Procesy korozji i zużycia tribologicznego wybranych biomateriałów metalowych w środowisku śliny i jej substytutów

Postępy w ortodoncji i protetyce stomatologicznej w dużym stopniu zależą od rozwoju nowych materiałów i konstrukcji oraz poznania złożonych procesów ich adaptacji tkankowej. Związane z tym zjawiska tarcia i korozji w dużym stopniu decydują o trwałości i jakości biomateriałów metalowych, wpływając tym samym na komfort ich użytkowania. Zagadnienia te są przedmiotem wielu badań. W pracy przedstawiono zagadnienia dotyczące niszczenia tribologicznego i korozyjnego materiałów na złącza protez ruchomych i elementów aparatów ortodontycznych, z uwzględnieniem roli śliny i biofilmu. Badaniom poddano wybrane biomateriały metalowe: stal 316LV, stop Co-Cr-Mo i stop Ti-6Al-4V.

Corrosion and friction wear processes of selected metallic biomaterials in the environment of saliva and its substitutes Advances in orthodontics and dental prosthetics largely depend on the develop- ment of new materials and designs as well as on learning about the complex pro- cesses of their tissue adaptation. The friction and corrosion phenomena associated with this decide the lifetime and quality of metal biomaterials to a large extent, which also affects the comfort of their use. These problems are the subject of many studies. However, most of them are focused on tests performed in fluids simulating natural saliva, with physicochemical and rheological properties that vary greatly from those of their natural standard of reference. Such an approach does not enable reliable evaluation of friction, wear and corrosion with regard to the tested metallic biomaterials. The tribological properties of a system containing saliva largely de- pend on the chemical composition, which shapes, among other things, saliva’s rheological characteristics. Besides saliva’s viscoelastic properties, processes of biological boundary layer formation play an important role in the microbiologically diverse environment of the oral cavity. The presence of biofilm on the surface of metallic biomaterials may speed up corrosion processes, including biologically induced corrosion. The environment of the oral cavity, as well as the presence of saliva and mi- croorganisms, play an important role in preventing these processes. Salivary secre- tion disorders (dry mouth) intensify the processes of biomaterials’ destruction. Substitute formulas are used in such cases. However there is an absence saliva substitutes meeting protection requirements with regard to friction, wear and corro- sion of biomaterials. In relation to the above, this paper presents an attempt to develop original sali- va formulas. It was proposed to use ingredients with confirmed anti-microbial properties in the composition of these formulas, besides mucin and xanthan gum - which have a particular influence on rheological and tribological characteristics. For this purpose, an antibacterial peptide analog and gold-coated nanostructures were introduced. Comprehensive tests of physicochemical and rheological properties were per- formed on the prepared saliva compositions (including of viscoelasticity, in partic- ular). Obtained test results demonstrated that the proposed formulas were charac- terized by properties similar to those of natural saliva. Problems concerning tribological and corrosive destruction of materials used to make joints of mobile prosthetics and parts of orthodontic appliances are pre- sented in this paper, with consideration of the role played by saliva and biofilm. Selected metallic biomaterials were tested: 316LV steel, Co-Cr-Mo alloy and Ti- 6Al-4V alloy. Obtained results of tribological tests indicated reduction of re- sistance to motion of the tested tribological systems, particularly in the environ- ment of the mucin-based composition. In turn, the lowest tribological wear among the tested biomaterials was noted in tests performed in the environment of mucin and xanthan gum. It was observed that wear processes are of a combined, predom- inantly abrasive and adhesive, nature. In addition, it was demonstrated that reduc- tion of resistance to motion and of tribological wear can be already achieved in the presence of the adsorptive layers coating the surfaces of tested metallic biomateri- als. Fretting and fretting-corrosion tests, the results of which made it possible to develop a phenomenological model of the phenomena occurring over the course of these processes as well as their effect on the operation of metallic biomaterials and on the body, were a valuable supplement to the problems discussed above. An important aspect of research was to assess the potential for occurrence of the biocorrosion process induced by the activity of sulfate-reducing bacteria (SRB) on the surface of metallic biomaterials. The negative impact of Desulfotomaculum nigrificans sulfate-reducing bacteria on surfaces of metallic biomaterials has been demonstrated to be the cause of corrosion pitting and an elevated number of bio- corrosion nuclei over the course of the bacteria’s contact with the tested biomateri- als. Biological tests have demonstrated that the introduction of synthetic LL-37 peptide analog and gold-coated nanoparticles endows formulas with antimicrobial action with respect to pathogens in the oral cavity and reduces the adsorption of these pathogens to surfaces of dental prosthetics. To summarize the presented test results, it must be stated that, thanks to their multi-functional action, the developed synthetic saliva formulas can be used by persons wearing dental prosthetics, orthodontic appliances as well as by patients with salivary secretory disorders. These formulas require further tests, particularly with regard to their biological assessment and potentials for application. The inter- est of manufacturers in such formulas that has already been documented is a hard argument confirming that both the studies until now and future research are justi- fied.