Prediction of critical energy release rate for cortical bone structure under different failure modes / 中国组织工程研究

BACKGROUND:Critical energy release rate is a global fracture parameter that could be measured during the failing process,and its value may change under different failure modes even in the same structure. OBJECTIVE:To propose an approach to predict the critical energy release rate in the femoral cortical bone structure under different failure modes. METHODS:Three-point bending and axial compression experiments and the corresponding fracture simulations were performed on the rat femoral cortical bone structures.Different critical energy release rates were repeatedly assigned to the models to perform fracture simulation,and the predicted load-displacement curves in each simulation were compared with the experimental data to back-calculate the critical energy release rate.The successful fit was that the differences in the fracture parameters between the predicted and experimental results were less than 5%. RESULTS AND CONCLUSION:(1)The results showed that the cortical bone structure occurred tensile open failure under three-point bending load,and the predicted critical energy release rate was 0.16 N/mm.(2)The same cortical bone structure occurred shear open failure under axial compression load,and the predicted critical energy release rate was 0.12 N/mm,which indicates that the critical energy release rate of the same cortical bone structure under different failure modes was different.(3)A comprehensive analysis from the perspectives of material mechanical properties and damage mechanism was conducted to reveal the reasons for the differences in the critical energy release rate in the cortical bone structure under different failure modes,which provided a theoretical basis for the measurement of the energy release rate and the accurate fracture simulation.

Effects of Different Running Speeds on Tissue-Level Failure Strain in Rat Femoral Cortical Bone / 医用生物力学

Objective To predict the tissue-level failure strain of the cortical bone and discuss the effects of different running speeds on the mechanical properties of rat femoral cortical bone.Methods The threshold for cortical bone tissue-level failure strain was assigned,and fracture simulation under three-point bending was performed on a rat femoral finite element model.The predicted load-displacement curves in each simulation were compared and fitted with the experimental data to back-calculate the tissue-level failure strain.Results The cortical bone tissue-level failure strains at different running speeds were statistically different,which indicated that different running speeds had certain impacts on the micromechanical properties of the cortical bone structures.At a running speed of 12 m/min,the cortical bone structure expressed the greatest tissue-level failure strain,and at a running speed of 20 m/min,the cortical bone structure expressed the lowest tissue-level failure strain.Conclusions Based on the changing trends of tissue-level failure strain and in combination with the changes in macro-level failure load and tissue-level elastic modulus of cortical bone structures,the effects of different running speeds on the mechanical properties of cortical bone structures were discussed in this study.The appropriate running speed for improving the mechanical properties of the cortical bone was explored,thereby providing a theoretical basis for improving bone strength through running exercises.

The First Application of Domestically Produced Self-expanding Transcatheter Aortic Valve Controllable Bending Delivery System in China / 中国循环杂志

A domestically produced self-expanding transcatheter aortic valve controllable bending delivery system(VitaFlow? Ⅲcontrollable bending retrievable delivery system)was first used to perform transcatheter aortic valve replacement(TAVR)in a symptomatic severe aortic valve stenosis patient with severe heart failure and high risk of surgery in China on September 22,2023.The patient successfully completed TAVR under general anesthesia,with good valve position and function after the operation.Before discharge and at one month of follow-up,the patient's symptoms and degree of heart failure were significantly improved.The follow-up results of this case showed that the VitaFlow? Ⅲ controllable bending retrievable delivery system for TAVR is safe and feasible,and future prospective,multicenter clinical trials are expected to evaluate its efficacy.

Biomechanical Effects of Angiotensin 1-7 in Diabetes Rats Femur / Efectos Biomecánicos de la Angiotensina 1-7 en el Fémur de Ratas Diabéticas

SUMMARY: It is known that diabetes mellitus has late complications, including microvascular and macrovascular diseases. Diabetes can affect bones through biochemical markers of bone structure, density, and turnover. This study aimed to biomechanically investigate the bone-protective effects of angiotensin 1-7 (Ang 1-7), one of the active peptides in the renin-angiotensin system, in rats with diabetes. Thirty male Wistar albino rats, three months old and weighing 250-300 g, were divided into four groups: diabetes, Ang 1- 7, diabetes plus Ang 1-7, and control. One month later, diabetes developed in rats; the rats were sacrificed, and their right femur was removed. Three-point bending biomechanical tests were performed on the femurs. The diabetic group had significantly higher bone fragility than the other groups (Pr >.05). Bone fragility was lower, and bone flexibility was higher in the Ang 1-7 groups (Pr>F value 0.05). As a result of our study, the effect of Ang 1-7 on the bones of rats with diabetes was investigated biomechanically. Ang 1-7 has a protective impact on the bones of rats with diabetes.

Se sabe que la diabetes mellitus tiene complicaciones tardías, incluyendo enfermedades microvasculares y macrovasculares. La diabetes puede afectar los huesos a través de los marcadores bioquímicos de la estructura, la densidad y el recambio óseo. Este estudio tuvo como objetivo investigar biomecánicamente los efectos protectores en los huesos de la angiotensina 1-7 (Ang 1-7), uno de los péptidos activos en el sistema renina-angiotensina, en ratas con diabetes. Treinta ratas albinas Wistar macho, de tres meses de edad y con un peso de 250-300 g, se dividieron en cuatro grupos: diabetes, Ang 1-7, diabetes más Ang 1-7 y control. Un mes después, se desarrolló diabetes en ratas; se sacrificaron los animales y se extrajo su fémur derecho. Se realizaron pruebas biomecánicas de flexión de tres puntos en los fémures. El grupo diabéticos tenía una fragilidad ósea significativamente mayor que los otros grupos (Pr > 0,05). La fragilidad ósea fue menor y la flexibilidad ósea fue mayor en los grupos Ang 1-7 (valor Pr>F 0,05). Como resultado de nuestro estudio, se determinó biomecánicamente el efecto de Ang 1-7 en los huesos de ratas con diabetes. Se concluye que Ang 1-7 tiene un impacto protector en los huesos de ratas diabéticas.

Application of back-forward Bending CT localization image in the prediction of proximal junctional kyphosis after spinal deformity surgery in adults / 中国修复重建外科杂志

OBJECTIVE@#To investigate the feasibility of predicting proximal junctional kyphosis (PJK) in adults after spinal deformity surgery based on back-forward Bending CT localization images and related predictive indicators.@*METHODS@#A retrospective analysis was performed for 31 adult patients with spinal deformity who underwent posterior osteotomy and long-segment fusion fixation between March 2017 and March 2020. There were 5 males and 26 females with an average age of 62.5 years (range, 30-77 years). The upper instrumented vertebrae (UIV) located at T 5 in 1 case, T 6 in 1 case, T 9 in 13 cases, T 10 in 12 cases, and T 11 in 4 cases. The lowest instrumented vertebrae (LIV) located at L 1 in 3 cases, L 2 in 3 cases, L 3 in 10 cases, L 4 in 7 cases, L 5 in 5 cases, and S 1 in 3 cases. Based on the full-length lateral X-ray film of the spine in the standing position before and after operation and back-forward Bending CT localization images before operation, the sagittal sequence of the spine was obtained, and the relevant indexes were measured, including thoracic kyphosis (TK), lumbar lordosis (LL), local kyphosis Cobb angle (LKCA) [the difference between the different positions before operation (recovery value) was calculated], kyphosis flexibility, hyperextension sagittal vertical axis (hSVA), T 2-L 5 hyperextension C 7-vertebral sagittal offset (hC 7-VSO), and pre- and post-operative proximal junctional angle (PJA). At last follow-up, the patients were divided into PJK and non-PJK groups based on PJA to determine whether they had PJK. The gender, age, body mass index (BMI), number of fusion segments, number of cases with coronal plane deformity, bone mineral density (T value), UIV position, LIV position, operation time, intraoperative blood loss, osteotomy grading, and related imaging indicators were compared between the two groups. The hC 7-VSO of the vertebral body with significant differences between groups was taken, and the receiver operating characteristic curve (ROC) was used to evaluate its accuracy in predicting the occurrence of PJK.@*RESULTS@#All 31 patients were followed up 13-52 months, with an average of 30.0 months. The patient's PJA was 1.4°-29.0° at last follow-up, with an average of 10.4°; PJK occurred in 8 cases (25.8%). There was no significant difference in gender, age, BMI, number of fusion segments, number of cases with coronal plane deformity, bone mineral density (T value), UIV position, LIV position, operation time, intraoperative blood loss, and osteotomy grading between the two groups ( P>0.05). Imaging measurements showed that the LL recovery value and T 8-L 3 vertebral hC 7-VSO in the PJK group were significantly higher than those in the non-PJK group ( P>0.05). There was no significant difference in hyperextension TK, hyperextension LL, hyperextension LKCA, TK recovery value, LL recovery value, kyphosis flexibility, hSVA, and T 2-T 7, L 4, L 5 vertebral hC 7-VSO ( P>0.05). T 8-L 3 vertebral hC 7-VSO was analyzed for ROC curve, and combined with the area under curve and the comprehensive evaluation of sensitivity and specificity, the best predictive index was hC 7-L 2, the cut-off value was 2.54 cm, the sensitivity was 100%, and the specificity was 60.9%.@*CONCLUSION@#Preoperative back-forward Bending CT localization image can be used to predict the occurrence of PJK after posterior osteotomy and long-segment fusion fixation in adult spinal deformity. If the patient's T 8-L 2 vertebral hC 7-VSO is too large, it indicates a higher risk of postoperative PJK. The best predictive index is hC 7-L 2, and the cut-off value is 2.54 cm.

Establishment and evaluation of rabbit model of closed tibial fracture / 中国骨伤

OBJECTIVE@#To explore the effect of a modified three-point bending fracture device for establishing a rabbit model of closed tibial fracture.@*METHODS@#The model of closed tibial fracture was established in 40 6-month-old male New Zealand white rabbits with a body weight of 2.5 to 3.0 kg, and the model was verified at 6 weeks after operation. Five rabbits underwent pre modeling without temporary external fixation before modeling, and then were fractured with a modified three-point bending fracture device;35 rabbits underwent formal modeling. Before modeling, needles were inserted, and splints were fixed externally, and then the fracture was performed with a modified three-point bending fracture device. The fracture model and healing process were evaluated by imaging and histopathology at 2 hours, 4 weeks, and 6 weeks after operation.@*RESULTS@#Two hours after modeling, the prefabricated module showed oblique fracture in varying degrees and the broken end shifted significantly;Except for 1 comminuted fracture, 2 curved butterfly fractures and 2 without obvious fracture line, the rest were simple transverse and oblique fractures without obvious displacement in formal modeling group. According to the judgment criteria, the success rate of the model was 85.71%. Four weeks after modeling, the fixed needle and splint of the experimental rabbits were in good position, the fracture alignment was good, the fracture line was blurred, many continuous callus growths could be seen around the fracture end, and the callus density was high. Six weeks after modeling, many thick new bone trabeculae at the fracture, marginal osteoblasts attached, and a small number of macrophages were seen under the microscope. The intramembrane osteogenesis area was in the preparation bone stage, the medullary cavity at the fracture had been partially reopened, the callus was in the absorption plastic stage, and many osteoclasts were visible. The X-ray showed that the fracture line almost disappeared, part of the medullary cavity had been opened, the external callus was reduced around, the callus was in the plastic stage, and the bone cortex was continuous. It suggests that the fracture model showed secondary healing.@*CONCLUSION@#The improved three-point bending fracture device can establish a stable rabbit model of closed tibial fracture, and the operation is simple, which meets the requirements of closed fracture model in basic research related to fracture healing.

Application of ANSYS Fatigue Analysis in Type Selection and Evaluation of Bone Plate / 医用生物力学

Objective By comparing the fatigue strength of type A and type B locking compression plates (LCP) in distal femoral plate, a theoretical evaluation method was provided for type selection of bone plate when testing its bending strength and fatigue performance. Methods Through bending strength performance test and fatigue performance test on bone plates with different types, combined with ANSYS Workbench, the finite element analysis on total deformation, von Mises stress and fatigue service life of bone plates were conducted. Results The fatigue strength of type A plate was 30.7% higher than that of type B plate, the stress of type A plate was lower than that of type B plate, and the minimum fatigue service life of type A plate was 17% higher than that of type B plate. Conclusions The fatigue performance of type A plate is better than that of type B plate, so the failure possibility of type A plate was lower than that of type B plate.The results provide references for assisting selection of different bone plates when testing the performance of two newly developed bone plates.

An operative position of foot stepping and knee bending in toe replantation for avulsed and fractured great toe / 中华显微外科杂志

Objective:To summarise the advantages and disadvantages of applying the method of retrograde replantation with an operative position of foot stepping and knee bending for replantation of rotational avulsed and fractured great toes.Methods:From January 2016 to June 2021, 11 rotational avulsed and fractured great toes were replanted with the method of retrograde replantation in an operative position of foot stepping and knee bending. Of the 11 patients, 10 were males and 1 was female, aged 18 to 50 years old with an average of 32 years old. Causes of injury: 5 of driving belt, 4 of machinery crush and 2 of car accident. Injury sites: 4 on left great toes and 7 on right great toes. All of the injuries were with fracture and exposure of proximal tendons of flexor and extensor. Seven patients had the follow-up reviews by outpatient clinic visiting, 2 over mobile phone and 2 via WeChat.Results:After surgery, 9 great toes completely survived and 2 great toes had necrosis. The survival rate of toe replantation was 81.8%(9/11). The operation time was 2 to 3 hours, with an average of 2.5 hours. Postoperative X-ray film showed that 8 to 12 weeks after the operation, the fracture and joint fusion were healed at first stage in the survived toes. All patients were entered in follow-up for 3 to 18 months with 10.5 months in average. The survived great toes were plump and the toenail grown well. At the final follow-up, the static TPD at the toes was 8-12 mm, with an average of 10 mm. There was no effect shown on either walking or running.Conclusion:The retrograde replantation method with an operative position of foot stepping and knee bending for great toe replantation has the characteristics of a good field of view and convenient in operation under microscope, a short operation time, and a high survival rate of replantation.

Preparation and antibacterial properties of Cu-ZnO-loaded dental veneering porcelain / 口腔疾病防治

Objective@#To investigate the antibacterial properties, biocompatibility and mechanical properties of Cu-ZnO-loaded dental veneering porcelain to provide an experimental basis for the development of new dental veneering porcelain. @*Methods@#Cu-ZnO nanoparticles were added to IPS E.max Ceram for restorative veneer porcelain at different mass percentages of 0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, and 6 wt% using ball milling in ceramic powder. A cylindrical specimen with a diameter of 20 mm and a thickness of 2 mm was prepared by high-temperature sintering. Scanning electron microscopy was used to observe the surface morphologies of nano-Cu-ZnO and the specimens. The antibacterial effect of Escherichia coli (E. coli) was quantitatively studied by the plate colony counting method. The CCK-8 method was used to evaluate in vitro the cytotoxicity of the tested piece to mouse fibroblasts (L929). Live and dead cells were observed by fluorescence microscopy. The mechanical properties of modified IPS E. Max Ceram veneering porcelain were tested by a three-point bending strength test. @* Results @# Under the scanning electron microscope, Cu-ZnO appears with a block-like structure and can be seen dispersed in the veneering porcelain. When the nano Cu-ZnO loading was 1 wt%, 2 wt%, 3 wt%, and 4 wt%, the antibacterial rates of the specimens were 24.85%, 67.94%, 96.92%, and 99.99%, respectively, and the difference between the experimental groups and the control group was statistically significant (F = 23.308,P = 0.001). The relative growth rate of each group was greater than 80% after coculture with mouse fibroblast cells (L929) for 1 day and 3 days, and there was no significant difference between the groups. The morphology of L929 cells was normal after coculture for 24 hours. With the increase in the Cu-ZnO concentration, the flexural strength of the specimen exhibited an increasing trend followed by a decreasing trend. The bending strength of the specimen loaded with 3 wt% nano Cu-ZnO reached the maximum value (84.728 ± 6.82) MPa, and there was no statistically significant difference between groups (F = 0.633,P = 0.702).@*Conclusion@#The antibacterial rate of IPS E. max Ceram veneering porcelain loaded with 3 wt% nano Cu-ZnO was more than 96% against E. coli after high-temperature sintering at 750 ℃. The bending strength reached the maximum (84.728 ± 6.82) MPa, and there was no obvious cytotoxicity.

Single Cell Traction Force Measured by Foldable Microplates / 医用生物力学

Objective To fabricate a foldable microplate for single cell culture and establish finite element model of the folding microplate, so as to calculate traction force of single cells during contraction in three-dimensional (3D) state.Methods The folding angle of the microplate casued by cell traction force was calculated. Then the relation between bending moment and folding angle as well as the relation between traction force and bending moment were derived by using finite element simulation, so as to realize the characterization of traction force for singel cell in 3D state.Results The folding angles of the microplate with HSF and MC3T3-E1 cells in 3D state were 73°-173° and 49°-138°, respectively. The single cell traction forces of HSF and MC3T3-E1 cells were 55-210 nN and 52-161 nN, respectively.Conclusions The proposed method for measuring traction force of single cells in 3D state by fabricating the foldable microplate for single cell culture will provide some references for further development of calculating traction forces in 3D cell adhesion, spreading and migration.

Effects of Athlete’s Posture on Aerodynamic Characteristics During Flight in Ski Jumping / 医用生物力学

Objective To investigate the effects of athlete’s posture (including bending angle of upper body and angle between body and skis) on aerodynamic characteristics during flight in ski jumping. Methods The athlete and skis were regarded as a multi-body system. By using partially averaged Navier-Stokes (PANS) turbulence model and numerical simulation of computational fluid dynamics (CFD), the aerodynamic characteristics during flight under different postures were predicted. The calculation conditions for bending angle of upper body were 10°, 14°, 18°, 22° and 26°, and the calculation conditions of angle between body and skis were 8°, 12°, 16°, 20° and 24°. Results As the bending angle of upper body increased, the lift force and drag force of the multi-body system, the athlete and skis, and the pitch moment of skis all showed a monotonously decreasing trend, but the ratio of total lift force to total drag force increased first and then decreased. Meanwhile, the pitch moment of the multi-body system decreased first and then increased, and the pitch moment of athlete increased slightly and then decreased. As the angle between body and skis increased, the lift force and drag force of the multi-body system and skis increased first, then decreased and then increased, but the ratio of total lift force to total drag force decreased first, then increased and then decreased. Meanwhile, the lift force, drag force and pitch moment of the athlete increased monotonously, and the pitch moment of the multi-body system and the skis increased first and then decreased. The effect of bending angle of upper body on aerodynamic characteristics during flight in ski jumping was generally significantly larger than that of angle between body and skis. Conclusions The optimal range for bending angle of upper body is 14°-18°, and the optimal range of angle between body and skis is 16°-20°. The influence mechanism for bending angle of upper body and angle between body and skis on aerodynamic characteristics during flight in ski jumping can provide effective auxiliary support for on-the-spot prediction and decisionmaking,

Effects of Locking Screws with Different Head Angles on Mechanical Properties of Screw-Plate System / 医用生物力学

Objective To investigate the effects from head angle and locking times of locking screws on mechanical properties of the screw-plate system, so as to provide a theoretical basis for doctors to select appropriate locking screws and master the locking times in clinical surgical procedure. Methods Locking screws with different head angles were selected to match with locking compression plates in the case of different locking times, and cantilever bending method was used to compare the differences of mechanical properties in each group. Results There were significant differences in failure load and bending stiffness between locking compression plate and locking screw with different head angles (P0-05). The failure modes of locking screw with different head angles and different locking times were different, and the failure mode of locking screw had a positive correlation with its head angle and locking times. Conclusions The differences in mechanical properties between locking screw with different head angles and locking compression plate cannot be neglected. It is suggested that doctors should choose locking screw and locking compression plate with the best locking degree in clinical procedure, and choose the right torque wrench to lock in multiple times if necessary, thus to prevent screw loosening from affecting recovery of the patients.

Simulation accuracy of cortical bone fracture based on different types of strain criterion / 中国组织工程研究

BACKGROUND: Cortical bone crack caused by accident or other external factors is one of the main causes of fracture, so the mechanism of crack formation and propagation for cortical bone under different loads should be understood primarily to avoid fracture. Bone specimens may be destructed in experiments, which can lead to a difficulty to observe the interior mechanical state of bone structure before and after fracture. Therefore, it is important to find a finite element method that can accurately simulate the processes of cortical bone crack formation, propagation, and fracture. Current simulations mainly use the principal strain or the equivalent strain to determine the mechanical state of the element in the finite element model and to perform fracture simulation, but there are few studies on the simulation accuracy when using these two types of strains. OBJECTIVE: To testify the simulation accuracy of cortical bone fracture with the principal strain and the equivalent strain. METHODS: The principal strain and the equivalent strain were applied to perform the three-point bending simulation, and the simulation results were compared with the experimental results to determine which strain was more accurate. RESULTS AND CONCLUSION: (1) The failure time of the cortical bone simulated by the principal strain was significantly later than that obtained by the equivalent strain. (2) Compared with the experimental results, it was found that the simulation results obtained by equivalent strain were closer to the experimental results. (3) Therefore, simulating cortical bone crack and fracture using the equivalent strain is accurate.

Preparation and mechanical properties of zirconia-based nano-hydroxyapatite functionally graded material / 中国组织工程研究

BACKGROUND: Studies have shown that the nano-hydroxyapatite coating on the surface of zirconia has not only high strength and toughness, but also good biocompatibility. It is an ideal substitute for hard tissue. However, the coating is easy to fall off from the surface of zirconia, which is a fatal defect. OBJECTIVE: To prepare functionally graded bioceramics with pure zirconia as matrix, gradient layer in the middle and nano-hydroxyapatite on the surface by gradient composite technology and to screen the optimal mechanical properties and sintering temperature. METHODS: Using zirconia and nano hydroxyapatite powder as raw materials, ceramic specimens were prepared by the lamination method in powder metallurgy. According to the thickness of zirconia layer, three groups A (40 mm), B (30 mm) and C (20 mm) were designated. Each group was sub-divided into three subgroups 1 (3 layers), 2 (5 layers) and 3 (7 layers). Thus, there were 162 ceramic specimens in nine subgroups. The ceramic specimens were sintered at different temperatures (1 300,1 350,1 400,1 450,1500, and 1 550°C) and then processed into rectangular specimens for mechanical property testing. RESULTS AND CONCLUSION: The zirconia-based nano-hydroxyapatite functionally graded material can be formed by 10 MPa single side vertical pressure. With the increases in the number of gradient layers and sintering temperature, the mechanical properties of the functionally graded bioceremics in each group were enhanced. The functionally graded bioceramics had the optimal mechanical properties when sintering temperature was 1 550°C, the number of gradient layers was 7, and substrate thickness was 40 mm. The optimal mechanical property of the functionally graded bioceramics produced at above parameter was significantly superior to that produced at other eight sets of parameters (P<0.05). According to the optimal gradient design, the zirconia-based nano-hydroxyapatite functionally graded ceramic specimens prepared by high temperature sintering technique have stronger mechanical properties.

Mechanical properties of rat tibia under high-G environment / 中国组织工程研究

BACKGROUND: With the development of Chinese space industry, pilots are exposed to high-G mechanical environment, which will seriously affect their bones. However, as one of the bones that are most prone to fracture, the biomechanical behavior of the tibia under extreme mechanical environment is rarely reported. OBJECTIVE: To explore the effects of different high-G mechanical environments on the rat growth and development and the mechanical properties of the tibia. METHODS: Male Wistar rats were provided by Laboratory Animal Center of Academy of Military Sciences. The cantilever was set to run at different speeds and accelerations with a high-G centrifugal loading device, and the high-G rat model was made. The rats were weighed weekly. The left tibia of rats was used for undergoing a three-point bending experiment, and the deflection and elastic modulus of the tibia were calculated. The right tibia was subjected to a creep test, and constant stress was applied on the surface of tibial cortical bone and kept 3 600 seconds, so as to observe the changes of creep strain. The study was approved by the Laboratory Animal Ethical Committee of Tianjin University of Technology. RESULTS AND CONCLUSION: The high-G environment affected the normal growth and development of rats, inhibited weight gain and reduced the mechanical properties of the tibia, and reduced the limit deflection of the tibia by 8.1%, 12.2%, 37.8%, and 51.4%, respectively. Limit loads were decreased by 16%, 9%, 25.2%, and 29% respectively. To conclude, extremely high-G environment exerts serious negative effects on rats.

Mechanical Deformation of Superelastic NiTi Wire at Different Deflections in an Orthodontic Bracket System

@#Introduction: Most patients with malocclusion are given orthodontic leveling therapy with the aim of reducing the vertical discrepancy between teeth. This computational study aims to evaluate the degree of deformation of superelastic NiTi arch wire upon bending at different deflections in a bracket system. Methods: A three-dimensional finite-element model of a wire-bracket system was developed to simulate the bending behavior of superelastic NiTi arch wire in three-brackets configuration. A superelastic subroutine was integrated in the model to anticipate the superelastic behavior of the arch wire. The mid span of the arch wire was loaded to different extent of deflections, ranging from 1.0 to 4.0 mm. The mechanical deformation of the arch wires was accessed from three parameters, in specific the unloading force, the bending stress and the martensite fraction. Results: The superelastic wire deflected at 4.0 mm yielded smaller unloading force than the wire bent at 1.0 mm. The bending stress was highly localized at the wire curvature, with the stress magnitude increased from 465 MPa at 1.0 mm to 951 MPa at 4.0 mm deflection. The martensite volume consistently increased throughout the bending, with a fully transformed martensite was observed as early as 2.0 mm of deflection. The magnitude of bending stress and the volume of fully transformed martensite increased gradually in relation to the wire deflection. Conclusion: The wire-bracket system induced localize wire deformation, hindering complete utilization of superelasticity during orthodontic treatment.

Comparison of Segmental Mobility in Lumbar Extension Radiographs between a New Technique (“Fulcrum Bending Position”) and Conventional Standing Position in Spondylolisthesis Patients

STUDY DESIGN: Cross-sectional study.PURPOSE: This was carried out to evaluate the benefit of a ‘fulcrum bending position’ compared with the standing position for evaluation of sagittal translation and sagittal rotation in symptomatic patients with spondylolisthesis.OVERVIEW OF LITERATURE: In lumbar X-ray, the standing position is the most common position used in determining abnormalities in lumbar movement. Lack of standardized method is one of the pitfalls in this technique. We hypothesized that the new technique, that is, fulcrum bending position, may reveal a higher translation and rotation in spondylolisthesis patients.METHODS: The extension lumbar radiographs of 36 patients with low-grade spondylolisthesis were included in the analysis and measurement. Sagittal translation and sagittal rotation were measured in both the routine standing position and in our new technique, the fulcrum bending position, which involves taking lateral cross-table images in the supine position wherein the patient lies on a cylindrical pipe to achieve maximum passive back extension by the fulcrum principle.RESULTS: Results of the measurement of sagittal translation in both positions revealed that compared with the extension standing position, the fulcrum bending position achieved a statistically significant increase of 1.57 mm in translation of the vertebra position (95% confidence interval [CI], 0.52–2.61; p=0.004). The measurement of sagittal rotation in both positions revealed that when compared with the extension standing position, the fulcrum bending position achieved a statistically significant increase of 3.47° in the rotation of the vertebra (95% CI, 1.64–5.30; p<0.001).CONCLUSIONS: For evaluation of both sagittal translation and sagittal rotation in symptomatic patients with spondylolisthesis, compared with the extension standing position, the fulcrum bending position can achieve an increased change in magnitude. Our technique, that is, the fulcrum bending position, may offer an alternative method in the detection or exclusion of pathological mobility in patients with spondylolisthesis.

Effect of two kinds of surface pretreatments on bending strength to the modified polyetheretherketone / 华西口腔医学杂志

OBJECTIVE@#To evaluate the effect of sandblasting or acid etching on the three-point bending strength to the modified polyetheretherketone (PEEK).@*METHODS@#Forty-eight bars (15 mm×2 mm×1 mm) of specimens were fabricated from the modified PEEK (BioHPP). They were randomly divided into the following groups: A, B, C and D groups, which were blasted with alumina particles; E, F, and G groups, which were etched with 98% concentrated sulfuric acid; and control group H. The sand blast pressure of groups A, B and C was 0.2 MPa, and the grain sizes of the sand blasted were 120, 50, and 250 µm, respectively. Group D was blasted with 120 µm particle size at 0.7 MPa pressure. Groups E, F and G were acid etched for 60, 120, and 300 s, respectively. No surface treatment was conducted in group H. After all the specimens were processed, one sample was randomly selected from each group to observe its surface morphology under a scanning electron microscope (SEM), and the other specimens were tested for their three-point bending strength. SPSS 22.0 software was used to analyze the experimental data and to test whether the difference was statistically significant.@*RESULTS@#SEM observation showed that the surface morphology of the specimen changed after the treatment and revealed different degrees of cracks, pits, or voids. The three-point bending test indicated that the strength of the specimens treated with sandblasting or concentrated sulfuric acid decreased compared with that of the control group (P0.05). The strength of group D was lower than that of group A at the same particle size (P0.05).@*CONCLUSIONS@#The bending strength of BioHPP could be significantly decreased by surface sand blasting or concentrated sulfate etching as the sandblasting pressure increased, but the bending strength did not decrease as sand particle size and acid etching time changed.

Influence of nano alumina coating on the flexural bond strength between zirconia and resin cement

PURPOSE: The purpose of this in vitro study is to examine the effects of a nano-structured alumina coating on the adhesion between resin cements and zirconia ceramics using a four-point bending test. MATERIALS AND METHODS: 100 pairs of zirconium bar specimens were prepared with dimensions of 25 mm × 2 mm × 5 mm and cementation surfaces of 5 mm × 2 mm. The samples were divided into 5 groups of 20 pairs each. The groups are as follows: Group I (C) – Control with no surface modification, Group II (APA) – airborne-particle-abrasion with 110 µm high-purity aluminum oxide (Al2O3) particles, Group III (ROC) – airborne-particle-abrasion with 110 µm silica modified aluminum oxide (Al₂O₃ + SiO2) particles, Group IV (TCS) – tribochemical silica coated with Al2O3 particles, and Group V (AlC) – nano alumina coating. The surface modifications were assessed on two samples selected from each group by atomic force microscopy and scanning electron microscopy. The samples were cemented with two different self-adhesive resin cements. The bending bond strength was evaluated by mechanical testing. RESULTS: According to the ANOVA results, surface treatments, different cement types, and their interactions were statistically significant (P < .05). The highest flexural bond strengths were obtained in nanostructured alumina coated zirconia surfaces (50.4 MPa) and the lowest values were obtained in the control group (12.00 MPa), both of which were cemented using a self-adhesive resin cement. CONCLUSION: The surface modifications tested in the current study affected the surface roughness and flexural bond strength of zirconia. The nano alumina coating method significantly increased the flexural bond strength of zirconia ceramics.

Metal-ceramic bond strength between a feldspathic porcelain and a Co-Cr alloy fabricated with Direct Metal Laser Sintering technique

PURPOSE: The aim of the present study was to record the metal-ceramic bond strength of a feldspathic dental porcelain and a Co-Cr alloy, using the Direct Metal Laser Sintering technique (DMLS) for the fabrication of metal substrates. MATERIALS AND METHODS: Ten metal substrates were fabricated with powder of a dental Co-Cr alloy using DMLS technique (test group) in dimensions according to ISO 9693. Another ten substrates were fabricated with a casing dental Co-Cr alloy using classic casting technique (control group) for comparison. Another three substrates were fabricated using each technique to record the Modulus of Elasticity (E) of the used alloys. All substrates were examined to record external and internal porosity. Feldspathic porcelain was applied on the substrates. Specimens were tested using the three-point bending test. The failure mode was determined using optical and scanning electron microscopy. The statistical analysis was performed using t-test. RESULTS: Substrates prepared using DMLS technique did not show internal porosity as compared to those produced using the casting technique. The E of control and test group was 222 ± 5.13 GPa and 227 ± 3 GPa, respectively. The bond strength was 51.87 ± 7.50 MPa for test group and 54.60 ± 6.20 MPa for control group. No statistically significant differences between the two groups were recorded. The mode of failure was mainly cohesive for all specimens. CONCLUSION: Specimens produced by the DMLS technique cover the lowest acceptable metal-ceramic bond strength of 25 MPa specified in ISO 9693 and present satisfactory bond strength for clinical use.