Comparative study of the corrosion behavior between casting and recasting of three types of non- precious alloys

الملخص EN

Background: The practice of recasting in dentistry became familiar long time ago and many studies concerned with the effect of recasting on the physical and mechanical properties of non-precious alloys but only few studies concerned with the effect of recasting on the electrochemical properties .The aim of this study is to evaluate the corrosion behavior of three types of non-precious alloys which are Co-Cr, Ni-Cr (hard type) and Ni-Cr (soft type) before casting and after recasting.

Materials and methods: Three types of dental alloys were used in this study Co-Cr and two types of Ni-Cr alloys (hard type used for denture base material and soft type used for crown and bridge ).A cylindrical disc-shape design was used in this study to prepare the specimen ,this in accordance to ASTM.

The specimen were exposed to corrosion evaluation before casting and after recasting by potentiostatic polarization measurements .In addition to that the specimen were evaluated by microscopic examination before casting and after casting as well as after recasting Results: The results which is concerned with Co-Cr alloys showed that the corrosion potential shifted to more negative values with increasing recasting operation while for Ni-Cr hard type the corrosion potential shifted to less negative potential indicating a decrease in its activity for corrosion .On the other hand ,the soft type of Ni-Cr demonstrated that the corrosion potential became slightly more negative with recasting indicating some increase in the activity of the specimen for corrosion .

Conclusion: Recasting generally increased the tendency of the alloys for corrosion as indicated by the behavior of Co-Cr and (Ni-Cr)2 alloys but the reverse behavior was observed with (Ni-Cr)1 alloy .Also the diffusion controlled corrosion was appreciably high on (Ni-Cr) alloys but recasting generally increased the (dcc) suggesting its effect in decreasing the ability of oxide film for corrosion protection.

Keywords: Ecorr, Icorr, dcc, tafel slop, βcathdic, βanodic .

(J Bagh Coll Dentistry 2008; 20(2):14-19)