Fluoridation of partially demineralized human enamel in vivo. A comparison of SIMS and microdrill fluoride analysis

Mineralization in bovine dentin adjacent to glass-ionomer restorations

OBJECTIVES

To assess the uptake of fluoride as well as the increase in mineralization by bovine dentin after restoring an experimentally made cavity with conventional glass-ionomer cement or a polyacid resin composite.

METHODS

Cylindrical cavities were prepared on the labial root surfaces in bovine dentin. The cavities were restored with the test material. The restored teeth were individually suspended in distilled water at 37 degrees C for 30 days. The teeth were sectioned and the superficial dentin cavity walls were analyzed for fluoride, calcium, and phosphorus by an EPMA device. The effects of the different fluoride-releasing materials on the hardness of the dentin were determined by indentation (20-microm intervals below the filled surface into the underlying sound dentin from the surface to a depth of 100microm).

RESULTS

Conventional glass-ionomer cement had a significant effect on fluoride uptake. In addition, the calcium and phosphorus scan revealed the elevation of calcium and phosphorus levels in a deeper zone corresponding to the locations of the fluoride uptake at the surface of axial wall. However, the polyacid resin composite did not exhibit a zone of calcium and phosphorus elevation. The average dentin hardness under conventional glass-ionomer cement in the studied five distances ranged from 84.3 to 61.3KHN, however, that of the polyacid resin composite ranged from 62.5 to 64.9KHN. Analysis of variance for these data demonstrated a significant difference in hardness between the 20-microm depth and the other depths (P<0.01, ANOVA Fisher's PSLD).

CONCLUSION

The present paper indicates that the fluoride penetrated deeper into the dentin with conventional glass-ionomer cement than the polyacid resin composite. Conventional glass-ionomer cement had a significant effect on fluoride uptake. In addition, hypermineralization occurred within the superficial dentin cavity wall region of conventional glass-ionomer cement.

The effects of a sodium hypochlorite treatment on demineralized root dentin

The effects of a 10% NaOCl treatment for 2 min on demineralized human root dentin were investigated by means of: microradiography (MR), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and secondary ion mass spectroscopy (SIMS). MR measurements revealed that NaOCl caused a tissue contraction not related to water loss but to removal of organic substance(s), resulting in reductions of the lesion depth and mineral loss values by 15% and 42%, respectively. CLSM observations on wet dentin showed that the dentinal tubules underneath the surface are clearly observable and not deformed substantially by the NaOCl, except near the outermost surface. This indicates the importance of wet as well as of dried (high vacuum) observations. SEM micrographs (high vacuum) showed definite changes in the outer dentin surface structure; 85% of the originally open dentinal tubules were closed after NaOCl treatment. No marked changes were observed in the dentin ultrastructure inside lesions, as shown by SEM on fractured surfaces. SIMS data, pertaining to samples in high vacuum, showed a remarkable increase of chlorine (Cl) content in the entire lesion due to the NaOCl, indicating deep penetration of the original OC1 ions. The results suggest that the 2-min treatment of demineralized dentin by NaOCl solutions removes and/or changes part of the dentin matrix in nearly the whole lesion. As a consequence the mineral is somewhat redistributed, the outermost surface of a few mu m is changed, but the main dentin structure and element composition are still intact. These findings indicate that NaOCl treatments are of interest in remineralization and hyper-remineralization studies of dentin.

Comparison of fluoride profiles by SIMS with mineral density of subsurface enamel lesions treated intra-orally with a fluoride-releasing device

A variety of intra-oral model systems has evolved which allows for the study of remineralization of coronal and/or root-surface lesions following application of topical fluoride (F) agents. The problem of interpretation of the results has led to a variety of analytical methods (i.e., microhardness, F biopsy, microradiography, and polarizing light microscopy), each of which provides important but limited information related to the overall understanding of remineralization. Microhardness measures change in mineral content which is more precisely localized by microradiography and polarized light microscopy. F biopsy allows for assessment of the F uptake of lesions, but does not suggest the chemical state of the F. Previous work has demonstrated that patterns of mineral deposition during remineralization do not necessarily parallel the F uptake profiles, and fluoridated apatites cannot be distinguished from non-specifically-adsorbed F (Clark et al., 1988). Because artificial lesions demonstrate variations in depth and mineral content, complementary analytical methods that demonstrate profiles of both F content and mineral density curves on the same section are needed so that the process of remineralization can be more clearly understood. This study used secondary ion mass spectrometry (SIMS) for F profiles and quantitative microradiography for assessment of mineral deposition on the same section. These state-of-the-art methods demonstrate the precision with which information about remineralization can be obtained. Subsurface lesions in human enamel specimens were developed by immersion in 0.1 M lactate buffer with 1% CMC at a pH of 4.5 for 48 h.(ABSTRACT TRUNCATED AT 250 WORDS)

'Calcium fluoride-like' material formed in partially demineralized human enamel in vivo owing to the action of fluoridated toothpastes

In this paper are presented the results of a chemical analysis of partially demineralized enamel lesions positioned under plaque in vivo for 3 weeks. During the experimental period the samples were brushed with fluoridated or non-fluoridated toothpaste systems. After the experiment the fluoride and protein uptake was determined. Furthermore, KOH extractions of the lesions were carried out and the solutions analyzed for calcium, fluoride, and phosphate. The results show that 'CaF2-like' material is most likely formed inside lesions during the in vivo period. This in indicated from chemical analysis, Raman spectroscopy, and SEM observations. The amount of CaF2-like material is on the order of 0.1 wt% if we consider its formation all over the enamel lesions, or 1 wt% if we assume its formation in interprismatic regions of the enamel only. About 40% of the fluoride taken up from toothpaste systems is in the form of CaF2-like material. In vivo there is a substantial influx of proteins (approximately 0.3%) and also a very large influx of phosphate ions. The effect of CaF2-like material is most likely strongly dependent on conditions in the lesion, such as pH change.

Degradation of surface enamel and formation of precipitates after topical applications of sodium fluoride solutions in vitro

After topical treatment of enamel pieces cut from bovine incisors, the chemical composition of the solution phases and of the topmost layers of enamel were determined by special techniques of elemental and surface analysis. Fluoride seems to degrade surface enamel when applied in acidic and neutral solutions. Calcium remains immobile on the enamel surfaces, whereas phosphate goes into solution. When treated with acidic solutions (0.05-0.5 mol/l fluoride), a calcium-fluoride-rich phase is precipitated on the enamel surfaces.