Influence of recasting on biological and microstructural properties of dental alloys

Abstract

Microstructure is the basic factor that determines the properties of any material. The aim of this study is to evaluate the effect of recasting of two commercially available dental alloys, Ni-Cr (Wiron 99) and Co-Cr (Dentalit C), on physiology of cells, as well as comparation those two dental alloys, one containing Ni and the other not. In this study the it was presumed that many times recasted dental alloy has changed microstructure, which influences the physical and mechanical properties and biological quality of the alloy. The specimens of both tested alloys were casted after the first, fourth and eight melting, without adding any amount of new alloy. The microstructural characterization by optical microscopy showed typical dendritic structure of Co-Cr and Ni-Cr alloys after different numbers of recasting. It is well known that the dendritic structure shows differences in chemical composition and that the dendrite branches contain less alloying and trace elements than the interdendritic zone. There were noticed some microstructural changes that were much more obvious by Co-Cr dental alloy. SEM analysis has given more explicit informations about the structure of the examined dental alloys. Based on the binary phase diagram, Ni-Cr alloy shows a wide region of solubillity in solid condition Cr in Ni. In a complex system, as it is in Wiron 99, beside the solid solution of Ni rich phase, there are also phases in the interdendritic zones with irregular shapes, depending of the number of recasting. EDS analysis showed the differences in chemical composition of dendritic and the interdendritic zones, that were very small for Wiron 99. For the Co-Cr alloy it was possible to detect the differences in chemical compositions between two zones, dentritic and interdendritic. As the number of recasting was increased, the structure became more homogenous and the difference in the chemical composition was decreased for Co and Mo, while the rest of the traceing elements Cr, Fe and Si were homogenous in the analyzed zones. X-ray analysis of the specimens of the Ni-Cr dental alloy indicate that there were only reflections of face centered cubic crystal lattice of solid solution of α-Ni phase. It was established that the increase of the number of recasting changes the relative intensity of diffraction maximum. Also, there were changes in the preferred orientation of the crystallites with the increase of the number of recasting...

Mikrostruktura je osnovni faktor koji određuje svojstva nekog materijala. Cilj ove studije je procena mikrostrukturnih promena nakon višestrukog pretapanja dve komercijalne dentalne legure, Ni-Cr (Wiron 99) i Co-Cr (Dentalit C) i njihov uticaj na fiziološke procese ćelija, kao i komparacija kvaliteta dve ispitivane legure, od kojih jedna sadrži, a druga ne sadrži Ni. U ovom istraživanju pošlo se od pretpostavke da više puta topljenja i livenja dentalna legura ima promenjenu mikrostrukturu, koja utiče na izmenu fizičko-mehaničkih svojstava i biološkog kvaliteta legura. Uzorci obe ispitivane legure izliveni su nakon prvog, četvrtog i osmog topljenja, bez dodavanja nove legure. U cilju mikrostrukturne karakterizacije optičkom mikroskopijom uočena je tipična dendritna struktura uzoraka Co-Cr, kao i Ni-Cr dentalne legure, nakon različitog broja topljenja i livenja. Poznato je da dendritna struktura pokazuje razliku u hemijskom sastavu i da dendritne grane sadrže manje legirajućih i pratećih elemenata nego međudendritni prostor. Uočene su promene u mikrostrukturi koje su znatno izražejnije kod Co-Cr dentalne legure. SEM analiza je dala jasnije podatke o strukturi ispitivanih uzoraka dentalnih legura. Poznato je na osnovu binarnog dijagrama stanja da Ni-Cr sistem pokazuje široku oblast rastvorljivosti u čvrstom stanju Cr u Ni. U složenom sistemu kao što je Wiron 99 pored čvrstog rastvora bogatog Ni uočavaju se i faze u međudendritnom prostoru nepravilnog oblika, koje menjaju svoj raspored u zavisnosti od broja ponavljanih topljenja i livenja. EDS analizom utvrđeno je da se razlika u hemijskom sastavu dendrita i međudendritnog prostora veoma mala za leguru Wiron 99. Kada je u pitanju legura na bazi Co-Cr, bilo je moguće praćenje razlike u hemijskom sastavu između dve zone, dendrit-međudendritni prostor. Sa povećanjem broja ponovljenog topljenja i livenja uočeno je da dolazi do homogenizacije strukture, odnosno do smanjenja razlike u hemijskom sastavu i da je to najuočljivije za elemente Co i Mo, dok ostali praćeni elemente Cr, Fe i Si imaju ravnomernu (homegenu) raspodelu u analiziranim zonama. Rendgenostrukturnom analizom uzoraka Ni-Cr dentalne legure uočene su samo refleksije površinski centrirane kubne kristalne rešetke čvrstog rastvora α-Ni. Utvrđeno je da sa povećanjem broja topljenja i livenja legure, menjaju relativni intenziteti difrakcionih maksimuma. Takođe se menja i preferentna orjentacija kristalita sa povećanjem broja ponovljenog topljenja i livenja...