Remineralizing effect of a new strontium-doped bioactive glass and fluoride on demineralized enamel and dentine

Impact of amino acid-regulated beta tricalcium phosphate hydroxyapatite on enamel: An updated perspective on hydroxyapatite crystal growth for adhesive bonding?

AIMS AND OBJECTIVES

To analyse development of hydroxyapatite (HAp) crystals doped with glutamic acid and phosphorine residue (Ser-OPO3) having self-remineralization, biocompatible and optimum bonding properties MATERIALS AND METHODS: β-tri calcium phosphate, ammonium phosphate dibasic HAp was dissolved with strontium Flouride Glu or Ser-OPO3 components and utilised in two 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL groups. HAp formulation was evaluated for particle-size analysis, crystal size and indices using FTIR. Demineralized enamel specimens were treated and characterized using transmission electron microscopy (TEM), Xray diffraction (XRD), solid state NMR, and mechanical properties. MC3T3 mouse fibroblastic cells were evaluated for alkaline-phosphate activity (ALP). Human gingival fibroblasts (PGF) were evaluated for morphology. After modifying Universal adhesives, tensile force was assessed at 24 hr and 3 months.

RESULT

Increasing concentrations of experimental solution exposure significantly affect mean diameter of HAp. The increasing FTIR intensity, were displayed; 0.2% TCPCa3(PO4)2 Str/FL > 0.1% TCPCa3(PO4)2 Str/FL> control. 0.2% TCPCa3(PO4)2 Str/FL revealed existence of distinct crystals, with planes orientated perpendicular to longer axis of tooth. XRD pattern indicated crystal growth with a rise in peak intensities in 0.2% TCPCa3(PO4)2 Str/FL group. The NMR spectra for Glu and Ser-OPO3 elucidated interactions between carbon atoms in amino acid and hydrogen atoms on HAp surfaces. Surface microhardness of 0.2% TCPCa3(PO4)2 Str/FL specimens showed significantly higher values on day 28 (p< 0.05). ALP density value of cells was significantly higher for 0.2% TCPCa3(PO4)2 Str/FL group on day 7 and 14. 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL enhanced migration of PGF cells in comparison to the control group (p<0.05). 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL groups showed significant differences in bond strength at different time points CONCLUSION: 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL were structurally integrated into the lattice demonstrating changes within the crystallite size and became conducive for adhesive bonding.

CLINICAL SIGNIFICANCE

The new amino acid-based hydroxyapatite formulation is chemically stable due to the substitution of OH- with F- and is crucial in the rehardening of caries and adhesive bonding.

Evaluation methods of artificial demineralization protocols for coronal dentin: a systematic review of laboratory studies

BACKGROUND

Despite the widespread use of various laboratory models such as chemical, bacterial, or combination as demineralization protocols to induce artificial caries in dentin, there is lack in the literature regarding a comparison of their effectiveness and assessment of dentin mineral density through using several analytical techniques, including microscopic and spectroscopic ones. The purpose of this review was to determine the appropriate demineralization protocols for inducing artificial caries utilizing coronal dentin. Furthermore, this evidence-based study was conducted to identify the most reliable evaluation methods in assessing the efficiency of the reviewed protocols.

MATERIALS AND METHODS

An electronic search was conducted on three databases: MEDLINE/PubMed, Scopus, and ScienceDirect, following PRISMA guidelines. Only the studies published between 2019 and 2024 were considered. All studies were assessed based on predefined eligibility criteria. English laboratory studies that employed chemical models for induction of artificial caries on human mid-coronal dentin were included. The selected studies were individually reviewed for potential bias according to predetermined criteria.

RESULTS

A total of 23 studies met the inclusion and exclusion criteria of this systematic review. From the included studies, 11 studies utilized pH-cycling model, 10 studies reported using simple demineralization model, while only one study reported an undetailed protocol. Moreover, combined 'chemical and biological' protocol for dentin demineralization was reported in two studies. According to the outcome of included studies, dentin mineral density, depth of lesions, crystalline structure, surface morphology, and surface microhardness were evaluated using a variety of laboratory methods offering, either qualitative, quantitative, or semi-quantitative analysis. The conclusions of the studies revealed confirmatory results regarding the use of multiple devices.

CONCLUSIONS

The pH-cycling model was found to be the most common type of chemical model used to induce dentin demineralization for 14 days immersion time, followed by a simple demineralization model through using an acetic acid solution. There was no single evaluation approach found to provide comprehensive information about the mineral content independently. Therefore, a combination of multiple techniques is recommended to yield sufficient and more accurate data.

The Effect of Different pH and Temperature Values on Ca2+, F-, PO43-, OH-, Si, and Sr2+ Release from Different Bioactive Restorative Dental Materials: An In Vitro Study

Bioactive restorative materials are crucial for promoting remineralization and protecting dental tissues through ion release. This study examines how pH and temperature influence the short- and long-term ion (F-, Ca2+, Sr2+, OH-, Si, and PO43-) release from seven commercial materials: Cention Forte Filling Material, Cention Primer, Stela Self Cure, Riva Light Cure HV, Riva Self Cure, Equia Forte HT Fil, and Fuji IX GP Fast. Disks were prepared according to the manufacturers' instructions; immersed in buffer solutions at pH 4.8, 6.8, and 8.8; and stored at 37 °C and 44 °C. Ion release was measured after 1, 7, and 28 days using ion chromatography and mass spectrometry. Results revealed that ion release was significantly affected by pH, temperature, and exposure time. The highest fluoride (40.14 ± 0.32 mg/L) and calcium (74.23 ± 0.37 mg/L) releases were observed in Riva Light Cure at pH 4.8 and 44 °C after 28 days, with the highest strontium release (5.87 ± 0.06 mg/L) occurring under the same conditions. In contrast, silicon release peaked in Cention Forte Filling (31.72 ± 0.68 mg/L) at pH 4.8 and 37 °C. These findings highlight the impact of environmental factors on material performance, assisting clinicians in selecting optimal restorative materials for long-term dental health.

Size-controllable synthesis of hydroxyapatite nanorods via fluorine modulation: applications in dental adhesives for enhanced enamel remineralization

BACKGROUND

There has been little application of fluorine-substituted hydroxyapatites (FHAs) in dental adhesives. Previous studies primarily focused on the effect of fluoride content on enamel remineralization, neglecting the role of FHA particle size. This study aimed to synthesize uniform FHA nanorods of varying sizes by adjusting the fluorine doping levels, and to investigate the synergistic effects of the fluorine content and nanorod size on enamel remineralization by incorporating the FHA nanorods into adhesives.

METHODS

FHA nanorods with varying fluorine doping levels and sizes were synthesized based on a hydrothermal method. The characterization analyses of FHA nanorods were demonstrated by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The composite adhesives containing 10 wt% different FHA nanorods were characterized via scanning electron microscopy (SEM). The colloidal stability, light-curing poperties, and degree of conversion (DC %) were assessed. The shear bond strength (SBS) was determined and the failure mode analysis was reported. The release of Ca2+ and F- within 30 days was detected. The remineralization was evaluated via SEM, energy dispersive X-ray spectroscopy (EDS), XRD, and micro-hardness through in vitro and in vivo experiments. Statistical analyses were performed using the Shapiro-Wilk test, Levene test, one-way ANOVA, Tukey HSD method, Welch test, Tamhane test, Fisher's exact test and Kruskal-Wallis test (α = 0.05).

RESULTS

Uniform FHA nanorods of varying sizes were synthesized by adjusting the fluorine doping level (2 wt%, 6 wt%, and 10 wt%). The lengths of these FHA nanorods were 505.31 ± 104.43 nm, 111.27 ± 22.89 nm, and 66.21 ± 12.68 nm, respectively. The composite adhesives containing FHA nanorods showed good colloidal stability and appropriate light-curing properties. The SBS of composite adhesives decreased due to the incorporation of FHA nanorods, but the values still remained within the clinically required range. Three groups of the composite adhesives could release Ca2+ and F- continuously. The group of 10 wt% F-doped HA nanorods with shorter lengths exhibited more mineral deposition and absorption of Ca²⁺ onto the adhesive and enamel surfaces.

CONCLUSIONS

The strategy of adding the synthesized FHA nanorods into dental adhesives can be an effective approach to promote enamel remineralization, while maintaining adequate bond strength. The 10 wt% F-doped HA nanorods with shorter lengths exhibited superior remineralization.

Enhancing elemental release and antibacterial properties of resin-based dental sealants with calcium phosphate, bioactive glass, and polylysine

BACKGROUND

This study aimed to develop ion-releasing and antibacterial resin-based dental sealants comprising 3 to 6 wt% monocalcium phosphate monohydrate (MCPM, M), 3 to 6 wt% bioactive glass (BAG, B), and 3 to 6 wt% polylysine (PLS, P). The physical properties, mechanical performance, cytotoxicity, and inhibition of S. mutans biofilm by these materials were subsequently evaluated.

METHODS

Five experimental dental sealants were formulated as follows: F1 (M6B6P6), F2 (M6B6P3), F3 (M3B3P6), F4 (M3B3P3), and F5 (M0B0P0, serving as the control). ClinproXT (CP, 3 M, Saint Paul, MN, USA) was used for commercial comparison. The degree of monomer conversion (DC) was determined using attenuated total reflectance-Fourier transform infrared spectroscopy (n = 5). The biaxial flexural strength (n = 6) and Vickers surface microhardness (n = 5) of the materials were evaluated after a 24-hour immersion in water. The element release over 4 weeks was measured using inductively coupled plasma-optical emission spectrometry (ICP-OES) (n = 3). The cell viability of mouse fibrosarcoma cells exposed to the extract was assessed via an MTT assay (n = 3). Additionally, the inhibition of S. mutans biofilm was tested (n = 3). Statistical analysis was conducted using one-way ANOVA and the Tukey HSD test.

RESULTS

The lowest DC among experimental sealants was obtained from F1 (66 ± 4%), which was significantly higher than CP (54 ± 2%, p < 0.001). The lowest biaxial flexural strength was obtained from F3 (131 ± 47 MPa). This was comparable to that of CP (140 ± 58 MPa, p = 0.992). The lowest surface microhardness among experimental materials was detected with F2 (19 ± 2 Vickers hardness number), which was higher than that of CP (12 ± 1 Vickers hardness number, p = 0.003). Furthermore, high cell viability of > 90% after exposure to extracts from the experimental materials was detected, which was similar to that observed with CP. Additionally, the experimental materials exhibited higher Ca and P release compared to CP and showed a potential trend for reducing S. mutans biofilm formation. Increasing additive concentrations exhibited minimal effects on material properties, except for enhanced elemental release and a slight reduction in BFM with higher PLS content.

CONCLUSION

The experimental sealants provided sufficient physical and mechanical strength and maintained cell viability and bacterial inhibition with higher elemental release than the commercial product.

Effect of diabetes and hyperglycaemia on the physical and mechanical properties of dentine: a systematic review

OBJECTIVES

The aim of this systematic review was to assess the effect of DM (Type 1 and Type 2 Diabetes) and hyperglycaemia on the physical and mechanical properties of dentine which is critical for successful endodontic treatment.

METHOD

An electronic search of the following databases: PubMed, MEDLINE, Web of Science and the grey literature was performed up until July 2024. In vitro and in vivo studies on the effect of DM or hyperglycaemia on the mechanical and physical properties of dentine were included. Non-English language literature was excluded.

RESULTS

Of the 234 articles identified, 15 met the inclusion criteria. Four studies evaluated how artificially induced glycation or natural glycation of dentine due to aging affects the mechanical properties of dentine. Five studies investigated the influence of Type 2 Diabetes (T2D) on dentine's mechanical properties, while two studies focused on the effects of Type 1 Diabetes (T1D). A further, four studies compared the effects of both T1D and T2D on the dentine. The studies were heterogeneous and a range of mechanical and physical properties were evaluated.

CONCLUSION

DM and AGEs negatively influence the physical and mechanical properties of dentine however, there remains a paucity of evidence and further studies are needed.

CLINICAL SIGNIFICANCE

Diabetes Mellitus (DM) is a chronic metabolic disease characterised by hyperglycaemia, an altered immune response and complications associated with collagen connective tissues. DM can influence bone metabolism and alter its physical and mechanical properties via glycation processes within collagen and changes to osteoblast activities. While bone and dentine share similarities, dentine is unique as it is intimately associated with the dental pulp. Inflammation within the pulp can induce calcification and tertiary dentine deposition and so exploring the influence of DM on the mechanical properties of dentine is warranted to understand the clinical significance.

Applications of smart materials in minimally invasive dentistry - some research and clinical perspectives

OBJECTIVES

Dental caries is one of the most prevalent bacteria-induced non-communicable diseases globally. It is known to be the top oral health burden in both developing and developed nations. There is substantial literature on the disease process and there is still debate on the extent of caries removal needed and the adequacy of the materials available to restore the lost tooth structure. The current review discusses the disease process together with the contemporary management of the carious lesion and also presents substantial evidence on novel materials and techniques that make minimally invasive dentistry predictable.

METHODS

The written work presented shows the most relevant literature for the management of dental caries focusing on novel materials used in minimally invasive dentistry.

RESULTS

There is still much to learn about specific antimicrobial and caries prevention mechanisms of novel materials. Materials that respond to a single or a few stimuli remain "weakly intelligent" in the face of the complex microenvironment in the oral cavity. Engineered systems that combine artificial intelligence and chemical engineering, are expected to possess higher intelligence, self-healing capabilities as well as environmental adaptability, and may be future promising research directions.

SIGNIFICANCE

The targeted approach in managing dental caries will hopefully have a better clinical outcome. The strategies discussed are alternatives to the contemporary approach and will improve the clinical management.

Comparative analysis of remineralizing efficacy of strontium-doped bioactive glass, BioMin, and NovaMin containing dentifrice on artificial white spot lesions after chlorhexidine pretreatment - An in vitro study

Aim

This study aimed to compare the remineralizing efficacy of strontium-doped bioactive glass, BioMin, and NovaMin containing dentifrices on artificial white spot lesions (WSLs) after chlorhexidine (CHX) pretreatment using energy-dispersive X-ray analysis (EDAX).

Materials and Methodology

Twenty-four samples of maxillary first premolars extracted for orthodontic purposes were selected. Artificial WSLs were produced by immersing the samples in a prepared demineralizing solution for 3 days. All the samples were pretreated with CHX and divided into four groups and six samples each. Group A treated with strontium-doped bioactive glass, Group B with BioMin, Group C with NovaMin, and Group D with artificial saliva as the control group for 14 days. pH-cycling model was used to simulate the oral cavity changes. EDAX was used to record the values at baseline, demineralization, and after remineralization.

Statistical Analysis

Data were analyzed using one-way ANOVA (post hoc), followed by unpaired t-test and Scheffe tests with Statistical Package for the Social Sciences version 16.

Results

Strontium-doped bioactive glass exhibited a greater mineral regain compared to BioMin, NovaMin, and control groups.

Conclusion

Strontium-doped bioactive glass has enhanced mineral deposition on carious teeth and may provide an alternative clinical strategy for remineralizing early enamel lesions.

Advancing dentin remineralization: Exploring amorphous calcium phosphate and its stabilizers in biomimetic approaches

OBJECTIVE

This review elucidates the mechanisms underpinning intrafibrillar mineralization, examines various amorphous calcium phosphate (ACP) stabilizers employed in dentin's intrafibrillar mineralization, and addresses the challenges encountered in clinical applications of ACP-based bioactive materials.

METHODS

The literature search for this review was conducted using three electronic databases: PubMed, Web of Science, and Google Scholar, with specific keywords. Articles were selected based on inclusion and exclusion criteria, allowing for a detailed examination and summary of current research on dentin remineralization facilitated by ACP under the influence of various types of stabilizers.

RESULTS

This review underscores the latest advancements in the role of ACP in promoting dentin remineralization, particularly intrafibrillar mineralization, under the regulation of various stabilizers. These stabilizers predominantly comprise non-collagenous proteins, their analogs, and polymers. Despite the diversity of stabilizers, the mechanisms they employ to enhance intrafibrillar remineralization are found to be interrelated, indicating multiple driving forces behind this process. However, challenges remain in effectively designing clinically viable products using stabilized ACP and maximizing intrafibrillar mineralization with limited materials in practical applications.

SIGNIFICANCE

The role of ACP in remineralization has gained significant attention in dental research, with substantial progress made in the study of dentin biomimetic mineralization. Given ACP's instability without additives, the presence of ACP stabilizers is crucial for achieving in vitro intrafibrillar mineralization. However, there is a lack of comprehensive and exhaustive reviews on ACP bioactive materials under the regulation of stabilizers. A detailed summary of these stabilizers is also instrumental in better understanding the complex process of intrafibrillar mineralization. Compared to traditional remineralization methods, bioactive materials capable of regulating ACP stability and controlling release demonstrate immense potential in enhancing clinical treatment standards.

Applications of Bioactive Strontium Compounds in Dentistry

Divalent cations have captured the interest of researchers in biomedical and dental fields due to their beneficial effects on bone formation. These metallic elements are similar to trace elements found in human bone. Strontium is a divalent cation commonly found in various biomaterials. Since strontium has a radius similar to calcium, it has been used to replace calcium in many calcium-containing biomaterials. Strontium has the ability to inhibit bone resorption and increase bone deposition, making it useful in the treatment of osteoporosis. Strontium has also been used as a radiopacifier in dentistry and has been incorporated into a variety of dental materials to improve their radiopacity. Furthermore, strontium has been shown to improve the antimicrobial and mechanical properties of dental materials, promote enamel remineralization, alleviate dentin hypersensitivity, and enhance dentin regeneration. The objective of this review is to provide a comprehensive review of the applications of strontium in dentistry.

Effect of strontium fluoride on mechanical and remineralization properties of enamel: An in-vitro study on a modified orthodontic adhesive

OBJECTIVES

Evaluate the ability of strontium fluoride on bond strength and enamel integrity after incorporation within orthodontic adhesive system as a delivery vehicle.

METHODS

Experimental orthodontic adhesive system Transbond™ XT were modified with 1% Sr2+, 0.5% SrF2, 1% strontium, 0.5% Sr2+, 1% F-, 0.5% F-, and no additions were control. Mixing of formulation was monitored using Fourier transform infrared spectroscopy. Small-molecule drug-discovery suite was used to gain insights into Sr2+, F-, and SrF2 binding. Shear bond testing was performed after 6-months of ageing. Enamel blocks were cut, and STEM pictures were recorded. Specimens were indented to evaluate elastic modulus. Raman microscope was used to collect Raman spectra and inspected using a scanning electron microscope. Crystal structural analysis was performed using X-ray diffraction. Effect of material on cellular proliferation was determined. Confocal was performed to evaluate the effect of formulation on biofilms.

RESULTS

FTIR of modified adhesives depicted peak changes within range due to various functional groups existing within samples. TEM represented structurally optimized hexagonal unit-cell of hydroxyapatite. Mean shear bond strength is recorded highest for Transbond XT with 1% SrF2. Dead bacterial percentage appeared higher in 0.5% SrF2 and 1% F- specimens. Crystal lengths showed an increase in 0.5% and 1% SrF2 specimens. Phase contrast within TEM images showed a union of 0.5% SrF2 crystal with enamel crystal with higher elastic modulus and highly mineralized crystalline hydroxyapatite. Intensity of ν1 PO43- and ν1 CO32- along with carbonate - / ν1PO43- ratio displayed good association with strontium fluoride. The formulation showed acceptable cell biocompatibility (p < 0.353). All specimens displayed characteristic diffraction maxima of different apatite angles within XRD.

SIGNIFICANCE

Experimental results suggested good biocompatibility, adequate mechanical strength, and far-ranging crystallization ability. This would provide a new strategy to overcome the two major challenges of fixed orthodontics, biofilm growth, and demineralization of enamel.

Mechanical properties of simulated dentin caries treated with metal cations and L-ascorbic acid 2-phosphate

This pH cycling study aimed to investigate the effects of L-Ascorbic acid 2-phosphate (AA2P) salts of Mg, Zn, Mn, Sr, and Ba on the surface microhardness, compressive strength, diametral tensile strength (DTS), and solubility of root canal dentin. 186 cylindrical dentin specimens from 93 teeth were fortified with optimal concentrations of AA2P salts of Mg (0.18 mM), Zn (5.3 µM), Mn (2.2 × 10-8 M), Sr (1.8 µM), and Ba (1.9 µM). Saline was used as the control group. These dentin specimens underwent a 3-day cycling process simulating dentin caries formation through repeated sequences of demineralization and remineralization. Surface microhardness at 100 and 500 µm depths (n = 10/subgroup), scanning electron microscopy (n = 3/group), compressive strength (n = 10/group), DTS (n = 6/group), and solubility (n = 5/group) tests were performed to analyze the dentin specimens. Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA, and Post Hoc Tukey tests (p < 0.05). The control group had significantly lower microhardness at both depths (p < 0.001), reduced DTS (p = 0.001), decreased compressive strength (p < 0.001), and higher weight loss (p < 0.001) than all other groups. The Sr group had the highest compressive strength and microhardness among all the groups. The microhardness was significantly higher for the 500 µm depth than the 100 µm depth (p < 0.001), but the difference in microhardness between depths across groups was not significant (p = 0.211). All fortifying solutions provided some protection against artificial caries lesions. Therefore, these elements might have penetrated and reinforced the demineralized dentin against acid dissolution.

Enhanced remineralisation ability and antibacterial properties of sol-gel glass ionomer cement modified by fluoride containing strontium-based bioactive glass or strontium-containing fluorapatite

OBJECTIVES

This study aimed to compare two types of bioactive additives which were strontium-containing fluorinated bioactive glass (SrBGF) or strontium-containing fluorapatite (SrFA) added to sol-gel derived glass ionomer cement (SGIC). The objective was to develop antibacterial and mineralisation properties, using bioactive additives, to minimize the occurrence of caries lesions in caries disease.

METHODS

Synthesized SrBGF and SrFA nanoparticles were added to SGIC at 1 wt% concentration to improve antibacterial properties against S. mutans, promote remineralisation, and hASCs and hDPSCs viability. Surface roughness and ion-releasing behavior were also evaluated to clarify the effect on the materials. Antibacterial activity was measured via agar disc diffusion and bacterial adhesion. Remineralisation ability was assessed by applying the material to demineralised teeth and subjecting them to a 14-day pH cycle, followed by microCT and SEM-EDS analysis.

RESULTS

The addition of SrFA into SGIC significantly improved its antibacterial property. SGIC modified with either SrBGF or SrFA additives could similarly induce apatite crystal precipitation onto demineralised dentin and increase dentin density, indicating its ability to remineralise dentin. Moreover, this study also showed that SGIC modified with SrBGF or SrFA additives had promising results on the in vitro cytotoxicity of hASC and hDPSC.

SIGNIFICANT

SrFA has superior antibacterial property as compared to SrBGF while demonstrating equal remineralisation ability. Furthermore, the modified SGIC showed promising results in reducing the cytotoxicity of hASCs and hDPSCs, indicating its potential for managing caries.

An in vitro assessment of biaxial flexural strength, degree of monomer conversion, color stability, and ion release in provisional restorations containing Sr-bioactive glass nanoparticles

This study examined the mechanical and chemical properties of an experimental provisional restoration containing Sr-bioactive glass nanoparticles (Sr-BGNPs) compared to commercial provisional materials. The experimental material (TempS10) contained dimethacrylate monomers with added 10 wt% Sr-BGNPs. The degree of monomer conversion (DC) of self-curing (n = 5), biaxial flexural strength (BFS)/modulus (BFM) (n = 5), and color changes (ΔE*00) of materials in red wine (n = 5) were determined. Additionally, ion release (Ca, P, and Sr) in water at 2 weeks was examined (n = 3). The commercial materials tested included polymethyl methacrylate-based provisional material (Unifast) and bis-acrylic materials (Protemp4 and Cooltemp). TempS10 exhibited a comparable degree of monomer conversion (49%) to that of Protemp4 (60%) and Cooltemp (54%) (p > 0.05). The DC of Unifast (81%) was significantly higher than that of other materials (p < 0.05). TempS10 showed a BFS (126 MPa) similar to Cooltemp (102 MPa) and Unifast (123 MPa), but lower than Protemp4 (194 MPa). The immersion time for 2 weeks exhibited no detrimental effect on the strength and modulus of all materials. The highest ΔE*00 at 24 h and 2 weeks was observed with TempS10, followed by Cooltemp, Unifast, and Protemp4. Only TempS10 showed a detectable amount of Ca (0.69 ppm), P (0.12 ppm), and Sr (3.01 ppm). The experimental provisional resin restoration containing Sr-BGNPs demonstrated polymerization and strength comparable to those of bis-acryl provisional restorations but with the added benefit of ion-releasing properties. However, the experimental material demonstrated unsatisfactory color stability.

Remineralization Potential of Three Restorative Glass Ionomer Cements: An In Vitro Study

The aim of this in vitro study was to evaluate the remineralizing ability of three glass ionomers on demineralized dentin with different thicknesses and time periods. Fifty third molars were obtained and were sectioned into 1-, 2-, and 3-mm thick slices (n = 36 for each thickness). The specimens were demineralized with 18% EDTA for 2 h. From the glass ionomer cements (GICs) under study (Ketac Molar Aplicap, Equia Forte, or Riva Light Cure), 1 mm was placed over each slice, set, and preserved in PBS until observation after 1, 7, 14, and 28 days after placement. For each material, thickness, and time, three samples were prepared. Using Fourier Transform Infrared Spectrometry (FTIR), apatite formation was determined on the side opposite to that on which the material had been placed. By means of Energy Dispersive Spectroscopy (EDX), the changes in the Calcium/Phosphate (Ca/P) ratio were evaluated. These changes were compared between the different materials by means of a two-way ANOVA test, considering time and dentin thickness, for a significance level of p < 0.05. Results: FTIR showed a peak at 1420 cm^-1, evidencing the presence of carbonated hydroxyapatite in all the materials after 14 days, which indicates that a remineralization process occurred. Riva Light Cure showed the most homogeneous results at all depths at 28 days. The Ca/P ratio was maximum at 7 days in 2 mm of dentin for Riva Light Cure and Equia Forte HT (3.16 and 3.07; respectively) and for Ketac Molar at 14 days in 1 mm (3.67). All materials induced remineralization. Equia Forte achieved the greatest effect at 2 mm and Ketac Molar at 1 mm, whereas Riva Light Cure showed similar results at all depths. In terms of Ca/P ratio, Equia Forte and Riva Light Cure remineralized best at 2 mm, whereas for Ketac Molar, it was 1 mm. Carbonate apatite formation was higher at 24 h and 7 days for Ketac Molar, whereas it decreased at 14 days for Ketac Molar and peaked in Riva Light Cure and Equia Forte.

Potential Beneficial Effects of Hydroxyapatite Nanoparticles on Caries Lesions In Vitro-A Review of the Literature

Dental caries is one of the most common human diseases which can occur in both primary and permanent dentitions throughout the life of an individual. Hydroxyapatite is the major inorganic component of human teeth, consequently, nanosized hydroxyapatite (nHAP) has recently attracted researchers' attention due to its unique properties and potential for caries management. This article provides a contemporary review of the potential beneficial effects of nHAP on caries lesions demonstrated in in vitro studies. Data showed that nHAP has potential to promote mineralization in initial caries, by being incorporated into the porous tooth structure, which resulted from the caries process, and subsequently increased mineral content and hardness. Notably, it is the particle size of nHAP which plays an important role in the mineralization process. Antimicrobial effects of nHAP can also be achieved by metal substitution in nHAP. Dual action property (mineralizing and antimicrobial) and enhanced chemical stability and bioactivity of nHAP can potentially be obtained using metal-substituted fluorhydroxyapatite nanoparticles. This provides a promising synergistic strategy which should be explored in further clinical research to enable the development of dental therapeutics for use in the treatment and management of caries.

The effect of minimally invasive treatments on enamel microhardness and resistance to further demineralization

Objectives: The present study aimed to compare microhardness of inactive proximal lesions treated by resin infiltration, Er:YAG laser + resin infiltration and Bioactive glass, and investigate the resistance of treated lesions to further demineralization challenge. Methods: In this in-vitro study, 30 human molars with inactive proximal lesions were selected and randomly divided into three groups of 10. In group 1 (resin infiltration), the lesions were treated by a resin infiltrant (Icon). In group 2, the surface was conditioned by an Er:YAG laser prior to resin infiltration. The specimens in group 3 were remineralized by bioactive glass. The treated specimens were kept in artificial saliva for 1 week and then immersed in a demineralization solution for 8 weeks. Surface microhardness was measured at baseline (T0), after remineralization (T1) and after exposure to the demineralization solution (T2), and the difference in microhardness between time points (ΔVHN) was calculated. Results: Microhardness after demineralization (T2) was significantly lower than those of other intervals (P0.05). The statistical analysis revealed no significant difference either in ΔVHNT1-T0 or in ΔVHNT2-T1 among the study groups (P>0.05) Conclusion: Pretreatment by the Er:YAG laser prior to resin infiltration was more effective that other treatments in enhancing microhardness and protecting the tooth against acidic challenge. However, the difference between groups did not reach a statistical significance, implying the need for further studies to achieve more conclusive results.

Effect of strontium-doped bioactive glass-ceramic containing toothpaste on prevention of artificial dentine caries formation: an in vitro study

Backgroud

Root caries in aging population was prevalent worldwide. Due to the absence of enamel and specific structure of dentine, bacteria are able to penetrate further into dentine at an earlier stage of lesion development. The aim of this study was to investigate the effect of adding of a strontium-doped bioactive glass-ceramic (HX-BGC) to a fluoride-free toothpaste on prevention of formation of artificial dentine caries.

Methods

Thirty-six human tooth specimens were allocated to three groups (n = 12 per group). Group 1 treated with slurry containing a fluoride-free toothpaste and 5% HX-BGC, Group 2 was treated with fluoride-free toothpaste slurry, and Group 3 received deionized water as a negative control. The specimens were subjected to four cycles (15 h demineralization and 8 h remineralization for one cycle) of biochemical cycling. A mixed suspension of five bacteria species (Streptococcus mutans, Streptococcus sobrinus, Lactobacillus acidophilus, Lactobacillus rhamnosus, and Actinomyces naeslundii) were prepared in brain heart infusion broth with 5% sucrose and used as acidic challenge in biochemical cycling. Subsequently, surface morphology of the dentine lesion was assessed by scanning electron microscopy, while the lesion depths and mineral loss were assessed by micro-computed tomography.

Results

The mean lesion depths in dentine in Groups 1 to 3 were 87.79 ± 16.99 μm, 101.06 ± 10.04 μm and 113.60 ± 16.36 μm, respectively (p = 0.002). The mean amounts of mineral loss in Groups 1 to 3 were 0.82 ± 0.10 g/cm³, 0.89 ± 0.09 g/cm³ and 0.96 ± 0.11 g/cm³, respectively (p = 0.016). No obvious differences in the surface morphology were seen among the groups.

Conclusion

Addition of strontium-doped bioactive glass-ceramic to fluoride-free toothpaste has potential to reduce formation of dentine lesions.

Hydrochemical Characteristics and Formation Mechanism of Strontium-Rich Groundwater in Tianjiazhai, Fugu, China

Strontium-rich groundwater exists in the underlying carbonate rocks of the Tianjiazhai Shimachuan River basin, Fugu, China. In this study, the hydrochemical characteristics and formation mechanisms of Sr-rich groundwater were assessed using mathematical statistics and traditional water chemistry, combining geological and hydrogeological conditions, as well as hydrogeochemical theory. The results showed that the Sr2+ content range in Sr-rich groundwater was 0.85~2.99 mg·L−1, which is weakly alkaline fresh water. HCO3− Ca·Mg·Na was the main facies type of Sr-rich groundwater. Sr-rich groundwater has relatively stable contents of chemical elements. The water–rock interaction was the main factor controlling the hydrochemical characteristics of Sr-rich groundwater, particularly carbonate dissolution, influenced by some degree of cation exchange. The Sr element in groundwater mainly comes from the dissolution of the sandstone of the Yanchang Formation. The higher the degree of weathering and the longer the water–rock reaction time, the more favorable the dissolution and enrichment of Sr in groundwater. Moreover, the large weathering thickness and fracture development of the rocks in the Tianjiazhai area provide favorable conditions for the formation of Sr-rich groundwater. The results of this study provide a scientific basis for developing effective policies to protect Sr-rich groundwater resources.

Functional role of inorganic trace elements in dentin apatite tissue-Part 1: Mg, Sr, Zn, and Fe

Many essential elements exist in nature with significant influence on dentin and bone apatite tissue. Hydroxyapatite (HAp) is the major inorganic crystalline structure of dentin that provides a site for various physiological functions such as surface layer ion exchange. Decades of apatite research have shown that enamel is a high-substituted crystalline apatite, but recent findings suggest that dentin apatite may play a more important role in regulating ion exchange as well as mineral crystallinity. This article is the first part of a review series on the functional role of inorganic trace elements including magnesium, strontium, zinc, and iron in dentin hydroxyapatite. The morphology, physiology, crystallinity, and solubility of these elements as they get substituted into the HAp lattice are extensively discussed. An electronic search was performed on the role of these elements in dentin apatite from January 2007 to September 2021. The relationship between different elements and their role in the mineral upkeep of dentin apatite was evaluated. Several studies recognized the role of these elements in dentinal apatite composition and its subsequent effects on morphology, crystallinity, and solubility. These elements are of great importance in physiological processes and an essential part of living organisms. Magnesium and strontium stimulate osteoblast activity, while zinc can improve overall bone quality with its antibacterial properties. Iron nanoparticles are also vital in promoting bone tissue growth as they donate or accept electrons in redox reactions. Thus, understanding how these elements impact dentin apatite structure is of great clinical significance.

Nanosized calcium deficient hydroxyapatites for tooth enamel protection

Calcium phosphates (CaP) are extensively studied as additives to dental care products for tooth enamel protection against caries. However, it is not clear yet whether substituted CaP could provide better enamel protection. In this study we produced, characterized and tested in vitro substituted and co‐substituted calcium deficient hydroxyapatite (CDHAp) with Sr²⁺ and F⁻ ions. X‐ray powder diffractometry, Fourier transformation infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray analysis, Brunauer–Emmett–Teller were used to characterize synthesized powders and also cytotoxicity was evaluated. pH = f(t) test was performed to estimate, weather synthesized CDHAp suspensions are able to increase pH of experimental media after acid addition. Synthesis products were incorporated into paste to perform in vitro remineralization on the bovine enamel. In addition to mentioned instrumental methods, profilometry was used for evaluation of remineralised enamel samples. The obtained results confirmed formation of CDHAp substituted with 1.5–1.6 wt% of fluoride and 7.4–7.8 wt% of strontium. pH = f(t) experiment pointed out that pH increased by approximately 0.3 within 10 min after acid addition for all CDHAp suspensions. A new layer of the corresponding CDHAp was formed on the enamel. Its thickness increased by 0.8 ± 0.1 μm per day and reached up to 5.8 μm after 7 days. Additionally, octa calcium phosphates were detected on the surface of control samples. In conclusion, we can assume that CDHAp substituted with Sr²⁺ and/or F⁻ could be used as an effective additive to dental care products promoting formation of protecting layer on the enamel, but there was no significant difference among sample groups.

Effect of Strontium-Doped Bioactive Glass on Preventing Formation of Demineralized Lesion

This study investigated the effect of strontium-doped bioactive glass (SBAG) on the formation of dental demineralized lesions. Materials and methods: The study materials were 48 sound human tooth specimens with both dentine and enamel, divided equally into four groups: Group 1 (SBAG), Group 2 (SBAG+Fluoride), Group 3 (Fluoride), and Group 4 (Water as control). After 14 days of pH cycling, the surface morphology of the specimens was observed by scanning electron microscopy. Crystal characteristics of the precipitates were assessed by X-ray diffraction (XRD). Micro-CT was used to measure the mineral loss and the depths of the demineralized lesions formed. Results: Exposure of collagen in inter-tubular areas in dentine was seen in the control group (Group 4) but not in Groups 1 to 3. In Group 2, there were obvious granular particles on the surface of the dentine. XRD revealed precipitation of apatites on the surface of the tooth specimens in Groups 1 to 3. The mean lesion depths in dentine were 81.80 μm, 30.68 μm, 39.04 μm, and 146.36 μm in Groups 1 to 4, respectively (p < 0.001). Lesions in enamel were only found in the control group. The mean mineral loss values in the dentine lesions were 1.25 g/cm³, 0.88 g/cm³, 0.87 g/cm³, and 1.65 g/cm³, in Groups 1 to 4, respectively (p < 0.001). Conclusion: Strontium-doped bioactive glass has a preventive effect on the formation of demineralized lesions in enamel and dentine.