Early occlusal caries detection using targeted fluorescent starch nanoparticles.

OBJECTIVES: We have previously shown fluorescent cationic starch nanoparticles (FCSNs) penetrate enamel surface porosity of active carious lesions, potentially aiding their detection. Here, we evaluate the in vitro diagnostic accuracy of FCSNs in detecting occlusal caries compared to histologic reference standard. METHODS: 100 extracted human teeth were selected with sound (50), or either non-cavitated (25) or cavitated (25) lesions. A region of interest (ROI) on the occlusal surface was assessed for fluorescence by two independent examiners, after immersion in FCSN solution, water rinse, and illumination by dental curing lamp viewed through orange UV-filter glasses. ROIs were sectioned and evaluated by histology (Downer Criteria) as a gold standard for caries presence. Cohen's Kappa was determined for inter- and intra-examiner agreement, and sensitivity, specificity, and area under the curve of Receiver Operator Curves (ROCAUC) were calculated. The analysis was repeated for the subset of "early" lesions, defined as being limited to enamel. RESULTS: FCSN use resulted in substantial inter-user (k=0.74±0.07), and high intra-user agreement (k=0.80±0.06; 0.94±0.03, by examiner). Sensitivity, specificity and ROCAUC for FCSNs were 88.9%; 94.6%; 0.92±0.06 for all, and 76.9%, 94.6%, and 0.86±0.10 for early lesions. In post hoc analysis, sensitivity seemed to be greater with the FCSN than the expert visual exam, particularly for early lesions. CONCLUSIONS/CLINICAL SIGNIFICANCE: FCSNs are a reproducible and accurate novel technology for occlusal caries detection, with high sensitivity and specificity compared to histology. Future clinical validation is necessary. FCSNs can improve early caries detection and shift treatment towards non-invasive approaches, improving oral health.

A Highly Ordered, Nanostructured Fluorinated CaP-Coated Melt Electrowritten Scaffold for Periodontal Tissue Regeneration.

Periodontitis is a chronic inflammatory, bacteria-triggered disorder affecting nearly half of American adults. Although some level of tissue regeneration is realized, its low success in complex cases demands superior strategies to amplify regenerative capacity. Herein, highly ordered scaffolds are engineered via Melt ElectroWriting (MEW), and the effects of strand spacing, as well as the presence of a nanostructured fluorinated calcium phosphate (F/CaP) coating on the adhesion/proliferation, and osteogenic differentiation of human-derived periodontal ligament stem cells, are investigated. Upon initial cell-scaffold interaction screening aimed at defining the most suitable design, MEW poly(ε-caprolactone) scaffolds with 500 µm strand spacing are chosen. Following an alkali treatment, scaffolds are immersed in a pre-established solution to allow for coating formation. The presence of a nanostructured F/CaP coating leads to a marked upregulation of osteogenic genes and attenuated bacterial growth. In vivo findings confirm that the F/CaP-coated scaffolds are biocompatible and lead to periodontal regeneration when implanted in a rat mandibular periodontal fenestration defect model. In aggregate, it is considered that this work can contribute to the development of personalized scaffolds capable of enabling tissue-specific differentiation of progenitor cells, and thus guide simultaneous and coordinated regeneration of soft and hard periodontal tissues, while providing antimicrobial protection.

Nanoparticle-Based Targeting and Detection of Microcavities.

Although dental caries is the most prevalent oral disease worldwide, currently, many dentists continue to use the traditional mirror and probe (dental explorer) method of caries diagnosis. This method of caries detection has the drawback that it is often difficult to distinguish between active and inactive carious lesions. In this work, novel bio-based nanoparticles are developed to specifically detect active caries in vitro. The nanoparticles are made from a cationic fluorescein-labeled food-grade starch in order to fluoresce when illuminated by a standard dental curing light, and to degrade in the oral cavity into nontoxic compounds after detecting the active carious lesion. When exposed to extracted human teeth, cationic fluorescent (+5.8 ± 1.2 mV) nanoparticles (size 101 ± 56 nm) selectively illuminate active caries, but not the healthy tooth surface. Two-photon microscopy confirms the selective binding and accumulation of cationic fluorescent nanoparticles into microscopic carious pores in enamel. These novel nanoparticles provide a unique method to assist in the early diagnosis of active carious lesions with the potential to directly impact dental treatment.

Physicochemical and Antibacterial Characterization of a Novel Fluorapatite Coating.

Peri-implantitis remains the major impediment to the long-term use of dental implants. With increasing concern over the growth in antibiotic resistance, there is considerable interest in the preparation of antimicrobial dental implant coatings that also induce osseointegration. One such potential coating material is fluorapatite (FA). The aim of this study was to relate the antibacterial effectiveness of FA coatings against pathogens implicated in peri-implantitis to the physicochemical properties of the coating. Ordered and disordered FA coatings were produced on the under and upper surfaces of stainless steel (SS) discs, respectively, using a hydrothermal method. Surface charge, surface roughness, wettability, and fluoride release were measured for each coating. Surface chemistry was assessed using X-ray photoelectron spectroscopy and FA crystallinity using X-ray diffraction. Antibacterial activity against periodontopathogens was assessed in vitro using viable counts, confocal microscopy, and scanning electron microscopy (SEM). SEM showed that the hydrothermal method produced FA coatings that were predominately aligned perpendicular to the SS substrate or disordered FA coatings consisting of randomly aligned rodlike crystals. Both FA coatings significantly reduced the growth of all examined bacterial strains in comparison to the control. The FA coatings, especially the disordered ones, presented significantly lower charge, greater roughness, and higher area when compared to the control, enhancing bacteria-material interactions and therefore bacterial deactivation by fluoride ions. The ordered FA layer reduced not only bacterial viability but adhesion too. The ordered FA crystals produced as a potential novel implant coating showed significant antibacterial activity against bacteria implicated in peri-implantitis, which could be explained by a detailed understanding of their physicochemical properties.

Hexaarylbiimidazoles as visible light thiol-ene photoinitiators.

OBJECTIVES: The aim of this study is to determine if hexaarylbiimidazoles (HABIs) are efficient, visible light-active photoinitiators for thiol-ene systems. We hypothesize that, owing to the reactivity of lophyl radicals with thiols and the necessarily high concentration of thiol in thiol-ene formulations, HABIs will effectively initiate thiol-ene polymerization upon visible light irradiation. METHODS: UV-vis absorption spectra of photoinitiator solutions were obtained using UV-vis spectroscopy, while EPR spectroscopy was used to confirm radical species generation upon HABI photolysis. Functional group conversions during photopolymerization were monitored using FTIR spectroscopy, and thermomechanical properties were determined using dynamic mechanical analysis. RESULTS: The HABI derivatives investigated exhibit less absorptivity than camphorquinone at 469nm; however, they afford increased sensitivity at this wavelength when compared with bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide. Photolysis of the investigated HABIs affords lophyl radicals. Affixing hydroxyhexyl functional groups to the HABI core significantly improved solubility. Thiol-ene resins formulated with HABI photoinitiators polymerized rapidly upon irradiation with 469nm. The glass transition temperatures of the thiol-ene resin formulated with a bis(hydroxyhexyl)-functionalized HABI and photopolymerized at room and body temperature were 49.5±0.5°C and 52.2±0.1°C, respectively. SIGNIFICANCE: Although thiol-enes show promise as continuous phases for composite dental restorative materials, they show poor reactivity with the conventional camphorquinone/tertiary amine photoinitiation system. Conversely, despite their relatively low visible light absorptivity, HABI photoinitiators afford rapid thiol-ene photopolymerization rates. Moreover, minor structural modifications suggest pathways for improved HABI solubility and visible light absorption.

Nano/micro fluorhydroxyapatite crystal pastes in the treatment of dentin hypersensitivity: an in vitro study.

OBJECTIVES: Dentin hypersensitivity (DH) is a prevalent problem. This study aimed to formulate a paste using fluorhydroxyapatite (FA) crystals dispersed in different carriers to treat DH. The ability to occlude patent dentinal tubules and to release ions was investigated. MATERIALS AND METHODS: Twenty percent FA/sodium alginate, 40% FA/poly(hydroxyethyl methacylate(HEMA)), and 40% FA/poly(DMA-co-MEA) were applied to etched dentin samples and examined with scanning electron microscopy (SEM) to determine the degree of tubule occlusion. Fluoride electrode was used to measure F release and spectroscopy to evaluate Ca and PO4 release. The cytotoxicity of the synthesized poly(DMA-co-MEA) gel was tested. Kruskall-Wallis test was used to test the differences in ion release between the groups. RESULTS: FA/poly(DMA-co-MEA) paste obstructed up to 80% of the dentinal tubules, while the coverage was up to 70% for FA/poly(HEMA) and less than 50% for FA/sodium alginate. Fluoride and Ca release was the highest for FA/P(HEMA), 7.2 ± 0.7 and 139.8 ± 32.5 ppm, respectively. The highest concentration of PO4 was 46.2 ± 16.4 ppm for FA/Sodium alginate. No statistical significance was found. CONCLUSIONS: FA/Poly(DMA-co-MEA) and FA/poly(HEMA) pastes may offer immediate short-term relief of DH because of their ability to occlude the tubules and adhere to wet dentin surfaces. The release of the F, Ca, and PO4 ions may offer long-term relief by forming a mineral barrier both within the dentinal tubules and on the dentin surface. CLINICAL SIGNIFICANCE: The tested materials may offer a long-term treatment for DH.

Fluorapatite enhances mineralization of mesenchymal/endothelial cocultures.

In addition to the widely used mesenchymal stem cells (MSCs), endothelial cells appear to be a favorable cell source for hard tissue regeneration. Previously, fluorapatite was shown to stimulate and enhance mineralization of MSCs. This study aims to investigate the growth of endothelial cells on synthesized ordered fluorapatite surfaces and their effect on the mineralization of adipose-derived stem cells (ASCs) through coculture. Endothelial cells were grown on fluorapatite surfaces and characterized by cell counting, flow cytometry, scanning electron microscopy, and enzyme-linked immunosorbent assay (ELISA). Cells were then cocultured with ASCs and stained for alkaline phosphatase and mineral formation. Fibroblast growth factor (FGF) pathway perturbation and basic FGF (bFGF) treatment of the ASCs were also conducted to observe their effects on differentiation and mineralization of these cells. Fluorapatite surfaces showed good biocompatibility in supporting endothelial cells. Without a mineralization supplement, coculture with endothelial cells induced osteogenic differentiation of ASCs, which was further enhanced by the fluorapatite surfaces. This suggested a combined stimulating effect of endothelial cells and fluorapatite surfaces on the enhanced mineralization of ASCs. Greater amounts of bFGF release by endothelial cells alone or cocultures with ASCs stimulated by fluorapatite surfaces, together with FGF pathway perturbation and bFGF treatment results, suggested that the FGF signaling pathway may function in this process.

In vitro differentiation and mineralization of dental pulp stem cells on enamel-like fluorapatite surfaces.

Our previous studies have shown good biocompatibility of fluorapatite (FA) crystal surfaces in providing a favorable environment for functional cell-matrix interactions of human dental pulp stem cells (DPSCs) and also in supporting their long-term growth. The aim of the current study was to further investigate whether this enamel-like surface can support the differentiation and mineralization of DPSCs, and, therefore, act as a potential model for studying the enamel/dentin interface and, perhaps, dentine/pulp regeneration in tooth tissue engineering. The human pathway-focused osteogenesis polymerase chain reaction (PCR) array demonstrated that the expression of osteogenesis-related genes of human DPSCs was increased on FA surfaces compared with that on etched stainless steel (SSE). Consistent with the PCR array, FA promoted mineralization compared with the SSE surface with or without the addition of a mineralization promoting supplement (MS). This was confirmed by alkaline phosphatase (ALP) staining, Alizarin red staining, and tetracycline staining for mineral formation. In conclusion, FA crystal surfaces, especially ordered (OR) FA surfaces, which mimicked the physical architecture of enamel, provided a favorable extracellular matrix microenvironment for the cells. This resulted in the differentiation of human DPSCs and mineralized tissue formation, and, thus, demonstrated that it may be a promising biomimetic model for dentin-pulp tissue engineering.

The stimulation of adipose-derived stem cell differentiation and mineralization by ordered rod-like fluorapatite coatings.

In this study, the effect of ordered rod-like FA coatings of metal discs on adipose-derived stem cell (ASC)'s growth, differentiation and mineralization was studied in vitro; and their mineral inductive effects in vivo. After 3 and 7 days, the cell number on the metal surfaces was significantly higher than those on the ordered and disordered FA surfaces. However, after 4 weeks much greater amounts of mineral formation was induced on the two FA surfaces with and even without osteogenesis induction. The osteogenic profiles showed the up regulation of a set of pro-osteogenic transcripts and bone mineralization phenotypic markers when the ASCs were grown on FA surfaces compared to metal surfaces at 7 and 21 days. In addition to BMP and TGFß signaling pathways, EGF and FGF pathways also appeared to be involved in ASC differentiation and mineralization. In vivo studies showed accelerated and enhanced mineralized tissue formation integrated within ordered FA coatings. After 5 weeks, over 80% of the ordered FA coating was integrated with a mineralized tissue layer covering the implants. Both the intrinsic properties of the FA crystals and the topography of the FA coating appeared to dominate the cell differentiation and mineralization process.

The effect of novel fluorapatite surfaces on osteoblast-like cell adhesion, growth, and mineralization.

There is increasing demand for biomedical implants to correct skeletal defects caused by trauma, disease, or genetic disorder. In this study, the MG-63 cells were grown on metals coated with ordered and disordered fluorapatite (FA) crystal surfaces to study the biocompatibility, initial cellular response, and the underlying mechanisms during this process. The long-term growth and mineralization of the cells were also investigated. After 3 days, the cell numbers on etched metal surface are significantly higher than those on the ordered and disordered FA surfaces, but the initial adherence of a greater number of cells did not lead to earlier mineral formation at the cell-implant interface. Of the 84 cell adhesion and matrix-focused pathway genes, an up- or down-regulation of a total of 15 genes such as integrin molecules, integrin alpha M and integrin alpha 7 and 8 was noted, suggesting a modulating effect on these adhesion molecules by the ordered FA surface compared with the disordered. Osteocalcin expression and the mineral nodule formation are most evident on the FA surfaces after osteogenic induction (OI) for 7 weeks. The binding of the ordered FA surfaces to the metal, with and without OI, was significantly higher than that of the disordered FA surfaces with OI. Most significantly, even without the OI supplement, the MG-63 cells grown on FA crystal surfaces start to differentiate and mineralize, suggesting that the FA crystal could be a simple and bioactive implant coating material.

Matrix and TGF-beta-related gene expression during human dental pulp stem cell (DPSC) mineralization.

We have recently reported the induction of dental pulp stem cells (DPSCs) into dentin-secreting odontoblast-like cells after stimulation by isolated dentin matrix components, thus mimicking the nature of tissue regeneration seen after tooth disease and injury. After confluency, the cells were further cultured for 21 d in the 10% fetal bovine serum (FBS) Dulbecco's modified Eagle's medium (DMEM) (control), and in this medium, with the addition of dentin extract (DE) and the mineralization supplement (MS) of ascorbic acid and beta-glycerophosphate (treatment). To identify genes associated with this process, specimens were analyzed with a HG-U133A human gene chip and Arrayassist software. A total of 425 genes, among them 21 matrix and eight TGF-beta-related genes, were either up- or downregulated in the experimental group in which the cells showed odontoblast-like differentiation and mineralization. Expression of selected genes was further confirmed by real-time polymerase chain reaction (PCR) analysis. Of the extracellular matrix (ECM)-related genes, two types of collagen genes were upregulated and seven others downregulated. Other ECM-related genes, for example fibulin-1, tenascin C, and particularly thrombospondin 1, were upregulated, and fibulin-2 was downregulated. Most noticeably, the matrix metalloproteinase 1 was induced by the treatment. In the TGF-beta superfamily, upregulation of the type II receptor, endoglin, and growth/differentiation factor 5 was coordinated with the downregulation of activin A, TGF-beta2, and TGF-beta1 itself. This study identifies the matrix and TGF-beta-related gene profiles during the DPSC cell mineralization in which several genes are reported for the first time to be associated with this process, thus greatly expanding our molecular knowledge of the induced disease repair process.

Synthesis of Fluorapatite Nanorods and Nanowires by Direct Precipitation from Solution.

In natural tooth enamel fluoride is always present in the carbonated hydroxyapatite mineral and plays a key role in the prevention of tooth decay. In this study we aimed at mimicking this natural anti-caries ability of the tooth by developing new, effective anticaries materials using fluorapatite nanorods or nanowires. We therefore investigated the conditions necessary to synthesize fluorapatite nanorods of different size, shape and composition for future use either directly or indirectly, that is by incorporation into dental materials, in the treatment and prevention of caries. By controlling the chemical conditions, nanorods of desirable chemical composition and dimension were produced. The mechanism of how these structures were formed is also proposed.

In vitro differentiation and mineralization of human dental pulp cells induced by dentin extract.

In this study, the progenitor cells isolated from the human dental pulp were used to study the effects of ethylenediaminetetraacetic acid-soluble dentin extract (DE) on their differentiation and mineralization to better understand tissue injury and repair in the tooth. Mineralization of the matrix was increasingly evident at 14, 21, and 28 d after treatment with a mineralization supplement (MS) (ascorbic acid [AA], beta-glycerophosphate [beta-GP]) and MS + DE. Real-time polymerase chain reaction results showed type I collagen upregulation after the addition of MS + DE at 7 d. Alkaline phosphatase was downregulated after the mineralization became obvious at 14 d. Bone sialoprotein was shown to be upregulated in the mineralized cell groups at all time points and dentin sialophosphoprotein after 7 d. Core binding factor a 1 was upregulated by the treatment of MS and DE at 7, 14, and 21 d. These results indicated that the MS of AA, beta-GP, and DE synergistically induced cell differentiation of pulp progenitor cells into odontoblast-like cells and induced in vitro mineralization.

Self-assembly of synthetic hydroxyapatite nanorods into an enamel prism-like structure.

The application of surfactants as reverse micelles or microemulsions for the synthesis and self-assembly of nanoscale structures is one of the most widely adopted methods in nanotechnology. These synthesized nanostructure assemblies sometimes have an ordered arrangement. The aim of this research was to take advantage of these latest developments in the area of nanotechnology to mimic the natural biomineralization process to create the hardest tissue in the human body, dental enamel. This is the outermost layer of the teeth and consists of enamel prisms, highly organized micro-architectural units of nanorod-like calcium hydroxyapatite (HA) crystals arranged roughly parallel to each other. In particular, we have synthesized and modified the hydroxyapatite nanorods surface with monolayers of surfactants to create specific surface characteristics which will allow the nanorods to self-assemble into an enamel prism-like structure at a water/air interface. The size of the synthetic hydroxyapatite nanorods can be controlled and we have synthesized nanorods similar in size to both human and rat enamel. The prepared nanorod assemblies were examined using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The specific Langmuir-Blodgett films were shown to be comprised of enamel prism-like nanorod assemblies with a Ca/P ratio between 1.6 and 1.7.

Nanoscale probing of the enamel nanorod surface using polyamidoamine dendrimers.

Although it is known that noncollagenous proteins of dental origin bind to the hydroxyapatite crystal surfaces, no measure of their binding strength has been calculated. This experiment used -COOH-capped generation 7 PAMAM dendrimers as nanoprobes of the biological hydroxyapatite nanorod surfaces. Dendrimer distribution was characterized using AFM. The results showed dendrimers to be spaced at intervals along the c-axis of the crystals. From these observations and assuming a fully ionized -COOH dendrimer, a mathematical model of the binding capacity of the crystal surface with the dendrimer was developed. The Monte Carlo method was used to simulate the binding process between the dendrimer and crystal surface, and the binding strength of the -COOH groups to the surface was calculated to be 90 +/- 20 kJ/mol. These results support the CFM studies which have described alternating bands of charge domains on the crystal surface and that the binding strength will be dependent on both the intensity of the charge on the protein and the crystal surface.