In vitro inhibition of enamel demineralization by a polymerizable amphiphilic film.

An amphiphilic coating is configured as a substantive film that has a tendency for an in-plane two-dimensional polymerization. This coating is hypothesized to protect enamel from in vitro acid decalcification, assessed through the following artificial caries model. Three regions on labial enamel of eight bovine incisors were treated with an acid resistant varnish (A), the amphiphilic coating (B), or left undisturbed (C), and the teeth were immersed for 3 wk in lactic acid gel. Mineral loss (deltaZ-value) was determined by a cross-sectional microhardness technique. deltaZ-values (mean +/- SD; volume percent mineral-microm) were: -4 +/- 24 (A), 29 +/- 69 (B), and 7,372 +/- 1,766 (C). deltaZ-value of the uncoated enamel (C) was significantly different from the other groups. Scanning electron microscopy showed enamel etched pattern from citric acid, and the coating firmly attached on enamel surface. This amphiphilic coating can inhibit enamel decalcification under the present experimental condition.

Long-term mechanical properties of glass ionomers.

OBJECTIVE: Several methacrylate/glass ionomer hybrid materials are now available for clinical use as restorative filling materials. However, the long-term resistance of these materials to physical degradation in the humid oral condition is not known. The objective of this investigation was to determine the mechanical properties, e.g., ultimate compressive strength and diametral tensile strength, of several glass ionomer materials as a function of time after aging in water at oral temperature. METHODS: Eight glass ionomer filling materials indicated for restorative or core build-up applications were studied. Three conventional glass ionomers, two metal-containing conventional glass ionomers and three methacrylate-modified systems were included in the study. Cured specimens of each were aged in distilled water at 37 degrees C for 24 h, 1 wk, 4 wk, 12 wk, 24 wk and 52 wk. RESULTS: Like the conventional glass ionomers, the methacrylate-modified glass ionomers of this study, with one exception, did not exhibit a decrease in compressive strength, modulus and diametral tensile strength as a result of prolonged storage in water at oral temperature. Some differences among the various groups were apparent. The compressive strengths of the conventional glass ionomers were lower than the methacrylate-modified system, except for one material, Fuji II (GC Dental Corp.), of the former group. A significant difference in the compressive strength was seen between the encapsulated and hand-mixed versions of the same commercial brand product. The compressive modulus was higher and the diametral tensile strength was lower for the conventional systems indicating that, as a group, these materials are more brittle than the methacrylate-modified hybrid ionomers. With the exception of VariGlass VLC (L.D. Caulk), most of the materials studied showed little decrease in mechanical properties after aging in water for 52 wk. SIGNIFICANCE: These materials could, therefore, be indicated for use in applications where they are in contact with oral fluids under physiological conditions.

Adhesion to dentin and physical properties of a light-cured glass-ionomer liner/base.

The objective of this study was to determine the adhesion to dentin and the physical properties of Vitrabond Light Cure Glass Ionomer Liner/Base and to compare these values with those of a conventional material, 3M Glass Ionomer Liner (3MGI). Shear bond strengths to bovine dentin after 24 h in distilled water were determined to be 12 +/- 3 MPa for Vitrabond Liner/Base, while for 3MGI, bond strengths were 4 +/- 2 MPa. The failure mode was cohesive in dentin or the ionomer. Immediate adhesion of the light-cured material was also significantly higher than that of the conventional glass-ionomer liner. Thermal cycling experiments showed that the bond of Vitrabond Liner/Base to dentin was a stable one. Adhesion studies carried out on human dentin showed high adhesion values as well. Compressive and diametral tensile strengths for Vitrabond Liner/Base were determined immediately after light curing and also after storage in water for 24 h, one week, one month, and seven months. There was no significant difference in the values of compressive and diametral tensile strengths obtained immediately after curing and after extended storage in water at 37 degrees C.

In vitro fluoride release from a light-cured glass-ionomer liner/base.

This paper reports the results of an in vitro study of fluoride release from Vitrabond Light-Cure Glass Ionomer Liner/Base. The material released fluoride ions into the surrounding medium for up to 740 days. The rate of release of fluoride ions was independent of the cure time in the range studied. Combining a conventional polyalkenoic acid solution with the powder portion of Vitrabond Liner/Base did not significantly alter the release profile, thus indicating that light curing did not hinder the rate of fluoride release in this system. Secondary ion mass spectrometry studies of the dentin underlying the cured glass ionomer revealed that there was considerable incorporation of fluoride ions. There was no significant change in the mechanical properties of the cured cement aged in water at 37 degrees C for prolonged periods, thus indicating that long-term fluoride release did not adversely affect the strength of this material.

Development and use of a radioimmunoassay for D-(-)-norgestrel 17 beta-cyclopentanecarboxylate.

The synthesis of the 6 alpha-carboxymethylmercapto BSA and homologous histamine conjugate of D-(-)-norgestrel 17 beta-cyclopentanecarboxylate is reported. Using the BSA conjugate as an immunogen for the development of antibody in the rabbit and the 125I-histamine conjugate as the radioligand, a radioimmunoassay (RIA) for the ester was developed. Serum profiles of the free alcohol and ester were determined following IV or IM injection in macaques. Peak values for the ester (about 12 ng/mL) were observed 2 min following an IV bolus of 0.5 mg in one rhesus monkey. Blood levels dropped rapidly within the first 30 min and were barely detectable at 24 h. Serum levels of the free alcohol rose to a peak at 30 min and then declined slowly to very low values by 24 h. Following IM injection of 20 mg in cynomolgus monkeys, peak levels of the ester were observed within a few days while the free alcohol reached a maximum about day 30. Serum concentrations of D-(-)-norgestrel had fallen to about 0.4 ng/mL 160 days post-injection when levels of the ester fell below 0.2 ng/mL.

Effect of dose on the pharmacokinetics of levonorgestrel in the rat during the rapid elimination phase following subcutaneous administration.

Adult female rats were given a single, subcutaneous injection of 8, 16 or 32 micrograms of levonorgestrel (LNG). Blood samples were collected at various time intervals and serum concentrations of LNG were determined by radioimmunoassay. The patterns of temporal decline in LNG concentrations in the three dose groups indicated that the pharmacokinetics of LNG during the post-absorptive, rapid-elimination (beta) phase in the rat may be dose-dependent. Half-life, Co and AUC increased with the dose and -beta decreased as the dose increased. Mathematical relationships have been presented which can be used to predict the four parameters as well as concentrations of LNG at any given time after subcutaneous administration during the beta-phase for a given dose in the range of 8-32 micrograms. Significance of dose-dependent pharmacokinetic studies is discussed.

Pharmacokinetics of levonorgestrel in the rat.

Levonorgestrel was administered intravenously as a bolus to adult female rats and blood samples were collected at various time intervals. Serum concentrations of levonorgestrel were measured by radioimmunoassay. Analysis of data for two- and three-compartment open models indicated that in the rat, as in the human and the rabbit, a tri-exponential equation provided a better fit of the data. The half-lives for the alpha, beta and gamma phases were 10.1 min, 42.7 min and 23.1 hours, respectively. These values were closer to those reported for women than were the half-lives reported for the rabbit. The alpha and the beta phases appeared to last for 51 min and 1.3 hours, respectively, and the gamma phase was longer than 45 hours.