Effect of alloy type and surface conditioning on roughness and bond strength of metal brackets

The effect of 5 different surface conditioning methods on bonding of metal brackets to cast dental alloys was examined. The surface conditioning methods were fine (30-µm) or rough (125-µm) diamond bur, sandblasting (50-µm or 110-µm aluminum oxide [Al2O3]), and silica coating (30-µm silica). Fifty disc-shaped specimens of 5 different alloys (gold-silver, palladium-silver, nickel-chromium, cobaltchromium, and titanium) were ground with 1200-grit silicone carbide abrasive and polished before being reused for each conditioning method. Polished surfaces were used as negative controls. After measuring surface roughness (RZ), metal brackets were bonded to the conditioned alloys with a self-curing resin composite. Specimens were thermocycled (5000 times, 5°–55°C, 30 seconds), and shear bond tests were performed. Significantly higher (P .001) surface roughnesses were observed with use of the rough diamond bur (RZ ~33 µm), 110-µm Al2 O3 (RZ ~14 µm), and fine diamond bur (RZ ~10 µm), compared with the controls (RZ ~1 µm). Silica coating (RZ ~4 µm) and 50-µm Al2 O3 (RZ ~4 µm) demonstrated no significant difference (P > .001) in roughness when compared with the controls. The control group showed no resistance to shear forces (0 MPa). Bond values were greater (19 MPa) when silica coating was used, compared with 50-µm Al2O3 (7 MPa) and 110-µm Al2O3 (8 MPa) for all alloys tested. However, interaction between alloys and conditioning methods exhibited significant differences (P > .0001)

Influence of various surface-conditioning methods on the bond strength of metal brackets to ceramic surfaces

With the increase in adult orthodontic treatment comes the need to find a reliable method for bonding orthodontic brackets onto metal or ceramic crowns and fixed partial dentures. In this study, shear bond strength and surface roughness tests were used to examine the effect of 4 different surface conditioning methods: fine diamond bur, sandblasting, 5% hydrofluoric acid, and silica coating for bonding metal brackets to ceramic surfaces of feldspathic porcelain. Sandblasting and hydrofluoric acid were further tested after silane application. A total of 120 ceramic disc samples were produced, and 50 were used for surface roughness measurements. The glazed ceramic surfaces were used as controls. Metal brackets were bonded to the ceramic substrates with a self-curing composite. The samples were stored in 0.9% NaCl solution for 24 hours and then thermocycled (5000 times, 5degreesC to 55degreesC, 30 seconds). Shear bond tests were performed with a universal testing device, and the results were statistically analyzed. Chemical surface conditioning with either hydrofluoric acid (4.3 mum) or silicatization (4.4 mum) resulted in significantly lower surface roughness than mechanical conditioning (9.3 mum, diamond bur; 9.7 mum, sandblasting) (P <.001). The surface roughness values reflect the mean peak-and-valley distances. The bond strengths of the brackets bonded to the ceramic surfaces treated by hydrofluoric acid with and without silane (12.2 and 14.7 MPa, respectively), silicatization (14.9 MPa), and sandblasting with silane (15.8 MPa) were significantly higher (P <.001) than those treated by mechanical roughening with fine diamond burs (1.6 MPa) or sandblasting (2.8 MPa). The highest bond strength values were obtained with sandblasting and silicatization with silane or hydrofluoric acid without silane; these fulfilled the required threshold. The use of silane after hydrofluoric acid etching did not increase the bond strength. Diamond roughening and sandblasting showed the highest surface roughness; they can damage the ceramic surface. Acid etching gave acceptable results for clinical use, but the health risks should be considered. The silicatization technique has the potential to replace the other methods; yet cohesive failures were observed in the ceramic during removal of the brackets

On non-L2L^2 solutions to the Seiberg-Witten equations

We show that a previous paper of Freund describing a solution to the Seiberg-Witten equations has a sign error rendering it a solution to a related but different set of equations. The non-$L^2$ nature of Freund's solution is discussed and clarified and we also construct a whole class of solutions to the Seiberg-Witten equations.Comment: 8 pages, Te

Household survival strategies of the urban poor in Turkey

Cataloged from PDF version of article.In this thesis, it is aimed to explore the survival strategies of gecekondu households living in Turkish cities and their changing aspects by drawing upon a case study conducted in Ankara. In this respect, migration type, labor force participation, access to urban land and gecekondu, solidarity networks, and access to urban infrastructure and services are the focal points as they constitute the main strategies of the urban poor living in gecekondu settlements. Within this framework, the emerging trends in the households’ strategies in the post-1980s are discussed with reference to the case study of gecekondu settlements in AnkaraArdıç, M. NergizM.S

Towards trajectory anonymization: A generalization-based approach

Trajectory datasets are becoming,popular,due,to the massive,usage,of GPS and,location- based services. In this paper, we address privacy issues regarding the identification of individuals in static trajectory datasets. We first adopt the notion of k-anonymity,to trajectories and propose,a novel generalization-based approach,for anonymization,of trajectories. We further show,that releasing anonymized,trajectories may,still have,some,privacy,leaks. Therefore we propose,a randomization based,reconstruction,algorithm,for releasing anonymized,trajectory data and,also present how,the underlying,techniques,can be adapted,to other anonymity,standards. The experimental,results on real and,synthetic trajectory datasets show,the effectiveness of the proposed,techniques

A Quasiperiodic Gibbons--Hawking Metric and Spacetime Foam

We present a quasiperiodic self-dual metric of the Gibbons--Hawking type with one gravitational instanton per spacetime cell. The solution, based on an adaptation of Weierstrassian $\zeta$ and $\sigma$ functions to three dimensions, conforms to a definition of spacetime foam given by Hawking.Comment: 14 pages, Late

The fit of tapered posts in root canals luted with zinc phosphate cement:A histological study

Objectives. Stress transmission to the root through passive fitting dental posts is partly influenced by the thickness of the cement layer between the post and the prepared root canal surface as well as the fit of the post in the root canal. The objective of this study was to compare the cement gap between the post surfaces and the root canals using five prefabricated, tapered, unthreaded titanium posts of different manufacturers, without and with cement. Methods. Following the endodontic treatment with hand instruments of 100 intact anterior teeth, post spaces were prepared using opening drills of the corresponding size of post. Fifty posts were cemented with zinc phosphate cement into the roots for each system while another 50 posts were inserted into the canal without using the cement. After histological sectioning, the cement gap was measured at six sites for three times at the coronal, middle and apical regions between the root canal wall and the post surface under a light microscope before and after cementation. Results. Before cementation, the highest overall cement gap was observed with the Dr Mooser post system (R) (46 mu m) and the lowest with the Velva post system (R) and Cylindro-Conical system (R) (30 mu m). Significantly less (P <0.05) mean cement gap was observed with respect to the Erlangen post system (R) (41 mu m), the Dr Mooser post system (R) (48 mu m), the MP Pirec post system (R) (34 mu m) and Velva post system (R) (33 pm) when compared with the Cylindro-Conical system (R) (62 tm). The Cylindro-Conical system (R) (79, 61 gm) and MP Pirec post system (R) (25, 24 tm) demonstrated no significant difference (P > 0.001) compared with Velva-Post (R) (38, 20 mu m) at the coronal and middle part, respectively (Mann-Whitney U-test, Boneferroni correction). Significant differences (P <0.001) were observed between the cement gap at the coronal and apical part for the Cylindro-Conical system (R) (79, 46 mu m), Dr Mooser post system (R) (45, 56 mu m) and MP Pirec post system (R) (25, 52 mu m). After cementation, the highest cement gap at the coronal part was obtained with the Cylindro-Conical system (R) (79 +/- 21 mu m) and the lowest with the MP Pirec post system (R) (25 +/- 9 mu m). However, at the apical end, the MP Pirec post system (R) (52 +/- 89 gm) and Dr Mooser post system (R) (56 +/- 16 gm) revealed the highest gap. Significance. Form-congruence between the preparation drill and the post systems exhibited differences. The most consistent cement gap either at the coronal, middle or apical parts of the root canals was obtained with the Erlangen post system (R). (c) 2005 Academy of Dental Materials. Published by Elsevier Ltd. All. rights reserve

Stabilizing role of platelet P2Y(12) receptors in shear-dependent thrombus formation on ruptured plaques

Background: In most models of experimental thrombosis, healthy blood vessels are damaged. This results in the formation of a platelet thrombus that is stabilized by ADP signaling via P2Y(12) receptors. However, such models do not predict involvement of P2Y(12) in the clinically relevant situation of thrombosis upon rupture of atherosclerotic plaques. We investigated the role of P2Y(12) in thrombus formation on (collagen-containing) atherosclerotic plaques in vitro and in vivo, by using a novel mouse model of atherothrombosis. Methodology: Plaques in the carotid arteries from Apoe(-/-) mice were acutely ruptured by ultrasound treatment, and the thrombotic process was monitored via intravital fluorescence microscopy. Thrombus formation in vitro was assessed in mouse and human blood perfused over collagen or plaque material under variable conditions of shear rate and coagulation. Effects of two reversible P2Y(12) blockers, ticagrelor (AZD6140) and cangrelor (AR-C69931MX), were investigated. Principal Findings: Acute plaque rupture by ultrasound treatment provoked rapid formation of non-occlusive thrombi, which were smaller in size and unstable in the presence of P2Y(12) blockers. In vitro, when mouse or human blood was perfused over collagen or atherosclerotic plaque material, blockage or deficiency of P2Y(12) reduced the thrombi and increased embolization events. These P2Y(12) effects were present at shear rates >500 s(-1), and they persisted in the presence of coagulation. P2Y(12)-dependent thrombus stabilization was accompanied by increased fibrin(ogen) binding. Conclusions/Significance: Platelet P2Y(12) receptors play a crucial role in the stabilization of thrombi formed on atherosclerotic plaques. This P2Y(12) function is restricted to high shear flow conditions, and is preserved in the presence of coagulation

N=2 Supersymmetric Model with Dirac-Kahler Fermions from Generalized Gauge Theory in Two Dimensions

We investigate the generalized gauge theory which has been proposed previously and show that in two dimensions the instanton gauge fixing of the generalized topological Yang-Mills action leads to a twisted N=2 supersymmetric action. We have found that the R-symmetry of N=2 supersymmetry can be identified with the flavour symmetry of Dirac-Kahler fermion formulation. Thus the procedure of twist allows topological ghost fields to be interpreted as the Dirac-Kahler matter fermions.Comment: 22 pages, LaTe