Long-term bond strength of fiber posts cement to dentin with self-adhesive or conventional resin cements

The aim of this study was to evaluate the immediate and the long-term push-out bond strength of glass fiber posts (GFP) cemented with conventional or self-adhesive dual-curing resin cements, at different root depths. Prior to cementation, the GFP (Reforpost #3, Angelus) were etched with 37% phosphoric acid for 30 s followed by silane for 1 min. Thirty canine roots were divided into two groups (n = 15) according to resin cement type: ARC – dual resin cement (RelyX ARC/3M ESPE) combined with an three-step etch-and-rinse adhesive (Adper Scotch Bond Multi-Purpose Plus 3M/ESPE) or U200 – self-adhesive resin cement (RelyX U200/3M ESPE). The manufacturer’s instructions were followed. After 48 h, the roots were cross-sectioned at three different depths, resulting in serial slices corresponding to the cervical, middle, and apical root thirds. Slices were randomly divided into two groups, according to the period of water storage prior to push-out bond strength analysis: 48 h or 180 days. The data (MPa) were analyzed using three-way ANOVA for randomized blocks (p < 0.05), which showed no significant interaction between the three factors (p = 0.716). The main study factors were also proven not significant (cement: p = 0.711; time: 0.288; root third: p = 0.646). In conclusion, root depth, cement type (self-adhesive or conventional), and storage in water for 180 days did not influence the bond strength of GFP to intracanal dentin.     

Determining the anisotropic content in a petroleum pitch - Comparison of centrifugation and optical microscopy techniques

The anisotropic content of a pitch is one of the most important parameters for characterizing such materials. Polarized light optical microscopy is the technique most commonly employed (ASTM D 4616 standard procedure) to measure this pitch parameter. However, this standard procedure is limited to pitches with mesophase contents only up to 20%. An alternative technique for determining the anisotropic content of a pitch is high-temperature centrifugation, which can be used without limitation for pitches with up to 100% anisotropic content. In this work, the two techniques have been compared; samples of four pitches with mesophase contents lower than 20% have been analyzed by both techniques and the results have been compared. The high-temperature centrifugation technique showed good repeatability, and the results that it yielded matched those obtained from optical microscopy when the anisotropic content of the pitch was higher than around 5%. The centrifugation technique is always faster, simpler, and possibly more accurate than optical microscopy for pitches with mesophase contents higher than 20%.     

Poly(hydroxybutyrate-co-hydroxyvalerate) microspheres loaded with atrazine herbicide: screening of conditions for preparation,physico-chemical characterization,and in vitro release studies

Due to their widespread use in agriculture as well as in urban areas, agricultural chemicals are globally some of the most commonly encountered substances in waters. The objective of this study is to develop (including preparation and characterization) a new modified release system for the herbicide atrazine, employing poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) microspheres. The microspheres were prepared by the emulsification/solvent evaporation method, emulsifying an organic phase (atrazine and PHBV dissolved in chloroform) into an aqueous phase containing polyvinyl alcohol (PVA) as surfactant, under stirring, and then evaporating the solvent. A 2^4-1 fractional factorial design, investigating the influence of four variables at two levels, was performed to obtain formulations with optimized association efficiencies. There was a greater dependence of association efficiency on PVA concentration (negative) and the mass of polymer (positive) with lesser influence of both stirring speed and organic phase volume. The size of the particles was assessed using scanning electron microscopy, which showed that the particles were rough-surfaced spheres. The results obtained are promising, since the formulations presented encapsulation efficiency near 25% and the release kinetics profile of atrazine was altered when it was encapsulated in the microparticles, indicating that these systems may be efficient in reducing the environmental impact caused by the herbicide, hence making it safer to use.