Statement of problem: Prior investigations into dimensional shrinkage of fast-cast postand- cores resulted in variable dimensions. There is a need for consistent shrinkage of cast post-and-cores to reduce or eliminate lateral stresses on the remaining tooth structure. Purpose: The purpose of this research was to find a method of casting post-and-cores that would result in consistent shrinkage. Material and Methods: A total of 45 methyl methacrylate post-and-core patterns, 10 mm long, were fabricated from a standardized steel block. Three methods were used to cast the post-and-core. Investment materials used were Fast Fire 15 (Whip Mix Corp, Louisville, KY, USA) and Beauty Cast gypsum (Whip Mix Corp). Three groups of sample post and core patterns were cast, varying the investment material used and the burnout time. Results: Results show a statistical significance between the investment materials (p<0.05). The accelerated technique produced the most consistent results, and all samples had shrinkage of the casting. Conclusions: The use of a phosphate investment with an accelerated technique can produce consistent and predictable shrinkage of cast post-and-cores.
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