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Biomedical subjects

J L Fox

Publications and source records attributed to J L Fox.

At least 109 records · Page 6Linked to original sources
PubMed1996

Calculation of intercrystalline solution composition during in vitro subsurface lesion formation in dental minerals.

Applications of a novel technique to calculate intercrystalline solution composition during enamel demineralization are presented. Bovine tooth enamel blocks and carbonated apatite (CAP) compressed disks were demineralized in an in vitro subsurface lesion system. The demineralization medium was a 0.1 M acetate buffer at pH 4.5, containing calcium, phosphate, and fluoride (0.5 ppm). Mineral samples were demineralized for various times, and fluoride profiles and mineral density profiles of these samples were determined by electron microprobe and X-ray microradiography, respectively. A model independent data analysis (MIDA) technique uses these data along with the differential equations for mass transfer and permits calculation of the local intercrystalline solution composition profiles inside the porous mineral matrix as functions of time and position. The invariance in diffusivity with time as calculated in the analysis was taken as an indicator of the physical reasonableness of the method. Current outcomes suggest that it is the sharp gradient of fluoride concentration in the intercrystalline solution which causes the formation of subsurface lesions. Since the driving force for mineral dissolution is a function of solution composition, a gradient of this driving force is consequently formed. Using a compressed disk of carbonated apatite powder as a model for block enamel excluded the possibility of the existence of a gradient of mineral composition which could also cause a gradient of the driving force for mineral dissolution. An FAP surface complex hypothesis is consistent with the current view that fluoride in the intercrystalline solution has a stronger inhibition effect on the dissolution of mineral than does fluoride in the mineral phase. With the help of the MIDA technique, calculated results indicate that the mechanism of the formation of subsurface lesions is dynamically controlled by the intercrystalline solution composition.

Animals↗
PubMed1995

Stability of ondansetron hydrochloride injection in various beverages.

The stability of ondansetron hydrochloride injection in beverages likely to be acceptable to patients was studied. Ondansetron hydrochloride injection (containing ondansetron 2 mg/mL) was added to apple juice, fruit punch, cherry-flavored drink, carbonated soft drinks, and hot tea to provide a nominal ondansetron concentration of 32.8, 64.5, or 95.2 micrograms/mL. Samples were stored at -3 to 28 degrees C (noncarbonated-beverage mixtures except tea), 2 to 28 degrees C (carbonated-beverage mixtures), and 25 degrees C (tea) and assayed for ondansetron concentration by high-performance liquid chromatography at 6, 24, 48, and 72 hours (noncarbonated-beverage mixtures except tea); 6, 24, and 48 hours (carbonated-beverage mixtures); and 1 hour (tea). More than 95% of the initial ondansetron concentration was retained in apple juice, fruit punch, cherry-flavored drink, Sprite, and Diet Coke throughout the periods studied. A precipitate formed immediately after ondansetron was added to hot tea, but the drug was chemically stable for at least one hour in this preparation. Ondansetron hydrochloride injection 32.7, 64.5, and 95.2 micrograms/mL (expressed as free base) was stable in various beverages when stored at -3 to 28 degrees C for up to 72 hours. Ondansetron at these same concentrations precipitated in hot tea preparations but was chemically stable for at least one hour.

Anti-Anxiety Agents↗
PubMed1995

Effect of particle size of metastable calcium phosphates on mechanical strength of a novel self-setting bioactive calcium phosphate cement.

Resistance to compressive strength after setting of the calcium phosphate cement consisting of tetracalcium phosphate (TECP), dicalcium phosphate dihydrate (DCPD), and 40 wt/wt% of a synthetic hydroxyapatite (HAP) was tested. An equimolar mixture of the calcium phosphate powder containing DCPD (particle diameter [D] 0.52-3.33 microns) and TECP (D, 1.1-13.1 microns) transformed into HAP at 37 degrees C, 100% RH after being mixed with 25 mM phosphoric acid. X-ray diffraction suggested that the cement containing fine particles of DCPD and TECP completely transformed to HAP, but that mixtures containing larger particles did not. Because particle size of both DCPD and TECP affected the compressive strength of the cement, the crystal growth of HAP during cement formation depended on the specific surface area (Sw) of the raw materials. The crystallite size of transformed HAP was estimated based on X-ray diffraction peaks at 25.8 and 32.8 degrees attributable to the 002 and 300 planes. The crystalline size attributable to the 300 plane decreased with increasing Sw, but that attributable to the 002 plane showed no significant relationship. The compressive strength of the cement after hardening increased with an increase of its Sw. This suggested that the harder calcium phosphate cement was (derived) from the smaller particle size of the raw materials.

Bone Cements↗
PubMed1995

A novel skeletal drug delivery system using self-setting calcium phosphate cement. 9: Effects of the mixing solution volume on anticancer drug release from homogeneous drug-loaded cement.

The effects of mixing solution volume (0.25-0.65 mL/g) on in vitro drug release from a self-setting bioactive calcium phosphate cement containing the anticancer agent 6-mercaptopurine (6-MP) as a model compound were investigated. The drug release profiles from isolated planar surfaces as well as the entire surfaces of cement systems containing 5% 6-MP were measured in simulated body fluid at pH 7.25 and 37.0 degrees C. The drug release rate from both cement system geometries increased with increasing mixing solution volume. Drug release profiles from the planar-release and entire-surface-release cement matrix systems were analyzed by and found to agree with the Higuchi and Cobby equations, and the kinetic parameters were estimated with a nonlinear least-squares computer program. Linear relationships were found between the mixing solution volume and the drug release rate constants or time required for 50% drug release for both cement release geometries. Furthermore, the total pore volume of the cements, as measured by mercury porosimetry, increased with increasing mixing solution volume.

Antineoplastic Agents↗
PubMed1995

Physical model for lesion formation in the presence of low levels of solution fluoride.

A quantitative physical model is presented for the formation of subsurface carious lesions in the presence of low levels of solution fluoride. Calculations using independently determined model parameters are in agreement with mineral density profiles measured in bovine enamel lesions. The proposed mechanism is controlled by fluoride in the following way: as fluoride diffuses into enamel, it is rapidly adsorbed to enamel crystallites, resulting in very low microenvironmental fluoride concentrations, so long as the crystals are not saturated with respect to fluoride adsorption. The result of this saturable adsorption is a widening band of fluoride-saturated crystals near the surface, beneath which the microenvironmental fluoride concentrations are negligible. In the saturated band, the microenvironmental fluoride concentration in the pore solution is high enough to suppress dissolution, while in the deeper, relatively fluoride free region, dissolution can occur. In addition to predicting observed mineral density profiles, the model also predicts the demarcation in solution conditions between the regime where subsurface lesion formation occurs and that where the dissolution pattern is that of surface erosion; and the lack of insensitivity of dissolution rate to hydrodynamics in the presence of low levels of fluoride, as contrasted to the square root of stirring rate dependency observed in the absence of fluoride.

Animals↗