Intact Enamel Research Articles

Determination of the calcium fluoride formed from in vitro exposure of human enamel to fluoride solutions

Equilibration in 1M KOH for 24 hr of from 0.6 to 30 μg ml −1 of CaF 2 and different amounts of fluorapatite resulted in dissolution of the CaF 2 while the fluorapatite remained intact. CaF 2 was also selectively dissolved from mixtures of CaF 2 and pre-fluoridated powdered human enamel. No fluoride was dissolved from blocks of intact enamel treated in 10 ml of KOH for 24 hr, but most of the fluoride deposited from topical treatments was lost by this treatment. Findings on enamel blocks treated with topical solutions of acidulated phosphate fluoride and NH 4F showed that the fluoride retained after exposure to KOH was not related to the initial uptake. Scanning electron microscopic examinations of F-treated enamel surfaces verified the removal of CaF 2 by KOH. The concentrations of Ca, P and F in the KOH solution after equilibration with different amounts of CaF 2, hydroxyapatite and fluorapatite showed that rapid release of F and Ca from CaF 2 depressed dissolution of the apatites, and that the system was governed by the solubility products of CaF 2 and Ca(OH) 2. It is concluded that 1M KOH can be used for the assessment of the CaF 2 formed from topical treatments in in vitro systems.

Diffusion fluxes of tritiated water across human enamel membranes

Isothermal diffusion fluxes of tritiated water across human incisor and canine enamel membranes were measured using a small volume diaphragm cell in the temperature range 13–37 °C. The plano-parallel intact enamel membranes were identified by geometric surface area, thickness, age and sex of donor. The calculated apparent diffusion coefficient values, D a , revealed that significant differences in the water fluxes exist between these two membranes, with the incisors displaying the larger D a values. Diffusional activation energies, E a , calculated from the D a data obtained at three temperatures indicated an interaction between the diffusing water and the enamel pores, with the larger values observed for the canines. The data are discussed in terms of a parallel pore model in which pore constrictions of the enamel serve as energy barriers to diffusion.

The effect of topically applied fluoride on enamel remineralization in vitro

The effect of fluoride applied to mildly etched enamel was studied in a remineralizing system in vitro utilizing 32P labelled neutral phosphate buffer to assess change. Blocks of intact surface enamel were cut from teeth and divided among eight treatment groups. The blocks were mounted in specially constructed holders which permitted identical placement of the blocks in a gas flow counter. The findings showed increased 32P exchange in etched enamel. Exposure of etched enamel to a mineralizing solution for 24 hr after a 24 hr treatment with 2.2 per cent sodium fluoride or without fluoride treatment did not result in a significant reduction in 32P exchange. Exchange was significantly reduced in etched enamel which was treated for four minutes with a 2.2 or 0.022 per cent sodium fluoride or for 24 hr with 0.022 per cent sodium fluoride prior to exposure to a mineralizing solution.

Chemically induced in vitro lesions in dental enamel.

abstract— Intact enamel surfaces were exposed to continuously stirred buffers which were either supersaturated or unsaturated with respect to fluorapatite and hydroxyapatite. When the buffer was supersaturated with respect to fluorapatite and unsaturated with respect to hydroxyapatite, caries‐like lesions developed. When the liquid was unsaturated with respect to both apatites, erosion‐like lesions developed. The preservation of the radiopaque surface layer of caries lesions was ascribed to formation of a fluorapatite, and the subsurface loss of mineral was ascribed to a dissolution of hydroxyapatite. The lack of a well‐preserved surface layer in erosions was explained by a coincident dissolution of both hydroxyapatite and fluorapatite.

Potential of yttrium-aluminum-garnet laser in caries prevention.

Abstract. Intact tooth enamel of extracted human teeth was exposed to a pulsed Nd‐YAG laser at an energy density of 10 to 20 joules/cm2. In vitro demineralization by lactic acid was accomplished by dextran‐producing strains of Streptococcus mutatis PK‐1 growing on the enamel surface. Scanning electron microscopic observations on the laser irradiated enamel supported micro‐radiographic findings and indicated that the laser irradiated enamel surface was more resistant to decalcification than the non‐irradiated control enamel. Surface changes suggestive of fusion occurred at the low energy density of 10 to 20 joules/cm2. Laser beam irradiation imparted a degree of alteration to enamel surface that subsequently reduced subsurface demineralization. A significant difference in solubility was found between laser irradiated and non‐irradiated enamel.

The pore structure of human dental enamel

Water vapour sorption isotherms of intact enamel reveal permanent and reproducible hysteresis loops extending to very low relative pressures. However, a detailed pore volume analysis shows that true micropores are absent. These results and those obtained by scanning the hysteresis loops are consistent with the presence of constrictions extending down to molecular dimensions. The bimodal pore volume distribution, obtained without resource to any assumed geometrical model, may relate to the inter- and intra-prismatic spacings of dental enamel.

Zinc silicophosphate cement: Influence of composition on the acid solubility and fluoride content of enamel

A series of experiments were conducted to determine the effect of the silicate concentration in zinc silicophosphate cements on the fluoride uptake and acid solubility of intact enamel. The cement prepared from powders that contained 50 and 90 per cent silicate powder produced an increase in fluoride and a reduction in the calcium solubility. The magnitude of change was approximately twice as great with the 90 per cent silicate as with the 50 per cent silicate formulation. Use of the cement prepared from the powder which contained only 10 per cent silicate had no appreciable effect.

Uptake and retention of fluoride by intact enamel in vivo after application of neutral sodium fluoride.

abstract – The uptake and retention of fluoride in surface enamel in vivo after a single topical application of a neutral 2 % NaF solution was studied on the basis of 2–3 μm thick enamel biopsies from maxillary central incisors in adults and children. The biopsy technique included delimiting of the sampling area by means of abrasive‐resistant, adhesive tape, punched with perforations of known sizes admitting of two biopsies on different places on the same tooth surface. This method made it possible to calculate the depth of each biopsy and to perform the comparative studies with intradental control. The F uptake was estimated by comparing F concentrations in biopsies taken before and 1 week after topical treatment. In teeth of 10‐ to 11‐year‐old children the F concentration increased 259 ± 393 parts/106, which is statistically significant (P < 0.002). The mean uptake in teeth of adults, 22–27 years of age, was 179 ± 401 parts/106 which did not exhibit statistical significance (P > 0.10). The F concentrations in biopsies taken 1 week and 8 weeks after treatment from teeth in children were almost identical, indicating that the acquired F is firmly fixed in the enamel for 2 months or longer.

Fluoride Uptake and Acid Solubility of Enamel Exposed to Carboxylate Cement Containing MFP

Sound enamel had a significantly higher fluoride content when it was in contact for 7 or 30 days with a carboxylate cement to which 2% or 10% concentrations of sodium monofluorophosphate were added. The solubility of the intact enamel also was reduced by contact with the cement that contained MFP. No significant reduction in enamel solubility was observed when the non-fluoride-containing carboxylate cement was used.

Effects of daily rinsing and ingestion of fluoride solutions upon dental caries and enamel fluoride

Three groups of children (age 8–11 yr), rinsed daily in school for 3 yr with 5 ml of either (1) acidulated phosphate fluoride (APF, 0.02 per cent F, 0.1 M phosphate, pH 4.0); (2) neutral NaF (0.02 per cent F) or (3) a neutral placebo. The solutions were kept in the mouth for 1 min and then swallowed. At the end of the study, reductions in DFS of 30 and 27 per cent were observed in the APF and the neutral NaF groups, respectively. The caries reduction in the teeth initially erupted was 25 per cent in both groups. Analyses of enamel biopsies from teeth initially erupted indicated small posteruptive F uptakes in both treatment groups. The APF solution was superior to the neutral NaF in depositing fluoride in intact enamel. The fluoride acquisition of teeth erupting during the study was substantially greater than that of teeth initially erupted.

Laser Inhibition of Dental Caries Suggested by First Tests in Vivo

Intact tooth enamel from humans was exposed extraorally to a superpulsed, carbon-dioxide laser at energy densities of 10 to 15 joules/cm 2 . When it was tested in the mouth of one of the investigators, the lased enamel proved much more resistant than unlased control enamel to the oral environmental influences generally conducive to dental caries.

Kinetic calcium, phosphate, and fluoride dissolution after topical fluoride application to intact enamel surfaces.

In a system without accumulation of products dissolved from enamel, the total mineral dissolved was reduced by about 10% for NaF- and SnF2-treated surfaces and was increased by about 10% for APF-treated surfaces. Accumulation in solution of products dissolved from the enamel surfaces enhanced surface remineralization to account for a net decreased dissolution as compared with dissolution without accumulation of products.

Reactions of isotopic SnF2, NaF and acid phosphate fluoride on the enamel surface

The reactions of 113SnF2, Sn18F2, Na18F, and APF (acid phosphate fluoride, labelled with 18F) solutions on human dental enamel surface under conditions similar to topical application in vivo were investigated.The experiments supported the following conclusions.1) A remarkable accumulation of Sn in or on the enamel surface was found after the runs of repetition with SnF2 solution, whereas a minimum amount of F accumulated as compared with NaF or APF solution.2) The enamel surface treated with SnF2 solution aquired more remarkable resistance to acid than treated with NaF or APF solutions.3) After the treatment wtih SnF2 solution, the greater part of Sn taken on the enamel rapidly turned into acid-insoluble compounds.The major amount of these Sn compounds was found on the enamel surface.4) Fluoride taken by the enamel from fluoride solution diffused immediately into the surface layer of the enamel. The easy release of these fluorides by decalcification indicated that a fair amount of fluoride in the enamel remains in unreacted form.5) Statistic analyses, however, revealed no significant correlation between Sn or F uptake and increased resistance of enamel to acid.6) In the analyses of the Sn/F ratio accumulated on the enamel and the amount of F and the Ca/P ratio released by acid, it could not be shown that the Sn compounds on the enamel are either SnPO4, Sn4 (PO4) 2 (OH) 2H2O, or Sn3F3PO4, as had been formerly reported.7) Although the enamel surface was polished with Al2O3, a striking variation of Sn uptake by the enamel was found. This variation of Sn uptake might be dependent on both random difference from place to place in one tooth enamel and on individual tooth differences, both of which consist of unknown factors.F uptake also varied markedly from tooth to tooth, but variation from place to place in one tooth enamel was negligible.8) Incipient carious enamel took up Sn more strongly than the intact enamel.

The inorganic composition and solubility of dental enamel from several specified population groups

The solubility in lactate buffer (pH 4.5) and the inorganic composition of intact enamel surfaces of 234 teeth obtained from eleven specified and diverse sources including trisomic 21 subjects, were studied. The solubility was determined at conditions approximating to equilibrium and the surface and two succeeding enamel layers (each approx. 30 μm thick) analysed. Significant differences in solubility and composition were found between some groups but trisomic enamel was not considered unusual in these respects. Enamel groups could be ranked in order of solubility; all deciduous enamel groups were more soluble than permanent enamels. For most enamels, the solubility was inversely correlated with enamel fluoride concentrations and directly correlated with carbonate concentrations and the ratio of these two components. Fluoride concentrations in the acid buffer correlated with the solubility and fluoride level in the respective enamel groups. It was concluded that environmental factors present during or following enamel maturation influence enamel composition and solubility.

An in vivo study on enamel fluoride in children living in a fluoridated and in a non-fluoridated area

Fluoride was determined in intact surface enamel from three tooth types in 9–11 yr old continuous residents of the communities of Salem (water F: 1 ppm) and Hyannis (water F < 0.1 ppm) in Massachusetts. The mean F concentrations of central incisors at the approximate depth of 0.5 μm were 3000 ppm and 2100 ppm in Salem and Hyannis, respectively. The concentrations decreased by about 1000 ppm over the subsequent 1.5 μm depth interval. Comparisons between the two populations on the basis of lateral incisors and of first molars yielded similar results. The findings also indicated that differences within a mouth between various tooth types were fairly small. There was a marked individual variation within each population. In Salem, the F levels of enamel in males were significantly higher than in females. A similar trend was found in Hyannis. No elevation of enamel F shortly after the use of an F dentifrice could be shown.

Response of human enamel to topical application of ammonium fluoride

In-vitro uptake of F by intact enamel from 0.62 M solutions of NH 4F was greater than that from NaF at low pH, but similar at nearly neutral or alkaline pH. Fluoride contents in enamel biopsies taken 2 weeks after a 3 min topical treatment with the acid solutions also were higher for the NH 4F treatment. The in-vitro and in-vivo uptake from both solutions was enhanced by pretreating the enamel for one minute with 0.05 M phosphoric acid. Examination by the electron microscope of the F-exposed enamel before and after washing revealed the deposit formed from NH 4F was retained more tenaciously than that formed from NaF. X-ray diffraction patterns showed formation of CaF 2 when ground enamel was treated with either of the two acid fluoride solutions.

Solubility of surface enamel treated with precipitate-free aqueous solutions of stannous fluoride.

The antisolubility effect of some precipitate-free, dilute aqueous solutions of stannous fluoride against acid demineralization was determined through an in vitro decalcification test on the intact surface enamel of human teeth. Significant decrease in solubility occurred after treatment in spite of the highly reduced concentrations of titratable stannous ions found.

Infrared internal reflection spectroscopy of human enamel surfaces

Techniques previously utilized for chemical analysis of enamel surfaces are generally unsuitable for in-vivo testing. This study explored the utility of internal reflection spectroscopy (IRS) as a non-destructive method for enamel-surface analysis. Powders (enamel plus reference inorganic materials) and solids (flattened and unaltered enamel slabs) were analysed by IRS. Most samples were mounted in a Wilks Model 45 Micro-ATR Accessory and scanned from 2 to 25 μm to obtain i.r. spectra. Comparability of IRS data with that of transmission methods was established. Typical apatitic ν 3 phosphorous-oxygen absorption was observed at 1090 cm −1 and 1040 cm −1 in spectra of natural fluorapatites and enamel powders. Spectral differences were demonstrated between powdered and intact enamel. The presence of carbonate was confirmed in both powdered and solid enamel. Intact surface enamel and fluorapatites failed to absorb at 630 cm −1. Weak absorption at 630 cm −1 after disking of the enamel surface was interpreted as a relative loss of fluorapatite due to mechanical reduction to subsurface levels. Internal reflection spectroscopy enabled subtle chemical differences in enamel surface to be distinguished. This non-destructive method offers promise for in-vivo enamel surface analysis.

Monofluorophosphate interaction with hydroxyapatite and intact enamel.

Hydroxyapatite was exposed to solutions of monofluorophosphate (MFP) at pH 5 and pH 7, for periods up to 48 h, and fluoride (F^––) and F as MFP were measured in solution and solid. The exposed solid was dissolved in 0.5 m HC104 at 2 °C and F^–– measured immediately, and after hydrolysis had been completed 24 h later, employing a fluoride electrode. Solutions were analyzed in a similar manner. Solution F^–– (3% of total F) decreased rapidly and then gradually increased to concentrations above the original level. Solution MFP decreased continuously, the rate decreasing with time. The corresponding deposition of F on the solid was in the forms of both F^–– and MFP. The fraction of deposited F^–– increased with increased time of exposure while the fraction of F as MFP decreased. MFP was removed more readily by washing than F^––. MFP in MFP exposed apatite decreased while forming F^–– under humid conditions, but remained constant under dry conditions. Only small amounts of F were deposited from MFP in intact enamel. MFP retained in the mouth after a MFP rinse was subjected to rapid hydrolysis. The findings showed that the uptake of F from MFP was greater at pH 5 than at pH 7 and that MFP is hydrolyzed by two mechanisms, one operating at the solid solution interface of the apatite and the other in saliva and/or plaque. It is concluded that the caries-reducing effect of MFP is due to F^–– released by hydrolysis.

Determination of tin in enamel and dentin by atomic absorption spectroscopy.

The determination of tin by atomic absorption spectroscopy was developed to such a degree that it could be applied to the analysis of tin in dental tissues at the 1 ppm level. This development involved the elimination of the interference due to calcium and its phosphates and the improvement of operating conditions to maximize sensitivity. By use of this method, tin was determined in untreated and stannous fluoride-treated powdered and intact enamel and dentin.