In vitro corrosion resistance of titanium made using different fabricationmethods

The corrosion of cast or milled ASTM Grade II CP titanium with different su rface conditions was studied by potentiodynamic anodic polarization and imm ersion testing. Specimens were fabricated using three dental titanium casti ng systems and from machined titanium. Three surface conditions were tested : (1) sandblasted with surface reaction layers remaining; (2) polished surf ace without surface reaction layers; and (3) sandblasted surface without su rface reaction layers. An acidic saline solution (0.1 M lactic acid/0.1 M N aCl [pH = 2]) and an artificial saliva were used as the corrosion media. An odic polarization was performed starting at 50 mV below the rest potential and terminating at +2250 mV vs Ag/AgCl. Two surface conditions (sandblasted with the surface reaction layers and polished without such layers) were ex amined in the immersion test. Specimens were immersed in the corrosion medi a at 37 degrees C for six months. The recovered solution was analyzed by an atomic absorption spectrophotometer for titanium dissolution. A distinctiv e passive region on the polarization diagram, ranging from similar to 0 to similar to +1300 mV, was observed for all specimens in both media. Great si milarity was observed for all the sandblasted specimens which had larger pr imary passive current densities and passive regions compared to the polishe d ones. A current density peak at similar to +1600 mV seen for all the spec imens with sandblasted surfaces was less well defined for the polished spec imens. Immersion testing in the acidic saline solution revealed no signific ant differences among the polished specimens. A significant increase (P < 0 .05) in titanium dissolution was found for the sandblasted specimens with s urface reaction layers remaining on the surfaces made with phosphate-bonded SiO2/Al2O3 investment compared to the polished ones. Significant differenc es were also found between sandblasted specimens with the surface reaction layers resulting from different investment materials and different casting methods. Measurable amounts of titanium were not found for all specimens in the artificial saliva after six months. It is evident that the corrosion b ehavior of cast CP titanium is similar to that of machined titanium. The su rface roughness appears to be a more prominent factor than do the surface r eaction layers on the polarization behavior of the CP titanium under the pr esent experimental conditions. Surface roughness and the presence of the su rface reaction layers both affect the dissolution of titanium. (C) 1998 Els evier Science Ltd. All rights reserved.