Effect Of Abrasion Research Articles

Antifungal activity of boric acid, triclosan and zinc oxide against different clinically relevant Candida species.

The genus Candida includes about 200 different species, but only a few are able to produce disease in humans. The species responsible for the highest proportion of human infections is Candida albicans. However, in the last two decades there has been an increase in the proportion of infections caused by other Candida species, including C.glabrata (Nakaseomyces glabrata), C.parapsilosis, C.tropicalis, C.krusei (Pichia kudriavzevi) and more recently C.auris. Decolonisation of patients has been used as an infection control strategy for bacterial infections, but information about decolonisation products used in clinical practice for Candida and other fungal pathogens is limited. Compounds with antimicrobial activity, such as triclosan (TR), boric acid (BA) and zinc oxide (ZO), are mainly used in personal care products. These products can be used for long periods of time without an abrasive skin effect and are a possible alternative for patient decolonisation in healthcare settings. The aim of this study was to evaluate the antifungal activity of boric acid (BA), triclosan (TR) and zinc oxide (ZO), individually and combined, against clinically relevant Candida species. Compounds to be screened for antifungal activity were evaluated at different concentrations, alone, and combined, using a well diffusion assay. The statistical evaluation was performed using analysis of variance (ANOVA) and a post hoc analysis using the multiple comparisons method. Individually, BA and TR showed antifungal activity against all Candida species evaluated but ZO did not show any antifungal activity. Mixtures of BA [5%]-TR [0.2%]; BA [5%]-TR [0.3%]; BA [5%]-TR [0.2%]-ZO [8.6%]; and BA [5%]-TR [0.2%]-ZO [25%] yielded the highest antifungal activity. An increased antifungal effect was observed in some mixtures when compared with individual compounds. We demonstrated antifungal activity of BA and TR against multiple Candida species, including against a clade of the emerging healthcare-associated pathogen C.auris. Additionally, this study shows enhancement of the antifungal effect and no antagonism among the mixtures of these compounds. Further research is needed to determine whether these compounds can reduce the burden of Candida on skin.

The function of the south-Levantine Late Chalcolithic and Early Bronze Age basalt vessels bearing circumferential depressions: Insights from use-wear analyses.

One of the most characteristic aspects of the Late Chalcolithic and Early Bronze Age periods in the southern Levant is the appearance of large assemblages of basalt vessels. These vessels, frequently meticulously made, appear sometimes a considerable distance from the raw material sources and are found mainly at habitation sites. While these and their prestigious value have been widely discussed in the past, their function is still obscure. In the current paper, we address their functionality through microscopic use-wear analysis. Emphasis was placed on basalt vessels with a distinct wear pattern–circumferential depressions, which appear along the perimeter of their interior bases. The documented traces were compared to results of an experimental study we conducted to characterize the effects of abrasion, grinding, and lubrication on basalt surfaces. The results of the comparative experimental study suggest that the circumferential depression was formed from a repetitive rotational activity using a narrow-ended tool. Further, it seems that two material types acted in combination as the circling device and processed material. One was hard and abrasive, such as stone, and the other was semi-resilient, such as wood or mineral powder. Water was likely used as a lubricant in the rotational process. While the actual function of the bowls bearing the circumferential depressions is not entirely clear, the use-wear analyses suggest that they may have been devices involved in craft industries, used for processing materials unrelated to food (minerals in particular). Whatever the exact function was, it clear that this use continued from the Chalcolithic through the Early Bronze Age, providing evidence for functional continuity between these two periods.

Ash-burn test according to ISO 3340 for the evaluation of the abrasive effect of particleboard on cutting tools

ABSTRACT The mineral content of particleboard (PB) is suspected to be one of the main factors influencing cutting-tool life. The aim of this study was therefore to investigate the influence of the mineral content of PBs on tool life as a function of the mineral content and the size of the largest sand grains. The mineral content of PB according to ISO 3340 was used as a value for the abrasiveness. Different samples of PB were analysed by comparison of the mineral content and the lifetime of a tungsten-carbide knife. In addition, the maximum size of the mineral grains in comparison with the total amount of mineral content was studied. The investigation showed that the mineral content of the PB and maximum sand-grain size are not sufficient to predict tool life. In comparison with the result of a lifetime test, which directly measures the wear behaviour of a board, the treatment of the ashes with hydrochloric acid after combustion, according to ISO 3340, destroys abrasive ingredients in the PB; therefore, this method is not suitable for identifying all abrasive components of a PB.

Surface microscopic properties of various aggregates using laser scanning confocal microscope

The surface morphology of aggregates has a significant effect on the aggregates, which in turn affects the technical performance of asphalt mixtures and cement concrete. In this study, the surface micro-morphology (SMM) of a) four typical natural aggregates, b) recycled concrete aggregate (RCA), and c) recycled brick aggregate (RCB) were investigated using laser scanning confocal microscope, and combined with image analysis technology, roughness theory and fractal theory for quantitative evaluation. Limewater immersion and physical abrasion were performed on each aggregate to investigate the effect of these processes on SMM. Results show that the surface micro-roughness and fractal dimensions of different aggregates varied predictably with the formation conditions of aggregates. After being immersed in limewater, the surface micro-roughness of basalt, limestone and diabase increased, but their fractal dimensions did not change, while the surface micro-roughness of granite, RCA and RCB decreased by 20–30%, and their fractal dimensions increased by 0.65.%, 1.69% and 0.43%, respectively. The effect of physical abrasion on the SMM of aggregates was related to the hardness of the aggregates. After physical abrasion, the surface micro-roughness and fractal dimensions of the six aggregates were reduced.

Effects of toothbrush abrasion on surface and antibacterial properties of hydroxyapatite-tryptophan complex with gray titania.

Photocatalysts have attracted attention in the medical field for their antibacterial effects. However, typical photocatalysts are activated by ultraviolet rays, which may have adverse effects. Therefore, we focused on a new photocatalyst that is activated by visible light, hydroxyapatite (HAp), and amino acid complex with gray titania, and evaluated its antibacterial effects against Porphyromonas gingivalis and effect by toothbrushing. The test sample was a titanium alloy substrate, and four surface treatments were applied: (1) substrate only, (2) substrate with HAp complex, (3) substrate with HAp complex with gray titania, and (4) HAp-tryptophan complex with gray titania (TR). These surface treatments were evaluated with or without toothbrushing (8 total groups). Surface roughness (Sa), fluorescent X-ray analysis (XRF), and scanning electron microscopy (SEM) were used to evaluate surface properties. To investigate antibacterial effects, each sample was seeded with P. gingivalis, irradiated with red light, and total viable bacterial count was determined. For Sa measurement, TR showed no significant difference after toothbrushing. However, in XRF and SEM observation, TR exhibited peeling of the applied coating after toothbrushing. In the antibacterial test, TR showed a decrease in P. gingivalis under no toothbrushing condition. Conversely, with toothbrushing, the TR coating appeared to peel. However, no significant difference in P. gingivalis count was observed among all groups. HAp-tryptophan complex with gray titania coating showed an antibacterial effect against P. gingivalis when irradiated with visible light. However, toothbrushing can result in coat peeling and consequently reduce the antibacterial effect.

Effects of Active Food Media on Properties of Materials Usedin Local Food Processing Machine

Food contains edible biochemical compounds, which serves as sources of nutrients to human being. However, their contamination through processing can bring about adverse effects on humans when consumed. Food blending is one of the major processing done in preparing edible meals. The effect of active food media on the material used in fabricating the grinding shaft of the blending machine cannot be ignored taking into consideration the resultant subsequent effects on blended food. Some of the effects of active food media on metallic parts of food blending machines are protein adhesion, abrasive effect, reduction in mechanical properties and conditions favouring corrosion. Three types of food materials, onion, pepper, and tomato, were chosen to be the focus of this study owing to the prevalence index of their processing amongst the local communities. They were processed using a selected blending machine while the ultimate analyses and determination of elemental compositions were carried out on the processed samples. The mean values of ascorbic acid from four runs of onion, pepper, and tomato samples through a blending machine were found to be 5.94 mg/100ml, 13.13 mg/100ml, and 16.99 mg/100ml, respectively. Some other mineral elements, such as iron, calcium, sodium, potassium and magnesium, were found in varied compositions as the number of blending runs increased. The results obtained showed that these food items contain active ingredients and complex compounds which have gross effect on the mild steel used in fabricating the grinding shaft of the blending machine.

Abrasive polishing load effect on surface roughness and material removal rate of Al2O3, ZTA and SiC

The surface quality determines the performance of ceramic tribological components, e.g., bearings and seals. Surface conditioning processes, like polishing, are generally responsible for the largest portion of the manufacturing costs of these components. Therefore, process parameters, such as polishing load, should be optimized for economic reasons. Sintered alumina (Al2O3), zirconia-toughened alumina (ZTA) and silicon carbide (SiC) samples were polished in a sequential two-step process using a water-based diamond abrasive slurry with particle sizes of 3 μm (P1) and 1 μm (P2) on woven and nap cloths, respectively. The effect of material and polishing load (40, 50 and 60 N) on 2D roughness parameters (Ra, RSm, Rz and Rsk) and material removal rate (MRR) were evaluated by a MANCOVA statistically designed experiment. Polishing steps reduced Ra and Rz in succession, with the greatest absolute reduction occurring at P1. Load and material affected only MRR and RSm, when controlled by the effect of initial roughness parameters of surfaces. The low surface porosity fraction combined with very low Ra of surface topography plateaus, especially after P2, resulted in much higher RSm values for SiC. Atomic force microscopy (AFM) images of polished surfaces revealed that, on a finer scale, material removal mechanisms were ductile. MRR for SiC was the highest and proportional to polishing load, while the load did not affect it for the oxide ceramics. The synergy between the mechanical action of abrasives and tribochemistry between SiC and water explains its higher MRR and better surface finish, while Al2O3 and ZTA relied mainly on the ductile mechanisms to improve their surface quality.

Effect of Mechanical Pretreatments on Damage Mechanisms and Fracture Toughness in CFRP/Epoxy Joints.

Adhesive bonding of carbon-fiber-reinforced polymers (CFRPs) is a key enabling technology for the assembly of lightweight structures. Surface pretreatment is necessary to remove contaminants related to material manufacturing and ensure bond reliability. The present experimental study focuses on the effect of mechanical abrasion on the damage mechanisms and fracture toughness of CFRP/epoxy joints. The analyzed CFRP plates were provided with a thin layer of surface epoxy matrix and featured enhanced sensitivity to surface preparation. Various degrees of morphological modification and fairly controllable carbon fiber exposure were obtained using sanding with emery paper and grit-blasting with glass particles. In the sanding process, different grit sizes of SiC paper were used, while the grit blasting treatment was carried by varying the sample-to-gun distance and the number of passes. Detailed surveys of surface topography and wettability were carried out using various methods, including scanning electron microscopy (SEM), contact profilometry, and wettability measurements. Mechanical tests were performed using double cantilever beam (DCB) adhesive joints. Two surface conditions were selected for the experiments: sanded interfaces mostly made of a polymer matrix and grit-blasted interfaces featuring a significant degree of exposed carbon fibers. Despite the different topographies, the selected surfaces displayed similar wettability. Besides, the adhesive joints with sanded interfaces had a smooth fracture response (steady-state crack growth). In contrast, the exposed fibers at grit-blasted interfaces enabled large-scale bridging and a significant R-curve behavior. While it is often predicated that quality composite joints require surfaces with a high percentage of the polymer matrix, our mechanical tests show that the exposure of carbon fibers can facilitate a remarkable toughening effect. These results open up for additional interesting prospects for future works concerning toughening of composite joints in automotive and aerospace applications.

Comparison of the abrasive effects of children's toothpaste on glass ionomer cement

To evaluate the effect of two different children's toothpaste on the surface properties of conventional glass ionomer cement (GIC), which is used in Atraumatic Restorative Treatment (ART) method. There were 3 groups and 10 glass ionomer cements in each group. The distribution was as follows: Group 1, Splat; Group 2, R.O.C.S.; Group 3, Control. A test aparatus made of steel with a screw design that allows the replacement of electric toothbrushes was designed to provide 2 N force. Brushing was carried out for each samples for duration of 2 min, twice a day, for seven days. One-way ANOVA for intergroup comparison and paired sample T tests for intragroup comparisons were used in statistical analysis, the significance level was p < 0.05. According to the results, no statistically significant difference was found between the baseline and 7th day roughness values within and between groups (p > 0.05). Although not statistically significant, as a percental increase in roughness was found in each group compared to the initial values. This amount of increase was found in Group 2, Group 1 and Group 3 as a descending order. The results were supported by scanning electron microscopy analysis. As a result of this study, child pastes that do not cause a statistically significant increase in roughness were found to be safe for daily use. When considering long-lasting restorations, low relative dentin abrasivity (RDA) value child pastes can be recommended as they will encourage brushing with both taste and smell compared to brushing with water.

Numerical study on the resistance of rigid projectiles penetrating into semi-infinite concrete targets

A study on the resistance of rigid projectiles penetrating into semi-infinite concrete targets is performed in this paper. Experimental data are analyzed to examine the penetration resistance during various stages of the penetration process. A numerical tool using AUTODYN hydrocode is applied in the study. The numerical results on both deceleration-time history and depth of penetration of projectiles are in good agreement with experimental data, which demonstrate the feasibility of the numerical model in these conditions. Based on the numerical model with a two-staged pre-drilled hole, the rigid projectile penetration in tunneling stage is studied for concrete targets with different strengths in a wide range of impact velocities. The results show that the penetration in tunnel stage can be divided into two different cases in terms of initial impact velocity. In the first case, when the impact velocity is approximately less than 600 m/s, the deceleration depends on initial impact velocity. In the second case, when the impact velocity is greater than 600 m/s, the effect of target inertia becomes apparent, which agrees with commonly used concrete penetration resistance equations based on cavity expansion model. A two-staged pre-drilled hole model was developed and the results show that the depth of entrance stage tends to decrease with the increase of impact velocity. The influence of the inertial term at low velocity range (approximately close to 600 m/s) is inconspicuous. With further increase of the penetration velocity, the effect of the target inertia becomes apparent as proposed by Forrestal. The effect of mass abrasion of projectiles, entrance phase and strain effect of concrete materials on the tendency of deceleration was clarified.

Improving the bonding stability between resin cements and zirconia-based ceramic using different surface treatments.

To evaluate the effects of airborne-particle abrasion with alumina particles or silicamodified alumina particles on the bond strength between zirconia and conventional MDP-based (Ph; Panavia F 2.0, Kuraray) or self-adhesive (SA; RelyX U200, 3M ESPE) resin cements. Five surface treatments were evaluated: C = no surface treatment; AB = airborne-particle abrasion with alumina particles (BIO-ART Dental Supplies and Equipment); ABP = AB combined with MDP-based primer (Alloy Primer, Kuraray); SS = airborne-particle abrasion with silica-modified alumina particles (CoJet, 3M ESPE) combined with silane (RelyX Ceramic Primer, 3M ESPE); and SSP = SS combined with MDP-based primer. The surface roughness (Ra) of the airborne particle-abraded samples (n = 5) was measured by a contact profilometer (Mitutoyo Surftest SJ-401, Mitutoyo). Cylinders of the resin cements tested were bonded to the surface-treated zirconia. The microshear test was performed by the application of a load with a wire loop parallel to the adhesive interface until debonding of the resin cement cylinders. The microshear bond strength (μSBS) of the samples was measured before and after being subjected to thermocycling (TC; 5°C to 55°C, 60 seconds dwell time for 3,000 cycles; MSCT, Marcelo Nucci). One-way (Ra) and two-way (μSBS) analysis of variance followed by Tukey post hoc test (α = .05) were used. The SS (Ph: 12.6 MPa; Ph-TC: 6.37 MPa; SA: 11.8 MPa; SA-TC: 9.37) and SSP (Ph: 10.4 MPa; Ph-TC: 5.82 MPa; SA: 10.4 MPa; SA-TC: 10.0) surface treatments produced the highest surface roughness values (P < .001). The SS samples achieved the highest immediate bond strength for both resin cements. However, after TC, SA resin cement associated with any surface treatment produced the highest bond strength values. The self-adhesive resin cement promoted higher and more stable bond strength values when associated with a surface roughening method.

Effects of Radiant Heat and Frictional Abrasion on Thermal Protective Performance of Clothing Against High Pressurized Steam

This study focused on changes in protective performance of steam protective clothing after exposure to conditions such as thermal radiation and frictional abrasion. Totally eight radiation conditions varying on exposure duration and times, four types of abrasion scenarios with different friction cycles and three different combined treatments were designed. Results demonstrated that any increase in radiant exposure duration or exposure times would lead to an initial increase and then a following decrease in the steam protective performance. However, the steam protective performance seemed relatively immune to the friction cycles. When thermal radiation and frictional abrasion acted together, interactions between them existed and their specific interaction highly depended on the distribution of heat exposure duration and friction cycles. Findings of this study provided insight into factors influencing steam protective performance, and could be an aid in developing high performance materials or guidelines for use and maintenance of protective clothing.

Experiment and simulation about the effect of wear-ring abrasion on the performance of a marine centrifugal pump

The wear-ring abrasion can cause performance degradation of the marine centrifugal pump. In order to study the effect of front and back wear-ring clearance on a pump, test and numerical simulation were used to investigate the performance change of a pump. The test results show that the head and efficiency of pump decrease by 3.56% and 9.62% respectively at 1.0 Qd due to the wear-ring abrasion. Under 1.0 Qd, with the increase of the front wear-ring the vibration velocity at pump foot increases from 0.4 mm/s to 1.0 mm/s. The axis passing frequency (APF) at the measuring points increases significantly and there appears new characteristic frequency of 3APF and 4APF. The numerical simulation results show that the front wear-ring abrasion affects the flow at the inlet of the front chamber of the pump and impeller passage. And the back wear-ring abrasion has obvious effect on the flow in the back chamber of the pump and impeller passage, while the multi-malfunction of the front wear-ring abrasion and back wear-ring abrasion has the most obvious effect on the flow velocity and flow stability inside pump. The pressure pulsation at Blade Passing Frequency (BPF) of the three schemes all decrease with the increase of the clearance.

Long-term abrasion of rocks assessed by micro-Deval tests and estimation of the abrasion process of rock types based on strength parameters

Abstract Testing long-term properties of aggregates requires time consuming laboratory tests. Alternatively, mathematical models can also be used to describe the abrasion process of aggregates. The paper uses another approach it links long-term abrasion to rock mechanical properties to facilitate a quick assessment of long term behavior of aggregates. It explores the long-term durability of aggregates through the application of long-term micro-Deval tests, extending the validity range of the relevant European standard (EN 1097-1:2012), that only requires 12,000 rotations for quality testing. Seven andesite lithotypes obtained from four Hungarian quarries were analyzed. The long-term micro-Deval coefficients were determined by increasing the number of rotations from the standardized 12,000 until the material loss reached the value of 99 m%. With some andesites, only 240,000 rotations were needed, while other ones required 2,000,000 rotations to a material loss of 80 m%. Regression analyses were used to find suitable models that describe the behaviour of the aggregates subjected to abrasion. The test results and the regression analyses supported previous studies suggesting that exponential functions are suitable to model abrasion. The abrasion model parameters introduced here were compared with the rock mechanical parameters of andesites and other lithotypes. It was found, that the newly introduced abrasion parameter A, which is a material-dependent empirical parameter, correlates with the ratio of the uniaxial compressive strength and water absorption. The introduction of the abrasion parameter provides an easy-to-use tool for the description of the behavior of aggregates exposed to natural or artificial abrasive effects. The knowledge of the abrasion process is essential for the lifetime analyses of crushed stones used as construction material or for the investigation of mass change of the grains in sedimentary systems such as riverbeds or coastal zones.

ОПРЕДЕЛЕНИЕ ПОКАЗАТЕЛЕЙ ВЗАИМОДЕЙСТВУЮЩИХ ПОДСИСТЕМ ПРОМЫШЛЕННЫХ ПРЕДПРИЯТИЙ ДЛЯ ДОСТИЖЕНИЯ ЦЕЛЕЙ В ОБЛАСТИ КАЧЕСТВА

Highways are the most important component of country's economic development. They are a complex of engineering structures that are subject to various kinds of deformations during operation. The causes of premature defects are outdated technologies, poor quality materials, high traffic loads, and weather conditions. On average, after 2–3 years of the new road operation, pits, overflows, potholes, cracks, rutting occur on asphalt concrete pavement, its presence worsens the traffic conditions on the road and violates the unimpeded passage of cars. To extend the life cycle of a transport object, there are preventive measures that prevent the destruction of road surfaces. Such activities include regular maintenance and repair work. One of the effective measures is the use of road impregnation materials (RIM). Road-impregnation materials are used in case of need to prevent aging of the organic binder in the composition of asphalt concrete in the coating, as well as to reduce the impact of external factors. In this article, the influence of the basis of the impregnating material of two manufacturers on the indicators of the properties of asphalt concrete of various degrees of destruction is investigated. Among the considered impregnating compositions, solvent-based road impregnation materials proved to be the most effective. It has been established that the abrasive effect on samples of asphalt concrete significantly reduces the effectiveness of impregnating materials, especially based on bitumen emulsion.

Abrasive Wear Behavior of CNT-Filled Unidirectional Kenaf–Epoxy Composites

Kenaf (Hibiscus Cannabinus) fibers have received significant attention for replacing the usage of synthetic fibers, especially glass fiber, in the fabrication of fiber-reinforced polymer (FRP) composites. The aim of this research was to study the change in wear behavior of kenaf-epoxy fiber composites by filling them with multiwall carbon nanotubes (MWCNT). In particular, the effect of untreated MWCNT (PMWCNT), acid-treated MWCNT (AMWCNT), and silane-treated MWCNT (SMWCNT) was studied, using three different MWCNT loadings, i.e., 0.5, 0.75, and 1 wt.%. The abrasive wear test was conducted to measure the wear properties of the composites. A thermal infrared camera was also used to measure the punctual contact temperature during the abrasive wear test, while the abraded surfaces were analyzed using the stereomicroscope. Starting from the considerable reduction of wear rate with the introduction of kenaf fibers, it was observed that PMWCNT provided some further, yet modest, reduction of wear rate only at the higher loadings. In contrast, the inclusion of AMWCNT proved to increase the specific wear rate of the epoxy-kenaf composites, an effect worsened at higher loadings. This may be due to the weakened interfacial bonding between the AMWCNT and epoxy. On the other hand, the presence of SMWCNT improved the interfacial bonding between CNT and epoxy, as shown by an increase in contact temperature. However, the increase in bonding strength was stipulated to have caused the rougher worn debris, thus inducing a three-body abrasive wear effect.

"Comparative evaluation of effect of toothbrush-dentifrice abrasion on surface roughness of resin composites with different filler loading:" An in vitro study.

Objectives:This in vitro study evaluated the effect of toothbrush-dentifrice abrasion on the surface roughness of two restorative posterior resin composites, Filtek Z250 and Z350 after simulated toothbrushing twice daily for a period of 3 months.Methods:All the specimens were polished and cleaned and surface topography was evaluated by Veeco di CP-II Atomic Force Microscope (AFM) at six different points; similarly, these specimens were again subjected to evaluation after simulated toothbrushing using dentifrice. The surface roughness evaluation was done for AFM images using software made available and the factor measured were average roughness (Ra) and maximum peak to valley distance R(p v). Data were normally distributed as tested using the Shapiro–Wilk W-test (P > 0.05). Therefore, analysis was performed using the parametric tests, i.e., independent “t”-test (for comparing two groups). The level of statistical significance was set at P < 0.05.Results:The mean change in Ra and the mean change in Rp-v for Z350 were less as compared to Z250, and this difference was statistically significant.Conclusions:Within the limitation of the present study, it can be concluded that toothbrushing increased the roughness in Z250 in comparison to Z350.

Environmental Change and Modernization of Fishing Gear for Fishermen in Depok Beach, Bantul, Yogyakarta 1995-2010

The purpose of this study is to analyze environmental changes and modernization of fishing gear for fishermen. This article identifies and evaluates several impacts of the implementation of modernization of fishing gear, particularly by taking a case study on the fishing environment of Depok Beach, Bantul, Yogyakarta. This research is categorized as maritime history research. This study uses the historical method with a sociological approach. The results of this study state that Depok fishermen have experienced several changes in their fishing gear. Those who used to use traditional fishing gear then use modern fishing gear. Characterized by the use of the engine as a means of propulsion of the boat which in turn causes the fishing range to be wider. The influence of modernization has changed the mindset of the fishing community of Depok Beach. In addition, the threat of abrasion is very dangerous for buildings around the coast. Abrasion that occurs is caused by strong waves. Strong waves occur due to gusts of wind from the Indian Ocean. The waves continuously erode the sediment on the beach. The scour will affect the land area and will also affect the reduced activity. The effect of abrasion on buildings is very dangerous and detrimental to the people of Depok Beach.

Wear evaluation of CAD-CAM dental ceramic materials by chewing simulation.

PURPOSETo evaluate the wear of computer-aided design/computer-aided manufacturing (CAD-CAM) dental ceramic materials opposed by enamel as a function of increased chewing forces.MATERIALS AND METHODSThe enamel cusps of healthy human third molar teeth (n = 40) opposed by materials from CAD-CAM dental ceramic groups (n = 10), including Vita Enamic® (ENA), a polymer-infiltrated ceramic network (PICN); GC Cerasmart® (CERA), a resin nano-ceramic; Celtra® Duo (DUO), a zirconia-reinforced lithium silicate (ZLS) ceramic; and IPS e.max ZirCAD (ZIR), a polycrystalline zirconia, were exposed to chewing simulation (1,200,000 cycles; 120 N load; 1 Hz frequency; 0.7 mm lateral and 2 mm vertical motion). The wear of both enamel cusps and materials was quantified using a 3D laser scanner, and the wear mechanisms were evaluated by scanning electron microscopy (SEM). The results were analysed using Welch ANOVA and Kruskal Wallis test (α = .05).RESULTSZIR showed lower volume loss (0.02 ± 0.01 mm3) than ENA, CERA and DUO (P = .001, P = .018 and P = .005, respectively). The wear of cusp/DUO [0.59 mm3 (0.50-1.63 mm3)] was higher than cusp/CERA[0.17 mm3 (0.04-0.41 mm3)] (P = .007). ZIR showed completely different wear mechanism in SEM.CONCLUSIONComposite structured materials such as PICN and ZLS ceramic exhibit more abrasive effect on opposing enamel due to their loss against wear, compared to uniform structured zirconia. The resin nano-ceramic causes the lowest enamel wear thanks to its flexible nano-ceramic microstructure. While zirconia appears to be an enamel-friendly material in wear volume loss, it can cause microstructural defects of enamel.

Quo vadimus? Fundamental problems of developing hybrid prostheses of thoracic aorta

This article is a review briefly characterizing the state of the art of hybrid surgery of the thoracic aorta using the frozen elephant trunk technique worldwide and in Russia, also discussing unsolved problems of fundamental science, being key issues in creation of new models of hybrid prostheses of the thoracic aorta. The main attention is paid to the problem of radial stiffness of the stent-graft portion of the prosthesis. Performed is a detailed analysis of the factors influencing this characteristic of the sent graft: shape, size and number of cells of the stent element, thickness of the nitinol wire it is made of, method of edge connection, nitinol properties depending on the alloy grade and methods of thermoforming. It is shown that excessive stiffness leads to the development of d-SINE syndrome. This is followed by discussing the problem of optimal stiffness of stent grafts, based on the design of stent graft elements and elastic properties of the wall of the true channel of a dissecting aortic aneurysm. Also proposed is an approach to solving the problem of d-SINE, consisting in creation of conical stent grafts and/or a gradual decrease of radial stiffness of stent elements in the direction of the distal portion. Comprehensively addressed are disadvantages of the graft portion of the prosthesis, in 95% of items made of polyethylene terephthalate fiber: susceptibility to degradation associated with manufacturing defects and intraoperative microdamages, abrasive effect in the zone of contact with stent elements, partial postoperative hydrolysis and an inflammatory reaction to a foreign body, often being clinically pronounced. Also touched upon are certain aspects of creating hermetic coatings of the graft portion, with the use of vancomycin possessing low cytotoxicity as part of an antibacterial component being promising. As a whole, it is demonstrated that advances in creating a novel generation of hybrid prostheses should be associated with new approaches and materials, to be obtained at the junction of medicine and fundamental sciences.