Efficiency of diamond like carbon coating on the galvanic corrosion between implant suprastuctures.

Galvanic corrosion is the term used for the accelerated attack occurring on a less noble metal when electrochemically dissimilar metals are in electrical contact within a liquid or corrosive environment. Multi-metallic dental construction assemblies bring different composition of metals into physical contact inside the mouth, which may lead to galvanic corrosion problems due to infiltration of saliva into the structures. Ni-Cr alloys continue to be used successfully to construct conventional prosthetic restorations and superstructures over dental implants due to some of their superior properties such as; low cost, excellent mechanical strength, good castability, good adherence to ceramic layer and availability to construct hygienic superstructure designs. Several investigations have been focused on the galvanic corrosion phenomena of titanium when coupled with various dental alloys. Results of these studies advocate that, there may occur a galvanic interaction when Ti coupled with Ni-Cr alloy.As a protection method for galvanic corrosion; it is known that if dissimilar metals in the same electrolyte are insulated from each other by suitable electrical insulators, current flow is prevented and galvanic corrosion could be minimized or avoided.Diamond-Like Carbon (DLC) films are amorphous carbon based coatings containing sp2 and sp3 bonded carbon atoms with varying hydrogen concentrations. Their significantly high concentration of sp3 carbon bonds confers valuable ?diamond-like? properties. Considering the excellent properties of DLC coatings, especially electrical insulation and corrosion resistance, DLC coating should be investigated as a protective film for galvanic corrosion problem between electrochemically dissimilar metals.The purpose of this study is, (i) to evaluate the galvanic corrosion behavior between titanium implant alloy and nickel-chromium implant superstructure alloy. (ii) to investigate the effect of diamond-like carbon coating over titanium on galvanic corrosion behavior between titanium alloy and nickel-chromium alloy. (iii) to evaluate the effect of diamond-like carbon coating over titanium abutment on the fit and integrity of prosthetic assembly by scanning electron microscopy. Five nickel chromium and 10 titanium disc shaped specimens were prepared with the diameter of 5mm and thickness of 3mm. DLC coating was done over 5 titanium discs with PECVD technique. A copper wire was connected on one side of the samples and embedded in epoxy resin. After the surface preparations of the electrode samples open circuit potential measurements, galvanic current measurements over platinum electrode and potentiodynamic polarization tests were done. For SEM evaluation, 20 Ni-Cr alloy, 10 gold alloy prosthetic superstructures were cast and prepared over 30 bar-bridge abutments. Diamond-like carbon coating was applied over 10 titanium abutments. Following fixation of the prosthetic assembly, samples were embedded in acrylic resin. After the polymerization, samples were cross sectioned longitudinally. Surface preparations of the sectioned samples were done with 500, 800, 1200, 2500 grid SiC papers. Following the surface preparations, SEM photographs were taken in x1000 magnification. From the SEM photographs marginal gap measurements were carried out. Results were statistically analyzed. Results of the electrochemical tests shows that, titanium is a more noble and electrochemically stable metal according to Ni-Cr alloy. Hence, the use of this alloys in conjunction in oral cavity may cause galvanic corrosion. DLC coating over the cathode electrode serves as an insulating film layer over the surface and avoids galvanic coupling. Results of the SEM evaluation indicated that, marginal gap values of gold superstructure / Ti abutment prosthetic assembly were significantly lower than the Ni-Cr superstructure / Ti abutment and Ni-Cr superstructure / DLC coated Ti abutment prosthetic assemblies. Hence, no adverse effect has been found on application of diamond-like carbon coating.