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This paper discusses the concept of critical pH for dissolution of enamel in oral fluids. The critical pH does not have a fixed value but rather is inversely proportional to the calcium and phosphate concentrations in the solution. The paper also discusses why teeth dissolve in acid, why remineralization of white-spot caries lesions is possible and why remineralization of teeth eroded by acid is not possible.
The purpose of this in vitro study was to evaluate the effects of acidulated calcifying fluids (CF) on remineralization of caries-like lesions of enamel. Lesions were created in sound enamel using an acidified gel. Central longitudinal sections were taken from each tooth (N = 20) following lesion formation to serve as control lesions (CL). Each tooth was sectioned into quarters and each quarter was assigned to one of four groups: 1) 1 mM calcium CF at pH 7.0 (CF1); 2) 1 mM calcium CF at pH 5.0 (ACF1); 3) 3 mM calcium CF at pH 7.0 (CF3); 4) 3 mM calcium CF at pH 5.0 (ACF3). Tooth quarters were treated with assigned CFs (HAP [Ca/P = 1.63], pH 7.0 or 5.0, 0.05 mM Fl) for ten 60-sec periods. Longitudinal sections were prepared and imbibed in water for polarized light study. Mean lesion depths were determined and compared (ANOVA and DMR). With 1 mM calcium CFs, mean lesion depths were 187 microns for CL, 154 microns for CF1 and 133 microns for ACF1. With 3 mM calcium CFs, mean lesion depths were 192 microns for CL, 172 for CF3 and 149 for ACF3. Acidulated (22%, 29%) and nonacidulated (10%, 18%) CFs resulted in significant reductions (P < 0.05) in lesion depths when compared with control lesions. Acidulated CFs (13%, 14%) resulted in significant lesion depth reductions (P < 0.05) when compared with nonacidulated CFs. The acidulated 1 mM calcium CF produced the greatest degree of remineralization. Acidulation of CFs enhanced the degree of remineralization over that attained by nonacidulated CFs. This improvement in remineralizing ability of acidulated calcifying fluids may be due to creation of a more reactive enamel surface.
The early stages of enamel surface dissolution (erosion) are of high scientific relevance; however, little is known about if and to what extent these early stages, which result in the softening of the enamel surface, are reversible. The present study investigated the possible rehardening of surface softened enamel in two separate experiments in vitro, employing physiologically relevant demineralization and remineralization times and remineralizing solutions possessing chemical properties close to those of human saliva. Atomic force microscopy (AFM) based nanoindentation has been used to study the nanomechanical properties and the ultrastructure of polished enamel samples as affected by demineralization/remineralization cycles. In contradiction to previous studies employing microhardness techniques, no enamel rehardening has been observed after remineralization; however, the demineralization schemes used in the present study (short treatments with a citric acid buffer) are not comparable to the ones used in previous studies, making a comparison difficult. A mineral deposition after remineralization on softened enamel samples has been observed by AFM; however, a protective effect of this deposited layer could not be revealed. The exposure of softened enamel samples to either a remineralizing solution or a mineral water led to an improved acid resistance of these samples as shown in a demineralization/remineralization cycle. The present study has demonstrated that AFM based nanoindentation is a useful tool to investigate the demineralization and remineralization of surface softened enamel with high accuracy.
Plaque and plaque fluid, rather than saliva, are of prime importance in determining the result of the interaction between tooth enamel and its environment. The concentration of calcium and phosphate ions is higher in plaque fluid than in saliva. Local supersaturation may result in the remineralization of white spot lesions or in the formation of calculus. The latter may be inhibited with containing dentifrices. Undersaturation, resulting from bacterial acids production, promotes dental caries. Fluorides are effective against caries, although the limited transporting properties of saliva would be recognized when designing caries preventive treatments. Suppleting saliva with calcium and phosphat ions through mouthrinses is another method to fight caries, while stimulation of the secretion by chewing gum is also very effective.
Dental research over the last century has advanced our understanding of the etiology and pathogenesis of caries lesions. Increasing knowledge of the dynamic demineralization/remineralization processes has led to the current consensus that bacteria-mediated tooth destruction can be arrested or even to some degree reversed by adopting fluoride and other preventive measures without using restorative materials. Our experimental approach provided new insight into the stoichiometries and solubility properties of human enamel and dentin mineral. The determination of the solubility product constant on the basis of the stoichiometric model (Ca)5.x(Mg)q(Na)u(HPO4)v(CO3)w(PO4)3.y(OH,F)1.z, verifies the difference in their solubility properties, supporting the phase transformation between tooth mineral and calcium phosphates in a wide range of fluid compositions as found in the oral environment. Further refinement of the stoichiometry and solubility parameters is essential to assess quantitatively the driving force for de- and remineralization of enamel and dentin in the oral fluid environment. Prediction of the effects of a combination of inhibitors and accelerator(s) on remineralization kinetics is also required. In order to develop devices efficient for optimizing remineralization in the lesion body, it is a critical question how, and to what extent, fluoride can compensate for the activity of any inhibitors in the mineralizing media.
Substantial pH fluctuations within the biofilm on the tooth surface are a ubiquitous and natural phenomenon, taking place at any time during the day and night. The result may be recordable in the dental tissues at only a chemical and/or ultrastructural level (subclinical level). Alternatively, a net loss of mineral leading to dissolution of dental hard tissues may result in a caries lesion that can be seen clinically. Thus, the appearance of the lesion may vary from an initial loss of mineral, seen only in the very surface layers at the ultrastructural level, to total tooth destruction. Regular removal of the biofilm, preferably with a toothpaste containing fluoride, delays or even arrests lesion progression. This can occur at any stage of lesion progression, because it is the biofilm at the tooth or cavity surface that drives the caries process. Active enamel lesions involve surface erosion and subsurface porosity. Inactive or arrested lesions have an abraded surface, but subsurface mineral loss remains, and a true subsurface remineralization is rarely achievable, because the surface zone acts as a diffusion barrier. The dentin reacts to the stimulus in the biofilm by tubular sclerosis and reactionary dentin.
The purpose of this study was to determine whether quantitative light-induced fluorescence (QLF) could detect very early demineralization and remineralization longitudinally adjacent to orthodontic components in an in vitro model. Extracted human premolars (n = 13) were sectioned sagittally to produce two equal halves and an orthodontic cleat was bonded to the buccal surface of each tooth. Transparent nail varnish was placed over the remaining surface, leaving exposed enamel windows adjacent to the cleat on the coronal and gingival aspects. Each half-tooth was placed into the lid of an Eppendorf tube and randomly assigned to either control (distilled water) or experimental (lactic acid demineralizing buffer, pH 4.5) regimes. Digital photographs and QLF baseline images were taken. The tubes were mounted into a rotating holder and left for 24 hours. QLF and digital photographs were taken, the solutions refreshed and the teeth returned. This was continued every 48 hours for 288 hours. At this time the lactic acid buffer was replaced with a remineralizing solution (artificial saliva, fluoride, calcium) and the experiment continued with weekly examinations. QLF images were analysed and deltaQ at the 5 per cent threshold recorded. Analysis of the QLF images showed that both demineralization and remineralization were identified and monitored. Statistical differences between each of the timed examinations were found (P < 0.05). Analysis of the photographs demonstrated that QLF detected subclinical lesions. This initial pilot study has demonstrated the potential for QLF to longitudinally monitor de- and re-mineralization of enamel adjacent to orthodontic cleats in vitro.
Casein phosphopeptides (CPP) stabilize amorphous calcium phosphate (ACP) and may be used to localize ACP in dental plaque, maintaining a state of supersaturation with respect to tooth enamel, reducing demineralization and enhancing remineralization. The aim here was to investigate these effects by measuring the effect of CPP-ACP on calcium diffusion in plaque. Using Dibdin's effusion system, calcium diffusion was measured in streptococcal model plaques. This demonstrated that by providing a large number of possible binding sites for calcium, 0.1% CPP-ACP reduces the calcium diffusion coefficient by about 65% at pH 7 and 35% at pH 5. Hence, CPP-ACP binds well to plaque, providing a large calcium reservoir within the plaque and slowing diffusion of free calcium. This is likely to restrict mineral loss during a cariogenic episode and provide a potential source of calcium for subsequent remineralization. Overall, once in place, CPP-ACP will restrict the caries process.
The aims of this study were to evaluate the effect of two caries-preventive programs, and to apply the laser fluorescence method, DIAGNOdent, for longitudinal quantification of changes in incipient carious lesions. Twelve subjects with 127 test teeth exhibiting white spot lesions on the buccal surfaces after completed orthodontic therapy were enrolled in the study. Visual examination was performed at baseline and after 12 months. The subjects were divided into two groups: one group received repeated professional tooth cleaning combined with oral hygiene instruction; and the control group received repeated oral hygiene instruction only. The white spot lesions were measured by DIAGNOdent at baseline, and at 3, 6, 9, and 12 months thereafter. There was a significant difference in the DIAGNOdent readings between the first and the final evaluations. However, there was no statistically significant difference between the two treatment groups regarding changes of DIAGNOdent values over time. In conclusion, it may be possible to use DIAGNOdent for longitudinal quantification of carious lesions on smooth surfaces over a period of 1 yr under in vivo conditions. The combination of professional tooth cleaning and oral hygiene instruction had a similar efficacy to professional tooth cleaning only for promoting the remineralization of white spot lesions.
Effects of Mg2+ electrophoresis and galvanization on tooth and bone mineralization was experimentally studied with the use of radioactive Ca and P isotopes. Mg2+ electrophoresis and, to a lesser degree, galvanization enhanced 32P incorporation in incisors and maxillary bones. Mg2+ significantly increased 45Ca incorporation in teeth and maxillary bones. Experimental data permit clinical trials of Mg2+ efficacy in patients with disordered mineralization and remineralization.
Biological factors such as saliva, acquired dental pellicle, tooth structure and positioning in relation to soft tissues and tongue are related to dental erosion development. Saliva has been shown to be the most important biological factor in the prevention of dental erosion. It starts acting even before the acid attack, with the increase of the salivary flow rate as a response to the acidic stimuli. This creates a favorable scenario, increasing the buffering system of saliva and effectively diluting and clearing acids on dental surfaces during the erosive challenge. Saliva plays a role in the formation of the acquired dental pellicle, which acts as a perm-selective membrane preventing contact of the acid with the tooth surfaces. The protective level of the pellicle seems to be regulated by its composition, thickness and maturation time. Due to its mineral content, saliva can also prevent demineralization as well as enhance remineralization. However, these preventive and reparative factors of saliva may not be enough against highly erosive challenges, leading to erosion development. The progress rate of erosion can be significantly influenced by the type of dental substrate, occurrence of mechanical and chemical attacks, fluoride exposure, and also by contact with the oral soft tissues and tongue.
In accordance with the principles of modern operative dentistry, to conserve tooth structure and to use therapeutic restorative materials, an understanding of the carious process in dentine and the biological properties of glass-ionomer cements (GICs) are necessary. Delineation of the outer necrotic from the inner vital and remineralisable carious dentine allows for the preservation of tooth structure. This delineation is not possible when relying on visual and tactile perceptions, but requires the use of a caries detecting dye. GICs are ideal dentine substitutes because of their anticariogenic properties, stable long-term ionic bonding, and ability to assist the process of remineralization. The range of usage of these restorative materials continues to expand with the development of improved products.
OBJECTIVE: This study was carried out to determine in vitro the effect of fluoride on (1) the demineralization of sound human enamel and (2) the progression of artificial caries-like lesions, under relevant oral conditions. METHODS: Thin sections of sound human enamel were exposed to solutions undersaturated with respect to tooth enamel to a degree similar to that found in dental plaque fluid following sucrose exposure in vivo, containing fluoride concentrations (0-0.38ppm) found in plaque fluid. Mineral changes were monitored for 98 days, using quantitative microradiography. The effect of fluoride (1.0-25.0ppm) on the progression of artificial caries-like lesions was similarly studied. RESULTS: Fluoride concentrations of 0.19ppm and greater were found to prevent the demineralization of sound enamel in vitro. However, significantly higher concentrations of fluoride (25.0ppm) were required to prevent further demineralization of artificial caries-like lesions. Demineralizing solutions with intermediate fluoride concentrations (2.1-10.1ppm) induced simultaneously remineralization in the outer portion of the lesion and demineralization in the inner portion. Simultaneous remineralization and demineralization were also observed in hydroxyapatite pellets. CONCLUSIONS: Our results show that the observed effect of fluoride on enamel demineralization is not solely a function of bulk solution properties, but also depends on the caries-status of the enamel surface. A mechanistic model presented indicates that, in comparison to sound enamel surfaces, higher concentrations of fluoride are required to prevent the progression of artificial caries-like lesions under in vivo-like conditions since the diffusion of mineral ions that promote remineralization is rate-limiting.
OBJECTIVE: This study examined strength and bioactive (remineralizing) properties of a powder/liquid formulation (Cement I) and a more practical two-paste formulation (Cement II) of a fluoride-releasing resin-based Ca-PO(4) cement. METHODS: For the remineralization potential, the dissolution of calcium, total ionic phosphate and fluoride from set cement specimens were determined in buffered saline and saliva-like solution (SLS). Artificial caries lesions were produced on coronal dentin of extracted human molars. On each tooth, two defined areas were coated, one with a composite resin (calcium-free control), the other with either Cement I or II. After incubation in SLS, the mineral loss under the cement was analyzed by digitized microradiography and compared to that under the control. RESULTS: The diametral tensile strength of Cement II of approximately 30 MPa after 24 h and 23 MPa after 4 weeks was 2 to 3 times higher than that of Cement I (ANOVA, t-test, p<0.05). Calculations of the ion-activity products and Gibb's free energy from solution ion concentrations indicated a significant potential for the formation of fluor- and/or hydroxyapatite. Concurrently, both cements caused increases of 47% (Cement I) and 38% (Cement II) in the lesion mineral content over that underneath the corresponding controls. SIGNIFICANCE: These in vitro results suggest that the stronger Cement II could serve as a restoration-supporting lining material and could remineralize dentin in areas where complete removal of carious tissue is contra-indicated.
PURPOSE: To evaluate the effectiveness of a 5% sodium fluoride (NaF) bioerodible gel to remineralize demineralized enamel. METHODS: Artificial enamel lesions were created at the gingivofacial surface of 36 extracted teeth. Longitudinal sections were obtained through the lesions, photographed under polarized light microscopy, and the demineralized areas were quantitated. Sections were painted with an acid-protective varnish, leaving only the facial surface of the enamel lesion exposed, and positioned naturally into the tooth from which they were obtained. Teeth were randomly mounted in sets of four that simulated a natural anterior arch form. Equal numbers were subjected to a NaF gel, control gel dr received no treatment, with the gel being placed and retained by the interproximal embrasures of the teeth. Following 30 days exposure to artificial saliva, the lesions were photographed and quantitated in the same manner as prior to treatment. RESULTS: The NaF gel showed significantly more remineralization than the control groups (P< 0.05), with a 68.9% (+/- 17.7) mean lesion remineralization.
The objective of this in vitro study was to evaluate a possible remineralization of human carious dentin by calcium hydroxide. Thirty-nine freshly extracted human permanent and deciduous carious teeth were split into two halves. One half was used as control and the other as experimental. In the latter, a cavity was prepared and the remaining bottom layer of demineralized dentin capped with chemically pure calcium hydroxide. The experimental samples were stored at 37 masculine C. Time intervals were 2, 4, 6, 8, 10 and 12 weeks. All tooth halves were sawed and ground to plano-parallel sections with a thickness varying from 75 to 117 microm. Qualitative microradiographs showed a qualitative increase in radiopacity of the calcium hydroxide treated samples. Quantitative microradiography showed a statistically significant increase in total mineral content in the experimental samples compared to the control samples. These results indicate an in vitro remineralization of carious dentin by calcium hydroxide.
To evaluate chewing gums as a vehicle to increase salivary mineral saturation levels and enhance salivation, monocalcium phosphate monohydrate (MCPM) and an equimolar mixture of tetracalcium phosphate (TTCP) with dicalcium phosphate anhydrous (DCPA) were chosen as experimental chewing gum additives. Each of eight subjects chewed a commercial sugarless bubble gum (control) for 16 min or the same gum to which 5 wt% of MCPM or the TTCP-DCPM mixture had been added. The saliva samples collected every 2 min were analyzed for weight, pH, and total calcium (Ca) and phosphate (P) concentrations. Both experimental gums were found to increase significantly the Ca and P concentrations of saliva during the 16-minute period even more than with a previously evaluated gum that contained dicalcium phosphate dihydrate. The degree of saturation of tooth mineral was significantly increased by both experimental gums, with the greater increase being produced by the TTCP-DCPA gum. The MCPM gum produced a significantly greater saliva flow and a lower salivary pH than did the control and TTCP-DCPA gums. The results suggest that the experimental gums may be useful for promoting remineralization in general and for inducing salivation in xerostomic patients.
This study is of a novel toothpaste which induced remineralization of carious lesions in specific pathogen-free Osborne-Mendel rats. Randomly distributed weanlings in 7 groups (n = 10) each were initially induced to develop carious lesions as a result of a severe dietary and bacteriological challenge. Thus, all were inoculated with S. mutans 10449S, ate diet 2000CS (containing 56% cornstarch) ad libitum, and, upon weaning and for 10 additional days, drank demineralized water supplemented to 10% (w/v) with sucrose (SW) ad libitum. During these 10 days, 6 of the 7 groups of rats were topically treated with a slurried F(-)-free placebo toothpaste. On the 10th day after initial inoculation, two groups were sacrificed, one which had been treated with the placebo and the one which had been untreated. The remaining groups were then provided unsupplemented demineralized water (DW), fed diet 2000CS, and topically treated with either of 5 coded toothpastes: a slurry of the F(-)-free placebo, a similar slurry of a conventional sodium fluoride toothpaste (Crest Regular) containing about 383 ppm F-, or one of three prototype toothpastes formulated by Enamelon, Inc. containing soluble calcium and phosphate salts. Two of these contained 377 ppm F- after mixing their components, either as sodium monofluorophosphate (E-MFP) or as NaF (E-NaF). The third prototype contained 0 ppm F- (E-w/o F). Test items were applied to the dentition for one minute/day, five days/week. These 5 remaining groups were sacrificed 13 days after the DW provision. After defleshing, heads were coded randomly and scored blindly for carious lesions. The exchange of DW for SW was associated with highly significant reductions of 10449S recoveries (p < 0.001), but there were no differences in recoveries among the groups as a function of toothpaste type. Total mandibular and maxillary sulcal and smooth surface caries scores were statistically significantly lower for the E-NaF-treated group at 23 days than for the 23-day placebo-, E-w/o F(-)-, and conventional NaF toothpaste-treated group. Reductions were most impressive quantitatively on approximal tooth surfaces, where both the E-MFP and E-NaF groups had the lowest scores, but were also statistically significant at sulcal surfaces for the E-NaF group. Thus, this study model can be used to detect significant remineralization effects, as occurred with the prototype toothpaste E-NaF.