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

A Study of the Association between Primary Oral Pathologies (Dental Caries and Periodontal Diseases) Using Synchrotron Molecular FTIR Spectroscopy in View of the Patient's Personalized Clinical Picture (Demographics and Anamnesis)

In this exploratory study, we searched for associations between the two most common diseases of the oral cavity-dental caries and periodontal diseases-taking into account additional factors, such as personalized clinical pictures (the individual risk factors of the patient), based on the method of a multivariate data analysis of the molecular changes in the composition of human gingival crevicular fluid (GCF). For this purpose, a set of synchrotron Fourier-transform infrared spectroscopy (FTIR) spectra of gingival crevicular fluid samples from patients with different demographics, levels of dental caries development and periodontal diseases, and the presence/absence of concomitant chronic diseases were obtained and analyzed. Using a set of techniques (v-, F-, Chi-square tests; a principal component analysis (PCA); and the hierarchical clustering of principal components (HCPCs)) implemented in the R package FactoMineR allowed us to assess the relationship between the principal components (PCs) and characteristics of the respondents. By identifying the features (vibrational modes in the FTIR spectra) that contribute most to the differentiation of the spectral dataset, and by taking into account the interrelationships between the patients' characteristics, we were able to match specific biological markers (specific molecular groups) to the two factors of interest-two types of oral pathologies. The results obtained show that the observed changes in the quantitative and qualitative composition of the modes in the infrared (IR) spectra of the GCF samples from patients with different dental caries developments and periodontal diseases present confirm the difficulty of identifying patient-specific spectral information. At the same time, different periodontal pathologies are more closely associated with other characteristics of the patients than the level of their caries development. The multivariate analysis performed on the spectral dataset indicates the need to take into account not only the co-occurrence of oral diseases, but also some other factors. The lack of this consideration (typical in lots of studies in this area) may lead to misinterpretations and consequently to a loss of data when searching for biological markers of certain oral diseases.

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.

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.

Biomimetic Mineralization of Tooth Enamel Using Nanocrystalline Hydroxyapatite under Various Dental Surface Pretreatment Conditions

In this report, we demonstrated the formation of a biomimetic mineralizing layer obtained on the surface of dental enamel (biotemplate) using bioinspired nanocrystalline carbonate-substituted calcium hydroxyapatite (ncHAp), whose physical and chemical properties are closest to the natural apatite dental matrix, together with a complex of polyfunctional organic and polar amino acids. Using a set of structural, spectroscopy, and advanced microscopy techniques, we confirmed the formation of a nanosized ncHAp-based mineralized layer, as well as studying its chemical, substructural, and morphological features by means of various methods for the pretreatment of dental enamel. The pretreatment of a biotemplate in an alkaline solution of Ca(OH)₂ and an amino acid booster, together with the executed subsequent mineralization with ncHAp, led to the formation of a mineralized layer with homogeneous micromorphology and the preferential orientation of the ncHAp nanocrystals. It was shown that the homogeneous crystallization of hydroxyapatite on the biotemplate surface and binding of individual nanocrystals and agglomerates into a single complex by an amino acid booster resulted in an increase (~15%) in the nanohardness value in the enamel rods area, compared to that of healthy natural enamel. Obtaining a similar hierarchy and cleavage characteristics as natural enamel in the mineralized layer, taking into account the micromorphological features of dental tissue, is an urgent problem for future research.

Effect of Exo/Endogenous Prophylaxis Dentifrice/Drug and Cariogenic Conditions of Patient on Molecular Property of Dental Biofilm: Synchrotron FTIR Spectroscopic Study

(1) Objectives: This study is the first one to investigate the molecular composition of the dental biofilm during the exogenous and endogenous prophylaxis stages (use of dentifrice/drug) of individuals with different cariogenic conditions using molecular spectroscopy methods. (2) Materials and Methods: The study involved 100 participants (50 males and 50 females), aged 18–25 years with different caries conditions. Biofilm samples were collected from the teeth surface of all participants. The molecular composition of biofilms was investigated using synchrotron infrared microspectroscopy. Changes in the molecular composition were studied through calculation and analysis of ratios between organic and mineral components of biofilm samples. (3) Results: Based on the data obtained by synchrotron FTIR, calculations of organic and mineral component ratios, and statistical analysis of the data, we were able to assess changes occurring in the molecular composition of the dental biofilm. Variations in the phosphate/protein/lipid, phosphate/mineral, and phospholipid/lipid ratios and the presence of statistically significant intra- and inter-group differences in these ratios indicate that the mechanisms of ion adsorption, compounds and complexes arriving from oral fluid into dental biofilm during exo/endogenous prophylaxis, differ for patients in norm and caries development. (4) Conclusions: The conformational environment and charge interaction in the microbiota and the electrostatic state of the biofilm protein network in patients with different cariogenic conditions play an important role. (5) Clinical Significance: Understanding the changes that occur in the molecular composition of the dental biofilm in different oral homeostasis conditions will enable successful transition to a personalised approach in dentistry and high-tech healthcare.

The Molecular and Mechanical Characteristics of Biomimetic Composite Dental Materials Composed of Nanocrystalline Hydroxyapatite and Light-Cured Adhesive

The application of biomimetic strategies and nanotechnologies (nanodentology) has led to numerous innovations and provided a considerable impetus by creating a new class of modern adhesion restoration materials, including different nanofillers. An analysis of the molecular properties of biomimetic adhesives was performed in this work to find the optimal composition that provides high polymerisation and mechanical hardness. Nanocrystalline carbonate-substituted calcium hydroxyapatite (nano-cHAp) was used as the filler of the light-cured adhesive Bis-GMA (bisphenol A-glycidyl methacrylate). The characteristics of this substance correspond to the apatite of human enamel and dentin, as well as to the biogenic source of calcium: avian eggshells. The introduction and distribution of nano-cHAp fillers in the adhesive matrix resulted in changes in chemical bonding, which were observed using Fourier transform infrared (FTIR) spectroscopy. As a result of the chemical bonding, the Vickers hardness (VH) and the degree of conversion under photopolymerisation of the nano-cHAp/Bis-GMA adhesive increased for the specified concentration of nanofiller. This result could contribute to the application of the developed biomimetic adhesives and the clinical success of restorations.

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.

Raman and XANES Spectroscopic Study of the Influence of Coordination Atomic and Molecular Environments in Biomimetic Composite Materials Integrated with Dental Tissue

In this work, for the first time, the influence of the coordination environment as well as Ca and P atomic states on biomimetic composites integrated with dental tissue was investigated. Bioinspired dental composites were synthesised based on nanocrystalline calcium carbonate-substituted hydroxyapatite Ca4ICa6IIPO46−xCO3x+yOH2−y (nano-cHAp) obtained from a biogenic source and a set of polar amino acids that modelled the organic matrix. Biomimetic composites, as well as natural dental tissue samples, were investigated using Raman spectromicroscopy and synchrotron X-ray absorption near edge structure (XANES) spectroscopy. Molecular structure and energy structure studies revealed several important features related to the different calcium atomic environments. It was shown that biomimetic composites created in order to reproduce the physicochemical properties of dental tissue provide good imitation of molecular and electron energetic properties, including the carbonate anion CO₃²⁻ and the atomic Ca/P ratio in nanocrystals. The features of the molecular structure of biomimetic composites are inherited from the nano-cHAp (to a greater extent) and the amino acid cocktail used for their creation, and are caused by the ratio between the mineral and organic components, which is similar to the composition of natural enamel and dentine. In this case, violation of the nano-cHAp stoichiometry, which is the mineral basis of the natural and bioinspired composites, as well as the inclusion of different molecular groups in the nano-cHAp lattice, do not affect the coordination environment of phosphorus atoms. The differences observed in the molecular and electron energetic structures of the natural enamel and dentine and the imitation of their properties by biomimetic materials are caused by rearrangement in the local environment of the calcium atoms in the HAp crystal lattice. The surface of the nano-cHAp crystals in the natural enamel and dentine involved in the formation of bonds with the organic matrix is characterised by the coordination environment of the calcium atom, corresponding to its location in the Ca^I position—that is, bound through common oxygen atoms with PO₄ tetrahedrons. At the same time, on the surface of nano-cHAp crystals in bioinspired dental materials, the calcium atom is characteristically located in the Ca^II position, bound to the hydroxyl OH group. The features detected in the atomic and molecular coordination environment in nano-cHAp play a fundamental role in recreating a biomimetic dental composite of the natural organomineral interaction in mineralised tissue and will help to find an optimal way to integrate the dental biocomposite with natural tissue.