[Mechanical studies on cast clasps by a superelastic Ni-Ti alloy. Part 3. Fitness of cast clasps].

The purpose of this study is to investigate the influence of setting expansion and thermal expansion of the phosphate-bonded investment on the fitness of cast claspsfabricated by a superelastic Ni-Ti alloy. Investment models were made from the columnar stainless-steel model supposed the abutment tooth the various dilusion colloidal silica solutions.Cast clasps were fabricated using by using a superelastic Ni-Ti alloy, then dimensional changes at the tip and mid-point of clasp arm between before and after fitness of cast clasps to the stainless-steel model were measured by the using of a profile projector. In addition, setting expansion and thermal expansion of investments were measured. Results were as follows: (1) Setting expansion increased with the increase of the concentration of colloidal silca solution, however thermal expansion kept constant. (2) Cast clasps fabrcated by using the investment model with 1.6% of setting expansion and 1.0% of thermal expansion showed the best fitness.