K3 ENDO, PRO TAPER, AND PRO FILE SYSTEMS: BREAKAGE AND DISTORTION IN SEVERELY CURVED ROOTS OF MOLARS.By Matthew T. Ankrum, D.D.S.A Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science at Virginia Commonwealth University.Virginia Commonwealth University, 2003Major Director: Gary R. Hartwell, D.D.S., M.S.Chairman and Professor, Department of EndodonticsIt was the aim of this study to investigate the incidence of file breakage and distortion when the Pro Taper, K3 Endo and ProFile systems were used to instrument canals in the severely curved roots of extracted molars.Forty-five roots of extracted mandibular and maxillary molars with curvatures between 40 and 75 degrees were chosen for use in this study. The roots in Group One were instrumented with the Pro File (PF) system and served as the control group. Roots in Group Two were instrumented with the Pro Taper (PT) system and those in Group Three were instrumented with the K3 Endo (K3) system. The three systems were used according to the manufacturers' instructions.The proportion of files distorted was 15.3% for the PF group, 2.4% for the PT group, and 8.3% for the K3 group. There was a statistically significant difference between the PF and PT groups (p = .0079). The percentage of broken files was 1.7% for the PF group, 6.0% for the PT group and 2.1% for the K3 group. No statistically significant differences were found between these three groups (p = .4243). The results of this study showed that these three rotary tapered systems were not significantly different with regard to breakage. There were significantly more distorted files in the PF group when compared to the PT group, with regard to distortion there was no significant difference between the PT and K3 and the PF and K3 groups.

O desenvolvimento de instrumentos endodônticos em ligas de níquel-titânio (Ni-Ti) derivou maior rapidez na modelagem do canal radicular o que nos leva a questionar se realmente estariam as substâncias químicas auxiliares tendo oportunidade de agir convenientemente, considerando que o tempo de atuação das mesmas foi significantemente encurtado. Tendo em vista esse aspecto foi objeto deste trabalho avaliar, com auxílio de microscopia eletrônica de varredura (MEV) e leituras computadorizadas, a limpeza da superfície dentinária radicular, terços cervical, médio e apical, em canais radiculares de incisivos inferiores humanos, preparados pelo sistema rotatório K3?ENDO diante do uso de hipoclorito de sódio a 2,5%, (pH 11,0), do creme de Endo PTC reagindo com hipoclorito de sódio a 0,5%, (pH 11,0), empregando-se essa substância em duas diferentes consistências; sua consistência normal (Endo PTC-N) e uma outra de menor densidade (Endo-PTC-L); e, de um gel de clorexidina (Endogel®) com dois tipos de irrigação final. Concluída a fase de preparo todos os grupos receberam irrigação-aspiração final com soluções de hipoclorito de sódio a 0,5%, (pH 11,0) e de EDTA-T a 17%, exceção feita ao grupo em que se empregou o Endogel®, para o qual seguiu-se dois regimes de irrigação, em um grupo, irrigação-aspiração final com 20 mL de soro fisiológico, conforme recomendações do fabricante e em outro grupo empregou-se irrigação com EDTA-T. As amostras foram então preparadas para MEV e suas imagens analisadas pelo programa Scion Image. Os resultados revelaram haver diferença estatisticamente significante entre os grupos, sendo que o grupo do Endo-PTC-L se mostrou superior aos demais grupos testados no terço médio e apical já o grupo do Endogel seguido da irrigação final com EDTA-T apenas no terço médio, não havendo diferença estatística entre eles. / The development of nickel-titanium (NiTi) endodontic instruments results in more quickness during the root canal shaping phase that induce us to discuss if really would be the chemical substances are having opportunities to act properly, considering that the time of action of the same was significantly reduced. The object of this research was evaluate, using the scanning electron microscopy (SEM) and computerized analysis, the cleaning on root canal walls in coronal, middle and apical thirds in mandibular human incisives prepared with K3 NiTi rotary instruments and different chemical substances: 2,5% sodium hypochlorite (pH 11,0), Endo PTC cream at normal consistency (Endo PTC-N) neutralized by 0,5% sodium hypochlorite (pH 11,0), Endo PTC cream with lower density (Endo PTC-L) neutralized by 0,5% sodium hypochlorite (pH 11,0) and chlorhexidine gel (Endogel). Concluded the cleaning and shaping phase, all the groups received a final irrigation with of 0,5% sodium hypochlorite solution (pH 11,0) followed by 17% EDTA-T solution, except the Endogel group that received two different regimens of final irrigation, one group with 20 ml of physiological serum and another with the 17% EDTA-T solution. The samples were prepared for the SEM analysis and the images obtained were analyzed using the Scion Image program. The results showed a significant difference between the groups tested seeing that the Endo PTC-L group, in middle and apical thirds and Endogel followed by the final irrigation with EDTA-T group, in middle third were superiors in comparation with the other groups.

Shape memory alloys (SMAs) are a unique class of smart materials exhibiting extraordinary properties with a wide range of applications in engineering, biomedical, and aerospace technologies. In this study, an advanced, efficient, low-cost, and highly scalable laser-assisted imprinting method with low environmental impact to create thermally controllable surface patterns is reported. Two different imprinting methods were carried out mainly on Ni50Ti50 (at. %) SMAs by using a nanosecond pulsed Nd:YAG laser operating at 1064 nm wavelength and 10 Hz frequency. First, laser pulses at selected fluences were directly focused on the NiTi surface, which generated pressure pulses of up to a few gigapascal (GPa), and thus created micro-indents. Second, a suitable transparent overlay serving as a confining medium, a sacrificial layer, and a mesh grid was placed on the NiTi sample, whereafter the laser was focused through the confinement medium, ablating the sacrificial layer to create plasma and pressure, and thus pushing and transferring the grid pattern onto the sample. Scanning electron microscope (SEM) and laser profiler images show that surface patterns with tailorable sizes and high fidelity could be obtained. The depth of the patterns was shown to increase and later level off with the increase in laser power and irradiation time. Upon heating, the depth profile of the imprinted SMA surfaces changed where the maximum depth recovery ratio of 30 % was observed. Recovery ratio decreased and saturated at about 15 % when the number of pulses were increased. A numerical simulation of the laser irradiation process was performed showing that considerably high pressure and temperature could be generated depending on the laser fluence. The stress wave closely followed the rise time of the laser pulse to its peak value and followed by the rapid attenuation and dispersion of the stress through the sample.

The bottom-up processing techniques used for making Microelectromechanical systems (MEMS) devices can produce material properties different from bulk processing. The material properties must be evaluated with the process parameters used and for changes in the process parameters. The mechanical properties are needed to design MEMS devices. A material of interest for MEMS devices is nickel titanium (NiTi) shape memory alloy (SMA) because of the high work output (~107 J/m3). This thesis will focus on the fabrication of thin film NiTi by DC magnetron sputtering deposition and testing mechanical properties of the fabricated films by nanoindentation. Thin film NiTi SMA was successfully created by DC magnetron sputtering deposition and high vacuum annealing in the Microfabrication Laboratory at California Polytechnic State University – San Luis Obispo. Characterization of the thin film by nanoindentation produced an elastic modulus of the thin film NiTi SMA with the developed processing parameters was 67.9 GPa with a hardness of 2.1 GPa. The measured thin film NiTi elastic modulus was greater than bulk NiTi of 40 GPa because of the residual stress from the deposition process. The shape memory effect was evaluated at the nanometer scale by measuring the nanoindents before and after thermally inducing a phase transformation. A maximum indentation depth recovery of 58% was measured upon the heat induced martensitic phase transformation. The low recovery was attributed to the high strain of 8% induced by the Berkovich tip. The effects of deposition power on the NiTi as-sputtered film stress, elastic modulus, hardness, and electrical conductivity were evaluated. At the highest sputtering deposition power of 450 Watts, an elastic modulus of 186 GPa with a hardness of 8.3 GPa was measured by nanoindentation. An increase in deposition power increased the residual film compressive stress, elastic modulus, and hardness while the electrical resistivity increased. The mechanisms for the measured properties are discussed in this thesis.

NiTiHf alloys have attracted considerable attention as potential high temperature Shape Memory Alloy (SMA) but the instability in transformation temperatures and significant irrecoverable strain during thermal cycling under constant stress remains a major concern. The main reason for irrecoverable strain and change in transformation temperatures as a function of thermal cycling can be attributed to dislocation formation due to relatively large volume change during transformation from austenite to martensite. The formation of dislocations decreases the elastic stored energy, and during back transformation a reduced amount of strain is recovered. All these observations can be attributed to relatively soft lattice that cannot accommodate volume change by other means. We have used Equal Channel Angular Extrusion (ECAE), hot rolling and marforming to strengthen the 49.8Ni-42.2Ti-8Hf (in at. %) material and to introduce desired texture to overcome these problems in NiTiHf alloys. ECAE offers the advantage of preserving billet cross-section and the application of various routes, which give us the possibility to introduce various texture components and grain morphologies. ECAE was performed using a die of 90º tool angle and was performed at high temperatures from 500ºC up to 650ºC. All extrusions went well at these temperatures. Minor surface cracks were observed only in the material extruded at 500 °C, possibly due to the non-isothermal nature of the extrusion. It is believed that these surface cracks can be eliminated during isothermal extrusion at this temperature. This result of improved formability of NiTiHf alloy using ECAE is significant because an earlier review of the formability of NiTiHf using 50% rolling reduction concluded that the minimum temperature for rolling NiTi12%Hf alloy without cracks is 700°C. The strain level imposed during one 90° ECAE pass is equivalent to 69% rolling reduction. Subsequent to ECAE processing, a reduction in irrecoverable strain from 0.6% to 0.21% and an increase in transformation strain from 1.25% to 2.18% were observed at a load of 100 MPa as compared to the homogenized material. The present results show that the ECAE process permits the strengthening of the material by work hardening, grain size reduction, homogeneous distribution of fine precipitates, and the introduction of texture in the material. These four factors contribute in the increase of stability of the material. In this thesis I will be discussing the improvement of mechanical behavior and stability of the material achieved after various passes of ECAE.

A testing method was developed to cycle quickly and repeatably Ni60Ti40 (wt. %) SMA specimens through temperature-induced transformation while under constant stress until failure. Previous works have shown fatigue cracks to initiate in or around Ni3Ti precipitates during repeated thermal cycling in this highly Ni-rich alloy. Actuation fatigue tests were conducted on specimens produced from material from different material suppliers and direction relative to cold-rolling. The specimens were placed under a constant applied stress of 200 MPa and thermally cycled through complete transformation. Some of the specimens were homogenized for 1 hour in a vacuum furnace and the rest were homogenized for 2 hours in a nitrogen furnace, and were all aged for 20 hours. It was seen during actuation fatigue testing that specimens homogenized for two hours had higher actuation strain, accumulated more irrecoverable strain and had longer actuation fatigue lives compared to specimens homogenized for one hour. Another trend observed was that specimens with the greatest amount of accumulated irrecoverable strain, which was caused predominately by transformation induced plasticity, had the longest actuation fatigue lives. Postmortem analysis showed a change in cracking behavior with precipitate orientation. Cracks initiated inside the Ni3Ti precipitates oriented parallel to the loading direction and at the interface between the precipitate and matrix when perpendicular. Two dimensional plane stress finite element simulations of a linear elastic ellipsoidal precipitate inside a non-linear transforming SMA matrix were conducted to explain further the change in cracking behavior by analyzing the stress fields in and around the precipitates. The results showed the stress inside the precipitate was greater when oriented parallel than perpendicular to the loading direction, which explains the observed change in cracking behavior. Another objective of actuation fatigue testing is to generate useful data to create predictive tools for future SMA actuator designs. A work-based method has been developed using actuation fatigue results found in literature. The method is shown to fit accurately data found in literature to a curve with only two material parameters. The results of this method show promise to predict accurately the actuation fatigue life of SMA components, however more testing is necessary to validate completely the method.

Effect of stress-assisted aging on stress induced martensitic transformation in hot-rolled Ni-rich 50.7at. Ni%-Ti alloy has been investigated. Alloys are aged freely and under 20 MPa, 100 MPa, and 200 MPa stress at 400 o C for 90 minutes. Aging procedure affected both stress-induced and thermally induced transformation behavior. Superelasticity behavior is correlated with the multistep transformation in aged Ni-rich NiTi alloys and the aging stress level is found to be effective. Relative to the free aged alloy, the alloy aged under 20 MPa exhibited a slight and the alloy aged under 100 MPa exhibited a considerable reduction, whereas the alloy aged under 200 MPa exhibited an increase in the critical transformation stress. DSC studies have shown that the transformation is multistep for freely aged and aged under 20 MPa alloys, whereas it is single step and two-step for alloys aged under 100 MPa and 200 MPa, respectively, and this has been attributed to the effect of stress on nucleation and growth rates. As a result of the different response mechanisms to the applied stress upon loading during superelasticity testing, the recovered strain amounts varied considerably depending on the aging conditions and the test temperatures.

NiTiHf alloys have attracted considerable attention as potential high temperature Shape Memory Alloy (SMA) but the instability in transformation temperatures and significant irrecoverable strain during thermal cycling under constant stress remains a major concern. The main reason for irrecoverable strain and change in transformation temperatures as a function of thermal cycling can be attributed to dislocation formation due to relatively large volume change during transformation from austenite to martensite. The formation of dislocations decreases the elastic stored energy, and during back transformation a reduced amount of strain is recovered. All these observations can be attributed to relatively soft lattice that cannot accommodate volume change by other means. We have used Equal Channel Angular Extrusion (ECAE), hot rolling and marforming to strengthen the 49.8Ni-42.2Ti-8Hf (in at. %) material and to introduce desired texture to overcome these problems in NiTiHf alloys. ECAE offers the advantage of preserving billet cross-section and the application of various routes, which give us the possibility to introduce various texture components and grain morphologies. ECAE was performed using a die of 90º tool angle and was performed at high temperatures from 500ºC up to 650ºC. All extrusions went well at these temperatures. Minor surface cracks were observed only in the material extruded at 500 °C, possibly due to the non-isothermal nature of the extrusion. It is believed that these surface cracks can be eliminated during isothermal extrusion at this temperature. This result of improved formability of NiTiHf alloy using ECAE is significant because an earlier review of the formability of NiTiHf using 50% rolling reduction concluded that the minimum temperature for rolling NiTi12%Hf alloy without cracks is 700°C. The strain level imposed during one 90° ECAE pass is equivalent to 69% rolling reduction. Subsequent to ECAE processing, a reduction in irrecoverable strain from 0.6% to 0.21% and an increase in transformation strain from 1.25% to 2.18% were observed at a load of 100 MPa as compared to the homogenized material. The present results show that the ECAE process permits the strengthening of the material by work hardening, grain size reduction, homogeneous distribution of fine precipitates, and the introduction of texture in the material. These four factors contribute in the increase of stability of the material. In this thesis I will be discussing the improvement of mechanical behavior and stability of the material achieved after various passes of ECAE.

Repair and remodeling of bone during healing and fusion require a combination of bone resorption and formation to successfully restore the bone to its previous strength. The healing process is highly responsive to the mechanical conditions of the construct, where excessive loading can cause high strains that delay healing, but moderate loading can be beneficial. Maintaining compression at the site of fracture can benefit healing by maintaining bone congruency and increasing the stability of the bone-implant construct to prevent excessive shifting. For these reasons, compressive mechanisms are employed in many orthopaedic devices, including both intramedullary (IM) nails and external fixators for ankle arthrodesis applications. Tibiotalocalcaneal (TTC) arthrodesis is a salvage procedure that fuses both the ankle and the subtalar joints. It has become the standard of care in ankle degeneration, which can be brought on by posttraumatic arthritis, failed total ankle arthroplasty, or diabetic conditions such as Charcot arthropathy. While current devices are effective in many cases, TTC arthrodesis procedures still incur failure rates as high as 22%, where failure of the bones to successfully fuse can result in amputation. Because bone healing relies upon bone resorption, the initial compression applied to the implanted constructs can be quickly lost, which may sacrifice the stability of the structure and delay or inhibit further healing. By employing a mechanism that can sustain compression during the bone healing process, it was possible to increase the stability of the construct even during bone resorption, minimizing the failures that still occur. The focus of this study was to determine the effects of compression on the mechanical stability of the implant-bone construct found in TTC arthrodesis. A comparison was made between the torsional stability of two currently marketed intramedullary devices, as well as a prototype IM device comprised of a nickel titanium core, designed to hold constant compression for up to 9mm of resorption. Additionally, the stability of each construct over time was evaluated by correlating bone resorption to a loss in compressive force.

The purpose of this research was to investigate the surface modifications that take place during the machining of NiTi SMA and Ti-6Al-4V with micro-EDM. This was done by creating an array of blind holes and micro-patterns on both work-pieces. To analyze the machined surface and investigate the results, scanning electron microscope (SEM), energy dispersive X- ray spectroscopy (EDS) and X-ray diffraction (XRD) techniques were employed. In addition, the effects of various operating parameters on the machining performance was studied to identify the optimum parameters for micro-EDM of NiTi SMA and Ti-6Al-4V. Recently, aerospace and biomedical industries have placed a high demand on nonconventional machining processes, which can be used to machine high strength and hardto- cut materials such as Titanium alloys, Shape Memory Alloys (SMA) and Super Alloys. Electrical Discharge Machining (EDM) is one of the non-traditional technologies that remove materials from the workpiece through a series of electrical sparks that occur between the workpiece and cutting tool with the presence of dielectric liquid. Obtaining smooth and defect-free surfaces on both workpieces was one of the challenges due to the re-solidified debris on the machined surface. The experimental results showed that there was significant amount of re-casting and formation of resolidification of debris on the Ti surface after machining. On the other hand, the surface generated in NiTi SMA were comparatively smoother with lesser amount of resolidified debris on the surface. By analyzing the results from XRD and EDS, some elements of electrode and dielectric materials such as Tungsten, Carbon and Oxygen were observed on NiTi and Ti surface after machining. In the study of effect of operating parameters, it was found that the voltage, capacitance and tool rotational speed had significant effect on machining time. The machining time was reduced by increasing the voltage, capacitance and tool rotational speed. The machining time was found to be comparatively higher for machining NiTi SMA than Ti alloy. Comparing all the parameters, the voltage of 60 V, capacitance of 1000 PF, and tool rotational speed of 3500 RPM were selected as optimum parameters for this study. Although signs of tool electrode wear and debris particles on the machined surface were observed for both workpieces during the micro-EDM process, Ti alloy and NiTi SMA could be machined successfully using the micro-EDM process.