Investigations of the Corrosive Effects of Fluoride on Titanium

Objectives: High fluoride concentration and acidic pH are known to impair the corrosion resistance of titanium. The effects of fluoride-containing caries-preventive prophylactic rinses and gels on the surface structure of titanium used for implants or other dental devices were investigated. Methods: Polished titanium discs (CP grade 4, CAMLOG Biotechnologies AG) were treated for 1 hour with one of the following solutions: mouthwash (250 ppm F^-), gel containing 12500 ppm (1.25 %) fluoride, and a solution of 1% NaF (pH 4.5). The changes in the surface structure were determined by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Human epithelial cell attachment and proliferation were investigated by scanning electron microscope (SEM), MTT measurement and protein content assay. Results: The treatment of titanium surface with high fluoride content gel and acidic NaF solution resulted in a strong corrosion and a modification of the composition of the surface. XPS spectra revealed formation of fluoride containing complexes (NaF and Na₂TiF₆) bound strongly to the surface and the AFM measurements indicated an increase in the roughness (R_a) of the surfaces (2 times for gel and 10 times for 1% NaF solution) as compared to the control surface. In case of mouthwash no change was detected. MTT and protein content measurements proved that epithelial cell attachment (1 day observation) on titanium surface was not disturbed by the use of high fluoride containing gel and 1% NaF solution. Cell proliferation (3 day observation) was decreased only in case of gel treated samples. Conclusion: These results suggest that it is advisable to take into consideration the adverse effects of high fluoride concentration and low pH when applying prophylactic gels in case of patients having implants or other dental appliances made of titanium. Supported by the GVOP-3.2.1.-2004-04-0408/3.0 project funded by the EC and the Hungarian Ministry of Economy.