Deformation behavior of normal human enamel: A study by nanoindentation

Three-Dimensional Assessment of Dental Enamel Microcrack Progression After Orthodontic Bracket Debonding Using Optical Coherence Tomography

The current study aimed to quantify the length progression of enamel microcracks (EMCs) after debonding metal and ceramic brackets, implementing OCT as a diagnostic tool. The secondary objectives included a three-dimensional assessment of EMC width and depth and the formation of new EMCs. OCT imaging was performed on 16 extracted human premolars before bonding and after debonding. Debonding was conducted with a universal Instron machine, with ARI values recorded. Additionally, 2D and 3D OCT images were employed to detect EMC formation and progression. Enface images quantified the length, width, and number of EMCs, and the length and width were analyzed using Image J (1.54f) and MATLAB (R2014b), respectively. Sagittal cross-sectional images were used for EMC depth analysis. A paired t-test showed significant differences in the length, width, and number of EMCs after debonding (p-value < 0.05), while the Wilcoxon non-parametric test indicated significant EMC depth changes (p-value < 0.05). No significant results were identified for the EMC number in ceramic brackets and EMC depth in metal brackets. Three-dimensional OCT imaging monitored existing EMCs at higher risk of progression and detected new EMCs following orthodontic bracket debonding. This study provides novel insights into EMC progression regarding the length, width, depth, and number after debonding.

Effect of air-abrasion pretreatment with three desensitizing agents on efficacy of in-office tooth bleaching

OBJECTIVE

To evaluate the influence of air-abrasion of enamel with three different desensitizing powders on the whitening effect of a bleaching gel containing 40% H2O2, which was used for in-office tooth bleaching.

MATERIALS AND METHODS

Forty human incisors, extracted and prepared, were acquired for this study and subsequently randomized into four groups (n = 10). The control group specimens underwent no pretreatment prior to the bleaching procedure, whereas the remaining three groups underwent air abrasion using distinct desensitizing powders; (a) Sylc, which contains bioglass 45S5; (b) BioMinF, which contains calcium phospho-fluoro-silicate glass; and (c) MI Pearls, which contains nano-hydroxyapatite, 1 h preceding the Opalescence Boost PF 40% bleaching procedure. Color measurements were conducted using a double-beam UV-Vis spectrophotometer at four distinct time points (prior to bleaching, 24 h, 15 days, and 30 days post-bleaching).

RESULTS

Tooth color change outcomes revealed that there were no statistically significant results with respect to the interaction of the two criteria (treatments and time) (p = 0.990). Additionally, there were no statistically significant results with respect to the main effects of treatments (p = 0.385), while there were statistically significant effects with respect to the time criterion (p = 0.013).

CONCLUSIONS

The use of the tested desensitizing powders prior the bleaching procedure did not affect the tooth color change induced by the tested bleaching agent.

CLINICAL SIGNIFICANCE

Tooth color change and whiteness are not affected by air-abrasion desensitizing treatments when applied prior to in-office bleaching procedures.

Unraveling the orientation-dependent mechanics of dental enamel in the red-necked wallaby

Dental enamels of different species exhibit a wide variety of microstructural patterns that are attractive to mimic in bioinspired composites to simultaneously achieve high stiffness and superior toughness. Non-human enamel types, however, have not yet received the deserved attention and their mechanical behaviour is largely unknown. Using nanoindentation tests and finite element modelling, we investigate the mechanical behaviour of Macropus rufogriseus enamel, revealing a dominating influence of the microstructure on the effective mechanical behaviour and allowing insight into structural dependencies. We find a shallow gradient in stiffness and low degree of anisotropy over the enamel thickness that is attributed to the orientation and size of microstructural features. Most notably, M. rufogriseus's modified radial enamel has a far simpler structural pattern than other species', but achieves great property amplification. It is therefore a very promising template for biomimetic design. STATEMENT OF SIGNIFICANCE: The diversity of dental enamel structures in different species is well documented, but the mechanical behaviour of non-human enamel types is largely unknown. In this work, we investigate the microstructure and structure-dependent mechanical properties of marsupial enamel by nanoindentation and finite element simulations. Combining these methods gives valuable insights into the performance of modified radial enamel structures. Their stiffness and toughness stems from a unique structural design that is far less complex than well-studied human enamel types, which makes it a uniquely suitable template for biomimetic design.

The Stresses and Deformations in the Abfraction Lesions of the Lower Premolars Studied by the Finite Element Analyses: Case Report and Review of Literature

BACKGROUND

The purpose of the study was to investigate the behavior of hard dental structures of the teeth with abfraction lesions when experimental occlusal loads were applied.

METHODS

A 65-year-old patient came to the dentist because she had painful sensitivity in the temporomandibular joints and the lower right premolars. The patient was examined, and cone-beam computed tomography (CBCT) of the orofacial area was indicated. The data provided from the CBCT were processed with Mimics Innovation Suite 17 software to create the desired anatomical area in 3D format. Then, the structural calculation module was used in order to perform a finite element analysis of the lower right premolar teeth. A focused review of articles published between 2014 and 2023 from specialty literature regarding the FEA of premolars with abfraction lesions was also conducted.

RESULTS

The parcel area and the cervical third of the analyzed premolars proved to be the most vulnerable areas under the inclined direction of occlusal loads. The inclined application of experimental loads induced 3-4 times higher maximum shears, stresses, and deformations than the axial application of the same forces.

CONCLUSIONS

FEA can be used to identify structural deficiencies in teeth with abfractions, a fact that is particularly important during dental treatments to correct occlusal imbalances.

A parametrical finite element analysis for functionally graded material overlay restoration

The main cause of failure in bonded ceramic restorations is material fracture due to excessive stress concentration at the base of the prosthesis. The design of restorative functionally graded materials (FGM) could represent a major advance in dissipating mechanical stresses during occlusal contacts. The aim of this paper is to carry out a complete factorial design of finite element analyses to optimize a multilayer FGM introduced at the bottom of an overlay prosthesis. The number and thickness of layers vary within a spectrum compatible with ceramic shaping processes whereas Young's moduli variations are set in the range of dental tissues. For a 1.5-mm thick prosthesis, the optimal FGM configuration appears to be a 5 layers of 0.2 mm thickness with a linear distribution of Young's modulus from 30 to 70 GPa. This configuration was implemented in a 3D model of a restored tooth with realistic geometry to validate the proof-of-concept.

Tissue Interactions in Dense Tissues of the Orofacial Region in Patients with Connective Tissue Dysplasia

AIMS

This study aimed to investigate the rate and quality of maturation of the mineral component of impacted teeth 38 and 48 and a fragment of the human lower jaw with connective tissue dysplasia (CTD) in different periods of postnatal ontogenesis.

METHODS AND MATERIAL

The study involved 102 males (76 with CTD and 26 without CTD), divided into age groups: 31-40, 41-50 and 51-60 years. For medical reasons, teeth 38 and 48 were removed from each patient, as well as a fragment of the alveolar part of the lower jaw in the projection of teeth 38 and 48 measuring 0.5 × 0.5 cm. The odontological parameters, the mineral density of the enamel and the lower jaw, the length and width of the enamel prisms, the spatial organisation of collagen fibrils and the dimensions of the bone plates of the lower jaw were determined.

RESULTS

A decrease in optical density was observed at the age of 41-50 and 51-60 years with dysplasia, which indicated a decrease in mineral density and the presence of total areas of hypomineralisation relative to the age of 31-40 years. In the age groups of 41-50 and 51-60 years, pronounced sclerosis and deformation of the delimiting elements were observed at the border of the connective tissue structures and the periosteum. At the age of 31-40 years, the level of stratification of the bone plates was local; after 40 years, it was generalised.

CONCLUSIONS

Progressive osteoporosis of the lower jaw and incomplete amelogenesis are obstacles to the correct and harmonious eruption of the lower 'wisdom' teeth after 30 years.

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.

Bio-inspired nacre-like zirconia/PMMA composites for chairside CAD/CAM dental restorations

OBJECTIVES

To introduce a versatile fabrication process to fabricate zirconia/PMMA composites for chairside CAD/CAM dental restorations. These zirconia composites have nacre-like lamellar microstructures, competent and tooth-matched mechanical properties, as well as crack resistance behaviours.

METHODS

Bi-directional freeze casting was used to fabricate ceramic green bodies with highly aligned lamellar structure. Pressure was then applied to control the ceramic volume fraction. PMMA was infiltrated into the ceramic scaffold. Mechanical tests including 3-point bending, Vickers hardness, and fracture toughness were performed on the composites. The machinability of the composites was also characterised.

RESULTS

Two types of nacre-like zirconia/PMMA composites, i.e., 3Y-YZP/PMMA and 5Y-PSZ/PMMA composites were fabricated. The microstructure created was similar to the 'brick and mortar' structure of nacre. Excellent flexural strength (up to 400 MPa and 290 MPa for 3Y-TZP/PMMA and 5Y-PSZ/PMMA composite, respectively), tuneable hardness and elastic modulus within the range similar to enamel, along with improved crack-resistance behaviour were demonstrated on both zirconia composites. In addition, both zirconia/PMMA composites showed acceptable machinability, being easy to mill, as would be required to produce a dental crown.

SIGNIFICANCE

Nacre-like zirconia/PMMA composites therefore exhibit the potential for use in the production of chairside CAD/CAM dental restorations.

Microstructural features, physicο-mechanical properties, and wear behavior of dental translucent polychromic multilayer zirconia of hybrid composition prepared by milling technology

OBJECTIVE

The present study determined the mechanical properties and the wear behavior, as results of the micro(nano)structure, of the enamel, transition, and dentine layers, which comprise the polychromic multilayer zirconia materials of hybrid composition fabricated by milling technology.

MATERIALS AND METHODS

Prismatic blocks were fabricated from two commercial pre-sintered dental polychromic multilayer zirconia materials of hybrid composition, IPS e.max ZirCAD Prime (medium and high translucency, from the dentine to the incisal layer) and 3D Pro ML (translucency gradient, from the dentine to the incisal layer) by milling technique, and then, cut into 3 distinct parts to separate the enamel, transition, and dentine layers. The samples were sintered, thermally treated (similarly to the glazing procedure), and polished for characterization. Their microstructure, mechanical properties (determined by nanoindentation and microhardness), and wear behavior (evaluated by scratch test), were examined.

RESULTS

The produced materials had a homogeneous and dense nanostructure, where the grain size decreased from the enamel to dentine layer. The mechanical properties decreased from the dentine to enamel layer. However, the three layers manifested similar dynamic friction coefficient.

CONCLUSION

The differences in the above properties in the three layers negligibly influenced the wear behavior of the entire multilayer zirconia material.

CLINICAL SIGNIFICANCE

The properties of dental restorations produced from polychromic multilayer zirconia of hybrid composition by milling technology (i.e., strong, non-fragile, and esthetic materials), anticipate good performance in oral cavity.

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.

Tooth Diversity Underpins Future Biomimetic Replications

Although the evolution of tooth structure seems highly conserved, remarkable diversity exists among species due to different living environments and survival requirements. Along with the conservation, this diversity of evolution allows for the optimized structures and functions of teeth under various service conditions, providing valuable resources for the rational design of biomimetic materials. In this review, we survey the current knowledge about teeth from representative mammals and aquatic animals, including human teeth, herbivore and carnivore teeth, shark teeth, calcite teeth in sea urchins, magnetite teeth in chitons, and transparent teeth in dragonfish, to name a few. The highlight of tooth diversity in terms of compositions, structures, properties, and functions may stimulate further efforts in the synthesis of tooth-inspired materials with enhanced mechanical performance and broader property sets. The state-of-the-art syntheses of enamel mimetics and their properties are briefly covered. We envision that future development in this field will need to take the advantage of both conservation and diversity of teeth. Our own view on the opportunities and key challenges in this pathway is presented with a focus on the hierarchical and gradient structures, multifunctional design, and precise and scalable synthesis.

Protein adsorption by nanomechanical mass spectrometry: Beyond the real-time molecular weighting

During past decades, enormous progress in understanding the mechanisms of the intermolecular interactions between the protein and surface at the single-molecule level has been achieved. These advances could only be possible by the ongoing development of highly sophisticated experimental methods such as atomic force microscopy, optical microscopy, surface plasmon resonance, ellipsometry, quartz crystal microbalance, conventional mass spectrometry, and, more recently, the nanomechanical systems. Here, we highlight the main findings of recent studies on the label-free single-molecule (protein) detection by nanomechanical systems including those focusing on the protein adsorption on various substrate surfaces. Since the nanomechanical techniques are capable of detecting and manipulating proteins even at the single-molecule level, therefore, they are expected to open a new way of studying the dynamics of protein functions. It is noteworthy that, in contrast to other experimental methods, where only given protein properties like molecular weight or protein stiffness can be determined, the nanomechanical systems enable a real-time measurement of the multiple protein properties (e.g., mass, stiffness, and/or generated surface stress), making them suitable for the study of protein adsorption mechanisms. Moreover, we also discuss the possible future trends in label-free detection and analysis of dynamics of protein complexes with these nanomechanical systems.

Hunter-Schreger Band configuration in human molars reveals more decussation in the lateral enamel of 'functional' cusps than 'guiding' cusps

OBJECTIVES

Enamel prism decussation, which manifests as Hunter-Schreger Bands (HSB), is considered a mechanism to mitigate crack propagation. During the chewing cycle, the 'functional' cusps that are involved in Phase II crushing and grinding experience more complex patterns of stress than do those that 'guide' the molars into occlusion (Phase I). This study examines HSB configuration in the lateral enamel of human molars to identify potential differences between these cusps as predicted from their functional distinctions.

DESIGN

Measurements were recorded from scanning electron micrographs of sections through the mesial cusps of unworn permanent molars. For each section, HSB packing density and the relative thickness of decussated enamel were quantified in the cuspal and middle segments of lateral enamel over the guiding and functional cusps.

RESULTS

No clear trend from first to third molars in HSB configuration was found in either jaw. In maxillary molars, the functional cusp displays higher HSB packing density in the cuspal and middle segments, and relatively thicker decussated enamel in the cuspal segment than does the guiding cusp. In mandibular molars, the functional cusp displays higher HSB packing density in the middle segment than does the guiding cusp, but no difference in relative thickness was found between them. Enamel of mandibular molars shows weaker decussation than maxillary molars.

CONCLUSIONS

The results suggest that guiding cusps are intrinsically more susceptible to crack propagation than functional cusps in human permanent molars. Structural factors such as enamel decussation should be considered when interpreting enamel chipping patterns in dietary contexts.

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.

Structure-function relationships in dog dentin

Investigations into teeth mechanical properties provide insight into physiological functions and pathological changes. This study sought to 1) quantify the spatial distribution of elastic modulus, hardness and the microstructural features of dog dentin and to 2) investigate quantitative relationships between the mechanical properties and the complex microstructure of dog dentin. Maxillary canine teeth of 10 mature dogs were sectioned in the transverse and vertical planes, then tested using nanoindentation and scanning electron microscopy (SEM). Microstructural features (dentin area fraction and dentinal tubule density) and mechanical properties (elastic modulus and hardness) were quantified. Results demonstrated significant anisotropy and spatial variation in elastic modulus, hardness, dentin area fraction and tubule density. These spatial variations adhered to a consistent distribution pattern; hardness, elastic modulus and dentin area fraction generally decreased from superficial to deep dentin and from crown tip to base; tubule density generally increased from superficial to deep dentin. Poor to moderate correlations between microstructural features and mechanical properties (R² = 0.032-0.466) were determined. The results of this study suggest that the other constituents may contribute to the mechanical behavior of mammalian dentin. Our results also present several remaining opportunities for further investigation into the roles of organic components (e.g., collagen) and mineral content on dentin mechanical behavior.

Research of connective tissue dysplasia influence on teething

Purpose

This work aimed to study the rate and quality of maturation of the mineral component of retained teeth 3.8, 4.8 and lower jaw fragment of a human in connective tissue dysplasia in different periods of postpartum ontogenesis.

Methods

The study involved 102 men (76 with connective tissue dysplasia and 26 without connective tissue dysplasia) divided into groups by age: 31–40, 41–50, 51–60 years. One tooth 3.8, 4.8 and a fragment of the alveolar part of the lower jaw in the projection of teeth 3.8, 4.8 0.5*0.5 cm in size were extracted from each examinee for medical indications.

Results

Low optical density values are observed at the age of 41–50 years, at the age of 51–60 years, indicating decreased mineral density and the presence of total areas of hypomineralization from the age 31–40 years in connective tissue dysplasia. At the age of 41–50, 51–60 years, at the boundary of connective tissue structures and periosteum, a pronounced sclerosis and deformation of delineation elements were observed; at the age of 31–40 years, the indicated changes were less pronounced. At the age of 31–40 years, the level of bone plate dissection has a local character, after 40 years, it has a generalized character.

Conclusion

Progressive osteoporosis of the mandible and incomplete amelogenesis are an obstacle to the correct and harmonious teething of the lower wisdom teeth after the age of 30.

Applications of scanning electron microscopy and focused ion beam milling in dental research

The abilities of scanning electron microscopy (SEM) and focused ion beam (FIB) milling for obtaining high-resolution images from top surfaces, cross-sectional surfaces, and even in three dimensions, are becoming increasingly important for imaging and analyzing tooth structures such as enamel and dentin. FIB was originally developed for material research in the semiconductor industry. However, use of SEM/FIB has been growing recently in dental research due to the versatility of dual platform instruments that can be used as a milling device to obtain low-artifact cross-sections of samples combined with high-resolution images. The advent of the SEM/FIB system and accessories may offer access to previously inaccessible length scales for characterizing tooth structures for dental research, opening exciting opportunities to address many central questions in dental research. New discoveries and fundamental breakthroughs in understanding are likely to follow. This review covers the applications, key findings, and future direction of SEM/FIB in dental research in morphology imaging, specimen preparation for transmission electron microscopy (TEM) analysis, and three-dimensional volume imaging using SEM/FIB tomography.

Pathophysiology of Demineralization, Part I: Attrition, Erosion, Abfraction, and Noncarious Cervical Lesions

PURPOSE OF THE REVIEW

Compare pathophysiology for infectious and noninfectious demineralization disease relative to mineral maintenance, physiologic fluoride levels, and mechanical degradation.

RECENT FINDINGS

Environmental acidity, biomechanics, and intercrystalline percolation of endemic fluoride regulate resistance to demineralization relative to osteopenia, noncarious cervical lesions, and dental caries. Demineralization is the most prevalent chronic disease in the world: osteoporosis (OP) >10%, dental caries ~100%. OP is severely debilitating while caries is potentially fatal. Mineralized tissues have a common physiology: cell-mediated apposition, protein matrix, fluid logistics (blood, saliva), intercrystalline ion percolation, cyclic demineralization/remineralization, and acid-based degradation (microbes, clastic cells). Etiology of demineralization involves fluid percolation, metabolism, homeostasis, biomechanics, mechanical wear (attrition or abrasion), and biofilm-related infections. Bone mineral density measurement assesses skeletal mass. Attrition, abrasion, erosion, and abfraction are diagnosed visually, but invisible subsurface caries <400μm cannot be detected. Controlling demineralization at all levels is an important horizon for cost-effective wellness worldwide.

Mechanical properties, microstructure and chemical composition of naked mole rat incisors

The naked mole rat incisors (NMRI) exhibit excellent mechanical properties, which make it a good prototype for design and fabrication of bionic mechanical systems and materials. In this work, we characterised the chemical composition, microstructure and mechanical properties of NMRI, and further compared these properties with the laboratory rat incisors (LRI). We found out that (i) Enamel and dentin are composed of organic matter, inorganic matter and water. The ratio of Ca/P in NMRI enamel is higher than that of LRI enamel. (ii) The dentin has a porous structure. The enamel has a three-dimensional reticular structure, which is more complex, regular and denser than the lamellar structure of LRI enamel. (iii) Enamel has anisotropy. Its longitudinal nano-hardness is greater than that of transverse nano-hardness, and both of them are higher than that of LRI enamel. Their nano-hardness and elastic modulus increase with the increase in distance from enamel-dentin boundary. The nano-hardness of dentin is smaller than that of enamel. The chemical composition and microstructure are considered to be the reasons for the excellent properties of NMRI. The chemical composition and unique microstructure can provide inspiration and guide for the design of bionic machinery and materials.

[The research of the connective tissue dysplasia effect on dental eruption and hard tissues mineralization]

OBJECTIVE

The purpose of this investigation was to explore the quality of 38, 48 teeth's hard tissues at different eruption stages and mandibular bone in different postpartum ontogenesis periods.

MATERIAL AND METHODS

The research involved 102 male patients divided into groups according to their age: 15-20, 21-30 years old, they were extracted one tooth 38, 48 without inflammatory process signs and a fragment of the mandibular bone alveolar part in the projection of the teeth 38, 48 for orthodontic indications. In the comparison group (49 observations without signs of connective tissue dysplasia), in the study group (53 observations with signs of connective tissue dysplasia) we extracted teeth 38, 48 which were in the bone tissue. We analyzed condition of crown and root systems of extracted 38, 48 teeth, densitometric density of mineral component, size of enamel prisms, size of prismatic shells of organic matrix, spatial organization of collagen fibers in bone tissue, size characteristics of bone plates and mineralization centers of bone tissue. Processing of the obtained data was performed by methods of variation statistics using standard packages Microsoft Excel 2008, Statistica 12.0.

RESULTS

The paper reveals one of the surgical dentistry pressing issues related to the tething mechanism of lower human wisdom teeth, considered by the authors from the position of tissue disorders in collagen type 1 observed in connective tissue dysplasia. At age of 15-20 years in connective tissue dysplasia, the enamel prisms hypomineralized areas are generalized; at age of 21-30 years the hypomineralized areas are characterized by local changes. At the age of 15-20 years in connective tissue dysplasia the bone plates splitting is observed at the level of most fibrils, collagen fibers have insufficiently oriented direction in contrast to the age group of 21-30 years where bone plates splitting is characteristic for single fibrils and collagen fibrils are clearly oriented.

CONCLUSION

Morphological and histological changes in teeth 38, 48 and in bone tissue prevent correct and timely teething at 15-20 years and create more favorable conditions for teething at 21-30 years with a slower rate in connective tissue dysplasia, but in both groups teeth eruption occurs under unfavorable anatomic conditions.

[Study of the human enamel prisms maturation nature in different periods of postpartum ontogenesis by atomic force microscopy]

OBJECTIVE

It is necessary to study the human enamel prisms size at different periods of postpartum ontogenesis by atomic force microscopy.

MATERIAL AND METHODS

The study involved 94 males which were divided into groups by age: 15-20, 21-30, 31-40, 41-50, 51-60 years old, each examined male had one 3.8 or 4.8 tooth removed (from the fracture line in the region angle of the mandible, according to orthodontic indications) for medical reasons. The shape, roughness, length and width of the enamel prisms were studied in the Image Analysis NT-VDT program according to the method of Omsk State Medical University.

RESULTS

The enamel prisms structure at all ages has a regular, ordered shape with 6-sided and 7-sided figures. The most constant structure occurs at the age group of 41-50, 51-60 years. The fastest enamel prisms growth occurs in the direction that increases the prism length at all ages. Growth on a plane which increases the prism width is slow at 41-50 years. It is catching up with the growth rate of enamel prisms in length at 51-60 years old. Enamel prisms at 15-20, 21-30 years old stretch faster in the horizontal direction.

CONCLUSION

In maturation process, due to correct and harmonious growth, enamel prisms are timely modified from pyramidal form in the early postpartum period to a prismatic form in the late postpartum period of ontogenesis.