Effect of low levels of fluoride in solution on enamel demineralization in vitro

Fluoride Release and Rechargeability of Poly(lactic acid) Composites with Glass Ionomer Cement

This study investigates the fluoride release, rechargeability and degradation behaviors of newly developed anticariogenic poly(lactic acid) (PLA) composites. The PLA composite with various concentrations (0%, 5%, 10%, 15% and 20% by weight) of glass ionomer cement (GIC) and sodium fluoride (NaF) were prepared using solvent casting method. The fluoride release, fluoride rechargeability and degradation behavior were evaluated. All experimental groups demonstrated fluoride-releasing ability. The highest level of fluoride ions released was found in PLA composite with sodium fluoride (PLA/NaF). Following the 28-day period, both groups showed a gradual reduction in fluoride ion released, ranging between 0.03 ± 0.01 and 0.53 ± 0.06 ppm, although remaining within the effective range for tooth remineralization. However, the rechargeability was only observed in PLA composite with GIC (PLA/GIC). Following an eight-week in vitro degradation test, all PLA/NaF groups displayed a significantly higher percentage of weight change and water absorption compared to the PLA/GIC and the control group. In SEM analysis, the formation of surface porosities was clearly noticed in all PLA/NaF. All specimens retained their structural integrity throughout the study. In conclusion, the newly developed PLA/GIC displays promising possibilities as an anticariogenic material. Furthermore, the rechargeability of these ions are repeatable, ensuring their long-term utility.

Highlights on Drug and Ion Release and Recharge Capacity of Antimicrobial Removable Prostheses

This article aimed to review the ion and drug release, recharge abilities, and antimicrobial properties of drug/ion-releasing removable prostheses, and to assess their capability in preventing and inhibiting denture stomatitis as well preventing caries and reversing carious lesions. Data was collected from published scientific papers listed in PubMed database from January 1975 to December 2021. English full-text articles, involving clinical or in vitro studies, focusing on removable prostheses and are concerned with drug/ion release and rechargeability as a way to prevent or inhibit denture stomatitis or dental caries were included. The relevant articles reported that ion- or drug-modified polymethylmethacrylate acts as a reservoir for these ions and drugs and is capable of releasing significant amounts with sustained release effect. Recharging of modified resin resulted in greater sustainability of ion and drug release, thus improving the long-term effects of protection against demineralization and reducing the adhesion of Streptococcus mutans and Candida albicans. Modifications of removable prostheses with rechargeable ions and drugs enhance remineralization, hinder demineralization, and reduce microbial adhesion in difficult-to-access areas. Selection of denture base for clinical use will consider its ability to act as an ion/drug reservoir that is capable of release and recharge.

Fluoride exchange by glass-ionomer dental cements and its clinical effects: a review

The topic of fluoride release and uptake by glass-ionomer (glass polyalkenoate) dental cements is reviewed. The study was based on a literature search carried out using PubMed. The main key words used were glass-ionomer and fluoride, and further refinements were made by adding the keywords anti-microbial, anti-caries and remineralization. Papers were selected from the initial search, which concentrated on fundamental aspects of fluoride release, including kinetics and the influence of the cement composition, and resulting clinical performance against caries. Other relevant papers were cited where they added useful and relevant data. From these published papers, it was possible to explain the detailed mechanism of fluoride release by glass-ionomer cements and also its uptake. Fluoride release has been shown to be a two-step process. In neutral solutions, the steps can be divided into early wash-out and long-term diffusion. In acid conditions, the early wash-out remains, though with greater amounts of fluoride released, and the long-term release becomes one of slow dissolution. The effect of fluoride on the viability of oral micro-organisms has been described, and glass-ionomers have been shown to release sufficient fluoride to reduce the size and viability of adjacent populations of oral bacteria. The effect of low levels of fluoride on the remineralization of tooth tissue has been considered. Levels needed to increase remineralization are much lower than those needed to adversely affect oral bacteria, from which we conclude that glass-ionomers release sufficient fluoride to promote remineralization. Despite this, there remains uncertainty about their overall contribution to sound oral health, given the widespread use of other sources of fluoride, such as toothpastes.

The Effect of Biomimetic Remineralization of Calcium Phosphate Ion Clusters-Treated Enamel Surfaces on Bracket Shear Bond Strength

Purpose

To evaluate the remineralization effect of calcium phosphate ion clusters (CPICs) on demineralized enamel surfaces and their effects on bracket shear bond strength.

Patients and Methods

Extracted premolars were prepared in resin blocks. The samples in the form of resin blocks were divided into five experimental groups: control group, demineralized group, and groups of CPIC solution treatment for 30, 60, and 90s. The specimens were examined using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), microhardness testing, micro-computed tomography (micro-CT) assessment, shear bond strength (SBS) test, and adhesive remnant index (ARI) score.

Results

The SEM images revealed epitaxial growth of enamel and a decrease in the thickness of the demineralized enamel layer when treated with CPIC solution. The EDX analysis revealed an increase in the Ca/P ratio in the CPIC-treated groups. The microhardness value significantly increased when treated with CPICs; however, it showed a lower value than that of the sound enamel groups. As a result of the micro-CT test, radiolucency decreased gradually as the CPIC treatment time increased. The SBS test and ARI score results showed an improvement in bonding stability after treatment with CPICs.

Conclusion

We demonstrated an enamel biomodification approach using CPIC solution treatment, which is a promising strategy for enamel remineralization. Specifically, remineralization of demineralized enamel improves the orthodontic bracket SBS.

Organic volume and permeability variations in the surface layer of artificial and natural enamel carious lesions

OBJECTIVES

Test the hypothesis the type of enamel caries (natural, artificial induced by gel, and artificial induced by acid solutions) affect the organic volume and the permeability of the surface layer in enamel caries lesions.

DESIGN

Artificial enamel caries, induced by either acidic solution (organic-poor; Group 1) or acidic gel (organic-rich; Group 2), and natural non-cavitated inactive approximal enamel caries lesions (NEC; Group 3) were obtained, from which longitudinal ground sections were prepared. Measurements of the mineral (V_min) (by microradiography), and water (α) and organic (β) volumes (by optical birefringence) were obtained at three points in the surface layer (n = 30/group).

RESULTS

The main outcomes were the ratio between experimental β by predicted β (β Ratio) and the ratio between experimental and predicted permeabilities (α_d Ratio). β Ratio in Group 1 was lower than in Groups 2 (Cohen's d: -1.81; 95% CI:-1.45,-2.32; p < 0.001) and 3 (Cohen's d: -0.71; 95% CI:-0.27,-1.18; p = 0.004), and Group 2 surpassed Group 3 (Cohen's d: 0.49; 95% CI:0.07,0.94; p = 0.03). α_d Ratio in Group 1 was higher than in Groups 2 (Cohen's d: 1.86; 95% CI:1.49,2.33; p < 0.001) and 3 (Cohen's d: 0.60; 95% CI:0.18,1.14; p = 0.01), and Group 3 surpassed Group 2 (Cohen's d: 0.61; 95% CI:0.23,1.07; p = 0.01).

CONCLUSIONS

The highest organic volume and the lowest permeability occurred at the surface layer of gel-induced artificial enamel caries lesions, which should be preferred in in vitro studies on de- and remineralization and resin infiltration.

Is professionally applied topical fluoride effective in treating incipient caries? A systematic review

The present systematic review aimed to investigate the effectiveness of professionally applied topical fluoride as therapeutic agent for incipient carious lesions in permanent teeth. Randomised clinical trials (RCTs) comparing the effectiveness of professionally applied topical fluoride (varnish or gel) with that of placebo, no intervention, and toothbrushing (control group) in the treatment of incipient carious lesions in permanent dentition were included. An electronic search was performed in the PubMed, Web of Science, Scopus, Virtual Health Library, Embase, and Cochrane databases, in the grey literature, and in clinical trials registered until January 2021. Two reviewers independently screened titles and abstracts and assessed the risk of bias using the Cochrane tool. The certainty of evidence was classified using GRADE. A total of 2,223 articles were screened using titles/abstracts. After full-text reading of the 22 selected studies, nine RCTs were included. Five RCTs found that topical fluoride may be effective in reversing incipient carious lesions in permanent teeth. Overall, five studies were classified as having a low risk of bias and four as having some concerns. Only descriptive analysis was performed because of the heterogeneity of the data. Studies comparing fluoride varnish with usual home care oral hygiene have demonstrated topical fluoride does not appear to be more effective in improving the appearance of incipient carious lesions. Therefore, usual home care oral hygiene with fluoride toothpaste may be sufficient to treat incipient carious lesions in permanent dentition. Further studies with greater methodological rigor are, however, required to reduce bias, to allow a meta-analysis, and to draw well-founded conclusions (CRD42019120406).

Application of Amorphous Calcium Phosphate Agents in the Prevention and Treatment of Enamel Demineralization

Enamel demineralization, as a type of frequently-occurring dental problem that affects both the health and aesthetics of patients, is a concern for both dental professionals and patients. The main chemical composition of the enamel, hydroxyapatite, is easy to be dissolved under acid attack, resulting in the occurrence of enamel demineralization. Among agents for the preventing or treatment of enamel demineralization, amorphous calcium phosphate (ACP) has gradually become a focus of research. Based on the nonclassical crystallization theory, ACP can induce the formation of enamel-like hydroxyapatite and thereby achieve enamel remineralization. However, ACP has poor stability and tends to turn into hydroxyapatite in an aqueous solution resulting in the loss of remineralization ability. Therefore, ACP needs to be stabilized in an amorphous state before application. Herein, ACP stabilizers, including amelogenin and its analogs, casein phosphopeptides, polymers like chitosan derivatives, carboxymethylated PAMAM and polyelectrolytes, together with their mechanisms for stabilizing ACP are briefly reviewed. Scientific evidence supporting the remineralization ability of these ACP agents are introduced. Limitations of existing research and further prospects of ACP agents for clinical translation are also discussed.

Mechanical Properties, Cytotoxicity, and Fluoride Ion Release Capacity of Bioactive Glass-Modified Methacrylate Resin Used in Three-Dimensional Printing Technology

Background: Clinically, three-dimensional (3D) printing technology is becoming a popular and efficient dental processing technology. Recently, there has been an increasing demand for dental materials that exhibit bioactive properties. The present study aimed to evaluate the mechanical properties, cytotoxicity, and fluoride ion release capacity of 3D-printed dental resins modified with bioactive glass. Materials and methods: The resin FotoDent splint used in the production of removable orthodontic splints, was modified by the addition of two types of bioactive glasses that are capable of releasing fluoride ions. The novel materials used for the production of dental splints were examined for their mechanical, physical, and biological properties (fracture resistance, sorption, solubility, elution of nonpolymeric substances, and release of fluoride ions over time) and cytotoxic effects on cell cultures. Results: Initially, the fracture toughness of the 3D-printed resin was found to be 55 MPa, but after modification with glass, the resistance was reduced to about 50 MPa. Sorption and solubility values of the materials (19.01 ÷ 21.23 µg/mm³ and 0.42 ÷ 1.12 µg/mm³, respectively) complied with the safety limits imposed by ISO standard. Modified resins were capable of releasing fluoride ions, and the maximum releasing effect was observed after 14 days of incubation. Both the modified resins, after four days of contact with human gingival fibroblasts, exhibited moderate cytotoxic properties. Conclusions: The experimental results showed that modification of methacrylate resin, used in 3D printing technology, with bioactive glasses produces novel dental materials that possess desirable bioactive properties. The findings of this study indicate the potential ability of modified polymethacrylate resins to release fluoride ions in the oral cavity environment. The modified materials are characterized with a moderate decrease in physical properties and mild cytotoxicity on direct contact with human fibroblasts.

Advanced non-fluoride approaches to dental enamel remineralization: The next level in enamel repair management

In modern dentistry, a minimally invasive management of early caries lesions or early-stage erosive tooth wear (ETW) with synthetic remineralization systems has become indispensable. In addition to fluoride, which is still the non-plus-ultra in these early caries/ETW treatments, a number of new developments are in the test phase or have already been commercialized. Some of these systems claim that they are comparable or even superior to fluoride in terms of their ability to remineralize enamel. Besides, their use can help avoid some of the risks associated with fluoride and support treatments of patients with a high risk of caries. Two individual non-fluoride systems can be distinguished; intrinsic and extrinsic remineralization approaches. Intrinsic (protein/peptide) systems adsorb to hydroxyapatite crystals/organics located within enamel prisms and accumulate endogenous calcium and phosphate ions from saliva, which ultimately leads to the re-growth of enamel crystals. Extrinsic remineralization systems function on the basis of the external (non-saliva) supply of calcium and phosphate to the crystals to be re-grown. This article, following an introduction into enamel (re)mineralization and fluoride-assisted remineralization, discusses the requirements for non-fluoride remineralization systems, particularly their mechanisms and challenges, and summarizes the findings that underpin the most promising advances in enamel remineralization therapy.

Characterization of a novel enamel sealer for bioactive remineralization of white spot lesions

OBJECTIVES

45S5 Bioglass is a bioactive glass capable of releasing ions that can interact with dental hard tissues. The current study aimed at examining the effectiveness of 45S5 Bioglass in remineralizing enamel white spot lesion (WSL) as well as its effect on the bond strength of orthodontic brackets bonded to demineralized enamel.

MATERIALS AND METHODS

WSLs were induced in the buccal surfaces of 135 human extracted teeth by storage in acid solution pH 4.5 for four days. The specimens were then equally divided into three groups; Demineralized group, Bioglass group (BG), and control group (intact enamel). The groups were chemically analyzed using (FTIR/ATR) Fourier-transform infrared spectroscopy/attenuated total reflectance, (XRD) X-ray diffraction, and (SEM/EDS) scanning electron microscope equipped with electron-dispersive-spectroscopy. Moreover, 10 specimens from each group were tested using Transverse Micro Radiography (TMR) technique, and 15 specimens from each group were bonded with metal orthodontic brackets and tested for shear bond strength test (SBS). The data were analyzed statistically using One way ANOVA p < 0.05.

RESULTS

TMR study showed that bioglass group samples recorded lesion depth of 70.19 ± 29.21 μm and Δ Z (mineral loss) 732.15 ± 210.16 vol% μm which was significantly lower than the demineralized specimens having lesion depth of 115.75 ± 19.98 μm and Δ Z (mineral loss) 3472.69 ± 738.38 vol%μm, moreover, bioglass specimens recorded 14.15 ± 2.35 Mpa which was significantly higher than demineralized specimens 6.82+1.83 Mpa but less than the control specimens 20.5 + 6.1 MPa (p < 0.05). FTIR/ATR, XRD, and SEM/EDS tests showed that bioglass paste formed a layer of brushite crystals onto the treated enamel surface.

CONCLUSION

45S5 bioglass paste may serve as an effective remineralizing agent for demineralized enamel.

Release and Recharge of Fluoride Ions from Acrylic Resin Modified with Bioactive Glass

Background: Oral hygiene is essential for maintaining residual dentition of partial denture wearers. The dental material should positively affect the oral environment. Fluoride-releasing dental materials help to inhibit microbial colonization and formation of plaque as well as to initiate the remineralization process in the early cavity area. Aim: To evaluate fluoride ion release and recharge capacity, sorption, and solubility of polymethyl methacrylate (PMMA) dental resin modified with bioactive glass addition. Materials and methods: Two bioactive glass materials (5 wt% Kavitan, 10 wt% Kavitan, and 10 wt% Fritex) and pure 10 wt% NaF were added to dental acrylic resin. After polymerization of the modified resins, the release levels of fluoride anions were measured based on color complex formation by using a spectrophotometer after 7, 14, 28, and 35 days of storage in distilled water at 37 °C. Subsequently, specimens were brushed with a fluoride-containing tooth paste on each side for 30 s, and the fluoride recharge and release potential was investigated after 1, 7, and 14 days. Sorption and solubility after 7 days of storage in distilled water was also investigated. Results: The acrylic resins with addition of 10% bioactive glass materials released fluoride ions for over 4 weeks (from 0.14 to 2.27 µg/cm²). The amount of fluoride ions released from the PMMA resin with addition of 10 wt% Fritex glass was higher than that from the resin with addition of 10 wt% Kavitan. The acrylic resin containing 10 wt% NaF released a high amount of ions over a period of 1 week (1.58 µg/cm²), but the amount of released ions decreased rapidly after 14 days of storage. For specimens containing 5 wt% Kavitan glass, the ion-releasing capacity also lasted only for 14 days. Fluoride ion rechargeable properties were observed for the PMMA resin modified with addition of 10 wt% Fritex glass. The ion release levels after recharge ranged from 0.32 to 0.48 µg/cm². Sorption values ranged from 10.23 μm/mm³ for unmodified PMMA resin to 12.11 μm/mm³ for specimens modified with 10 wt% Kavitan glass. No significant differences were found regarding solubility levels after 7 days. Conclusions: The addition of 10 wt% Fritex and 10 wt% Kavitan bioactive glass materials to heat-cured acrylic resin may improve its material properties, with bioactive fluoride ion release ability lasting for over 4 weeks. The resin modified with 10 wt% Fritex glass could absorb fluoride ions from the toothpaste solution and then effectively release them. Addition of fluoride releasing fillers have a small effect on sorption and solubility increase of the modified PMMA resin. Clinical significance: The addition of bioactive glass may be promising in the development of the novel bioactive heat-cured denture base resin.

Preventive effect of experimental polymer-based desensitizers with NaF on demineralization of root dentin -observed using micro-CT

This study compared the effect of experimental polymer-based desensitizers with NaF and oxalic acid (OA) for preventing root demineralization via observation using micro-CT. Bovine root dentin surfaces were treated with coating materials: no treatment; MS0(+) (MS Coat One^®); MS3000(+) (MS Coat^®); MS0(-); MS3000(-); MS7000(+/-); fluoride gel (NaF9000). MS; MS polymer, 0-7000; NaF concentrations, (+/-); OA. The specimens were scanned using micro-CT before and after demineralization (pH4.5, 10 h). Following this, the mean mineral loss (ML) after demineralization was calculated, and the specimens were observed under a scanning electron microscope (SEM). The ML values of MS3000(+), MS7000(-), MS7000(+) and NaF9000 were significantly lower than the other groups (p<0.05). Under an SEM, a membrane structure was observed to have formed on the dentin surface in the presence of the MS, fluoride, and OA. The experimental polymer-based desensitizer with oxalic acid and a high concentration of fluoride is effective for preventing root demineralization.

Novel fluoride rechargeable dental composites containing MgAl and CaAl layered double hydroxide (LDH)

OBJECTIVE

This study aims to incorporate 2:1 MgAl and 2:1 CaAl layered double hydroxides (LDHs) in experimental dental-composites to render them fluoride rechargeable. The effect of LDH on fluoride absorption and release, and their physico-mechanical properties are investigated.

METHODS

2:1 CaAl and 2:1 MgAl LDH-composite discs prepared with 0, 10 and 30wt% LDH were charged with fluoride (48h) and transferred to deionized water (DW)/artificial saliva (AS). Fluoride release/re-release was measured every 24h (ion-selective electrodes) with DW/AS replaced daily, and samples re-charged (5min) with fluoride every 2 days. Five absorption-release cycles were conducted over 10 days. CaAl and MgAl LDH rod-shaped specimens (dry and hydrated; 0, 10 and 30wt%) were studied for flexural strength and modulus. CaAl and MgAl LDH-composite discs (0, 10, 30 and 45wt% LDH) were prepared to study water uptake (over 7 weeks), water desorption (3 weeks), diffusion coefficients, solubility and cation release (ICP-OES).

RESULTS

CaAl LDH and MgAl LDH-composites significantly increased the amount of fluoride released in both media (P<0.05). In AS, the mean release after every recharge was greater for MgAl LDH-composites compared to CaAl LDH-composites (P<0.05). After every recharge, the fluoride release was greater than the previous release cycle (P<0.05) for all LDH-composites. Physico-mechanical properties of the LDH-composites demonstrated similar values to those reported in literature. The solubility and cation release showed a linear increase with LDH loading.

SIGNIFICANCE

LDH-composites repeatedly absorbed/released fluoride and maintained desired physico-mechanical properties. A sustained low-level fluoride release with LDH-composites could lead to a potential breakthrough in preventing early stage carious-lesions.

Differential induction of surface chemical compositional change on tooth structure by glass ionomer restorative materials

Glass ionomer cement (GIC) is a restorative dental material capable of promoting mineral deposition on surrounding tooth substrates. However, it is unclear as to whether demineralization and remineralization due to an oral pH change of the tooth affect the dissolution pattern of tooth crown and root differently. It also remains to be elucidated how GIC alters superficial chemical compositions of tooth crown structurally known as enamel, in relation to the root. In this study, we investigated an effect of pH challenge on chemical compositional change of tooth crown and root, as well as the contribution of GIC restorations on a shift of elemental abundance on tooth crown and root. Our findings demonstrated that an exposure to a pH cycling resulted in a drastic change of elemental profile of the root, but not the crown. Modification of superficial elemental ingredients of GIC-restored cavities located on different anatomical part of the tooth was found after an acid attack. Notably, a differential induction of chemical compositional shift was dependent on the type of GIC used and the location of restored GIC. Our study highlights a susceptibility of root portion to acid-induced elemental dissolution, and that GIC use might be implicated in the delayed dissolution rate of the tooth structure.

Fluoride varnish containing chitosan demonstrated sustained fluoride release

Fluoride varnish is a professionally applied product that prevents dental caries. However, fluoride varnishes do not provide sustained fluoride release. The objective of this study was to prepare fluoride varnish formulations containing various amounts of chitosan that would generate sustained fluoride release. We evaluated their chemical structure, viscosity, and in vitro fluoride release. Furthermore, the 3-(4, 5-dimethylthiazolyl-2)-2,5diphenyltetrazolium bromide (MTT) assay and direct contact test were used to determine varnish cytotoxicity. We found that all fluoride varnish formulations had the same chemical structure. Their viscosity demonstrated a chitosan concentration-dependent increase. In vitro fluoride release showed a sustained fluoride release. The chitosan fluoride varnishes were cytotoxic to human gingival fibroblasts. We propose the new fluoride varnish formulation as a potential material to be used as a sustained release fluoride varnish.

Biological and Mechanical Evaluation of Novel Prototype Dental Composites

The breakdown of the polymeric component of contemporary composite dental restorative materials compromises their longevity, while leachable compounds from these materials have cellular consequences. Thus, a new generation of composite materials needed to be designed to have a longer service life and ensure that any leachable compounds are not harmful to appropriate cell lines. To accomplish this, we have developed concurrent thiol-ene-based polymerization and allyl sulfide-based addition-fragmentation chain transfer chemistries to afford cross-linked polymeric resins that demonstrate low shrinkage and low shrinkage stress. In the past, the filler used in dental composites mainly consisted of glass, which is biologically inert. In several of our prototype composites, we introduced fluorapatite (FA) crystals, which resemble enamel crystals and are bioactive. These novel prototype composites were benchmarked against similarly filled methacrylate-based bisphenol A diglycidyl ether dimethacrylate / triethylene glycol dimethacrylate (bisGMA/TEGDMA) composite for their cytotoxicity, mechanical properties, biofilm formation, and fluoride release. The leachables at pH 7 from all the composites were nontoxic to dental pulp stem cells. There was a trend toward an increase in total toughness of the glass-only-filled prototype composites as compared with the similarly filled bisGMA/TEGDMA composite. Other mechanical properties of the glass-only-filled prototype composites were comparable to the similarly filled bisGMA/TEGDMA composite. Incorporation of the FA reduced the mechanical properties of the prototype and bisGMA/TEGDMA composite. Biofilm mass and colony-forming units per milliliter were reduced on the glass-only-filled prototype composites as compared with the glass-only-filled bisGMA/TEGDMA composite and were significantly reduced by the addition of FA to all composites. Fluoride release at pH 7 was greatest after 24 h for the bisGMA/TEGDMA glass + FA composite as compared with the similarly filled prototypes, but overall the F^- release was marginal and not at a concentration to affect bacterial metabolism.

Increasing the efficiency of CPP-ACP to remineralize enamel white spot lesions

OBJECTIVES

To compare the remineralization efficacy of using the MI paste plus according to manufacturer's instructions to MI varnish and to using a modified method of MI-paste plus application.

MATERIALS AND METHODS

100 enamel specimens were obtained from the buccal and lingual surfaces of 50 extracted human non-caries third molars. All specimens were challenged by a buffered demineralization solution for 4 days, and were divided in 4 groups with 25 specimens in each group. 25 demineralized specimens had MI paste plus applied for 4 min and then wiped out (MI), 25 specimens had MI paste applied followed by application of SE-bonding agent (MI + Bond), 25 specimens had MI Varnish applied according to manufacturer instructions (MI Varnish) the rest of specimens served as controls (C). All specimens were stored for 7 days in artificial saliva. All specimens had their surface hardness (SH) measured by micro-hardness tester before/after the acidic challenge and after the treatment procedures. After the SH test all specimens were crosssectioned to obtain 100-150 micron thickness specimens to observe the lesion depth before/after treatment by the TMR (Transverse Micro Radiography) technique.

RESULTS

TMR experiment showed that (MI + Bond) and (MI varnish) groups recorded significant decrease in lesion depth and mineral loss of the tested subsurface lesion p < 0.05. (MI + Bond) group scored the highest significant regain of surface micro hardness results p < 0.05.

CONCLUSION

(MI varnish) and the modified application of MI paste are methods that can increase the efficacy of CPP-ACP in remineralizing the enamel surface lesions.

High Amount of Organic Matter during Caries Formation Reduces Remineralization and Resin Infiltration of Enamel Caries

The amount of organic material in the cariogenic environment correlates with the amount of organic material incorporated in carious enamel. The incorporated organic material may be expected to reduce the pore volumes available for remineralization and resin infiltration, but these expected outcomes have not yet been quantified. We tested the effect of the amount of organic content in the cariogenic agent on remineralization and the resin-occluded pore volume in artificial subsurface enamel caries. An acid gel (organic-rich; G1) and an aqueous solution (organic-poor; G2) were used to induce subsurface lesions in human enamel. Undemineralized histological sections were prepared, microradiographed, and then submitted to resin infiltration in vitro. The enamel component volumes (mineral, organic, remineralizable [total water volume], loosely and firmly bound water volumes, and resin-occluded volume) were measured (by microradiography and polarizing microscopy) at histological sites (n = 38, G1; n = 34, G2). The main outcomes were the differences between the experimental and the predicted volumes (Δremineralizable and Δresin-occluded volumes). Resin infiltration was confirmed by confocal scanning laser microscopy. Compared to G2, G1 presented more incorporated organic volume and lower Δremineralizable volume (p = 0.003; Hedges g = 0.66; power = 0.87), a lower increase in loosely bound water volume (p = 0.0013; Hedges g = 0.74; power = 0.93), a lower remineralization volume in the surface layer (p = 0.017; Hedges g = 0.68; power = 0.8), and a lower Δresin-occluded volume (p = 0.0015; Hedges g = 0.73; power = 0.92). In conclusion, the higher amount of organic matter in the cariogenic gel negatively affected remineralization and the resin-occluded volume in subsurface lesions.

Comparison of resin-based and glass ionomer sealants with regard to fluoride-release and anti-demineralization efficacy on adjacent unsealed enamel

This study compared resin-based and glass ionomer sealants with regard to their fluoride-release behavior and anti-demineralization potential on adjacent unsealed enamel surfaces. Sealant cavities prepared on bovine enamel blocks were filled with fluoride-containing resin sealants [TeethmateF-1 (TF), Clinpro^TM (CP)], and glass ionomer sealant [Fuji VII (FVII)]. Specimens were then incubated in artificial saliva for 14 days to measure fluoride. Thereafter, demineralization was performed for 10 days, and the anti-demineralization efficacy was assessed by Swept Source Optical Coherence Tomography (SS-OCT), and cross-sectional nanohardness. All data were statistically analyzed by using ANOVA. FVII exhibited the highest fluoride release. SS-OCT and nanohardness findings indicated that anti-demineralization efficacy of TF was the greatest, whereas FVII was not significantly different from that of CP. Resin sealants released a lower amount of fluoride but exhibited anti-demineralization effects on the adjacent unsealed enamel surfaces that were comparable to that of a glass ionomer sealant.

Surface reactivity of octacalcium phosphate-derived fluoride-containing apatite in the presence of polyols and fluoride

The present study was designed to characterize co-precipitated fluoridated apatitic materials from octacalcium phosphate (OCP) precursor and to investigate their surface reactions with polyols including glycerol in the presence of fluoride ions. Laboratory-synthesized fluoridated apatite crystals (LS-FA) were obtained in a solution containing fluoride (F) from 25 to 500 ppm. LS-FAs and commercially available fluoroapatite (FA) and hydroxyapatite (HA) were characterized by physical techniques, such as X-ray diffraction. LS-FA obtained in the presence of 100 ppmF (100 ppm-LS-FA) had an apatitic structure, but its solubility was close to HA in a culture medium (α-MEM) despite the fact it contains over 3 wt % of F. 100 ppm-LS-FA, FA, and HA were then subjected to the human serum albumin (HSA) adsorption test at pH 7.4 (in a 150 mM Tris-HCl buffer) and the dissolution and re-mineralization experiments in the presence of xylitol, D-sorbitol, or glycerol, and F under acidic and neutral conditions. Adsorption affinity of HSA was estimated as highest for FA and lowest for LS-FA. LS-FA, FA, and HA were immersed in a lactic acid solution with the polyols and/or F ion-containing solution up to 200 ppm to analyze the dissolution behavior. LS-FA had the highest dissolution tendency in the conditions examined. Glycerol enhanced the dissolution of phosphate from apatite crystals in particular from LS-FA. The results suggest that the apatite crystals, obtained through the hydrolysis of OCP in the presence of F, provide a more reactive surface than FA or HA under physiological environments. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2235-2244, 2018.

Effect of a calcium phosphate and fluoride paste on prevention of enamel demineralization

This study aimed to examine the anti-demineralization capacities of (a) tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) and 950 ppm fluoride paste, (b) casein phosphopeptide amorphous calcium phosphate paste and (c) 950 ppm fluoride solution using optical coherence tomography (OCT). Enamel blocks were cut from the bovine incisors and treated using one of the above-mentioned three materials or deionized water as control (n=10). All samples were subjected to a demineralization gel for 1 h followed by a remineralization solution for 23 h. This experimental cycle was repeated for 28 days. The specimens were imaged using OCT at baseline and at four stages and measured lesion depth using image analysis software (ImageJ). Repeated measures ANOVA revealed that demineralization time, material and their interaction significantly affected the optical lesion depth (p<0.001). TTCP and DCPA and 950 ppm fluoride paste and 950 ppm fluoride solution showed significantly lower lesion progress compare to other groups (p<0.05).

The pH effect of solvent in silanization on fluoride released and mechanical properties of heat-cured acrylic resin containing fluoride-releasing filler

This study aimed to evaluate the effect of an acidic-adjusted pH of solvent in silanization on the amount of fluoride released and mechanical properties of heat-cured acrylic resin containing a silanized fluoride-releasing filler. The experimental groups were divided into 4 groups; non-silanized, acidic-adjusted pH, non-adjusted pH, and no filler as control. For fluoride measurement, each specimen was placed in deionized water which was changed every day for 7 days, every week for 7 weeks and measured. The flexural strength and flexural modulus were evaluated after aging for 48 h, 1, and 2 months. Two-way ANOVA indicated significant differences among groups, storage times, and its interaction in fluoride measurement and flexural modulus. For flexural strength, there was significant difference only among groups. Acidic-adjusted pH of solvent in silanization enhanced the amount of fluoride released from acrylic resin, while non-adjusted pH of solvent exhibited better flexural strength of acrylic resin.

Dental caries

Dental caries is a biofilm-mediated, sugar-driven, multifactorial, dynamic disease that results in the phasic demineralization and remineralization of dental hard tissues. Caries can occur throughout life, both in primary and permanent dentitions, and can damage the tooth crown and, in later life, exposed root surfaces. The balance between pathological and protective factors influences the initiation and progression of caries. This interplay between factors underpins the classification of individuals and groups into caries risk categories, allowing an increasingly tailored approach to care. Dental caries is an unevenly distributed, preventable disease with considerable economic and quality-of-life burdens. The daily use of fluoride toothpaste is seen as the main reason for the overall decline of caries worldwide over recent decades. This Primer aims to provide a global overview of caries, acknowledging the historical era dominated by restoration of tooth decay by surgical means, but focuses on current, progressive and more holistic long-term, patient-centred, tooth-preserving preventive care.

Microcomputed tomography evaluation of white spot lesion remineralization with various procedures

INTRODUCTION

The aim of this study was to use microcomputed tomography to evaluate the effects on white spot lesions of 3 remineralizing agents compared with artificial saliva (Inonu University, Malatya, Turkey). The agents were GC Tooth Mousse (GC International, Itabashi-ku, Tokyo, Japan), 50-ppm sodium fluoride solution (Inonu University, Malatya, Turkey), and Clinpro 5000 (3M ESPE Dental Products (St Paul, Minn). The experimental and control teeth were stored in artificial saliva.

METHODS

Forty-four extracted premolars were divided into 4 groups of 11 teeth each (3 experimental groups and 1 control group). After white spot lesions were created on the teeth, a remineralizing agent was applied. Microcomputed tomography scanning was performed at the following times: T0 (sound enamel), T1 (day 0, when the white spot lesion was formed), T2 (day 15), and T3 (day 30). Volume, depth, surface area, and mineral density changes of the white spot lesions were evaluated at different time points using CTAn software (SkyScan; Bruker, Kontich, Belgium).

RESULTS

GC Tooth Mousse and Clinpro 5000 improved all measurements after 30 days. However, Clinpro 5000 was not as effective in reducing lesion depth as it was in the other parameters. The artificial saliva group and the 50-ppm sodium fluoride solution did not show significant effects in the regression of the white spot lesions at the end of the 30-day experiment.

CONCLUSIONS

GC Tooth Mousse and Clinpro 5000 were more effective in remineralization of white spot lesions than sodium fluoride solution and artificial saliva. They can be preferred for use clinically. Microcomputed tomography is a novel and effective method that shows promise in accurately evaluating white spot lesions and remineralization.

Review of Fluoride Release and Secondary Caries Reduction by Fluoridating Composites

Secondary caries is one of the main reasons to replace restorations. Due to the pressure to eliminate or reduce the number of amalgam restorations in many countries, fluoride-releasing composites have gained in importance. This review limits itself to information relevant to secondary caries near fluoride-releasing anterior or posterior composites. Although many parameters are very important in composite functioning, a weak spot near a filling is always the interface and the locally present interfacial gap between the composite and the hard tissues, where secondary caries takes place due to plaque action. Relevant parameters such as the amount of fluoride released in vitro in μg.cm-2, the rate of fluoride release, and the period of fluoride release are compared for several composites. In vitro F release has been measured for some fluoridating composites for more than five years. Unfortunately, F release in vivo or in situ cannot be measured adequately.

The fluoride released by the composites considered is partly taken up by the surrounding tissues, partly released to the saliva, and partly efficacious in possible marginal gaps and defects. A major part of this paper pertains to in vitro, in situ, and in vivo secondary caries reduction experiments. In vitro caries reductions in the order of 40% from F-releasing composites vs. controls have been found. In in situ model investigations under plaque and saliva conditions, secondary caries reduction percentages of between 40 and 50% have been experimentally measured in gaps in enamel near F composites.

Effects of coating materials on nanoindentation hardness of enamel and adjacent areas

OBJECTIVES

Materials that can be applied as thin coatings and actively release fluoride or other bioavailable ions for reinforcing dental hard tissue deserve further investigation. In this study we assessed the potential of resin coating materials in protection of underlying and adjacent enamel against demineralization challenge using nanoindentation.

METHODS

Enamel was coated using Giomer (PRG Barrier Coat, PBC), resin-modified glass-ionomer (Clinpro XT Varnish, CXT), two-step self-etch adhesive (Clearfil SE Protect, SEP) or no coating (control). After 5000 thermal cycles and one-week demineralization challenge, Martens hardness of enamel beneath the coating, uncoated area and intermediate areas was measured using a Berkovich tip under 2mN load up to 200μm depth. Integrated hardness and 10-μm surface zone hardness were compared among groups.

RESULTS

Nanoindentation and scanning electron microscopy suggested that all materials effectively prevented demineralization in coated area. Uncoated areas presented different hardness trends; PBC showed a remarkable peak at the surface zone before reaching as low as the control, while CXT showed relatively high hardness values at all depths.

SIGNIFICANCE

Ion-release from coating materials affects different layers of enamel. Coatings with fluoride-releasing glass fillers contributed to reinforcement of adjacent enamel. Surface prereacted glass filler-containing PBC superficially protected neighboring enamel against demineralization, while resin-modified glass-ionomer with calcium (CXT) improved in-depth protection. Cross-sectional hardness mapping of enamel on a wide range of locations revealed minute differences in its structure.

Fluoridated elastomers:in vivoversusin vitrofluoride release

OBJECTIVES

To compare (i) the in vivo release of fluoride from fluoridated elastomers to the in vitro release, and (ii) the residual fluoride content of the elastomers after 1 week in the mouth with and without fluoride toothpaste and mouthrinse.

DESIGN

A prospective, longitudinal, cross-over study.

SUBJECTS AND METHOD

Six subjects were recruited by poster to take part in the study. Each subject had one premolar in each quadrant to which a bracket could be fixed and exemplary oral hygiene. Elastomers were then placed on these brackets.

INTERVENTION

The study was divided into two parts: (i) subjects used oral hygiene products with fluoride and (ii) oral hygiene products with fluoride were excluded. Both groups of elastomers were left in the mouth for 1 week. After collection the elastomers were stored in distilled water.

MAIN OUTCOME MEASURES

The amount of residual fluoride in the ligatures after they have been placed in the mouth for 1 week was compared with the cumulative fluoride release in vitro over 1 week and 6 months.

RESULTS

Only 13 per cent of the total amount of fluoride in fluoridated elastomers was released during the first week in vitro, compared with 90 per cent in vivo. There was a significantly greater amount (P = 0.001) of residual fluoride when the elastomers were in the mouth for 1 week in the presence of fluoride toothpaste and mouthrinse, than when fluoride supplements were excluded.

CONCLUSIONS

(1) Higher levels of fluoride are lost from the fluoride elastomers in vivo than in vitro during the first week. (2) A significantly greater amount of residual fluoride was released from the elastomers placed in the mouth when fluoride toothpaste and mouthrinse were used.

Effect of different desensitizers on inhibition of bovine dentin demineralization: micro-computed tomography assessment

This study evaluated the effect of two desensitizers on inhibition of dentin demineralization, after immersion in artificial saliva using micro-computed tomography (μCT). Dentin blocks cut from bovine incisors were treated with deionized water (DW, a negative control) or one of three desensitizers: a fluoride varnish (Duraphat, a positive control), a calcium phosphate desensitizer (Teethmate Desensitizer), and a fluoro-alumino-calcium silicate-based desensitizer (Nanoseal). After each treatment, the specimens in Duraphat, Nanoseal, and Teethmate Desensitizer groups were pre-immersed in artificial saliva (pH 6.5) for either 1 d or 1 wk. The mineral loss of the specimens after demineralization (pH 5.0, 3 h) was evaluated by μCT. The treated surface was investigated with scanning electron microscopy. Mineral loss in all treatment groups was significantly lower than that in DW. Duraphat was the most effective treatment against demineralization, followed by Nanoseal. Nanoseal showed significantly better reduction in mineral loss following immersion for 1 wk in artificial saliva than for 1 d. However, Teethmate Desensitizer and Duraphat did not exhibit enhanced inhibition of demineralization over a longer period of immersion in artificial saliva. Scanning electron microscopy images showed deposition of particles on the dentin in both Teethmate Desensitizer. The application of Teethmate Desensitizer and Nanoseal to the exposed dentin surface resulted in inhibition of demineralization, with Nanoseal resulting in improved inhibition after prolonged immersion in artificial saliva.

Diet and the microbial aetiology of dental caries: new paradigms

The microbial and dietary factors that drive caries have been studied scientifically for 120 years. Frequent and/or excessive sugar (especially sucrose) consumption has been ascribed a central role in caries causation, while Streptococcus mutans appeared to play the key role in metabolising sucrose to produce lactic acid, which can demineralise enamel. Many authors described caries as a transmissible infectious disease. However, more recent data have shifted these paradigms. Streptococcus mutans does not fulfil Koch's postulates - presence of the organism leading to disease, and absence of the organism precluding disease. Furthermore, molecular microbiological methods have shown that, even with a sugar-rich diet, a much broader spectrum of acidogenic microbes is found in dental plaque. While simple sugars can be cariogenic, cooked starches are also now recognised to be a caries threat, especially because such starches, while not 'sticky in the hand', can be highly retentive in the mouth. Metabolism of starch particles can yield a prolonged acidic challenge, especially at retentive, caries-prone sites. These changes in the paradigms of caries aetiology have important implications for caries control strategies. Preventing the transmission of S. mutans will likely be inadequate to prevent caries if a sufficiently carbohydrate-rich diet continues. Similarly, restriction of sucrose intake, although welcome, would be unlikely to be a panacea for caries, especially if frequent starch intake persisted. Instead, approaches to optimise fluoride delivery, to target plaque acidogenicity or acidogenic microbes, to promote plaque alkali generation, to increase salivary flow or replace fermentable carbohydrates with non-fermentable alternatives may be more promising.

Fluoride content in plaque solids and fluid after ingestion of fluoridated milk

This study explored differences in dental biofilm solids and fluid fluoride after ingestion of NaF or Na2FPO3 in milk or non-fluoridated milk. Eighteen volunteers ingested 1 mg fluoride in 200 mL of milk or 200 mL of non-fluoridated milk. Biofilm samples were collected at baseline, 30, 60, and 240 min and biofilm solids and fluid were micro-analyzed for fluoride. Analysis of variance was performed and the total delivery, retention, and clearance of fluoride to biofilm solids and fluid were estimated as the area under the curve between 0 and 240 min. No statistically significant differences were found for baseline values. Biofilm fluid fluoride values ranged from 0.11 ± 0.05 to 0.21 ± 0.08 µg F/mL while biofilm solid values ranged from 0.62 ± 0.39 to 1.75 ± 1.16 µg F/g. Biofilm fluid values were significantly lower at 60 min for Na2FPO3 in milk. Clearance profiles for biofilm fluid diverged after the initial 60 min. Na2FPO3 had a smaller area under the curve from 60 to 240 min than NaF. Results of this study indicate that the release and clearance of fluoride in biofilm vary among fluoridation compounds and that the concentrations in biofilm solids and fluid also vary and are not correlated to each other in many cases.

Quantitative determination of lattice fluoride effects on the solubility and crystallinity of carbonated apatites with incorporated fluoride

The purpose of this study was to evaluate quantitatively the effects of fluoride on the solubility and crystallinity of carbonated apatites (CAPs) after its incorporation into the crystal lattice using the metastable equilibrium solubility (MES) distribution method. Fluoride-incorporated CAPs (F-CAPs) of two different carbonate levels (3 and 5%) and fluoride contents from 0 to 20,000 µg/g were synthesized. X-ray diffraction experiments and Rietveld analysis were conducted to obtain crystallite microstrain and unit cell parameters. Acetate buffer MES solution media were prepared at two solution fluoride concentrations (0.2 and 2.0 mg/l) and at two pHs (5.0 and 5.7). The unit cell a-axis values of the F-CAPs were found to decrease as the fluoride content increased, consistent with the fluoride being incorporated into the crystal lattice. The fluoride concentrations in the MES solution media were high enough to provide a 'swamping' effect such that the fluoride released from the F-CAPs during dissolution was minimal in changing the solution fluoride concentration. Employing the MES distribution superposition method, it was shown that the surface complex possessing the fluorapatite (FAP) stoichiometry [Ca10(PO4)6F2] accounted for the MES distribution behavior of all experiments. In addition, the mean pIFAP [the value of -log(aCa(10)aPO4(6)aF(2)) calculated from the ionic activity product based on FAP stoichiometry of the MES dissolution media in which 50% of the F-CAPs had dissolved] correlated well with the crystallite microstrain parameters of the F-CAPs. The incorporated fluoride in the F-CAPs showed only modest effects on F-CAP crystallinity and solubility.

The release of zinc, copper, lead, and cadmium from the mineral tissue of teeth under the influence of soft drinks and sour-tasting food

This study was carried out with the aim of identifying the effects of consuming sour-tasting food and refreshing drinks on the bone tissue of teeth among teenagers. The cumulative effect of a year-long exposure of teeth to the erosive effects of a model system of acidic media (citric acid, lactic acid, acetic acid, apple vinegar, lemonade, the soft drink Sprite, mineral water) was studied. The effects were registered based on the amount of released biometal ions, of zinc and copper, and toxic lead, during a period of 24 hr at room temperature, using the potentiometric stripping analysis. In the given time span, amounts ranging from 75 to 750 ppm of zinc, from 0.1 to 1.0 ppm of copper, and up to 1.5 ppm of lead were released from the dental matrix, while the release of cadmium was below the level of detection. The changes to the mineral structure of the bone tissue were monitored by the Fourier's transformation infrared spectroscopy and scanning electron microscopy technique. These studies have shown that under the influence of an acidic medium significant erosion to the tooth enamel ensues and that the eroded surfaces had a radius of 1-5 μm.

Comparison of salivary fluoride concentrations after administration of a bioadhesive slow-release tablet and a conventional fluoride tablet

The in-vitro and in-vivo fluoride release of bioadhesive, slow-release tablets prepared from a mixture of polyethylene glycol polymers, containing 0·1 mg of fluoride as NaF was studied, and their ability to sustain fluoride levels in saliva were compared with conventional fluoride tablets with the same fluoride content. In-vitro release experiments showed that the bioadhesive tablets needed 8 h to release all their fluoride compared with &lt; 1 h for the conventional fluoride tablets. In-vivo, the bioadhesive tablets had a retention period of 6 h and could sustain a salivary fluoride level of more than 10 μm above the baseline for 7 h. The conventional fluoride tablets achieved a peak concentration of 0·5 Mm directly after dissolution in the mouth, but the fluoride level could not be sustained for longer than 1 h. A good agreement was found between the in-vitro swelling behaviour of the bioadhesive tablets and their in-vitro and in-vivo release characteristics and their in-vivo retention time.

The chemistry of caries: remineralization and demineralization events with direct clinical relevance

Dental caries is a site-specific disease that undergoes many cycles of demineralization and remineralization during lesion development. Because of its developmental characteristics dynamics, the caries lesion can be arrested and even repaired at its early stages without operative intervention by increasing the net mineral gain during the demineralization and remineralization cycles. This result can be accomplished by reducing the effect of etiological factors such as cariogenic biofilms and diet, and increasing the efficacy of remineralizing agents such as saliva and fluoride.