R.A.M. Exterkate

Quantification of formation and remineralization of artificial enamel lesions with a new portable fluorescence device.

Quantitative laser fluorescence has been reported as a useful method for the non-destructive in vitro and in vivo diagnosis of early enamel caries. A portable system for intraoral use has been developed with a new light source and filter system replacing the laser light to facilitate clinical application. This new device was validated with microradiographic and chemical analyses for assessment of mineral changes in enamel during lesion formation and remineralization in vitro and compared with the laser light equipment. A significant correlation was found between fluorescence changes and mineral loss: r = 0.79 (laser system) and r = 0.84 (portable lamp system). The correlation between the two fluorescence methods was r = 0.93. The portable fluorescence device seemed to be a promising new tool for reproducible and sensitive assesment of the severity of incipient enamel lesions.

Elevated Fluoride Products Enhance Remineralization of Advanced Enamel Lesions

Caries prevention might benefit from the use of toothpastes containing over 1500 ppm F. With few clinical studies available, the aim of this pH-cycling study was to investigate the dose response between 0 and 5000 ppm F of de- and remineralization of advanced (> 150 μm) enamel lesions. Treatments included sodium and amine fluoride, and a fluoride-free control. Mineral uptake and loss were assessed from solution calcium changes and microradiographs. Treatments with 5000 ppm F both significantly enhanced remineralization and inhibited demineralization when compared with treatments with 1500 ppm F. Slight differences in favor of amine fluoride over sodium fluoride were observed. The ratio of de- over remineralization rates decreased from 13.8 to 2.1 in the range 0 to 5000 ppm F. As much as 71 (6)% of the remineralized mineral was calculated to be resistant to dissolution during subsequent demineralization periods. With 5000-ppm-F treatments, more demineralizing episodes per day (10 vs. 2 for placebo) would still be repaired by remineralization.

Light-Induced Fluorescence Studies on Dehydration of Incipient Enamel Lesions

Changes in the hydration state of enamel affect its optical qualities, such as light scattering and fluorescence. In this study, the rate of fluorescence loss was measured when incipient enamel lesions with different de-remineralization history were left to dehydrate. Four groups of lesions were studied. In groups A, B and C, the lesions were prepared in vitro in an acid-gel system. Group A was kept as control, and groups B and C were remineralized (4 weeks) without and with 1 ppm F in solution, respectively. Group D consisted of natural incipient lesions. Enamel fluorescence was measured for all lesions immediately after removal from water and subsequently at short intervals for 30 min. The change in fluorescence with dehydration varied between the groups. In lesions from groups A and B, it followed a double exponential decrease, while in lesions from groups C and D, it followed a mono-exponential decrease. In all groups, the fluorescence of sound surfaces declined mono-exponentially. The ‘fractional fluorescence difference’, defined as (Lsound – Lcarious )/Lsound, became constant after periods of dehydration of about 5, 5, 20 and 5 min for groups A to D, respectively. The observation of the change of fluorescence with dehydration should be taken into consideration when planning studies that use fluorescence as an assessment method. However, it might also be used to gain insight into the properties for fluid transport inside the various lesions, relevant to de-remineralization or fluoride treatments.

The Relative Efficacy of Fluoride Toothpastes Assessed with pH Cycling

This study addressed the dose response between fluoride toothpastes and in vitro de- and remineralization, to predict the efficacy of toothpastes and understand the mode of action in the range 0–3,000 ppm F. Enamel lesions were pH-cycled with calcium uptake and loss being assessed daily. Both ‘shallow’ (about 50 µm deep) and ‘deep’ (about 200 µm deep) lesions were studied. F treatments were given in 30 (w/v)% toothpaste dilutions for up to 5 min daily. Calcium loss during the demineralization periods showed a dose response, resulting in 72% reduction for 3,000 ppm F compared to 0 ppm F. Calcium uptake during remineralization was increased in the F compared to non-F groups, with F concentration being less important than its mere presence. Significant differences were observed in F response between shallow and deep lesions, suggesting that this parameter should be included when testing caries-preventive products. Microradiographic analysis showed that lesion depth and severity had increased significantly in the non-F groups. In the F groups, the original lesion was partly remineralized, while a new lesion had formed beyond the original lesion front. Mineral loss of this second lesion correlated inversely with the F concentration of the treatments. These data revealed that fluoride can drive demineralization further into enamel by making the surface tissue less soluble, hence by not neutralizing acids penetrating into the tissue. It is also concluded that depth analysis of mineral uptake and loss is important to understand the mode of action of different F products.

Effect of Galla chinensis on growth and metabolism of microcosm biofilms.

Galla chinensis extract (GCE) interferes with de- and remineralization of dental enamel and the growth and metabolism in planktonic bacteria. However, no information is available on GCE effects on biofilms formed with saliva as inoculum. The aim of the current experiments was to investigate the effects of GCE at different stages of salivary microcosm biofilm formation. Biofilms formed on glass or enamel surfaces were treated with GCE solutions at different concentrations and at different time points. Effects were assessed by lactic acid formation and colony-forming unit (CFU) counts of the biofilms. The results showed that GCE treatments inhibited growth and acid metabolism of both nascent and mature microcosm biofilms. Pretreatment of the substratum with GCE solutions inhibited growth and lactic acid production of biofilms grown on enamel, but had little effects on biofilms formed on glass surfaces. A maximum GCE effect was found when biofilms, on either surface type, were treated after 8 h of formation with 40 h of subsequent growth. In medium with sucrose-fermenting biofilms, low concentrations of GCE (0.2 and 0.1 mg/ml) inhibited acid production without killing bacteria of the biofilm. Differences were found in GCE effects on biofilms formed with saliva from different donors, with reductions in acid formation and CFU values ranging between 0 and 78%. In conclusion, bioactive components in GCE reduce or inhibit both growth and lactic acid formation in biofilms.

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 ofremineralizing ions from low concentration solutions to the lesion front.

Evaluation of different fluoride concentrations supplemented with trimetaphosphate on enamel de- and remineralization in vitro.

Trimetaphosphate (TMP) effects on demineralized bovine enamel were studied after 15 days of pH cycling. Treatments included 30 wt% (weight percent) dilutions of 0, 500, 1,500 or 3,000 µg F/g aqueous NaF solutions with or without 3% TMP. Treated specimens were assessed by transverse microradiography. With the exception of the 3,000 µg F/g case, 3% TMP addition provided significant additional overall remineralization compared with F alone. Mineral content profiles differed significantly between corresponding F and F + TMP groups. Fluoride alone resulted in more remineralization in the original demineralized zone, whereas F + TMP caused less demineralization in the underlying, originally sound enamel.

Effect of Fluoride-Releasing Filling Materials on Underlying Dentinal Lesions in vitro

Fluoride-releasing materials placed over carious tissue are assumed to enhance remineralisation of the underlying lesion. This remineralisation, however, also depends on the availability of calcium and phosphate, which may be supplied by the pulpal fluid. The aim of this study was to measure the fluoride release of glass ionomer cements (GICs) into underlying dentin and to measure the effect of the released fluoride on the remineralisation of the underlying dentinal lesions using transversal microradiography. Discs of fluoride-releasing GIC were placed on top of dentinal lesions in an in vitro model. The discs and the dentin slabs were covered completely by a protective layer of nail varnish, leaving only the pulpal side of the dentin slab open, and hence the dentinal tubules as the pathway for the incubation fluid to the GIC disc. Specimens were incubated in a remineralisation buffer. The materials tested were a conventional GIC, an experimental GIC that was designed to have a high fluoride release, and an inert material. Fluoride was found to penetrate through the dentin slab into the surrounding fluid. Fluoride uptake from the experimental GIC was higher than from the conventional GIC. Mineral content-depth profiles after 10 weeks’ remineralisation revealed that in the outer 30 µm of the lesion a higher mineral deposition occurred for the experimental GIC than in both other groups. No differences in the overall change of integrated mineral loss were found for the tested materials. We conclude that high fluoride release from filling materials only results in superficially increased remineralisation of underlying demineralised dentin.

In vivo Bovine Enamel Remineralization and Fluoride Uptake from two Dentifrices Containing Different Fluoride Concentrations

In this study, the differences in lesion remineralization and fluoride uptake after brushing with a 300 ppm F or a 1000 ppm F dentifrice (as NaF) were investigated. Twenty volunteers with partial dentures in their lower jaws were divided into two groups. Bovine enamel slabs with artificial lesions were mounted in the dentures. After a test period of six weeks, the slabs were taken out and analyzed. There was no statistically significant difference between the two groups, in F-uptake and susceptibility of the enamel to demineralization, although the findings favored the 1000 ppm F toothpaste. The microradiograms in the 300 ppm F group showed lesions more pronounced than those in the 1000 ppm group. The present study cannot support the presumption that the fluoride content of regular NaF dentifrices can be lowered to 300 ppm F without undesirable effects on lesion arrest and remineralization.

Effect of pH on Galla chinensis extract's stability and anti-caries properties in vitro.

OBJECTIVES Considering that Galla chinensis extract (GCE) solution has a low pH, which might dissolve dental enamel, we investigated the effects of elevation of pH on GCE stability, and on its anti-caries properties. DESIGNS Stability of GCE solutions, either in H(2)O (pH less than 4.0) or when buffered at pH 5.5, 7.0 and 10.0, was assessed from UV-VIS spectra. Inhibition of enamel demineralization was determined in a pH-cycling set up, comprising treatments with either GCE solutions or negative control buffers and acid and neutral buffer immersions. Demineralization was assessed by calcium in the acetate buffers. To determine antimicrobial properties, polymicrobial biofilms were formed after saliva inoculation on glass surfaces which were treated after 48 h. Treatment output parameters were lactic acid formation and viability, the latter by colony forming unit (CFU) counts. RESULTS At pH 7.0 and higher GCE solutions changed colour and absorption spectra in UV-VIS, indicative of chemical changes. Regarding enamel demineralization, significant inhibitions (P<0.05) were found for all GCE treatments when compared with corresponding controls. In polymicrobial biofilms, GCE reduced the acid production, compared with the negative controls (P<0.05). However, this difference was only significant at the lower pH values. CONCLUSIONS GCE solutions were unstable under neutral and alkaline conditions. pH did not significantly influence the inhibiting effect of GCE on enamel demineralization. However, GCE was not effective on polymicrobial biofilms at alkaline pH (8.5). To avoid enamel damage due to acidic treatment, GCE solutions should be used at about pH 5.5.