Sliding Friction and Wear Characteristics of Wire Rope Contact with Sheave under Long-Distance Transmission Conditions.

Wire rope has different degrees of surface wear under long-distance transmission conditions, which leads to performance degradation and greatly threatens its safety and reliability in service. In this paper, friction and wear tests between the transmission wire rope and sheave under different sliding velocities (from 0.8 m/s to 1.6 m/s) were carried out using a homemade test rig. The material of the steel wires was low carbon steel, and pulley material was ASTM A36 steel plate. The sliding friction coefficient (COF), friction temperature rise, wear characteristic parameters and wear mechanisms of the wire rope were analyzed. Additionally, the effect of different wear on the fracture behavior of the wire rope was investigated by a breaking tensile test. The results show that the average COF in the relatively stable stage decreased from approximately 0.58 to 0.51 with the increase of sliding velocity. The temperature rise of the wire rope increased rapidly with an increase of sliding velocity, from approximately 52.7 °C to 116.2 °C. The maximum wear width was the smallest when the sliding velocity was 1.2 m/s (approximately 1.5 mm). The surface wear was characterized by spalling, furrowing and plastic deformation, which are strongly affected by the sliding velocity. The wear mechanisms of the wire rope were mainly adhesive wear and abrasive wear. Surface wear changes the fracture morphology of the wire rope and accelerates its fracture speed.

CAD/CAM Resin-Based Composites for Use in Long-Term Temporary Fixed Dental Prostheses.

The aim of this in vitro study was to analyse the performance of CAD/CAM resin-based composites for the fabrication of long-term temporary fixed dental prostheses (FDP) and to compare it to other commercially available alternative materials regarding its long-term stability. Four CAD/CAM materials [Structur CAD (SC), VITA CAD-Temp (CT), Grandio disc (GD), and Lava Esthetic (LE)] and two direct RBCs [(Structur 3 (S3) and LuxaCrown (LC)] were used to fabricate three-unit FDPs. 10/20 FDPs were subjected to thermal cycling and mechanical loading by chewing simulation and 10/20 FDPs were stored in distilled water. Two FDPs of each material were forwarded to additional image diagnostics prior and after chewing simulation. Fracture loads were measured and data were statistically analysed. SC is suitable for use as a long-term temporary (two years) three-unit FDP. In comparison to CT, SC featured significantly higher breaking forces (SC > 800 N; CT < 600 N) and the surface wear of the antagonists was (significantly) lower and the abrasion of the FDP was similar. The high breaking forces (1100-1327 N) of GD and the small difference compared to LE regarding flexural strength showed that the material might be used for the fabrication of three-unit FDPs. With the exception of S3, all analysed direct or indirect materials are suitable for the fabrication of temporary FDPs.

The unfavorable role of titanium particles released from dental implants.

Titanium is considered to be a metal material with the best biological safety. Studies have proved that the titanium implanted in the bone continuously releases titanium particles (Ti particles), significantly increasing the total titanium content in human body. Generally, Ti particles are released slowly without causing a systemic immune response. However, the continuous increased local concentration may result in damage to the intraepithelial homeostasis, aggravation of inflammatory reaction in the surrounding tissues, bone resorption and implant detachment. They also migrate with blood flow and aggregate in the distal organ. The release of Ti particles is affected by the score of the implant surface structure, microenvironment wear and corrosion, medical operation wear, and so on, but the specific mechanism is not clear. Thus, it difficult to prevent the release completely. This paper reviews the causes of the Ti particles formation, the damage to the surrounding tissue, and its mechanism, in particular, methods for reducing the release and toxicity of the Ti particles.

Irradiation therapy and chewing simulation: effect on zirconia and human enamel.

PURPOSE: Ionizing radiation therapy (RT) is the main option for head and neck cancer treatment, but it is associated with multiple side effects. This study aimed to evaluate the effect of RT associated with chewing simulation on the surface of human enamel and Yttria-partially stabilized zirconia (Y-TZP). METHODS: Maxillary premolar cusps and Y-TZP slabs were divided in 7 experimental groups: CO: no RT (control); EZ groups had irradiation applied to both, enamel and zirconia samples (simulating restoration prior to RT); E groups had irradiation applied to enamel only (simulating restoration after RT). RT doses were either 30, 50 or 70 Gray (Gy). Enamel cusps were abraded against zirconia slabs in a chewing simulator (CS - one million cycles/ 80 N/ 60 mm/min, 2 mm horizontal path, artificial saliva, 37˚ C). Zirconia hardness was evaluated before CS; zirconia roughness and enamel volume (wear) were evaluated before and after CS. Hardness and wear data were analyzed by one-way Analysis of Variance and Tukey post hoc test. Roughness was analyzed by Repeated Measures test and Bonferroni test (p=0.05). RESULTS: There was no significant effect of enamel or zirconia irradiation on enamel cusp wear (p=0.226), regardless of the irradiation dose used - up to 70 Gy. Irradiation also did not affect Y-TZP surface roughness (p=0.127) and hardness (p=0.964). CONCLUSIONS: RT does not promote significant changes to the surface characteristics of zirconia. Irradiated enamel abraded against zirconia does not show higher wear volume when compared to non-irradiated enamel.

Wear Morphology on the Surfaces of CoCrMo Unicompartmental Knee Joint Endoprostheses as Elements of Metal-Metal Friction Nodes.

The article assesses the strength and structural parameters of load-bearing layers of metal biobearings made of CoCrMo alloy. The research material consisted of unicompartmental knee joint endoprostheses used in the human body, removed due to excessive wear. No patient participated in the examinations. The endoprostheses used as research material underwent the liquidation procedures in the hospital, which has all necessary permissions and certifications to perform endoprosthetic procedures. Endoprostheses selected for the examinations had been used for 6 to 12 years at similar load conditions as declared by the patients, i.e., body weight of F = 835 N, declared activity expressed as the number of load cycles up to 100 thousand/year, and no artificial joint infections. To assess the homogeneity of the research material, the analysis of chemical composition using a Joel scanning electron microscope with EDS (Energy-dispersive X-ray spectroscopy) was made to exclude endoprostheses with various alloying additives. Microscopic examinations were performed using the Phenom XL microscope, while the wear surface was examined using a Keyence VHX-900F microscope. Several experimental tests were also carried out on load-bearing surfaces to assess changes in strength parameters of the base material after a known life cycle and load conditions. Material hardness using the Vickers method, yield point, critical value of stress intensity coefficient, and the coefficient of friction µ were evaluated. The examinations allowed for the systematization of wear in the knee and femoral components of unicompartmental hip endoprostheses. The statistical evaluation of the number and costs of hip joint replacement surgeries in Poland was also made.

Comparison of Fracture Load and Surface Wear of Microhybrid Composite and Ceramic Occlusal Veneers.

PURPOSE: To compare in vitro fracture load, surface wear, and roughness after thermal cycling and cyclic mechanical fatigue loading among cemented microhybrid resin-based composite and ceramic occlusal veneers fabricated at two thicknesses (1.5 and 2.5 mm). MATERIALS AND METHODS: Sixty-four extracted premolars without root canal treatment were prepared and restored with occlusal veneers of two thicknesses (1.5 and 2.5 mm), using four different materials: microhybrid composite (MC), fiber-reinforced microhybrid composite (FMC), heat-pressed lithium disilicate ceramic (HPC), and computer-aided design/computer-aided manufactured lithium disilicate ceramic (CCC). The specimens underwent thermal cycling and cyclic mechanical fatigue loading, and were then subjected to fracture testing, with loads at failure recorded as fracture load. Wear and surface roughness were recorded before and after fatigue loading. Results were analyzed using one-way ANOVA, two-way ANOVA (α = 0.05). RESULTS: All specimens survived thermal cycling and cyclic mechanical fatigue loading. At 1.5-mm thickness, the mean fracture load of FMC was highest (3926.48 ± 556.54 N), while that of CCC was highest (3066.45 ± 559.94 N) at 2.5 mm. Regardless of thickness, the fracture load of CCC was higher than that of HPC (p = 0.004 and p = 0.023). The wear of MC and FMC was significantly higher than those of HPC and CCC (p ≤ 0.001), but was similar in terms of the wear rate of tooth enamel. HPC exhibited the lowest surface roughness after fatigue loading (p ≤ 0.001). CONCLUSION: All tested occlusal veneers exhibited a fracture load considerably exceeding the maximum occlusal force in the posterior dentition. When the attainable space for restoration varies, different occlusal veneer materials should be considered. The surface wear and roughness also need to be considered when selecting materials.

Shaping effectiveness and surface topography of reciprocating files after multiple simulated uses.

This in vitro study assessed morphological changes and efficiency of reciprocating files after multiple uses. Sixty standardized Endo Training Blocks and 10 ReciprocR25 files were selected (six blocks for each file). Each file was its own control (before use vs. after each instrumentation). The instruments were used according to the manufacturer's instructions, and scanning electron microscopy was used to observe fatigue cracks, metal strips/metal flash, pitting, fretting, debris, disruption of the cutting edge, and plastic deformations after each instrumentation. The presence of seven wear variables was scored semiquantitatively by viewing micrographs collected before and after use. The prepared areas in resin blocks were calculated and compared by using AutoCAD software. The control group had significantly lower values for all wear variables except fretting and plastic deformation. The presence of fatigue cracks and metal strips/metal flash significantly differed between unused instruments and instruments used four or five times, in all observed sections. The area of instrumented Endo Training Blocks significantly differed in relation to the number of instrument uses. The Reciproc files wore progressively, and repeated use affected their shaping efficiency in simulated canals.

A national survey of tooth wear on facial and oral surfaces and risk factors in young Nigerian adults.

OBJECTIVE: The objective of this study is to assess the prevalence of tooth wear and to identify risk factors in a sample of young Nigerian adults. MATERIALS AND METHODS: Participants were individuals aged 18-35 years, attending dental clinics located in eight centers representing the six geopolitical zones of the country. Calibrated examiners measured tooth wear using basic erosive wear examination (BEWE) index. Individuals were characterized by the highest BEWE score recorded for any facial/oral tooth surface. Previously validated questionnaire was used to gather information on demographics and risk factors. RESULTS: A total of 1349 participants were examined. The prevalence of tooth wear was 60.2%. Bivariate analysis showed significant differences in the prevalence of tooth wear with age, educational level, and occupation (P ≤ 0.05). There were significant differences in tooth wear among the participants from the different states. Tooth wear was found to increase with smoking. Tooth wear was associated with brushing frequency, use of chewing stick, and other local cleaning agents. Multiple regression analysis showed that age, brushing frequency, brushing after breakfast added statistically significantly to the prediction of tooth wear (P < 0.05). CONCLUSION: Tooth wear was common in the population. The frequency of tooth brushing, use of chewing sticks and other local tooth cleaning agents may be contributory.

Wear testing of a canine hip resurfacing implant that uses highly cross-linked polyethylene.

Hip resurfacing offers advantages for young, active patients afflicted with hip osteoarthritis and may also be a beneficial treatment for adult canines. Conventional hip resurfacing uses metal-on-metal bearings to preserve bone stock, but it may be feasible to use metal-on-polyethylene bearings to reduce metal wear debris while still preserving bone. This study characterized the short-term wear behavior of a novel hip resurfacing implant for canines that uses a 1.5 mm thick liner of highly cross-linked polyethylene in the acetabular component. This implant was tested in an orbital bearing machine that simulated canine gait for 1.1 million cycles. Wear of the liner was evaluated using gravimetric analysis and by measuring wear depth with an optical scanner. The liners had a steady-state mass wear rate of 0.99 ± 0.17 mg per million cycles and an average wear depth in the central liner region of 0.028 mm. No liners, shells, or femoral heads had any catastrophic failure due to yielding or fracture. These results suggest that the thin liners will not prematurely crack after implantation in canines. This is the first hip resurfacing device developed for canines, and this study is the first to characterize the in vitro wear of highly cross-linked polyethylene liners in a hip resurfacing implant. The canine implant developed in this study may be an attractive treatment option for canines afflicted with hip osteoarthritis, and since canines are the preferred animal model for human hip replacement, this implant can support the development of metal-on-polyethylene hip resurfacing technology for human patients. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1196-1205, 2018.

Surface wear of resin composites used for Invisalign® attachments.

Orthodontic treatments with Invisalign® require the use of attachments, which are composite resin buttons attached to tooth surfaces. Attachments constitute one of the most powerful tools for improving the efficiency of orthodontic tooth movement. The main purpose of this study was to evaluate surface wear over six months in two resin composites (Filtek Z350 XT, 3MESPE and Amelogen Plus TW, Ultradent Products Inc. ) used for making Invisalign® attachments. These composites were selected for their esthetic and mechanical properties. Forty attachments were bonded to the buccal surface of maxillary teeth. Materials were randomized and assigned in a double blind manner. Impressions were taken of the attachments using a preestablished technique immediately after bonding and following 6 months of clinical use. The impressions were examined by Scanning Electron Microscopy (SEM) at 12-fold magnification to identify changes in surface texture and attachment shape. Data were analyzed using Mann-Whitney's test on the overall ranking of detected changes in those variables. Statistically significant differences (P<0. 001) were found for surface wear, with greater changes in Amelogen Plus. Attachment shape did not change significantly in either material (P>0. 05). According to the results of this study, the alteration of the attachment surface during the first six months of treatment depends on the composite used, while attachment shape does not appear to be affected, so the clinical performance of the materials evaluated could be considered acceptable.

Los tratamientos ortodóncicos con alineadores Invisalign® utilizan aditamentos construidos en resinas compuestas llamados "attachments" adheridos a la superficie dentaria. El "attachment" es una de las herramientas más potentes para mejorar la eficiencia del movimiento dental. El propósito de este estudio fue evaluar el desgaste superficial de dos resinas compuestas utilizadas para construir los "attachments" en el tratamiento de ortodoncia con la técnica de alineadores Invisalign®. Se evaluaron 40 "attachments" adheridos a la superficie vestibular de piezas dentarias del maxilar superior en un período de 6 meses. Los "attachments" fueron construidos en forma aleatoria y a doble ciego con dos resinas compuestas (Filtek Z350 XT de 3M ESPE y Amelogen Plus TW Ultradent Products Inc) elegidas de acuerdo con las propiedades estéticas y mecánicas requeridas. Los "attachments" fueron impresionados con una técnica preestablecida inmediatamente luego de ser adheridos y a los 6 meses. Las muestras fueron preparadas para su observación mediante Microscopía Electrónica de Barrido (MEB) a 12 aumentos. Se observaron los cambios producidos en la textura superficial y la forma entre el inicio y los seis meses de tratamiento. Los datos fueron analizados y comparados utilizando la prueba de Mann-Whitney, realizada en función del ordenamiento global, de menor a mayor según el cambio producido en esas variables. Los materiales analizados mostraron una diferencia estadísticamente significativa (P<0, 001) en el desgaste superficial, siendo el Amelogen Plus el material que evidenció mayor cambio. Las modificaciones en la forma de los "attachments" no fueron estadísticamente significativas en ambos materiales (P>0, 05). Según los resultados obtenidos en este estudio, la modificación de la superficie de los "attachments" durante los primeros seis meses de tratamiento varía en función del composite empleado, en tanto la forma del "attachment" no parece ser afectada de manera similar, por lo que el desempeno clínico podría ser considerado aceptable cuando se emplean los materiales evaluados.

Surface wear of resin composites used for Invisalign(R) attachments / Desgaste superficial de las resinas compuestas utilizadas en los "attachments" de la técnica Invisalign®

Orthodontic treatments with Invisalign® require the use of attachments, which are composite resin buttons attached to tooth surfaces. Attachments constitute one of the most powerful tools for improving the efficiency of orthodontic tooth movement. The main purpose of this study was to evaluate surface wear over six months in two resin composites (Filtek Z350 XT, 3M ESPE and Amelogen Plus TW, Ultradent Products Inc.) used for making Invisalign® attachments. These composites were selected for their esthetic and mechanical properties. Forty attachments were bonded to the buccal surface of maxillary teeth. Materials were randomized and assigned in a double blind manner. Impressions were taken of the attachments using a preestablished technique immediately after bonding and following 6 months of clinical use. The impressions were examined by Scanning Electron Microscopy (SEM) at 12fold magnification to identify changes in surface texture and attachment shape. Data were analyzed using MannWhitney's test on the overall ranking of detected changes in those variables. Statistically significant differences (P<0.001) were found for surface wear, with greater changes in Amelogen Plus. Attachment shape did not change significantly in either material (P>0.05). According to the results of this study, the alteration of the attachment surface during the first six months of treatment depends on the composite used, while attachment shape does not appear to be affected, so the clinical performance of the materials evaluated could be considered acceptable (AU)

Los tratamientos ortodóncicos con alineadores Invisalign® utilizan aditamentos construidos en resinas compuestas llamados "attachments" adheridos a la superficie dentaria. El "attachment" es una de las herramientas más potentes para mejorar la eficiencia del movimiento dental. El propósito de este estudio fue evaluar el desgaste superficial de dos resinas compuestas utilizadas para construir los "attachments" en el tratamiento de ortodoncia con la técnica de alineadores Invisalign®. Se evaluaron 40 "attachments" adheridos a la superficie vesti bular de piezas dentarias del maxilar superior en un período de 6 meses. Los "attachments" fueron construidos en forma aleatoria y a doble ciego con dos resinas compuestas (Filtek Z350 XT de 3M ESPE y Amelogen Plus TW Ultradent Products Inc) elegidas de acuerdo con las propiedades estéticas y mecánicas requeridas. Los "attachments" fueron impresionados con una técnica preestablecida inmediatamente luego de ser adheridos y a los 6 meses. Las muestras fueron preparadas para su observación mediante Microscopía Electrónica de Barrido (MEB) a 12 aumentos. Se observaron los cambios producidos en la textura superficial y la forma entre el inicio y los seis meses de tratamiento. Los datos fueron analizados y comparados utilizando la prueba de MannWhitney, realizada en función del ordena miento global, de menor a mayor según el cambio producido en esas variables. Los materiales analizados mostraron una diferencia estadísti camente significativa (P<0,001) en el desgaste superficial, siendo el Amelogen Plus el material que evidenció mayor cambio. Las modificaciones en la forma de los "attachments" no fueron estadísticamente significativas en ambos materiales (P>0,05). Según los resultados obtenidos en este estudio, la modificación de la superficie de los "attachments" durante los primeros seis meses de tratamiento varía en función del composite empleado, en tanto la forma del "attachment" no parece ser afectada de manera similar, por lo que el desempeño clínico podría ser considerado aceptable cuando se emplean los materiales evaluados (AU)

Comparison of changes in retentive force of three stud attachments for implant overdentures.

PURPOSE: The aim of this study was to compare the changes in retentive force of stud attachments for implant overdentures by in vitro 2-year-wear simulation. MATERIALS AND METHODS: Three commercially available attachment systems were investigated: Kerator blue, O-ring red, and EZ lock. Two implant fixtures were embedded in parallel in each custom base mounting. Five pairs of each attachment system were tested. A universal testing machine was used to measure the retentive force during 2500 insertion and removal cycles. Surface changes on the components were evaluated by scanning electron microscopy (SEM). A Kruskal-Wallis test, followed by Pairwise comparison, was used to compare the retentive force between the groups, and to determine groups that were significantly different (α<.05). RESULTS: A comparison of the initial retentive force revealed the highest value for Kerator, followed by the O-ring and EZ lock attachments. However, no significant difference was detected between Kerator and O-ring (P>.05). After 2500 insertion and removal cycles, the highest retention loss was recorded for O-ring, and no significant difference between Kerator and EZ lock (P>.05). Also, Kerator showed the highest retentive force, followed by EZ lock and O-ring, after 2500 cycles (P<.05). Based on SEM analysis, the polymeric components in O-ring and Kerator were observed to exhibit surface wear and deformation. CONCLUSION: After 2500 insertion and removal cycles, all attachments exhibited significant loss in retention. Mechanism of retention loss can only be partially explained by surface changes.

Comparison of changes in retentive force of three stud attachments for implant overdentures

PURPOSE: The aim of this study was to compare the changes in retentive force of stud attachments for implant overdentures by in vitro 2-year-wear simulation. MATERIALS AND METHODS: Three commercially available attachment systems were investigated: Kerator blue, O-ring red, and EZ lock. Two implant fixtures were embedded in parallel in each custom base mounting. Five pairs of each attachment system were tested. A universal testing machine was used to measure the retentive force during 2500 insertion and removal cycles. Surface changes on the components were evaluated by scanning electron microscopy (SEM). A Kruskal-Wallis test, followed by Pairwise comparison, was used to compare the retentive force between the groups, and to determine groups that were significantly different (alpha.05). After 2500 insertion and removal cycles, the highest retention loss was recorded for O-ring, and no significant difference between Kerator and EZ lock (P>.05). Also, Kerator showed the highest retentive force, followed by EZ lock and O-ring, after 2500 cycles (P<.05). Based on SEM analysis, the polymeric components in O-ring and Kerator were observed to exhibit surface wear and deformation. CONCLUSION: After 2500 insertion and removal cycles, all attachments exhibited significant loss in retention. Mechanism of retention loss can only be partially explained by surface changes.

Wear and metallographic analysis of WaveOne and reciproc NiTi instruments before and after three uses in root canals.

Reciprocating instruments made from M-wire alloy have been proposed to reduce the risk of fracture. No information is available on the surface alteration after single and multiple uses in root canals. Two reciprocating NiTi instruments were used on extracted teeth up to three times. ESEM/EDS analysis was conducted to determine defects, alterations, and wear features of the apical third of instruments and metallographic analysis was performed on the cross-section of new and used instruments to compare alloy properties. Topography of apical portion was evaluated by AFM before and after uses. Extracted single-rooted teeth were divided into two groups and instrumented according to the manufacturer's recommendations with: (A) WaveOne Primary and (B) Reciproc R25. Each group was divided into three subgroups according to the number of canals instrumented: 1, 2, and 3, respectively. Chi square test was performed to verify homogeneity of defects distribution and GLM to evaluate the differences of RMS at baseline and after use for both groups (α level 0.05). No instrument fractured and no spiral distortions were observed under optical microscope even when the number of uses increased. Not significant differences were found for WaveOne and Reciproc. Blades presented a wrapped portion in WaveOne group and a more symmetrical feature in Reciproc group. Metallographic analysis revealed in both groups the presence of twinned martensitic grains with isolated flat austenitic areas. Both instruments demonstrated limited alteration, such as tip deformation and wear. This study confirmed the safe clinical use of both instruments for shaping multi-rooted teeth.