[Effect of pH value and fluoride ions on corrosion resistance of pure Ti and Ni-Cr-Ti alloy in artificial saliva].

OBJECTIVE: To investigate the effect of pH value and fluoride ions on the corrosion resistance of pure Ti and Ni-Cr-Ti alloy in the artificial saliva. METHODS: Electrochemical technique was used to measure the electric potential of corrosion (Ecorr), current density of corrosion (Icorr) and polarization resistance (Rp) of pure titanium and Ti-Ni-Cr alloy in the artificial saliva with different pH value and fluoride concentrations. After electrochemical analysis, microstructure and phase diffraction were examined by FSEM. RESULTS: With the lower pH value, the Ecorr and Icorr of pure titanium and Ti-Ni-Cr alloy increased, the Rp decreased, there was a significant difference (P<0.05). The Ecorr and Icorr increased markedly, the Rp significantly reduced in the artificial saliva containing 0.2% NaF (P<0.01). FSEM showed that pure titanium and Ti-Ni-Cr alloy surface corrosion, pure titanium in the artificial saliva containing 0.2% NaF was most serious. CONCLUSION: Lower pH value decreases the corrosion resistance of pure titanium and Ti-Ni-Cr alloy and the artificial saliva containing fluoride ions decreases the corrosion resistance of pure titanium.

[Study of the correlation between Streptococcus mutans' adhesion and surface corrosion in casting titanium and Ti alloy].

PURPOSE: To investigate the correlation between Streptococcus mutans' adhesion and surface corrosion of the casting titanium and Ti alloy with different kinds of polishing. METHODS: The casting titanium and Ti alloy were respectively processed into size of 30 mm x 8mm x 1mm in tablets. Each material was prepared for 32 specimens, randomly divided into two groups, dealt with mechanical polishing and electrochemistry polishing, and then randomly divided into four groups (blank control, media control, inoculated media control for three months and six months).Four specimens were used in each group under hypoxia conditions. The labeled specimen surfaces were then aseptically placed in the test tube with one transfer per week. The specimens were removed and sterilized. The surface roughness of specimens was measured by FTS i120 contourgraph and the alteration of the surface was observed under SIRION scanning electron microscope. One-way ANOVA was performed with SPSS11.O software package. RESULTS: In casting titanium, blank control media control, inoculated media control for three months and six months showed no influence on Ra value(P>0.05).In Ti alloy, the Ra value of the inoculated media control group was significantly different from those of blank control group(P<0.05) and metal control group(P<0.05). All the specimen surfaces had pits in disorder and in different size. CONCLUSIONS: Streptococcus mutans' adhesion causes surface corrosion of the casting titanium and Ti alloy, and mechanical polishing and electrochemistry polishing have no influence on corrosion.