Entwicklung und Test einer aktiven Messelektrode für das Prepometer-Eine In-vitro-Untersuchung-

Zusammenfassung Das Überkronen von Zähnen ist eine Technik, die zum Standard der heutigen Zahnmedizin gehört. Um eine Krone auf dem zu behandelnden Zahn des Patienten platzieren zu können, muss der Zahn vorher präpariert werden. Bei diesem invasiven Eingriff, aus dem stets eine Dentinwunde resultiert, besteht immer die Gefahr der Schädigung des Zahnmarks und ein daraus möglich resultierender Verlust der Sensibilität und Vitalität des Zahns (Gente 2007). Desweiteren kann es bei jeder tiefen Präparation auch zu einer Eröffnung des Pulpacavums kommen. Es wird auch in einer wissenschaftlichen Stellungnahme der DGZMK für vitale Zähne eine Restdicke des vitalen Dentins von 0,7 mm bei Zähnen mit engen und von 1,4 mm bei Zähnen mit weiten Dentinkanälchen bei einer Präparation für eine Überkronung gefordert (Hellwig, E., Kimmel, K., Lehmann, K. M.). Die Untersuchungen von (Gente 1987, Feige 1989, Wenz 1990, Gente und Wenz 1991, Gente 1992, Becker-Detert 1993, Gente 1995, Bruchmann 2002, Bruchmann 2003, Gente 2007) bis hin zur Entwicklung und in-vivo Studie des Prepometers® (Bruchmann 2003) bestätigen, dass der elektrischen Widerstandsmessung am Dentin zur Begrenzung der Präparationstechnik der Vorzug vor anderen Methoden wie der Interpretation von Röntgenbildern oder Präparationsrillen zu geben ist. Laut Diss. Bruchmann wird von Seiten des Herstellers und Vertreibers erklärt, dass während Informationsveranstaltungen, der Nutzen und die Praktikabilität von niedergelassenen Zahnärzten, die das Prepometer® nicht benutzen in Frage gestellt wird. Diese Zurückhaltung in der Nutzung des Gerätes wird mit dem Messverhalten der Elektrode begründet. Beim Aufsetzen der Elektrode kann zunächst ein niedriger Widerstandswert angezeigt werden, der einer geringeren Rest-Dentindicke entspricht als noch real vorhanden. Dieser Wert wird allerdings größer bei festerem Andrücken der Elektrode an die Zahnhartsubstanz was der größeren und tatsächlich vorhandenen Dentindicke entspricht. Deshalb war es Ziel dieser Arbeit einen neuen Elektrodenkopf zu entwickeln, dessen Messwerte beim Annähern der Elektrode an die Dentinoberfläche sich von einem großen Wert auf den kleinen tatsächlichen Endwert stabilisieren. Im Laufe dieser Studie wurde ein neuer Elektrodenkopf entwickelt, der aus zwei Elektroden besteht, die konzentrisch angeordnet und voneinander isoliert sind. Diese Elektrodenkonstruktion lässt eine elektronische Verbesserung des Messvererhaltens beim Annähern an die Dentinoberfläche, bei Anwendung der jetzt einsetzbaren Abschirm- Treibertechnik, zu. Durch eine Optimierung des Steuerungs- Schaltkreises der aktiven äußeren Elektrode konnte man auch auf eine isolierende Kunststoffmanschette, die vor der Optimierung notwendig war, dauerhaft verzichten. Anhand der durchgeführten in- vitro Studie an frisch extrahierten Zähnen wurde das Messverhalten der neuen Elektrode mit dem der alten Elektrode des Prepometers® beim Annähern an die Dentinoberfläche verglichen. Die Ergebnisse der in- vitro- Untersuchung bescheinigen der neu entwickelten Elektrode günstigeres Messverhalten. Beim Annähern der neuen Elektrode an die Dentinoberfläche wird bis zum ersten Stromfluss ein Wert des Widerstandes gegen unendlich angegeben. Beginnt der Strom beim weiteren Annähern der Elektrode zu fließen, fällt der Widerstanswert auf einen niedrigeren Wert ab, der mit einer durchschnittlichen Abweichung von 13 % von dem Wert für den Elektrodenabstand 0 µm gemessenen abweicht. Während der Studie wurden auch die Messwerte der neuen Elektrode in Bezug auf die vorhandene Restdentindicke mit denen der alten Elektrode verglichen. Im für die Behandlung relevanten Dentindickenbereich von 0 mm – 1,5 mm liegt die Differenz der Messwerte bei gleicher Dentindicke bei ca. 25 kOhm. Wie die Abb. 42 zeigt ist das Messverhalten in diesem Bereich konstant. Damit weist die neue Elektrode auch in diesem Vergleich zur alten Elektrode keine Nachteile auf und bestätigt ihre Funktionalität. Anhand dieser Untersuchung konnte eine Verbesserung im Messverhalten gegenüber der alten Elektrode erreicht werden. Auch durch den jetzt möglichen Verzicht auf eine isolierende Kunststoffmanschette konnte die Handhabung verbessert werden. Diese Aspekte lassen den Schluss zu, dass das Prepometer® der ersten Generation durch ein neues Prepometer®, welches auf der Basis dieser Studie konstruiert wird, ersetzt werden könnte. Voraussetzung wären weiterführende in- vitro- als auch in- vivo- Untersuchungen

A new perspective on the competent programmer hypothesis through the reproduction of bugs with repeated mutations

The competent programmer hypothesis states that most programmers are competent enough to create correct or almost correct source code. Because this implies that bugs should usually manifest through small variations of the correct code, the competent programmer hypothesis is one of the fundamental assumptions of mutation testing. Unfortunately, it is still unclear if the competent programmer hypothesis holds and past research presents contradictory claims. Within this article, we provide a new perspective on the competent programmer hypothesis and its relation to mutation testing. We try to re-create real-world bugs through chains of mutations to understand if there is a direct link between mutation testing and bugs. The lengths of these paths help us to understand if the source code is really almost correct, or if large variations are required. Our results indicate that while the competent programmer hypothesis seems to be true, mutation testing is missing important operators to generate representative real-world bugs.Comment: Submitted and under revie

High-resolution models of solar granulation: the 2D case

Using grid refinement, we have simulated solar granulation in 2D. The refined region measures 1.97*2.58 Mm (vertical*horizontal). Grid spacing there is 1.82*2.84 km. The downflows exhibit strong Kelvin-Helmholtz instabilities. Below the photosphere, acoustic pulses are generated. They proceed laterally (in some cases distances of at least the size of our refined domain) and may be enhanced when transversing downflows) as well as upwards where, in the photosphere they contribute significantly to 'turbulence' (velocity gradients, etc.) The acoustic pulses are ubiquitous in that at any time several of them are seen in our high-resolution domain. Their possible contributions to p-mode excitation or heating of the chromosphere needs to be investigated

Effect of jaw clenching on balance recovery: Dynamic stability and lower extremity joint kinematics after forward loss of balance

Postural control is crucial for most tasks of daily living, delineating postural orientation and balance, with its main goal of fall prevention. Nevertheless, falls are common events, and have been associated with deficits in muscle strength and dynamic postural stability. Recent studies reported on improvements in rate of force development and static postural control evoked by jaw clenching activities, potentially induced by facilitation of human motor system excitability. However, there are no studies describing the effects on dynamic stability. The present study, therefore, aimed to investigate the effects of submaximum jaw clenching on recovery behavior from forward loss of balance. Participants were 12 healthy young adults, who were instructed to recover balance from a simulated forward fall by taking a single step while either biting at a submaximum force or keeping the mandible at rest. Bite forces were measured by means of hydrostatic splints, whereas a 3D motion capture system was used to analyze spatiotemporal parameters and joint angles, respectively. Additionally, dynamic stability was quantified by the extrapolated CoM concept, designed to determine postural stability in dynamic situations. Paired t-tests revealed that submaximum biting did not significantly influence recovery behavior with respect to any variable under investigation. Therefore, reductions in postural sway evoked by submaximum biting are obviously not transferable to balance recovery as it was assessed in the present study. It is suggested that these contradictions are the result of different motor demands associated with the abovementioned tasks. Furthermore, floor effects and the sample size might be discussed as potential reasons for the absence of significances. Notwithstanding this, the present study also revealed that bite forces under both conditions significantly increased from subjects’ release to touchdown of the recovery limb. Clenching the jaw, hence, seems to be part of a common physiological repertoire used to improve motor performance

Numerical simulations of surface convection in a late M-dwarf

Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD) simulations of time-dependent compressible convection, we have studied the dynamics and thermal structure of the convective surface layers of a prototypical late-type M-dwarf (Teff~2800K log(g)=5.0, solar chemical composition). The RHD models predict stellar granulation qualitatively similar to the familiar solar pattern. Quantitatively, the granular cells show a convective turn-over time scale of ~100s, and a horizontal scale of 80km; the relative intensity contrast of the granular pattern amounts to 1.1%, and root-mean-square vertical velocities reach 240m/s at maximum. Deviations from radiative equilibrium in the higher, formally convectively stable atmospheric layers are found to be insignificant allowing a reliable modeling of the atmosphere with 1D standard model atmospheres. A mixing-length parameter of alpha=2.1 provides the best representation of the average thermal structure of the RHD model atmosphere while alternative values are found when fitting the asymptotic entropy encountered in deeper layers of the stellar envelope alpha=1.5, or when matching the vertical velocity field alpha=3.5. The close correspondence between RHD and standard model atmospheres implies that presently existing discrepancies between observed and predicted stellar colors in the M-dwarf regime cannot be traced back to an inadequate treatment of convection in the 1D standard models. The RHD models predict a modest extension of the convectively mixed region beyond the formal Schwarzschild stability boundary which provides hints for the distribution of dust grains in cooler (brown dwarf) atmospheres.Comment: 19 pages, 16 figures, accepted for publication in A&

Influence of Controlled Stomatognathic Motor Activity on Sway, Control and Stability of the Center of Mass During Dynamic Steady-State Balance—An Uncontrolled Manifold Analysis

Multiple sensory signals from visual, somatosensory and vestibular systems are used for human postural control. To maintain postural stability, the central nervous system keeps the center of mass (CoM) within the base of support. The influence of the stomatognathic motor system on postural control has been established under static conditions, but it has not yet been investigated during dynamic steady-state balance. The purpose of the study was to investigate the effects of controlled stomatognathic motor activity on the control and stability of the CoM during dynamic steady-state balance. A total of 48 physically active and healthy adults were assigned to three groups with different stomatognathic motor conditions: jaw clenching, tongue pressing and habitual stomatognathic behavior. Dynamic steady-state balance was assessed using an oscillating platform and the kinematic data were collected with a 3D motion capturing system. The path length (PL) of the 3D CoM trajectory was used for quantifying CoM sway. Temporal dynamics of the CoM movement was assessed with a detrended fluctuation analysis (DFA). An uncontrolled manifold (UCM) analysis was applied to assess the stability and control of the CoM with a subject-specific anthropometric 3D model. The statistical analysis revealed that the groups did not differ significantly in PL, DFA scaling exponents or UCM parameters. The results indicated that deliberate jaw clenching or tongue pressing did not seem to affect the sway, control or stability of the CoM on an oscillating platform significantly. Because of the task-specificity of balance, further research investigating the effects of stomatognathic motor activities on dynamic steady-state balance with different movement tasks are needed. Additionally, further analysis by use of muscle synergies or co-contractions may reveal effects on the level of muscles, which were not visible on the level of kinematics. This study can contribute to the understanding of postural control mechanisms, particularly in relation to stomatognathic motor activities and under dynamic conditions

Why one-dimensional models fail in the diagnosis of average spectra from inhomogeneous stellar atmospheres

We investigate the feasibility of representing a structured multi-dimensional stellar atmosphere with a single one-dimensional average stratification for the purpose of spectral diagnosis of the atmosphere's average spectrum. In particular we construct four different one-dimensional stratifications from a single snapshot of a magneto-hydrodynamic simulation of solar convection: one by averaging its properties over surfaces of constant height, and three different ones by averaging over surfaces of constant optical depth at 500 nm. Using these models we calculate continuum, and atomic and molecular line intensities and their center-to-limb variations. From analysis of the emerging spectra we identify three main reasons why these average representations are inadequate for accurate determination of stellar atmospheric properties through spectroscopic analysis. These reasons are: non-linearity in the Planck function with temperature, which raises the average emergent intensity of an inhomogeneous atmosphere above that of an average-property atmosphere, even if their temperature-optical depth stratification is identical; non-linearities in molecular formation with temperature and density, which raise the abundance of molecules of an inhomogeneous atmosphere over that in a one-dimensional model with the same average properties; the anisotropy of convective motions, which strongly affects the center-to-limb variation of line-core intensities. We argue therefore that a one-dimensional atmospheric model that reproduces the mean spectrum of an inhomogeneous atmosphere necessarily does not reflect the average physical properties of that atmosphere, and are therefore inherently unreliable.Comment: 27 pages, 9 figure