Accuracy of Orthodontic 3D Printed Retainers versus Thermoformed Retainers

Background: The integration of the current technology of CBCT and 3D CAD/CAM technology has great potential in the field of orthodontics, which is not yet fully investigated. The purpose of this article is to evaluate the accuracy of 3D printed retainers in comparison to vacuum formed retainers. Methods: Alginate impressions were taken for ten patients who have a CBCT scan. A 3D printed retainer and vacuum formed retainer were fabricated. Linear measure-ments were measured by two assessors using digital caliper. Every measure-ment on the 3D printed retainer was compared to the corresponding measure-ment on the thermoformed retainer. The linear measurements were Inter-canine width, Inter-premolar width (first and second premolars), Inter-molar width, Canine-midline length (both sides) and Canine-molar length (both sides). Intra-observer, and inter-observer reliability measurements were done. Results: Results showed excellent intra-observer reliability for the thermoformed retainer and the 3D printed retainer. Inter-observer measurements showed strong agreement between the measurements of the two assessors, for both retainers. The comparison of the thermoformed retainer to the 3D printed retainer showed high statistical agreement, except for the canine-molar on the right side, but with no clinical significance, p value of 0.038 and mean difference 0.19. Conclusions: The new method for fabricating a 3D printed retainer is accurate and reliable in comparison to the vacuum formed retainer (conventional method). CBCT proved to be efficient for fabrication of a custom made appliances.

Lateral earth pressure of granular backfills on retaining walls with expanded polystyrene geofoam inclusions under limited surcharge loading

Existing studies have focused on the behavior of the retaining wall equipped with expanded polystyrene(EPS)geofoam inclusions under semi-infinite surcharge loading rather than limited surcharge loading.In this paper,the failure mode and the earth pressure acting on the rigid retaining wall with EPS geofoam inclusions and granular backfills(henceforth referred to as EPS-wall),under limited surcharge loading are investigated through two-and three-dimensional model tests.The testing results show that different from the sliding of almost all the backfill in the EPS-wall under semi-infinite surcharge loading,only an approximately triangular backfill slides in the wall under limited surcharge loading.The distribution of the lateral earth pressure on the EPS-wall under limited surcharge loading is non-linear,and the distribution changes from the increase of the wall depth to the decrease with the increase of the limited surcharge loading.An approach based on the force equilibrium of a differential element is developed to predict the lateral earth pressure behind the EPS-wall subjected to limited surcharge loading,and its performance was fully validated by the three-dimensional model tests.

Review on the plastic instability of medium -Mn steels for identifying the formation mechanisms of Lüders and Portevin -Le Chatelier bands

Plastic instability,including both the discontinuous yielding and stress serrations,has been frequently observed during the tensile deformation of medium-Mn steels(MMnS)and has been intensively studied in recent years.Unfortunately,research results are controversial,and no consensus has been achieved regarding the topic.Here,we first summarize all the possible factors that affect the yielding and flow stress serrations in MMnS,including the morphology and stability of austenite,the feature of the phase interface,and the deformation parameters.Then,we propose a universal mechanism to explain the conflicting experimental results.We conclude that the discontinuous yielding can be attributed to the lack of mobile dislocation before deformation and the rapid dislocation multiplication at the beginning of plastic deformation.Meanwhile,the results show that the stress serrations are formed due to the pinning and depinning between dislocations and interstitial atoms in austenite.Strain-induced martensitic transformation,influenced by the mechanical stability of austenite grain and deformation parameters,should not be the intrinsic cause of plastic instability.However,it can intensify or weaken the discontinuous yielding and the stress serrations by affecting the mobility and density of dislocations,as well as the interaction between the interstitial atoms and dislocations in austenite grains.

Limit state analysis of rigid retaining structures against seismically induced passive failure in heterogeneous soils

Soils are not necessarily uniform and may present linearly varied or layered characteristics,for example the backfilled soils behind rigid retaining walls.In the presence of large lateral thrust imposed by arch bridge,passive soil failure is possible.A reliable prediction of passive earth pressure for the design of such wall is challenging in complicated soil strata,when adopting the conventional limit analysis method.In order to overcome the challenge for generating a kinematically admissible velocity field and a statically allowable stress field,finite element method is incorporated into limit analysis,forming finiteelement upper-bound(FEUB)and finite-element lower-bound(FELB)methods.Pseudo-static,original and modified pseudo-dynamic approaches are adopted to represent seismic acceleration inputs.After generating feasible velocity and stress fields within discretized elements based on specific criteria,FEUB and FELB formulations of seismic passive earth pressure(coefficient K_(P))can be derived from work rate balance equation and stress equilibrium.Resorting to an interior point algorithm,optimal upper and lower bound solutions are obtained.The proposed FEUB and FELB procedures are well validated by limit equilibrium as well as lower-bound and kinematic analyses.Parametric studies are carried out to investigate the effects of influential factors on seismic K_(P).Notably,true solution of K_(P) is well estimated based on less than 5%difference between FEUB and FELB solutions under such complex scenarios.

Protective effect of retaining wall on rock avalanche:A case study of Nayong rock avalanche in China

Rock avalanches are generally difficult to prevent and control due to their high velocities and the extensive destruction they cause.However,barrier structures constructed along the path of a rock avalanche can partially mitigate the magnitudes and consequences of such catastrophic events.We selected a rock avalanche in Nayong County,Guizhou Province,China as a case to study the effect of the location and height of a retaining wall on the dynamic characteristics of rock avalanche by using both actual terrain-based laboratory-model tests and coupled PFC3D-FLAC3D numerical simulations.Our findings demonstrate that a retaining wall can largely block a rock avalanche and its protective efficacy is significantly influenced by the integrity of the retaining wall.Coupled numerical simulation can serve as a powerful tool for analyzing the interaction between a rock avalanche and a retaining wall,facilitating precise observations of its deformation and destruction.The impact-curve characteristics of the retaining wall depend upon whether or not the rock avalanche-induced destruction is taken into account.The location of the retaining wall exerts a greater influence on the outcome compared to the height and materials of the retaining wall,while implementing a stepped retaining-wall pattern in accordance with the terrain demonstrates optimal efficacy in controlling rock avalanche.

The Influence of Chemical Admixtures on the Fluidity,Viscosity and Rheological Properties of Ultra-High Performance Concrete

To achieve higher strength and better durability,ultra-high performance concrete(UHPC)typically employs a relatively small water-binder ratio.However,this generally leads to an undesired increase in the paste viscosity.In this study,the effects of liquid and powder polycarboxylate superplasticizers(PCE)on UHPC are compared and critically discussed.Moreover,the following influential factors are considered:air-entraining agents(AE),slump retaining agents(SA),and defoaming agents(DF)and the resulting flow characteristics,mechanical properties,and hydration properties are evaluated assuming UHPC containing 8‰powder PCE(PCE-based UHPC).It is found that the spread diameter of powder PCE is 5%higher than that of liquid PCE.Among the chemical admixtures studied,AEs have the best effect on improving UHPC workability,while DFs have the worst effect.When the addition of AE and SA is 1.25‰and 14.7%of PCE,paste viscosity reduces by 35%and 19%,respectively compared to the paste with only 8‰PCE.A low AE dosage(1.25‰)decreases compressive strength by 4.1%,while SA(8.1%)increases UHPC compressive strength by 9.1%.Both AE and SA significantly delay the UHPC hydration process,reducing the hydration heat release peaks by 76%and 27%,respectively.

Mid-term outcomes of a kinematically designed cruciate retaining total knee arthroplasty

BACKGROUND Advances in implant material and design have allowed for improvements in total knee arthroplasty(TKA)outcomes.A cruciate retaining(CR)TKA provides the least constraint of TKA designs by preserving the native posterior cruciate ligament.Limited research exists that has examined clinical outcomes or patient reported outcome measures(PROMs)of a large cohort of patients undergoing a CR TKA utilizing a kinematically designed implant.It was hypothesized that the studied CR Knee System would demonstrate favorable outcomes and a clinically significant improvement in pain and functional scores.AIM To assess both short-term and mid-term clinical outcomes and PROMs of a novel CR TKA design.METHODS A retrospective,multi-surgeon study identified 255 knees undergoing a TKA utilizing a kinematically designed CR Knee System(JOURNEY™II CR;Smith and Nephew,Inc.,Memphis,TN)at an urban,academic medical institution between March 2015 and July 2021 with a minimum of two-years of clinical follow-up with an orthopedic surgeon.Patient demographics,surgical information,clinical outcomes,and PROMs data were collected via query of electronic medical records.The PROMs collected in the present study included the Knee Injury and Osteoarthritis Outcome Score for Joint Replacement(KOOS JR)and Patient-Reported Outcomes Measurement Information System(PROMIS■)scores.The significance of improvements in mean PROM scores from preoperative scores to scores collected at six months and two-years postoperatively was analyzed using Independent Samples t-tests.RESULTS Of the 255 patients,65.5%were female,43.8%were White,and patients had an average age of 60.6 years.Primary osteoarthritis(96.9%)was the most common primary diagnosis.The mean surgical time was 105.3 minutes and mean length of stay was 2.1 d with most patients discharged home(92.5%).There were 18 emergency department(ED)visits within 90 d of surgery resulting in a 90 d ED visit rate of 7.1%,including a 2.4%orthopedic-related ED visit rate and a 4.7%non-orthopedic-related ED visit rate.There were three(1.2%)hospital readmissions within 90 d postoperatively.With a mean time to latest follow-up of 3.3 years,four patients(1.6%)required revision,two for arthrofibrosis,one for aseptic femoral loosening,and one for peri-prosthetic joint infection.There were significant improvements in KOOS JR,PROMIS Pain Intensity,PROMIS Pain Interference,PROMIS Mobility,and PROMIS Physical Health from preoperative scores to six month and two-year postoperative scores.CONCLUSION The evaluated implant is an effective,novel design offering excellent outcomes and low complication rates.At a mean follow up of 3.3 years,four patients required revisions,three aseptic and one septic,resulting in an overall implant survival rate of 98.4%and an aseptic survival rate of 98.8%.The results of our study demonstrate the utility of this kinematically designed implant in the setting of primary TKA.

Development and microstructure characterization of BG110E high-strength expansion pipe

The BG110E high-strength expansion pipe was developed using medium manganese steel and subjected to a two-phase zone heat treatment process.Mechanical properties and microstructure analysis results have proven that the BG110E expansion pipe exhibits uniform elongation of more than 19%.Moreover,after undergoing expan-sion deformation,its strength,toughness,and plasticity are found to meet the stringent requirements of the P110 pipe.The microstructure of this high-strength expansion pipe,which has a strength of 110 ksi(1 ksi=6.895 MPa),consists of tempered martensite,ferrite,retained austenite,and granular bainite.The propotion of retained austenite reaches up to 12%,ensuring high plasticity and the occurrence of the transformation-induced plasticity effect during the deformation process.Consequently,it enhances the coordinated deformation ability between different phases,which significantly improves the internal yield pressure of the BG110E high-strength expansion pipe in turn.

Time-History Dynamic Characteristics of Reinforced Soil-Retaining Walls

Given the complexities of reinforced soil materials’constitutive relationships,this paper compares reinforced soil composite materials to a sliding structure between steel bars and soil and proposes a reinforced soil constitutive model that takes this sliding into account.A finite element dynamic time history calculation software for composite response analysis was created using the Fortran programming language,and time history analysis was performed on reinforced soil retaining walls and gravity retaining walls.The vibration time histories of reinforced soil retaining walls and gravity retaining walls were computed,and the dynamic reactions of the two types of retaining walls to vibration were compared and studied.The dynamic performance of reinforced earth retaining walls was evaluated.

Management of a Retained Epidural Catheter in a Pregnant Patient: A Case Report and Review of Literature

Background: Epidural anesthesia is an effective intervention to treat labor pain and provide analgesia for orthopedic procedures. A rare complication of this technique is epidural catheter retention. Case Presentation: In this case report, we present an otherwise healthy 21-year-old G2P0010 woman at 39 weeks and 3 days gestation whose anesthetic management was complicated by a symptomatic retained epidural catheter fragment. Computed tomography (CT) imaging of her spine showed the fractured catheter within her paraspinal muscles and neurosurgery recommended no surgical intervention at that time. The patient reported resolution of back pain while in the postpartum unit which she continues to endorse two weeks after discharge. Conclusion: Retained epidural catheter is a medical emergency that requires immediate imaging and neurological evaluation. While magnetic resonance imaging is typically regarded as the standard imaging modality for this complication, in epidural sets that contain metallic components, we suggest using CT to avoid the risk of thermal nerve damage. In cases where the patient does not report any acute complaints, nonsurgical management may be appropriate but close follow-up is required to monitor for catheter migration.

Consideration of the Application and Risk Prevention of VAT Tax Rebate Policy for Construction Enterprises at the End of the Period

The“Announcement on Deepening the Value-Added Tax Reform”clearly outlines the preferential policy regarding incremental retention tax rebates.With the advancement of value-added tax(VAT)reform and the improvement of VAT legislation in China,VAT tax planning for construction enterprises,particularly related to retained tax credits,has become routine.This paper,focusing on the characteristics of construction enterprises,analyzes VAT retained tax credits at the end of the period,the status of tax refunds,practical issues,and related processes,and offers suggestions for policy application and risk prevention.

Microstructure Characterization and Mechanical Properties of FGH 95 Turbine Blade Retainers

FGH 95 is a powder metallurgy （P/M） processed superalloy, which was developed in the 1980s in China. One of the applications of FGH 95 was high pressure turbine blade retainers. The manufacturing processes used to produce FGH 95 blade retainers consisted of atomization by plasma rotating electrode process （PREP）, hot isostatic pressing （HIP） at super-solvus temperature and a sub-solvus solution heat treatment. The material had an equiaxed grain structure （ASTM 6.5-7.5）. The γ precipitates in as-HIP FGH 95 showed a tri-model distribution. Carbides in the alloy were MC type and precipitated at grain boundaries. The prior particle boundaries （PPB） in the material originated mainly from γ＇ phase. Statistics of the mechanical properties data from batch production of the FGH 95 blade retainers were investigated. The as-HIP FGH 95 blade retainers showed high strength at room temperature and 650 ℃, excellent creep resistance and outstanding stress rupture strength at 650 ℃.

基于RETAIN模型的对外汉字教育游戏的设计与开发

基于系统化的教学设计原则,Gunter等提出了RETAIN教育游戏设计模型,该模型能够很好地兼顾教育性与游戏性,受到广泛关注。以RETAIN模型为基础,结合对外汉字教学的相关研究成果,重点针对字形研发汉字教育游戏。首次构建出对外汉语汉字教育游戏的设计框架,并使用Unity3D进行PENZZLE的设计与开发,探讨教育性与游戏性的有机融合途径。调查结果显示,在学习兴趣提升、知识目标达成度、学习效果提升度三个方面,该游戏的开发都取得良好效果。

Effect of heat treatment on microstructure and mechanical properties of Ti-containing low alloy martensitic wear-resistant steel

Effects of quenching temperature and cooling conditions(water cooling and 10%NaCl cooling)on microstructure and mechanical properties of a 0.2%Ti low alloy martensitic wear-resistant steel used for die casting ejector plate were investigated.The results show that lath martensite can be obtained after austenitizing in the range of 860-980℃and then water cooling.With an increase in austenitizing temperature,the precipitate content gradually decreases.The precipitates are mainly composed of TiC and Ti4C2S2,and their total content is between 1.15wt.%and 1.64wt.%.The precipitate phase concentration by water-cooling is higher than that by10%NaCl cooling due to the lower cooling rate of water cooling.As the austeniting temperature increases,the hardness and tensile strength of both water cooled and 10%NaCl cooled steels firstly increase and then decrease.The experimental steel exhibits the best comprehensive mechanical properties after being austenitized at 900℃,cooled by 10%NaCl,and then tempered at 200℃.Its hardness,ultimate tensile strength,and wear rate reach551.4 HBW,1,438.2 MPa,and 0.48×10^(-2)mg·m^(-1),respectively.

Characteristics and exploration targets of Chang 7 shale oil in Triassic Yanchang Formation, Ordos Basin, NW China

The geological characteristics and enrichment laws of the shale oil in the third submember of the seventh member of Triassic Yanchang Formation(Chang 7_(3)) in the Ordos Basin were analyzed by using the information of core observations, experiments and logging, and then the exploration potential and orientation of the Chang 7_(3) shale oil were discussed. The research findings are obtained in three aspects. First, two types of shale oil, i.e. migratory-retained and retained, are recognized in Chang 7_(3). The former is slightly better than the latter in quality. The migratory-retained shale oil reservoir is featured with the frequent interbedding and overlapping of silty-sandy laminae caused by sandy debris flow and low-density turbidity current and semi-deep-deep lacustrine organic-rich shale laminae. The retained shale oil reservoir is composed of black shale with frequent occurrence of bedding and micro-laminae. Second, high-quality source rocks provide a large quantity of hydrocarbon-rich high-quality fluids with high potential energy. The source-reservoir pressure difference provides power for oil accumulation in thin interbeds of organic-poor sandstones with good seepage conditions and in felsic lamina, tuffaceous lamina and bedding fractures in shales. Hydrocarbon generation-induced fractures, bedding fractures and microfractures provide high-speed pathways for oil micro-migration. Frequent sandstone interlayers and felsic laminae provide a good space for large-scale hydrocarbon accumulation, and also effectively improve the hydrocarbon movability. Third, sand-rich areas around the depression are the main targets for exploring migratory-retained shale oil. Mature deep depression areas are the main targets for exploring retained oil with medium to high maturity. Theoretical research and field application of in-situ conversion in low-mature deep depression areas are the main technical orientations for exploring retained shale oil with low to medium maturity.

Dynamic modeling of fluid-conveying pipes restrained by a retaining clip

Although most pipes are restrained by retaining clips in aircraft,the influence of the clip parameters on the vibration of the fluid-conveying pipe has not been revealed.By considering the clip width,a new dynamic model of a fluid-conveying pipe restrained by an intermediate clip is established in this paper.To demonstrate the necessity of the proposed model,a half pipe model is established by modeling the clip as one end.By comparing the two models,it is found that the half pipe model overestimates the critical velocity and may estimate the dynamical behavior of the pipe incorrectly.In addition,with the increase in the clip stiffness,the conversion processes of the first two modes of the pipe are shown.Furthermore,by ignoring the width of the clip,the effect of the flow velocity on the accuracy of a concentrated restraint clip model is presented.When the flow velocity is close to the critical velocity,the accuracy of the concentrated restraint clip model significantly reduces,especially when the width of the clip is large.In general,the contribution of this paper is to establish a dynamic model of the fluid-conveying pipe which can describe the influence of the clip parameters,and to demonstrate the necessity of this model.

Tailoring Carbon Distribution inα/γPhase of Ductile Iron and Its Effects on Thermal Conductivity

The effects of carbon distribution on the microstructure and thermal conductivity of ductile iron were investigated in the present study.The microstructure of as-cast and quenched ductile iron were characterized by OM and SEM.Results showed that the microstructure of as-cast ductile iron was composed of spheroidal graphite,ferrite with the volume of 80%,and a small amount of pearlite,and quenched ductile iron was composed of spheroidal graphite,coarse/fine acicular martensite(α_(M)phase)and high-carbon retained austenite(γphase).The volume fraction of retained austensite and its carbon content for direct quenched ductile iron and tepmered ductile iron were quantitatively analysed by XRD.Results revealed that carbon atoms diffused fromα_(M)phase toγphase during tempering at low temperatures,which resulted in carbon content in retainedγphase increasing from 1.2 wt%for the direct quenched sample to about 1.9 wt%for the tempered samples.Consequently,the lattice distortion was significantly reduced and gave rise to an increase of thermal conductivity for ductile iron.

Effect of surface retaining elements on rock stability:laboratory investigation with sand powder 3D printing

This study aims to investigate the benefcial efects of surface retaining elements (SREs) on the mechanical behaviors of bolted rock and roadway stability. 3D printing (3DP) technology is utilized to create rock analogue prismatic specimens for conducting this investigation. Uniaxial compression tests with acoustic emission (AE) and digital image correlation techniques have been conducted on 3DP specimens bolted with diferent SREs. The results demonstrate that the strength and modulus of elasticity of the bolted specimens show a positive correlation with the area of the SRE;the AE characteristics of the bolted specimens are higher than those of the unbolted specimen, but they decrease with an increase in SRE area, thus further improving the integrity of the bolted specimens. The reinforcement efect of SREs on the surrounding rock of roadways is further analyzed using numerical modelling and feld test. The results provide a better understanding of the role of SREs in rock bolting and the optimization of rock bolting design. Furthermore, they verify the feasibility of 3DP for rock analogues in rock mechanics tests.

Stability Analysis of Landfills Contained by Retaining Walls Using Continuous Stress Method

An analytical method for determining the stresses and deformations of landfills contained by retaining walls is proposed in this paper.In the proposedmethod,the sliding resisting normal and tangential stresses of the retaining wall and the stress field of the sliding body are obtained considering the differential stress equilibrium equations,boundary conditions,and macroscopic forces and moments applied to the system,assuming continuous stresses at the interface between the sliding body and the retaining wall.The solutions to determine stresses and deformations of landfills contained by retaining walls are obtained using the Duncan-Chang and Hooke constitutive models.A case study of a landfill in the Hubei Province in China is used to validate the proposed method.The theoretical stress results for a slope with a retaining wall are compared with FEMresults,and the proposed theoreticalmethod is found appropriate for calculating the stress field of a slope with a retaining wall.

Troubleshooting a Difficult Trans-Tibial/Fibula Amputation: A Case Report

Necrotic feet secondary to vascular compromise in the diabetic patient may require an emergent guillotine amputation. Unrecognized, retained hardware in a distal ankle years after fracture repair may complicate the intraoperative guillotine amputation at the transtibial/fibula level. Troubleshooting such an unexpected surgical problem is not necessarily straightforward depending on the clinical situation. Presented is a case report where a patient with a necrotic burned foot failed to inform the burn team that he had implanted ankle hardware, prior to his surgical intervention. A successful amputation was completed after proceeding down a specific algorithm devised for such a scenario.