Alex Deepa, Shetty Y Bharath, Miranda Glynis Anita, Prabhu M Bharath, Karkera Reshma
Department of Prosthodontics, A.J. Institute of Dental Sciences, Mangalore, Karnataka, India.
J Indian Prosthodont Soc. 2015 Jan-Mar;15(1):58-64. doi: 10.4103/0972-4052.155043.
Conventional investing and casting techniques are time-consuming and usually requires 2-4 h for completion. Accelerated nonstandard, casting techniques have been reported to achieve similar quality results in significantly less time, namely, in 30-40 min. During casting, it is essential to achieve compensation for the shrinkage of solidifying alloy by investment expansion. The metal casting ring restricts the thermal expansion of investment because the thermal expansion of the ring is lesser than that of the investment. The use of casting ring was challenged with the introduction of the ringless technique.
A total of 40 test samples of nickel chromium (Ni-Cr) cast copings were obtained from the patterns fabricated using inlay casting wax. The 20 wax patterns were invested using metal ring and 20 wax patterns were invested using the ringless investment system. Of both the groups, 10 samples underwent conventional casting, and the other 10 underwent accelerated casting. The patterns were casted using the induction casting technique. All the test samples of cast copings were evaluated for vertical marginal gaps at four points on the die employing a stereo optical microscope.
The vertical marginal discrepancy data obtained were tabulated. Mean and standard deviations were obtained. Vertical discrepancies were analyzed using analysis of variance and Tukey honestly significantly different. The data obtained were found to be very highly significant (P < 0.001). Mean vertical gap was the maximum for Group II (53.64 μm) followed by Group IV (47.62 μm), Group I (44.83 μm) and Group III (35.35 μm).
The Ni-Cr cast copings fabricated with the conventional casting using ringless investment system showed significantly better marginal fit than that of cast copings fabricated from conventional and accelerated casting with metal ring investment and accelerated casting using ringless investment since those copings had shown the least vertical marginal discrepancies among the four methods evaluated in this study.
传统的包埋和铸造技术耗时较长，通常需要2至4小时才能完成。据报道，加速非标准铸造技术能在显著更短的时间内，即30至40分钟内获得相似的质量结果。在铸造过程中，通过包埋材料膨胀来补偿凝固合金的收缩至关重要。金属铸造环会限制包埋材料的热膨胀，因为铸造环的热膨胀小于包埋材料。无环技术的引入对铸造环的使用提出了挑战。
从使用嵌体铸造蜡制作的模型中获取了总共40个镍铬（Ni-Cr）铸造冠的测试样本。20个蜡型使用金属环包埋，20个蜡型使用无环包埋系统包埋。两组中，10个样本进行传统铸造，另外10个进行加速铸造。使用感应铸造技术对模型进行铸造。使用立体光学显微镜在模型上的四个点评估所有铸造冠的测试样本的垂直边缘间隙。
将获得的垂直边缘差异数据制成表格。计算出均值和标准差。使用方差分析和Tukey真实显著差异法分析垂直差异。发现获得的数据具有非常高度的显著性（P < 0.001）。平均垂直间隙最大的是第二组（53.64μm），其次是第四组（47.62μm）、第一组（44.83μm）和第三组（35.35μm）。
在本研究评估的四种方法中，使用无环包埋系统进行传统铸造制作的Ni-Cr铸造冠显示出比使用金属环包埋的传统和加速铸造以及使用无环包埋的加速铸造制作的铸造冠具有显著更好的边缘适合性，因为那些铸造冠在垂直边缘差异方面最小。
