M. Frotscher

Pilot study of modification of the bilateral sagittal split osteotomy (BSSO) in pig mandibles

OBJECTIVE This study investigated a new technique for the bilateral sagittal split osteotomy (BSSO) by adding a new osteotomy line at the inferior border of the mandible in the Obwegeser-Dal Pont operation. MATERIAL AND METHODS For this purpose a test system was designed and 100 pig mandibles were split to assess the tests reliability, to compare the torque necessary to split the mandible in both techniques and to record the fracture lines. The splitting technique was standardized, avoiding any contact with the inferior alveolar nerve. All outcomes were statistically examined by paired t-tests. RESULTS By using the new technique, we demonstrated a decrease in the torque force required to split the mandible of 29.7% (t(69)=-12.68; p<0.05, paired t-test) compared to the Obwegeser-Dal Pont technique. The fracture lines were close to ideal. CONCLUSION The additional osteotomy facilitates the BSSO technique and it reduces the likelihood of bad splits and damage to the inferior alveolar nerve in pig mandibles.

Achieving Small Structures in Thin NiTi Sheets for Medical Applications with Water Jet and Micro Machining: A Comparison

NiTi shape memory alloys (SMA) are used for a variety of applications including medical implants and tools as well as actuators, making use of their unique properties. However, due to the hardness and strength, in combination with the high elasticity of the material, the machining of components can be challenging. The most common machining techniques used today are laser cutting and electrical discharge machining (EDM). In this study, we report on the machining of small structures into binary NiTi sheets, applying alternative processing methods being well-established for other metallic materials. Our results indicate that water jet machining and micro milling can be used to machine delicate structures, even in very thin NiTi sheets. Further work is required to optimize the cut quality and the machining speed in order to increase the cost-effectiveness and to make both methods more competitive.

Modification of the bilateral sagittal split osteotomy (BSSO) in a study using pig mandibles

In a bilateral sagittal split osteotomy (BSSO) mechanical irritation of the inferior alveolar nerve (IAN) (e.g. by chiselling) should be avoided to prevent neural damage. A modification of the Obwegeser-Dal Pont operation technique was studied by splitting 100 pig mandibles ex vivo. An additional osteotomy at the caudal border of the mandible was used to facilitate the sagittal split by means of a locus of minor resistance. The chisel was inserted distal to the second molar and far away from the IAN. The mandible was split by torque. The modified technique reduced the required torque to split the mandible about 30% compared with the original technique (paired t-test, t(69)=-12.89; p<0.05). 75% of all mandibles split by the modified technique were classified as bad splits compared with 100% using the original technique using the same protocol without the additional osteotomy.

Design and fabrication of a bending rotation fatigue test rig for in situ electrochemical analysis during fatigue testing of NiTi shape memory alloy wires

The current investigation proposes a novel method for simultaneous assessment of the electrochemical and structural fatigue properties of nickel-titanium shape memory alloy (NiTi SMA) wires. The design and layout of an in situ electrochemical cell in a custom-made bending rotation fatigue (BRF) test rig is presented. This newly designed test rig allows performing a wide spectrum of experiments for studying the influence of fatigue on corrosion and vice versa. This can be achieved by performing ex situ and∕or in situ measurements. The versatility of the combined electrochemical∕mechanical test rig is demonstrated by studying the electrochemical behavior of NiTi SMA wires in 0.9% NaCl electrolyte under load. The ex situ measurements allow addressing various issues, for example, the influence of pre-fatigue on the localized corrosion resistance, or the influence of hydrogen on fatigue life. Ex situ experiments showed that a pre-fatigued wire is more susceptible to localized corrosion. The synergetic effect can be concluded from the polarization studies and specifically from an in situ study of the open circuit potential (OCP) transients, which sensitively react to the elementary repassivation events related to the local failure of the oxide layer. It can also be used as an indicator for identifying the onset of the fatigue failure.

Nanoindentation of pseudoelastic NiTi containing Ni4Ti3 precipitates

Abstract Depending on the processing method, pseudoelastic NiTi alloys can have small, lenticular Ni4Ti3 precipitates; however, the mechanical properties of these precipitates are not well understood. By performing nanoindentation with a spherical indenter, Ni4Ti3 precipitates within a pseudoelastic NiTi alloy were examined. Scanning electron microscopy was used to examine the indents after nanoindentation. After unloading, the hardness and remnant depth ratios of the indents in the Ni4Ti3 precipitates, the NiTi matrix, and the “average” NiTi alloy were compared. To decouple the effects of elasticity from those of pseudoelasticity, similar nanoindentation experiments were performed on an NiAl sample and compared with results from the NiTi sample.

Elektronenmikroskopische Untersuchung der Mikrostruktur von pseudoelastischen NiTi-Stents

Kurzfassung Nickel-Titan-Formgedächtnislegierungen (NiTi-FGL) werden seit einigen Jahren kommerziell erfolgreich eingesetzt. Insbesondere im Bereich der Medizintechnik gibt es zahlreiche Anwendungen, bei denen sich NiTi etabliert hat. Ein Beispiel dafür sind Gefäßprothesen (Stents). Auch wenn NiTi-Stents zur Zeit nur einen Anteil von cirka 12% der weltweit mehr als 3,5 Millionen implantierten Stents pro Jahr ausmachen, wird der Markt für endo- und kardiovaskuläre Stents 2006 ein Volumen von 5,5 Milliarden Euro überschreiten [1, 2]. Bei der Stent-Produktion entstehen Oberflächendefekte, welche unter Ermüdungsbeanspruchung zur Rissbildung beitragen können. Für die Hersteller von Stents sind daher Oberflächenqualität und Mikrostruktur mit Hinblick auf die funktionalen Eigenschaften und Ermüdungsbeständigkeit wichtige Faktoren. In der vorliegenden Arbeit wurden NiTi-Stents mit Hilfe von raster- sowie transmissionselektronenmikroskopischen (TEM) Methoden untersucht. Die Probenpräparation für TEM-Untersuchung wurde mit Hilfe einer Fokussierbaren Ionenstrahlanlage (FIB) durchgeführt, weil aufgrund der geringen Dimensionen eine andere Probenpräparation extrem schwierig ist. Dieses Verfahren wird ausführlich beschrieben und die Ergebnisse diskutiert.

Recent Developments and Challenges in Shape Memory Technology

Nickel-Titanium-based alloys (NiTi) represent structural materials with actor and sensor functions due to their shape memory properties. This is especially useful for actuator applications, e.g. in valves or switches. A temperature sensor is no longer needed because the material can be set to exhibit the shape memory effect at a given temperature in a certain temperature range. High actuator forces and strains can be generated in a small material volume, which is ideal for the miniaturization of technical devices. Recent developments and technological challenges in shape memory technology with a focus on the research of the interdisciplinary Center for Shape Memory Technology (SFB 459 - Formgedachtnistechnik) at the Ruhr-University Bochum are discussed.