Youichi Iijima

Acid Resistance of Enamel Subsurface Lesions Remineralized by a Sugar-Free Chewing Gum Containing Casein Phosphopeptide-Amorphous Calcium Phosphate

The aim of this clinical study was to investigate the acid resistance of enamel lesions remineralized in situ by a sugar-free chewing gum containing casein phosphopeptide-amorphous calcium phosphate nanocomplexes (CPP-ACP: Recaldent™). The study utilized a double-blind, randomized, crossover design with two treatments: (i) sugar-free gum containing 18.8 mg of CPP-ACP, and (ii) sugar-free gum not containing CPP-ACP as control. Subjects wore removable palatal appliances with insets of human enamel containing demineralized subsurface lesions and chewed the gum for 20 min 4 times per day for 14 days. After each treatment the enamel slabs were removed and half of each lesion challenged with acid in vitro for 8 or 16 h. The level of remineralization was determined using microradiography. The gum containing CPP-ACP produced approximately twice the level of remineralization as the control sugar-free gum. The 8- and 16-hour acid challenge of the lesions remineralized with the control gum resulted in 65.4 and 88.0% reductions, respectively, of deposited mineral, while for the CPP-ACP-remineralized lesions the corresponding reductions were 30.5 and 41.8%. The acid challenge after in situ remineralization for both control and CPP-ACP-treated lesions resulted in demineralization underneath the remineralized zone, indicating that the remineralized mineral was more resistant to subsequent acid challenge. The results show that sugar-free gum containing CPP-ACP is superior to an equivalent gum not containing CPP-ACP in remineralization of enamel subsurface lesions in situ with mineral that is more resistant to subsequent acid challenge.

In situ Acid Resistance of in vivo Formed White Spot Lesions

Thin sections of natural enamel lesions, so–called white spots (WS), and areas of sound enamel (SEn) adjacent to the WS were exposed to an intraoral environment for 2 weeks. Thin sections of WS samples, clamped in a PMMA holder, were microradiographed before and after exposure to intraoral conditions. Acid resistance was evaluated by lesion depth and mineral changes during the cariogenic challenge. The results show that there were statistically significant differences in lesion depth, mineral loss and mineral volume percent at the surface before and after the intraoral cariogenic challenge at least at p<0.05, except for a change in mineral volume percent at the surface of WS samples. This exception indicates that no mineral change occurred in the surface layer of WS. The fact of 2.8 and 1.8 times higher ratios of SEn over WS of mean changes in lesion depth and mineral loss data, respectively, seems to indicate a quantitative difference in acid resistance level of WS lesions compared with the areas of SEn. Regarding the site of mineral changes, a distinctive feature of WS samples is that mineral loss occurs at the bottom of lesions. In contrast, areas of SEn produce a typical subsurface type of lesions. From this in situ study, it can be concluded that the surface of WS samples was apparently much more acid–resistant (at least approximately 2 times) than the areas of SEn that received a similar intraoral acid challenge.

Early detection of white spot lesions with digital camera and remineralization therapy

BACKGROUND In this paper, the characteristics of the early stage of dental caries are discussed and the methods we used to treat the early stage of dental caries to increase the number of caries-free patients are presented. Studies from in vitro to in situ experiments and a clinical study were carried out to support clinical remineralization therapy. METHODS AND RESULTS To clarify the effect of time for remineralization, the degree of remineralization was assessed at 2 days, 6 days, and 10 days after 2-day demineralization in 0.01 M/L lactic acid buffer (pH 4.0 at 37 degrees ). The remineralization solution contained 3.0 mM/L Ca, 1.8 mM/L P, and 3 ppm fluoride adjusted to pH 7.0. A 10-day continuous remineralization with a 3 ppm fluoride resulted in a high fluoride concentration. To evaluate mineral loss from sound tooth structure and white spot lesions, thin sections (about 90 microm) including white spots (WS) were prepared and exposed to oral conditions for 2 weeks continuously. The mineral loss from sound tooth structure was found to be twice that from WS. In another experiment during the remineralization period, enamel samples were immersed in three different bicarbonate solutions; 0.5, 5.0 and 50 mM/L for 30 minutes, two times per day. Both the bicarbonate and fluoride applied groups showed higher improvement in acid resistance and the amount of remaining mineral was almost two times higher than the controls (p < 0.01). In a clinical study we demonstrated remineralization in patients who followed professional mechanical tooth cleaning and fluoride prophylaxis paste. Using this regime, in patients with deciduous caries present at baseline, over 80 per cent of permanent teeth were caries free at the age of 12 years. In these studies the digital camera with CasMaTCH and an image analysis system showed several advantages for monitoring in de- and remineralization. CONCLUSIONS White spot lesions, rather than intact tooth surfaces, can be mineralized through the daily clinical procedures described in this paper.

Remineralization and acid resistance of enamel lesions after chewing gum containing fluoride extracted from green tea.

BACKGROUND The aim of this study was to evaluate enamel remineralization and the acquisition of acid resistance by using sugar-free chewing gum containing fluoride extracted from green tea. METHODS Forty-five volunteers participated in a crossover, double-blind study and wore intraoral appliances with human demineralized enamel. Subjects chewed fluoride chewing gum (FCG: 50 μg fluoride) or placebo gum. Remineralization and acid resistance were evaluated using the mineral change value (ΔZ, in vol%·μm). Fluoride concentrations in saliva and remineralized enamel were analysed. RESULTS The peak salivary fluoride concentration was 3.93 ± 1.28 ppm (mean ± SD). The elevated salivary fluoride concentration resulted in a higher fluoride concentration of 656 ± 95 ppm in the remineralized region versus 159 ± 26 ppm for placebo gum (p < 0.001). After remineralization, the ΔZ of the FCG group was higher than that of the placebo gum group. After an acid challenge, ΔZ of the FCG group was lower than the placebo gum group. Both ΔZ were statistically significant. CONCLUSIONS FCG produced a superior level of remineralization and acid resistance, as compared to the placebo gum. The in situ results suggest that regular use of FCG is useful for preventing dental caries.

Influence of Nail Varnish on the Remineralization of Enamel Single Sections Assessed by Microradiography and Confocal Laser Scanning Microscopy

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.

Fluoride and Mineral Content in Hyper-Remineralized Coronal Bovine Dentine in vitro after an Acid Challenge

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.

Acid resistance of human enamel in vitro after bicarbonate application during remineralization

OBJECTIVES The aim of this study was to investigate the acid resistance of subsurface enamel lesions remineralized with bicarbonate solutions during remineralization. METHODS Two experiments were carried out. In experiment 1, mineral uptake and acid resistance of remineralized enamel lesions were analyzed quantitatively by microradiography for mineral changes. Bicarbonate solutions of 0.5, 5.0 and 50.0 mM were used. In experiment 2, to clarify acid resistance mechanisms, the pH changes in demineralizing solutions on the remineralized enamel surfaces were measured continuously. Only a bicarbonate solution of 5.0 mM was used. RESULTS In experiment 1, the bicarbonate-treated groups were more acid resistant than the non-treated groups (p<0.05). However, no statistically significant difference was observed among the different concentrations of bicarbonate. In experiment 2, the pH rise of the bicarbonate group was greater than the other groups. CONCLUSION It was found that bicarbonate-treated enamel lesions were resistant to acid. It would suggest that bicarbonate ions applied during remineralization may have penetrated into the subsurface lesions. These ions may have worked as buffer agents against the acid challenge and inhibited the decrease in pH.

Comparative study of the measurement of enamel demineralization and remineralization using transverse microradiography and electron probe microanalysis.

Transverse microradiography (TMR) and electron probe microanalysis (EPMA) are commonly used for characterizing dental tissues. TMR utilizes an approximately monochromatic X-ray beam to determine the mass attenuation of the sample, which is converted to volume percent mineral (vol%min). An EPMA stimulates the emission of characteristic X-rays from a variable volume of sample (dependent on density) to provide compositional information. The aim of this study was to compare the assessment of sound, demineralized, and remineralized enamel using both techniques. Human enamel samples were demineralized and a part of each was subsequently remineralized. The same line profile through each demineralized lesion was analyzed using TMR and EPMA to determine vol%min and wt% elemental composition and atomic concentration ratio information, respectively. The vol%min and wt% values determined by each technique were significantly correlated but the absolute values were not similar. This was attributable to the complex ultrastructural composition, the variable density of the samples analyzed, and the nonlinear interaction of the EPMA-generated X-rays. EPMA remains an important technique for obtaining atomic ratio information, but its limitations in determining absolute mineral content indicate that it should not be used in place of TMR for determining the mineral density of dental hard tissues.