Effect of iron on inhibition of acid demineralisation of bovine dental enamel in vitro

OBJECTIVES: Iron ions (Fe(2+)) have been shown to be cariostatic in many studies particularly by their ability to reduce bacterial metabolism. Nevertheless, the role of iron ions on dissolution of enamel is unexplored. The aim of the present study was therefore to investigate the protective effect of increasing concentrations (0-120mmol/L) of Fe(2+) on the dissolution of enamel. DESIGN: Enamel powder was subjected to acetic acid made with increasing concentrations with respect to FeSO(4)x7H(2)O. In order to determine the amount of enamel dissolved, the phosphate released in the medium was analysed spectrophotometrically using the Fiske-Subarrow method. Data were tested using Kruskall-Wall and Dunn's tests (p<0.05). The degree of protection was found to approach maximum at about 15mmol/L Fe(2+). Higher concentrations of Fe(2+) did not have an extra effect on inhibition of dissolution of enamel powder. In the next step, the protective effect of 15mmol/L Fe(2+) against mineral dissolution of the bovine enamel was evaluated using a simple abiotic model system. Enamel blocks were exposed to a sequence of seven plastic vials, each containing 1mL of 10mmol/L acetic acid. The acid in vial 4 was made 15mmol/L with respect to FeSO(4)x7H(2)O. The mineral dissolved during each challenge was thus determined by phosphate released as described above. Data were tested using two-way ANOVA (p<0.05). RESULTS: Lower demineralisation (around 45%) was found in vial 4 (with Fe) that continued stable until vial 7. CONCLUSIONS: Thus, our data suggest that Fe(2+) can be effective on inhibition of dissolution of enamel and that this effect may be durable.     

Characterisation of enamel white spot lesions using X-ray micro-tomography

OBJECTIVES: The aim of this study was to characterise the mineral density (MD) of natural enamel white spot lesions (WSLs) using X-ray micro-tomography calibrated with different density hydroxyapatite phantoms. METHODS: Seven natural WSLs from four extracted non-carious premolar teeth were scanned at a voxel size of 7.6 microm using a desktop X-ray micro-tomography system. Five hydroxyapatite phantoms (sintered pellets of hydroxyapatite powder) with densities ranging from 1.52 to 3.14 g/cm(3) were used as calibration standards for each scan. Three-dimensional image reconstruction enabled MD gradients throughout the lesion to be quantified using an MD calibration equation derived from hydroxyapatite phantoms. Background noise generated during the measurement of MD was reduced using a Gaussian filter. RESULTS: Gaussian filter reduced the signal-to-noise ratio (standard deviation) significantly while the basic MD information (average value) remained intact. The mineral gradients through the WSLs examined were compared and are discussed in terms of existing literature. The MD of sound enamel, apparent intact surface layer of WSL, and lowest level of WSL was found to be 2.65-2.89 g/cm(3), 2.23-2.58 g/cm(3) and 1.48-2.03 g/cm(3), respectively. Our MD results are comparable with other studies. CONCLUSIONS: X-ray micro-tomography is a sensitive in vitro technique capable of characterising and quantifying MD of small non-cavitated WSLs. This method has a promising potential for future carious and quantitative remineralisation studies.     

The effect of increasing sodium fluoride concentrations on erosion and attrition of enamel and dentine in vitro

Objectives

To investigate the effect of an aqueous sodium fluoride solution of increasing concentration on erosion and attrition of enamel and dentine in vitro.

Methods

Enamel and dentine sections from caries-free human third molars were polished flat and taped (exposing a 3 mm × 3 mm area) before being randomly allocated to 1 of 5 groups per substrate (n = 10/gp): G1 (distilled water control); G2 (225 ppm NaF); G3 (1450 ppm NaF); G4 (5000 ppm NaF); G5 (19,000 ppm NaF). All specimens were subjected to 5, 10 and 15 cycles of experimental wear [1 cycle = artificial saliva (2 h, pH 7.0) + erosion (0.3% citric acid, pH 3.2, 5 min) + fluoride/control (5 min) + attrition (60 linear strokes in artificial saliva from enamel antagonists loaded to 300 g)]. Following tape removal, step height (SH) in μm was measured using optical profilometry.

Results

When the number of cycles increased the amount of tooth surface loss increased significantly in enamel and dentine after attrition and erosion and for dentine after attrition. Attrition and erosion resulted in greater surface loss than attrition alone after 15 cycles of experimental wear of enamel. 5000 ppm and 19,000 ppm sodium fluoride solutions had a protective effect on erosive and attritional enamel tooth wear in vitro, however no other groups showed significant differences.

Conclusions

The more intensive the fluoride regime the more protection was afforded to enamel from attrition and erosion. However, in this study no such protective effect was demonstrated for dentine.     

Preventive effect of an iron varnish on bovine enamel erosion in vitro

Objective

The aim of this study was to evaluate, in vitro, the effect of an experimental varnish containing iron on the dissolution of bovine enamel by carbonated beverage.

Methods

Eighty specimens were randomly allocated to four groups (n = 20 per group), according to the following treatments: Fe varnish (FeV, 10 mmol/L Fe), F varnish (FV, 2.71% F), placebo varnish (PV) and control (not treated, NT). The varnishes were applied in a thin layer and removed after 6 h. Then, the samples were submitted to six cycles, alternating re- and demineralisation (only 1 day). Demineralisation was performed with the beverage Coca-Cola^® (10 min, 30 mL/block) and remineralisation with artificial saliva for 1 h. In order to determine the amount of enamel dissolved, the wear was analysed by profilometry. Data were analysed by ANOVA and Tukey's test (p < 0.05).

Results

The mean wear (±S.E.) was significantly lesser for the FeV (0.451 ± 0.018 μm) when compared to the other treatments. The FV caused significantly less wear (0.554 ± 0.022 μm) when compared to PV (0.991 ± 0.039 μm) and NT (1.014 ± 0.033), which did not significantly differ from each other.

Conclusions

The results suggest that the iron varnish can interfere with the dissolution of dental enamel in the presence of acidic beverages.     

A comparison of in vitro erosion-like mineral loss between continuous and intermittent acidic exposure with and without human saliva

Aim

This in vitro study aimed to compare erosion-like mineral loss following intermittent or continuous acidic exposures, and considered the role that human saliva may play.

Materials and methods

180 bovine enamel blocks were divided randomly into four equally-sized groups and exposed to one of the 4 protocols 6 times daily over 6 days (total acidic exposure time of 6 h): Group 1, continuous 10 min in orange juice (OJ) followed by 10 min in deionised water; Group 2, continuous 10 min in OJ followed by 10 min in stimulated saliva; Group 3, ten 1-min OJ exposures alternating with ten 1-min deionised water exposures; Group 4, ten 1-min OJ exposures alternating with ten 1-min stimulated saliva exposures. Specimens were stored in a remineralising solution between acidic exposures. Sections were cut and transverse microradiography was used to measure lesion depth in each specimen.

Results

Mean (sd) lesion depths were 21.5 (8.1), 21.2 (6.2), 81.7 (12.2) and 72.8 (12.4) μm for Groups 1–4, respectively. Significant differences existed between all protocols except Groups 1 and 2 (mean difference −0.3 μm, 95% CI: −6.1 to 5.5). The mean difference between Groups 3 and 4 was 8.9 μm (95% CI: 3.2–14.7).

Conclusions

Repeated, intermittent exposure to an acidic drink in vitro resulted in greater lesion depth than a continuous exposure of the same duration. Saliva offered some protection against intermittent acidic exposure.     

13C NMR analysis of the etching efficacy of acidic monomers in self-etching primers

It is well understood that the application of a self-etching primer enhances the bonding of the resin to the tooth. In this study, the demineralisation aspects by the Mega Bond Primer (MB) or the UniFil Bond Primer (UB) on the tooth were investigated by using liquid-state and solid-state 13C NMR techniques. The addition of hydroxyapatite or dentine to MB and the addition of dentine to UB resulted in the decrease in the peak intensity of the 13C NMR peaks attributed to the methacryloxy decyl phosphoric acid, MDP in the MB or 4-methacryloyloxy ethoxy carbonylphthalic acid, 4-MET in the UB. This decrease was because the MDP or 4-MET demineralised the tooth and the calcium salts produced from the MDP or 4-MET were precipitated from the MB or UB solution. The NMR technique is very powerful in evaluating the demineralisation aspects of the tooth by a self-etching primer. However, the calcium salts produced by the MDP or 4-MET on the tooth surface would not facilitate retention in bonding, since these calcium salts were merely deposited on to the surface of the tooth.     

Microradiographic study on the effects of mucin-based solutions used as saliva substitutes on demineralised bovine enamel in vitro

Sialic acids and proteins bound to mucins are known to form complexes with calcium, and this mechanism may hamper the remineralization of calcium-containing mucin-based saliva substitutes. Thus, the aim of this investigation was to evaluate the effects of adding various concentrations of calcium phosphate to self-made mucin-containing solutions on demineralised bovine enamel in vitro. Bovine specimens were prepared, embedded in epoxy resin, and polished to 4000 grit. Subsequently, the surfaces of the specimens were partially covered with nail varnish, thus serving as a control of sound enamel, and demineralised (37 degrees C; pH 5.0) for 14 (19 groups; n=10) or 28 days (three groups; n=9). After demineralization, the specimens were exposed to mucin-based solutions (30 g/l) with various saturations with respect to apatites containing 0.1 mM NaF, CaCl(2) (0-20 mM) and KH(2)PO(4) (0-52 mM) at two different pH values (5.5 or 6.5). A fluoride-free solution and the commercially available saliva substitute Saliva Orthana (Orthana, Kastrup, Copenhagen Denmark) served as controls. The differences in mineral loss (DeltaDeltaZ) between the values prior to (DeltaZ(Demin)) and after storage (DeltaZ(Effect)) in the various solutions were evaluated from microradiographs of thin sections (100 microm). The general linear model revealed a significant dependency of DeltaDeltaZ for calcium (P=0.006), but not for phosphate (P=0.081) or pH (P=0.114). DeltaZ(Effect) was only significantly reduced compared with DeltaZ(Demin) in the group with the highest saturation with respect to hydroxyapatite (P<0.05; t-test). In conclusion, mucin-based saliva substitutes with an adequate composition are able to remineralize bovine enamel in vitro.     

Evaluation of fermented milk containing probiotic on dental enamel and biofilm: In situ study

Objectives

The aim of this study was to in situ evaluate the pH before and after the application of the fermented milk product; the fluoride (F), calcium (Ca), phosphate (P), and insoluble extracellular polysaccharides (EPS) concentration on the dental biofilm; the demineralisation of the bovine dental enamel.

Design

Ten volunteers wore palatine devices containing four blocks of bovine dental enamel during three phases of 14 days each. In each phase, the treatment was accomplished with either fermented milk A (Yakult^®), or 20% sucrose solution (control) or fermented milk B (Batavito^®). Then, dental biofilm was collected, processed and the ionic concentration and insoluble extracellular polysaccharides appraised. For evaluation of the mineral loss, both the initial and final microhardness were determined.

Results

The results showed that the ionic concentration (F, Ca and P) was significantly higher in the fermented milk B in comparison with both the fermented milk A and the 20% sucrose solution. There was no significant difference amongst these last two. With regarding EPS was significantly lower in fermented milk B compared to fermented milk A and sucrose (P < 0.05), without significant difference amongst these last two. The two experimental groups did not differ significantly but had smaller mineral losses than control group.

Conclusion

It was concluded that all treatment decreased the pH of dental biofilm and promoted demineralisation of the enamel, although fermented milk B presented the lowest EPS content and percentage change and integrated loss of surface hardness. More studies should be developed to evaluate the action of probiotics on the bacterial activity and its interference on demineralisation, once the literature has been showing probiotics as a promissory caries reducing agent.     

Effect of various calcium/phosphates ratios of carboxymethylcellulose-based saliva substitutes on mineral loss of bovine enamel in vitro

OBJECTIVES: The present study evaluated the effects of various calcium and phosphate concentrations and ratios of carboxymethylcellulose (CMC)-based solutions on the mineral loss of predemineralised bovine enamel in vitro. METHODS: Bovine enamel specimens were prepared, polished and partly covered with nail varnish, thus serving as control of sound enamel. After demineralisation (37 degrees C; pH 5.0; 14 days) the specimens were exposed to CMC-based solutions (20g/l) with various saturations with respect to apatites containing 0.1mM NaF, CaCl2 (0-32 mM) and KH2PO4 (0-52 mM) at two different pH values (5.5 or 6.5). A fluoride-free solution served as control, and four commercially available products were tested as well. The differences in mineral loss (DeltaDeltaZ) between the values prior to (DeltaZ Demin) and after storage (DeltaZ Effect) in the various solutions were evaluated from microradiographs of thin sections (100microm). RESULTS: The general linear model revealed a significant dependency for DeltaDeltaZ on 'calcium' (p<0.001), 'phosphate' (p=0.023), 'fluoride' (p=0.002) and 'pH' (p<0.001). With increasing calcium and phosphate concentrations an increase in DeltaDeltaZ could be observed up to the solution containing the third highest saturation with respect to octacalciumphosphate (3.2), showing a significant remineralisation (p<0.05; t-test). The commercially available products as well as the control groups revealed significantly reduced DeltaDeltaZ values compared to this group (p<0.01; Bonferroni). CONCLUSIONS: A saturation with respect to octacalciumphosphate of 3.2 and a pH of 6.5 enables CMC-based solutions to remineralise bovine enamel in vitro.     

Effect of an iron mouthrinse on enamel and dentine erosion subjected or not to abrasion: an in situ/ex vivo study

OBJECTIVES: This in situ/ex vivo study evaluated whether a rinse with an iron solution could reduce wear and the percentage of microhardness change of human enamel and dentine submitted to erosion followed by brushing after 1 or 30min. DESIGN: During 2 experimental 5-day crossover phases (wash-out period of 10 days), 10 volunteers wore intraoral palatal devices, with 12 specimens (6 of enamel and 6 of dentine) arranged in 3 horizontal rows (4 specimens each). In one phase, the volunteers immersed the device for 5min in 150mL of cola drink, 4 times a day. Immediately after immersion, no treatment was performed in one row. The other row was brushed after 1min using a fluoride dentifrice and the device was replaced into mouth. After 30min, the remaining row was brushed. In the other phase, the procedures were repeated, but after immersion the volunteers rinsed for 1min with 10mL of a 10mM ferrous sulphate solution. Changes in surface microhardness (%SMH) and wear (profilometry) of enamel and dentine were measured. Data were tested using ANOVA and Tukey's tests (p<0.05). RESULTS: The enamel presented more wear than dentine, under all experimental conditions. The iron solution caused a significant reduction on the %SMH in enamel, and a significant reduction on the wear in dentine, regardless the other conditions. CONCLUSIONS: Rinsing with an iron solution after an erosive attack, followed or not by an abrasive episode, may be a viable alternative to reduce the loss of dental structure.