the 2 bacterial species used in the amount of extruded bacteria; however, there was a highly significant effect for occlusal loading (P = .0001). CONCLUSIONS: The potential for occlusal forces to enhance bacterial extrusion from infected root canals should be further explored.

Implantoplasty and the risk of fracture of narrow implants with advanced bone loss: A laboratory study.

OBJECTIVES: To assess the impact of implantoplasty (IP) on maximum implant failure strength of narrow diameter implants of different type/design and material, with simulated advanced bone loss. MATERIALS AND METHODS: Narrow, parallel-walled implants (3.3 mm in diameter × 10 mm long) with an internal connection of different type/design [bone level (BL), tissue level (TL)] and material [Titanium grade IV (Ti), Titanium-Zirconium alloy (TiZr)] from one specific manufacturer were used. Half of the implants were subjected to IP in their coronal 5 mm; the remaining were used as controls (seven implants per group). Dynamic loading prior to maximum load strength testing was included. RESULTS: During dynamic loading, the fracture rate of BL implants was low and independent of IP, while that of TL implants increased significantly with IP compared with controls (p = .001). Maximum implant failure strength reduction (in %) due to IP, was 1.3%-25.4%; TiZr BL implants were least affected. Implants subjected to IP compared to those without IP as well as TL implants compared to BL implants showed a significantly lower maximum implant failure strength (p < .002); implant material was not significant (p = .845). CONCLUSIONS: Based on data from implants of one specific manufacturer, IP has a significant negative impact on the fracture strength of narrow implants suffering from advanced peri-implantitis. TL implants have been more severely affected compared to BL implants and presented an increased risk for failure during normal chewing forces. In addition, this negative impact of IP on TL implants was independent of the implant material (i.e., Ti or TiZr). CLINICAL RELEVANCE: Narrow single TL implants with advanced horizontal bone loss (e.g., 5 mm), when subjected to IP, appear to have an increased fracture risk during normal function.

Highly Stretchable Printed Poly(vinylidene fluoride) Sensors through the Formation of a Continuous Elastomer Phase.

Stretchable piezoelectric stress/strain sensing materials have attracted substantial research interest in the fields of wearable health monitoring, motion capturing, and soft robotics. These sensors require operation under dynamic loading conditions with high strain range, changing strain/loading rates, and varying pre-stretch states, which are challenging conditions for existing sensors to produce reliable measurements. To overcome these challenges, an intrinsically stretchable poly(vinylidene fluoride) (PVDF) sensor is developed through the polymer blending of PVDF and acrylonitrile butadiene rubber (NBR). Through precipitation printing and vulcanization, the resulting PVDF/NBR blends exhibit strong ß phase PVDF and a blend morphology with submicron-level phase separation, but also strains up to 544%. Both the blend morphology and the mechanical properties indicate that this PVDF/NBR blend can be considered as a continuous elastomer phase above micron scale. After electric poling and adding electrodes, the PVDF/NBR blends have excellent piezoelectric properties to be used as both stretching mode strain sensors and compression mode stress/force sensors. The stretching mode sensors can measure strain up to 70% without strain rate and pre-stretch dependence, while the compression mode sensors have a loading-rate-independent linear voltage-stress relationship up to 4.8 MPa stress and a negligible pre-stretch dependence. Therefore, the PVDF/NBR sensors can provide accurate and reliable stress/strain measurements when attached to soft structures, which paves the way for sensing and calibration of soft robots under dynamic loading conditions.

Repairing Annulus Fibrosus Fissures Using Methacrylated Gellan Gum Combined with Novel Silk.

Intervertebral disc (IVD) herniation often causes severe pain and is frequently associated with the degeneration of the IVD. As the IVD degenerates, more fissures with increasing size appear within the outer region of the IVD, the annulus fibrosus (AF), favoring the initiation and progression of IVD herniation. For this reason, we propose an AF repair approach based on methacrylated gellan gum (GG-MA) and silk fibroin. Therefore, coccygeal bovine IVDs were injured using a biopsy puncher (⌀ 2 mm) and then repaired with 2% GG-MA as a filler material and sealed with an embroidered silk yarn fabric. Then, the IVDs were cultured for 14 days either without any load, static loading, or complex dynamic loading. After 14 days of culture, no significant differences were found between the damaged and repaired IVDs, except for a significant decrease in the IVDs' relative height under dynamic loading. Based on our findings combined with the current literature that focuses on ex vivo AF repair approaches, we conclude that it is likely that the repair approach did not fail but rather insufficient harm was done to the IVD.

Does preclinical analysis based on static loading underestimate post-surgery stem micromotion in THA as opposed to dynamic gait loading?

The success of cementless hip stems depends on the primary stability of the implant quantified by the amount of micromotion at the bone-stem interface. Most finite element (FE)-based preclinical studies on post-surgery stem stability rely on static analysis. Hence, the effect of dynamic gait loading on bone-stem relative micromotion remains virtually unexplored. Furthermore, there is a paucity of research on the primary stability of grooved stems as opposed to plain stem design. The primary aim of this FE study was to understand whether transient dynamic gait had any incremental effect on the net micromotion results and to further draw insights into the effects of grooved texture vis-à-vis a plain model on micromotion and proximal load transfer in host bone. Two musculoskeletal loading regimes corresponding to normal walking (NW) and stair climbing (SC) were considered. Although marginally improved load transfer was predicted proximally for the grooved construct under static loading, the micromotion values (max: NW ~ 7 µm; SC ~ 10 µm) were found to be considerably less in comparison to plain stem (max: NW ~ 50 µm; SC ~ 20 µm). For both physiological load cases, a significant surge in micromotion values was predicted in dynamic analyses as opposed to static analyses for the grooved stem (~ 390% greater). For the plain model, the increase in these values from static to dynamic loading is relatively moderate yet clinically significant (~ 230% greater). This suggests that the qualitative similarities notwithstanding, there were significant dissimilarities in the quantitative trends of micromotion for different cases under both analyses.

Effects of dexamethasone and dynamic loading on cartilage of human osteochondral explants challenged with inflammatory cytokines.

Post-traumatic osteoarthritis (PTOA), characterized by articular cartilage degradation initiated in an inflammatory environment after traumatic joint injury, can lead to alterations in cartilage biomechanical properties. Low dose dexamethasone (Dex) shows chondroprotection in cartilage challenged with inflammatory cytokines, but little is known about the structural biomechanical response of human cartilage to Dex in such a diseased state. This study examined changes in the biomechanical properties and biochemical composition of the cartilage within human osteochondral explants in response to treatment with exogenous cytokines, Dex, and a regimen of cyclic loading at the start and end of culture. Osteochondral explants were harvested from five pairs of human ankle talocrural joints (Collins grade 0-1) and cultured for 10 days with/without exogenous cytokines (100 ng/mL TNFα, 50 ng/mL IL-6, 250 ng/mL sIL-6R) ± Dex (100 nM). Biomechanical testing on day-0 and day-10 enabled estimation of the unconfined compression equilibrium modulus (Ey), dynamic stiffness (Ed) and hydraulic permeability (kp) of cartilage excised from bone, accompanied by biochemical assessment of media and cartilage tissue. Dex preserved chondrocyte cell viability and decreased sulfated glycosaminoglycan (sGAG) loss and nitric oxide release, but did not alter Ey, Ed and kp (before or after loading) on day-10. In the cytokine/cytokine+Dex treated groups, sGAG content exhibited a weaker correlation with Ey and Ed than at baseline, suggesting an important role for structural rather than biochemical changes in producing biomechanical alterations in response to cytokines and Dex. These findings aid in forming a more complete profile of potential clinical effects of Dex for use in OA/PTOA treatment regimens.

The effect of surface treatments on the adhesive bond in all-ceramic dental crowns using four-point bending and dynamic loading tests.

The aim of this study was to determine the effect of sandblasting, grinding and plasma treatment on the adhesive bond strength between framework ceramic (Y-TZP) and veneering ceramic (feldspar ceramic). Therefore, four-point bending specimens (n = 180) were cut from densely sintered 3Y-TZP blanks. Subsequently, 80 of these samples received surface treatment by sandblasting and 80 samples by grinding. A reference group (20 samples) was not processed. Half of the specimens that received a surface treatment were additionally exposed to an oxygen plasma treatment. After processing, all specimens were manually veneered with feldspar ceramic and examined with a four-point bending test to evaluate the strain energy release rate G. The surface treatment parameters that achieved the highest and lowest G were transferred to real geometries of a posterior crown (n = 45). The crowns' ceramic framework was sandblasted and veneered by hand. The all-ceramic crowns were tested in a dynamic loading test and Wöhler curves were evaluated. Four-point bending samples blasted at an angle of 90° at 6 bar and a working distance of 1.5 cm without plasma treatment achieved the highest energy release rate. Samples blasted at an angle of 90° at 2 bar and a working distance of 1 cm with plasma treatment achieved the lowest energy release rate. Overall, plasma treatment did not improve bond strength. In the dynamic loading test, the group blasted with 2 bar showed the best results.

Effect of Vent Hole and Cement Type on Fracture Resistance of CAD-CAM Monolithic Zirconia Crowns.

PURPOSE: To assess the fracture resistance of monolithic zirconia crowns cemented with different types of cement on cement-retained implant abutments. MATERIALS AND METHODS: Forty implant analogs were positioned in acrylic resin blocks, and cement-retained straight implant abutments were fastened to the analogs. Crowns were designed with/without occlusal vent holes and produced from monolithic zirconia blocks by the CAD-CAM technique. The two crown types were divided into two groups and cemented with resin and zinc-polycarboxylate cement under 5 kg weight. A universal testing machine applied compressive forces to the crowns until fracture. Fracture resistance values were analyzed using two-way ANOVA and the independent samples t-test with statistical significance set at p < 0.05. RESULTS: According to the two-way ANOVA results, although the crown design did not have a significant effect on fracture resistance (1417.65 ± 337.39 N, 1565.16 ± 517.12 N; crowns with and without vent holes, respectively), the main effect of the cement variable on the fracture resistance was significant. Zinc-polycarboxylate cement (1680.1 ± 375.23 N) showed higher fracture resistance than resin cement (1302.71 ± 420.64 N) in the crowns designed with vent holes (p < 0.005). CONCLUSION: The use of cement-retained implant-supported monolithic zirconia crowns with an occlusal vent hole is safe, and zinc-polycarboxylate cement use may be an appropriate choice for cementation of these crowns.

Combined Acoustic Emission and Digital Image Correlation for Early Detection and Measurement of Fatigue Cracks in Rails and Train Parts under Dynamic Loading.

Fatigue crack in rails and cyclic-loaded train parts is a contributory factor in multiple railroad accidents. We address the problem of crack detection and measurement at early stages, when total failure has not yet occurred. We propose to combine acoustic emission (AE) testing for prediction of crack growth with digital image correlation (DIC) for its accurate quantitative characterization. In this study, we imitated fatigue crack appearance and growth in samples of railway rail and two train parts by cyclic loading, and applied these two techniques for inspection. Experimental results clearly indicate the efficiency of AE in the early detection of fatigue cracks, and excellent DIC capabilities in terms of geometrical measurements. Combination of these techniques reveals a promising basis for real-time and non-destructive monitoring of rails and train parts.

Dynamic loading stimulates mandibular condyle remodeling.

BACKGROUND: We and others have reported that low-magnitude high-frequency dynamic loading has an osteogenic effect on alveolar bone. Since chondrocytes and osteoblasts originate from the same progenitor cells, we reasoned that dynamic loading may stimulate a similar response in chondrocytes. A stimulating effect could be beneficial for patients with damaged condylar cartilage or mandibular deficiency. METHODS: Studies were conducted on growing Sprague-Dawley rats divided into three groups: control, static load, and dynamic load. The dynamic load group received a dynamic load on the lower right molars 5 minutes per day with a 0.3 g acceleration and peak strain of 30 µÎµ registered by accelerometer and strain gauge. The static load group received an equivalent magnitude of static force (30 µÎµ). The control group did not receive any treatment. Samples were collected at days 0, 28, and 56 for reverse transcriptase polymerase chain reaction analysis, microcomputed tomography, and histology and fluorescent microscopy analysis. RESULTS: Our experiments showed that dynamic loading had a striking effect on condylar cartilage, increasing the proliferation and differentiation of mesenchymal cells into chondrocytes, and promoting chondrocyte maturation. This effect was accompanied by increased endochondral bone formation resulting in lengthening of the condylar process. CONCLUSIONS: Low-magnitude, high-frequency dynamic loading can have a positive effect on condylar cartilage and endochondral bone formation in vivo. This effect has the potential to be used as a treatment for regenerating condylar cartilage and to enhance the effect of orthopedic appliances on mandibular growth.

Computational wear of knee implant polyethylene insert surface under continuous dynamic loading and posterior tibial slope variation based on cadaver experiments with comparative verification.

BACKGROUND: The effect of posterior tibial slope on the maximum contact pressure and wear volume of polyethylene (PE) insert were not given special attention. The effects of flexion angle, Anterior-Posterior (AP) Translation, and Tibial slope on the max contact pressure and wear of PE insert of TKR were investigated under loadings which were obtained in cadaver experiments by using Archard's wear law. This study uses not only loads obtained from cadaver experiments but also dynamic flexion starting from 0 to 90 degrees. METHOD: Wear on knee implant PE insert was investigated using a 2.5 size 3 dimensional (3D) cruciate sacrificing total knee replacement model and Finite Element Method (FEM) under loadings and AP Translation data ranging from 0 to 90 flexion angles validated by cadaver experiments. Two types of analyses were done to measure the wear effect on knee implant PE insert. The first set of analyses included the flexion angles dynamically changing with the knee rotating from 0 to 90 angles according to the femur axis and the transient analyses for loadings changing with a certain angle and duration. RESULTS: It is seen that the contact pressure on the PE insert decreases as the cycle increases for both Flexion and Flexion+AP Translation. It is clear that as the cycle increases, the wear obtained for both cases increases. The loadings acting on the PE insert cannot create sufficient pressure due to the AP Translation effect at low speeds and have an effect to reduce the wear, while the effect increases with the wear as the cycle increases, and the AP Translation now contributes to the wear at high speeds. It is seen that as the posterior tibial slope angle increases, the maximum contact pressure values slightly decrease for the same cycle. CONCLUSIONS: This study indicated that AP Translation, which changes direction during flexion, had a significant effect on both contact pressure and wear. Unlike previous similar studies, it was seen that the amount of wear continues to increase as the cycle increases. This situation strengthens the argument that loading and AP Translation values that change with flexion shape the wear effects on PE Insert.