I.R. Oliveira

Root canal filling with cements based on mineral aggregates: an in vitro analysis of bacterial microleakage.

The aim of this study was to assess bacterial microleakage through 2 different cements used as root canal filling materials: mineral-trioxide-aggregate (White MTA, Angelus, Londrina, PR, Brazil); and an experimental material containing calcium aluminate plus additives (EndoBinder, University of São Carlos [UFSCar-Brazil], patent number PI0704502-6). Forty incisors were divided into 4 groups: (1) white-MTA, (2) calcium aluminate cement, and (3) positive and (4) negative control group. Falcon tubes were prepared for this experiment, divided into 2 separated chambers; the lower part was filled with RTF-transport media so that only the root apex was in contact with the transport media, whereas the coronal part was immersed in BHI containing Enterococcus faecalis to investigate bacterial microleakage. The evaluated materials used as root canal filling materials showed an absence of microbial growth. Both materials when used as the root canal filling were efficient in sealing root canals and preventing E. faecalis microleakage for the 30-day evaluation period using an in vitro model.

Bioactivity of Calcium Aluminate Endodontic Cement

INTRODUCTION Calcium aluminate endodontic cement (CAEC) developed for use in root canal therapy has been produced with additives that improve handling properties and provide higher mechanical strength than mineral trioxide aggregate (MTA) according to prior studies. The aim of this study was to evaluate the bioactivity of CAEC containing accelerating additives (A-CAEC) in comparison with MTA, both in contact with simulated body fluid (SBF) solutions. METHODS pH measurements were taken for set cement samples immersed in water or SBF solutions prepared according to the Kokubo and Rigo techniques. The surface of these materials kept in contact with SBF solutions were also evaluated by means of scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray diffraction. RESULTS Because of the calcium hydroxide dissociation, MTA cement is able to release more Ca(2+) ions and results in a higher pH increase compared with A-CAEC. This behavior enhances the supersaturation of Kokubo solution, resulting in the precipitation of calcium phosphate phases on the MTA surface. On the other hand, for MTA in Rigo SBF solution, the pH value attained was higher than for the Kokubo SBF solution as a result of the Mg(2+) ion precipitation, which inhibited the calcium phosphate phase formation. For A-CAEC, the optimal precipitation conditions of calcium phosphate phases are achieved in Rigo SBF solution. CONCLUSIONS MTA and A-CAEC present bioactivity in contact with SBF solution although the composition of this solution defines the type of phase precipitated.

Effects of a novel calcium aluminate cement on the early events of the progression of osteogenic cell cultures

The present study evaluated the progression of osteogenic cell cultures exposed to a novel calcium aluminate cement (CAC+) in comparison with the gold standard mineral trioxide aggregate (MTA). Cells were enzimatically isolated from newborn rat calvarial bone, plated on glass coverslips containing either CAC+ or a control MTA samples in the center, and grown under standard osteogenic conditions. Over the 10-day culture period, roundening of sample edges was clearly noticed only for MTA group. Although both cements supported osteogenic cell adhesion, spreading, and proliferation, CAC+-exposed cultures showed significantly higher values in terms of total cell number at days 3 and 7, and total protein content and alkaline phosphatase activity at day 10. The present in vitro results indicate that the exposure to CAC+ supports a higher differentiation of osteogenic cells compared with the ones exposed to MTA. Further experimental studies should consider CAC+ as a potential alternative to MTA when the repair of mineralized tissues is one of the desired outcomes in endodontic therapy.

Setting behavior of ultra-low cement refractory castables in the presence of citrate and polymethacrylate salts

The effect of citrate and polymethacrylate salts on the setting behavior of ultra-low cement (ULC) refractory castables was addressed in this paper, with special attention to the interactions of such chemical additives with the cement particles in the aqueous medium. Rheological experiments, electrical conductivimetry, temperature measurements, SEM, X-ray diffractometry and mechanical tests were performed to characterize the cement-based compositions prepared in this work. In spite of its strong inhibiting effect on the precipitation of cement hydrated phases, sodium citrate was found to induce the earlier setting of ULC refractory castables, due most likely to the formation of a gelled phase between the citrate anions and the ions originated from the dissolution of cement particles. The most probable reasons for the formation of this unexpected gelled phase are discussed in this paper.

Cinética de hidratação de ligantes à base de alumina hidratável ou aluminato de cálcio Kinetics of hydration of binders based on hydratable alumina or calcium aluminate cement

The dispersion of refractory castables matrix presents a great influence on their rheological behavior, which defines the most appropriate methods for placing these materials. The growing demand for automatically transported refractory castables has promoted the use of pumpable castables, usually specified as self flow compositions. Nevertheless, castables with higher fluidity present longer workability, leading to extended demoulding times. Because the strength development is intimately linked to the hydration process of calcium aluminate cement or hydratable alumina, it needs to be controlled in order to reach the minimum time for demoulding, contributing to reducing overall costs. The control of cement hydration depends on the knowledge of the variables that determine the kinetics of the involved reactions. In this context, the objective of this work was to evaluate the influence of the sources of the hydraulic binder, the temperature and the presence of matrix or inorganic additives on the hydration process, carried out through temperature measurements and oscillatory rheological tests, as a function of the time.

Refractory castables rheology in the presence of different sort of additive and hydraulic binders

Chemical additives may be added to the castables for different purposes, as for example, to disperse matrix fine particles through electrostatic/electrosteric mechanisms (dispersants) and to control the hydration process of cement particles (retarders/accelerators). The state of dispersion of the castables matrix particles presents a direct influence in their rheological behavior, defyning the techniques that can be used for their installation. The growing demand for automatically transported refractory castables has stimulated the use of pumpable castables due to its fast and high quality placing, without losses and with reduced costs. However, in order to explore the technological advantages of this process it is necessary that the rheological behavior and setting characteristics of castables are in tune with the process. In this context, the objective of this work was simultaneously evaluate the influence of the different additives on the matrix particles dispersion and the hydration process of different hydraulic binder, through fluidity and setting time measurements of refractory castables.

Influence of Radiopacifier Additives on Calcium Aluminate Cement Properties

The aim of this study was to determine the best radiopaque additive to be incorporated to calcium aluminate cement (CAC) to promote radiopacity. Measurements of optical density were carried out on white MTA and CAC with and without additives such as: polymeric dispersant, plasticizer and various radiopacifiers. The effects of the radiopacifying addition on some properties of CAC were also evaluated. The radiopacity value for CAC-Bi2O3 (25%) was higher than the other radiopacifying agents tested. The addition of ZnO (25%) and 15%ZnO:10%Bi2O3 increased the compressive strength of CAC, whereas for Bi2O3 (25%) containing samples the strength was lower than for the CAC. The ZnO (25%) and 15%ZnO:10%Bi2O3 additions also reduced the apparent porosity. CAC does not have sufficient radiopacity to be distinguished from adjacent anatomic structures, such as dental tissues and bone. The addition of 15%ZnO:10%Bi2O3 can be suggested as the most suitable one to obtain the best compromise between good physical and mechanical properties and ideal radiopacity for clinical purposes.

Hidratação de ligantes na presença de matriz e aditivos

Hydraulic binders such as hydratable alumina and calcium aluminate cement present a major influence on the rheological properties and mechanical strength development of castables, defining their workability and demoulding times, respectively. Such behavior is related to the hydration process and its control depends on the knowledge of the variables that determine the kinetics of the involved reactions. The matrix addition to cement influences the hydration behaviour, as well as, the length of the induction period, the composition of the phases and of the hydration products. Additives such as the retarders can inhibit the process of cement dissolution, by the build up of insoluble barriers around the cement particles, and enhance the formation of more soluble hydrates. They can also behave as accelerators inducing the formation of less soluble hydrates and speeding up the beginning of the hydrate nucleation. In this context, the objective of this work was to evaluate the influence of different kind of matrix and additives on the hydration process of different sources of the hydraulic binder.

Heterocoagulação como técnica para obtenção de cerâmicas porosas

The crisis faced by the energy sector has led to a growing interest in the use of refractory porous ceramics as high temperature insulators, due to their unique combination of properties: chemical inertia, refractoriness and low thermal conductivity. Among the several techniques employed in the production of these materials, the addition of organic particles, which volatilize during the first heat-up, to the ceramic matrix is one of the most promising techniques. This procedure can be optimized in order to attain a better control over the porosity using the heterocoagulation of the inorganic and organic parts of a suspension. The purpose of the present work was to evaluate the impact of the heterocoagulation on the production of porous ceramics using PVC and starch as organic and alumina as inorganic compounds. The most suitable conditions to promote heterocoagulation of the constituents were previously determined. The increasing of the volume fraction of the organic parts generated more porous materials for both additives. However, the maximum amount of organics was set in 50 vol.% in order to achieve acceptable mechanical strength. It was also found out that compared to the conventional process, the porous ceramics obtained by heterocoagulation presented superior microestrutural homogeneity and mechanical strength.

Aditivos e sua influência no comportamento de secagem e resistência à tração de concretos refratários

The growing technology applied in the refractory castables production has become more difficult the drying process due the reduction of their permeability and the consequent increasing difficult of vapor migration from the inner region of the body to the surface. The hydration of calcium aluminate cement is also responsible for the castables permeability reduction. This process is significatively affected by the presence of additives used to disperse the castables. In this context, the objective of this work was to evaluate the influence of the different kind of additives on the drying behavior and traction strength of castables. It was verified that additives not only influence in the dispersion of matrix and binder particles but also in the type resulting hydrate. The additive CS favored the dispersion of castable and decreased water consumption resulting in the main formation of hydrates C3AH6 and AH3. The formation of AH3 is particularly favored by precipitation of C3AH6 due to alumina content available to its formation to be larger. This phase appears frequently as gel and due its high capacity to fill interparticle voids can be correlated to the traction strength development. On the other hand, in the presence of additive AC it was observed reduction in relation the formation these hydrates due his retarder effect which occurred by calcium ions consumption. Moreover, the presence of bigger water content contributed for increase of porosity and decrease of traction strength of castable.