Ion release and recharge from a fissure sealant containing amorphous calcium phosphate

Ion release dynamics of bioactive resin cement under variable pH conditions

Introduction

Understanding the ion release behaviour of bioactive resin cements is essential for evaluating their potential in restorative dentistry. Sustained ion release, especially at cariogenic pH levels, can enhance remineralization and prolong the longevity of dental restorations. This study investigates the influence of pH on the ion release profiles of a bioactive resin cement before and after recharging.

Methods

Disk-shaped specimens (n = 15) of bioactive resin cement were prepared and exposed to three different pH conditions (4.5, 5.5, and 6.5) to simulate normal and cariogenic environments. Calcium ion release was quantified using atomic spectrophotometry, while fluoride and phosphate ions were analyzed using quantitative spectrophotometry. After an initial 30-day depletion phase, recharging was performed using casein phosphopeptide-amorphous calcium phosphate with fluoride (CPP-ACPF) paste.

Results

In the pre-recharging phase (Stage 1), calcium ion release was more pronounced at acidic pH (4.5-5.5), particularly in the first five days. Fluoride and phosphate ions also demonstrated higher release at pH 4.5 and 5.5 compared to pH 6.5. Post-recharging (Stage 2) exhibited similar trends, emphasizing the role of regular recharge in sustaining ion availability. The absence of an initial burst release, commonly seen in other bioactive materials, suggests a distinct ion release mechanism in these resin cements.

Conclusion

The findings highlight the pH-dependent release characteristics of bioactive resin cements and reinforce the importance of recharging for maintaining their therapeutic potential. The unique release kinetics observed may offer advantages in long-term remineralization strategies for dental restorations.

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.

Ion Release and Apatite Formation of Resin Based Pit and Fissure Sealants Containing 45S5 Bioactive Glass

The purpose of this study was to evaluate a resin based pit and fissure sealant containing 45S5 bioactive glass (BAG) by examining its ion release, pH variation, and apatite-forming properties. To prepare the experimental materials, 45S5 BAG, used as a filler, was incorporated into the light curable resin matrix at concentrations of 0 (control), 12.5, 37.5, and 50.0 wt.%. Ion release, pH variation, and apatite formation (Raman spectrometer and scanning electron microscopy-energy-dispersive X-ray spectrometry measurements) were performed. While no ions were released from the control group, the experimental groups containing 45S5 BAG showed an increased release of Ca and P ions with increasing amounts of 45S5 BAG (p < 0.05). The pH of the experimental group remained high and was significantly different from the control group (p < 0.05). Unlike the control group, it was confirmed that the apatite peak was formed in the 50.0 wt.% BAG group for 90 days, and the apatite layer consisting of Ca and P was deposited on the surface. Thus, a resin based pit and fissure sealant containing 45S5 BAG is a promising material for preventing secondary caries by releasing ions and forming apatite.

Brief Narrative Review on Commercial Dental Sealants-Comparison with Respect to Their Composition and Potential Modifications

The scope of this paper is to compare different dental sealants and flow materials indicated for sealing pits and fissures considering their chemical formula. The narrative review aims to address the following questions: What is the essence of different dental sealants' activity, how does their chemical formula affect their mechanisms of caries prevention, and what makes a dental sealant efficient mean of caries prevention? Another vital issue is whether the sealants that contain fluoride, or any other additions, have potentially increased antimicrobial properties. An electronic search of the PubMed, Cochrane, Web of Science, and Scopus databases was performed. The following keywords were used: (dental sealants) AND (chemical composition). Additionally, information about composition and indications for clinical use provided by manufacturers were utilized. All of the considered materials are indicated for use both in permanent and primary dentition for sealing fissures, pits, and foramina caeca. The selection of suitable material should be made individually and adjusted to conditions of the sealing procedure and patient's needs. Cariostatic mechanisms increasing sealants' effectiveness such as fluoride release are desired in modern dentistry appreciating preventive approach. The review aims are to find crucial elements of sealants' composition which affect their cariostatic mechanisms.

Effect of a bioactive pit and fissure sealant on demineralized human enamel: in vitro study

BACKGROUND

Incorporation of bioactive agent into pit and fissure sealant would halt demineralization and promote further remineralization. The aim was to assess the effect of bioactive and fluoride fissure sealants on calcium and phosphate content and surface topography of artificially demineralized enamel in young permanent teeth.

METHODS

30 sound extracted premolars free from cracks or any developmental anomalies were used. They were divided into group I bioactive fissure sealant, group II fluoride fissure sealant and group III no material applied. Each tooth was divided into halves in a buccolingual direction and evaluated by energy dispersive X-ray spectrometer (EDX) at baseline, demineralization and after applying the material. Another set of 7 sound extracted premolars was evaluated by scanning electron microscopy (SEM) at the same phases.

RESULTS

EDX showed that regaining calcium to demineralized enamel was significantly higher with bioactive sealant than either fluoride or the control group. SEM revealed minerals deposits with formation of distinct white zone at tooth/sealant interface for both pit and fissure sealant groups. Whereas no white zone formation was detected in control group.

CONCLUSIONS

Incorporating bioactive material into pit and fissure sealant through microcapsules provided better results than incorporating fluoride by enhancing the biological process of remineralization.

CLINICAL RELEVANCE

The more use of bioactive pit and fissure sealant would maintain the occlusal surfaces as sound structures and decrease the need for operative procedures to restore teeth cavitation.

Osteoinductive hybrid hydrogel membranes for in situ bone regeneration in hyperglycemia

In hyperglycemia patients, suffering from insufficient vascularization and vascular network lesion, tissue regeneration, such as bone repair, is limited and maybe delayed by the secondary injury and hyperglycemic microenvironment. Typically, dental therapies involving guided bone regeneration is facing a difficult condition in the patients with diabetes. In this study, a hybrid membrane was endowed with biomimetic function to create an angiogenesis-inductive microenvironment by calcium ion release to overcome the limitations of bone tissue regeneration in diabetic patients. Biomineralized calcium resource was Janus-structured onto the surface of hybrid hydrogel by layer-by-layer technique to enhance vascularization and improve the bone regeneration in this study. The release of calcium ions from mineralized phases was controlled by the solubility of inorganic phases and the degradation of gels, promoting HIF-1α expression and creating a key role in angiogenesis stimulation. With highly enhanced calcium signaling and blood vessel formation, the hybrid hydrogel membranes improved the recruitment, proliferation and differentiation of mesenchymal stem cells and endothelial progenitors, confirmed by the enhancement of microvascular regeneration and new bone formation in the critical-sized calvarial defect in diabetic model in vivo. Our study demonstrates a translational potential of hybrid hydrogels engineered with inorganic minerals for orthopedic applications in hyperglycemia.

Penetration ability and microhardness of infiltrant resin and two pit and fissure sealants in primary teeth with early enamel lesions

To determine the penetration depth and enamel microhardness (EMH) of an infiltrant resin and two fissure sealants in primary teeth with early enamel lesions. We randomly divided 174 sound teeth into six groups (n = 29): (1) phosphoric acid (PA) + Clinpro, (2) PA + Aegis, (3) Icon, (4) hydrochloric acid (HCl) + Clinpro, (5) HCl + Aegis, and (6) control. Percentage penetration (%PP) was analyzed by confocal laser scanning microscopy (n = 15). EMH was measured (n = 12), and the percentage of EMH recovery (%REMH) was calculated. Twelve samples were examined under a scanning electron microscope (SEM). All data were analyzed with the Kruskal–Wallis and one-way ANOVA tests (p < 0.05). Groups 3 and 4 showed the highest %PP (all, p < 0.05). Icon application led to significantly higher %REMH compared to the others (p < 0.05). Groups 2 and 5 showed the lowest reduction in %REMH after pH-cycling. Application of Icon and Clinpro with HCl pretreatment showed the greatest %PP. pH-cycling led to a decrease in %REMH for all of the materials, although this effect was lower in teeth treated with Aegis.

In Vitro Biocompatibility of CPP-ACP and Fluoride-containing Desensitizers on Human Gingival Cells

OBJECTIVES

To analyze the biocompatibility of different desensitizers containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and fluoride in their composition: MI Varnish (MV), Clinpro White Varnish (3M Oral Care), Profluorid Varnish (VOCO), Duraphat (Colgate) and Embrace Varnish (Pulpdent) on human gingival fibroblast cells (hGF).

METHODS AND MATERIALS

Human gingival fibroblast (hGF) cells were exposed to several desensitizer extracts at different concentrations (0.1%, 1%, and 4% eluates). Then, in vitro biocompatibility was studied by analyzing the IC50 value, cell proliferation (MTT assay and cell cycle), cell migration (wound healing assay), cell morphology and F-actin content (immunocytofluorescence), and induction of apoptosis/necrosis (flow cytometry). Data were analyzed by one-way analysis of variance (ANOVA) followed by Tukey test.

RESULTS

The lowest cell viability and IC50 were observed in all concentrations of Embrace Varnish-treated hGFs (p<0.001), whereas the highest were exhibited by those treated with Clinpro White Varnish. Similar effects were evidenced when induction of apoptosis/necrosis and cell migration assays were assessed. Finally, MI Varnish, Profluorid Varnish, Duraphat, and Embrace Varnish extracts showed lower numbers of attached cells, some of them with an unusual fibroblastic morphology when cultured with 4% concentration of the varnishes, while Clinpro White Varnish exhibited a similar number of cells with an evident actin cytoskeleton compared to the control group.

CONCLUSIONS

The results obtained in this study indicate that hGFs show better in vitro biocompatibility after exposure to Clinpro White Varnish, even at the highest concentration employed, making it the most eligible for topical applications. In contrast, Embrace Varnish exhibited a high cytotoxicity towards hGFs that could potentially delay the healing process and regeneration of the oral mucosa, although more studies are needed to confirm this hypothesis.

Synthetic amorphous calcium phosphates (ACPs): preparation, structure, properties, and biomedical applications

Amorphous calcium phosphates (ACPs) represent a metastable amorphous state of other calcium orthophosphates (abbreviated as CaPO₄) possessing variable compositional but rather identical glass-like physical properties, in which there are neither translational nor orientational long-range orders of the atomic positions. In nature, ACPs of a biological origin are found in the calcified tissues of mammals, some parts of primitive organisms, as well as in the mammalian milk. Manmade ACPs can be synthesized in a laboratory by various methods including wet-chemical precipitation, in which they are the first solid phases, precipitated after a rapid mixing of aqueous solutions containing dissolved ions of Ca²⁺ and PO₄^3- in sufficient amounts. Due to the amorphous nature, all types of synthetic ACPs appear to be thermodynamically unstable and, unless stored in dry conditions or doped by stabilizers, they tend to transform spontaneously to crystalline CaPO₄, mainly to ones with an apatitic structure. This intrinsic metastability of the ACPs is of a great biological relevance. In particular, the initiating role that metastable ACPs play in matrix vesicle biomineralization raises their importance from a mere laboratory curiosity to that of a reasonable key intermediate in skeletal calcifications. In addition, synthetic ACPs appear to be very promising biomaterials both for manufacturing artificial bone grafts and for dental applications. In this review, the current knowledge on the occurrence, structural design, chemical composition, preparation, properties, and biomedical applications of the synthetic ACPs have been summarized.