The purpose of this study was to evaluate marginal fit of the Ni-Cr alloy castings invested with quick-heating phosphate-bonded investments. To do this, we used four commercial quick-heating phosphate-bonded investments for fixed partial dentures using Degussa GF, Fujivest Ⅱ, Maruvest-SPEED and Z4 C&B. We then examined the setting and thermal expansion of the investments using an accelerated casting technique and evaluated the fit of casting to determine whether there was any discrepancy between the gap in the wax and the casting. The Degussa GF investment with 75% special liquid had a significantly larger setting expansion, which was 1.28% greater than that of other investments with the same concentration special liquid after 20-min setting time. The thermal expansion of the investments at casting temperatures ranged between 1.23 to 1.71%. The marginal discrepancies of all castings obtained from four investments were slightly oversized. The marginal discrepancy obtained from the Maruvest-SPEED 100% was largest (255 μm). Fujivest Ⅱ, Maruvest-SPEED and Z4 C&B were significantly superior to that obtained from the Degussa GF, even though the concentration of the special liquid was the same. The marginal fit of the casting from the Maruvest-SPEED with 75% special liquid was significantly improved by using 100% special liquid and was found to have an 83% reduction in marginal discrepancy. These results suggest that the marginal fit of the castings might be improved by controlling the concentration of a special liquid. 目的：本研究探討使用不同快速加熱型磷酸鹽系包埋材時，鎳鉻合金鑄造物之邊緣密合度。
方法：實驗選用四種市售快速加熱型磷酸鹽系包埋材(Degussa GF, Fujivest Ⅱ, Maruvest-SPEED and Z4 C&B)，測試包埋材的凝固膨脹與熱膨脹率，並測量使用不同包埋材進行包埋、鑄造的鎳鉻合金鑄造物的邊緣差異。
結果：實驗結果顯示，使用75%專用液的Degussa GF在凝固後20分鐘時的凝固膨脹率為1.28%，明顯大於其他的包埋材之結果；四種快速加熱型包埋材的熱膨脹率為1.23至1.71%。在鑄造物適合性方面，所有鎳鉻合金鑄造物邊緣都稍微增大，尤其以100%專用液的Maruvest-SPEED之邊緣差異最大(255μm)。各包埋材均使用75%專用液時，Fujivest Ⅱ、Maruvest-SPEED及Z4 C&B的鑄造物密合度明顯優於Degussa GF的結果，當Maruvest-SPEED使用75%專用液後邊緣密合度明顯改善，邊緣差異減少了83%。
結論：適當調整包埋材的專用液濃度可以改善鑄造物的邊緣密合度。
