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Biomedical subjects

H Grad

Publications and source records attributed to H Grad.

11 recordsLinked to original sources
PubMed2000

In vitro studies and modeling of a controlled-release device for root canal therapy.

Endodontic disease is caused primarily by bacteria that interact with periradicular host tissues. Therefore, treatment of endodontic disease aims at the exclusion of bacteria from the root canal system. This work focused on in vitro studies and modeling of a controlled-release device for delivering antimicrobial agents in root canals. A cylindrical, needle-shaped device was prepared consisting of a matrix core and a polymer coating, loaded with 30-45% chlorhexidine (CHX). The composition of the core, a blend of water-permeable polymers, and the thickness of the coating were tailored to impart various release rates. A relatively steady release rate for over 40 days after an initial burst was achieved using a formulation for long-term release, which is desirable for establishing and maintaining the necessary therapeutic levels. Mathematical models were developed for both in vitro and in vivo drug release into a liquid of limited volume, taking into account a moving boundary of the dispersed drug and a time-dependent boundary condition. A concentration-dependent effective diffusion coefficient was used to count increased porosity as the solid drug had dissolved. The finite element method and computer programs were applied to solve the differential equations and predict the in vitro and in vivo release kinetics. The model prediction agreed well with the in vitro experimental data and provided guidance for designing the device for in vivo release in root canals. The result of in vitro antimicrobial tests, performed using a bovine tooth model, suggested that the device was effective in reducing growth of microbes.

Algorithms↗
PubMed2000

Antimicrobial substantivity of chlorhexidine-treated bovine root dentin.

Previous studies have demonstrated antimicrobial substantivity in root canal dentin up to 7 days after treatment with chlorhexidine. This in vitro study assessed the antimicrobial substantivity of chlorhexidine-treated bovine root dentin over a period of 21 days. Sixty standardized bovine root sections were randomly divided into three equal groups, and their canals immersed in one of the following solutions: (i) sterile saline; (ii) 2.5% NaOCl; or (iii) 0.2% chlorhexidine (CHX). Half the specimens in each group were treated with the solution for 5 min and the other half for 7 days. After solutions were removed, the specimens were incubated at 37 degrees C in Brain Heart Infusion broth containing Enterococcus faecalis (ATCC 29212). A fresh inoculum was added to the broth every other day over a 21-day period. The canals were then enlarged with sterile burs, and the dentin shavings collected and cultured for the presence of cultivable bacteria in the dentinal tubules. Specimens treated with CHX for 7 days demonstrated significantly less dentin colonization by E. faecalis than the other specimens. CHX has potential as an intracanal medicament, if it can be applied for a period of at least 7 days.

Animals↗
PubMed2000

Antimicrobial substantivity of bovine root dentin exposed to different chlorhexidine delivery vehicles.

Root canal dentin acquires antimicrobial substantivity after exposure to chlorhexidine gluconate (CHX) for 1 wk. Therefore development of a vehicle for delivery of CHX as an intracanal medication is desirable. This in vitro study assessed the efficacy of two CHX delivery vehicles, a controlled-release device and a gel, to affect antimicrobial substantivity of bovine root dentin. Sixty bovine incisor root specimens were prepared with standardized length (10 mm) and canal diameter (3.3 mm), and coated externally with nail polish. Specimens were divided into four equal groups and their canals medicated for 7 days with either: (i) an experimental controlled-release device containing 25% CHX that was immersed in sterile saline; (ii) 2% CHX gel; or (iii) Ca(OH)2 paste. Sterile saline was used as the positive control. After medication, the canals of the specimens were inoculated with Enterococcus faecalis for 21 days. Root canal dentin samples ranging in depth from 0.1 to 0.45 mm were then obtained using sterile round burs of ascending diameter. Each dentin sample was placed in a separate test tube containing Brain Heart Infusion broth and incubated for 24 h. The optical density (OD) of the broth was then measured spectrophotometrically at 540 nm. The positive control showed significantly higher mean OD values (one-way ANOVA and Tukey's Studentized Range Test; p < 0.001) than the three test groups. The CHX controlled-release device group showed significantly lower OD values than the Ca(OH)2 group; however only at dentin depths up to 0.2 mm. In contrast, the CHX gel group consistently showed significantly lower OD values than both the CHX controlled-release device and Ca(OH)2 groups. These results suggest that bovine root canals medicated with 2% CHX gel for 7 days acquire antimicrobial properties for at least 21 days.

Analysis of Variance↗
PubMed1994

A new bioerodible polymer insert for the controlled release of metronidazole.

This study evaluates a new class of bioerodible polymers as periodontal inserts for the controlled release of metronidazole. The system is based on association polymers formed from compatible blends of cellulose acetate phthalate (CAP) and a hydrophobic block copolymer of polyoxyethylene and polyoxypropylene, Pluronic L101. In addition to characterizing these polymers by thermal analysis, their erosion and metronidazole release characteristics were determined both in vitro, and in vivo using a rat model. The results show that increasing the concentration of Pluronic L101 in the blend to 50% and above leads to a sharp reduction in the rates of polymer erosion and metronidazole release. The characteristics of these slowly eroding films are potentially suitable for use as periodontal drug inserts with an effective duration of up to several days. Depending on the blend composition, the mechanism of metronidazole release was found to range from a surface erosion-controlled process to an erosion-modulated diffusion process. In all in vivo experiments, no signs of adverse tissue reactions were detected. Based on these results, prototype delivery inserts were designed and subsequently evaluated in volunteer patients. Preliminary results from this pilot study show that the metronidazole concentration in the gingival crevicular fluid was significant throughout the sampling period of up to 3 hr and remained well above the minimum inhibitory concentration for most periodontal pathogens. In addition, no discomfort or irritation was reported by the test subjects.

Biodegradation, Environmental↗
PubMed1975

Adiabatic evolution of plasma equilibrium.

A new theory of plasma equilibrium is introduced in which adiabatic constraints are specified. This leads to a mathematically nonstandard structure, as compared to the usual equilibrium theory, in which prescription of pressure and current profiles leads to an elliptic partial differential equation. Topologically complex configurations require further generalization of the concept of adiabaticity to allow irreversible mixing of plasma and magnetic flux among islands. Matching conditions across a boundary layer at the separatrix are obtained from appropriate conservation laws. Applications are made to configurations with planned islands (as in Doublet) and accidental islands (as in Tokamaks). Two-dimensional, axially symmetric, helically symmetric, and closed line equilibria are included.

Journal Article↗
PubMed1973

Magnetofluid-dynamic spectrum and low shear stability.

For a perfectly conducting, cylindrical plasma equilibrium ("screw-pinch"), the spectrum contains four distinct continua, three of which can extend to the origin. This implies the existence of irreversible damping and heating in the nondissipative model. The continuum becomes (Suydam) unstable by instantly shedding an infinite number of point eigenvalues. More generally, any local instability implies an infinity of unstable eigenvalues. Spectral analysis of a new class of low shear, semilocal unstable modes provides a connection between Suydam modes, found only in sheared systems, and interchanges, found only in closed line (shearless) systems, and gives rise to the concept of an effective marginal stability threshold. Study of the spectrum should also provide a unified picture of many other plasma phenomena.

Journal Article↗
PubMedDate not supplied

Human platelet response to three salicylate dosage forms.

Acetylsalicylic acid (ASA) inhibition of platelet aggregation as evaluated by collagen-induced 14C-serotonin release, has been measured in 12 healthy male subjects. Each subject received a single oral dose (650 mg) of enteric-coated ASA (ecASA) and compressed ASA tablets (cASA), or ecASA and sodium salicylate (578 mg) separated by a minimum of 5 weeks. The platelet response was related to plasma ASA and salicyclic acid determined by high-pressure liquid chromatography. Both ecASA and cASA inhibited 14C-serotonin release; no significant difference was observed in the maximum effect between these two products (p less than 0.05). No relationship was found between the maximum observed plasma ASA level and the maximum effect. Further, no correlation was found between the maximum inhibition of 14C-serotonin release in vivo and the release predicted from in vitro experiments wherein the effect was measured after incubating plasma containing specified ASA concentrations.

Adult↗