Jan Ryszard Dąbrowski

Porosity structure and mechanical properties of vitalium-type alloy for implants

Abstract Results of porosity investigations performed on a Co–Cr–Mo alloy for implants, produced using powder metallurgy methods, are presented. Nonetched polished surfaces of as-sintered, rotary cold-repressed, and heat-treated material, respectively, were examined. Both, the face and axial section surfaces of cylindrical specimens were tested. Porosity assessment was accompanied by mechanical tests. It was demonstrated on the basis of the results obtained that rotary cold repressing and subsequent heat treatment decreases the porosity and improves the homogeneity, which, consequently, improves the mechanical properties of the material tested.

Biocorrosion of 316LV steel used in oral cavity due to Desulfotomaculum nigrificans bacteria.

Corrosion processes of metallic biomaterials in the oral cavity pose a significant limitation to the life and reliable functioning of dental materials. In this article, the influence of environment bacteria Desulfotomaculum nigrificans sulfate reducing bacteria on the corrosion processes of 316LV steel was assessed. After 14 and 28 days of contact of the material with the bacterial environment, the surfaces of the tested biomaterial were observed by means of confocal scanning laser microscopy, and their chemical composition was studied using X-Ray Photoelectron Spectrometry and a scanning transmission electron microscopy. Corrosive changes, the presence of sulfur (with atomic concentration of 0.5%) on the surface of the biomaterial and the presence of a thin oxide layer (thickness of ∼20 nm) under the surface of the steel were observed. This corrosion layer with significant size reduction of grains was characterized by an increased amount of oxygen (18% mas., p < 0.001) in comparison to untreated 316LV steel (where oxygen concentration - 10% mas.). Image analysis conducted using APHELION software indicated that corrosion pits took up ∼2.8% of the total tested surface. The greatest number of corrosion pits had a surface area within the range of 100-200 μm2 .

Tribological Properties of Selected Self-Made Solutions of Synthetic Saliva

The present paper describes the results of tests on the influence of selected self-made solutions of synthetic saliva on tribological characteristics of implant materials on the example of the Co-Cr-Mo alloy. The used saliva substitutes were prepared on the basis of gums (xanthan, guar, arabic and carob bean) dissolved in saline buffer. Analysis of the values of the coefficient of friction and the wear of the tested dental alloy in tested solutions was performed. Different values of the coefficient of friction were observed for friction pairs tested in individual solutions. Its lowest values were achieved during tests using xanthan gum with SDS (sodium dodecyl sulfate) addition, and the highest values were achieved for xanthan gum. As regards wear analysis, its lowest value was registered during lubrication with natural saliva. Among saliva substitutes, the lowest value of mass wear of dental alloy was observed in solution of xanthan gum, and the highest value was registered for carob bean gum. After friction tests, elements of the friction pair were subjected to microscope analysis using the Olympus BX61 optical microscope.

The Role of Oral Cavity Biofilm on Metallic Biomaterial Surface Destruction–Corrosion and Friction Aspects

Metallic biomaterials in the oral cavity are exposed to many factors such as saliva, bacterial microflora, food, temperature fluctuations, and mechanical forces. Extreme conditions present in the oral cavity affect biomaterial exploitation and significantly reduce its biofunctionality, limiting the time of exploitation stability. We mainly refer to friction, corrosion, and biocorrosion processes. Saliva plays an important role and is responsible for lubrication and biofilm formation as a transporter of nutrients for microorganisms. The presence of metallic elements in the oral cavity may lead to the formation of electro-galvanic cells and, as a result, may induce corrosion. Transitional microorganisms such as sulfate-reducing bacteria may also be present among the metabolic microflora in the oral cavity, which can induce biological corrosion. Microorganisms that form a biofilm locally change the conditions on the surface of biomaterials and contribute to the intensification of the biocorrosion processes. These processes may enhance allergy to metals, inflammation, or cancer development. On the other hand, the presence of saliva and biofilm may significantly reduce friction and wear on enamel as well as on biomaterials. This work summarizes data on the influence of saliva and oral biofilms on the destruction of metallic biomaterials.

Use of magnetic nanoparticles as a drug delivery system to improve chlorhexidine antimicrobial activity

Nanotechnology offers new tools for developing therapies to prevent and treat oral infections, particularly biofilm-dependent disorders, such as dental plaques and endodontic and periodontal diseases. Chlorhexidine (CHX) is a well-characterized antiseptic agent used in dentistry with broad spectrum activity. However, its application is limited due to inactivation in body fluid and cytotoxicity toward human cells, particularly at high concentrations. To overcome these limitations, we synthesized nanosystems composed of aminosilane-coated magnetic nanoparticles functionalized with chlorhexidine (MNP@CHX). In the presence of human saliva, MNPs@CHX displayed significantly greater bactericidal and fungicidal activity against planktonic and biofilm-forming microorganisms than free CHX. In addition, CHX attached to MNPs has an increased ability to restrict the growth of mixed-species biofilms compared to free CHX. The observed depolarization of mitochondria in fungal cells treated with MNP@CHX suggests that induction of oxidative stress and oxidation of fungal structures may be a part of the mechanism responsible for pathogen killing. Nanoparticles functionalized by CHX did not affect host cell proliferation or their ability to release the proinflammatory cytokine, IL-8. The use of MNPs as a carrier of CHX has great potential for the development of antiseptic nanosystems.

Biotribological properties of dentures lubricated with artificial saliva

This paper presents the results of tests on the effect of adsorbed films of saliva substitutes on the tribological characteristics of metal alloys based on the example of stainless steel 316LVM and two alloys, Co–Cr–Mo and Ti‒6Al–4V. Saliva substitutes were prepared based on animal mucin and xanthan gum dissolved in phosphate buffered saline (PBS). The adsorbed salivary films significantly reduced the coefficient of friction of the tested biomaterials. Low values of coefficient of friction have been achieved during the tests using PBS + mucin. The analysis of wear of tested materials showed lowest values in the process of friction using PBS + mucin + xanthan gum. An IR analysis of the studied surfaces confirmed the presence of wear marks on the adsorbed salivary films.

Assessment of aliphatic poly(ester-carbonate-urea-urethane)s potential as materials for biomedical application

Selected mechanical and biological properties of biodegradable elastomeric poly(ester-carbonate-urea-urethane)s (PECUUs) point towards their potential to be applied as scaffolds in tissue engineering. Here we explore their medical applicability taking into account their hemocompatibility and cytotoxicity. The influence of the ester monomer (derivatives of adipic and succinic acids), as well as diisocyanate type (IPDI and HDI) on the investigated PECUUs properties is presented. The presence of aliphatic diisocyanates, cyclic IPDI or linear HDI, governs the adhesion of Candida cells to these polymers offering the possibility to control the biofilm formation on their surface. In comparison to the linear form, cyclic diisocyanates with pentamethylene succinate or adipate fragments had two to three times lower biofilm mass formation on their surface. Reduced hemoglobin release from red blood cells observed during incubation of tested polymers with human erythrocytes suspension indicates their potential biocompatibility with human tissues. PECUUs were also able to support the growth of human keratinocytes HaCaT on their surface when coated with collagen. In effect, IPDI derivatives might possess a high potential for use in biomedical applications.

TiC-composite materials in applications for kinematic denture connections

PURPOSE This paper presents an own proposal for the construction of a ball latch intended for use in prosthetic dentistry. Attention was paid to the existing commercial constructions of elements of the same type, indicating their advantages and disadvantages. Based on the analysis of the present solutions, own ones were proposed. MATERIALS AND METHODS The following materials were chosen for the tests: pure titanium, 316 L V steel, Ti15Mo2.8Nb obtained using powder metallurgy and through mechanical alloying, 10 and 20% of titanium carbide - obtained using powder metallurgy, as well as 10 and 20% of graphite - obtained using powder metallurgy. For the prepared materials, tribological tests were performed using a friction simulator in a ring/shield system. RESULTS Fairly extensive tests were performed to verify the suitability of the selected material for use in the specific conditions of the oral cavity. The performed tests showed that the proposed material is not only beneficial in relation to the existing commercial dental alloys but also meets the general criteria set for this type of elements. CONCLUSIONS A more beneficial use of two-part ball latches (two key parts - patrix, matrix) was noticed in comparison to latches consisting of three parts (patrix, insert, matrix). On the basis of the obtained test results, it can be concluded that the proposed own design of a ball latch is a good alternative for traditional constructional and material solutions of commercial ball latches.

Fretting Wear of NiTi - Shape-Memory Alloy

This study presents the results of tests of friction processes and fretting wear of NiTi shape-memory alloy, which is used in orthodontics and surgery. This research problem is significant because nickel ions released as a result of nitinol wear exhibit toxic action in the human body. Knowledge about wear mechanisms will allow for more effective prevention of processes leading to the destruction of elements of medical constructions and extend the time of their safe operation. Tests were performed on a pin-on-disc fretting tester under dry friction conditions and in a simulated oral cavity environment. Wear assessments were conducted on the basis of microscopy (SEM, TEM, CLM). Obtained results indicate that friction conditions have a significant impact on the mechanism of fretting wear, which is primarily related to oxidation and phase transformation of nitinol.

The method of fretting wear assessment with the application of 3D laser measuring microscope

Degradation processes of implant materials have a significant effect on the reactions taking place around them. Processes related to mechanical wear, corrosion and tribological wear can be distinguished here. The phenomenon of fretting has a particularly significant impact on changes around the implant. The fretting process has a mechanism specific to it, based on simultaneous joining and intensive oxidation. This paper presents a new method for fretting wear assessment was developed, based on the application of an Olympus Lext OLS4000 confocal laser scanning microscope in tests. The main advantage of the described method is that measurements can be performed in three dimensions at very high resolution. However the greatest innovation of this method of fretting wear testing is the capability of inputting digital threshold values of a given sample’s profile. This allows for easy differentiation between material depleted and accrued as a result of fretting.