Investigating Dental Alloy Element Release Using PVD Thin Films

Objectives: NiCr cast alloys are widely used in dentistry as a cheap alternative to the more noble alloys. Unfortunately the biocompatibility of the alloy is a concern. The objective of this present study was to use thin films prepared by a Physical Vapour Deposition (PVD) method so that the biocompatibility of materials with controlled chemistry and topography could be studied in detail. Methods: NiCr test pieces were prepared using the ‘lost wax' technique as is commonly carried out in dental laboratories. They were polished to varying surface finishes. Thin films, of similar nominal composition, were prepared using an ion beam assisted PVD technique. These again had various surface finishes. Each batch of test pieces (cast alloy or thin film) was placed into phosphate-buffered saline solution used as artificial saliva for a week. The amount of Ni released into the solution was determined using graphite furnace atomic absorption spectrophotometry. Results: All samples showed that the amount of Ni release into the solution increased as the amount of Cr in the alloy decreased. A greater amount of Ni was also released from the unmodified surface compared to the modified surface test pieces. Preliminary studies with thin films of similar composition have shown a similar, but enhanced, trend. A comparison of microstructure and EDX maps has been used to explain and evaluate the cause of Ni release. Conclusion: The amount of Cr, as well as the surface finish and microstructure, plays an important role in the release of Ni. Similar trends were observed for PVD films - suggesting that the use of such films may be valid as a quick and easy way to undertake such element release investigations in the future.