Failure analysis of fractured dental implants

The success and predictability of titanium implants over long periods of time are well established, and there has been a tremendous increase in implant popularity among patients and clinicians over the last four decades. However, complications can occur, resulting in the loss of both the implant and the prosthesis. Dental implant fracture is uncommon; however, implants or abutment screws can fracture and cause significant problems for both the clinician and the patient. Improper design, overload, fatigue, and corrosion are all potential causes of implant fracture. Six retrieved fractured dental implants of varying diameter and thread design were collected on a regular basis to characterize their fracture behavior by SEM and assess the fracture mechanism. The majority of the implants were fractured as a result of fatigue crack initiation and propagation from the thread roots

On Silicides in High Temperature Titanium Alloys

High temperature titanium alloys like IMI 685 contain small amounts of silicon (~ 0.25 wt. per cent) to improve creep resistance. Different types of silicides, namely Ti5Si3 (TiZr)5Si3(S1) and (TiZr)6 Si3 (S2), have been observed to precipitate in various silicon-bearing titanium alloys depending upon their composition and heat treatment. The precipitation of silicides, their orientation relationship with the matrix in different alloys, and the beneficial influence of thermo-mechanical treatment on the distribution of silicides have been pointed out. The effect of silicides on mechanical properties and fracture of the commercial alloy IMI 685 is also indicated

In vitro biomechanical comparison of various implants in Pauwels type 3 fracture neck femur

Background: The objective of this study was to find out the correlation among type of implant, type of fracture and quality of bone in a cadaveric model of unstable fracture neck of femur (Pauwels type 3) fixed with either; proximal femoral nail (PFN), dynamic hip screw (DHS), dynamic hip screw with an anti-rotation screw (DHS and ARS) or cannulated cancellous screws (CCS).Methods: This study was conducted on 24 cadaveric bones (6 in each group) in which unstable fracture neck of femur (Pauwels type 3) were created and fractures in each group were fixed with different implants after creating a comparable group using DEXA scan. These were tested on a cyclic physiological loading machine at 2 cycles per second with a load of 200kg. The test was observed for 10,000 loading cycles or till failure whichever occurred earlier. Subsidence was measured and analyzed.Results: Five specimens in the PFN group, 3 specimens in the DHS and ARS and DHS group completed 10,000 cycles while all the specimens in CCS group failed before 10000 cycles. Mean subsidence of the PFN group was significantly lower than the other groups.Conclusions: PFN constructs were stronger than the other constructs. However, these data must be interpreted as strictly biomechanical, representing only part of the scenario at work in vivo. Nonetheless, the significant findings of increased strength of fixation over the DHS, DHS with ARS and CCS certainly appear to support the use of PFN clinically.

Undercooling studies on dispersed bismuth droplets

In the zinc-bismuth system, a monotectic reaction occurs at 689 K and 0·6 at.% Bi composition. Rapid solidification of the as-cast monotectic alloy led to a micromorphology in which bismuth was uniformly and bimodally distributed as small droplets in the zinc matrix. Statistical analysis of the electron micrographs obtained from different transparent regions of the foils revealed that the size of most of the droplets was about 6 nm. These droplets undercooled by 132 K. An analysis of the nucleation rate measurements shows that the activation energy barrier to nucleation is of the order of 39·8 kcal/mol at the maximum undercooling

Effect of Salt Coatings on Low Cycle Fatigue Behavior of Nickel -base Superalloy GTM-SU-718

AbstractNickel-base superalloys are used as components of gas turbines both of jet engines as well as marine engines. Sin e these components are subjected to high temperature and oxidizing environment, their performance is drastically affected by the environmental conditions. Marine environment further aggravates the situation due to presence of salt (NaCl) particles in air. This salt along with sulphur and vanadium present in the fuel oil, leads to formation of compounds like sodium sulfate (Na2SO4) and vanadium pentaoxide (V2O5) during combustion and causes hot corrosion and stress corrosion cracking of engine components. Strain controlled low cycle fatigue tests were conducted on the nickel base superalloy GTM-SU-718 in air, at room temperature on unexposed, exposed at 550°C for 25h, exposed at 650°C for 25h as well as on the specimens coated with layers of NaCl, 25wt.%NaCl+75wt.%Na2SO4 and 90wt.%Na2SO4+5wt.%NaCl+5wt.%V2O5 salt/salt mixtures separately and exposed at elevated temperatures for 25h. While the NaCl coated sample was exposed at 550°C, those coated with other two salt mixtures were exposed at 650°C. It was observed that fatigue life of the NaCl coated sample, exposed at 550°C for 25h was reduced, however, there was little effect on fatigue life of the other specimens referred to above, including even those coated with salt mixtures and exposed at 650°C

Differential, Tissue-specific, Transcriptional Regulation of Apolipoprotein B Secretion by Transforming Growth Factor β

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Dual top gated graphene transistor in the quantum Hall regime

We study the effect of local modulation of charge density and carrier type in graphene field effect transistors using a double top gate geometry. The two top gates lead to the formation of multiple \emph{p-n} junctions. Electron transport measurements at low temperature and in the presence of magnetic field show various integer and fractionally quantized conductance plateaus. We explain these results based on the mixing of the edge channels and find that inhomogeneity plays an important role in defining the exact quantization of these plateaus, an issue critical for the metrology applications of \emph{p-n} junctions.Comment: 4 pages, supporting information at http"//www.tifr.res.in/~nan

BOB CAT: a Large-Scale Review and Delphi Consensus for Management of Barrett’s Esophagus With No Dysplasia, Indefinite for, or Low-Grade Dysplasia

OBJECTIVES: Barrett’s esophagus (BE) is a common premalignant lesion for which surveillance is recommended. This strategy is limited by considerable variations in clinical practice. We conducted an international, multidisciplinary, systematic search and evidence-based review of BE and provided consensus recommendations for clinical use in patients with nondysplastic, indefinite, and low-grade dysplasia (LGD). METHODS: We defined the scope, proposed statements, and searched electronic databases, yielding 20,558 publications that were screened, selected online, and formed the evidence base. We used a Delphi consensus process, with an 80% agreement threshold, using GRADE (Grading of Recommendations Assessment, Development and Evaluation) to categorize the quality of evidence and strength of recommendations. RESULTS: In total, 80% of respondents agreed with 55 of 127 statements in the final voting rounds. Population endoscopic screening is not recommended and screening should target only very high-risk cases of males aged over 60 years with chronic uncontrolled reflux. A new international definition of BE was agreed upon. For any degree of dysplasia, at least two specialist gastrointestinal (GI) pathologists are required. Risk factors for cancer include male gender, length of BE, and central obesity. Endoscopic resection should be used for visible, nodular areas. Surveillance is not recommended for <5 years of life expectancy. Management strategies for indefinite dysplasia (IND) and LGD were identified, including a de-escalation strategy for lower-risk patients and escalation to intervention with follow-up for higher-risk patients. CONCLUSIONS: In this uniquely large consensus process in gastroenterology, we made key clinical recommendations for the escalation/de-escalation of BE in clinical practice. We made strong recommendations for the prioritization of future research