Efeito de consecutivas refusões de ligas de Ni-Cr utilizadas em prótese fixa

Metalceramic crowns are usually used in dentistry because they provide a resistant structure due to its metallic base and its aesthetics originating from the porcelain that recovers this structure. To manufacture metalceramic crowns, a series of stages should be accomplished in prosthetic laboratories and many variables may influence the success of this process. Changes in these variables cause alterations in metallic alloys and in the porcelains and, as a consequence, in the adhesion between them. The composition of the metal alloy can be modified by recasting alloys, a common practice in some laboratories. This fact can cause qualitative and quantitative losses of the alloy elements and as consequence, difference in its properties, being a cause of failures in some crowns. The aim of this paper was to carry out a systematic study investigating metalceramic crowns as well as analyzing the effect of recasting Ni-Cr alloys on the microestruture, porosity and microhardness of this alloy. Ni-Cr alloys were cast once, twice and 3 times in two laboratories of prosthesis in the city of Natal-RN. The microestruture was observed by optical microscopy. Micrographs were obtained using the software Image Pro-Plus and the porosity was evaluated. The alloy cast once exhibit a maximum porosity of 9% in the laboratory 1 and 11% in the laboratory 2. The alloys cast twice and 3 times exhibit porosity respectively up to 14% and 86% in the laboratory 1 and 12% and 70% in the laboratory 2. The microhardness decrease when the alloy was reused in both laboratories.