Effect Of Chloride Ion On The Corrosion Resistance Of Dental Casting Metal

Objectives：To study titanium alloy, cobalt-chromium alloy and pure titanium’s corrosionresistence in artificial saliva with different NaCl concentration.Methods：Three kinds of metal were casted18each and were divided into2groups afterthe same surface pretreatment. In the first group three metal’s electrochemicalimpedance spectroscopy were tested in artificial saliva with different NaClconcentration (0.9%、2.0%、3.0%). The parameters of solution resistance(Rs)、charge-transferred resistance(Rct)、passive film resistance(RP)、electrical double layercapacitor(CPEdl)、 passive film capacitor(CPEP)、interface electrical double layerdiffusion index(ndl) and passive film electrical double layer diffusion index(np) wereacquired according to the fitting result of the equivalent circuit. In the other groupthree metal’s surface roughness were measured after immersed for3weeks and thentheir surface morphology was observed by field emission scanning electronmicroscope(FESEM). The experimental results were analyzed by one-way anovaanalysis.Results：1. Electrochemical impedance spectroscopy test：1)With the concentration of chloride increasing, Rsvalue、Rctvalue、Rpvalue andnpvalue of three types of metal decreased, CPEPvalue increased, CPEdlvalue and ndlvalue had no obvious regularity.2)Titanium alloy group: There was no difference for titanium alloy’s n1value、CPEpvalue in different NaCl concentration (P>0.05). There was statistical differencefor other parameters (P<0.05). Cobalt-chromium alloy group： There was nodifference for Co-Cr’s n1value in different NaCl concentration(P>0.05), Rctvalue in the chloride concentration of0.9%and2.0%(P>0.05).There was statistical differencefor other parameters (P<0.05). Pure titanium group:There was no statistical differencefor pure Ti’s ndlvalue、Rctvalue in different NaCl concentration(P>0.05). There wasstatistical difference for other parameters (P<0.05).3)There was no statistical difference for three kinds of metal’s Rsvalue、ndlvalue、 npvalue in different NaCl concentration(P>0.05).There was statisticaldifference for other parameters (P<0.05).2．Immersion corrosion test：The surface roughness of metal was increased with the NaCl concentrationincreasing.The surface roughness of the cobalt-chromium alloy group and puretitanium group had no statistical difference between before and after being immersedat the NaCl concentration of0.9％(P>0.05);There was no statistical difference forcobalt-chromium alloy group and pure titanium group at the NaCl concentration of0.9％(P>0.05).The surface roughness of the pure Ti’s2.0%NaCl group and0.9%NaCl group,3.0%NaCl group and2.0%NaCl group had no statistical difference(P>0.05).Others had statistical difference(P<0.05).Conclusions：1) The corrosion resistance of three types of metal decreased with the NaClconcentration increasing.2) In artificial saliva of the same NaCl concentration the corrosion resistance ofpure titanium is the best, and cobalt-chromium alloy is better than titanium alloy.3) Patients who have the behavior of high-salt intake should not use titaniumalloy prosthesis, and should consider to choose cobalt-chromium alloys and puretitanium. Patients with prostheses of these three metal should be advised to reduce theintake of sodium chloride.