Impact of Fluoride on the Corrosion Pattern of Pure Titanium and Titanium Alloy Combined with Nickel-Chromium Alloy and Gold Alloy: An In-vitro Study

Introduction: Currently, Fluoride ions are added to commercially available tooth paste, mouth washes and cariostatic gels for their prophylactic action. However, the preventive effect may also be accompanied by the corrosive activity, through infiltration of fluoride-containing saliva in the contact between crowns and bridges or into the implant supported structure.

Aim: To evaluate the corrosion action of Sodium Fluoride (NaF) on Pure Titanium (PT) and its alloy coupled with Nickel-Chromium (Ni-Cr) alloy (NC) and Gold (Au) Alloy (GA).

Materials and Methods: This in-vitro study was conducted in the Department of Prosthodontics at Central Electrochemical Research Institute, Karaikudi, Tamil Nadu, India. The duration of the study was six months, from April 2010 to September 2010. A total of 48 specimens were categorised under four groups. The four groups included for the study were pure group I (PT+GA), group II (PT+NC alloy), group III {Titanium Alloy (TA)+GA) and group IV (TA+NC alloy}. The specimens under each group were divided into half and were immersed in 100 mL of either artificial saliva or artificial saliva with 1000 Parts Per Million (ppm) fluoride. The current was passed at a scanning rate of 1800 mV/hour for 60 minutes and changes in corrosion potential were observed. The elemental release analysis test was conducted by using inductively coupled plasma-mass spectrometry to quantitatively analyse the elements (metal ions) released in the test solution from the galvanic coupling alloys. In order to evaluate the corrosion behaviour, the surfaces of the specimens were examined with an optical microscope (Eclipse LV100D, Nikon, USA). Analysis of Variance (ANOVA) was done for intergroup comparison. Statistical significance was set at 5%.

Results: The mean value of corrosion of PT+GA and PT+NC was 13 μg/cm2 and 27 μg/cm2 respectively. The mean value of corrosion of TA+GA and TA+NC was 12 μg/cm2 and 24 μg/cm2 respectively, in artificial saliva without sodium fluoride. In the presence of sodium fluoride, the mean value of corrosion of PT+GA and PT+NC was 17 μg/cm2 and 60 μg/cm2 respectively, and the mean value of corrosion of TA+GA and TA+NC was 15 μg/cm2 and 41 μg/cm2. The PT and TA specimens coupled with NC alloy specimens showed more corrosion in saliva either with or without sodium fluoride compared to GA.

Conclusion: The NC alloy specimens coupled with PT and TA specimens showed severe pitting corrosion in artificial saliva containing sodium fluoride.