Thermal and mechanical properties of PVDF/PANI blends

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Adhesives with different pHs: Effect on the MTBS of chemically activated and light-activated composites to human dentin

Purpose: To evaluate the bond strength between human dentin and composites, using two light-activated single-bottle total-etch adhesive systems with different pHs combined with chemically activated and light-activated-composites. The tested hypothesis was that the dentin bond strength is not influenced by an adhesive system of low pH, combined with chemically activated or light-activated composites. Material and Method: Flat dentin surfaces of twenty-eight human third molars were allocated in 4 groups (n=7), depending on the adhesive system: (One Step Plus-OS and Prime & Bond NT-PB) and composite (light-activated Filtek Z-100 [Z100] and chemically activated Bisfil 2B [B2B]). Each adhesive system was applied on acid-etched dentin and then one of the composites was added to form a 5 mm-high resin block. The specimens were stored in tap water (37 degrees C/24 h) and sectioned into two axes, x and y. This was done with a diamond disk under coolant irrigation to obtain beams with a cross-section area of approximately 0.8 mm(2). Each specimen was then attached to a custom-made device and submitted to the microtensile test (1 mm.min(-1)). Data were analyzed using two-way ANOVA and Tukey's tests (p<0.05). Results: the anticipated hypothesis was not confirmed (p<0.0001). The bond strengths (MPa) were not statistically different between the two adhesive systems when light-activated composite was used (OS+Z100 = 24.7 +/- 7.1(a); PB+Z100 = 23.8 +/- 5.7(a)). However, with use of the chemically activated composite (B2B), PB (7.8 +/- 3.6(b) MPa) showed significantly lower dentin bond strengths than OS (32.2 +/- 7.6(a)). Conclusion: the low pH of the adhesive system can affect the bond of chemically activated composite to dentin. on the other hand, under the present conditions, the low pH did not seem to affect the bond of light-activated composites to dentin significantly.

Polymerization shrinkage: effects of boundary conditions and filling technique of resin composite restorations

Objective: To evaluate the linear polymerization shrinkage (LPS) and the effect of polymerization shrinkage of a resin composite and resin-dentin bond strength under different boundary conditions and filling techniques.Methods: Two cavities (4 x 4 x 2 MM) were prepared in bovine incisors (n = 30). The teeth were divided into three groups, according to boundary conditions: In group TE, the total-etch technique was used. In group EE, only enamel was conditioned, and in group NE, none of the watts of the cavities were conditioned. A two-step adhesive system was applied to all cavities. The resin composite was inserted in one (B) or three increments (1), and tight-cured with 600 mW/cm(2) (80 s). The LPS (%) was measured in the top-bottom direction, by placing a probe in contact with resin composite during curing. Enamel and total mean gap widths were measured (400 x) in three slices obtained after sectioning the restorations. Then, the slices were sectioned again, either to obtain sticks from the adhesive interface from the bottom of the cavity or to obtain resin composite sticks (0.8 mm(2)) to be tested for tensile strength (Kratos machine, 0.5 mm/min). The data was subjected to a two-way repeated measures ANOVA and Tukey's test for comparison of the means (alpha = 0.05).Results: the highest percentage of LPS was found for the TE when bulk fitted, and the lowest percentage of LPS was found in the Hand NE when incrementally fitted. The resin dentin bond strength was higher and the total mean gap width was tower for TE group; no significant effect was detected for the main factor fitting techniques. No difference was detected for the tensile strength of resin composite among the experimental groups.Conclusions: the filling technique is not able to minimize effects of the polymerization shrinkage, and bonding to the cavity watts is necessary to assure reduced mean gap width and high bond strength values. (C) 2004 Elsevier Ltd. All rights reserved.

Mechanical properties, hydrophilicity and water activity of starch-gum film: effect of additives and deacetylated xanthan gum

The effect of deacetylated xanthan gum, additives (sucrose, soybean oil, sodium phosphate and propylene glycol) and pH modifications on mechanical properties, hydrophilicity and water activity of cassava starch-xanthan gum films has been studied. Sucrose addition resulted in the highest effect observed on cassava starch films elongation at break. The deacetylated xanthan gum had higher effect on elongation at break when comparing to the acetylated gum, although both gums presented an inferior effect in relation to the obtained with sucrose. However, when comparing to the control and PVC films, lower tensile strength resistance values were observed when adding sucrose. Increased water activity was observed for films added with sucrose, thus, increasing the material biodegradation. Sucrose and deacetylated xanthan gum addition resulted in a slight hydrophilicity increase. (C) 2004 Elsevier Ltd. All rights reserved.

Evaluation of glass ionomer cements properties obtained from niobium silicate glasses prepared by chemical process

Glass ionomer cements (GICs) are glass and polymer composite materials. These materials currently find use in the dental field. The purpose of this work is to obtain systems based on composition 4.5SiO(2)-3Al(2)O(3)-XNb2O5-2CaO to be used in Dentistry. The systems were prepared by chemical route at 700 degrees C. The results obtained by XRD and DTA showed that all systems prepared are glasses. The structures of the obtained glasses were compared to commercial material using Al-27 and Si-29 MAS NMR. The analysis of MAS NMR spectra indicated that the systems developed and commercial material are formed by SiO4 and AlO4 linked tetrahedra. The properties of glass ionomer cements based on the glasses prepared with several niobium contents were studied. Setting and working times of the cement pastes, microhardness and diametral tensile strength were evaluated for the experimental GICs and commercial luting cements. It was concluded that setting time of the cement pastes increased with increasing niobium content of the glasses (X). The properties to the GICs such as setting time and microhardness were influenced by niobium content. (c) 2005 Elsevier B.V. All rights reserved.

Effect of cold plasma treatment on mechanical properties of PET/PMMA composites

Mechanical strength of polyethylene terephthalate (PET) fibres and polymethyl methacrylate (PMMA) matrix composites were studied with particular interest on the effects of oxygen and argon plasma treated fibres. PET. fibres were treated in a radio frequency plasma reactor using argon or oxygen for different treatment times to increase the interface adhesion. Fibre volume fraction was measured through digital image analysis. Elastic moduli resulted between 3 GPa for untreated to 6 GPa for treated composites. Tensile tests on PET fibres showed that plasma treatment caused a decrease in average tensile strength compared to untreated fibres. Fracture analysis confirmed the increase in interfacial adhesion due to plasma treatment. (c) 2004 Elsevier Ltd. All rights reserved.

New strategies in the preparation of exfoliated thermoplastic starch-montmorillonite nanocomposites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Transparent bacterial cellulose-boehmite-epoxi-siloxane nanocomposites

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Role of polyethylene-graft-glycidyl methacrylate compatibilizer on the biodegradation of poly(epsilon-calprolactone)/cellulose acetate blends

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Barrier and Mechanical Properties of Clay-Reinforced Polymeric Nanocomposites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influência de diferentes agentes de fixação na resistência de união, por tração, de ligas metálicas fixadas à dentina.

They were casted pieces using three kinds of alloy (Ni-Cr, Ag-Sn and Cu-Al) with circular and smooth surface. They were cemented to human teeth, on occlusal surface, grounded at dentin level, through three different materials kind (zinc polycarboxylate cement, glassionomer cement and composite). After 24 hours storing, the samples were subjected to the tensile test. The results showed that the samples cemented with composite and the casts made with Ag-Sn alloy had higher bond strength.

Estudo comaprativo da resistência da união esmalt/resina/metal. Efeito de resinas de fixação, artifícios retentivos e ligas metálicas.

The purpose of this study was to compare the enamel/resin/metal bond tensile strength by using human canines, in which castings were bonded. These castings were obtained by Co-Cr or Ni-Cr alloys and showed four types of mechanisms of retention: 50 micrograms aluminum oxide abrasive, electrochemical etch, acrylic beads metal mesh. The castings were bonded utilizing Comspan Opaque and Panavia Ex. The specimens were subjected to tensile forces after 24 hours in an Instron machine. The castings subjected to 50 micrograms aluminum oxide abrasive and bonded utilizing Panavia EX showed the biggest bond tensile strength.

Ação do diclofenaco de sódio, após a interrupção da peritonite estercorácea, no cólon de ratos. Estudo da resistência mecânica e do colágeno tecidual.

The objective of the present study was to investigate changes in colon wall in rats with fecal peritonitis (Per) associated with sodium diclofenac (SD) by studying breaking strength and tissue collagen concentration. The rats were divided into the following experimental groups: GROUP 1-SD: 60 animals injected intramuscularly with sodium diclofenac at the dose of 2 mg/kg body weight; GROUP 2-Per: 60 animals injected intraperitoneally with a suspension of human feces. Peritonitis was interrupted after six hours of evolution; GROUP 3-Per+SD: 60 animals injected intraperitoneally with a suspension of human feces and receiving SD according to the schedule used for Groups 1 and 2; CONTROL GROUP: 12 animals injected intramuscularly with physiological saline. The animals of Group 1, 2 and 3 were successively sacrificed 2, 4, 7, 14 and 21 days after interruption of peritonitis an/or the beginning of treatment. Under conditions of the experimental model and of the methods used, we conclude that sodium diclofenac, peritonitis and the peritonitis-sodium diclofenac association decrease the breaking strength and the concentration of tissue collagen in the colon segment.

Mechanical behaviour of strain aged dual phase steels

Dual phase steels, characterised by good formability and excellent surface finish, are suitable for applications where processing involves cold deformation. In this context an investigation has been conducted into the cold deformation aging susceptibility of carbon steel API-5L-B and microalloyed steel API-5L-X52, both with dual phase microstructures. Changes in mechanical properties such as phase microhardness, ultimate tensile strength, and yield strength in both types of steel were observed at aging temperatures of 25, 80, and 150°C. This aging is associated with dislocation structures formed on ferrite grains in the vicinity of ferrite/martensite interfaces during intercritical treatments, which become preferential sites for solute atom diffusion. © 1999 IoM Communications Ltd.

Effect of whitening agents on dentin bonding

Background: Several studies have shown a reduction in enamel bond strengths when the bonding procedure is carried out immediately after vital bleaching with peroxides. This reduction in bond strengths has become a concern in cosmetic dentistry with the introduction of new in-office and waiting-room bleaching techniques. The aim of this in vitro study was to evaluate the effect of three bleaching regimens: 35% hydrogen peroxide (HP), 35% carbamide peroxide (CP), and 10% CP, on dentin bond strengths. Materials and Methods: One hundred and twenty fresh bovine incisors were used in this study. The labial surface of each tooth was ground flat to expose dentin and was subsequently polished with 600-grit wet silicon carbide paper. The remaining dentin thickness was monitored and kept at an average of 2 mm. The teeth were randomly assigned to four bleaching regimens (n = 30): (A) control, no bleaching treatment; (B) 35% HP for 30 minutes; (C) 35% CP for 30 minutes; and (D) 10% CP for 6 hours. For each group, half of the specimens (n = 15) were bonded with Single Bond/Z100 immediately after the bleaching treatment, whereas the other half was bonded after the specimens were stored for 1 week in artificial saliva at 37°C. The specimens were fractured in shear using an Instron machine. Results: For the groups bonded immediately after bleaching, one-way analysis of variance (ANOVA) followed by the Duncan's post hoc test revealed a statistically significant reduction in bond strengths in a range from 71% to 76%. For the groups bonded at 1 week, one-way ANOVA showed that group B (35% HP for 30 min) resulted in the highest bond strengths, whereas 10% CP resulted in the lowest bond strengths. Student's t-test showed that delayed bonding resulted in a significant increase in bond strengths for groups B (35% HP) and C (35% CP); whereas the group bleached with 10% CP (group D) remained in the same range obtained for immediate bonding. Storage in artificial saliva also affected the control group, reducing its bond strengths to 53% of the original. ©2000 BC Decker Inc.