On surface corrosion of dental ceramics in vitro

Abstract

Purpose: The aims of this thesis were: To assess the effects of in vitro corrosion of various dental ceramic on surface characteristics like topography, surface free energy and protein adsorption materials, but also to study possible differences in surface elemental composition and ion dissolution in an aqueous corrosive media.Materials and methods: Dental ceramic materials ranging from glass-phased to oxide ceramics of equal initial surface conditions were exposed to high- and low intensity in vitro corrosion, as well as contact with saliva and plasma. The 3-D surface - architecture was studied by laser profilometry and SEM, and the surface free energy calculated from the Young-DuprÈ equation after surface contact angle measurements using different probe liquids. The protein adsorption before and after corrosion, and saliva/plasma incubation was analysed by SDS-PAGE and the adsorbed proteins identified by Western blotting technique. The surface elemental composition of the dental ceramics was studied by ESCA, and the effects of different corrosion intensities evaluated. Qualitative and quantitative characteristics of ion-dissolution into a surrounding media were analysed by ICP-OES, and compared to initial elemental composition and corrosive solution intensity.Results: In comparison to oxide ceramics, the glass-phased ceramics displayed a higher susceptibility to surface degradation after high-intensity corrosion, whereas the surface topography of micro crystalline and non-crystalline ceramics were less influenced by corrosion. In spite of surface structural changes taken place at corrosion, the TSFE did not differ significantly between the different ceramics, before or after corrosion. Incubated with saliva or plasma, inter-individual differences in protein adsorption were observed. All plasma proteins, but none of the specific salivary proteins, were surface-bound onto alumina and zirconia ceramics. The permanency of the oxide ceramics manifested through low surface degradation and leaching-out values,while the glass-phased ceramics displayed overall higher values. Increased acidity and temperature of the corrosion media increased ion-leaching.Conclusion: The degree of surface topographical changes due to corrosion was related to the characteristic microstructure and only minor changes occurred. Whereas the TSFE remained virtually unchanged at corrosion (50±5 mN/m), the acid-basic (y+ and y-) component of TSFE, were significantly changed. The differences in protein adsorption among the various ceramics due to corrosion were probably caused by the changes in surface elemental composition, shown to take place at high-intensity corrosion and to a lower extent at low-intensity corrosion. Although traditionally considered as inert materials, the glass-phased ceramics in specific, were found to leach alkali, alkaline-earth, alumina and silicon, and simultaneously display of increased silica content in surface layers. Everything considered, the bioinert concept associated with bio-ceramics should be re-evaluated and given a relative rather than absolute meaning.