The aim was to investigate shear bond strengths and failure modes of four self-etch bonding agents to bovine dentin and enamel and to compare evaluation of data sets with or without exclusion of ...cohesive failure specimens.
Composite-cylinders were bonded perpendicularly to bovine dentin and enamel surfaces. Shear-strengths were measured 24 h post-bonding of: Scotchbond Universal® (SBU, 3 M), OptiBond™ XTR (OBXTR, Kerr), OptiBond™ universal (OBU, KaVo-Kerr) and Prime & Bond active® (PBA, Dentsply-Sirona). Analysis of overall data was made via a linear mixed-model. This was repeated after exclusion of specimens associated with cohesive failures.
When both adhesive and cohesive failures were considered, OBU and OBXTR showed comparable dentin and enamel bond strengths, whereas lower strengths were found on enamel for SBU (p < 0.001) and PBA (p = 0.015). For OBXTR higher shear strengths were measured for specimens associated with cohesive failures. When cohesive failures were excluded, the majority of shear bond strengths of adhesive failure specimens were only slightly different from overall results. However, uniquely with OBXTR dramatically lower shear bond strengths were found for dentin substrate.
After exclusion of cases with cohesive failures OBXTR adhesive fell behind other materials in the sequence of average shear strengths. This did not reflect the actual performance of the material. Therefore, in statistical analysis we do not recommend exclusion of data based on a specific fracture mode.
Highlights • 88 prospective, clinical trials (1996–2015) were analyzed in terms of survival of posterior composite restorations. • Significant findings were only observed for short-term studies and ...by including all studies (short- and long-term studies). • The observation period, the recall rate, the ratio of Class I/II fillings and the number of restorations/patients had a significant influence on the overall failure rate when including all studies (short- and long-term). • No influence of operator status, isolation method or bonding systems on the overall failure rate was found. • In this study a trend of excluding patients at-risk (e.g. high caries activity) and including patients with good oral hygiene was identified, which produces more favorable results.
The aim of this study was to determine whether pretreatment of the dentin surface is beneficial or not by analysis of the bond strengths of four self-adhesive restoratives and four restoration ...materials where pretreatment of dentin was necessary.
Bovine incisors (n = 160) were ground flat on the labial surfaces to expose dentin using a grinder and silicon carbide (SiC) abrasive papers under running water. Between preparation and bonding procedures, the crowns were stored in Chloramine-T solution at 4 °C. Eight different restorative materials were studied: Activa BioActive (ABA), Cention Forte (CNF), Ceram.x Spectra ST (CXS), Riva self-cure (RSC), Equia Forte (EQF), Fuji II LC (FJI), Ketac Molar (KTM), Surefil one (SFO). Four materials required pretreatment of the dental hard tissue before placement, whereas the other four were self-adhesive (no pretreatment). The specimens were mounted vertically in plaster. A preload of 5 N was applied and the subsequent cross-head speed was 0.8 mm/min. Shear bond strengths (MPa) were calculated as the failure load divided by the bonding area. Failure modes were recorded as adhesive, cohesive or pretest. Data were statistically analyzed via ordinal regression for inference and Tukey’s method to adjust for multiple comparisons. All computations were done using R version 4.1.2 (R Core Team 2021).
Smax (failure stress in MPa) of the combined groups with pretreatment were significantly higher than the self-adhesive materials. The highest frequency of pretest-failure was seen with FJI. Glass-ionomer cements without pretreatment were the only restoratives with pretest failures. Amongst materials without pretreatment, SFO had the highest bond strengths.
The further reduction of the placement steps for materials used as an amalgam alternative, namely the omission of pretreatment of the dentin, results in these self-adhesive materials having lower bond strengths than materials that require pretreatment of the dentin.
The aims were to evaluate, via multi-year student cohorts: (i) the incidence of pre-test failures and (ii) shear bond strengths of single- and multi-step adhesives to bovine dentin.
The experiments ...were performed by cohorts of dental students (2008–2016). Each year the bond strengths of three dental adhesives to bovine dentin were tested. Four self-etching adhesives (Optibond-All-in-One, OBAIO; Optibond XTR OBXTR); Xeno V XV; Xeno V+ XV+; a three-step etch-and-rinse-system (Optibond FL, OBFL), a self-etch universal adhesive (Scotchbond Universal SBU) and a self-etch/etch-and-rinse adhesive (Xeno Select, XS) were included in the study. Composite-cylinders were bonded perpendicularly to prepared bovine dentin surfaces. Shear-tests were performed with a universal-testing-machine.
Both overall, and within years, XV and XV+ showed significantly (p<0.01) higher percentages of pre-test failures versus other adhesive systems tested in the period 2008–2014 (OAIO, OBFL, OBXTR). Fewest pre-test failures were observed for OBFL, OBXTR and SBU. Trends in mean bond strengths and Weibull distributions were noted, per adhesive, with trends in the incidence of pre-test failures. Pre-test-failures and bond strengths depended on the air-drying technique. The adhesive systems showed variable technique sensitivity.
Multistep bonding systems (Optibond FL and Optibond XTR) showed minimal pre-test failures and high bond strength applied by relatively inexperienced operators and irrespective of the applied air-drying technique. However, two single-step adhesives (OAIO and SBU) showed comparable results to the multi-step systems.
The clinical need for rapid application dentine adhesives can result in varied outcomes with relatively inexperienced operators. These outcomes include both the incidence of pre-test failures as well as the distributions of shear bond strengths achieved, although these measures appear to be related. However, both outcomes are dependent upon the adhesive products utilised and especially upon the applied air pressure (flow rate). Some rapid application systems appear to perform comparably with well-established multi-step adhesives.
The cyclic axial dynamisation of a stabilised fracture is intended to promote callus formation and bone healing. Most studies focused on biomechanical properties or the quantity of new bone ...formation. Far less is known about the quality of newly formed callus tissues, such as tissue distribution and arrangement within the callus. The aim of this current study was to investigate the effect of cyclic, axial dynamisation on the quantity and quality of callus in an established delayed fracture healing model. In 41 sheep transverse osteotomies with a gap size of 3 mm were stabilised with a unilateral external fixator. In 32 of these, fracture ends were axially stimulated with displacement amplitudes of 0.8 mm, 0.4 mm, 0.2 mm, or 0.0 mm, respectively, for six weeks. In the remaining 9 sheep of the control group, an additional external fixator was mounted to achieve almost total rigidity. Animal material originating from a past animal experiment was reanalysed in this study. Histological thin-ground sections were histomorphometrically analysed regarding the histological structure and composition of the defect region. A slight tendency towards an increase in size of total callus area, area of new bone (nB.Ar), and cartilage (Cg.Ar) was detected with increasing displacement amplitudes compared to the control group. At the anterior callus side nB.Ar and Cg.Ar were significantly larger than at the posterior side in all groups independent of treatment. Regarding the quality of callus, areas of very compact bone were predominant in the treatment groups whereas in the control group a slight shift to more porous bone was observed. No difference of callus compactness was observed between the anterior and the posterior side. The established method to assess the local compactness of callus areas is a useful tool to quantitatively determine the spatial distribution of new bone tissue within the callus. The application of this method in combination with biomechanical testing might reveal interesting relations between tissue distribution and bone strength that, with traditional histomorphometry, cannot be identified.
In performance evaluations of communication and computer networks the underlying topology is sometimes modeled as a random graph. To avoid unwanted side effects, some researchers force the simulated ...topologies to be connected. Consequently, the resulting distribution of the node degrees does then no longer correspond to that of the underlying random graph model. Being not aware of this change in the degree distribution might result in a simulation pitfall. This paper addresses the question as to how serious this pitfall might be. We analyze the node degree distribution in connected random networks, deriving an approximation for large networks and an upper bound for networks of arbitrary order. The tightness of these expressions is evaluated by simulation. The analysis of the distribution for large networks is extended to k-connected graphs. Results show that specific restricted binomial distributions match the actual degree distribution better than the random graph degree distribution does. Nevertheless, the pitfall of not being aware of the change in the distribution seems not to be a serious mistake in typical setups with large networks.
We characterized the ecological niches of several planktonic prostome ciliates with respect to their food demand and temperature. We found intergeneric differences between Balanion planctonicum and ...the 2 Urotricha spp., U. furcata and U. farcta. There were also significant interspecific differences within the genus Urotricha and intraspecific differences between 2 Balanion spp. and 3 U. furcata isolates from distant lakes. Relative to Urotricha spp., Balanion appeared to be the superior competitor at low to medium food concentrations and reached high growth rates at moderate temperatures. The threshold prey concentration for positive population growth of B. planctonicum was lower than that obtained for the 2 Urotricha spp., but higher than that reported earlier for the marine species, B. comatum. A third Urotricha species, U. castalia, was investigated for its temperature response only. The temperature response revealed species-specific temperature adaptation between B. planctonicum and the sympatric U. furcata, and further differences within the genus Urotricha: U. farcta grew fastest at high temperatures; U. castalia was adapted to low temperatures; and U. furcata peaked at moderately warm temperatures.
Abstract
Mit folgendem Aufsatz wird beabsichtigt, ein geplantes Dissertationsprojekt vorzustellen, wie dies auch bereits mit dem mündlichen Beitrag im Rahmen des Doktorand*innen-Forschungstages des ...Centre de Recherche et d’Études Germaniques (CREG) im Oktober 2020 in Toulouse geschehen ist. Das Thema, Schreibszenen (im Sinne der Definition von Martin Stingelin, Davide Giuriato und Sandro Zanetti) bei Stefan Zweig in Verbindung mit der umfassenden Auto-graphensammeltätigkeit dieses Autors, fügt sich dabei gut in die Fragestellung nach diversen Inszenierungsformen europäischen Erbes ein, welche besagtem Forschungstag in Toulouse zugrunde gelegt wurde. Mit seiner Autographensammlung kultiviert und inszeniert Zweig in vielen Facetten materielle Hinterlassenschaften des Werkentstehungsprozesses von Kunstikonen, die von ihm bewundert wurden. Nicht nur anhand von mit dem Sammelprozess einhergehenden Aktivitäten, sondern auch an Zweigs schriftstellerischer Tätigkeit, in der es auffällig oft um das Schaffen anderer Künstler geht, kann ein inszenierender Umgang mit diesem Material im Sinne einer In-Szene-Setzung bzw. Mise-en-Scène beobachtet werden. Ein längeres Zitat aus Zweigs unabgeschlossener Balzac-Biographie soll zur Veranschaulichung dieses Umstands dienen.
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