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Single–section techniques are attractive in enamel de– and remineralization investigations because they allow longitudinal studies in which mineral changes can be assessed by microradiography (TMR). Nail varnish (NV) is in general applied to coat the cut thin–section sides. The aims of this study were to investigate: (1) NV penetration depth in cut surfaces of demineralized enamel, (2) the influence of NV on cut surfaces of demineralized enamel on TMR, (3) the influence of NV penetration on a following remineralization. Cut surfaces of thin sections of demineralized enamel were NV coated; the NV was peeled off and the penetration depth assessed by confocal laser scanning microscopy. The NV penetration was 18±5 μm (mean±SD) in demineralized enamel. To evaluate the possible influence of NV on TMR, cut surfaces of thin sections of demineralized enamel were coated (twice) and microradiographed before and after nail varnishing. The NV effect (total effect of penetrated and surface NV) on the main parameters of TMR, Ld and ΔZ, was less than 5% of the mean values. In the remineralization experiment (remineralization with 1.5 mM Ca2+, 0.9 mM phosphate, pH 7, 1 ppm F for 1 and 2 weeks), lesions in bulk samples, lesions in thin sections with NV–coated cut surfaces and lesions in thin sections in a PMMA (polymethylmethacrylate) holder were compared. (1) The remineralization of bulk samples and of NV–coated thin sections is different in one aspect. The amounts of mineral deposited in the lesions expressed as ΔZ are comparable after 1 week. But because the NV penetrates part of the lesion outside, there was an Ld difference. The lesion depth difference between bulk lesions and NV–coated lesions in thin sections was statistically significant and was about 19% less in NV–coated lesions after 1 week; after 2 weeks of remineralization there was no difference in Ld between bulk– and NV–coated lesions any more. (2) There was no difference in remineralization efficacy between lesions in bulk samples and lesions in thin sections in the PMMA holder.

During the caries process complex reactions involving calcium, phosphate, hydrogen and fluoride ions as main species take place. In this study the precipitation and dissolution reactions occurring in suspensions of enamel, hydroxyapatite (HAP) and fluorapatite (FAP) on addition of fluoride were investigated under well-defined conditions. pH and pF were monitored; calcium and phosphate concentrations were measured at selected times; the solid phases were examined by infra-red, X-ray diffraction and transmission electron microscopy. Precipitation of phosphate-containing calcium fluoride crystals, CaF2(P), can cause severe reduction in the calcium ion concentration and release of hydrogen ions from the precipitated phosphate. These reactions result in considerable dissolution of enamel, HAP and even of FAP. More of the added mineral dissolves with 50 mmol/l fluoride than with 10 mmol/l fluoride, mainly due to the greater reduction in calcium ion concentration. This work shows that phosphate-containing calcium fluoride is most likely an important compound to be considered in the caries process.

The diameter of dentinal tubules after demineralization and/or air drying has been quantified using light microscopy and scanning electron microscopy (SEM). The tubule diameter was assessed at a dista

Seventeen subjects with more than 3 x 10(5) mutans streptococci per millilitre of saliva completed this randomised, cross-over study. Four different chewing-gums, containing: (1) 70% xylitol, (2) 35% xylitol + 35% sorbitol, (3) 17.5% xylitol + 52.5% sorbitol, and (4) 70% sorbitol, were tested. The participants used 12 pieces of each gum per day for 25 days. During the four experimental periods, they wore a removable palatinal plate containing two demineralised enamel samples, and brushed their teeth with a non-fluoridated toothpaste. The results showed that an increased concentration of xylitol in the gum resulted in a lower number of mutans streptococci in both saliva and dental plaque, although the decreases were only significant in the saliva samples (p

In this paper the acid resistance of hyper-remineralized dentine was quantified by means of fluoride and mineral measurements. Hyper-remineralization was achieved by demineralization of dentine in an acidic gel system (pH 5) for 3 weeks, followed by remineralization in a solution containing 1.5 mM Ca, 0.9 mM phosphate and 10 ppm F at pH 7 and 37-degrees-C for 8 days. The samples were subsequently again demineralized in the gel system mentioned for 1, 2 and 3 weeks. Analysis for fluoride was done by means of the microdrill biopsy technique and to obtain information on the fluoride distribution by secondary ion mass spectrometry (SIMS); mineral was assessed by microradiography. The results showed that in hyper-remineralized dentine the original fluoride content was approximately 30,000 ppm F. This value was still in the same order after the acid challenge of 3 weeks at pH 5. These values were substantially higher than the baseline values in sound or in demineralized dentine being about 900 ppm F. The main microradiographic result was that there was no significant mineral change in the hyper-remineralized dentine due to the acid challenges. There was, however, a tendency for mineral redistribution deeper into the dentine lesion leading to lamination phenomena. The SIMS experiments on some of the samples showed a fluoride distribution in agreement with the microdrill fluoride data. Furthermore a fluoride redistribution took place in deeper parts of the lesion due to the acid challenges. The combined fluoride concentration and microradiographical data indicate that fluoride-enriched and highly mineralized hyper-remineralized dentine is more acid resistant than sound or demineralized dentine.

In this paper, data are presented on the in situ demineralization of human enamel as a function of the demineralization period. To quantify the mineral loss parameters versus time, it is important to obtain information on the kinetics, and thus on the mechanism of dental caries. The results show that for in situ enamel demineralization, the lesion depth as well as the mineral loss parameter both vary linearly with the demineralization time. This is in contrast to in vitro lesion formation where the third power, or the square power of the lesion depth is linearly related to the demineralization time. In in situ demineralization, the rate-determining step of the demineralization process is the inhibitor-controlled dissolution process at the enamel crystallite surfaces, while the inhibitor content (F-, proteins etc.) in the lesion originating from the plaque, saliva and enamel is high. Furthermore, the study indicates that in in situ demineralization, interprismatic mineral loss is very important.

A new method is presented for the determination of chlorhexidine in centrifuged saliva and in aqueous solutions by means of fluorescence spectroscopy. The method relies on complex formation between chlorhexidine and eosin. The fluorescence value of the chlorhexidine-eosin system decreases with increasing chlorhexidine concentrations. In centrifuged saliva a linear relation was found between the fluorescence at 541 nm and the chlorhexidine content up to about 15 ppm; the reproducibility of the method was found to be better than 1 ppm chlorhexidine. The biological spreading for centrifuged saliva from different participants as well as the spreading due to the period of saliva collection are about 3%. In whole uncentrifuged saliva the fluorescence method has been a detection limit of about 8 ppm chlorhexidine, due to the binding of the compound to salivary constituents. Above 8 ppm chlorhexidine, the biological variation in saliva is such that chlorhexidine determinations by means of fluorescence can be done only with a reproducibility of +/- 10 ppm. Advantages and disadvantages of the ultraviolet spectroscopy method, the radioactive labelling technique, and the fluorescence method for chlorhexidine determinations are discussed.

The penetration profiles of F have been investigated using secondary ion mass spectrometry, at depths of ca. 0.1–1.5 μm in specimens of permanent and deciduous human enamel after application of different varnishes and toothpastes. The treatment with NaF containing varnishes was found to result in gains of more than 1,000 wt-ppm F even at 1.5 μm depth, roughly proportional to the root of the fluoride content in the agent. Silane varnish yields similarly high F uptake and a particularly flat penetration profile. While F from the NaF varnish in the main seems to enter the dental tissue, that from the silane to a large extent remains in the agent medium, penetrating the porosities of enamel. Some evidence is seen of a chemical transformation of superficial enamel in the presence of the silane agent. Acidulated NaF toothpastes yield considerably higher and flatter F penetration profiles than all neutral or basic toothpastes investigated.

In this study, Knoop hardness experiments on artificial carious enamel (pH 5.0, 4.5 and 4.0) are presented with the load perpendicular to the subsurface lesion. The results show that for human and bovine enamel the indentation length is proportional to the square root of the load. The proportionality constant is numerically estimated for all pH values for human and bovine enamel. The indentation measurements reflect the decalcification despite the presence of surface layer covering the lesion.

The exposure of bovine enamel to an albumin-containing demineralizing solution results in penetration of protein into the porous enamel. Washing of this albumin-containing enamel results in a complete (low pretreatment albumin concentrations) or partial removal of the albumin (pretreatment concentrations greater than or equal to 200 micrograms/ml-1). Subsequent exposure to increasing salt concentrations of fluoride, phosphate, calcium or chloride shows a partial removal of albumin at fluoride or phosphate concentrations of 75 mM while complete removal occurred at 150-200 mM fluoride or phosphate. Exposure to either calcium or chloride, even at 3 M concentrations, showed a negligible albumin release. It is proposed that protein removed at high fluoride or phosphate concentrations is bound by a strong interaction between protein-carboxyl groups and calcium on the surface of the enamel mineral. The partial removal of albumin released at low fluoride or phosphate concentrations indicates an enamel-albumin interaction by means of Ca-bridging between protein-carboxyl groups and mineral phosphates. Finally, it is suggested that salt-free washing removes albumin that has lost its native form upon binding to the partially dissolved crystallites of the enamel. It is concluded that enamel is mainly protected from demineralization by the inhibitory effects of protein penetrated into the pores, in addition to possible protection by the pellicle on the surface.

An investigation of the average crystallite diameters in human enamel has been carried out near the anatomical surface (≈2.5 μm) and far from the surface (≈ 150 μm). Mature human deciduous as well as unerupted human enamel was studied. The results show that in deciduous enamel the average crystallite diameter near the surface and subsurface are 88 and 46 nm, respectively. For mature human enamel the near-surface and far from the surface values were 59 and 38 nm, respectively. In non-erupted enamel, however, no significant differences between near-surface and subsurface enamel were measurable. Furthermore, the fluoride content has been measured at the various positions of interest. No correlation between fluoride content and crystallite diameter was found. The diameter differences measured may be due to the influence of the aggressive oral environment on the teeth surfaces after eruption. After eruption frequent de- and remineralization dissolves small crystallites and by reprecipitation and/or growth larger crystallites are formed near the surface.

This scanning electron microscopic (SEM) study summarizes observations made on 6 fluorosed, erupted human permanent teeth. As controls, normal permanent teeth were employed. The exterior surface of the fluorosed teeth as well as outer and inner parts of enamel surfaces obtained by breaking were studied without or following short treatment with citric acid. The exterior surface and the outer part of broken or cut surfaces regularly showed evidence of in vivo decalcification. Central defects in the c-axis direction of enamel crystallites were seen in non-acid-treated exterior surfaces. The outer part of broken, non-treated as well as polished surfaces displayed a highly variable pattern of dissolution, in which areas immediately surrounding prism sheath markings appeared particularly resistant. The basic texture in such areas was described as of a sintered nature, in which no structures akin to normal crystallites could be identified. The inner part of similarly prepared surfaces displayed a rather regular, but still more porous than normal, appearance. Central defects in the crystallites in the inner parts of fluorosed enamel were only seen after in vitro acid treatment. In broken, non-treated surfaces the inner parts showed remarkably well shaped crystallites with a width about three times larger than sound enamel.

Inorganic phosphate was determined by the reduction of a phosphomolybdate complex with ascorbic acid or stannous chloride. Fluoride interfered with both methods: (i) Absorbance of the complex reduced

In this study, the influence of urea solutions on both young and mature enamel was investigated. The urea concentrations were 5 and 0.1 M; the interaction period varied between 3 h and 3 months. The hydrogen (H)-bond destruction due to urea produces tiny micro-channels. The scanning electron microscope (SEM) investigations on replicas and by direct observations indicated that: (i) urea solutions destroy H-bonds in specific areas; (ii) these areas are most likely isolated prisms in the perikymata; (iii) interprismatic regions are, in contrast to these prisms, hardly influenced by the urea solutions. It is suggested that the special areas with relatively weak H-bonding are similar to the area attacked initially in artificial caries-like enamel lesions.

Dentine subjected to an in vivo demineralization challenge by plaque looses substantial amounts of mineral and is expected to change its ultrastructure. Results are presented of a combined microradiography and scanning electron microscopy (SEM) study on in vivo demineralized human dentine. The tissue was first demineralized in vivo under plaque for 3 weeks and subsequently analyzed by microradiography and SEM. In 6 participants dentine was positioned in a full prosthesis just under M2 in such a way that the outer surface of the tissue was 1.5 mm lower than the surface of the prosthesis; plaque accumulation takes place in the recessed area. A special technique allows SEM observations (at a given distance from the outer surface) on broken thin sections of demineralized dentine with a mineral content determined by microradiography. The results show that the ultrastructure of the dentine changes during severe demineralization. The main ultrastructural features are, however, still largely intact, even if half of the mineral originally present has been lost. In dentine with a mineral content of about 25 vol%, the dentinal tubules are enlarged by about 30%. In vivo demineralized dentine looses mineral in substantial amounts both from intertubular and from peritubular regions.

In this paper remineralization of bovine dentine is reported. After demineralization of the dentine in an acidic gel system creating lesions of about 180 μm depth, the tissue was remineralized in a 1.5 mMCa and 0.9 mM phosphate containing solution at pH 7 and 37 °C for 8 or 21 days. The F content in the remineralization solution was 0.02, 2, or 10 ppm as NaF. Samples were analyzed by means of microradiography and scanning electron microscopy. The results show that remineralization (without F added in solution) causes a decrease in mineral loss and in lesion depth. With 2 or 10 ppm in solution, however, a substantial mineral accumulation in the lesion, but particularly on the original dentine surface, was observed. During 3 weeks of remineralization, mineral accumulations of 67 and 70 vol% of mineral for 2 and 10 ppm F in solution, respectively, were found near the original outer surface, with the sound dentine mineral value being 48 vol%. The combined microradiography and scanning electron microscopy data show that the mineral accumulated is for a major part deposited on the dentine tissue and partly inside. The latter deposition occurred both inside the tubules as well as in the intertubular areas. Inside the tubules dense precipitates were observed. Because several differences exist between bovine and human dentine, an extrapolation to the human in vivo situation is speculative. The results indicate that the presence of fluoride in the parts per million range is important for dentine remineralization efficacy and that the outer surface area in dentine can be ‘overremineralized’.

The influence of daily fluoride mouthrinsing on development of enamel lesions was investigated in an in vivo caries model. A local cariogenic environment was created on the buccal surface of premolars

A single topical treatment with three different fluoride-containing systems on human enamel resulted both in an enrichment of the F content in the enamel and an accumulation of F re

The extent of abrasion of human enamel caused by tooth brushing was investigated in a laboratory study. The enamel was made radioactive by irradiation in a nuclear reactor. The amount of radioactive material removed by brushing with a 30% toothpaste slurry was quantitatively measured as a function of the number of strokes. A detailed description of the brushing machine, the slurry container, the sampling and the calibration is given. The results showed that from polished enamel initially material is removed fairly rapidly. After 500 strokes the amount abraded away was 12.5 μg cm––2 corresponding to a layer in the order of 0.2 μm. In the range between 500 and 10,000 strokes the rate of abrasion was slower; after 10,000 strokes a layer of about 0.4 μm had been removed. The results indicate a considerable biological variation between the various specimens.

High-resolution transmission electron microscopy is one of the few techniques where it is possible to investigate dental enamel at the individual crystallite level. By measuring interfringe spacings i

The surface free energy and its polar- and dispersion components pertaining to pellicle-covered human enamel, sintered hydroxyapatite, Diacryl® and fluorethy-lenepropylene were determined from contact angle measurements. During the first 5 min of pellicle formation, the total surface free energy of human enamel increased from 84 to 110 erg·cm––2. After these first 5 min the surface free energy of pellicle covered solids remained constant for at least 2 h. Pellicle formation on apolar solids like fluorethylenepropylene increased the surface free energy only slightly.

In this paper the influence of xylitol on the progress of the demineralization front in enamel is described and discussed. Xylitol reduces enamel demineralization; the influence can be observed mainly

The diffusion of 32P-labelled phosphate ions in whole bovine enamel was investigated in the pH range 5–9 at 37° C. The experiments were carried out in preequilibrated solutions (using contralateral teeth) to ensure that at the various pH values dissolution effects were absent. The diffusion profiles obtained are interpreted with a grain boundary diffusion model. The diffusion coefficients Dk and Dv for the interprismatic and intraprismatic diffusion, respectively, were found to increase with decreasing pH. The increase was most pronounced for Dv values. It is explained by the pH dependency of the fractions of the monovalent H2PO4- ions and divalent HPO42- ions in the enamel pores and on the enamel crystallites; at pH 7 phosphate is transported in enamel by both HPO42- and H2PO4-; H2PO4- diffusion dominates at pH 5 whereasHPO42- diffusion is dominating at pH 9.