急速加熱型リン酸塩系埋没材の膨張特性と適合性

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  • Expansion of Rapid Burnout Type Phosphate-bonded Investment and Fit of Gold Alloy Crown Castings

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The dental casting procedure involving slow drying and burnout of the mold is a time-consuming practice. Several techniques and investment materials have so far been developed to shorten the time required for the mold preparation. In the phosphate-bonded investment a rapid burnout type has been recently introduced. This type of investment is characterized by the ability to be subjected to early and rapid heating, in which the mold is directly placed in a preheated furnace at 800℃ after only 30 min from the start of mixing and held there for 30 min before casting. This study examined a rapid burnout type phosphate-bonded investment (CQ) in terms of setting and thermal expansions and fit of gold alloy castings for metal-ceramics when the L/P ratio, elapsed time before heating and burnout time were changed, comparing with a conventional phosphate-bonded investment (CG). The setting expansion of the rapid burnout investment significantly increased with smaller L/P ratio and increased elapsed time, while no significant change was found in the thermal expansion measured by rapid heating at 800℃. The fit of the full crown casting to the abutment die was evaluated by measuring the vertical gap at the shoulder margin between the casting and the stone abutment die. The gap observed in the castings by the rapid burnout investment mold significantly decreased with smaller L/P ratio and increased elapsed time before burnout. The effects of L/P ratio were much larger in the rapid burnout investment mold than in the conventional type. The linear regression analysis revealed that the changes in the setting expansion were significantly reflected in fit of the casting. These results indicate that the rapid burnout type phosphate-bonded investment mold may be much sensitive to the changes in L/P ratio and elapsed time before burnout in a sense of the fit of the castings, when compared with the conventional type investment mold. Although the use of the rapid burnout type investment can effectively reduce the time for casting procedure, therefore, these two variables should be more severely controlled than for the conventional type to obtain reproducible, well fitting castings.

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