The Empirical Study On Mechanical Properties Of Plating Gilded On Ni-Cr Dental Alloy With Non-cyanogen Gilding Technology

The coping of porcelain fused to metal crown is made usually from Nickel-chromium alloy, because of its excellent mechanical properties, good metal-ceramic bond strength and relatively low cost. It has been used widely in the field of prosthodontics for many years. But the clinical observations discovered that some patients suffered from gingivitis such as gingival hyperemia and edema when they used Ni-Cr alloy as the material of the copings sometimes, notwithstanding the good shape of the crown margin. Other patients suffered from the marginal gingival coloration. Many reserchers considered that it was primarily due to the application of Ni-Cr alloy. The gold plating technology which is widely used in industry is a good solution to this problem. Its low cost offers another advantage. It is used more and more widely in the field of dental prosthodontics.Nevertheless, literature review showed only limited articles about applying the gold plating on Ni-Cr alloy in dental fields nowadays, and all of them focused on the clinical observation after gold plating. No published article about the mechanical properties of the gold plating film was found.In this study, the gold plateing instrument was applicated to plate gold to nickel-chromium alloy applicating in clinic treatment, which is based on the newest technology of non-cyanogen gold plating, and the mechanical properties of plating coat was evaluated. This technology is applicated in the field of aerospace technology firstly, which is safe and environment-protective because of non-cyanogen gold plating fluid. It takes 10 minutes to finish the whole procedure of the technology, which is much shorter than the others, and it is in favour of shorting waiting time of patients.In the present study, SEM observation, scratch test, tooth brush abrasion test, shear bond strength test and thermocycling were performed. The influences of several factors on the mechanical properties of the gold plating film were examined, including the voltage and time for gold plating, wearability, surface roughness, dental cements and thermocycling. The purpose of this study was to screen out the optimal parameters of gold plating the Ni-Cr ceramic alloy for dental clinics, and to look for solutions to solve some common clinical problems, such as unsatisfied color and the exfoliation of the gold plating film. Major results and conclusions from the studies are:1. The voltage should be kept in the range of 5～19 mA during gold plating to achieve satisfied color of the plating film.2. The metal-ceramic bond strength was increased when the voltage is raised in the range of 0.7～1.0 V. The gold plating film was compact and homogeneous with the rising of the voltage.3. The thickness of the gold plating film was increased with the prolongation of gold plating, while the critical load of plating film went up first, then dropped.4. The wearability of the gold plating film was independent of the metal-ceramic bond strength, but was correlated with the thickness and the compactness of the plating film.5. The optimal parameters of gold plating Ni-Cr alloy are 1.0 V and 360 s, which can satisfy the demands for clinical work.6. The critical load of the gold plating film was in negative correlation with the surface roughness of the coping.7.Thermocycling (5～55℃) had no significant influence on the mechanical properties of the gold plating film.8. The glass-ionomer cement and zinc polycarboxylic cement did not cause exfoliation during shear bond strength test when using the optimal parameters for gold plating.To sum up, the optimal parameters of gold plating Ni-Cr alloy are 1.0 V and 360 s, which can satisfy the demands for clinical work. In this condition, the developed gold plating film had the best mechanical properties and lowest cost. The gingival margin of the crown should be highly polished as it was exposed to the oral cavity. The tissue surface of the coping should be treated by sand blasting and shot blasting. The type of cement and thermocycling had no significant influences on the gold plating film when using the optimal parameters mentioned above.