engleski

Changes of Co-Cr-Mo alloy surface and composition after biocorrosion in „ plaque“ and „ saliva“ solutions

Introduction: Metal ions released from dental alloys may be of clinical concern due to allergogenic, mutegenic and cytogenicproperties. Corrosion behaviour in oral fluids is strongly influenced by microstructural characteristics and surface properties of a dental alloy. Aim of the study: To examine the surface of cast CoCrMo alloy prior and after exposure into different solutions mimicking oral conditions. Materials and Methods: The cast and electropolished specimens of CoCrMo alloy (Wironit® ; , extra hard) were examined by SEM with EDS and by AFM prior and after immersion into two solutions simulating saliva („ saliva“ ) and dentobacterial plaque („ plaque“ ) for 30 days at 37 º ; C. To find the same surface after immersion, each sample was marked prior AFM imaging and soaking. Results: The surface of cast and electropolished specimens prior the contact with corroding solutions was characterized with at least 3-4 different phases: undulating surface corresponding to dendrites (matrix), clusters of nanocrystallites (islands) corresponding to interdendritic phase and some high conical crystallites emerging from both, interdendritic space and the matrix. Also some very small crystallites could also be observed. The undulating surface (matrix) was twice richer with Co than Cr, while the interdendritic phase had almost equal contents og Co and Cr. However, some cristallytes were dissolved after corrosion, but some new phases (dense sprinkles of very small crystallites) appeared. The respective alloy peaks in the EDS spectrum revealed that new phases are the result of a corrosion - primarily of metal dissolution, break-down of an oxide layer and metal salt formation. The presence of some elements from the corroding solution was registered on the alloy surface, as well. Conclusions: Probably metal salts (anions from corroding solutions) were binded at the surface as a new phase. Electrochemical behaviour of CoCrMo alloys is clearly affected by pH and composition of the fluids. It is obvious that some complex mechanisms involving reactions between ionic species are dominating the interfacial processes, which in turn affect the morphology and the composition of the phases formed.

Cobalt-chromium alloy ; corrosion ; surface phases and composition

nije evidentirano