The chemical changes which occur during the process of carious destruction of enamel are complex due to a number of factors. First, substituted hydroxyapatite, the main component of dental enamel, can behave in a very complex manner during dissolution. This is due not only to its ability to accept substituent ions but also to the wide range of calcium phosphate species which can form following dissolution. In addition, the composition, i.e., the extent of substitution, changes throughout enamel in the direction of carious attack, i.e., from surface to interior. Both surface and positively birefringent zones of the lesion clearly illustrate that carious destruction is not simple dissolution. Selective dissolution of soluble minerals occurs, and there is the probability of reprecipitation. The role of fluoride here is crucial in that not only does it protect enamel per se but also its presence in solution means that rather insoluble fluoridated species can form very easily, encouraging redeposition. The role of organic material clearly needs further investigation, but there is the real possibility of both inhibition of repair and facilitation of redeposition. For the future, delivering fluoride deep into the lesion would appear to offer the prospect of improved repair. This would entail a delivery vehicle which solved the problem of fluoride uptake by apatite at the tooth surface. Elucidation of the role of organic material may also reveal putative mechanisms for encouraging repair and/or protecting the enamel mineral. (+info)
Effect of experimental fluoride-releasing tooth separator on acid resistance of human enamel in vitro.
(2/23)
This study aimed to investigate the fluoride-releasing ability of an experimental tooth separator consisting of polyurethane elastomer with tin fluoride and its effect on the acid resistance of human enamel. The tooth separator was set around an enamel slab and stored in de-ionized water for 10 days. The daily concentration of fluoride in the de-ionized water was measured. Then the enamel surface was artificially decalcified by a lactic acid buffer solution (pH 4.5) for 96 hours. The mineral density at the surface layer of the enamel was measured to evaluate the acid resistance. The fluoride release increased with the amount of fluoride in the separator, but decreased with the immersion time. Both the enamel area contacting with the separator and its surrounding area showed lower mineral loss and lesion depth compared with the controls (P < 0.05). It is suggested that the experimental tooth separator would release enough fluoride and improve the acid resistance of the enamel surface layer. (+info)
A comparative study of fluoride-releasing adhesive resin materials.
(3/23)
One of the most important and exciting properties of recently introduced dental restorative materials is their ability to release fluoride ions, as this has several advantageous effects on tooth structures. They have been extensively used as fluoride-releasing filling and luting materials. Recently, fluoride-releasing adhesive resins and fluoride-releasing adhesive resin cement have been developed and introduced for clinical use. The purpose of this study was to evaluate the fluoride release from these adhesive resins and the fluoride uptake by both enamel and dentin, as well as the acid-resistance of these tooth structures. Based on our results, we conclude that fluoride-releasing adhesive resins and luting cements are useful for the prevention of initial or secondary caries, especially along the margins of restorations. (+info)
Relationship between the fluoride concentration of the fluoride-releasing elastomers and the acquired acid resistance of human enamel in vitro.
(4/23)
The objective of the study was to evaluate the relationship between the fluoride concentration of the fluoride-releasing elastomers and the acquired acid resistance of human enamel. Four kinds of fluoride concentration of the experimental fluoride-releasing elastomers were 1.25, 2.5, 3.75 and 5.0 wt%. An enamel block was cut into two smaller enamel blocks, one of which was set with an elastomer, the other as a control not set with elastomer. A plastic block that had the same shape as the small enamel block was also set with elastomer. Fluoride release and acid resistance tests were carried out. The mineral loss of the demineralized enamel was measured by microradiography. The results showed that the fluoride-releasing ability significantly increased with the increase of fluoride concentration in the elastomer (p < 0.05). The acid resistance of the enamel appeared to be enhanced greatly, however, its change was not proportional to the fluoride concentration in the elastomers. (+info)
Nd:YAG laser ablation and acid resistance of enamel.
(5/23)
The acid resistance of Nd:YAG laser-ablated enamel surfaces was studied by evaluating crystal structure, mineral distribution, and fluorescence radiance and image in the present study. For comparison, 37% phosphoric acid etching was performed. The formation of beta-tricalcium phosphate (beta-TCP) was confirmed in the laser-ablated surface. The Ca/P ratio increased after ablation due to mineral re-distribution. In contrast, the Ca/P ratio decreased after acid etching due to mineral loss. The laser-ablated enamels showed a smaller increase of fluorescence radiances and less clear laser confocal scanning microscope images than those observed in the acid-etched enamels. The former suggests a minimized mineral loss. The Nd:YAG laser irradiation will enhance the acid resistance and retard the carious progression in enamel. (+info)
What is the critical pH and why does a tooth dissolve in acid?
(6/23)
This paper discusses the concept of critical pH for dissolution of enamel in oral fluids. The critical pH does not have a fixed value but rather is inversely proportional to the calcium and phosphate concentrations in the solution. The paper also discusses why teeth dissolve in acid, why remineralization of white-spot caries lesions is possible and why remineralization of teeth eroded by acid is not possible. (+info)
Effects of a non-rinse conditioner on the enamel of primary teeth.
(7/23)
The aim of this in vitro study was to evaluate by scanning electron microscopy the morphological aspects of the enamel of primary teeth after etching with 36% phosphoric acid or a non-rinse conditioner. Ten naturally exfoliated anterior primary teeth were selected. The samples were subjected to prophylaxis with pumice paste and water using a low-speed hand piece. Etching was done on the buccal surface. Specimens were divided into 2 groups: G1 (n=10): etching with 36% phosphoric acid gel - Conditioner 36 (Dentsply) for 20 s, followed by water rinse for 15 s; G2 (n=10): etching with NRC - Non Rinse Conditioner (Dentsply) for 20 s, followed by air drying for 15 s. The samples were dehydrated, mounted on metal stubs, coated with gold and observed with Jeol JSM-6100 scanning electron microscope. Electron-micrographic analysis showed that both etching agents were effective for etching the enamel of primary teeth causing the formation of microporosities on the enamel surface, although the etching pattern was more effective with the use of 36% phosphoric acid gel. (+info)
The effect of gamma radiation on enamel hardness and its resistance to demineralization in vitro.
(8/23)
Given the importance of sterilizing human teeth before using them in research, the effects of a 25 kGy dose of gamma radiation on the mechanical properties of enamel and its resistance to demineralization were evaluated. Thirty human teeth were sectioned longitudinally, and while one half of each tooth was irradiated, the other half was kept as a control. Abraded and unabraded enamel slabs were obtained from these halves. The surface microhardness (SMH) of abraded slabs of irradiated and non-irradiated enamel was determined to evaluate the effect of radiation on enamel structure. Further, both abraded and unabraded slabs, either irradiated or non-irradiated, were submitted to a pH-cycling model to evaluate enamel resistance to demineralization, which was quantified by mineral loss (deltaZ) using cross-sectional microhardness. The data for SMH and deltaZ were statistically analyzed by t-test and ANOVA, respectively. The difference in enamel SMH between slabs from irradiated teeth and non-irradiated teeth was not statistically significant (P > 0.05). The abraded enamel slabs showed higher values of deltaZ than unabraded enamel slabs (P < 0.05), but the irradiation effect was not statistically significant (P > 0.05). The results suggest that the medical gamma radiation dose of 25 kGy does not affect either enamel hardness or its resistance to demineralization. (+info)