Introduction. From a clinical stand point it is important to know if the different casting techniques, using the same alloy, may change the stiffness of the cast denture clasp. Although rotary and vacuum-pressure casting methods have the same induction melting means, any similarity ends at this point. In the rotary method, the melting and casting process is carried out in air but for the vacuum-pressure method, melting is conducted in the vacuum and casting is done in forming gas. Aim of the study. The aim of this study was to compare the influence of two casting methods: a rotary-centrifugal method and a vacuum-pressure method on the deflection force of a straight clasp profile in vitro and disclose any differences in microstructure of cobalt chromium alloy cast profiles caused by using different casting technology. Material and Methods. A commercial cobalt-chromium alloy (Wironit® extrahard BEGO, Bremen, Germany) was used. The tested material were the straight clasp profiles of a half-round section, cast in standard wax patterns (BEGO, Bremen, Germany), by the use of two inductive casting devices: a vacuum-pressure microprocessor assisted method (VP) (in device Nautilus®-BEGO, Bremen, Germany) and a rotary (R) manually operated method (in device Fornax®--BEGO, Bremen, Germany). Thirteen castings were fabricated by each of the respective methods. The custom made measuring instrument consisted of a micrometer screw and an force into voltage extensometer converter was applied. After deflection force measurement chosen profiles undergone metallographic examination to reveal internal grain arrangements in them. Results. On the level of significance p = 0.05 the observed difference between the means was proved to be statistically significant with better results for vacuum-pressure method. The microstructure varied, and these differences correlated with differences in deflection force measurement with greater deflection force for bigger grains. The grains size of the samples was of different size from small to large.

Key words: clasp retention, induction melting, clasps profiles, metallographic structure, chrome cobalt alloy.