Vicente Tadeu Lopes Buono

Fatigue Resistance of Engine-Driven Rotary Nickel- Titanium Endodontic Instruments

A comparative study of the fatigue resistance of engine-driven nickel-titanium endodontic instruments was performed, aiming to access the influence of the cutting flute design and of the size of the files that reach the working length in curved canal shaping. Geometrical conditions similar to those found in practice were used. Series 29 #5 ProFile, together with #6 and #8 Quantec instruments, were tested in artificial canals with a 45-degree angle of curvature and 5-mm radius of curvature. It was observed that the size of the instrument, which determines the maximum strain amplitude during cyclic deformation, is the most important factor controlling fatigue resistance. The effect of heat sterilization on the fatigue resistance of the instruments was also examined. The results obtained indicate that the application of five sterilization procedures in dry heat increases the average number of cycles to failure of unused instruments by approximately 70%.

The influence of copper addition on the formability of AISI 304 stainless steel

The formability of AISI 304 austenitic stainless steel can be enhanced when it is designed to transform to martensite under appropriate strain levels, gaining additional plasticity (transformation induced plasticity). In this work, the effects of a partial substitution of Ni by Cu on the formability of AISI 304 steel were analyzed in terms of microstructure changes during tensile straining. Conventional metallographic techniques aided by scanning probe microscopy were employed to identify and characterize the stress-induced martensitic phases. The results obtained are discussed in terms of the relationship between chemical composition and the stability of austenite, taking into account the stacking fault energy and the characteristics of stress-induced martensite in these steels. It has been observed that the partial substitution of Ni by Cu gave rise to an increase in the strain level required to induce martensitic transformation, resulting in higher maximum uniform elongation and better stretch formability.

Flexibility and Torsional Strength of ProTaper and ProTaper Universal Rotary Instruments Assessed by Mechanical Tests

The purpose of this study was to assess how the geometric and dimensional changes made on ProTaper Universal (PTU) instruments in comparison with ProTaper (PT) instruments affected their flexibility and torsional strength. Two groups (n = 12) of each type of shaping (S1 and S2) and finishing (F1, F2, and F3) for both PT and PTU instruments were employed. Tip angle, instrument diameter at each millimeter, and cross-sectional area at 3 mm from the tip were the dimensional parameters measured. Flexibility and torsional strength of each instrument (n = 12) were assessed according to specification ISO 3630-1. Data were analyzed using analysis of variance (alpha = 0.05). Flexibility increased for S1 and F1 PTU instruments and decreased for F2 and F3, whereas torsional resistance increased for S2, F2, and F3. Changes in tip angle were accompanied by variation of tip geometry in all instruments.

Flexural Fatigue and Torsional Resistance of ProFile GT and ProFile GT Series X Instruments

INTRODUCTION The purpose of this study was to compare the flexural fatigue and torsional resistance of ProFile GT and GT Series X instruments, taking into account their structural and dimensional characteristics. METHODS Instrument diameter at each millimeter from the tip and pitch length were the dimensional parameters measured. Chemical composition was determined by energy-dispersive x-ray spectroscopy and phase constitution by x-ray diffraction. Vickers microhardness measurements were performed to assess instrument strength. One group of 20/.06 GT and GTX instruments (n = 10 each) was tested until failure in a flexural fatigue test device, whereas another group of 20/.04 files (n = 10 each) was tested in torsion based on ISO 3630-1. RESULTS GT and GTX instruments showed approximately the same chemical composition, namely 51at%Ni-49at%Ti (56wt%Ni-44wt%Ti) and contained mainly the beta-phase. GTX instruments showed higher intensity x-ray diffraction peaks and a statistically higher Vickers microhardness. There was a significant decrease in the diameter of GTX in relation to GT instruments from D6 to D9 for 20/.04 instruments and from D4 to D7 for 20/.06 instruments. Pitch length increased along the active part of both instruments, with a steeper increase in GTX. In general, GT Series X instruments were significantly more resistant to flexural fatigue than were similar GT instruments (p < 0.001) but exhibited lower torsional strength (p < 0.001). CONCLUSIONS Different structural and dimensional characteristics were found in GTX instruments in comparison with GT instruments; this is probably the cause for their higher flexural fatigue resistance and lower torsional strength.

Influence of cyclic torsional loading on the fatigue resistance of K3 instruments

AIM To evaluate the influence of cyclic torsional loading on the flexural fatigue resistance and torsional properties of rotary NiTi instruments. METHODOLOGY Twelve sets of new K3 instruments, sizes 20, 25 and 30 with an 0.04 taper, and sizes 20 and 25 with an 0.06 taper, were torsion tested until rupture, to establish their mean values of maximum torque and angular deflection. Twelve new K3 instruments of each of the following dimensions, size 30, 0.04 taper and sizes 20 and 25 with 0.06 taper, were tested to failure by rotation bending in a fatigue test device. Cyclic torsional loading was performed in 20 cycles from zero angular deflection to 180 degrees and then return to zero applied torque. After cyclic loading, the same number of instruments were tested until rupture in torsion and flexural fatigue. Data obtained were subjected to a one way analysis of variance (anova) at 95% confidence level. RESULTS Cyclic torsional loading caused no significant differences in maximum torque or in maximum angular deflection of the instruments analysed, but comparative statistical analysis between measured NCF values of new and previously cycled K3 instruments showed significant differences for all tested instrument. Longitudinal cracks, that is, cracks apparently parallel to the long axis of the instruments cycled in torsion was observed. CONCLUSIONS Cyclic torsional loading experiments in new K3 rotary endodontic instruments showed that torsional fatigue decreased the resistance of these instruments to flexural fatigue, although it did not affect their torsional resistance.

Dimensional characterization and mechanical behaviour of K3 rotary instruments.

AIM To correlate the mechanical behaviour in torsion, bending and fatigue tests of K3 instruments with their dimensional characteristics. METHODOLOGY Instrument length, tip angle, distance between blades (pitch length) and the diameter at each millimetre from the tip of sizes 20, 25 and 30, 0.04 taper and sizes 20 and 25, 0.06 taper K3 rotary instruments were measured in an optical microscope equipped with digital micrometers. The cross-sectional area at 3 mm from the tip of the same instruments was determined using digital image analysis of scanning electron microscopy images. Maximum torque and angular deflection, as well as bending moment at 45 degrees were measured according to specification of ISO 3630-1. Fatigue resistance of instruments size 30, 0.04 taper, and sizes 20 and 25, 0.06 taper was determined in a fatigue test bench device. RESULTS The analysed instruments presented no uniformity in the distance between adjacent blades, but the measured diameters at each millimetre from the tip were regular, showing compliance with manufacturing standards. Torque and bending moment of the tested instruments increased significantly with diameter and cross-sectional area at 3 mm from the instrument tip. The fatigue resistance of the instruments showed a tendency to decrease as the diameter of the instruments increased. CONCLUSIONS The bending moment at 45 degrees and the torsional resistance of K3 instruments can be predicted using instrument diameter and cross-sectional area at 3 mm from the tip. Fatigue resistance decreased as the instrument diameter increased.

Mechanical behavior of M-Wire and conventional NiTi wire used to manufacture rotary endodontic instruments

OBJECTIVE Comparison of physical and mechanical properties of one conventional and a new NiTi wire, which had received an additional thermomechanical treatment. METHODS Specimens of both conventional (NiTi) and the new type of wire, called M-Wire (MW), were subjected to tensile and three-point bending tests, Vickers microhardness measurements, and to rotating-bending fatigue tests at a strain-controlled level of 6%. Fracture surfaces were observed by scanning electron microscopy and the non-deformed microstructures by transmission electron microscopy. RESULTS The thermomechanical treatment applied to produce the M-Wire apparently increased the tensile strength and Vickers microhardness of the material, but its apparent Young modulus was smaller than that of conventionally treated NiTi. The three-point bending tests showed a higher flexibility for MW which also exhibited a significantly higher number of cycles to failure. SIGNIFICANCE M-Wire presented mechanical properties that can render endodontic instruments more flexible and fatigue resistant than those made with conventionally processed NiTi wires.

HYDROTHERMAL SYNTHESIS AND SINTERING OF NICKEL AND MANGANESE-ZINC FERRITES

The influence of the starting materials on the crystalline phases observed after hydrothermal synthesis of nickel and manganese-zinc ferrites was investigated. The combination of sulfates and sodium hydroxide showed the best results for the conditions studied. The morphological parameters of MnZn ferrites produced at different hydrothermal conditions (110–190 °C, 4–30 h) were analyzed. Changes in lattice parameter, particle size, density, size and total volume of pores, and in the surface area of the particles were analyzed as a function of temperature and processing time. The sintering process was employed in order to verify the reactivity of the hydrothermal powders at controlled atmosphere. High density and surface homogeneous ceramic bodies were obtained, without zinc volatilization. Lattice parameter variations were associated with changes in the cations distribution of the spinel during sintering.

Impact of Heat Treatments on the Fatigue Resistance of Different Rotary Nickel-titanium Instruments

INTRODUCTION The aim of this study was to assess the influence of M-Wire (Dentsply Tulsa Dental Specialties, Tulsa, OK) and controlled memory technologies on the fatigue resistance of rotary nickel-titanium (NiTi) files by comparing files made using these 2 technologies with conventional NiTi files. METHODS Files with a similar cross-sectional design and diameter were chosen for the study: new 30/.06 files of the EndoWave (EW; J. Morita Corp, Osaka, Japan), HyFlex (HF; Coltene/Whaledent, Inc, Cuyahoga Falls, OH), ProFile Vortex (PV; Dentsply Tulsa Dental Specialties, Tulsa, OK), and Typhoon (TYP; Clinicians Choice Dental Products, New Milford, CT) systems together with ProTaper Universal F2 instruments (PTU F2; Dentsply Maillefer, Ballaigues, Switzerland). The compositions and transformation temperatures of the instruments were analyzed using x-ray energy-dispersive spectroscopy and differential scanning calorimetry, whereas the mean file diameter values at 3 mm from the tip (D3) were measured using image analysis software. The average number of cycles to failure was determined using a fatigue test device. RESULTS X-ray energy-dispersive spectroscopy analysis showed that, on average, all the instruments exhibited the same chemical composition, namely, 51% Ni-49% Ti. The PV, TYP, and HF files exhibited increased transformation temperatures. The PTU F2, PV, and TYP files had similar D3 values, which were less than those of the EW and HF files. The average number of cycles to failure values were 150% higher for the TYP files compared with the PV files and 390% higher for the HF files compared with the EW files. CONCLUSIONS M-Wire and controlled memory technologies increase the fatigue resistance of rotary NiTi files.

Measurement of fine pearlite interlamellar spacing by atomic force microscopy

Pearlite interlamellar spacing is an important parameter controlling ductility and strain hardening of carbon steels. Fine pearlite is the appropriate initial microstructure for drawing high carbon steel with exponential strain hardening rate, leading to high final tensile strengths. The majority of optical and electron microscopy methods for measuring interlamellar spacing present difficulties when applied to fine microstructures. Atomic force microscopy (AFM) was employed to investigate pearlitic steels lead patented at 510 °C and then cold drawn to 86% reduction in area. Conventional specimen preparation techniques for optical metallography were appropriated to produce high resolution AFM images, on which measurements of minimum interlamellar spacing, in good agreement with spacings estimated using the Embury–Fisher model, were easily performed.