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At least 595 records · Page 33Linked to original sources
PubMed1986

Effects of two fluoride gels on fluoride uptake and phosphorus loss during artificial caries formation.

Blocks of human enamel were cycled through a demineralization--F-treatment-remineralization procedure and then analyzed for fluoride and the presence of caries-like lesions. Treatments with a sodium fluoride gel (5000 ppm F) increased the enamel fluoride concentration to 6500 ppm F, whereas a stannous fluoride gel (1000 ppm F) increased enamel fluoride to about 1200 ppm F. Although a control treatment (water) allowed caries-like lesions to form, as observed by microradiography, no lesions were found in either of the fluoride-treated groups. When the experiment was repeated with radioactive teeth, mineral loss, as determined by release of 32P, was again greatest in the water-treated control group, but some loss was observed in the fluoride treatment groups. The least loss was found in the sodium fluoride group. It was concluded that the fluoride treatments not only increased enamel resistance but also enhanced remineralization so that calcium phosphate was replaced during the subsequent remineralization phase. Because of the probability that stannous ions were deposited during the stannous fluoride treatments, some of the apparent calcium phosphate re-deposition in this group was probably stannous compounds.

Absorptiometry, Photon↗
PubMed1987

Physical model for non-steady-state dissolution of dental enamel.

The purpose of this study was to provide a rigorous theoretical understanding of the dissolution behavior of dental enamel over the entire time-course of demineralization and to simulate by computer an erosion-type caries lesion according to the physical "hydroxyapatite model". The appropriate diffusion equations which account for simultaneous diffusion and equilibrium of all species in enamel pores, boundary layer, and bulk solution, and which also take into consideration surface reaction kinetics, were employed to allow for calculation of the micro-environmental solution concentration and changes in the mineral density as a function of time and distance within the enamel. This comprehensive physical model for non-steady-state enamel dissolution also explicitly takes into account changes in the diffusivity and the dissolution rate constant as a function of mineral density. Demineralization experiments were conducted in 0.1 mol/L sink acetate buffer (pH = 4.50, mu = 0.50), with ground bovine dental enamel blocks of known surface area mounted (with beeswax) in a rotating disk apparatus. Mineral density profiles were quantified by means of contact x-ray microradiography. The physical model was used to predict mineral density profiles for given demineralization treatments. The experimental profiles agreed quite well with the predicted profiles, when the effective diffusivity of the enamel was assumed to be a function of porosity and when changes in surface area of the crystallites were taken into consideration.

Animals↗
PubMed1989

Scanning electron microscopic characterization of sensitive vs. insensitive human radicular dentin.

Our aim was to investigate the structural changes of dentinal tubules in specimens obtained from both hypersensitive and naturally desensitized areas in wedge-shaped defects on the same exposed cervical dentin surface of a hypersensitive tooth. A new biopsy technique that makes use of a hollow, cylindrical diamond bur was designed so that specimens from exposed root dentin of vital teeth could be obtained. Twenty-two dentin biopsy pairs were divided into two groups; one was prepared for scanning electron microscopy (SEM) and the other for microradiography (MR). Small hypersensitive areas were identified by a scratch test on exposed human dentin in vivo. SEM observation of the dentin biopsies showed that the orifices of many dentinal tubules in hypersensitive areas were open and that membranous structures appeared on the walls of dentinal tubules. In naturally desensitized areas on the same dentin surface, most of the dentinal tubules were obturated with rhombohedral crystals of all sizes; membranous structures were not observed in these tubules. These results showed that hypersensitivity occurred on the exposed dentin when most of the tubular orifices were open.

Adult↗
PubMed1990

The effect of plaque thickness on progression of artificial caries lesion formation in situ.

Eighty thin enamel sections with artificially-formed caries lesions were implanted in the buccal surfaces of molars (in the removable partial dentures of ten subjects) and covered with a steel mesh for plaque accumulation to occur. The mesh was placed in contact with the enamel surface in half the lesions and 0.5 mm above the lesions in the other half, thus facilitating formation of thin and thick plaque samples. Following two-week use of a non-fluoride dentifrice, the lesions were analyzed for mineral change by quantitative microradiography. Significant mineral was lost from lesions in both groups, but the loss was twice as large in the thick-plaque group. These findings are important to in vivo remineralization models, since they show that plaque thickness should be controlled for minimization of variation.

Dental Caries↗
PubMed1990

Optical quantification of caries-like lesions in vitro by use of a fluorescent dye.

An experimental method was developed for measurement of the fluorescence intensity of a dye that was introduced into caries-like lesions in vitro. A distinct pattern of change of fluorescence intensity with time appeared, displaying a plateau value and a peak value for each measurement. Both plateau and peak values showed a linear correlation with calcium loss, as measured with longitudinal microradiography. The correlation coefficients were r = 0.87 for plateau values and r = 0.89 for peak values. The difference in scattering by dry and wet caries lesions was also measured with the same equipment, which showed a linear correlation with calcium loss of r = -0.53.

Animals↗
PubMed1990

The inorganic components of cementum- and enamel-related dentin in the rat incisor.

Recently, we have shown that, in rodent incisors, the crown- and root-analogue dentin (enamel- and cementum-related dentin) show differences in mineralization rates (Beertsen and Niehof, 1986) and composition of the organic matrices (Steinfort et al., 1989). It was the aim of the present study to determine whether these differences were accompanied by differences in the inorganic components. Rat incisors were analyzed by means of hardness measurements, microradiography, and the determination of Ca, Mg, and PO4 content. The outer circumpulpal dentin layer of the enamel-related dentin (ERD) was considerably harder and denser than the comparable layer of the cementum-related dentin (CRD). Concomitantly, a higher Ca and PO4 content was found for the ERD than for the CRD, while the reverse occurred with respect to Mg. From the apical end of the incisor toward the incisal edge, the Ca/PO4 ratio tended to decrease for both ERD and CRD, while the Mg/PO4 ratio increased. All differences appeared to be statistically significant. It is concluded that differences in the non-collagenous organic matrix were accompanied by differences in the inorganic components. More specifically, a relatively high content of highly phosphorylated phosphoproteins (ERD) was associated with a higher Ca and a lower Mg content.

Animals↗
PubMed1990

Relative cariostatic effects of KOH-soluble and KOH-insoluble fluoride in situ.

The relative cariostatic effects of fluoride as fluorapatite, CaF2, loosely-bound fluoride, or KOH-soluble fluoride are debated. The present study was carried out to investigate this further in an intra-oral caries model. Pairs of premolars extracted for orthodontic reasons were used. Enamel from one tooth of each pair was used as control (untreated). Two slabs were cut from the enamel of the other contralateral premolar. These slabs were treated with 2% NaF for 24 h. One slab was then treated with 1 mol/L KOH twice for 24 h for removal of all loosely-bound fluoride. The slabs treated with 2% NaF and then with 1 mol/L KOH would contain the KOH-insoluble fluoride. Those treated with only 2% NaF would, in addition, contain KOH-soluble fluoride. Each slab, control, KOH-insoluble F, and KOH-soluble and insoluble F was mounted on different upper removable appliances. The slabs were covered with orthodontic banding material, thus allowing space for plaque accumulation. Five individuals wore the appliance in three separate four-week periods. The slabs were analyzed by quantitative microradiography. The average mineral loss (delta Z) was 1680 +/- 1000 vol% x microns in the control teeth, 620 +/- 76 vol% x microns in the KOH-soluble and -insoluble F teeth, and 2167 +/- 1278 vol% x microns in the KOH-insoluble F teeth. The average lesion depths were 90 +/- 41 microns in the control teeth, 35.3 +/- 5.5 microns in the KOH-soluble F teeth, and 88 +/- 35 microns in the KOH-insoluble F teeth. It was concluded that only KOH-soluble fluoride reduced mineral loss and lesion depths significantly, compared with the untreated teeth.

Calcium Fluoride↗
PubMed1991

Scanning and contact microradiographic study of the effect of degree of saturation on the rate of enamel demineralization.

The effect of degree of saturation with respect to hydroxyapatite (DSHA) on enamel section demineralization was studied by contact and scanning microradiography (CMR and SMR). Two aspects were studied: (1) the effect of different values of DSHA at constant pH, and (2) the effect of constant DSHA with variable pH. In the pH range (2.5-4.5) and time scale (0-120 h) studied, the DSHA was more important in determining the rate of enamel lesion progression than was the pH.

Adult↗
PubMed1991

A quantitative analysis of mineral loss and shrinkage of in vitro demineralized human root surfaces.

Demineralization of dentin specimens proceeds at a faster rate than that of enamel. Although this is generally accepted, a quantification of the rate of formation of root lesions is hampered by the shrinkage of the lesions when these are dried prior to microradiographic analysis. This leads to a significant underestimation of the lesion depth and total mineral loss. The aim of this paper was to quantitate the rate of mineral loss during root lesion formation in vitro and to determine the shrinkage of root specimens as a result of drying. Unerupted roots of human teeth were subjected to a demineralizing system of 0.1 mol/L lactate buffer (pH = 4.8) with 0.2 mmol/L methanehydroxydiphosphonate during four, 11, 22, and 44 days. The root lesions were assessed by quantitative microradiography. The demineralizing solutions were analyzed to determine the amounts of root tissue dissolved. A comparison of these two sets of data showed that, with the demineralizing system used, root lesions may shrink up to 62%. Fixation of the specimens in fixative did not affect this shrinkage. Chemical analysis showed that mineral loss proceeded linearly with time. From the data-sets of this study, a model was developed to compensate for the shrinkage in the dentin specimens. In this way, it was possible to calculate the lesion depth at four demineralization times as being 130, 220, 320, and 530 microns, respectively. These values were in agreement with a microscopic determination of the lesion depth.

Decalcification Technique↗
PubMed1991

Acid-susceptibility of lesions in bovine enamel after remineralization at different pH values and in the presence of different fluoride concentrations.

Artificial caries lesions were created in sound bovine enamel slices demineralized at pH 5.0. The lesions were then remineralized at either pH 5.5 or pH 6.8 in solutions containing either 1.5, 15, or 50 mumol/L fluoride. The remineralized slices were then demineralized at pH 5.0 for investigation of acid-susceptibility by means of quantitative microradiography. The results indicated that fluoride, incorporated during the preceding remineralization, had a retarding effect on the demineralization after remineralization, and that for the lowest concentration of fluoride in the remineralizing solution, the inhibitory influence of fluoride depended on the pH of the remineralization solutions used.

Acids↗
PubMed1992

An in vitro model for assessment of fluoride uptake from glass-ionomer cements by dentin and its effect on acid resistance.

This investigation presents an experimental model for studying interactions of glass-ionomer cements (GICs) with bovine dentin slabs. Fluoride incorporation was studied with five serial abrasion biopsies, each being approximately 10 microns thick. The time of interaction was a very important parameter, indicating continuous fluoride release from the GIC and diffusion into dentin over a 30-day period. Expressed in mass per volume (mg F/cm3), the fluoride incorporation reached 12.0 mg at the first and 2.5 mg at the fifth layer, several times greater than the baseline of 0.27 mg/cm3 in bovine dentin. A subsequent test of acid resistance in a lactic acid buffer (pH 4.0), followed by microradiography of lesions, showed a characteristic 40-microns-wide acid-resistant zone on surfaces exposed to the GICs. In contrast, the untreated control surfaces had lesions demineralized evenly from the surface to the intact tissue, without the higher-density zone at the surface of the lesion. The model seems promising for screening fluoride incorporation into dentin from fluoride-releasing dental materials.

Animals↗
PubMed1992

Effect of a two-solution fluoride mouthrinse on remineralization of enamel lesions in vitro.

A previous study showed that a two-solution fluoride (F) rinse deposited significantly more loosely-bound F on the tooth surface than did a sodium fluoride (NaF) rinse with the same F concentration (12 mmol/L). In the present study, this experimental rinse was evaluated for its ability to cause remineralization of enamel lesions in an in vitro pH-cycling model. Caries-like lesions were formed in the enamel of extracted human molars by means of a pH 4 demineralizing solution. Fifty-one approximately 120-microns-thick sections containing lesions were randomly divided into (1) control, (2) NaF rinse, and (3) two-solution F rinse groups. With the cut surfaces protected, the control samples were immersed in a pH 7 remineralizing solution for 12 days, and twice daily the sections were also exposed to a pH 4 demineralizing solution for 30 min. Samples in the NaF group received an additional one-minute rinse with a NaF (12 mmol/L) solution twice daily. Samples in the two-solution rinse group received the rinse treatment with a 12 mmol/L F solution prepared by combination of a Na2SiF6 and phosphate-containing solution with a calcium solution just before use. The mineral contents of the lesions were assessed by quantitative microradiography. The results showed that (1) no significant de- or remineralization was detected in the controls; (2) a 46% decrease in mineral loss (delta Z) of the lesion was produced by the NaF rinses; and (3) a 94% decrease in delta Z and a 20-microns-thick, mineral-dense surface-coating were produced by the two-solution F rinse treatment.

Apatites↗
PubMed1992

The ICT in situ experimental model in dental research.

The intra-oral cariogenicity test (ICT) in situ experimental model was introduced in 1964 for the study of caries on sample enamel in the human mouth. Slabs of human or bovine enamel are mounted with a Dacron gauze cover in the acrylic flanges of prosthetic appliances. The extent of enamel demineralization or remineralization of lesions is assessed from surface microhardness measurements and microradiography of the enamel sections. The ICT model offers the potential of studying various parameters related to caries. This publication presents a typical ICT study comparing the cariogenicity of 10% sucrose solutions containing 1, 3, 10, and 30 ppm F with that of the control solution, 10% sucrose (without fluoride). The treatments were applied to the ICT as 10-minute extra-oral immersions. The results indicate: (1) a strong effect of F in decreasing demineralization of sound enamel and increasing remineralization of pre-softened enamel in the ICT; (2) pronounced resistance to a subsequent in vitro acid test; (3) pronounced F incorporation into pre-softened enamel; and (4) a characteristic acid-resistant zone, as seen in microradiographs, associated with exposure to F. This in situ model enables one to study experimental caries with repeated testing of enamel that follows the development and/or the regression of subsurface enamel lesions, F incorporation, increased acid resistance, cariogenicity of substrates, and other parameters of caries that can be assessed under standard conditions of tooth substrate and microbial sheltering.

Animals↗
PubMed1992

Computer-based image analysis of natural approximal caries on radiographic films.

This paper reports on the development of computer software for automatic detection and measurement of approximal caries lesions on digital images obtained from radiographic films. If the program detects a lesion, it defines the lesion's border and measures and reports these lesion parameters: percent mineralization, area, maximum enamel penetration, and mean enamel penetration. Two experiments are reported; both were conducted with the use of extracted human premolar teeth. In the first experiment, thin sections were obtained from 13 approximal surfaces with caries lesions. Microradiographs were made of the sections, and software measurements of the lesions were obtained from the microradiographs. The software was able to separate the lesions into two groups: those that had penetrated less than 100% of the enamel and those that had penetrated 100% of the enamel. The software measurements agreed with evaluation of lesion penetration by polarized light microscopy of the thin sections. In the second experiment, simulated clinical radiographs were made of 16 approximal surfaces, 12 with lesions and four without. Thin sections were obtained for microradiography. Software was used for automatic detection and measurement of the lesions on both types of film. The ability of the software to detect the lesions on the clinical films was compared with that of 10 experienced clinicians. Correlations of the same parameter from the two types of radiographic films were statistically significant, 0.86 less than or equal to r less than or equal to 0.95 and p less than 0.05. The coefficients of variation were low for both microradiographs, 0.4-2.3%, and for clinical films, 0.7-8.5%.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1993

Scanning microradiographic study of the kinetics of subsurface demineralization in tooth sections under constant-composition and small constant-volume conditions.

The kinetics of subsurface demineralization of tooth sections has been studied in real-time by scanning microradiography (SMR). Demineralization was carried out: (1) with a large volume of solution buffered to pH = 4 to maintain a constant composition; and (2) in a small constant volume (approximately 3 mL), buffered initially at pH = 4, so that the degree of saturation at the tooth surface increased as the tooth dissolved. At constant composition, the change in lesion depth, Y, with time, T, followed a linear relation, Y = a + bT, for T > 44 +/- 5 h. Before this time, the relation could be approximated by a linear one with different a and b constants. At constant volume, Y = q(1-e-r(T + s)) for all T, where q, r and s are constants. Similar relations, with different constants, were found for the mineral loss per unit area of lesion exposed to acid. These results showed that the process of demineralization under the rather severe conditions used was essentially a surface-controlled process. The change of slope at approximately 44 h and the presence of the constant s in the exponential function were attributed to a change in kinetics after formation of the surface layer.

Dental Enamel↗
PubMed1993

A single-section model for enamel de- and remineralization studies. 1. The effects of different Ca/P ratios in remineralization solutions.

A prerequisite for the accurate measurement of differences between pre- and post-experimental mineral profiles in single sections by quantitative microradiography is a high degree of reproducibility of the analytical procedures. We have determined the reproducibility of both the production and analyses of microradiographs. Lesions were made in seven single bovine enamel sections and radiographed three times. Each microradiograph was then analyzed on three different occasions by use of an image analysis system. This resulted in only small standard deviations in the lesion parameters. The method was used to determine the sites of mineral deposition in lesions in single sections during remineralization in three different solutions, one of which contained 1.5 mmol/L Ca and 0.9 mmol/L PO4 (standard solution); the other two solutions were low in either Ca or PO4, but all three had the same degree of supersaturation. The mineral profiles and lesion parameters were determined after lesion formation and after remineralization for 4 days, 1, 2, and 3 weeks. The decrease in IML (integrated mineral loss) in the lesions remineralized in the standard solution was greatest during the first week. Lesion profiles revealed that, under non-standard conditions, mineral deposition was retarded in the deeper part of the lesion, in contrast to the even distribution of mineral deposition from the standard solution. Differences in IML changes and lesion profiles between these bovine enamel experimental groups diminished when remineralization continued for 2 and 3 weeks. Possibly, the reactivity of mineral surfaces in newly made lesions affected the diffusion of remineralizing ions from low concentration solutions to the lesion front.

Animals↗
PubMed1995

Hypermineralization of dentinal lesions adjacent to glass-ionomer cement restorations.

Previous reports have shown a release of fluoride from glass-ionomer cement (GIC) restorations into the oral fluids. Fluoride in the ambient fluids has a caries-preventive effect by enhancing remineralization and inhibiting demineralization of the dental hard tissues. Therefore, the current investigation was undertaken to determine whether GIC fillings could contribute to the remineralization of caries lesions in dentin. Small circular preparations were made in disks of dentin which had incipient caries-like lesions in the remaining tissue. The preparations were filled with amalgam or composite materials (as controls) or with GIC. The specimens thus contained a restoration close to a dentinal caries-like lesion. The specimens were placed contralaterally in the buccal surfaces of removable partial dentures and were worn intra-orally by volunteers for a 12-week experimental period, after which the specimens were sectioned and analyzed by microradiography. All specimens with GIC restorations exhibited hypermineralization in the tissue bordering the filling and in the wall of the preparation which had been in contact with the restoration. The (caries-like) lesions were remineralized, even under conditions of heavy plaque formation. In contrast, specimens with amalgam or composite restorations showed further extensive demineralization. This study demonstrates a significant remineralization potential exerted by the fluoride-releasing GIC restorative material. Consequently, the choice of the restorative material might be crucial for the occurrence or prevention of recurrent caries around restorations.

Aluminum Silicates↗
PubMed1995

Lipoteichoic acid inhibits remineralization of artificial subsurface lesions and surface-softened enamel.

Dental plaque produces not only acids by which underlying enamel is demineralized but also compounds which may inhibit repair of the lesions. The aim of this study was to determine how lipoteichoic acid, a bacterial compound that is abundant in dental plaque and inhibits calcium phosphate precipitation in vitro, affects the remineralization of incipient enamel lesions. Subsurface and surface-softened lesions were made in thin sections of bovine enamel, incubated with various amounts of lipoteichoic acid (isolated from Lactobacillus casei), and remineralized in 1.5 mmol/L CaCl2, 0.9 mmol/L KH2PO4, 130 mmol/L KCl, and 20 mmol/L Hepes, pH 7.0. Remineralization was followed during several weeks by repeated microradiography of the sections, and characterized by the changes in the integrated mineral loss of the lesions and the differential mineral profiles. The results showed that: (1) the effects of lipoteichoic acid on lesion remineralization were dose-dependent; (2) in subsurface lesions only the highest dose of lipoteichoic acid affected remineralization, which was delayed throughout the lesions; and (3) in surface-softened enamel, lipoteichoic acid did not affect the remineralization of the deeper parts, but remineralization of a surface zone of from 25 to 30 microns was increasingly inhibited with increasing doses. These effects were explained by different permeabilities of the surfaces of both types of lesions for the inhibitor: In subsurface lesions, lipoteichoic acid may have mainly clogged the porosities in the surface layer, whereas it could penetrate substantially into surface-softened enamel.

Animals↗