Johann Wernisch

Treatment of periodontal pockets with a diode laser

The aim of this study is to examine the long‐term effect of diode laser therapy on periodontal pockets with regard to its bactericidal abilities and the improvement of periodontal condition.

Imaging of dental material by polarization sensitive optical coherence tomography

Partial coherence interferometry (PCI) and optical coherence tomography (OCT) are noninvasive and noncontact techniques for high precision biometry and for obtaining cross- sectional images of biologic structures. OCT was initially introduced to depict the transparent tissue of the eye. It is based on interferometry employing the partial coherence properties of a light source with high spatial coherence ut short coherence length to image structures with a resolution of the order of a few microns. Recently this technique has been modified for cross section al imaging of dental and periodontal tissues. In vitro and in vivo OCT images have been recorded, which distinguish enamel, cemento and dentin structures and provide detailed structural information on clinical abnormalities. In contrast to convention OCT, where the magnitude of backscattered light as a function of depth is imaged, polarization sensitive OCT uses backscattered light to image the magnitude of the birefringence in the sample as a function of depth. First polarization sensitive OCT recordings show, that changes in the mineralization status of enamel or dentin caused by caries or non-caries lesions can result in changes of the polarization state of the light backscattered by dental material. Therefore polarization sensitive OCT might provide a new diagnostic imaging modality in clinical and research dentistry.

Electron Transmission Coefficient for Tilted Specimens

Starting from a scattering model, the transmission coefficient of electrons for an oblique angle of incidence is derived. The descent of the transmitted fraction is described by the backscattering of electrons and the energy loss caused by the decreasing mean free path. The angular and energy distribution of electrons is replaced by the most probable angle and mean energy. A comparison with other models and measurements valid for normal incidence was made. The altered transmission characteristics by tilting the sample were verified by comparison with results from Monte Carlo simulations and results from Neubert and Rogaschewski, which were based on measurements. An analytical expression for the transmission law was obtained.

A New Technique for Standardless Analysis by EPMA-TWIX

A new standardless method (TWIX) for quantification of thin films and bulk materials has been developed. Based on a correction model for oblique angle of incidence the effect of attenuation of the detected x-ray line resulting from path length elongation in tilted samples has been used for thickness determination of thin films and composition of binary samples. It should be noted that this method is also applicable on WDS systems. Results with an average deviation of less than 10 per cent are obtained.

Thickness Determination of Thin Insulating Layers

Thin insulating films (Si3N4 on titanium-substrate) with various thicknesses (40–360 nm) are investigated with EPMA (electron probe micro analysis). A carbon- and, alternatively, gold-coating is applied to avoid charging phenomena and beam deflection.

Electron Transmission Coefficient for Oblique Angle of Incidence

Starting from a scattering model the transmission coefficient of electrons for oblique angle of incidence is derived. The decrease of the transmitted fraction is described by the backscattering of electrons and the energy loss caused by the decreasing mean free path. The angular- and energy-distribution of electrons is replaced by the most probable angle and mean energy. A comparison with other models and measurements valid for normal incidence is performed. The altered transmission characteristics by tilting the sample are verified by comparison with results from Monte Carlo simulations and results from Neubert and Rogaschewski, which are based on measurements. An analytical expression for the transmission law is obtained.

Troubleshooting for DBS patients by a non-invasive method with subsequent examination of the implantable device

Multichannel devices are used for deep brain stimulation in patients suffering from Parkinson’s disease. A non invasive method to inspect each single output of these devices was applied in 12 patients. The clinician programmer indicates an electrode impedances beyond standard values in these patients or a non explainable loss of the therapeutic effect was given. A small device was developed to measure and display the stimulation impulse via surface electrodes. The results from the measurement pointed at an incorrect measurement by the programmer in 9 cases, broken electrode leads in 2 patients and an IPG failure in 1 patient. Leads and IPG was exchanged and inspected by light or electron microscopy. Each failure prognosis was confirmed by these examinations. The non invasive measurement of the stimulation pulse via surface electrodes turned out as an easy and accurate method for the detection of incomplete IPG malfunctions.

Sudden failure of implantable pulse generators: cause of failure and examination.

Abstract A sudden failure of implantable pulse generators used for spinal cord stimulation occurred in two patients. To identify the cause of this failure, an intensive destructive analysis of the explanted devices was carried out. A functional diagnosis was carried out by inspecting amplitude, pulse width and frequency on each output channel of the implantable pulse generators. Later, the titanium case of the pulse generators was opened by laser cutting to minimise any additional mechanical stress during the opening procedure. The functional test for both pulse generators showed faultless behaviour. Using light and electron microscopy, hairline cracks could be identified in the electrical connection between battery and electronic circuit. In both devices, the cracks spread through the whole bond wire in the connection to the plus pole of the battery and partially also to the minus pole. The analysis showed that both devices failed by broken bond wires. The electrical connection to the battery exists just by the spring characteristic of the wires. A push to the implant causes a short-term disconnection, resulting in a power on reset of the device. Manufacturing or design issues, allowing micromotion between battery and the hybrid part, may be the reason for this problem. Zusammenfassung Ein plötzlicher Ausfall von implantierten Pulsgebern zur Rückenmarkstimulation ereignete sich bei zwei Patienten. Die Implantate wurden einer gründlichen zerstörenden Untersuchung unterzogen, um die Ursache des Fehlers identifizieren zu können. Die Stimulationsamplitude, Pulsbreite und Frequenz jedes einzelnen Stimulationsausgangs wurden innerhalb eines Funktionstests überprüft. Anschließend wurden die Titangehäuse der Pulsgeneratoren durch einen Laser geöffnet, um jede zusätzliche mechanische Belastung innerhalb der Bearbeitung zu minimieren. Der Funktionstest zeigte ein fehlerloses Verhalten der Stimulatoren. Mittels Licht- und Elektronenmikroskopie konnten Haarrisse in den Verbindungsdrähten zwischen Batterie und dem elektronischen Schaltkreis erkannt werden. Die Bonddrähte wiesen in beiden Implantaten durchgehende Bruchstellen in der Verbindung zum Pluspol und teilweise zum Minuspol der Batterie auf. Die Analyse zeigte, dass der plötzliche Ausfall beider Pulsgeneratoren durch gebrochene Bonddrähte hervorgerufen wurde. Die elektrische Verbindung zur Batterie bestand nur noch durch die Federcharakteristik der Drähte. Ein mechanischer Stoß am Implantat bewirkte eine kurzzeitige Trennung von der Batterie, wodurch das Implantat in den Resetzustand versetzt wurde. Bedingt durch die Herstellung oder Konstruktion ist eine geringfügige Bewegung zwischen Batterie und Schaltkreis möglich, welche als Ursache dieses Problems angesehen werden kann.

Efficiency Calibration of a Si(Li) Detector by EPMA

A φ(ρz)-model, well known for its high accuracy, is employed for determining the detection efficiency of a Si(Li) detector by EPMA. Problems and advantages of this approach are pointed out and possible errors in the resulting thicknesses of the beryllium window, the silicon dead layer, the gold contact layer and the ice build-up on the detector surface are estimated. Furthermore the method allows the calculation of the cross section for L 3 subshell ionization to be made with high reliability.

CALCULATION OF THE SURFACE IONISATION USING ANALYTICAL MODELS OF ELECTRON BACKSCATTERING

The value of the surface ionisation for oblique incidence is calculated by testing various new approaches. A model based on a multiple reflection theory developed at the Institute for Applied and Technical Physics at the Technical University of Vienna is extended to oblique incidence by the use of a new fit for the angular distribution of backscattered electrons (according to data published by Kanter) under non-normal incidence. Furthermore two analytically derived models (proposed by Werner and Niedrig) are tested for their applicability to calculate the surface ionisation by numerical integration of the double differential backscattering coefficient versus angle and energy. The combined model of Werner is extended to oblique incidence to make a direct comparison possible. The results are compared with expressions published by Pouchou, by Cazaux and by Merlet; reasons for discrepancies are discussed; commonly used simplifications are reviewed critically.