Electro-oxidation of ethanol on Pt/C, Rh/C, and Pt/Rh/C-based electrocatalysts investigated by on-line DEMS

AbstractThe ethanol electro-oxidation reaction was studied on carbon-supported Pt, Rh, and on Pt overlayers deposited on Rh nanoparticles. The synthesized electrocatalysts were characterized by TEM and XRD. The reaction products were monitored by on-line DEMS experiments. Potentiodynamic curves showed higher overall reaction rate for Pt/C when compared to that for Rh/C. However, on-line DEMS measurements revealed higher average current efficiencies for complete ethanol electro-oxidation to CO2 on Rh/C. The average current efficiencies for CO2 formation increased with temperature and with the decrease in the ethanol concentration. The total amount of CO2, on the other hand, was slightly affected by the temperature and ethanol concentration. Additionally, the CO2 signal was observed only in the positive-going scan, none being observed in the negative-going scan, evidencing that the C–C bond breaking occurs only at lower potentials. Thus, the formation of CO2 mainly resulted from oxidative removal of adsorbed CO and CHx,ad species generated at the lower potentials, instead of the electrochemical oxidation of bulk ethanol molecules. The acetaldehyde mass signal, however, was greatly favored after increasing the ethanol concentration from 0.01 to 0.1molL−1, on both electrocatalysts, indicating that it is the major reaction product. For the Pt/Rh/C-based electrocatalysts, the Faradaic current and the conversion efficiency for CO2 formation was increased by adjusting the amount of Pt on the surface of the Rh/C nanoparticles. The higher conversion efficiency for CO2 formation on the Pt1Rh/C material was ascribed to its faster and more extensive ethanol deprotonation on the Pt–Rh sites, producing adsorbed intermediates in which the C–C bond cleavage is facilitated

Influence of cigarette smoke combined with different toothpastes on enamel erosion

This in vitro study aimed to evaluate the effect of different toothpastes on dental enamel subjected to an erosive cycle with and without exposure to cigarette smoke. Bovine enamel specimens were randomly allocated into 12 groups (n = 12). For the in vitro simulation of smoking, half the groups underwent an exposure cycle of 20 cigarettes per day for 5 days. Subsequently, all groups were subjected to a 5-day erosion cycle intercalating demineralization (1 min; 1% citric acid; pH = 3.5) and treatment with toothpaste slurries (2 min) of NaF, SnF2, F/Sn/Chitosan, F/CaSiO3/Na3PO4, and F/bioactive glass. The control group was immersed in distilled water. Surface microhardness (SMH) was measured initially, after exposure to smoke, and after the erosive cycle, and %SMH was calculated. At the end of the experimental cycle, surface roughness, profilometry, and atomic force microscopy (AFM) were performed. SMH increased after exposure to cigarette smoke (p 0.05). Besides increasing enamel SMH, cigarette smoke did not prevent enamel loss after the erosion cycle (p < 0.05). In profilometry, roughness and surface loss had the lowest values in the groups treated with SnF2 and F/Sn/Chitosan (p < 0.05). AFM showed lower mineral loss with F/CaSiO3/Na3PO4 and F/Sn/Chitosan. For all groups, except F/CaSiO3/Na3PO4, cigarette smoke resulted in higher enamel wear. F/Sn/Chitosan showed the best results against erosion3

Effectiveness Of Dental Bleaching In Depth After Using Different Bleaching Agents

This study evaluated the effectiveness of low- and high-concentration bleaching agents on enamel and deep dentin. Study design: Stained bovine incisors fragments were randomized placed into 10 groups (n=5), according to the sample thicknesses (2.0 mm or 3.5 mm) and bleaching agent: 10% carbamide peroxide (CP) (4 h a day/21 days); 6% hydrogen peroxide (HP) with calcium (1:30 h a day/21 days); HP 20% with calcium (50 min a day/3 sessions with a 7-day interval); HP 35% (3 x 15 min a day/3 sessions with a 7-day interval); HP 35% with calcium (40 min a day/3 sessions with a 7-day interval). The samples were stored in artificial saliva during the experiment. The color change was evaluated using a spectrophotometer at the initial analysis, after artificially staining with black tea and after each of the bleaching weeks, and data was expressed in CIE Lab System values. The L* coordinate data was submitted to analysis of variance and Tukey-Kramer test and the E values data was submitted for analysis of variance in a split-plot ANOVA and Tukey's test (α=0.05). Results: None of the bleaching agents tested differed from the reflectance values on the enamel surface. For deep dentin HP 20% and HP 35%, both with calcium, showed the lowest reflectance values, which differed from CP 10%. Conclusion: It is concluded that high concentration hydrogen peroxide with calcium was less effective in deep dentin than 10% carbamide peroxide.52e100e107Joiner, A., Review of the effects of peroxide on enamel and dentine properties (2007) J Dent, 35 (12), pp. 889-896Haywood, V.B., Heymann, H.O., Nightguard vital bleaching (1989) Quintessence Int, 20 (3), pp. 173-176Buchalla, W., Attin, T., External bleaching therapy with activa-tion by heat, light or laser--a systematic review (2007) Dent Mater, 23 (5), pp. 586-596Kim, Y.S., Kwon, H.K., Kim, B.I., Effect of nano-carbonate apa-tite to prevent re-stain after dental bleaching in vitro (2011) J Dent, 39 (9), pp. 636-642Sun, G., The role of lasers in cosmetic dentistry (2000) Dent Clin North Am, 44 (4), pp. 831-850Hanks, C.T., Fat, J.C., Wataha, J.C., Corcoran, J.F., Cytotoxicity and den-tin permeability of carbamide peroxide and hydrogen peroxide vital bleaching materials, in vitro (1993) J Dent Res, 72 (5), pp. 931-938Lima, D.A., Aguiar, F.H., Liporoni, P.C., Munin, E., Ambrosano, G.M., Lovadino, J.R., In vitro evaluation of the effectiveness of bleaching agents activated by different light sources (2009) J Prosthodont, 18 (3), pp. 249-254Matis, B.A., Mousa, H.N., Cochran, M.A., Eckert, G.J., Clinical evaluation of bleaching agents of different concentrations (2000) Quintessence Int, 31 (5), pp. 303-310Meireles, S.S., Heckmann, S.S., Santos, I.S., Della Bona, A., Demarco, F.F., A double blind randomized clinical trial of at-home tooth bleaching using two carbamide peroxide concentrations: 6-month follow-up (2008) J Dent, 36 (11), pp. 878-884Sulieman, M., An overview of bleaching techniques: I. History, chemistry, safety and legal aspects (2004) Dent Update, 31 (10), pp. 608-610. , 12-4,16Bernardon, J.K., Sartori, N., Ballarin, A., Perdigao, J., Lopes, G.C., Bara-tieri, L.N., Clinical performance of vital bleaching techniques (2010) Oper Dent, 35 (1), pp. 3-10Dietschi, D., Rossier, S., Krejci, I., In vitro colorimetric evaluation of theeffcacy of various bleaching methods and products (2006) Quintessence Int, 37 (7), pp. 515-526Wiegand, A., Vollmer, D., Foitzik, M., Attin, R., Attin, T., Effcacy of different whitening modalities on bovine enamel and dentin (2005) Clin Oral Investig, 9 (2), pp. 91-97Kihn, P.W., Barnes, D.M., Romberg, E., Peterson, K., A clinical evaluation of 10 percent vs. 15 percent carbamide peroxide tooth-whitening agents (2000) J Am Dent Assoc., 131 (10), pp. 1478-1484Barghi, N., Making a clinical decision for vital tooth bleaching: at-home or in-offce (1998) Compend Contin Educ Dent, 19 (8), pp. 831-838. , quiz 40Garber, D.A., Dentist-monitored bleaching: a discussion of combination andlaser bleaching (1997) J Am Dent Assoc, 128 (SUPPL.), pp. 26S-30SJoiner, A., Tooth colour: a review of the literature (2004) J Dent, 32 (1 SUPPL.), pp. 3-12Sulieman, M., Addy, M., Rees, J.S., Development and evaluation of a method in vitro to study the effectiveness of tooth bleaching (2003) J Dent, 31 (6), pp. 415-422D'Arce, M.B., Lima, D.A., Aguiar, F.H., Ambrosano, G.M., Munin, E., Lo-vadino, J.R., Evaluation of ultrasound and light sources as bleaching catalysts - an in vitro study (2012) Eur J Esthet Dent, 7 (2), pp. 176-184Dietschi, D., Benbachir, N., Krejci, I., In vitro colorimetric evaluation of the effcacy of home bleaching and over-the-counter bleaching products (2010) Quintessence Int, 41 (6), pp. 505-516Hannig, C., Weinhold, H.C., Becker, K., Attin, T., Diffusion of peroxides through dentine in vitro with and without prior use of a desensitizing varnish (2011) Clin Oral Investig, 15 (6), pp. 863-868Attia, M.L., Aguiar, F.H., Mathias, P., Ambrosano, G.M., Fontes, C.M., Li-poroni, P.C., The effect of coffee solution on tooth color during home bleaching applications (2009) Am J Dent, 22 (3), pp. 175-179Matis, B.A., Cochran, M.A., Eckert, G., Review of the effectiveness of various tooth whitening systems (2009) Oper Dent, 34 (2), pp. 230-235Marshall, K., Berry, T.G., Woolum, J., Tooth whitening: current status (2010) Compend Contin Educ Dent, 31 (7), pp. 486-492. , 94-5quiz 96, 508Kwon, Y.H., Huo, M.S., Kim, K.H., Kim, S.K., Kim, Y.J., Effects of hydrogen peroxide on the light refectance and morphology of bovine enamel (2002) J Oral Rehabil, 29 (5), pp. 473-477Hughes, J.A., West, N.X., Parker, D.M., van den Braak, M.H., Addy, M., Effects of pH and concentration of citric, malic and lactic acids on enamel, in vitro (2000) J Dent, 28 (2), pp. 147-152Gao, X.J., Elliott, J.C., Anderson, P., Scanning and contact microradio-graphic study of the effect of degree of saturation on the rate of enamel demineralization (1991) J Dent Res, 70 (10), pp. 1332-1337Turkun, M., Celik, E.U., Aladag, A., Gokay, N., One-year clinical evaluation of the effcacy of a new daytime at-home bleaching technique (2010) J Esthet Restor Dent, 22 (2), pp. 139-146Zekonis, R., Matis, B.A., Cochran, M.A., Al Shetri, S.E., Eckert, G.J., Carlson, T.J., Clinical evaluation of in-offce and at-home bleaching treatments (2003) Oper Dent, 28 (2), pp. 114-121Sulieman, M., Addy, M., MacDonald, E., Rees, J.S., The effect of hydrogen peroxide concentration on the outcome of tooth whitening: an in vitro study (2004) J Dent, 32 (4), pp. 295-29

Influence Of Successive Light-activation On Degree Of Conversion And Knoop Hardness Of The First Layered Composite Increment

Purpose: To evaluate the influence of light-activation of second, third and fourth increments on degree of conversion (DC) and microhardness (KHN) of the top (T) and bottom (B) surface of the first increment. Materials and methods. Forty samples (n = 5) were prepared. In groups 1-4, after each increment light-activation (multiple irradiation), T and B of the first increment were measured in DC and KHN. In groups 5-8, only the first increment was made (single irradiation) and measurements of DC and KHN were taken at 15 min intervals. The light-activation modes were (XL) 500 mW/cm2 × 38 s (G1/G5); (S) 1000 mW/cm2 × 19 s (G2/G6), (HP) 1400 mW/cm2 × 14 s (G3/G7); (PE) 3200 mW/cm2 × 6 s (G4/G8). Data for DC and KHN were analyzed separately by using PROC MIXED for repeated measures and Tukey-Kramer test (α = 0.05). Results. For KHN, B showed lower values than T. PE resulted in lower values of KHN in B surface. For single and multiple irradiations, T and B of first measurement showed the lowest KHN and the fourth measurement showed the highest, with significant difference between them. For single irradiation, first and second increments presented similar KHN, different from the third and fourth increment, which did not differ between them. For multiple irradiations, the second light-activation resulted in KHN similar to fi rst, third and fourth increments. For DC, except QTH, T presented higher DC than B. Conclusion. The light-activation of successive increments was not able to influence the KHN and DC of the fi rst increment.732126131Ferracane, J.L., Resin composite-State of the art (2011) Dent Mater, 27, pp. 29-38Knezevic, A., Tarle, Z., Menigaia, A., Sutalo, J., Pichler, G., Ristic, M., Degree of conversion and temperature rise during polymerization of composite resin samples with blue diodes (2012) J Oral Rehabil, 8, pp. 586-591Aguiar, F.H.B., Oliveira, T.R.V., Danl, L., Ambrosano, G.M., Lovadino, J.R., Microhardness of different thickness by conventional photocuring at different distances (2008) Gen Dent, 56, pp. 144-148Hansen, E.K., Asmussen, E., Visible-light curing units: Correlation between depth of cure and distance between exit window and resin surface (1997) Acta Odontol Scand, 55, pp. 162-166Rode, K.M., Kawano, Y., Turbino, M.L., Evaluation of curing light distance on resin composite microhardness and polymerization (2007) Oper Dent, 32, pp. 571-578Arikawa, H., Fujii, K., Kanie, T., Inoue, K., Light transmittance characteristics of light-cured composite resins (1998) Dent Mater, 14, pp. 401-411El-Mowafy, O., El-Badrawy, W., Wasef, M., Omar, H., Kermanshahi, S., Efficacy of new light-curing units in hardening of class IIcomposite restoration (2007) J Can Dent Assoc, 73, p. 253Ilie, N., Bauer, H., Draenert, M., Hickel, R., Resin-based composite light-cured properties assessed by laboratory standards and simulated clinical conditions (2013) Oper Dent, 38, pp. 159-167Rueggeberg, F.A., State-of-the-art: Dental photocuring - A review (2011) Dent Mater, 27, pp. 39-52Nomoto, R., Asada, M., McCabe, J., Hirano, S., Light exposure required for optimum conversion of light activated resin systems (2006) Dent Mater, 22, pp. 1135-1142Catelan, A., Mainardi, M.C.A.J., Soares, G.P., Lima, A.F., Ambrosanao, G.M.B., Lima, D.A.N.L., Effect of light curing protocol on degree of conversion of composites (2014) Acta Odontol Scand, 26, pp. 1-5Lima, A.F., Andrade, K.M.G., Alves, L.E.C., Soares, G.P., Marchi, G.M., Aguiar, F.H., Infl uence of light source and extended time of curing on microhardness and degree of conversion of different regions of a nanofilled composite resin (2012) Eur J Dent, 6, pp. 153-157Aguiar, F.H., Lazzari, C.R., Lima, D.A., Ambrosano, G.M., Lovadino, J.R., Effect of light curing tip distance and resin shade on microhardness of a hybrid resin composite (2005) Braz Oral Res, 19, pp. 302-306Niu, Y., Ma, X., Fan, M., Zhu, S., Effects of layering techniques on the micro-tensile bond strength to dentin in resin composite restorations (2009) Dent Mater, 25, pp. 129-134Dos Santos, G.B., Molte Alto, R.V., Sampaio Filho, H.R., Da Silva, E.M., Fellows, C.E., Light transmission on dental resin composites (2008) Dent Mater, 24, pp. 571-576Watts, D.C., Amer, O.M., Combe, E.C., Surface hardness development in light-cured composites (1987) Dent Mater, 3, pp. 265-269Yap, A.U., Wong, W., Siow, K.S., Composite cure and shrinkage associated with a high intensity curing unit (2003) Oper Dent, 28, pp. 357-364Hubbezoglu, I., Bolayir, G., Dogan, O.M., Dogan, A., Ozer, A., Bek, B., Microhardness evaluation of resin composite polymerized by three different light sources (2007) Dent Mater J, 26, pp. 845-853Sakaguchi, R.L., Berge, H.X., Reduced light energy density decreases post-gel contraction while maintaining degree of conversion in composites (1998) J Dent, 26, pp. 695-698Bracket, W.W., Hisch, L.D., Covey, D.A., Effect of plasma arc curing on microleakage of class V resin-based composite restoration (2000) Am J Dent, 13, pp. 121-122Oesterle, L.J., Newman, S.M., Shellhart, W.C., Rapid curing of bonding composite with a xenon plasma arc light (2001) Am J Orthod Dentofacial Orthop, 119, pp. 610-616Halvorson, R.H., Erickson, R.L., Davidson, C.L., Energy dependent polymerization of resin-based composite (2002) Dent Mater, 18, pp. 463-469Witzel, M.F., Calheiros, F.C., Gonc¸alves, F., Kawano, Y., Braga, R.R., Influence of photoactivation method on conversion, mechanical properties, degradation in ethanol and contraction stress of resin-based materials (2005) J Dent, 33, pp. 773-77

Mechanical properties of aged yttria-stabilized tetragonal zirconia polycrystal after abrasion with different aluminum oxide particles

A consensus on the benefits of airborne-particle abrasion of zirconia with alumina particles of different sizes is still lacking. Larger particle size may improve micromechanical retention but may generate deep microcracks on the zirconia surface. The purpose of this in vitro study was to evaluate the effect of different size of Al2O3 particles used for surface abrasion on the mechanical properties of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). Sixty Y-TZP specimens were divided into 6 groups according to the treatment: control (without treatment) or airborne-particle abrasion with Al2O3 particles (45 μm or 150 μm). Half the specimens were stored for 24 hours in water while the other half was exposed to 1.5×106 mechanical cycles before flexural strength analysis at 1 mm/min crosshead speed. Specimens were also characterized by micro-Raman spectroscopy and X-ray diffraction (XRD) to evaluate the crystalline composition. The data were subjected to 2-way ANOVA and Tukey HSD test (α=.05). Airborne-particle abrasion with alumina (P=.030) and mechanical fatigue (P<.001) had a significant effect on flexural strength. Specimens abraded with 45-μm Al2O3 particles (847 ±204 MPa) presented higher flexural strength than those of the control group (670 ±210 MPa). The size of the alumina particles was not significant for flexural strength. Flexural resistance (664 MPa) significantly decreased after mechanical fatigue. All groups showed only the tetragonal phase on the micro-Raman spectra, which was confirmed by XRD. Airborne-particle abrasion with smaller Al2O3 particles increased the flexural strength on Y-TZP without causing phase transformation. However, flexural strength was decreased after mechanical fatigue

Catalytic activity - d-band center correlation for the O2 reduction reaction on platinum in alkaline solutions

We determined, by the rotating disk electrode technique, the kinetics of the oxygen-reduction reaction (ORR) on the surfaces of single crystals of Au(111), Ag(111), Pd(111), Rh(111), Ir(111), and Ru(0001), on Pt monolayers deposited on their surfaces, and also on nanoparticles of these metals dispersed on high-surface-area carbon. Plotting the correlation between the experimentally determined activities of these three types of electrocatalysts with the calculated metal d-band center energies, εd, revealed a volcano-type dependence. In all cases, the electronic properties of the metal electrocatalysts, represented by the εd value, were used for elucidating the metal-dependent catalytic activities, and establishing their electronic properties - the ORR kinetics relationship. Pt(111), Pt/C, and Pt/Pd(111) were found to top their corresponding volcano plots. Pd in alkaline solutions showed particularly high activity, suggesting it may offer potential replacement for Pt in fuel cells. © 2007 American Chemical Society

In Situ Assessment Of The Saliva Effect On Enamel Morphology After Microabrasion Technique

Aim: This study evaluated saliva effects on enamel morphology surface after microabrasion technique. Methods: Enamel blocks (16 mm2) obtained from bovine incisors were divided into 9 groups as follows: one control group (no treatment), four groups with microabrasion treatment using 35% phosphoric acid and pumice (H3PO4+Pum) and other four groups treated with 6.6% hydrochloric acid and silica (HCl+Sil). One group of each treatment was submitted to 4 frames of saliva exposure: without exposure, 1-h exposure, 24-h exposure, and 7-days exposure on in situ regimen. Nineteen volunteers (n=19), considered as statistical blocks, used an intraoral appliance containing the specimens, for 7 days. Enamel roughness (Ra) was tested before and after treatment, and after saliva exposure. Confocal laser scanning microscopy (CLSM) was used to evaluate qualitatively the enamel morphology. Results: All groups exhibited increased Ra after microabrasion. With regards to saliva exposure, the treatment with HCl+Sil presented more susceptibility to the saliva action, but no period of time was efficient in re-establishing this characteristic compared with the control group. CLSM analysis showed reduction of the micro-abrasive damages during the experimental times. Conclusions: Seven days of saliva exposure were not sufficient for the treated enamel to reach its normal characteristics compared with the control group.133187192Croll, T.P., Enamel microabrasion: observations after 10 years (1997) J Am Dent Assoc., 128, pp. S45-S50Sundfeld, R.H., Rahal, V., Croll, T.P., De Alexandre, R.S., Briso, A.L., Enamel microabrasion followed by dental bleaching for patients after orthodontic treatment-case reports (2007) J Esthet and Restor Dent., 19, pp. 71-77Meireles, S.S., Andre, D.A., Leida, F.L., Bocangel, J.S., Demarco, F.F., Surface roughness and enamel loss with two microabrasion techniques (2009) J Contemp Dent Pract., 10, pp. 58-65Sundfeld, R.H., Croll, T.P., Briso, A.L., de Alexandre, R.S., Sundfeld-Neto, D., Considerations about enamel microabrasion after 18 years (2007) Am J Dent., 20, pp. 67-72Wang, Y., Sa, Y., Liang, S., Jiang, T., Minimally Invasive Treatment for Esthetic Management of Severe Dental Fluorosis: A Case Report (2012) Oper Dent., 38, pp. 358-362Bertoldo, C.E.S., Pini, N.I.P., Miranda, D.A., Catelan, A., Ambrosano, G.M.B., Lima, D.A.N.L., Physicochemical properties of enamel after microabrasion technique (2014) J Res Dent., 2, pp. 176-188Fragoso, L.S., Lima, D.A., de Alexandre, R.S., Bertoldo, C.E., Aguiar, F.H., Lovadino, J.R., Evaluation of physical properties of enamel after microabrasion, polishing, and storage in artificial saliva (2011) Biomed Mater., 6, p. 035001Calvo, A.F., Tabchy, C.P., Del Bel Cury, A.A., Tenuta, L.M., da Silva, W.J., Cury, J.A., Effect of acidulated phosphate fluoride gel application time on enamel demineralization of deciduous and permanent teeth (2012) Caries Res., 46, pp. 31-37Grazziotin, G.B., Rios, D., Honorio, H.M., Silva, S.M., Lima, J.E., In situ investigation of the remineralizing effect of saliva and fluoride on enamel following prophylaxis using sodium bicarbonate (2011) Eur J Dent., 5, pp. 40-46Ribeiro, H.Z., Lima, J.E., Vono, B.G., Machado, M.A., da Silva, S.M., Airpolishing effect on bovine enamel and the posterior remineralizing effect of saliva, An in vitro study (2006) J Appl Oral Sci., 14, pp. 193-197Sa, Y., Sun, L., Wang, Z., Ma, X., Liang, S., Xing, W., Effects of two in-office bleaching agents with different pH on the structure of human enamel: an in situ and in vitro study (2013) Oper Dent., 38, pp. 100-110Paic, M., Sener, B., Schug, J., Schmidlin, P.R., Effects of microabrasion on substance loss, surface roughness, and colorimetric changes on enamel in vitro (2008) Quint Int., 39, pp. 517-522Schmidlin, P.R., Gohring, T.N., Schug, J., Lutz, F., Histological, morphological, profilometric and optical changes of human tooth enamel after microabrasion (2003) Am J Dent., 16, pp. A4-A8Siqueira, W.L., Custodio, W., McDonald, E.E., New insights into the composition and functions of the acquired enamel pellicle (2012) J Dent Res., 91, pp. 1110-1118Hara, A.T., Gonzalez-Cabezas, C., Creeth, J., Zero, D.T., The effect of human saliva substitutes in an erosion-abrasion cycling model (2008) Eur J Oral Sci., 116, pp. 552-556De Abreu, D.A., Sasaki, R.T., Amaral, F.L., Florio, F.M., Basting, R.T., Effect of home-use and in-office bleaching agents containing hydrogen peroxide associated with amorphous calcium phosphate on enamel microhardness and surface roughness (2011) J Esthet Restor Dent., 23, pp. 158-168Gonzalez-Cabezas, C., Jiang, H., Fontana, M., Eckert, G., Effect of low pH on surface rehardening efficacy of high concentration fluoride treatments on non-cavitated lesions (2012) J Dent., 40, pp. 522-526Dong, Z.C.J., Deng, Y., Joiner, A., In vitro remineralization of acid-etched human enamel with Ca3SiO5 (2010) App Surf Sci., 256, p. 3Honorio, H.M., Rios, D., Abdo, R.C., Machado, M.A., Effect of different prophylaxis methods on sound and demineralized enamel (2006) J App Oral Sci., 14, pp. 117-123Buzalaf, M.A., Hannas, A.R., Magalhaes, A.C., Rios, D., Honorio, H.M., Delbem, A.C., pH-cycling models for in vitro evaluation of the efficacy of fluoridated dentifrices for caries control: strengths and limitations (2010) J App Oral Sci., 18, pp. 316-334Dominguez, J.A., Bittencourt, B., Michel, M., Sabino, N., Gomes, J.C., Gomes, O.M., Ultrastructural evaluation of enamel after dental bleaching associated with fluoride (2012) Microsc Res Tec., 75, pp. 1093-1098Dalzell, D.P., Howes, R.I., Hubler, P.M., Microabrasion: effect of time, number of applications, and pressure on enamel loss (1995) Ped Dent., 17, pp. 207-211Wiegand, A., Bliggenstorfer, S., Magalhaes, A.C., Sener, B., Attin, T., Impact of the in situ formed salivary pellicle on enamel and dentine erosion induced by different acids (2008) Acta Odontol Scand., 66, pp. 225-230Paes Leme, A.F., Dalcico, R., Tabchy, C.P., Del Bel Cury, A.A., Rosalen, P.L., Cury, J.A., In situ effect of frequent sucrose exposure on enamel demineralization and on plaque composition after APF application and F dentifrice use (2004) J Dent Res., 83, pp. 71-75Jager, D.H., Vieira, A.M., Ligtenberg, A.J., Bronkhorst, E., Huysmans, M.C., Vissink, A., Effect of salivary factors on the susceptibility of hydroxyapatite to early erosion (2011) Caries Res., 45, pp. 532-537Meyer-Lueckel, H., Paris, S., Kielbassa, A.M., Surface layer erosion of natural caries lesions with phosphoric and hydrochloric acid gels in preparation for resin infiltration (2007) Caries Res., 41, pp. 223-230Wang, Y., Li, X., Chang, J., Wu, C., Deng, Y., Effect of tricalcium silicate (Ca3SiO5) bioactive material on reducing enamel demineralization: An in vitro pH-cycling study (2012) J Dent., 40, pp. 1119-1126Torres-Rodriguez, C., Gonzalez-Lopez, S., Bolanos-Carmona, V., Sanchez-Sanchez, P., Rodriguez-Navarro, A., Attin, T., Demineralization effects of phosphoric acid on surface and subsurface bovine enamel bleached with in-office hydrogen peroxide (2011) J Adhes Dent., 13, pp. 315-321Li, C., Risnes, S., SEM observations of Retzius lines and prism crossstriations in human dental enamel after different acid etching regimes (2004) Arch Oral Biol., 49, pp. 45-5

Platinum monolayer on nonnoble metal-noble metal core-shell nanoparticle electrocatalysts for O 2 reduction

We synthesized a new class of O 2 electrocatalysts with a high activity and very low noble metal content. They consist of Pt monolayers deposited on the surfaces of carbon-supported nonnoble metal-noble metal core-shell nanoparticles. These core-shell nanoparticles were formed by segregating the atoms of the noble metal on to the nanoparticles' surfaces at elevated temperatures. A Pt monolayer was deposited by galvanic displacement of a Cu monolayer deposited at underpotentials. The mass activity of all the three Pt monolayer electrocatalysts investigated, viz., Pt/Au/Ni, Pt/Pd/Co, and Pt/Pt/Co, is more than order of magnitude higher than that of a state-of-the-art commercial Pt/C electrocatalyst. Geometric effects in the Pt monolayer and the effects of PtOH coverage, revealed by electrochemical data, X-ray diffraction, and X-ray absorption spectroscopy data, appear to be the source of the enhanced catalytic activity. Our results demonstrated that high-activity electrocatalysts can be devised that contain only a fractional amount of Pt and a very small amount of another noble metal. © 2005 American Chemical Society

Impact Of Light-curing Time And Aging On Dentin Bond Strength Of Methacrylate- And Siloranebased Restorative Systems

Aim: To evaluate the impact of different light-curing times on dentin microtensile bond strength of two restorative systems after 24 h and 6 months of water storage. Methods: Standardized Class II preparations were performed in 56 freshly-extracted human molars (n = 7), restored with methacrylate- or silorane-based restorative systems, and light-cured using a light-emitting diode at 1390 mW/cm2 by the recommended manufacturers' time or double this time. After storage for 24 h at 37 °C, the teeth were sectioned to yield a series of 0.8-mm thick slices. Each slab was trimmed into an hourglass shape of approximately 0.64 mm2 area at the gingival dentin-resin interface. Specimens were tested using universal testing machine at crosshead speed of 0.5 mm/min until failure, after 24 h and 6 months of storage. Data were statistically analyzed by three-way ANOVA and Tukey's test (α = 0.05). Results: The highest bond strength values were recorded for the groups restored with methacrylate system (p&lt;0.001) as well as for extended light-curing time (p = 0.0034). There was no statistically significant difference between 24 h and 6 months storage on bond strength (p&gt;0.05). Conclusions: Bond strength was influenced by the material and lightcuring time, but the 6-month storage did not affect the bond strength of restorations.133213218Van Ende, A., De Munck, J., Mine, A., Lambrechts, P., Van Meerbeek, B., Does a low-shrinking composite induce less stress at the adhesive interface? 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