University of Vienna

About: University of Vienna is a education organization based out in Vienna, Austria. It is known for research contribution in the topics: Population & Context (language use). The organization has 44686 authors who have published 95840 publications receiving 2907492 citations.

Longevity of direct resin composite restorations in posterior teeth.

Abstract: This review is a survey of prospective studies on the clinical performance of posterior resin composites published between 1996 and 2002. Material, patient- and operator-specific data, observation periods, isolation methods of the operative field, and failure rates are detailed in tables. The data were evaluated statistically in order to assess the role of materials (filler size, bonding system, base materials [e.g. glass ionomer cements], and lining materials), study design, and personnel on failure rates. The primary reasons for composite failure were secondary caries, restoration fracture, and marginal defects. The influence of different commercial material brands on failure rates was not evaluated due to the great variety of test substances and the lack of material-specific documentation. Effects of the isolation method of the operative field (rubber dam or cotton rolls) and the professional status of operators (university or general dentist) on composite failure rates were not found to be significant. Observation periods varied from 1 to 17 years, and failure rates ranged between 0% and 45%. A linear correlation between failure rate and observation period was found (P<0.0001). Thirteen of 24 studies were terminated after 3 years, while seven studies continued for more than 10 years, indicating that favourable results for composite materials are frequently based on short-term results, despite higher dropout rates in longer studies. To determine accurately the risk for patients, long-term, randomised, controlled clinical trials of treatment outcomes with composites used in posterior teeth are clearly needed.

Non-radial oscillation modes with long lifetimes in giant stars

Abstract: When main-sequence stars like the Sun near the end of their life, they expand to become oscillating red giants. Such evolved stars could in principle provide stringent tests of stellar theory via analysis of radial and non-radial stellar oscillations. Until now it has been unclear whether non-radial modes are observable at all in red giants. De Ridder et al. now report the presence of both radial and non-radial oscillations in over 300 giant stars. For some red giants, mode lifetimes are of the order of a month. Current stellar evolution theory cannot account for these observations. Towards the end of their lives, stars like the Sun expand greatly to become red giant stars that oscillate. Such evolved stars could provide stringent tests of stellar theory through the analysis of radial and non-radial stellar oscillations. Here, the presence of such oscillations in more than 300 giant stars is reported, with mode lifetimes of some of the giants in the order of a month. Towards the end of their lives, stars like the Sun greatly expand to become red giant stars. Such evolved stars could provide stringent tests of stellar theory, as many uncertainties of the internal stellar structure accumulate with age. Important examples are convective overshooting and rotational mixing during the central hydrogen-burning phase, which determine the mass of the helium core, but which are not well understood1. In principle, analysis of radial and non-radial stellar oscillations can be used to constrain the mass of the helium core. Although all giants are expected to oscillate2, it has hitherto been unclear whether non-radial modes are observable at all in red giants, or whether the oscillation modes have a short or a long mode lifetime3,4,5,6,7, which determines the observational precision of the frequencies. Here we report the presence of radial and non-radial oscillations in more than 300 giant stars. For at least some of the giants, the mode lifetimes are of the order of a month. We observe giant stars with equally spaced frequency peaks in the Fourier spectrum of the time series, as well as giants for which the spectrum seems to be more complex. No satisfactory theoretical explanation currently exists for our observations.