Antibacterial effect of a new bioactive glass on cariogenic bacteria

Injectable Hydrogels: A Paradigm Tailored with Design, Characterization, and Multifaceted Approaches

Biomaterials denoting self-healing and versatile structural integrity are highly curious in the biomedicine segment. The injectable and/or printable 3D printing technology is explored in a few decades back, which can alter their dimensions temporarily under shear stress, showing potential healing/recovery tendency with patient-specific intervention toward the development of personalized medicine. Thus, self-healing injectable hydrogels (IHs) are stunning toward developing a paradigm for tissue regeneration. This review comprises the designing of IHs, rheological characterization and stability, several benchmark consequences for self-healing IHs, their translation into tissue regeneration of specific types, applications of IHs in biomedical such as anticancer and immunomodulation, wound healing and tissue/bone regeneration, antimicrobial potentials, drugs, gene and vaccine delivery, ocular delivery, 3D printing, cosmeceuticals, and photothermal therapy as well as in other allied avenues like agriculture, aerospace, electronic/electrical industries, coating approaches, patents associated with therapeutic/nontherapeutic avenues, and numerous futuristic challenges and solutions.

Efficiency of cavitary varnishes containing experimental bioglass particles in the occlusion of dentinal tubules

This research aims to evaluate the efficiency of cavitary varnishes containing experimental bioglasses in the occlusion of dentinal tubules. One hundred and sixty-eight cervical buccal dentin samples were obtained from bovine teeth. Samples were randomized into the following groups: I. Distilled Water (DW); II. Cavity Varnish (CV); III. Colgate® Sensitive Pro-Relief™ (CS); IV. 45S5 Bioglass (45S5); V. KSr Bioglass strontium potassium (KSr); VI. P Bioglass phosphorus (P); and VII. PSi Bioglass phosphorus silica (PSi). The treatments were applied to the surfaces of the samples, which were then subjected to simulated brushing. The samples were analyzed for a) characterization of bioactive glasses; b) surface roughness; c) descriptive analysis of the dentin surface; d) total versus occluded number of dentinal tubules; e) diameter of the dentinal tubules; f) chemical composition of the dentin surfaces, and g) dentin permeability. All groups treated with biomaterials without the brushing challenge showed an increase in roughness and (total or partial) occlusion of the dentinal tubules. The PSi group had the best values for occlusion, while the KSr group had the highest calcium and phosphorus concentrations. After the brushing challenge the roughness was controlled by the presence of biomaterials; 45S5, KSr, and PSi showed occlusion of the dentin tubules. All bioactive glasses showed reduced tooth permeability compared to distilled water. The PSi group had the smallest tubule diameter and highest phosphorus concentration. KSr and PSi bioglasses are promising materials for dentin occlusion and remineralization and are promising new biomaterials for the treatment of dentin hypersensitivity.

Efficacy of BioMin F and NovaMin toothpastes against streptococcus mutans: an in vitro study

OBJECTIVE

This in vitro study was accomplished to demonstrate the antibacterial efficacy of BioMin F and NovaMin toothpastes against the recently-isolated Streptococcus Mutans in comparison with a commonly used fluoride toothpaste.

MATERIALS AND METHODS

Dental plaque collection method was adopted to isolate streptococcus mutans in children with dental caries. Then an ideal Streptococcus Mutans colony was incubated in 20 Petri dishes that contained Mueller-Hinton medium. Each dish had 3 wells; one well for each toothpaste (BioMin F, NovMin, and Signal) to perform the agar diffusion test. After incubating for 24 hours, the inhabitation zone around each well of each Petri dish was noticed and measured. Statistical Analysis was achieved using a statistical package, SPSS Windows version 17, by applying Kruskal-Wallis with Mann-Whitney U test (α = 0.05).

RESULTS

BioMin F showed the highest mean of inhibition zone diameter (x ¯  = 2.67 mm) in compared with NovaMin and Signal (x ¯  = 0.39 mm andx ¯  = 2.19 mm; p < 0.001 in each pairwise comparison).

CONCLUSION

BioMin F toothpaste showed superior antibacterial effect against Streptococcus mutans to Signal and NovaMin toothpastes. Novamin showed the lowest antibacterial effect. This in vitro study suggests that BioMin F toothpaste shows encouraging potential to be recommended as a preventive measure to reduce the caries risk.

Enamel remineralization potential and antimicrobial effect of a fluoride varnish containing calcium strontium silicate

OBJECTIVES

To investigate enamel remineralization and antimicrobial effect of sodium fluoride (NaF) varnish containing calcium strontium silicate (CSR).

METHODS

CSR was synthesized by sol-gel process and incorporated in 5 % NaF varnish at three different concentrations (1 %, 2 %, and 4 % w/v). The treatment/control groups were: 1 % CSR+NaF, 2 % CSR+NaF, 4 % CSR+NaF, NaF, and no treatment. Strontium and fluoride release from the varnishes was evaluated. Sound enamel specimens (n = 6) were demineralized, varnish-treated, and subjected to remineralization cycle. Mineral density of enamel specimens was evaluated using micro-CT. Antimicrobial effect of the varnishes on Streptococcus mutans and Lactobacillus acidophilus biofilms was assessed using confocal laser scanning microscopy. The HGF-1 cytotoxicity of the varnishes was examined using CCK-8 assay.

RESULTS

Both 2 % and 4 % CSR+NaF varnishes showed significantly higher F release and remineralization potential than NaF varnish (p < 0.05). Dead bacterial proportion of 4 % CSR+NaF varnish was significantly higher than NaF varnish (p < 0.05). The CFUs values of both S. mutans and L. acidophilus were significantly lower in 4 % CSR+NaF group than NaF group (p < 0.05). No significant difference in cell viability was observed among the groups (p > 0.05).

CONCLUSIONS

Incorporation of 4 % CSR in a NaF varnish significantly enhanced its enamel remineralization and antimicrobial potential with no cytotoxic effect.

CLINICAL SIGNIFICANCE

Dental caries is a major public health problem globally. The study highlights the great potential of CSR-doped NaF varnish as a novel anti-caries agent with synergistic remineralizing and antimicrobial properties to combat early enamel caries lesions in the general population.

Antibacterial Properties of the Antimicrobial Peptide Gallic Acid-Polyphemusin I (GAPI)

A novel antimicrobial peptide, GAPI, has been developed recently by grafting gallic acid (GA) to polyphemusin I (PI). The objective of this study was to investigate the antibacterial effects of GAPI on common oral pathogens. This laboratory study used minimum inhibitory concentrations and minimum bactericidal concentrations to assess the antimicrobial properties of GAPI against common oral pathogens. Transmission electron microscopy was used to examine the bacterial morphology both before and after GAPI treatment. The results showed that the minimum inhibitory concentration ranged from 20 μM (Lactobacillus rhamnosus) to 320 μM (Porphyromonas gingivalis), whereas the minimum bactericidal concentration ranged from 80 μM (Lactobacillus acidophilus) to 640 μM (Actinomyces naeslundii, Enterococcus faecalis, and Porphyromonas gingivalis). Transmission electron microscopy showed abnormal curvature of cell membranes, irregular cell shapes, leakage of cytoplasmic content, and disruption of cytoplasmic membranes and cell walls. In conclusion, the GAPI antimicrobial peptide is antibacterial to common oral pathogens, with the potential to be used to manage oral infections.

Cobalt-Doped Bioactive Glasses for Biomedical Applications: A Review

Improving angiogenesis is the key to the success of most regenerative medicine approaches. However, how and to which extent this may be performed is still a challenge. In this regard, cobalt (Co)-doped bioactive glasses show promise being able to combine the traditional bioactivity of these materials (especially bone-bonding and osteo-stimulatory properties) with the pro-angiogenic effect associated with the release of cobalt. Although the use and local delivery of Co²⁺ ions into the body have raised some concerns about the possible toxic effects on living cells and tissues, important biological improvements have been highlighted both in vitro and in vivo. This review aims at providing a comprehensive overview of Co-releasing glasses, which find biomedical applications as various products, including micro- and nanoparticles, composites in combination with biocompatible polymers, fibers and porous scaffolds. Therapeutic applications in the field of bone repair, wound healing and cancer treatment are discussed in the light of existing experimental evidence along with the open issues ahead.

Unraveling the mechanisms of inhibition of silver-doped bioactive glass-ceramic particles

Infections are a major concern in orthopedics. Antibacterial agents such as silver ions are of great interest as broad-spectrum biocides and have been incorporated into bioactive glass-ceramic particles to control the release of ions within a therapeutic concentration and provide tissue regenerative properties. In this work, the antibacterial capabilities of silver-doped bioactive glass (Ag-BG) microparticles were explored to reveal the unedited mechanisms of inhibition against methicillin-resistant Staphylococcus aureus (MRSA). The antibacterial properties were not limited to the delivery of silver ions but rather a combination of antibacterial degradation by-products. For example, nano-sized debris punctured holes in bacteria membranes, osmotic effects, and reactive oxygen species causing oxidative stress and almost 40% of the inhibition. Upon successive Ag-BG treatments, MRSA underwent phenotypic and genomic mutations which were not only insufficient to develop resistance but instead, the clones became more sensitive as the treatment was re-delivered. Additionally, the unprecedented restorative functionality of Ag-BG allowed the effective use of antibiotics that MRSA resists. The synergy mechanism was mainly identified for combinations targeting cell-wall activity and their action was proven in biofilm-like and virulent conditions. Unraveling these mechanisms may offer new insights into how to tailor healthcare materials to prevent or debilitate infections and join the fight against antibiotic resistance in clinical cases.

Bioceramic-based scaffolds with antibacterial function for bone tissue engineering: A review

Bone defects caused by trauma, tumor, congenital abnormality and osteoarthritis, etc. have been substantially impacted the lives and health of human. Artificial bone implants, like bioceramic-based scaffolds, provide significant benefits over biological counterparts and are critical for bone repair and regeneration. However, it is highly probable that bacterial infections occur in the surgical procedures or on bioceramic-based scaffolds. Therefore, it is of great significance to obtain bioceramic-based scaffolds with integrative antibacterial and osteogenic functions for treating bone implant-associated infection and promoting bone repair. To fight against infection problems, bioceramic-based scaffolds with various antibacterial strategies are developed for bone repair and regeneration and also have made great progresses. This review summarizes recent progresses in bioceramic-based scaffolds with antibacterial function, which include drug-induced, ion-mediated, physical-activated and their combined antibacterial strategies according to specific antibacterial mechanism. Finally, the challenges and opportunities of antibacterial bioceramic-based scaffolds are discussed.

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Bioceramic-based scaffolds with antibacterial function (BSAF) are reviewed.

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BSAF have a great potential in treating bone infection and promoting bone repair.

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Antibacterial strategies of BSAF include drug, ion, physical and combined ways.

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The combined strategy may be the optimal approach in fighting bone infection.

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Limitations, challenges and perspectives of BSAF are discussed.

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.

Bioactive glasses incorporating less-common ions to improve biological and physical properties

Bioactive glasses (BGs) have been a focus of research for over five decades for several biomedical applications. Although their use in bone substitution and bone tissue regeneration has gained important attention, recent developments have also seen the expansion of BG applications to the field of soft tissue engineering. Hard and soft tissue repair therapies can benefit from the biological activity of metallic ions released from BGs. These metallic ions are incorporated in the BG network not only for their biological therapeutic effects but also in many cases for influencing the structure and processability of the glass and to impart extra functional properties. The "classical" elements in silicate BG compositions are silicon (Si), phosphorous (P), calcium (Ca), sodium (Na), and potassium (K). In addition, other well-recognized biologically active ions have been incorporated in BGs to provide osteogenic, angiogenic, anti-inflammatory, and antibacterial effects such as zinc (Zn), magnesium (Mg), silver (Ag), strontium (Sr), gallium (Ga), fluorine (F), iron (Fe), cobalt (Co), boron (B), lithium (Li), titanium (Ti), and copper (Cu). More recently, rare earth and other elements considered less common or, some of them, even "exotic" for biomedical applications, have found room as doping elements in BGs to enhance their biological and physical properties. For example, barium (Ba), bismuth (Bi), chlorine (Cl), chromium (Cr), dysprosium (Dy), europium (Eu), gadolinium (Gd), ytterbium (Yb), thulium (Tm), germanium (Ge), gold (Au), holmium (Ho), iodine (I), lanthanum (La), manganese (Mn), molybdenum (Mo), nickel (Ni), niobium (Nb), nitrogen (N), palladium (Pd), rubidium (Rb), samarium (Sm), selenium (Se), tantalum (Ta), tellurium (Te), terbium (Tb), erbium (Er), tin (Sn), tungsten (W), vanadium (V), yttrium (Y) as well as zirconium (Zr) have been included in BGs. These ions have been found to be particularly interesting for enhancing the biological performance of doped BGs in novel compositions for tissue repair (both hard and soft tissue) and for providing, in some cases, extra functionalities to the BG, for example fluorescence, luminescence, radiation shielding, anti-inflammatory, and antibacterial properties. This review summarizes the influence of incorporating such less-common elements in BGs with focus on tissue engineering applications, usually exploiting the bioactivity of the BG in combination with other functional properties imparted by the presence of the added elements.

Effect of 45S5 bioactive glass on the microshear bond strength of dental fluorosis

The aim of this in vitro study was to estimate the effect of the species concentration of 45S5 bioactive glass (BAG) used as pretreatment on the microshear bond strength (MSBS) of dental fluorosis (DF). Based on the Thylstrup and Fejerskov index, 80 teeth were randomly divided equally into four groups: TFI 0, sound dentin; TFI 1-3, mild fluorosis; TFI 4-5, moderate fluorosis; and TFI 6-9, severe fluorosis. Each group was randomized into five subgroups. After preparing the dentin hypersensitivity model of DF, the dentin was pretreated as follows, Subgroup 1: deionized water (Control group); Subgroup 2: 1% BAG; Subgroup 3: 5% BAG; Subgroup 4: 10% BAG, and Subgroup 5: 20% BAG. Stochastically one specimen was selected from each subgroup for scanning electron microscope and energy dispersive spectrometer analysis. After being made of resin-tooth bonding samples, the remains were in water bath at 37 °C for 24 hr. Subsequently, samples from each subgroup were randomly selected to test MSBS without aging, or after a thermocycle of 5,000 and 10,000 times, respectively. The fracture modes were analyzed. Compared with the group of 1% BAG and Control, the exposure area of tubules in 5%, 10%, and 20% BAG group had significant difference (p < .05). MSBS results indicated that there were significant differences between 10% BAG with other groups. The 20% BAG group showed the lowest MSBS among all groups. Pretreatment of 10% BAG solution may be conductive to enhance the bond strength of DF, while 20% BAG solution adversely.

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.

Thermo-responsive injectable naringin-loaded hydrogel polymerised sodium alginate/bioglass delivery for articular cartilage

In the human body, joint cartilage is of great importance. It has long been a big therapeutic problem to fix joint cartilage lesions as it appears due to different conditions. Recent stories have shown that the cartilage replacement process must delay the extracellular (ECM) cartilage deterioration and modulate the host's inflammation response. For the reconstruction of the articular cartilage, drug-loaded injectable hydrogels were developed. This hydrogel could retain the chondrocyte phenotype, but the host's inflammatory reaction could also be controlled. The bioglass (BG)/sodium alginate (SA) injectable hydrogels was combined with agarose (AG)/Naringin hydrogel in injectable thermal response for articular cartilage regeneration with a non-chargeable hydrogel that contains both Naringin and BG (Naringin–BG hydrogels). The Naringin–BG hydrogel has an adequate swelling ratio that encourages the fusion of tissue formed with host tissue and enables the gradual release of Naringin bioavailabilities enhanced in situ. The Naringin–BG hydrogel can upgrade the typical chondrocyte phenotype by upregulating aggrecan, SRY-box 9, and collagen type II alpha one chain. It may also stimulate the polarization of M2 macrophage, lower inflammations, and prevent ECM degradations through the decrease of the expressions of the indictable metalloproteinase-13 matrix, nitric oxide synthase, and metalloproteinase-1 matrix. The formed tissues were identical to normal tissues and firmly incorporated with the surrounding tissue after administering the Naringin–BG hydrogels into the rat model articular cartilage defects. Then the injectable Naringin–BG hydrogel increases the bioavailable content of Naringin and retains the chondrocyte phenotype.

Novel Bioactive Glass-Modified Hybrid Composite Resin: Mechanical Properties, Biocompatibility, and Antibacterial and Remineralizing Activity

Secondary caries seriously limits the lifetime of composite resin. However, integrating all desirable properties (i.e., mechanical, antibacterial, bioactivity, and biocompatibility) into one composite resin is still challenging. Herein, a novel bioactive glass (BAG)-modified hybrid composite resin has been successfully developed to simultaneously achieve excellent mechanical properties, good biocompatibility, and antibacterial and remineralizing capabilities. When the mass fractions of BAG particles were added from 8 to 23 wt %, the original mechanical properties of the composite resin, including flexural strength and compressive strength, were not obviously affected without compromising the degree of conversion. Although the BAG incorporation of mass fractions of 16 wt % to 23 wt % in composite resins reduced cell viability, the viability could be recovered to normal by adjusting the pH value. Moreover, the BAG-modified composite resins that were obtained showed good antibacterial effects against Streptococcus mutans and enhanced remineralizing activity on demineralized dentin surfaces with increasing incorporation of BAG particles. The possible mechanisms for antibacterial and remineralizing activity might be closely related to the release of bioactive ions (Ca²⁺, Si⁴⁺), suggesting that its antibacterial and biological properties can be controlled by modulating the amounts of bioactive ions. The capability to balance the mechanical properties, cytotoxicity, antibacterial activity, and bioactivity makes the BAG-modified composite resin a promising prospect for clinical application. Our findings provide insight into better design and intelligent fabrication of bioactive composite resins.

Therapeutic effect of a novel bioactive glass-ceramics on early caries lesions: a single-center, randomized controlled clinical trial

OBJECTIVES

To investigate the therapeutic effect of a novel bioactive glass-ceramics (BGC) called Huaxi BGC (HX-BGC) on early caries lesions.

MATERIALS AND METHODS

A total of 195 patients who meeting inclusion criteria were recruited and randomized to three groups in a 1:1:1 ratio. The patients in the treatment group received fluoride varnish which contained 5% sodium fluoride (NaF) or distilled water which contained 7.5% HX-BGC once a month for 3 months, and the control group received placebos. Quantitative light-induced fluorescence (QLF) images were taken at baseline and at the 1-month and 3-month follow-ups.

RESULTS

The three groups had similar baseline characteristics, including age, gender, and QLF parameters (ΔF, area, and ΔQ). Compared with baseline, the ΔQ values were significantly decreased in the HX-BGC and NaF groups at 1 and 3 months (p<0.005), while no statistically significant changes were found in that of the control group. After adjusting for baseline measurements, both of the 5% NaF and 7.5% HX-BGC showed a significant therapeutic effect in the treatment of initial enamel lesions at 1 month and 3 months, when compared to those receiving placebos (ΔQ, p<0.05). Moreover, the ΔQ value of the HX-BGC group decreased by a slightly more amount than that of the NaF group at 1 month (p=0.048). Similar trends were also found for the values of ΔF and area.

CONCLUSION

Our results suggest that HX-BGC may serve as a promising bioactive material for the treatment of early caries lesions.

CLINICAL RELEVANCE

HX-BGC holds a great promise to be used as a novel bioactive material for the treatment of early caries lesions.

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

OBJECTIVE

To investigate the remineralizing effect of a strontium-doped bioactive glass (HX-BGC) and fluoride on demineralized enamel and dentine.

MATERIALS

Sixty demineralized human tooth specimens were allocated to four groups. Group 1 received 5% HX-BGC, Group 2 received 5% HX-BGC and 1450 ppm fluoride, Group 3 received 1450 ppm fluoride, and Group 4 received deionized water as negative control. The specimens were subjected to pH cycling for 14 days. The surface morphology, lesion depths, crystal characteristics and collagen matrix degradation of the specimens were assessed by scanning electron microscopy (SEM), micro-computed tomography (mico-CT), X-ray diffraction (XRD), and spectrophotometry with a hydroxyproline (HYP) assay, respectively.

RESULTS

SEM images showed the enamel surface was smooth with regularly arranged enamel rods in Groups 1-3. Granular grains were observed in both inter-tubular and intra-tubular dentine in Groups 1-3. The mean lesion depths in enamel were 80.8 μm, 50.6 μm, 72.7 μm and 130.7 μm in Groups 1-4, respectively (p < 0.001), and those in dentine were 152.6 μm, 140.9 μm, 165.4 μm and 214.1 μm, respectively (p < 0.001). The differences in mean mineral loss in enamel and in dentine between the four study groups follow the same pattern as that of the differences in lesion depth. XRD illustrated apatite formation in each group. There were no significant differences in the HYP concentrations among the four groups (p = 0.261).

CONCLUSION

Combined use of HX-BGC and fluoride can reduce mineral loss and promote remineralization of demineralized enamel and dentine through the precipitation of newly formed apatite.

CLINICAL SIGNIFICANCE

Adjunctive use of HX-BGC may enhance the remineralization effect of fluoride in the management of early dental caries lesions.

The effects of strontium-doped bioactive glass and fluoride on hydroxyapatite crystallization

OBJECTIVES

This study investigated the effects of a new strontium-doped bioactive glass and fluoride on hydroxyapatite crystallization.

METHODS

We designed an in vitro experiment with calcium phosphate (CaCl₂·2H₂O + K₂HPO₄ in buffer solution) with different concentrations of strontium-doped bioactive glass (1 mg/mL or 5 mg/mL), and different concentrations of fluoride (0 ppm, 1 ppm or 5 ppm). Tris-buffered saline served as negative control. After incubation at 37 ℃ for 48 h, the shape and organization of crystals were examined by transmission electron microscopy (TEM) and electron diffraction. Structure of the crystals was assessed by powder X-ray diffraction (P-XRD) and unit cell parameters were calculated. Characterization of the crystals were performed by Raman spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR).

RESULTS

TEM and selected-area electron diffraction revealed that the precipitates in all experimental groups were crystalline apatite. There was an interaction between strontium and fluoride with different concentrations on crystal thickness (p = 0.008). P-XRD indicated the formation of strontium-substituted-fluorohydroxyapatite and strontium-substituted-hydroxyapatite in the groups with both bioactive glass and fluoride. Expansion or contraction of crystal unit cell was influenced by the concentrations of strontium and fluoride. Raman spectra showed strong phosphate band at 960 cm^-1 in all experimental groups and displayed no obvious shift. FTIR results confirmed the formation of apatite.

CONCLUSIONS

The results of this study suggest that strontium-doped bioactive glass and fluoride have synergistic effects on hydroxyapatite crystallization.

CLINICAL SIGNIFICANCE

Strontium-doped bioactive glass and fluoride have synergistic effects on hydroxyapatite crystallization by producing strontium-substituted-hydroxyapatite and strontium-substituted-fluorohydroxyapatite with enhanced bioactivity and reduced solubility which could be beneficial for caries management.