Abrasion wear resistance of different artificial teeth opposed to metal and composite antagonists

One of the most important properties of artificial teeth is the abrasion wear resistance, which is determinant in the maintenance of the rehabilitation's occlusal pattern. OBJECTIVES: This in vitro study aims to evaluate the abrasion wear resistance of 7 brands of artificial teeth opposed to two types of antagonists. MATERIAL AND METHODS: Seven groups were prepared with 12 specimens each (BIOLUX & BL, TRILUX & TR, BLUE DENT & BD, BIOCLER & BC, POSTARIS & PO, ORTHOSIT & OR, GNATHOSTAR & GN), opposed to metallic (M & nickel-chromium alloy), and to composite antagonists (C & Solidex indirect composite). A mechanical loading device was used (240 cycles/min, 4 Hz speed, 10 mm antagonist course). Initial and final contours of each specimen were registered with aid of a profile projector (20x magnification). The linear difference between the two profiles was measured and the registered values were subjected to ANOVA and Tukey's test. RESULTS: Regarding the antagonists, only OR (M = 10.45 ± 1.42 µm and C = 2.77 ± 0.69 µm) and BC (M = 6.70 ± 1.37 µm and C = 4.48 ± 0.80 µm) presented statistically significant differences (p < 0.05). Best results were obtained with PO (C = 2.33 ± 0.91 µm and M = 1.78 ± 0.42 µm), followed by BL (C = 3.70 ± 1.32 µm and M = 3.70 ± 0.61 µm), statistically similar for both antagonists (p>0.05). Greater result variance was obtained with OR, which presented the worse results opposed to Ni-Cr (10.45 ± 1.42 µm), and results similar to the best ones against composite (2.77 ± 0.69 µm). CONCLUSIONS: Within the limitations of this study, it may be concluded that the antagonist material is a factor of major importance to be considered in the choice of the artificial teeth to be used in the prosthesis.

Particle size effect on abrasion resistance of mottled cast iron with different retained austenite contents

Effects of particle abrasive sizes on wear resistance of mottled cast iron with different retained austenite contents were studied. Abrasive wear tests using a pin test on alumina paper were carried out, using abrasive sizes between 16 mu m and 192 mu m. Retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of samples and the alumina paper were examined by scanning electron microscopy for identifying the wear micromechanism. The results show that at lower abrasive sizes the mass loss was similar for the iron with different austenite contents. However, at higher abrasive sizes the samples with higher retained austenite content presented higher abrasion resistance. For lower abrasive sizes tested, samples with higher and lower retained austenite content both presented microcutting. On the other hand, the main wear micromechanism for the samples with higher retained austenite content and higher abrasive sizes was microploughing. The samples with lower retained austenite content presented microcutting and wedge formation at higher abrasive sizes. Higher abrasive size induced more microcutting in samples with lower retained austenite. The iron with lower retained austenite content presented wider grooves for the different abrasive sizes measured. SEM on the abrasive paper used on samples with higher retained austenite showed continuous and discontinuous microchips and the samples with lower retained austenite showed discontinuous microchips at 66 and 141 mu m. This research demonstrates the relation between abrasive size, wear resistance, groove width and wear micromechanism for mottled cast iron with different retained austenite contents. (C) 2009 Elsevier B.V. All rights reserved.

Mild and severe wear of steels and cast irons in sliding abrasion

This paper presents the results obtained in pin-on-disk test apparatus using glass and alumina as abrasive materials, showing the rates and mechanisms of abrasive wear of 1070 and 52100 steels, and ductile and white cast irons. The test conditions were selected in order to obtain wear rates that correspond to mild and severe abrasion, using different metal hardness-to-abrasive hardness ratios(H/H(A)) and 0.2 or 0.06 mm abrasive grains. The use of bulk Vickers hardness, instead of microhardness, allows a better description of the different abrasion regions. Under severe abrasion, the microcutting mechanism of wear prevailed together with friction coefficients larger than 0.4. On the other hand, when relatively soft abrasives are tested, indentation of abrasive particles followed by its fragmentation, and a creation of a thin deformed layer were the main damage mechanisms, with the friction coefficient lying below 0.4. The abrasive particle size under mild regime is able to change the wear rates in an order of magnitude. (C) 2009 Elsevier B.V. All rights reserved.

In vitro wear resistance of three types of polymethyl methacrylate denture teeth

The wear resistance of denture teeth is important to the longevity of removable prostheses of edentulous patients. The ability of denture teeth to maintain a stable occlusal relationship over time may be influenced by this property. The purpose of this in vitro study was to evaluate the wear resistance of polymethyl methacrylate (PMMA) denture teeth based on their chemical composition when opposed by a ceramic antagonist. The maxillary canines (n=10) of 3 PMMA denture teeth (Trubyte Biotone, cross-linked PMMA; Trilux, highly cross-linked IPN (interpenetrating polymer network)-PMMA; and Vivodent, highly cross-linked PMMA) were secured in an in vitro 2-body wear-testing apparatus that produced sliding contact of the specimens (4.5 cycles/s, sliding distance of 20 mm, under 37°C running water) against glazed or airborne particle abraded ceramic. Wear resistance was measured as height loss (mm) under 300 g (sliding force) after 100,000 cycles, using a digital measuring microscope. Mean values were analyzed by 2-way ANOVA and Tukey's test (a=0.05). The wear of Trubyte Biotone (0.93 ± 0.14 mm) was significantly higher than that of both other types of teeth tested against abraded ceramic (p<0.05). The Vivodent tooth (0.64 ± 0.17 mm) exhibited the best wear resistance among the denture teeth tested against airborne particle abraded ceramic. There were no statistically significant differences (p>0.05) in wear among the 3 denture teeth evaluated against glazed ceramic. Trilux and Vivodent teeth tested against either glazed or airborne particle abraded ceramic did not differ significantly from each other (p<0.05). All teeth showed significantly more wear against airborne particle abraded ceramic than against glazed ceramic (p<0.05). In conclusion, the three types of PMMA denture teeth presented significantly different wear resistance against the abraded ceramic. The high-strength PMMA denture teeth were more wear-resistant than the conventional PMMA denture tooth.

Abrasion and corrosion resistance of new Ni-based coating deposited by HVOF thermal spray process

Coatings based on NiCrAlC intermetallic based alloy were applied on AISI 316L stainless steel substrates using a high velocity oxygen fuel torch. The influence of the spray parameters on friction and abrasive wear resistance were investigated using an instrumented rubber wheel abrasion test, able to measure the friction forces. The corrosion behaviour of the coatings were studied with electrochemical techniques and compared with the corrosion resistance of the substrate material. Specimens prepared using lower O(2)/C(3)H(8) ratios showed smaller porosity values. The abrasion wear rate of the NiCrAlC coatings was much smaller than that described in the literature for bulk as cast materials with similar composition and one order of magnitude higher than bulk cast and heat treated (aged) NiCrAlC alloy. All coatings showed higher corrosion resistance than the AISI 316L substrate in HCl (5%) aqueous solution at 40 degrees C.

Sphericity of apatite particles determined by gas permeability through packed beds

Because shape is an assessment of the three-dimensional form of a particle, it may be described in terms of sphericity (Psi), which is a measure of how closely a particle approaches a spherical configuration. In this study, Darcy`s law and the Kozeny-Carman model for fluid flow through porous media were applied to packed beds to determine the sphericity (Psi) of apatite particles. The beds were composed of glass spheres or particles of apatite (igneous from Brazil and sedimentary from the United States) of three classes of size (Class 1: -297 +210 mu m; Class 2: -210 +149 mu m; Class 3: -149 +105 mu m). Glass spheres were used to validate the model because of its known sphericity (Psi = 1.00). Apatite particles, either igneous or sedimentary, showed very close values for particle sphericity (Psi approximate to 0.6). Observations on particle images conducted by scanning electron microscopy illustrated that igneous (Psi = 0.623) and sedimentary (Psi = 0.644) particles of apatite of Class 2 predominantly exhibit elongated shape. The close value of particle sphericity (Psi approximate to 0.6) showed by either igneous or sedimentary apatite may be justified by the similarity in particle shape.

Multiscale Curvature Analysis of Asphaltic Aggregate Particles

A new method for characterization and analysis of asphaltic mixtures aggregate particles is reported. By relying on multiscale representation of the particles, curvature estimation, and discriminant analysis for optimal separation of the categories of mixtures, a particularly effective and comprehensive methodology is obtained. The potential of the methodology is illustrated with respect to three important types of particles used in asphaltic mixtures, namely basalt, gabbro, and gravel. The obtained results show that gravel particles are markedly distinct from the other two types of particles, with the gabbro category resulting with intermediate geometrical properties. The importance of each considered measurement in the discrimination between the three categories of particles was also quantified in terms of the adopted discriminant analysis.

Friction coefficient and abrasive wear modes in ball-cratering tests conducted at constant normal force and constant pressure-Preliminary results

The micro-scale abrasive wear test by rotative ball has gained large acceptance in universities and research centers, being widely used in studies on the abrasive wear of materials. Two wear modes are usually observed in this type of test: ""rolling abrasion"" results when the abrasive particles roll on the surface of the tested specimen, while ""grooving abrasion"" is observed when the abrasive particles slide; the type of wear mode has a significant effect on the overall behaviour of a tribological system. Several works on the friction coefficient during abrasive wear tests are available in the literature, but only a few were dedicated to the friction coefficient in micro-abrasive wear tests conducted with rotating ball. Additionally, recent works have identified that results may also be affected by the change in contact pressure that occurs when tests are conducted with constant applied force. Thus, the purpose of this work is to study the relationship between friction coefficient and abrasive wear modes in ball-cratering wear tests conducted at ""constant normal force"" and ""constant pressure"". Micro-scale abrasive wear tests were conducted with a ball of AISI52100 steel and a specimen of AISIH10 tool steel. The abrasive slurry was prepared with black silicon carbide (SiC) particles (average particle size of 3 mu m) and distilled water. Two constant normal force values and two constant pressure values were selected for the tests. The tangential and normal loads were monitored throughout the tests and their ratio was calculated to provide an indication of the friction coefficient. In all cases, optical microscopy analysis of the worn craters revelated only the presence of grooving abrasion. However, a more detailed analysis conducted by SEM has indicated that different degrees of rolling abrasion have also occurred along the grooves. The results have also shown that: (i) for the selected values of constant normal force and constant pressure, the friction coefficient presents, approximately, the same range of values and (ii) loading conditions play an important role on the occurrence of rolling abrasion or grooving abrasion and, consequently, on the average value and scatter of the friction coefficient in micro-abrasive wear tests. (C) 2009 Elsevier B.V. All rights reserved.

An in situ/ex vivo comparison of the ability of regular and light colas to induce enamel wear when erosion is combined with abrasion

Objective: To evaluate whether the type of cola drink (regular or diet) could influence the wear of enamel subjected to erosion followed by brushing abrasion, Method and !Materials: Ten volunteers wore intraoral devices that each had eight bovine enamel blocks divided into four groups; ER, erosion with regular cola; EAR, erosion with regular cola plus abrasion; EL, erosion with light cola; and EAL, erosion with light cola plus abrasion, Each day for 1 week, half of each device was immersed in regular cola for 5 minutes, Then, two blocks were brushed using a fluoridated toothpaste and electric toothbrush for 30 seconds four times daily, Immediately after, the other half of the device was subjected to the same procedure using a light cola, The pH, calcium, phosphorus, and fluoride concentrations of the colas were analyzed using standard procedures, Enamel alterations were measured by profilometry. Data were tested using two-way ANOVA and Bonferroni test (P < .05), Results: Regarding chemical characteristics, light cola presented pH 3.0, 13.7 mg Ca/L, 15.5 mg P/L, and 0.31 mg F/L, while regular cola had pH 2.6, 32.1 mg Ca/L, 1:8.1 mg P/L, and 0.26 mg F/L, The light cola promoted less enamel loss (EL, 0.36 pm; EAL, 0.39 pm) than its regular counterpart (ER, 0.72 pm; EAR, 0.95 pm) for both conditions, There was not a significant difference (P > .05) between erosion and erosion plus abrasion for light cola, However, for regular cola, erosion plus abrasion resulted in higher enamel loss than erosion alone,.nclusion: The data suggest that light cola promoted less enamel wear even when erosion was followed by brushing abrasion, (Quintessence Int 2011;42:xxx-xx)()

Tool wear aspects when applying high-speed tapping on grey cast iron

Tool wear is a very important subject affecting the economics of machining, especially in tapping, since it is one of the last operations to be performed within most operation sequences. In the present study, some aspects of tapping such as the mechanisms and types of wear were investigated in taps working at conventional and high-speed cutting (HSC). Additionally, different types of coatings and cooling /lubrication conditions were used. The tapping operation (M8 x 1.25) was performed in through holes with two cutting speeds (30 and 60 m/min) in grey cast iron GG25. Lubrication conditions tested were dry and with minimal quantity of lubricant. Tap materials were manufactured by powder metallurgy and coated with (TiAl)N and with TiCN. A go-non-go gauge criterion was used to assess tool life. The wear and surface aspects of the tools and workpiece were evaluated by scanning electron microscopy and energy dissipation spectroscopy. Torque signals were also measured during the tests. The main wear mechanism observed was adhesion, although some abrasion and diffusion may also have occurred, and the main type of wear was flank wear. The adhesion of workpiece material on the tool was the main and decisive factor ending tool life. Tool coatings proved to be an efficient way to minimize adhesion. Torque signals followed the same pattern as the flank wear and no significant change was observed when the cutting speed was increased.

Effect of Nd:YAG Laser and Acidulated Phosphate Fluoride on Bovine and Human Enamel Submitted to Erosion/Abrasion or Erosion Only: An in Vitro Preliminary Study

Objective: The aim of the present in vitro study was to evaluate, using two different methodologies, the effectiveness of pulsed Nd:YAG laser irradiation associated with topical acidulated phosphate fluoride (APF) for preventing enamel erosion and structure loss under regimes of erosion and abrasion or erosion only. Background Data: An increased incidence of noncarious lesions (erosion and abrasion) has been observed, consequently new preventative therapies have been proposed. Materials and Methods: Two different methodologies were performed. For the first, 100 bovine crowns were submitted to four different treatments (n = 25): no treatment (control), 4 min application of APF, Nd:YAG laser irradiation (1 W, 100 mJ, 10 Hz, 141.5 J/cm(2)), and Nd:YAG laser irradiation+4 min of APF. After the specimens were exposed to citric acid (2% w/v; 30 min), they were submitted to 5000 brushing cycles. Specimen mass was measured before and after the treatments. For the second methodology, 20 human crowns were embedded in acrylic resin and cut surfaces were exposed and polished. The specimens were divided into four groups (n = 10): no treatment (control), APF for 4 min, Nd:YAG laser irradiation (1 W, 100 mJ, 10 Hz, 125 J/cm(2)), and Nd:YAG laser irradiation+APF. The samples were then immersed in citric acid (2% w/v; 90 min). Vickers hardness was obtained before and after the treatments. Results: The Nd:YAG laser irradiation+APF (bovine and human enamel) was more effective and yielded statistically significant results for surface microhardness and enamel wear. Conclusion: Nd:YAG laser irradiation associated with APF reduced bovine enamel wear and human enamel softening when samples were submitted to a regime of erosion and abrasion or erosion only in vitro.

Transition in Yield and Azimuthal Shape Modification in Dihadron Correlations in Relativistic Heavy Ion Collisions

Hard-scattered parton probes produced in collisions of large nuclei indicate large partonic energy loss, possibly with collective produced-medium response to the lost energy. We present measurements of pi(0) trigger particles at transverse momenta p(T)(t) = 4-12 GeV/c and associated charged hadrons (p(T)(a) = 0.5-7 GeV/c) vs relative azimuthal angle Delta phi in Au + Au and p + p collisions at root s(NN) = 200 GeV. The Au + Au distribution at low p(T)(a), whose shape has been interpreted as a medium effect, is modified for p(T)(t) < 7 GeV/c. At higher p(T)(t), the data are consistent with unmodified or very weakly modified shapes, even for the lowest measured p(T)(a), which quantitatively challenges some medium response models. The associated yield of hadrons opposing the trigger particle in Au + Au relative to p + p (I(AA)) is suppressed at high p(T) (I(AA) approximate to 0.35-0.5), but less than for inclusive suppression (R(AA) approximate to 0.2).

Parton energy loss in heavy-ion collisions via direct-photon and charged-particle azimuthal correlations

Charged-particle spectra associated with direct photon (gamma(dir)) and pi(0) are measured in p + p and Au + Au collisions at center-of-mass energy root(S)(NN) = 200 GeV with the STAR detector at the Relativistic Heavy Ion Collider. A shower-shape analysis is used to partially discriminate between gamma(dir) and pi(0). Assuming no associated charged particles in the gamma(dir) direction ( near side) and small contribution from fragmentation photons (gamma(frag)), the associated charged-particle yields opposite to gamma(dir) (away side) are extracted. In central Au + Au collisions, the charged-particle yields at midrapidity (vertical bar eta vertical bar < 1) and high transverse momentum (3 < (assoc)(PT) < 16 GeV/c) associated with gamma(dir) and pi(0) (vertical bar eta vertical bar < 0.9, 8 < (trig)(PT) < 16 GeV/c) are suppressed by a factor of 3-5 compared with p + p collisions. The observed suppression of the associated charged particles is similar for gamma(dir) and pi(0) and independent of the gamma(dir) energy within uncertainties. These measurements indicate that, in the kinematic range covered and within our current experimental uncertainties, the parton energy loss shows no sensitivity to the parton initial energy, path length, or color charge.

Oxidation and abrasive wear of Fe-Si and Fe-Al intermetallic alloys

In the present work, intermetallic alloys Fe-Si and Fe-Al (Fe(3)Si-C-Cr and Fe(3)Al-C), produced by induction melting, were evaluated regarding their oxidation and abrasive resistance. The tests performed were quasi-isothermal oxidation, cyclic oxidation, and dry sand/rubber wheel abrasion. As reference, the ASTM A297-HH grade stainless steel was tested in the same conditions. In the oxidation tests, the Fe-Al based alloy presented the lowest oxidation rate, and the Fe-Si based alloy achieved the best results in the abrasion test, showing better performance than the HH type stainless steel.

Effect of binders and surface finish on wear resistance of HVOF coatings

The high velocity oxygen fuel (HVOF) thermal spray process produces highly wear and/or corrosion resistant coatings. Tungsten carbide with a metallic binder is often used for this purpose. In this work, tungsten carbide coatings containing cobalt or nickel binder were produced by HVOF and characterised by optical and electron microscopy, hardness and a dry sand/rubber wheel abrasion test. The HVOF process produced dense coatings with low porosity levels and high hardness. The wear resistance of the specimens, which were surface treated, increased as the roughness percentage decreased. Tungsten carbide nickel based coating yielded the best wear resistance in the as sprayed condition. However, the wear rate and wear of the two coatings converged to the same values as the number of revolutions increased. Wear behaviour in the ground condition was similar, although the tungsten carbide cobalt based coating yielded better performance with increasing distance travelled during the wear test.