properties, fatigue
Dotaz
Zobrazit nápovědu
Commercially pure Ti is a typical material for dental implants. Besides oral environmental effects, implants are seriously mechanically loaded during the lifetime. Mechanical resistance of coarse and ultra-fine grained Ti grade 4 was investigated. Significant grain size refinement resulting in the 65% increase of the proof stress is reported. The fatigue endurance limit increased from 523 MPa to 698 MPa due to grain refinement. The influence of sandblasting combined with acid etching on fatigue damage of both material states was analyzed. The surface treatment was proven as detrimental to the fatigue properties of both material states, due to reduction of the fatigue initiation stage. Nevertheless, the fatigue endurance limit of the surface-treated ultra-fine grained material remained higher than the fatigue endurance limit of the coarse-grained material without surface treatment. Reported results confirm better mechanical resistance of ultra-fine grained materials for dental implants in the comparison with coarse-grain one.
Surface finish of NiTi is widely perceived to affect its biocompatibility and corrosion fatigue performance. The aim of this work was to find out, whether a carefully engineered surface oxide shows any beneficial effect over electropolished surface on the fatigue performance of superelastic NiTi wire mechanically cycled in simulated biofluid. Series of corrosion and environmental fatigue tensile tests was performed on superelastic NiTi wire with two different surface finishes frequently used in medical device industry. Open Circuit Potential reflecting the activity of chemical reactions on the surface of the wire cycled in electrochemical cell was continuously monitored during the fatigue tests. Microcracks at the surface of the fatigued NiTi wires were characterized by SEM and TEM. It was found that the carefully engineered 70 nm thick TiO2 oxide provides the NiTi wire with similar level of protection against the static corrosion as the less than 10 nm thin natural oxide on the electropolished wire and that it does not have any positive effect on its performance in environmental fatigue tests, whatsoever. On the contrary, the wire covered by the carefully engineered 70 nm thick TiO2 oxide displayed systematically poorer fatigue performance upon tensile cycling under specific critical loading conditions (strain amplitude <0.5% at large mean strains 1-7%).
- MeSH
- koroze MeSH
- lidé MeSH
- ortodontické dráty MeSH
- oxidy * MeSH
- povrchové vlastnosti MeSH
- testování materiálů MeSH
- titan * MeSH
- únava MeSH
- zubní slitiny MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Complicated geometry in combination with surface treatment strongly deteriorates fatigue resistance of metallic dental implants. Mechanical properties of pure Ti grade 2, usually used for dental implant production, were shown to be significantly improved due to intensive grain refinement via Conform SPD. The increase of the tensile strength properties was accompanied by a significant increase in the fatigue resistance and fatigue endurance limit. However, the SLA treatment usually used for the implants' surface roughening, resulted in the fatigue properties and endurance limit decrease, while this effect was more pronounced for the ultrafine-grained comparing to the coarse-grained material when tested under tensile-tensile loading mode. The testing of the implants is usually provided under the bending mode. Even though different testing condition for the conventional specimens tests and implants testing was adopted, a numerical study revealed their comparable fatigue properties. The fatigue limit determined for the implants was 105% higher than the one for coarse-grained and only by 4 % lower than the one for ultrafine-grained Ti grade 2. Based on the obtained results, conventional specimens testing can be used for the prediction of the fatigue limit of the implants.
STATEMENT OF PROBLEM: Fatigue failure of implant components is a common clinical problem. Plasma nitriding, an in situ surface-strengthening method, may improve fatigue properties of dental implants. PURPOSE: The purpose of this in vitro study was to evaluate the effect of plasma nitriding on the fatigue behavior of implant systems. MATERIAL AND METHODS: The preload and friction coefficient of plasma nitrided abutment screws, as well as settlement of the implant-abutment interface, were measured. Then, the reverse torque values and pullout force were evaluated after cyclic loading. Finally, the fatigue properties of the implant system were investigated with static fracture and dynamic fatigue life tests, and the morphology of the fracture on the surface of the implant system was observed. RESULTS: The plasma nitriding treatment reduced the friction coefficient; increased the preload, settlement value, reverse torque values, pullout force, and static fracture load; and prolonged fatigue life. Furthermore, abutment screws with plasma nitriding treatment showed a different fatigue fracture mode. CONCLUSIONS: Plasma nitriding improved mechanical performance and may be a suitable way to optimize the fatigue behavior of dental implants.
Fatigue properties of cast AZ91 magnesium alloy processed by severe plastic deformation were investigated and compared with the properties of the initial cast state. The severe plastic deformation was carried out by equal channel angular pressing (ECAP). The ECAP treatment resulted in a bimodal structure. The bimodality consists in a coexistence of fine grained areas with higher content of Mg17Al12 particles and areas exhibiting larger grains and lower density of Mg17Al12 particles. Improvement of the basic mechanical properties of AZ91 (yield stress, tensile strength and ductility) by ECAP was significant. Also the improvement of the fatigue life in the low-cycle fatigue region was substantial. However the improvement of the fatigue strength in the high-cycle fatigue region was found to be negligible. The endurance limit based on 10(7) cycles for the cast alloy was 80 MPa and for the alloy processed by ECAP 85 MPa. The cyclic plastic response in both states was qualitatively similar; initial softening was followed by a long cyclic hardening. Fatigue cracks in cast alloy initiate in cyclic slip bands which were formed in areas of solid solution. In the case of severe plastic deformed material with bimodal structure two substantially different mechanisms of crack initiation were observed. Crack initiation in slip bands was a preferred process in the areas with large grains whereas the grain boundaries cracking was a characteristic mechanism in the fine grained regions.
Cases of cancer-related fatigue syndrome (CRFS) can be reliably indentified using a diagnostic interview combined with a structured psychiatric interview. However, these interviews are time consuming to conduct, require specialist training, and are not suitable for routine clinical use. The purpose of this study was to identify whether a screening questionnaire could identify patients at high risk of clinically significant fatigue who should be considered for a suitable intervention. PATIENTS AND METHODS: The diagnostic interview for CRFS and the structured clinical interview for the diagnostic and statistical manual of mental disorders were used in order to identify breast cancer survivors who fulfilled the criteria for CRFS. Two fatigue questionnaires (the Bidimensional Fatigue Scale [BFS] and the Functional Assessment of Cancer Therapy-Fatigue subscale [FACT-F]) were administered in order to determine their screening properties. RESULTS: Two hundred women were interviewed and 60 women fulfilled the criteria for CRFS. The BFS cutoff score of 11 had a sensitivity of 92%, a specificity of 53%, a positive predictive value (PPV) of 46%, and a negative predictive value (NPV) of 94%. The FACT-F cutoff score of 36 had a sensitivity of 80%, a specificity of 71%, a PPV of 55%, and a NPV of 89%. CONCLUSION: The BFS and FACT-F cutoff scores can be used to identify breast cancer survivors at higher risk of clinically significant ongoing post treatment fatigue. Neither scale can be used as a diagnostic instrument for CRFS.
Three different microstructures--equiaxed, bi-modal and coarse lamellar--are prepared from Ti-6Al-4V alloy. Electric discharge machining (EDM) with a high peak current (29 A) is performed in order to impose surface roughness and modify the chemical composition of the surface. Detailed scanning electron microscopy (SEM) investigation revealed a martensitic surface layer and subsurface heat affected zone (HAZ). EDX measurements showed carbon enriched remnants of the EDM process on the material surface. Rotating bending fatigue tests are undertaken for EDM processed samples for all three microstructures and also for electropolished-benchmark-samples. The fatigue performance is found to be rather poor and not particularly dependent on microstructure. The bi-modal microstructure shows a slightly superior high cycle fatigue performance. This performance can be further improved by a suitable heat treatment to an endurance limit of 200 MPa.
A novel approach of surface treatment of orthopaedic implants combining electric discharge machining (EDM), chemical milling (etching) and shot peening is presented in this study. Each of the three techniques have been used or proposed to be used as a favourable surface treatment of biomedical titanium alloys. But to our knowledge, the three techniques have not yet been used in combination. Surface morphology and chemistry were studied by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Fatigue life of the material was determined and finally several in-vitro biocompatibility tests have been performed. EDM and subsequent chemical milling leads to a significant improvement of osteoblast proliferation and viability thanks to favourable surface morphology and increased oxygen content on the surface. Subsequent shot-peening significantly improves the fatigue endurance of the material. Material after proposed combined surface treatment possesses favourable mechanical properties and enhanced osteoblast proliferation. EDM treatment and EDM with shot peening also supported early osteogenic cell differentiation, manifested by a higher expression of collagen type I. The combined surface treatment is therefore promising for a range of applications in orthopaedics.
- MeSH
- biokompatibilní materiály chemie MeSH
- buněčná adheze účinky léků MeSH
- buněčná diferenciace účinky léků MeSH
- fluorescenční protilátková technika MeSH
- fotoelektronová spektroskopie MeSH
- lidé MeSH
- mikroskopie elektronová rastrovací MeSH
- nádorové buněčné linie MeSH
- osteoblasty cytologie účinky léků MeSH
- povrchové vlastnosti MeSH
- proliferace buněk účinky léků MeSH
- protézy a implantáty MeSH
- titan chemie farmakologie MeSH
- viabilita buněk účinky léků MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Úvod a cíl: Problematika zalomení endodontických nikl-titanových (NiTi) nástrojů je velmi obsáhlá. Jedná se o slitinu, která má schopnost měnit vnitřní strukturu. Velké úsilí je věnováno vývoji slitiny s ideálními vlastnostmi. K zalomení nikl-titanových nástrojů v kořenovém kanálku může dojít ze dvou základních příčin. Jednou je překročení limitu odolnosti nástroje vůči cyklické únavě a druhou překročení limitu torzního zatížení nástroje. Většina autorů odborných publikací se shoduje v názoru, že hlavním faktorem ovlivňujícím zalamování nástroje je překročení limitu odolnosti vůči cyklické únavě. Cílem práce bylo zhodnotit odolnost nového nástroje Unicone Plus a jeho předchůdce Unicone vůči cyklické únavě za různých okolních podmínek. Metodika: Celkem čtyřicet nástrojů (20 + 20) Unicone 6/025 a Unicone Plus 6/025 (Medin, Česká republika) s identickým průměrem hrotu 0,25 mm a konstantní kónicitou 0,06 byly podrobeny testu cyklické únavy za teploty 20 °C ± 1 °C a za teploty 35 °C ± 1 °C. Sestava využívá arteficiálního kanálu imitujícího kořenový kanálek, vyrobeného z nerezové oceli o poloměru zakřivení 5 mm a úhlu zakřivení 60°. K sestavě byla přidána vodní lázeň, která byla naplněna vodou a udržována na požadované teplotě po celou dobu průběhu testu za kontroly infračerveného teploměru. Vzhledem k faktu, že se jedná o nástroje reciproční, byly testovány v módu Reciproc ALL. K hodnocení cyklické únavy nástrojů byl měřen čas od spuštění endomotoru do zlomu daného nástroje s přesností na celé sekundy. Pro statistické hodnocení byl využit neparametrický Kruskalův-Wallisův test s následnými Mannovými-Whitneyho U-testy mnohonásobného porovnání a Bonferroniho korekcí na hladině významnosti 5 %. Výsledky: Porovnávány byly výsledky ze čtyř skupin měření. Bylo prokázáno, že nástroje Unicone byly statisticky významně méně odolné než Unicone Plus. Rovněž teplota okolního prostředí měla statisticky významný vliv u obou testovaných teplot (p < 0,05). Vyšší okolní teplota měla statisticky významný vliv na zhoršování odolnosti vůči cyklické únavě (p < 0,05). Závěr: Unicone Plus nástroje jsou odolnější vůči cyklickému zatížení než nástroje Unicone. Větší odolnost je v tomto případě s největší pravděpodobností spojena s inovovaným výrobním procesem. S rostoucí okolní teplotou klesá odolnost nástrojů proti cyklické únavě.
Introduction, aim: The issue of fracture of endodontic nickel-titanium instruments is quite extensive. It is an alloy that has the ability to change its internal structure. A great deal of effort is devoted to the development of an alloy with ideal properties. Instruments fracture occurs for two basic reasons. The first one is exceeding the limit of resistence of the instrument to cyclic fatigue and the other one is exceeding the limit of torsional load of the instrument. Most authors agree, that the main factor influencing instruments fracture is exceeding the limit of cyclic fatigue. The aim of this study was to evaluate the resistence to cyclic fatigue of the Unicone Plus in comparison with its predecessor, Unicone, under different enviromental conditions. Methods: A total of forty (20 + 20) Unicone 6/025 and Unicone Plus 6/025 instruments (Medin, Czech republic) with identical tip diameter of 0.25 mm and constant taper of 0.06 were subjected to cyclic fatigue test at temperatures 20 °C ± 1 °C and 35 °C ± 1 °C. Special device was constructed for testing. This device uses the principle of using an artificial root canal made of stainless steel with a radius of the curvature of 5 mm, an angle of curvature of 60°. A thermostatic bath was added to the set-up. The liquid of the desired temperature was added to the container and maintained at that temperature throughout the test under the control of an infrared thermometer. Due to the fact that tested instruments are used in reciprocal movement, they were tested in Reciproc ALL mode. To evaluate cyclic fatigue of the instruments, the time was measured from the start of rotation of the instrument, until the fracture occured with an accuracy of whole seconds. The non-parametric Kruskal-Wallis test was used for statistical evaluation, followed by Mann-Whitney U-tests of multiple comparison and Bonferroni correction at the significance level of 5%. Results: The obtained results from four groups were compared. Unicone instruments were statistically significantly less durable than Unicone Plus at both temperatures tested (p < 0.05). Higher enviromental temperature had statistically significant effect on lowering of cyclic fatigue resistence (p < 0.05). Conclusion: Unicone Plus instruments are more resistant to cyclic loading than Unicone. In this case, greater durability is most likely associated with innovative manufacturing processes. Furthermore, the resistence of instruments to cyclic fatigue dereases with increasing ambient temperature.
The application of biodegradable magnesium-based materials in the biomedical field is highly restricted by their low fatigue strength and high corrosion rate in biological environments. Herein, we treated the surface of a biocompatible magnesium alloy AZ31 by severe shot peening in order to evaluate the potential of surface grain refinement to enhance this alloy's functionality in a biological environment. The AZ31 samples were studied in terms of micro/nanostructural, mechanical, and chemical characteristics in addition to cytocompatibility properties. The evolution of surface grain structure and surface morphology were investigated using optical, scanning and transmission electron microscopy. Surface roughness, wettability, and chemical composition, as well as in depth-microhardness and residual stress distribution, fatigue behaviour and corrosion resistance were investigated. Cytocompatibility tests with osteoblasts (bone forming cells) were performed using sample extracts. The results revealed for the first time that severe shot peening can significantly enhance mechanical properties of AZ31 without causing adverse effects on the growth of surrounding osteoblasts. The corrosion behavior, on the other hand, was not improved; nevertheless, removing the rough surface layer with a high density of crystallographic lattice defects, without removing the entire nanocrystallized layer, provided a good potential for improving corrosion characteristics after severe shot peening and thus, this method should be studied for a wide range of orthopedic applications in which biodegradable magnesium is used. STATEMENT OF SIGNIFICANCE: A major challenge for most commonly used metals for bio-implants is their non-biodegradability that necessitates revision surgery for implant retrieval when used as fixation plates, screws, etc. Magnesium is reported among the most biocompatible metals that resorb over time without adverse tissue reactions and is indispensable for many biochemical processes in human body. However, fast and uncontrolled degradation of magnesium alloys in the physiological environment in addition to their inadequate mechanical properties especially under repeated loading have limited their application in the biomedical field. The present study providesdata on the effect of a relatively simple surface nanocrystallziation method with high potential to tailor the mechanical and chemical behavior of magnesium based material while maintaining its cytocompatibility.
- MeSH
- elektrochemie MeSH
- koroze MeSH
- kultivované buňky MeSH
- lidé MeSH
- nanostruktury chemie ultrastruktura MeSH
- osteoblasty cytologie účinky léků MeSH
- povrchové vlastnosti MeSH
- slitiny farmakologie MeSH
- testování materiálů metody MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
