Olaf Specht

Experiments on the mechanism of underwater hearing

Abstract Conclusion: The findings suggest that underwater sound perception is realized by the middle ear rather than by bone conduction, at least in shallow water conditions. Objective: To prove whether underwater sound perception is effected by bone conduction or by conduction via the middle ear. Methods: Five divers, breathing through snorkels, were tested in a swimming pool, to determine whether a sound was louder when the acoustic source placed was in front of the head in comparison with a lateral application facing the ear region. The second experiment investigated whether sound perception is influenced by ear protection plugs in underwater conditions. Also, the effect of a 5 mm thick neoprene hood was determined, with and without an additional perforation in the ear region. Results: Sounds were louder when applied from a position laterally facing the ear, louder without than with a protection plug, louder without than with a neoprene hood on, and louder when the neoprene hood had a perforation in the region of the ear than with an intact hood.

Wigner-Verteilung als Werkzeug zur Zeit-Frequenz-Analyse nichtstationärer Signale

In der Meßtechnik sind häufig Zeit-Frequenz-Analysen erforderlich. Für diese Spektralanalysen hat sich seit langer Zeit die Fourier transformation bewährt. Sollen allerdings instationäre, sich zeitlich schnell ändernde Signale analysiert werden, erweist sich die Fouriertransformation als ungeeignet. Für derartige Analysen wird heutzutage das Spektrogramm verwendet. Allerdings weist auch das Spektrogramm bei starken Instationaritäten Unschärfen auf. Das hier vorgestellte Verfahren, die Wigner-Verteilung, ermöglicht eine Zeit-Frequenz-Analyse instationärer Signale mit hoher Zeitund Frequenzauflösung. Es wird ein Überblick über diese Methode gegeben, und wesentliche Eigenschaften dieser Verteilung werden dargestellt. An Beispielen wird die Leistungsfähigkeit dieser Analysemethode illustriert.

Peri-implantitis cleaning instrumentation influences the integrity of photoactive nanocoatings

OBJECTIVE To determine in vitro the loss of integrity caused on photocatalytic anatase coated implant surfaces by clinical instrumentation through changes in surface topography and loss of functionality. METHODS Anatase-coated titanium discs were treated with diamond burs, polishers, plastic and metal hand instruments, air scaler and air flow devices. The pressure exerted through instrumentation was measured online. Surface topography was evaluated through scanning electron microscopy and contact profilometry, surface function through hydrophilization capacity upon UV-A activation. RESULTS Treatment with diamond burs and instruments with metal tips resulted in an increase of roughness. Use of silicone polishers led to smoothening, which was more pronounced on the anatase surface. Plastic instruments, the air abrasive system and rubber cups left the surfaces intact. Functionality was partially lost on surfaces subjected to hand instruments and completely lost upon diamond burs and silicone polishers. SIGNIFICANCE The integrity of functional nanocoatings depends on the applied instrumentation. Air flow device, rubber cup with polishing paste and plastic tipped instruments prevent damage on these nanosurfaces and may be preferably used when decontaminating anatase and other nanocoatings in a clinical setting.

Materialographische Untersuchungen an Dentalwerkstoffen

Kurzfassung Aufgrund der demographischen Entwicklung steigt der Bedarf an geeigneten Werkstoffen und Biomaterialien für die Zahnerhaltung und auch für den Zahnersatz kontinuierlich. Im Fokus stehen hierbei Werkstoffe, die aufgrund ihrer physikochemischen, mechanischen und biologischen Eigenschaften die Qualität und Langlebigkeit in den Bereichen der minimalinvasiven Prophylaxe, Füllungstherapie, zahnärztlichen Prothetik und Implantologie signifikant verbessern. Nur durch die Kombination verschiedener mikroskopischer Untersuchungsverfahren ist es möglich, die Struktur-Eigenschaftskorrelation detailliert zu untersuchen und zu charakterisieren. Somit können die Funktionalitätsparameter der Werkstoffe optimiert werden, um dentale Werkstoffe mit optimierten Eigenschaften zu entwickeln.

Correlation of ultrasound microscopy and Vickers hardness measurements of human dentin and enamel — A pilot study

OBJECTIVE To investigate if Vickers microhardness of dentin and enamel correlated with acoustic velocity c(l) or acoustic reflection from the samples top (amplitude). METHODS Eight transversal sections of a sound human tooth were investigated with scanning acoustic microscopy (SAM) and Vickers microhardness measurements. Longitudinal acoustic velocity c(l), amplitude and microhardness MHV were evaluated and for each c(l) test point corresponding amplitude and MHV were linearly interpolated and graphically analyzed. Spearman rank order correlation (rS) was calculated (p<0.05). RESULTS c(l) was predominantly 6100-7000ms-1 in enamel and 3800-4600ms-1 in dentin and correlated significantly with MHV with 27-420 in enamel and 20-90 in dentin (rs=0,57). Amplitudes significantly correlated with MHV, too, but even better (rs=0,77). SIGNIFICANCE Acoustic velocity and amplitudes were appropriate to detect microhardness differences of dentin and enamel and certain value ranges of both could be assigned to certain MHV ranges. Further research is needed to differentiate more precisely between the different hard tooth tissues.

In vitro investigation of the radial compliance of porcine carotid arteries

Abstract The regaining elastic behavior of the artery after treatment with a bioresorbable scaffold is a measure for successful degradation. The investigation of the elastic properties of arteries is often performed using ultrasound based methods. The current study describes an in vitro test setup for the measurement of the elastic radial compliance of blood vessels with an automated laser scanning device. A porcine carotid artery was placed inside a phosphate buffered saline filled chamber and the outer diameter was measured during stepwise pressurization from 20 mmHg to 160 mmHg. Reference measurements were done with an ultrasound based method. The results show that the automated laser scanning device method provides similar values to the ultrasound measurements. Therefore, the automated laser scanning device method appears to be suitable to investigate radial compliance differences of a stented vessel segment during the degradation process of a bioresorbable scaffold in vitro. The high degree of automation allows for an effective investigation of a larger series of measurements.

Balloon-based measuring system for compliance investigations

Abstract For the development of new stent designs, the compliance of the surrounding biological tissue has to be considered. We expect to obtain parameters for simulation, stent dimensioning, and the forces acting on the stent after implantation. Starting point of the investigations is the commercially available Metricath system allowing cross-sectional lumen area measurements of arteries. Its working principle is based on the pressure-volume relationship using a balloon catheter, which is inflated to a specific pressure of about 250 mmHg and conforms to the shape and size of the lumen. However, for compliance charts multiple pressure levels and a larger pressure range are needed. To overcome this technical limitation, the Metricath balloon catheter is combined with a new inflation device, called pV-Monitor. The presented cross-sectional lumen area measurements in rigid tubes and compliance investigations of elastic tubes demonstrate the feasibility of the pV-Monitor system.

Materialographic Examination of Three Different Types of Failed Dental Implants

Abstract Focused on tissue interactions and the properties of the materials themselves, the causes of dental implant failure can be analysed successfully using methods developed within materials science. This will be exemplified by three failing implants. The implants represent a broad range of materials (titanium, PEEK, zirconium dioxide) and geometries (screw, cylindrical, disc). Materials and methods: Following appropriate specimen collection and preparation, EDX, ESEM, light microscopy and ultrasound examinations were performed. Since only the titanium implant exhibited osseointegration, the implant-bone interface of this implant was additionally analysed by FIB-TEM. Results: The absence of bone tissue residue on the zirconium dioxide and PEEK implants was confirmed by all imaging methods. Complete osseointegration is demonstrable only for a complete fragment of the titanium implant resected from the jaw bone, with a bone-to-metal contact of 82.5 %. Conclusion: A bioactive interaction with the target tissues was found only for the titanium implant. The loss of the titanium implant examined was due to a material failure. High-frequency ultrasonic microscopy has proven a suitable tool for the assessment of osseointegration. A reduced sample preparation effort and an ability to use ultrasound in situ would suggest that ultrasonic microscopy technology is a suitable technology for failure analysis.

Online Detection of Stent Fractures in Durability Tests by Monitoring the Electrical Resistance

New stent designs must be tested for fatigue resistance before approval for the medical application. Testing under worst-case loading conditions may lead to fractures. For assessment it is important to detect when or after how much test cycles the first strut fractures occur. The monitoring of the electrical resistance is an online method for fracture detection during the fatigue test. This article describes the investigation of a proof of principle of a potential compensation technique for measuring the resistance change at a stent structure break and a nonwelding technology for electrically contacting the metal stent.

Dental Ultrasound Diagnostics – a Simulation Study

Avoiding X-ray exposure makes an ultrasound system for the dental diagnosis strongly desirable. In comparison to standard ultrasound techniques for soft tissue further challenges have to be solved. Primarily the local variation of the sound speed and the high absorption rates of dental material are challenging. This study shows based on simulated ultrasonic data that in principle it is possible to image teeth with ultrasound. But for applying the ultrasound in dental practice further developments especially to improve the image resolution are necessary.