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An in situ model for simultaneous assessment of inhibition of demineralization and enhancement of remineralization.

In situ models to assess the ability of oral care products or food components to enhance remineralization and/or inhibit demineralization of tooth enamel or roots must be very carefully designed to minimize the confounding effects of the many variables involved. Controlling these variables as closely as possible is essential if meaningful answers are to be obtained from the models. We have developed an in situ model which combines the experience of several groups. Detailed screening of subjects is essential. Selection criteria should include good general health, good dental health, mandibular partial denture, at least eight natural teeth, no active caries lesions, known fluoride history, normal salivary function, and no medications that affect salivary function. Each subject carries a sound enamel slab and an enamel slab with a pre-formed caries-like lesion (demineralized in vitro) in his/her denture on each side of the mouth for test periods of two or four weeks. The demineralization challenge is controlled by extra-oral immersion of the appliances in sucrose daily. Daily product exposure or daily food component exposure is used as desired. Compliance indicators and a diet diary are included. Whole saliva flow rate (unstimulated), plaque acidogenicity, and salivary fluoride are monitored during the test periods. At the end of the test period, the test slabs are assessed for mineral change, after being sectioned, by means of cross-sectional microhardness or microradiography. The mineral loss or gain (delta M, microns x vol%), compared with adjacent control sections retained in the lab, is calculated as change in delta Z (microns x vol%), namely, delta M = delta ZTEST - delta ZCONTROL.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Effect of tooth-bound fluoride on enamel demineralization/ remineralization in vitro.

The effect of tooth-bound fluoride (F) on enamel caries formation was investigated under the condition that loosely bound F was essentially absent. Eighteen thin enamel sections, prepared from the lingual or buccal surfaces of extracted human molars, were embedded in acrylic resin with the enamel surfaces exposed. The sections were placed in a pH 7 remineralizing solution (RS; 1.2 mmol/l Ca, 0.72 mmol/l P, 30 mmol/l KCl, 50 mmol/l HEPES) for 5 days, and were randomly divided into 3 groups: (1) control group that received no treatment, (2) acidulated phosphate fluoride (APF) group that received 5 cycles of a 4 min treatment with APF gel followed by immersion in the RS for 2 days (RS changed daily) and (3) dicalcium phosphate dihydrate (DCPD) - APF group that received 5 cycles of a 4-min pH 2.1 DCPD-forming solution followed by 4 min APF gel and then placed in the RS for 2 days. After the treatment cycles, the sections were washed in a constant composition F titration system to remove loosely bound F. An in vitro model, which consisted of cycles of de- (6 h) and remineralization (18 h) each day for 5 days, was used to produce caries-like lesions in the specimens. The DeltaZ (mineral loss) values, measured by quantitative microradiography, of the lesions formed in the three groups were (mean +/- standard deviation; n = 6) 91.2+/-12.3 microm for the control group, 41.3+/-10.1 microm for the APF group and 21.2+/-4.8 microm for the DCPD-APF group. The same system produced lesions in untreated shark enamel with a mean DeltaZ of 4.4+/-0.3 microm (n = 12). One-way fixed-effects ANOVA indicated that mineral loss was significantly different among the different groups (p<0.05). The results showed that enamel resistance to lesion formation increased with increasing tooth-bound F content. Shark enamel was much more resistant to demineralization than human enamel.

Acidulated Phosphate Fluoride↗

The effect of fluoride on apatite structure and growth.

Fluoride participates in many aspects of calcium phosphate formation in vivo and has enormous effects on the process and on the nature and properties of formed mineral. The most well-documented effect of fluoride is that this ion substitutes for a column hydroxyl in the apatite structure, giving rise to a reduction of crystal volume and a concomitant increase in structural stability. In the process of enamel mineralization during amelogenesis (a unique model for the cell-mediated formation of well-crystallized carbonatoapatite), free fluoride ions in the fluid phase are supposed to accelerate the hydrolysis of acidic precursor(s) and increase the driving force for the growth of apatitic mineral. Once fluoride is incorporated into the enamel mineral, the ion likely affects the subsequent mineralization process by reducing the solubility of the mineral and thereby modulating the ionic composition in the fluid surrounding the mineral, and enhancing the matrix protein-mineral interaction. But excess fluoride leads to anomalous enamel formation by retarding tissue maturation. It is worth noting that enameloid/enamel minerals found in vertebrate teeth have a wide range of CO3 and fluoride substitutions. In the evolutionary process from elasmobranch through enameloid to mammalian enamel, the biosystems appear to develop regulatory functions for limiting the fluoridation of the formed mineral, but this development is accompanied by an increase of carbonate substitution or defects in the mineral. In research on the cariostatic effect of fluoride, considerable emphasis is placed on the roles of free fluoride ions (i.e., preventing the dissolution and accelerating the kinetics of remineralization) in the oral fluid bathing tooth mineral. Fluoride also has been used for the treatment of osteoporosis, but much still remains to be learned about maximizing the benefit and minimizing the risk of fluoride when used as a public health measure.

Amelogenesis↗

In vitro evaluation of fluoride-releasing restorative materials for sealing the root canals of overdenture abutments.

PURPOSE: The purpose of this study was to evaluate the ability of newer fluoride-releasing restorative materials to protect the root surface from acid attack. MATERIALS AND METHODS: The materials used were glass-ionomer cement (GIC), resin-modified glass-ionomer cement (RM-GIC), and a compomer (Comp). A composite resin (CR) was used as the control. The restored teeth were stored in deionized, distilled water for 14 days and subjected to 300 thermocycles (55 degrees C and 5 degrees C). The teeth were cycled in a demineralizing solution (pH 5.0 or 4.0) for 6 hours and in a remineralizing solution (pH 7.0) for 17 hours for 10 days. The depths of lesions created by acid challenge were measured at the interface of the tooth and the restorative material and then at a distance of 50, 100, and 300 microns from the tooth-restoration margin using polarized light microscopy and contact microradiography. RESULTS: At pH 4.0, there was significant difference in the depth at the interface between the tooth and the restorative material (P < .001). The GIC and RM-GIC were protective, and the lesion depths were significantly shallower than for Comp or CR. The protective effect varied depending on the distance from the interface of the tooth and the restorative material. At pH 5.0, the GIC and RM-GIC had no lesions at the interface, while the Comp and the CR had lesions (P < .001). CONCLUSION: Fluoride-releasing glass-ionomer cement seems to be an appropriate material to seal the root canals of overdenture abutments, because it has an inhibiting effect on demineralization at the cavity wall in vitro.

Aged↗

[Evaluation of remineralization solutions on the milk teeth].

The milk incisors of 80 infant-school children were demineralized. For the following 3 weeks the children then rinsed their mouths with mineral solutions. By manifold replica yields (analysis by light- and scanning electron microscope) and colouring tests a positive influence of calcium and phosphorus holding solutions, among others with magnesium, too, on the remineralization was discovered.

Child, Preschool↗

Effect of sodium hypochlorite treatment on remineralization of human root dentine in vitro.

Dentine consists simplified of mineral and of several organic components. Sodium hypochlorite (NaOCl) is a well-known nonspecific proteolytic agent capable to remove organic material. The aim of this study was to investigate the influence of organic material removal from artificial dentine lesions by means of NaOCl pretreatment on subsequent remineralization with and without fluoride. Human root dentine samples were demineralized in an acidic gel (pH = 5) at 37 degrees C for 2 weeks. After 2 min of pretreatment with a 0.4, 2 or 10% NaOCl solution, the samples were remineralized in a 20 mM HEPES buffer (pH = 7) containing 1.5 mM Ca(2) and 0.9 mM phosphate with or without addition of 10 ppm F(-) as NaF at 37 degrees C for 8 days. Mineral profiles were assessed by means of transversal microradiography after diol treatment to avoid shrinkage caused by drying. In a separate experiments the dentine contraction caused by 10% NaOCl was assessed. The contraction (negligible for sound dentine) was found to be about 12% for the lesions. The remineralization results showed that pretreatment with a 10% NaOCl solution for 2 min, increased lesion remineralization. After NaOCl treatment, the amount of accumulated mineral increased by about 27% without F in the remineralization solution, and by about 4% with 10 ppm in solution. The in vitro results suggest that removal of organic materials from dentine lesions is an interesting approach to enhance remineralization.

Adolescent↗

The improved remineralization and fluoride uptake in vivo of triclosan/copolymer/sodium fluoride toothpaste vs. sodium fluoride toothpaste.

OBJECTIVE: It has been shown that the twice-daily use of the triclosan/copolymer/sodium fluoride toothpaste can significantly reduce caries formation. The objective of this report was to review human studies comparing a triclosan/copolymer/sodium fluoride toothpaste to a placebo toothpaste (no fluoride), and a sodium fluoride toothpaste (positive control) for their ability to enhance remineralization of tooth enamel and increase the retention of fluoride by dental plaque for extended periods (up to 12 hours) after treatment. METHODOLOGY: Two human plaque fluoride studies were conducted, measuring fluoride levels before brushing (baseline) and at two, six and twelve hours after brushing. An in situ enamel remineralization study, using microhardness measurements, was conducted as well. RESULTS: In the first study, the triclosan/copolymer/sodium fluoride toothpaste group was associated with a two-times increase of mean plaque fluoride as compared to the placebo control dentifrice. This increase was statistically significant at p < 0.05. In the second study, the triclosan/copolymer/sodium fluoride toothpaste group was associated with a 38% increase of mean plaque fluoride as compared to the sodium fluoride toothpaste group. This increase was statistically significant at p < 0.05. In the enamel remineralization study, the triclosan/copolymer/sodium fluoride toothpaste was significantly better (p < 0.05) than the sodium fluoride toothpaste (positive control) at promoting percent mineral recovery. CONCLUSION: The results obtained from the plaque fluoride studies and in situ remineralization study corroborated the findings of a recently completed two-year caries clinical study, which demonstrated that the triclosan/copolymer/sodium fluoride toothpaste provided superior cavity protection over the sodium fluoride toothpaste.

Adolescent↗

In vivo study of fluoride chewing gum for the remineralization of human root lesions.

The purpose of this study was to study the efficacy of a fluoride-containing chewing gum (0.1 mg F/stick chewed 5 x/day) in the remineralization of artificial caries lesions in abraded root surfaces compared to sorbitol-containing chewing gum and a no gum control group in vivo. Root specimens were cut from human root surfaces and polished. The specimens were demineralized in a buffered lactate solution with low concentration of fluoride in order to preserve an intact surface layer. Six healthy subjects wore mandibular Hawley-type appliances containing up to fourteen slabs for each of one control and two experimental periods. The experimental protocol included chewing five pieces of gums per day and brushing with fluoride-free dentifrice for each 21 days period. All three regimens were analyzed for fluoride uptake and microradiography. The results indicate that fluoride-containing chewing gum has a highly significant fluoride uptake and remineralization compared to sorbitol gum and control regimens, suggesting that fluoride chewing gum may provide another vehicle for fluoride delivery.

Chewing Gum↗

Histopathology of root surface caries.

The histopathology of active and arrested human root caries was examined in extracted teeth by different optical methods. Significant differences were observed between the mechanisms operating on the various dental structures. Three different patterns of initial cementum and dentin lesions could be distinguished, depending on the severity of the cariogenic attack, the degree of sclerosis of the peripheral dentin, and the presence of calculus. Advanced lesions were characterized by various patterns of demineralization. In particular, a massive lateral spread of bacteria into intertubular dentin was observed. Consequently, unaffected dentinal areas became continuously undermined. In arrested lesions, either a partial or complete mineralization of the intertubular dentin was apparent. Dentinal tubules were sclerosed passively by re- or precipitation of Ca and PO4 ions. In contrast, tubules filled with ghosts of bacteria appeared mineralized by fine-granular crystals. Our observations indicate that both the arrestment and the remineralization of active lesions depend on (1) the degree of active sclerosis of dentinal tubules in areas underlying the lesion, (2) the degree of the bacterial infection of the dentin, (3) the degree of progression of the lesions, and (4) the location of the lesions at the various root surfaces. It is suggested that remineralization of active lesions can occur. This supports the concept of non-invasive treatment of root caries lesions without cavitation.

Dental Caries↗

Brushing abrasion of eroded dentin after application of sodium fluoride solutions.

The aim of the present in vitro study was to evaluate the influence of sodium fluoride solutions on brushing abrasion of eroded dentin. Dentin specimens were prepared from 60 bovine incisors. The specimens were embedded in acrylic resin, ground flat, polished and subsequently covered with tape exposing an area of 1.8 mm x 10.0 mm in the center of the exposed dentin. The samples were alternatingly stored in a demineralizing solution (5 min) and a remineralizing solution (1 min) for 5 times. The erosive soft drink Sprite light(R) served as a demineralizing solution and artificial saliva was used as a remineralizing solution. Prior to storage in artificial saliva 15 specimens were each treated for 1 min with 250 and 2,000 ppm fluoride solution, respectively. Fifteen specimens were treated with distilled water instead of the fluoride solution (= eroded controls). The remaining samples were neither eroded with the soft drink nor fluoridated (= uneroded controls). After each immersion in artificial saliva the specimens were submitted to abrasion in a toothbrushing machine. After 5 demineralization-remineralization brushing cycles the total amount of tooth wear due to erosion and subsequent abrasion was profilometrically evaluated. Statistical analysis revealed the significantly lowest wear in the uneroded controls and the highest amount of abrasion in the eroded controls. Application of the fluoride solutions increased the wear resistance of the eroded dentin specimens, showing significantly better protection by the high-concentration compared to the low-concentration solution. The susceptibility to abrasion of the eroded dentin specimens treated with the high-concentration fluoride solution did not differ significantly from the uneroded dentin samples. It is concluded that application of 2,000 ppm sodium fluoride solutions immediately before toothbrushing significantly reduces abrasion of eroded dentin in vitro.

Animals↗

Remineralization of advanced root dentin lesions in vitro.

The possibility for remineralization of advanced root dentin lesions was investigated in vitro. Lesions were produced in acidic buffer solution with 0.1 and 0.5 ppm fluoride, for 3 and 5 weeks, respectively, using a single-section model. Next, the sections were immersed in a remineralization solution containing 0.1 ppm F (as NaF) for 20 weeks. Microradiographs were made after each 4-week-period. The lesions were around 500 micro m deep, with mineral loss values between 11,000 and 18000 vol%.microm. After 20 weeks of remineralization, the absolute amounts of deposited mineral ranged from 7500 to 10000 vol%. micro m, corresponding to a repair between 50 and 85%. Lesion depth was, on average, reduced by 199 micro m. This was not significantly different (at p < 0.05) between the four experimental groups. This study showed that remineralization of advanced dentinal lesions is possible in spite of the virtual absence of mineral in the lesion body after demineralization. The surface layer of the lesion was the preferred site for mineral deposition until mineral content values reached those of sound dentine. The mineral content in the lesion body increased with time, at a rate reflecting the initial severity of the lesion. We conclude that a remineralized surface layer does not inhibit transport of mineral ions to the body and that the remineralization in the lesion body reflected the number of sites for crystal growth.

Analysis of Variance↗

Evaluation of the effectiveness of laser fluorescence in monitoring in vitro remineralization of incipient caries lesions in primary teeth.

The purpose of this investigation was to examine the effectiveness of laser fluorescence for monitoring in vitro remineralization of caries lesions. Seventeen natural enamel lesions in primary molars were each cut into two parts. One part was exposed, at room temperature, to a remineralizing solution (experimental) and the other part to water (control) for 28 days. Laser fluorescence readings were taken at the beginning of the experiment and during the experiment. At the end of the experiment, lesion depth in the experimental halves was significantly less than in the control halves (p < 0.01), suggesting that remineralization had occurred. However, the laser fluorescence readings showed no statistically significant changes during the experiment, either in the experimental or control halves. We conclude that laser fluorescence was not able to detect in vitro remineralization of natural incipient caries lesions of primary teeth.

Analysis of Variance↗

The effects of a sodium hypochlorite treatment on demineralized root dentin.

The effects of a 10% NaOCl treatment for 2 min on demineralized human root dentin were investigated by means of: microradiography (MR), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and secondary ion mass spectroscopy (SIMS). MR measurements revealed that NaOCl caused a tissue contraction not related to water loss but to removal of organic substance(s), resulting in reductions of the lesion depth and mineral loss values by 15% and 42%, respectively. CLSM observations on wet dentin showed that the dentinal tubules underneath the surface are clearly observable and not deformed substantially by the NaOCl, except near the outermost surface. This indicates the importance of wet as well as of dried (high vacuum) observations. SEM micrographs (high vacuum) showed definite changes in the outer dentin surface structure; 85% of the originally open dentinal tubules were closed after NaOCl treatment. No marked changes were observed in the dentin ultrastructure inside lesions, as shown by SEM on fractured surfaces. SIMS data, pertaining to samples in high vacuum, showed a remarkable increase of chlorine (Cl) content in the entire lesion due to the NaOCl, indicating deep penetration of the original OC1 ions. The results suggest that the 2-min treatment of demineralized dentin by NaOCl solutions removes and/or changes part of the dentin matrix in nearly the whole lesion. As a consequence the mineral is somewhat redistributed, the outermost surface of a few mu m is changed, but the main dentin structure and element composition are still intact. These findings indicate that NaOCl treatments are of interest in remineralization and hyper-remineralization studies of dentin.

Adolescent↗

Clinical study on the effect of amine fluoride/stannous fluoride on exposed root surfaces.

The aim of this study was to assess the remineralizing effect of an amine fluoride (AmF)- and stannous fluoride (SnF2)-containing toothpaste and mouthrinse on exposed root surfaces. A total of 44 adults participated in the 20-week, double-blind study and were grouped as follows: (1) 20 participants (mean age 45.7 years) used an AmF/SnF2 experimental toothpaste plus AmF/SnF2 (Meridol) mouthwash, and (2) 24 participants (mean age 48.8 years) used an NaF-containing toothpaste and mouthrinse. Root caries index (RCI) and root surface scores were determined by a modified method of Katz (J Dent Res, 1984). RCI mean values showed decreases of approximately 47% in the AmF/SnF2 group, and 10% in the NaF group. With respect to root caries scores, the number of persons with decreased softened (non-carious) surfaces between the baseline and control examinations was statistically significant (p less than 0.05) in the AmF/SnF2 group but not significant in the NaF group. A statistically significant difference (p less than 0.05) in the results of the groups favored the AmF/SnF2 subgroup. Thus, the data point to a possible remineralizing effect of topically applied AmF/SnF2 on softened root caries surfaces.

Amines↗

Remineralization of bovine incisor root lesions in vitro: the role of the collagenous matrix.

This study deals with the role of collagen in the remineralization of bovine incisor root lesions. The degradability of the collagenous matrix after in vitro remineralization was also investigated. The root surfaces were exposed to 0.1 M acetic acid, pH 4.0, to produce erosive lesions or to 0.1 M lactic acid, 0.2 mM methane hydroxy diphosphonate, pH 5.0, to produce subsurface lesions. After demineralization, the roots were subjected to remineralization, with or without prior treatment with a bacterial collagenase to remove accessible collagen. Remineralization was carried out in solutions with a Ca/Pi molar ratio of 1.67, and [Ca]. [Pi] concentration products of 0.6, 1.35 or 2.4 mM2, with all solutions having an ionic strength of 0.15 M, and a pH of 7.0. After remineralization, the roots that were not treated with collagenase were incubated with the enzyme. The results indicate that remineralization of erosive lesions is surface-controlled and that of subsurface lesions diffusion-controlled. For both lesion types it was shown that the removal of collagen before remineralization did not affect the rate of mineral deposition in the root lesions. Nevertheless, remineralization in those lesions where accessible collagen had not been removed resulted in a significant reduction in the amount of degradable collagen. The observations of this study suggest that remineralization did not occur by nucleation of mineral on the organic matrix but rather by growth of residual crystals in the partially demineralized root tissue.

Animals↗