Nadezda O. Bessudnova

A comparative evaluation of mechanical properties of nanofibrous materials

Restoration or replacement of lost or damaged hard tooth tissues remain a reconstructive clinical dentistry challenge. One of the most promising solutions to this problem is the development of novel concepts and methodologies of tissue engineering for the synthesis of three-dimensional graft constructs that are equivalent to original organs and tissues. This structural and functional compatibility can be reached by producing ultra-thin polymer filament scaffolds. This research aims through a series of studies to examine different methods of polymer filament material special preparation and test mechanical properties of the produced materials subjected to a tensile strain. Nanofibrous material preparation using chemically pure acetone and mixtures of ethanol/water has shown no significant changes in sample surface morphology. The high temperature impact on material morphology has resulted in the modification of fiber structure. In the course of mechanical tests it has been revealed the dependence of the material strength on the spinning solution compositions. The results achieved point to the possibility to develop nanofibrous materials with required parameters changing the methodology of spinning solution production.

A new x-ray adhesive system with embedded nanoparticulate silver markers for dental applications

In the present study a new adhesive system with embedded PVP-stabilized nano-particulate silver markers has been designed. Nanosized silver was used as a radio-opaque contrast material in SEM examination of adhesive system in dentine. It was studied the impact of nano-particulate silver fillers on rheological properties of adhesive system and its penetration in dentine volume. A SEM comparative evaluation of resin replicas produced using adhesive system with embedded silver nanoparticles and that without ones was carried out. It was shown that embedding of silver nanoparticles into adhesive system did not make its penetration worse. It was established that embedding of nanosized silver changed adhesive system morphology. The methodology that allows visualizing interfaces and intermediate layers between dentine, adhesive system and restorative material using silver nano-particulate markers was developed and approved. Silver nanoparticles were used to compare the objective depth of penetration of adhesive systems of different generations in root dentine with differently oriented dentinal tubules, bonding resin delivery and gravity.

Application of x-ray nano-particulate markers for the visualization of intermediate layers and interfaces using scanning electron microscopy

In this study the methodology of biological sample preparation for dental research using SEM/EDX has been elaborated. (1)The original cutting equipment supplied with 3D user-controlled sample fixation and an adjustable cooling system has been designed and evaluated. (2) A new approach to the root dentine drying procedure has been developed to preserve structure peculiarities of root dentine. (3) A novel adhesive system with embedded X-Ray nanoparticulate markers has been designed. (4)The technique allowing for visualization of bonding resins, interfaces and intermediate layers between tooth hard tissues and restorative materials of endodontically treated teeth using the X-ray nano-particulate markers has been developed and approved. These methods and approaches were used to compare the objective depth of penetration of adhesive systems of different generations in root dentine. It has been shown that the depth of penetration in dentine is less for adhesive systems of generation VI in comparison with bonding resins of generation V, which is in agreement with theoretical evidence. The depth of penetration depends on the correlation between the direction of dentinal tubules, bonding resin delivery and gravity.

Effect of thermal shock loadings on stability of dentin-composite polymer material adhesive interfaces

In the past several decades the problem of longevity and durability of adhesive interfaces between hard tooth tissues and composite resin-based materials are of great interest among dental researchers and clinicians. These parameters are partially determined by adhesive system mechanical properties. In the present research project nanoindentation has been examined to test hardness of dental adhesive systems. A series of laboratory experiments was performed to study the effect of light curing time and oxygen inhibition phenomenon on light-cured adhesive material hardness. An adhesive system AdperTM Single Bond (3M ESPE) was selected as a material for testing. The analysis of experimental data revealed that the maximum values of hardness were observed after the material had been light-cured for 20 seconds, as outlined in guidelines for polymerization time of the adhesive system. The experimental studies of oxygen inhibition influence on adhesive system hardness pointed out to the fact that the dispersive layer removal led to increase in adhesive system hardness. A long – time exposure of polymerized material of adhesive system at open air at room temperature resulted in no changes in its hardness, which was likely to be determined by the mutual effect of rival processes of air oxygen inhibition and directed light curing.

Application of color image processing and low-coherent optical computer tomography in evaluation of adhesive interfaces of dental restorations

Durability of bonded interfaces between dentin and a polymer material in resin-based composite restorations remains a clinical dentistry challenge. In the present study the evolution of bonded interfaces in biological active environment is estimated in vivo. A novel in vivo method of visual diagnostics that involves digital processing of color images of composite restorations and allows the evaluation of adhesive interface quality over time, has been developed and tested on a group of volunteers. However, the application of the method is limited to the analysis of superficial adhesive interfaces. Low-coherent optical computer tomography (OCT) has been tested as a powerful non-invasive tool for in vivo, in situ clinical diagnostics of adhesive interfaces over time. In the long-term perspective adhesive interface monitoring using standard methods of clinical diagnostics along with colour image analysis and OCT could make it possible to objectivise and prognosticate the clinical longevity of composite resin-based restorations with adhesive interfaces.

Mechanical properties of adhesive system with a silver nanoparticulate filler: an experimental study

In the present study nanoparticulate silver filler influence on adhesive system mechanical properties has been researched. In the course of laboratory experiments it has been shown that adhesive system mechanical properties are changing in a different manner as soon as silver percentage in adhesive system is increasing. It has been established that 0,5 –1% silver nanoparticle embedding into adhesive system that is enough to make the material X-Ray-sensitive holds its mechanical properties close to the optimum. Thus, the mechanical properties are enhancing in comparison with those of adhesive system without silver nanoparticles. Research findings point to the opportunity to use nanoparticulate silver as a filler while producing X-ray adhesive systems.

SEM Evaluation of Nanoparticulate Silver Penetration into Dentine Collagen Matrix

In the present study a novel approach to caries management based on the application of nanoparticles of different nature to increase the mineral phase of demineralized dentin has been developed. Silver nanoparticles have been tested as a material for dentine matrix infiltration. Research findings clearly show that collagen fibers of demineralized dentine could be considered as a scaffold for mineral component delivery and the place where mineral growth can occur.

XRD study of calcium-phosphate crystal formation on dentine surface

The characteristic sizes of elementary crystallites in the composition of dentine substrate with calciumphosphate crystal formations on its surface have been studied using x-ray diffraction (XRD) analysis for phase identification. Most probable mechanisms explaining changes in elementary crystallite sizes in the process of crystal formation were discussed.

The nature of calcium-phosphate crystal formations grown on dentine surface

Laboratory experiments conducted in Saratov State University in the first half of 2012 revealed crystal formations on the surface of etched dentine after it had been exposed to 95% ethanol in solution for 30 days at room temperature. It was discovered that the structures observed were calcium-phosphate crystals. The nature of crystal formation on rough dentine surface was described based on substance diffusion in solution, which resulted in dentine becoming spatially inhomogeneous over time. The crystal formation was established to be determined by the limited ion redistribution in dentine material.

3D visualization of calcium-phosphate crystals observed on dentine surface

Crystal formations were observed on the surface of etched dentine after it had been exposed to 95% ethanol in solution for 30 days at room temperature. 3D visualization of surface formations was carried out using a scanning electron microscope and Alicona 3D MeX software (Alicona GmbH). Metric characteristics of the mentioned above structures were evaluated and the nature of possible errors on the steps of model design was studied. It was shown that the shape of crystal models were likely to be approximated by ellipsoid segments.