Development of a new approach to diagnosis of the early fluorosis forms by means of FTIR and Raman microspectroscopy

Correlations between bone metabolism biomarkers and fluoride exposure in adults and children

Increased exposure to fluoride, which notably affects bone metabolism, is a global concern. However, the correlations and sensitivity of bone metabolism to fluoride remain controversial. In this cross-sectional study, 549 children (aged 7-12 years) and 504 adults (≥ 18 years old) were recruited in the high-fluoride areas of the Henan Province. Urinary fluoride (UF) level was determined using a fluoride electrode. Fasting venous blood serum was collected to measure bone metabolism biomarkers. The selected bone metabolism biomarkers for children included bone alkaline phosphatase (BALP), serum alkaline phosphatase (ALP), osteocalcin (OCN), calcitonin (CT), parathyroid hormone (PTH), phosphorus (P5+), and calcium (Ca2+). For adults, the biomarkers included ALP, CT, PTH, β-CrossLaps (β-CTX), P5+, and Ca2+. The correlations between UF and bone metabolism biomarkers were analyzed using binary logistic regression, a trend test, a generalized additive model, and threshold effect analysis. Regression analysis indicated a significant correlation between serum OCN, PTH, and UF levels in children aged 7-9 years. Serum OCN, PTH, and BALP contents were significantly correlated with UF in boys (P < 0.05). Furthermore, the interaction between age and UF affected serum P5+ and PTH (P < 0.05). The generalized additive model revealed nonlinear dose-response relationships between P5+, BALP, and UF contents in children (P < 0.05). Serum OCN level was linearly correlated with the UF concentration (P < 0.05). Similarly, a significant correlation was observed between β-CTX and UF levels in adults. In addition, significant correlations were observed between UF-age and serum Ca2+, β-CTX, and PTH contents. There was a non-linear correlation between serum Ca2+, P5+, and β- CTX and UF levels (P < 0.05). Overall, serum OCN, BALP, and P5+ levels can serve as sensitive bone metabolism biomarkers in children, while β-CTX, P5+, and Ca2+ can be considered fluoride-sensitive bone metabolism biomarkers in adults.

Rapid Deposition of the Biomimetic Hydroxyapatite-Polydopamine-Amino Acid Composite Layers onto the Natural Enamel

In this work, we developed a technology that enables rapid deposition of biomimetic composite films onto natural enamel slices (known as biotemplates). These films are composed of polydopamine (PDA) and nanocrystalline carbonate-substituted hydroxyapatite (nano-cHAp) that have been functionalized with amino acid l-Arginine. We utilized atomic force microscopy (AFM) and scattering scanning near-field optical microscopy (s-SNOM) combined with infrared (IR) synchrotron to achieve nanoscale spatial resolution for both IR absorption and topography analyses. This combined analytical modality allowed us to understand how morphology connects to local changes in the chemical environment on the biotemplate surface during the deposition of the bioinspired coating. Our findings revealed that when using the proposed technology and after the deposition of the first PDA layer, the film formed on the enamel surface nearly covers the entire surface of the specimen whose thickness is larger on the surface of the emerging enamel prisms. Calculation of the crystallinity index for the biomimetic layer showed a multiple increase compared with natural enamel. This indicates regular and dense aggregation of nano-cHAp into larger crystals, imitating the morphology of natural enamel rods. The microhardness of the formed PDA-based biomimetic layer mineralized with nano-cHAp functionalized with amino acid l-Arginine deposited on natural enamel was practically the same as that of natural enamel. The characterization of nano-cHAp-amino acid-PDA layers using IR and Raman microspectroscopy showed that l-arginine acts as a conjunction agent in the formation of mineralized biomimetic composite coatings. The uniformity of the mechanisms of PDA layer formation under different deposition conditions and substrate types allows for the formation of coatings regardless of the macro- and micromorphology of the template. Therefore, the results obtained in this work have a high potential for future clinical applications in dental practice.

Amelogenin-inspired peptide, calcium phosphate solution, fluoride and their synergistic effect on enamel biomimetic remineralization: an in vitro pH-cycling model

BACKGROUND

Several methods were introduced for enamel biomimetic remineralization that utilize a biomimetic analogue to interact and absorb bioavailable calcium and phosphate ions and induce crystal nucleation on demineralized enamel. Amelogenin is the most predominant enamel matrix protein that is involved in enamel biomineralization. It plays a major role in developing the enamel's hierarchical microstructure. Therefore, this study was conducted to evaluate the ability of an amelogenin-inspired peptide to promote the remineralization potential of fluoride and a supersaturated calcium phosphate solution in treating artificially induced enamel carious lesions under pH-cycling regimen.

METHODS

Fifty enamel slices were prepared with a window (4*4 mm2 ) on the surface. Five samples were set as control healthy enamel and 45 samples were subjected to demineralization for 3 days. Another 5 samples were set as control demineralized enamel and 40 enamel samples were assigned into 8 experimental groups (n=5) (P/I, P/II, P/III, P/AS, NP/I, NP/II, NP/III and NP/AS) according to peptide treatment (peptide P or non-peptide NP) and remineralizing solution used (I; calcium phosphate solution, II; calcium phosphate fluoride solution, III; fluoride solution and AS; artificial saliva). Samples were then subjected to demineralization/remineralization cycles for 9 days. Samples in all experimental groups were evaluated using Raman spectroscopy for mineral content recovery percentage, microhardness and nanoindentation as healthy, demineralized enamel and after pH-cycling. Data were statistically analysed using two-way repeated measures Anova followed by Bonferroni-corrected post hoc test for pairwise multiple comparisons between groups. Statistical significance was set at p= 0.05. Additionally, XRD, FESEM and EDXS were used for crystal orientation, surface morphology and elemental analysis after pH-cycling.

RESULTS

Nanocrystals clumped in a directional manner were detected in peptide-treated groups. P/II showed the highest significant mean values in mineral content recovery (63.31%), microhardness (268.81±6.52 VHN), elastic modulus (88.74±2.71 GPa), nanohardness (3.08±0.59 GPa) and the best crystal orientation with I002/I300 (1.87±0.08).

CONCLUSION

Despite pH changes, the tested peptide was capable of remineralizing enamel with ordered crystals. Moreover, the supplementary use of calcium phosphate fluoride solution with peptide granted an enhancement in enamel mechanical properties after remineralization.

Correlative Atomic Force Microscopy and Raman Spectroscopy in Acid Erosion of Dentin

Physical properties and chemical composition are fundamentally defining and interconnected surface characteristics. However, few techniques are able to capture both in a correlative fashion at the same sample location and orientation. This is especially important for complex materials such as dentin, which is an inner tooth structure and is a heterogeneous, composite inorganic-organic material with open channels (tubules) that extend toward the tooth pulp. Here, a combined microscope system consisting of an atomic force microscope and a confocal Raman spectrometer was used to study the correlative physical and chemical properties of human dentin. The local hardness of dentin was highly correlated with the Raman signal ratio of inorganic to organic material, and this was enhanced in the peritubular regions of dentin. When the samples were etched with citric acid, Young's modulus, hardness, and inorganic-to-organic material ratio decreased significantly, collagen fibrils on the surface were exposed, the peritubular regions were removed, and the tubule diameters increased. Thus, the combined atomic force microscopy (AFM)-Raman approach allows for comprehensive and correlative physical-chemical analysis of material surfaces and will be invaluable for evaluating oral therapeutic strategies.

Probing the micro- and nanoscopic properties of dental materials using infrared spectroscopy: A proof-of-principle study

The preservation of oral health over a person's lifespan is a key factor for a high quality of life. Sustaining oral health requires high-end dental materials with a plethora of attributes such as durability, non-toxicity and ease of application. The combination of different requirements leads to increasing miniaturization and complexity of the material components such as the composite and adhesives, which makes the precise characterization of the material blend challenging. Here, we demonstrate how modern IR spectroscopy and imaging from the micro- to the nanoscale can provide insights on the chemical composition of the different material sections of a dental filling. We show how the recorded IR-images can be used for a fast and non-destructive porosity determination of the studied adhesive. Furthermore, the nanoscale study allows precise assessment of glass cluster structures and distribution within their characteristic organically modified ceramic (ORMOCER) matrix and an assessment of the interface between the composite and adhesive material. For the study we used a Fourier-Transform-IR (FTIR) microscope and a quantum cascade laser-based IR-microscope (QCL-IR) for the microscale analysis and a scattering-type scanning near-field optical microscopy (s-SNOM) for the nanoscale analysis. The paper ends with an in-depth discussion of the strengths and weaknesses of the different imaging methods to give the reader a clear picture for which scientific question the microscopes are best suited for. STATEMENT OF SIGNIFICANCE: Modern resin-based composites for dental restoration are complex multi-compound materials. In order to improve these high-end materials, it is important to investigate the molecular composition and morphology of the different parts. An emergent method to characterize these materials is infrared spectroscopic imaging, which combines the strength of infrared spectroscopy and an imaging approach known from optical microscopy. In this work, three state of the art methods are compared for investigating a dental filling including FTIR- and quantum cascade laser IR-imaging microscopy for the microscale and scattering-type scanning near-field optical microscopy for the nanoscale.

The effect of calcium phosphate ion clusters in enhancing enamel conditions versus Duraphat and Icon

This study aimed to evaluate and compare the remineralisation, mechanical, anti-aging, acid resistance and antibacterial properties of calcium phosphate ion clusters (CPICs) materials with those of Duraphat and Icon. The remineralisation and mechanical properties were investigated using scanning electron microscopy, Fourier-transform infrared (FTIR) spectroscopy and nanoindentation. CPICs induced epitaxial crystal growth on the enamel surface, where the regrown enamel-like apatite layers had a similar hardness and elastic modulus to natural enamel (p > 0.05). Acid resistance and anti-aging properties were tested based on ion dissolution and surface roughness. CPICs exhibited similar calcium and phosphate ion dissolution to the control (p > 0.05), and its roughness decreased after thermocycling (p < 0.05), thereby decreasing the risk of enamel surface demineralisation. The minimum inhibitory concentration was 0.1 mg/ml, and the minimum bactericidal concentration ranged from 0.05 to 0.1 mg/ml. Overall, this biomimetic CPICs is a promising alternative to dental demineralisation.

A Study of the Peculiarities of the Formation of a Hybrid Interface Based on Polydopamine between Dental Tissues and Dental Composites, Using IR and Raman Microspectroscopy, at the Submicron Level

The creation of buffer (hybrid) layers that provide improved adhesion to two heterogeneous materials is a promising and high-priority research area in the field of dental materials science. In our work, using FTIR and Raman microspectroscopy at the submicron level in a system of dental composites/intact dental enamel, we assessed the molecular features of formation and chemically visualized the hybrid interface formed on the basis of a nature-like adhesive, polydopamine (PDA). It is shown that a homogeneous bioinspired PDA-hybrid interface with an increased content of O-Ca-O bonds can be created using traditional methods of dental tissue pretreatment (diamond micro drilling, acid etching), as well as the subsequent alkalinization procedure and the developed synthesis technology. The development of the proposed technology for accelerated deposition of PDA-hybrid layers, as well as the creation of self-assembled biomimetic nanocomposites with antibacterial properties, may in the future find clinical application for minimally invasive dental restoration procedures.

Synchrotron X-ray Studies of the Structural and Functional Hierarchies in Mineralised Human Dental Enamel: A State-of-the-Art Review

Hard dental tissues possess a complex hierarchical structure that is particularly evident in enamel, the most mineralised substance in the human body. Its complex and interlinked organisation at the Ångstrom (crystal lattice), nano-, micro-, and macro-scales is the result of evolutionary optimisation for mechanical and functional performance: hardness and stiffness, fracture toughness, thermal, and chemical resistance. Understanding the physical-chemical-structural relationships at each scale requires the application of appropriately sensitive and resolving probes. Synchrotron X-ray techniques offer the possibility to progress significantly beyond the capabilities of conventional laboratory instruments, i.e., X-ray diffractometers, and electron and atomic force microscopes. The last few decades have witnessed the accumulation of results obtained from X-ray scattering (diffraction), spectroscopy (including polarisation analysis), and imaging (including ptychography and tomography). The current article presents a multi-disciplinary review of nearly 40 years of discoveries and advancements, primarily pertaining to the study of enamel and its demineralisation (caries), but also linked to the investigations of other mineralised tissues such as dentine, bone, etc. The modelling approaches informed by these observations are also overviewed. The strategic aim of the present review was to identify and evaluate prospective avenues for analysing dental tissues and developing treatments and prophylaxis for improved dental health.

Efficient controlled release of cannabinoids loaded in γ-CD-MOFs and DPPC liposomes as novel delivery systems in oral health

Olivetol (OLV), as a cannabidiol (CBD) analog, was incorporated in γ-cyclodextrin metal-organic frameworks (γ-CD-MOFs) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes as potential analgesic drug delivery systems (DDS) for dental hypersensitivity (DH) treatment. These DDS have been scarcely employed in oral health, being the first time in case of MOFs loaded with cannabinoids. In vitro experiments using bovine teeth were performed to verify if the drug is able to reach the dentin, where it can flow to the pulp tissues and exert its analgesic effect; enamel and dentin regions were analyzed by synchrotron radiation-based FTIR microspectroscopy. Principal component analysis (PCA) was used to process the spectroscopic data as a powerful chemometric tool, and it revealed a similar behavior in both regions. The studied DDS have been characterized by different techniques, and is was demonstrated that DDS is an efficient way to carry the drug through dental tissues without compromising their structure.

[Distinctions in molecular composition of the dental biofilm depending on the method of exo-/endogeneous caries prevention and cariogenic condition of a patient]

PURPOSE OF THE STUDY

For the first time distinctions of molecular composition of the dental biofilm at the stages of exo- and endogeneous caries prevention were studied for persons with different cariogenic conditions involving synchrotron molecular spectroscopy techniques.

MATERIAL AND METHODS

The samples of the dental biofilm collected from participants of the research were studied at the different stages of experiment. The studies of molecular composition of the biofilms were employed involving the equipment set in the Infrared Microspectroscopy (IRM) laboratory of Australian synchrotron.

RESULTS

Basing on the data obtained by synchrotron infrared spectroscopy with Fourier transform as well as using the calculations of the ratios between organic and mineral components and also statistical analysis of the data we could estimate the changes proceeding in the molecular composition of dental biofilm in a dependence of homeostasis conditions in the oral cavity at the stages of exo- and endogeneous caries prevention.

CONCLUSION

Observed changes in the values of phosphate/protein/lipid, phosphate/mineral and phospholipid/lipid ratios as well as the presence of statistically significant intra- and intergroup in these coefficients mean that mechanisms of adsorption for the ions, compounds and molecular complexes incoming from the oral fluid into the dental biofilm at the stage of exo-/endogeneous caries prevention are different for the patients in normal condition and for those ones with the developing caries.

Compositional Analysis of the Dental Biomimetic Hybrid Nanomaterials Based on Bioinspired Nonstoichiometric Hydroxyapatite with Small Deviations in the Carbonate Incorporation

In our paper, we discuss the results of a comprehensive structural-spectroscopic and microscopic analysis of non-stoichiometric nanocrystalline hydroxyapatite (CHAp) with low carbonate anion content and biomimetic hybrid nanomaterials produced on its basis. It was shown that hydroxyapatite nanocrystals synthesized by chemical precipitation and biogenic calcium source mimic the properties of biogenic apatite and also have a morphological organization of "core-shell" type. The "core" of the CHAp nanocrystal is characterized by an overabundance of calcium Ca/P~1.9. Thus "a shell" with thickness of ~3-5 nm is formed from intermediate apatite-like phases where the most probable are octocalcium phosphate, dicalcium phosphate dihydrate and tricalcium phosphate. The multimode model of the Raman profile of samples CHAp and biomimetic composites for spectral region 900-1100 cm^-1 proposed in our work has allowed to allocate precise contribution of B-type carbonate substitution, taking into account the presence on a surface of "core" HAp nanocrystal of various third-party intermediate apatite-like phases. The calibration function constructed on the basis of the described model makes it possible to reliably determine small concentrations of carbonate in the structure of hydroxyapatite with the application of Raman express method of diagnostics. The results of our work can inspire researchers to study the processes of induced biomineralization in mineralized tissues of the human body, using non-destructive methods of control with simultaneous analysis of chemical bonding, as well as determining the role of impurity atoms in the functions exhibited by biotissue.

Development of a Hybrid Biomimetic Enamel-Biocomposite Interface and a Study of Its Molecular Features Using Synchrotron Submicron ATR-FTIR Microspectroscopy and Multivariate Analysis Techniques

Using a biomimetic strategy and bioinspired materials, our work proposed a new technological approach to create a hybrid transitional layer between enamel and dental biocomposite. For this purpose, an amino acid booster conditioner based on a set of polar amino acids (lysine, arginine, hyaluronic acid), calcium alkali, and a modified adhesive based on BisGMA and nanocrystalline carbonate-substituted hydroxyapatite are used during dental enamel restoration. The molecular properties of the hybrid interface formed using the proposed strategy were understood using methods of multivariate statistical analysis of spectral information collected using the technique of synchrotron infrared microspectroscopy. The results obtained indicate the possibility of forming a bonding that mimics the properties of natural tissue with controlled molecular properties in the hybrid layer. The diffusion of the amino acid booster conditioner component, the calcium alkali, and the modified adhesive with nanocrystalline carbonate-substituted hydroxyapatite in the hybrid interface region creates a structure that should stabilize the reconstituted crystalline enamel layer. The developed technology can form the basis for an individualized, personalized approach to dental enamel restorations.

Effects of Photodynamic Therapy on Streptococcus mutans and Enamel Remineralization of Multifunctional TiO2-HAP Composite Nanomaterials

BACKGROUND

As photosensitizer and photocatalyst, titanium dioxide (TiO₂) can produce a photodynamic reaction for antibacterial treatment. This study aims to explore a Titanium dioxide/nano-hydroxyapatite (TiO₂-HAP) composite combined with the dental curing lamp (385-515 nm) in clinical which could inhibit the dental plaque biofilm formed by Streptococcus mutans (S. mutans) and promote the enamel surface remineralization simultaneously.

METHODS

X-ray Diffraction (XRD) and high resolution transmission electron microscope (HRTEM) were used to detect the characterization of TiO₂-HAP composite nanomaterials. Photodynamic properties of TiO₂-HAP were detected by Diffuse reflectance spectrum (DRS) and fluorescence spectroscopy. Bacterial growth was measured by reading the absorbance of bacterial cultures and confocal microscope was used to observe the biofilm removal ability of nanomaterials. The ability of TiO₂-HAP to promote enamel remineralization was measured by Scanning electron microscope (SEM).

RESULTS

The OD 600 of S. mutans was 0.76 in the control group and 0.13 in group of TiO₂-HAP with exposure to light-emitting diode (LED) (150 mW/cm²) for 5 min, suggesting its sustained antibacterial potency and inhibition of the metabolic activity of dental plaque microcosm biofilm. Also, the release of calcium and phosphorus ions in TiO₂-HAP can promote enamel mineralization simultaneously. After 15 days of remineralization, the Ca/P ratio of demineralized enamel surface increased from 1.28 to 1.67, which was similar to that of normal enamel.

CONCLUSIONS

The TiO₂-HAP exhibit a promising anti-bacterial activity and remineralization capacity which can prevent the occurrence of caries to the greatest extent and promote the biomimetic mineralization of dental tissues.

Surface and Structural Studies of Age-Related Changes in Dental Enamel: An Animal Model

In the animal kingdom, continuously erupting incisors provided an attractive model for studying the enamel matrix and mineral composition of teeth during development. Enamel, the hardest mineral tissue in the vertebrates, is a tissue sensitive to external conditions, reflecting various disturbances in its structure. The developing dental enamel was monitored in a series of incisor samples extending the first four weeks of postnatal life in the spiny mouse. The age-dependent changes in enamel surface morphology in the micrometre and nanometre-scale and a qualitative assessment of its mechanical features were examined by applying scanning electron microscopy (SEM) and atomic force microscopy (AFM). At the same time, structural studies using XRD and vibrational spectroscopy made it possible to assess crystallinity and carbonate content in enamel mineral composition. Finally, a model for predicting the maturation based on chemical composition and structural factors was constructed using artificial neural networks (ANNs). The research presented here can extend the existing knowledge by proposing a pattern of enamel development that could be used as a comparative material in environmental, nutritional, and pharmaceutical research.

Development of a Visualisation Approach for Analysing Incipient and Clinically Unrecorded Enamel Fissure Caries Using Laser-Induced Contrast Imaging, MicroRaman Spectroscopy and Biomimetic Composites: A Pilot Study

This pilot study presents a practical approach to detecting and visualising the initial forms of caries that are not clinically registered. The use of a laser-induced contrast visualisation (LICV) technique was shown to provide detection of the originating caries based on the separation of emissions from sound tissue, areas with destroyed tissue and regions of bacterial invasion. Adding microRaman spectroscopy to the measuring system enables reliable detection of the transformation of the organic–mineral component in the dental tissue and the spread of bacterial microflora in the affected region. Further laboratory and clinical studies of the comprehensive use of LICV and microRaman spectroscopy enable data extension on the application of this approach for accurate determination of the boundaries in the changed dental tissue as a result of initial caries. The obtained data has the potential to develop an effective preventive medical diagnostic approach and as a result, further personalised medical treatment can be specified.

Metaphosphate-Bridged Interface Boosts High-Performance Lithium Storage

Carbon materials with well-dispersed SnO_x particles exhibit excellent lithium-storage performance. However, the volume change of SnO_x and the weak interaction between SnO_x and carbon induce an unsteady SnO_x-C interface during the lithiation/delithiation process. This phenomenon results in enhanced charge transfer resistance and reduced electrical contact of active materials, which leads to low reversibility of tin oxidation, restricted capacity, sluggish kinetics, structural deterioration, and rapid capacity decay. Herein, tin oxide/carbon composites with a metaphosphate-bridged interface are synthesized to construct a robust interfacial contact between tin oxides and carbon. The metaphosphate group functions as a bridge between SnO_x and carbon and results in excellent electrochemical stability during the charge/discharge process, which is favorable for electrode structural integrity. The formation of the metaphosphate-bridged interface provides a steady transport channel for e^-/Li⁺ and thus improves the reversibility of the conversion reaction. The enhanced charge transfer and interaction can also boost the charge transfer between SnO_x and carbon, which leads to higher SnO_x utilization. Thus, the prepared P-SnO_x/C anode exhibits enhanced lithium-storage performance in terms of specific capacity, cycling stability, and rate performance.

Study of Chitosan Ingestion Remitting the Bone Damage on Fluorosis Mice with Micro-CT

Chronic excessive fluoride exposure may lead to fluorosis, which causes health problems like a decrease in bone mechanical strength. It was speculated that chitosan may combine with fluorine to form in vivo organic fluorine, and may reduce the damage caused by fluorine. Hence, it is necessary to conduct a study to investigate the influence of chitosan on fluorosis mice. To investigate this problem, forty-four 4-week-old male Kunming mice were randomly divided into four groups, the control group, the fluoride group, the fluoride plus chitosan group, and the chitosan group. After 100 days of feeding, the femurs were collected to scan the Micro-CT image. The ultimate load of the femur in the fluoride group was significantly lower than control group. The trabecular separation was increased in the fluoride group compared with the fluoride plus chitosan group and the chitosan group. The level of trabecular thickness was increased in the fluoride plus chitosan group compared with the fluoride group. Our findings suggest that chitosan ingestion can improve the condition of cancellous bone and cortical bone affected by fluorine.

Vibrational Imaging Techniques for the Characterization of Hard Dental Tissues: From Bench-Top to Chair-Side

Currently, various analytical techniques, including scanning electron microscopy, X-Ray diffraction, microcomputed tomography, and energy dispersive X-ray spectroscopy, are available to study the structural or elemental features of hard dental tissues. In contrast to these approaches, Raman Microspectroscopy (RMS) has the great advantage of simultaneously providing, at the same time and on the same sample, a morpho-chemical correlation between the microscopic information from the visual analysis of the sample and its chemical and macromolecular composition. Hence, RMS represents an innovative and non-invasive technique to study both inorganic and organic teeth components in vitro. The aim of this narrative review is to shed new light on the applicative potential of Raman Microspectroscopy in the dental field. Specific Raman markers representative of sound and pathological hard dental tissues will be discussed, and the future diagnostic application of this technique will be outlined. The objective and detailed information provided by this technique in terms of the structure and chemical/macromolecular components of sound and pathological hard dental tissues could be useful for improving knowledge of several dental pathologies. Scientific articles regarding RMS studies of human hard dental tissues were retrieved from the principal databases by following specific inclusion and exclusion criteria.

Investigation of the Effect of Nanocrystalline Calcium Carbonate-Substituted Hydroxyapatite and L-Lysine and L-Arginine Surface Interactions on the Molecular Properties of Dental Biomimetic Composites

Differences in the surface interactions of non-stoichiometric nanocrystalline B-type carbonate-substituted hydroxyapatite (n-cHAp) with the amino acids L-Lysine hydrochloride (L-LysHCl) and L-Arginine hydrochloride (L-ArgHCl) in acidic and alkaline media were determined using structural and spectroscopic analysis methods. The obtained data confirm that hydroxyapatite synthesized using our technique, which was used to develop the n-cHAp/L-LysHCl and n-cHAp/L-ArgHCl composites, is nanocrystalline. Studies of molecular composition of the samples by Fourier transform infrared spectroscopy under the change in the charge state of L-Lysine in environments with different alkalinity are consistent with the results of X-ray diffraction analysis, as evidenced by the redistribution of the modes' intensities in the spectra that is correlated with the side chains, i.e., amide and carboxyl groups, of the amino acid. During the formation of a biomimetic composite containing L-Lysine hydrochloride and n-cHAp, the interaction occurred through bonding of the L-Lysine side chain and the hydroxyl groups of hydroxyapatite, which created an anionic form of L-Lysine at pH ≤ 5. In contrast, in biocomposites based on L-Arginine and n-cHAp, the interaction only slightly depends on pH value, and it proceeds by molecular orientation mechanisms. The X-ray diffraction and infrared spectroscopy results confirm that changes in the molecular composition of n-cHAp/L-ArgHCl biomimetic composites are caused by the electrostatic interaction between the L-ArgHCl molecule and the carbonate-substituted calcium hydroxyapatite. In this case, the bond formation was detected by Fourier transform infrared (FTIR) spectroscopy; the vibrational modes attributed to the main carbon chain and the guanidine group of L-Arginine are shifted during the interaction. The discovered interaction mechanisms between nanocrystalline carbonate-substituted hydroxyapatite that has physicochemical properties characteristic of the apatite in human dental enamel and specific amino acids are important for selecting the formation conditions of biomimetic composites and their integration with the natural dental tissue.

Diagnosis of Dental Fluorosis Using Micro-Raman Spectroscopy Applying a Principal Component-Linear Discriminant Analysis

Dental fluorosis is an irreversible condition caused by excessive fluoride consumption during tooth formation and is considered a public health problem in several world regions. The objective of this study was to evaluate the capability of micro-Raman spectroscopy to classify teeth of different fluorosis severities, applying principal component analysis and linear discriminant analysis (PCA-LDA), and estimate the model cross-validation accuracy. Forty teeth of different fluorosis severities and a control group were analyzed. Ten spectra were captured from each tooth and a total of 400 micro-Raman spectra were acquired in the wavenumber range of 250 to 1200 cm⁻¹, including the bands corresponding to stretching and bending internal vibrational modes ν₁, ν₂, ν₃, and ν₄ (PO₄³⁻). From the analysis of the micro-Raman spectra an increase in B-type carbonate ion substitution into the phosphate site of the hydroxyapatite as fluorosis severity increases was identified. The PCA-LDA model showed a sensitivity and specificity higher than 94% and 93% for the different fluorosis severity groups, respectively. The cross-validation accuracy was higher than 90%. Micro-Raman spectroscopy combined with PCA-LDA provides an adequate tool for the diagnosis of fluorosis severity. This is a non-invasive and non-destructive technique with promising applications in clinical and epidemiological fields.

[Raman spectroscopy and its application in different areas of medicine]

The aim of the review is to learn about the areas of application of the Raman spectroscopy in medicine, particularly in dentistry. The method is widely used in biology, medicine, pharmacy, forensic science, gemology, food industry and other industries. The main advantages of Raman spectroscopy are no need for sample preparation and small amounts of the object of study, as well as the ability to contactlessly obtain unique information about the conformation and microenvironment of living cell molecules. The disadvantages are high costs of the equipment that are compensated with the long-term use by having no costs for additional reagents. The combinatorial scattering is used in dermatology, as it is a high-accuracy automated method of visualization and diagnostics of both benign growths as pigmented nevus, seborrheic keratosis, and malignant neoplasms as melanoma and basal cell carcinoma. This method is an analytical tool for diagnosing various diseases, making the direct measurements in hard and liquid media easier, does not require special treatment of samples and is not sensitive to absorption bands. The Raman spectroscopy use in dentistry allows diagnosing and comparative analysis of the changes of hard tissues of teeth and mucous membrane of the mouth, which improves security and rationalization of treatment and further prevention of complications before and after making different operations.

To the Question on the Use of Multivariate Analysis and 2D Visualisation of Synchrotron ATR-FTIR Chemical Imaging Spectral Data in the Diagnostics of Biomimetic Sound Dentin/Dental Composite Interface

In this short communication, we provide information on the use of the hierarchical cluster analysis of synchrotron ATR-FTIR 2D chemical imaging spectral data as a useful and powerful approach to the microspectroscopic diagnostics of molecular composition in the hybrid sound dentin/dental composite interfaces and materials, including ones developed with the use of biomimetic strategies. The described diagnostic approach can be successfully transferred to the analysis and visualisation of 2D spectral data, collected using laboratory Raman and FTIR microspectroscopy techniques.

Engineering of a Biomimetic Interface between a Native Dental Tissue and Restorative Composite and Its Study Using Synchrotron FTIR Microscopic Mapping

The aim of this work is to develop a biomimetic interface between the natural tooth tissue and the restorative composite and to study it on the basis of synchrotron micro-FTIR mapping and multidimensional processing of the spectral data array. Using hierarchical cluster analysis of 3D FTIR data revealed marked improvements in the formation of the dentine/adhesive/dental hybrid interface using a biomimetic approach. The use of a biomimetic strategy (application of an amino acid-modified primer, alkaline calcium and a nano-c-HAp-modified adhesive) allowed the formation of a matrix that can be structurally integrated with natural dentine and dental composite. The biomimetic hybrid layer was characterised by homogeneous chemical composition and a higher degree of conversion of the adhesive during polymerisation, which should provide optimal integration of the dental composite with the dentine.