EffEct of rEcasting on thE usEful propErtiEs cocrMoW alloy WpłyW poWtórnEgo przEtapiania na WłaściWości użytkoWE stopu cocrMoW*

The recasting of previously casted alloy is a routine procedure used in dental laboratories in order to reduce the cost of permanent partial dentures. The prosthetic “scrap” encompasses the residuals generated in frame dentures casting process e.g. originating from the runners, from casting cones and improperly completed melts e.g. withmisruns, shrinkage porosities and cracks and is frequently used as a part of charge for recasting [20]. The state of load occurring in oral cavity in course of mastication process is diversified and causes various level of stress concentration in hard tooth tissues and in dental fillings which may result in damages of denture fasteners or in ceramic phase separation from prosthetic apparatuses with permanent porcelain veneers [5, 21]. The addition of 50% recast material to a brand new alloy is allowed by greater part of dental alloys manufacturers. Some manufacturers established the condition that the addition of so called scrap can be recasted only once and must wholly originate from the same batch. However the use of additions in the form of repeatedly remelted materials is not allowed by other alloys manufacturers or no information concerning potential use of post-production scrap is not published by them. In the opinion of Bauer et al. [4] the scrap produced in dentistry is extremely pure due to the fact that this metal is melted in controlled conditions without necessity to apply any chemical process used in industrial conditions. Dental alloys reuse seems promising in case of Ni–Cr [12] and Co–Cr alloys [1] as well as gold based alloys [17]. From references [4, 12, 13] it appears that the properties of recasted alloy may differ from the properties of a new alloy purchased from the manufacturer. The differences may be associated with its chemical composition [13], castability [12], as well as with mechanical properties [4]. However the opinions concerning mechanical properties are extremely divided. Some authors [1, 4] think that these properties can increase or decrease [11, 20] but the research carried out by Palaskar et al.[12] demonstrate that there is no statistically significant castability change as a result of alloys recasting. There are experimental studies described in literature [13] and reflecting changed chemical composition of final products under the influence of successive recasting processes and development of new phases determining the changes in alloy properties. The deterioration in the scope of corrosion properties [6] or even cytotoxicity [2] is also possible due to changed chemical composition in case of recasting. WAlczAk M, PieniAk D, nieWczAs AM. effect of recasting on the useful properties cocrMoW alloy. eksploatacja i niezawodnosc – Maintenance and Reliability 2014; 16 (2): 330–336.