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T H Jordan

Publications and source records attributed to T H Jordan.

9 recordsLinked to original sources
PubMed2001

Laser-matrix-fluoride effects on enamel demineralization.

Laser and fluoride have been shown to inhibit enamel demineralization. However, the role of organic matrix and their interactions remains unclear. This study investigated the interaction among CO2 laser irradiation, fluoride, and the organic matrix on the demineralization of human enamel. Twenty-four molars were selected and cut into halves. One half of each tooth was depleted of its lipid and protein. The other half served as a matched control. Each tooth half had two window areas, treated with a 2.0% NaF gel. All left windows then received a laser treatment. Next, the tooth halves were subjected to a four-day pH-cycling procedure that created caries-like lesions. Tooth sections were cut from the windows, and microradiographs were used for quantification of the demineralization. The combined fluoride-laser treatment led to 98.3% and 95.1% reductions in mineral loss for enamel with and without organic matrix, respectively, when compared with sound enamel.

Analysis of Variance↗
PubMed2000

Effects of low-energy CO2 laser irradiation and the organic matrix on inhibition of enamel demineralization.

In the past two decades, accumulated evidence has clearly demonstrated the inhibitory effects of laser irradiation on enamel demineralization, but the exact mechanisms of these effects remain unclear. The purpose of this study was to investigate the effects of low-energy CO2 laser irradiation on demineralization of both normal human enamel and human enamel with its organic matrix removed. Twenty-four human molars were collected, cleaned, and cut into two halves. One half of each tooth was randomly selected and its lipid and protein content extracted. The other half of each tooth was used as the matched control. Each tooth half had two window areas. All the left windows were treated with a low-energy laser irradiation, whereas the right windows served as the non-laser controls. After caries-like lesion formation in a pH-cycling environment, microradiographs of tooth sections were taken for quantification of demineralization. The mean mineral losses (with standard deviation) of the enamel control, the lased enamel, the non-organic enamel control, and the lased non-organic enamel subgroups were 3955 (1191), 52(49), 4565(1311), and 1191 (940), respectively. A factorial ANOVA showed significant effects of laser irradiation (p = 0.0001), organic matrix (p = 0.0125), and the laser-organic matrix interaction (p = 0.0377). The laser irradiation resulted in a greater than 98% reduction in mineral loss, but the laser effect dropped to about 70% when the organic matrix in the enamel was removed. The results suggest that clinically applicable CO2 laser irradiation may cause an almost complete inhibition of enamel demineralization.

Analysis of Variance↗
PubMed1997

Remineralization of root surfaces demineralized in solutions of differing fluoride levels.

The beneficial effects of fluoride on enamel have been well documented. However, limited data are available concerning the amount of fluoride required for beneficial effects on tooth root. Although studies have shown that fluoride inhibits root demineralization, the aim of this study was to investigate the location, extent and amount of remineralization on root dentin substrates after demineralization has occurred. The root surfaces of extracted human teeth were demineralized in a pure chemical buffer containing varying concentrations of sodium fluoride. After this lesion initiation, the same root sections were then placed into a remineralizing solution. The root sections were characterized after demineralization, and again after remineralization, by polarized light microscopy (PLM) and microradiography (MRG). Lesion depths after the demineralization phase were found to be inversely proportional to the fluoride concentration. When fluoride was present, bands or lines within the body of the lesion were observed with PLM and MRG. Using quantitative MRG, variations in mineral content and distribution were recorded. Examination of the root sections after the remineralization phase showed remineralization to have occurred on the remaining mineral and not on organic matrix devoid of mineral. The amount and location of mineral deposition may be of great significance in the arrestment and treatment of in vivo root surface caries.

Buffers↗
PubMed1995

Comparisons of in vitro root caries models.

The purpose of this article is to compare various model systems for the production of in vitro root caries and to assess their ability to simulate the naturally occurring root caries process. Partially saturated buffer models and gel models were evaluated using polarized light microscopy and both qualitative and quantitative microradiography. All model systems showed very similar lesion formation when examined under polarized light. When microradiographs were compared, the systems which contained fluoride, showed clear radiopaque bands within the lesion. The bands, which occurred only in the presence of fluoride, appeared to be due to remineralization. When using an in vitro system that simulates the natural root caries process, it is imperative to understand the components of the particular model, as well as its limitations, and to be aware of the need for more than one evaluative technique.

Buffers↗
PubMed1979

Structural geology of the Earth's interior.

Seismology is providing a more sharply focused picture of the Earth's internal structure that should lead to improved models of mantle dynamics. Lateral variations in seismic wave speeds have been documented in all major layers of the Earth external to its core, with horizontal scale lengths ranging from 10 to 10(4) km. These variations can be described in terms of three types of heterogeneity: compositional, aeolotropic, and thermobaric. All three types are represented in the lithosphere, but the properties of the deeper inhomogeneities remain hypothetical. It is argued that sublithospheric continental root structures are likely to involve compositional as well as thermobaric heterogeneities. The high-velocity anomalies characteristic of subduction zones-seismic evidence for detached and sinking thermal boundary layers-in some areas appear to extend below the seismicity cutoff and into the lower mantle or mesosphere. Mass exchange between the upper and lower mantles is implied, but the magnitude of the flux relative to the total mass flux involved in plate circulations is as yet unknown. Other observations, such as the vertical travel time anomalies seen in the western Pacific, may yield additional constraints on the flow geometries, but further documentation is necessary. Thermobaric heterogeneities associated with a thermal boundary layer at the base of the mantle could provide the explanation for some of the observations of heterogeneities in the deep mantle. The evidence for very small scale inhomogeneities (<50 km) in region D'' and for topography on the core-mantle interface motivate the speculation that there is a chemical boundary layer at this interface, as well as a thermal one.

Journal Article↗
PubMed1971

Optimal solutions to a linear inverse problem in geophysics.

This paper is concerned with the solution of the linear system obtained in the Backus-Gilbert formulation of the inverse problem for gross earth data. The theory of well-posed stochastic extensions to illposed linear problems, proposed by Franklin, is developed for this application. For given estimates of the statistical variance of the noise in the data, an optimal solution is obtained under the constraint that it be the output of a prescribed linear filter. Proper specification of this filter permits the introduction of information not contained in the data about the smoothness of an acceptable solution. As an example of the application of this theory, a preliminary model is presented for the density and shear velocity as a function of radius in the earth's interior.

Journal Article↗
PubMedDate not supplied

The reaction of stannous fluoride and hydroxyapatite.

Systematic investigation of the chemical reaction of a slurry of SnF2, Ca10(OH)2(PO4)6, and H2O shows that products other than CaF2 are determined by the relative concentrations of the reactants. In addition to Sn2OHPO4, and Sn3F3PO4, a previously unreported compound, Ca(SnF3)2, has been observed as a product of the reaction.

Calcium Fluoride↗