Comparative Microstructural Study of the Diffusion Zone Between Ni-Cr Alloy and Different Dental Ceramics

Detailed knowledge of bonding mechanisms, between the metal and ceramic parts in conventional dental systems, can help the development of new, improved systems and the optimisation of recent technologies. Despite their allergic potential, the NiCr alloys are still amongst the most often used dental materials so their investigation is important. The aim of the study was to carry out a detailed microstructural investigation and to compare the reaction layer developed between three different dental ceramics and NiCr alloy under different firing conditions. For the measurements six identical samples were cast from WIRON 99 (Bego, Konstantz, Germany) alloy. Ceramic opaquers were fired on the polished surface using Vision (Wohlwend AG), Vita VMK 95 (Vita) and Carat(DeTrey/Dentsplay) materials. Two samples were produced from each type of opaquers by different firing conditions. The TEM investigations were performed by using a 2000FX-II microscope with a Link-lsis EDS system. Similar growth processes of the phases were observed in all of the investigated systems in the sense that an amorphous phase was formed on the metal-ceramic interface producing bubble like inclusions on the metal surface. The main component of this phase is silicon oxide in the case of Carat and Vita ceramics, while in the case of Vision potassium and nickel oxides were observed after the normal firing process. In all systems and at all firing conditions a nanocrystalline Cr2O3 layer (with about 50 nm grain size) was commonly observed. This investigation was supported in part by ETT Grant 2001-3