Micromorphological evaluation of dentin treated with different desensitizing agents

The purpose of a desensitizing agent is a permanent coating or filling of dentin surface. Morphological analysis in vitro of this treated surface is essential to understand the interaction between desensitizing agent and hypersensitive dentin. The aim was to evaluate the morphology of four dentin surface treated with desensitizing agents. This was an in vitro laboratory study, where fifteen specimens from extracted human premolars were obtained. The enamel was removed to expose the dentin surface, polished with silicon carbide abrasive papers and etched with 6% citric acid for 2 min. The specimens were randomly divided into 5 groups: G1 - without treatment [control] [C], G2 - fluoride varnish [FV], G3 - potassium oxalate [PO], G4 - 2-step self-etching adhesive system [AS], G5 - diode laser [DL]. The specimens were cleaved in the lingualbuccal direction, prepared for analysis by Scanning Electron Microscope and the surface and interior of the dentinal tubules were observed at 1500 X magnification. In the control group, the dentin etching promoted smear layer removal and exposure of dentinal tubules. In the group of fluoride varnish, a film was observed on the surface, with plugs of varnish into tubules. In the group of oxalate, partial obliteration of the tubular entrances was observed. In the group of the adhesive system, the tubules were obstructed through the formation of hybrid layer and a physical barrier on the surface. In the group of the diode laser, dentin melting and solidification with partial occlusion of dentinal tubules were observed. All desensitizing agents evaluated demonstrated ability to modify the surface of dentin, with partial or total occlusion of dentinal tubules. Thus, it is suggested to do more clinical studies to verify the effectiveness of the findings

Shear bond strength of resin cement to an acid etched and a laser irradiated ceramic surface

PURPOSE: To evaluate the effects of hydrofluoric acid etching and Er,Cr:YSGG laser irradiation on the shear bond strength of resin cement to lithium disilicate ceramic. MATERIALS AND METHODS: Fifty-five ceramic blocks (5 mm x 5 mm x 2 mm) were fabricated and embedded in acrylic resin. Their surfaces were finished with 1000-grit silicon carbide paper. The blocks were assigned to five groups: 1) 9.5% hydrofluoric-acid etching for 60 s; 2-4), 1.5-, 2.5-, and 6-W Er,Cr:YSGG laser applications for 60 seconds, respectively; and 5) no treatment (control). One specimen from each group was examined using scanning electron microscopy. Ceramic primer (Rely X ceramic primer) and adhesive (Adper Single Bond) were applied to the ceramic surfaces, followed by resin cement to bond the composite cylinders, and light curing. Bonded specimens were stored in distilled water at 37degrees C for 24 hours. Shear bond strengths were determined by a universal testing machine at 1 mm/min crosshead speed. Data were analyzed using Kruskal-Wallis and Mann-Whitney U-tests (alpha=0.05). RESULTS: Adhesion was significantly stronger in Group 2 (3.88 +/- 1.94 MPa) and Group 3 (3.65 +/- 1.87 MPa) than in Control group (1.95 +/- 1.06 MPa), in which bonding values were lowest (P<.01). No significant difference was observed between Group 4 (3.59 +/- 1.19 MPa) and Control group. Shear bond strength was highest in Group 1 (8.42 +/- 1.86 MPa; P<.01). CONCLUSION: Er,Cr:YSGG laser irradiation at 1.5 and 2.5 W increased shear bond strengths between ceramic and resin cement compared with untreated ceramic surfaces. Irradiation at 6 W may not be an efficient ceramic surface treatment technique.

Shear bond strength of three self-adhesive resin cements to dentin.

Context: The result of the studies concerning the bonding of self-adhesive resin cements to dentin is controversial. Aims: To assess in vitro shear bond strength (SBS) of three self-adhesive dual-cured resin cements to dentin compared to a currently used dual-cured resin cement, using SBS test. Settings and Design: The extant study is an experimental in vitro one on extracted human third molars dentin. Material and Methods: 40 intact human third molars were selected and randomly divided into 4 groups of 10. Buccal dentin surfaces were exposed perpendicular to the long axis and prepared with SiC papers. A translucent plastic ring, was placed over the dentin surfaces. Group I (Control group): After 15 s of etching and application of Excite DSC Bond (Ex), Variolink II (Var II) resin cement was injected into the plastic ring and was light cured for 40 s. Group II: RelyX Unicem (RX) was injected into the plastic ring and after 30 s, was light cured for 40 s. Group III: Maxcem (Mc) was injected into the plastic ring and after 30 s, was light cured for 40 s. Group IV: Multilink Sprint (MS) was injected into the plastic ring and after 30 s, was light cured for 40 s. After thermal cycling, SBS were measured with a universal testing machine. Statistical Analysis Used: Statistical computations were conducted according to Student's t-test. Results: The mean SBS and standard deviations (in parentheses) for groups I, II, III, and IV were 12.95 (2.64), 6.73 (0.79), 3.01 (0.90), 4.60 (0.75) MPa, respectively. Statistical analysis, revealed that: (1) the mean SBS of Var II were significantly higher than the other groups (P<0.05). (2) The mean SBS of Mc and MS were significantly lower than RX (P<0.05). (3) The mean SBS of Mc and MS did not show significant difference (P>0.05). Conclusion: Bond strength of three self-adhesive resin cements was significantly lower than the conventional total-etch resin cement. RX significantly performed better SBS than Mc and MS to dentin.

The effect of urea on the corrosion behavior of different dental alloys.

Objective: Intraoral corrosion of dental alloys has biological, functional, and esthetic consequences. Since it is well known that the salivary urea concentrations undergo changes with various diseases, the present study was undertaken to determine the effect of salivary urea concentrations on the corrosion behavior of commonly used dental casting alloys. Materials and Methods: Three casting alloys were subjected to polarization scans in synthetic saliva with three different urea concentrations. Results: Cyclic polarization clearly showed that urea levels above 20 mg/100 ml decreased corrosion current densities, increased the corrosion potentials and, at much higher urea levels, the breakdown potentials. Conclusion: The data indicate that elevated urea levels reduced the corrosion susceptibility of all alloys, possibly through adsorption of organics onto the metal surface. This study indicates that corrosion testing performed in sterile saline or synthetic saliva without organic components could be misleading.

Changes in surface roughness and color stability of two composites caused by different bleaching agents

The objective of this study was to evaluate the effect of two bleaching agents (10% and 35% hydrogen peroxide) on the color stability and surface roughness of two composites, one nanohybrid and one nanoparticle. Specimens were polished, aged, stained, bleached and polished again. The action of the bleaching agents on the composites was analyzed using a profilometer (surface roughness) and a spectrophotometer (color stability). The effect of polishing the composites on the surface roughness and the resumption of the composite color was also evaluated. The results were analyzed statistically by ANOVA and Tukey's test at 5% significance level. The analysis indicated that the nanohybrid composite was more affected by staining. The bleaching agents were not able to promote bleaching of either composite over the evaluation period. Surface polishing returned nanohybrid composite to its original color condition, which did not occur for the nanoparticle composite. Additionally, polishing did not return the surface roughness of either composite to its original value. It may be concluded that polishing surface after bleaching should not be the treatment of choice, as it was not possible to reverse the roughness of the composites to their original values, suggesting that a more extensive and irreversible degradation might have occurred.

O objetivo deste estudo foi avaliar o efeito de dois agentes clareadores (peróxido de hidrogênio a 10% e 35%) sobre a estabilidade de cor e rugosidade superficial de dois compósitos, um nanohíbrido e um nanoparticulado. Os espécimes foram polidos, envelhecidos, manchados, clareados e polidos novamente. A ação dos agentes clareadores sobre os compósitos foi analisada em perfilômetro (rugosidade) e um espectrofotômetro (estabilidade de cor). A ação de polimento dos compósitos sobre a rugosidade superficial e a retomada da cor dos compósitos também foi avaliada. Os resultados foram analisados estatisticamente por ANOVA e teste de Tukey (5% de significância). A análise indicou que o compósito nanohíbrido foi mais afetado pelo manchamento. Os agentes clareadores não foram capazes de promover o clareamento dos compósitos ao longo do período de avaliação. O polimento da superfície retornou o compósito nanohíbrido à sua condição de cor original, o que não foi observado para o nanoparticulado. Além disso, o polimento não retornou a rugosidade de superfície dos compósitos para os valores originais. Os autores concluíram que o polimento da superfície após o clareamento não deve ser a opção de tratamento, uma vez que não foi possível inverter a rugosidade dos compósitos à sua rugosidade original, sugerindo que uma degradação mais extensa e irreversível pode ter ocorrido.

Effect of filler particles on surface roughness of experimental composite series

OBJECTIVE: The purpose of this study was to evaluate the effect of different filler sizes and shapes on the surface roughness of experimental resin-composite series. MATERIAL AND METHODS: Thirty-three disc-shaped specimens of the series (Spherical-RZD 102, 105, 106, 107, 114 and Irregular-RZD 103, 108, 109, 110, 111, 112) were prepared in a split Teflon mold and irradiated with an halogen light-curing unit (450 mW/cm² for 40 s) at both top and bottom surfaces. The specimens were stored for 3 months in distilled water. The surface roughness values in form of surface finish-vertical parameter (Ra), maximum roughness depth (Rmax) and horizontal roughness parameter (Sm) were recorded using a contact profilometer. The data were analyzed by one-way ANOVA and the means were compared by Scheffé post-hoc test (a=0.05). RESULTS: The lowest surface roughness (Ra) was observed in S-100 (0.079±0.013), while the roughest surface was noted in I-450/700/1000 (0.125±0.011) and I-450/1000 (0.124±0.004). The spherical-shape series showed the smoothest surface finish compared to the irregular-shape ones with higher significant difference (p>0.05). The vertical surface roughness parameter (Ra) values increased as the filler size increased yielding a linear relation (r²=0.82). On the contrary, the horizontal parameter (Sm) was not significantly affected by the filler size (r²=0.24) as well as the filler shape. CONCLUSIONS: Filler particle's size and shape have a great effect on the surface roughness parameters of these composite series.

Effect of temperature variation on the cytotoxicity of cast dental alloys and commercially pure titanium

Cell culture system has been used to evaluate alloy cytotoxicity under different environments, testing the extracts, but the effect of temperature variation on the cytotoxicity of dental alloys has not been analyzed. OBJECTIVE: The aim of the present study was to investigate if temperature variation could affect dental alloy cytotoxicity, testing alloy extracts in an epithelial cell culture system. MATERIAL AND METHODS: Discs of Ni-Cr, Co-Cr-Mo, Ni-Cr-Ti, Ti-6Al-4V and commercially pure titanium (cp Ti) were cast by arc melting, under argon atmosphere, injected by vacuum-pressure. Discs were immersed in artificial saliva and subjected to different temperatures: 37ºC and thermocycling (37ºC/5ºC/37ºC/55ºC/37ºC). After thermocycling, extracts were put in a subconfluent culture during 6 h, and the number of cells and their viability were used to evaluate cytotoxicity in these temperatures. For each alloy, data from temperature conditions were compared by Student's t-test (α=0.05). RESULTS: The cytotoxicity tests with alloy/metal extracts showed that Ni-Cr, Co-Cr-Mo, Ti-6Al-4V and cp Ti extracts (p>0.05) did not affect cell number or cell viability, while Ni-Cr-Ti (p<0.05) extract decreased cell number and viability when the alloy was subjected to thermocycling. CONCLUSION: Within the limitations of the present study, the Ni-Cr-Ti alloy had cell number and viability decreased when subjected to temperature variation, while the other alloys/metal extracts did not show these results.

Biocompatibility study of a hydroxyapatite-aiumina and silicon carbide composite scaffold for bone tissue engineering

To date, several scaffolds have been fabricated for application in bone tissue repair. However, there remains a need for synthesis of scaffolds with better mechanical properties, which can be applied to defects in weight-bearing bones. We constructed a composite ceramic bioscaffold of hydroxyapatite-alumina and silicon carbide [HA-Al2O3- SiC] to take advantage of the mechanical properties of this combination and show that it supports osteoblast-like cell attachment and growth. Ceramic composite microporous scaffolds were synthesized using an organic template [commercial polyurethane sponge with an open, interconnected microporosity]. Osteoblast-like cells [Saos-2] were then cultured on the scaffold and their growth pattern and viability were compared with those cultured in cell culture-treated flasks. Scanning electron microscopy [SEM] was used to assess cell attachment and migration. The fabricated scaffold shows fairly uniform pore morphologies. Cell growth and viability studies show that the scaffold is able to support osteoblast attachment and growth. However, SEM images indicated that the cells do not spread optimally on the scaffold surfaces. Our data suggest that that a ceramic hydroxyapatite-alumina and silicon carbide composite scaffold is a viable option for bone tissue repair. However, its surface properties should be optimized to maximise the attachment of osteoblasts

Effects of silicon carbide on the cure depth, hardness and compressive strength of composite resin / 生物医学工程学杂志

The hardness, compressive strength and cure depth are important indices of the composite resin. This investigation was made with regard to the effects of silicon carbide on the cure depth, hardness and compressive strength of the light-curing composite resin. Different amounts of silicon carbide were added to the light-curing composite resin, which accounted for 0 wt%, 1 wt%, 0.6 wt%, 0.3 wt%, 0.1 wt%, 0.05 wt% and 0.005 wt% of the composite resin, respectively. The hardness, compressive strength and cure depth of the six afore-mentioned groups of composite resin were measured by the vernier caliper, the vickers hardness tester and the tensile strength of machine, respectively. The results showed that silicon carbide improved the hardness and compressive strength of the light-curing composite resin,when the concentration was 0.05 wt%. And the cure depth was close to that of control.

The micro-tensile bond strength of two-step self-etch adhesive to ground enamel with and without prior acid-etching / 대한치과보철학회지

STATEMENT OF PROBLEMS: Self-etch adhesives exhibit some clinical benefits such as ease of manipulation and reduced technique-sensitivity. Nevertheless, some concern remains regarding the bonding effectiveness of self-etch adhesives to enamel, in particular when so-called 'mild'self-etch adhesives are employed. This study compared the microtensile bond strengths to ground enamel of the two-step self-etch adhesive Clearfil SE Bond (Kuraray) to the three-step etchand-rinse adhesive Scotchbond Multi-Purpose (3M ESPE) and the one-step self-etch adhesive iBond (Heraeus Kulzer). PURPOSE: The purpose of this study was to determine the effect of a preceding phosphoric acid conditioning step on the bonding effectiveness of a two-step self-etch adhesive to ground enamel. MATERIAL AND METHODS: The two-step self-etch adhesive Clearfil SE Bond non-etch group, Clearfil SE Bond etch group with prior 35% phosphoric acid etching, and the one-step self-etch adhesive iBond group were used as experimental groups. The three-step etch-and-rinse adhesive Scotchbond Multi-Purpose was used as a control group. The facial surfaces of bovine incisors were divided in four equal parts cruciformly, and randomly distributed into each group. The facial surface of each incisor was ground with 800-grit silicon carbide paper. Each adhesive group was applied according to the manufacturer's instructions to ground enamel, after which the surface was built up using Light-Core (Bisco). After storage in distilled water at 37 degreesC for 1 week, the restored teeth were sectioned into enamel beams approximately 0.8*0.8mm in cross section using a low speed precision diamond saw (TOPMET Metsaw-LS). After storage in distilled water at 37 degreesC for 1 month, 3 months, microtensile bond strength evaluations were performed using microspecimens. The microtensile bond strength (MPa) was derived by dividing the imposed force (N) at time of fracture by the bond area (mm(2)). The mode of failure at the interface was determined with a microscope (Microscope-B nocular, Nikon). The data of microtensile bond strength were statistically analyzed using a one-way ANOVA, followed by Least Significant Difference Post Hoc Test at a significance level of 5%. Results: The mean microtensile bond strength after 1 month of storage showed no statistically significant difference between all adhesive groups (P>0.05). After 3 months of storage, adhesion to ground enamel of iBond was not significantly different from Clearfil SE Bond etch (P>0.05), while Clearfil SE Bond non-etch and Scotchbond Multi-Purpose demonstrated significantly lower bond strengths (P<0.05), with no significant differences between the two adhesives. CONCLUSION: In this study the microtensile bond strength to ground enamel of two-step selfetch adhesive Clearfil SE Bond was not significantly different from three-step etch-and-rinse adhesive Scotchbond Multi-Purpose, and prior etching with 35% phosphoric acid significantly increased the bonding effectiveness of Clearfil SE Bond to enamel at 3 months.

Influences of soil properties on chromium [III] sorption

Soil adsorbing properties reduce sorption ability of the metal, which in turn may influence decision for remediation at contaminated sites. The objective of this study is presentation of a model based on soil properties to estimate the sorption of Cr[III] in chromium contaminated soils. Twenty uncontaminated soil samples, with properties similar to the contaminated soils were selected from around of city of Tabriz and treated with Cr and CrCl[3]. A multiple regression analysis with statgraph software was used to drive an expression that related Cr sorption to common soil properties. The results showed that four soil properties were important in determining the amount of Cr adsorbed by the soils including pH, cation exchange capacity, total inorganic carbon and clay content with nearly 80% variability in Cr sorption and a reasonable level of confidence by this model. The obtained model suggested that Cr[III] sorption was enhanced by higher soil pH, more total inorganic carbon, more clay, and higher cation exchange capacity

Effect of different initial light intensity by the soft-start photoactivation on the bond strength and Knoop hardness of a dental composite

This study evaluated the bond strength (push-out method) and Knoop hardness of Z250 composite resin, photoactivated with XL 2500 curing unit, using different protocols: continuous mode (700mW/cm² for 20s) (CO); soft-start (50 mW/cm² for 5 s, followed by 700 mW/cm² for 15 s) (SS1); soft-start (100 mW/cm² for 5 s, followed by 700 mW/cm² for 15 s) (SS2); soft-start (150 mW/cm² for 5 s, followed by 700mW/cm² for 15s) (SS3); soft-start (200mW/cm² for 5s, followed by 700mW/cm² for 15s) (SS4); soft-start (250mW/cm² for 5 s, followed by 700 mW/cm² for 15 s) (SS5); soft-start (300 mW/cm² for 5 s, followed by 700 mW/cm² for 15 s) (SS6). For the push-out test, the specimens were tested in a universal testing machine at a crosshead speed of 0.5 mm/min. For the hardness test, the specimens were polished for the hardness measurements, using a 50 g load for 15 s. Data were submitted to ANOVA and Tukey's test (alpha=5 percent). The results of bond strength showed that the SS3 group obtained the highest bond strength when compared to the CO group. There were no significant differences among the other modes in relation to the other groups. Regarding the other results in hardness, there were no significant differences among the groups in the surface region and up to 4 mm depth.

Este estudo avaliou a resistência de união (push-out) e a dureza Knoop do compósito Z250, fotoativado por luz de lâmpada halógena XL2500, com diferentes modos: Contínuo (700 mW/cm²/20 s) (CO); Soft-start (50 mW/cm²/5 s + 700 mW/cm²/15 s) (SS1), (100 mW/cm²/5 s + 700 mW/cm²/15 s) (SS2), (150 mW/cm²/5 s + 700 mW/cm²/15 s) (SS3), (200 mW/cm²/5 s + 700 mW/cm²/15 s) (SS4), (250 mW/cm²/5 s + 700 mW/cm²/15 s) (SS5), (300 mW/cm²/5 s + 700 mW/cm²/15 s) (SS6). Para o ensaio de resistência de união, os espécimes foram testados em máquina de ensaio universal com velocidade de 0,5 mm/min. Para o teste de dureza, os espécimes foram polidos para a realização das leituras de dureza, realizadas com carga de 50 g por 15 s. Os dados foram submetidos a ANOVA e ao teste de Tukey (alfa=5 por cento). Os resultados de resistência da união mostraram que o grupo SS3 apresentou maior resistência da união quando comparado ao grupo CO. Não houve diferença entre os demais grupos testados. O teste de dureza Knoop mostrou que não houve diferença entre os grupos até 4 mm de profundidade.

Scanning electron microscopic and profilometric study of different sharpening stones

Scaling and root planing contribute to the recovery of periodontal health. All periodontal instruments loose their fine cutting angle after use. To maintain this angle, correct sharpening is required using specifically designed stones. The characteristics of sharpening stones can be compared to the blade of the instruments and also transported to root surface during instrumentation. Root smoothness is related to the quality of the blade. Therefore, the purpose of this study was to evaluate the characteristics of 9 sharpening stones by scanning electron microscopic and profilometric analyses. Ceramic and Neumar stones were very fine and both may be recommended to maintain the sharpness of the instruments. Arkansas, Thompson and CE stones presented greater roughness with very regular and round particles, and are suitable for maintenance of the cutting angle. In addition, these stones may be indicated for the routine sharpening of the instruments that are partly dull. Oxide Aluminum, Carborundum and JON stones were the coarsest with large irregular particles and may be indicated for initial sharpening of totally dull instruments with completion of sharpening with finer stones.

Sabe-se que a raspagem e aplainamento (RAR) radicular contribuem na obtenção da saúde periodontal tornando a raiz compatível com os tecidos gengivais. Todo instrumento perde o corte após ser utilizado, tornando-se menos eficaz. Portanto, é necessário mantê-lo corretamente afiado utilizando pedras especificas para tal objetivo. Considerando que características do ângulo de corte após a afiação podem ser transportadas para a raiz formando irregularidades semelhantes às da pedra utilizada e que a lisura da raiz está relacionada com a qualidade do ângulo de corte, o objetivo deste estudo foi avaliar sob microscopia eletrônica de varredura e análise em rugosímetro as características de 9 pedras de afiar. As pedras cerâmica e tipo Arkansas (Neumar) mostraram-se muito finas sendo indicadas para a manutenção do corte durante o tratamento; as pedras de Arkansas (Hu-Friedy), Thompson e CE (Tipo Arkansas) apresentaram abrasividade maior com partículas muito regulares e arredondadas, sendo indicadas para a manutenção do corte e afiação rotineira de instrumentos parcialmente sem corte. As pedras de óxido de alumínio, carborundum, Norton e JON (Oxido de Alumínio tipo Arkansas) mostraram-se grossas, com partículas grandes e irregulares, sendo indicadas para a afiação inicial de instrumentos sem corte, requerendo pedras mais finas para o acabamento final.

Effect of different finishing and polishing techniques on the surface roughness of microfilled, hybrid and packable composite resins

Este estudo avaliou a rugosidade superficial (Ra, µm) de 2 resinas compostas microparticuladas (Durafill; Perfection), 1 híbrida (Filtek Z250) e 2 compactáveis (Surefil; Fill Magic), antes (baseline) e após a realização de 8 técnicas de acabamento e polimento. A rugosidade foi avaliada com rugosímetro. Dez espécimes de cada resina foram submetidos aos seguintes procedimentos: A - brocas cabide; B - pontas diamantadas fina/extrafina; C - sistema Sof-Lex; D - sistema Super-Snap; E - pontas de borracha + pastas de polimento; F - pontas diamantadas + pontas de borracha + pastas de polimento; G - pontas diamantadas + Sof-Lex; H - pontas diamantadas + Super-Snap. Os dados foram submetidos à análise de variância a dois critérios e teste de Tukey. Foi observada diferença estatisticamente significante (p<0.05) tanto entre as resinas compostas quanto entre as técnicas de acabamento/polimento. Para todas as resinas, a maior rugosidade foi produzida com o emprego das pontas diamantadas (Ra: 0.69-1.44 µm). O menor valor de rugosidade foi obtido com o sistema Sof-Lex (Ra: 0.11- 0.25 µm). A Durafill apresentou melhor lisura que a Perfection e a Z250, que apresentaram melhor lisura que as resinas compactáveis. A seqüência completa de discos Sof-Lex produziu a melhor lisura para todas as resinas. Em áreas sem acesso aos discos, as pontas de borracha e pastas de polimento produziram lisura de superfície satisfatória para as resinas híbridas enquanto as brocas carbide produziram polimento adequado para as resinas compactáveis.

Stability and electronic spectra of C76N2 isomers / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Study of geometries of 16 possible isomers for C76N2 based on C78(C2v) by intermediate neglect of differential overlap (INDO) series of methods indicated that the most stable geometry 25,78-C76N2 where two nitrogen atoms substitute two apexes C25 and C78 near the shortest X axis and Y axis formed by two hexagons and a pentagon. Electronic structures and spectra of C76N2 were investigated. The reason for the red-shift for absorptions of C76N2 compared with that of C78(C2v) is discussed.

Sintering and microstructure of silicon carbide ceramic with Y3Al5O12 added by sol-gel method / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 degrees C with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal 'bridging'.

Hydroxyapatite bioactive coating on carbon/carbon composites / 生物医学工程学杂志

A simple plasma spraying method was employed in coating hydroxyapaptite (HA) on to carbon/carbon composites (C/C composites). The morphology of the coating was examined under scanning electron microscope (SEM). The phase constitutions of the HA coating were determined by X-ray diffractometer (XRD). The shear strength of the HA coating-C/C composite substrates was detected. A hydroxyapatite coating with rough surface was observed. A considerable amount of amorphous phase appeared as a result from the coating process, which could be transformed into the morphous phase crystalline HA after subsequent heat treatment. The shear strength between the HA coating and C/C composite substrates was 7.15 MPa.

Estudo prospectivo e randomizado de pacientes tratados com e sem stents revestidos com carbeto de silício amorfo para a prevenção da reestenose coronariana. Avaliação ultra-sonográfica / Randomized intravascular ultrasound comparison between endoprostheses with and without amorphous silicon-carbide

OBJETIVO: A reestenose intra-stent é a maior limitação das intervenções coronárias percutâneas. O carbeto de silício amorfo (SiC-a), substância antitrombótica e antiinflamatória capaz de reduzir a deposição de fibrina, plaquetas e leucócitos sobre o stent, apresenta potencial de prevenir a hiperplasia neo-intimal e a reestenose. MÉTODOS: Estudo prospectivo, randomizado e tipo rótulo aberto comparando pacientes com doença coronariana tratados com e sem stents revestidos com o SiC-a, utilizando a angiografia quantitativa e o ultra-som intracoronário. Foram incluídos 100 pacientes (50 em cada grupo) a fim de mensurar o volume de hiperplasia neo-intimal intra-stent/extremidades. Como os stents comparados apresentavam extensões diferentes, o volume de hiperplasia foi analisado em valores absolutos (por paciente) e relativos (por milímetro de extensão do stent). Avaliaram-se ainda os eventos cardíacos maiores e os resultados da angiografia quantitativa. RESULTADOS: Os grupos apresentaram características de base semelhantes. Todos os pacientes foram tratados com sucesso. No 6° mês de evolução foram reestudados 94 por cento dos casos dos dois grupos, obtendo-se ultra-som em 92 por cento. O volume de hiperplasia neo-intimal absoluto foi significativamente maior nos tratados com os stents revestidos (51.2 DP 18.8 mm³ vs 41.9 DP 16.4 mm³; p=0.014), porém o relativo foi semelhante (2.9 DP 1.0 mm³/mm stent vs 2.5 DP 0.9 mm³/mm stent; p=0.108). A obstrução volumétrica da luz também foi similar (36.4 DP 11.1 por cento vs 37.9 DP 10.9 por cento; p=0.505). O diâmetro mínimo da luz (1.9 DP 0.7 mm vs 1.8 DO 0.6 mm; p=0.552), a reestenose (19.1 por cento vs 17 por cento; p>0.999) e a revascularização do vaso-alvo (16 por cento vs 14 por cento; p>0.999) não diferiram. CONCLUSÃO: Os stents revestidos apresentaram resultados clínicos, angiográficos e ultra-sonográficos similares aos controles.

Estimate of denitrifying microbiota in tertiary sewage treatment and kinetics of the denitrification process using different sources of carbon

A study of the kinetics of denitrification was carried out in the laboratory based on the quantification of N2O, the final product of the activity of denitrifying microorganisms, when the enzymatic reduction of N2O to N2 was blocked by acetylene. Concentrated mixed liquor (sludge from a reactor with intermittent aeration used for sewage treatment) was used as the inoculum, while methanol, acetic acid, glucose, effluent sewage from an anaerobic fluidized bed reactor and synthetic substrate simulating domestic sewage were used as carbon sources. The mean concentration of nitrate was 20 mg/L. Maxima of N2O production and NO3- consumption occurred between 0.5h and 2.0h of incubation using all the carbon sources, which characterized the denitrification process. Acetic acid and methanol were responsible for the highest rates of N2O production. The estimated number of denitrifying microorganisms in the reactor with intermittent aeration, using the MPN technique, varied from 10(9) to 10(10) MPN/g VSS, indicating a high potential for the occurrence of denitrification.