Assistant Professor, Prosthodontics Department, Lebanese University School of Dentistry, Beirut, Lebanon.
Clinical instructor, Prosthodontics Department, Lebanese University School of Dentistry, Beirut, Lebanon.
J Prosthet Dent. 2017 Jul;118(1):49-54. doi: 10.1016/j.prosdent.2016.10.003. Epub 2016 Dec 23.
Subtractive and additive computer-aided design and computer-aided manufacturing (CAD-CAM) wax pattern processing are 2 methods of fabricating a pressed ceramic crown. Whether a subtractive milled wax pattern or a pattern from the micro-stereolithography additive process produces lithium disilicate crowns with better marginal and internal fit is unclear.
Ten silicone impressions were made for a prepared canine tooth. Each die received 2 lithium disilicate (IPS e.max) copings, 1 from milled wax blocks and 1 from additive wax. The replica technique was used to measure the fit by scanning electron microscopy at ×80 magnification. Collected data were analyzed using the paired Student t test for the marginal and internal fit. For the occlusal fit, the difference in scores did not follow a normal distribution, and the Wilcoxon signed rank test was used (α=.05).
The mean marginal, axial, and occlusal fit showed no significant differences when the 2 CAD-CAM manufacturing processes were compared (P>.05). For the marginal fit, the mean (±SD) values were 105.1 μm ±39.6 with the milled process and 126.2 μm ±25.2 for the additive process. The mean values were 98.1 μm ±26.1 for the axial fit in the milled process and 106.8 μm ±21.2 in the additive process. For the occlusal fit, median values (interquartile interval) were 199.0 μm (141.5 to 269.9) for subtractive manufacturing and 257.2 μm (171.6 to 266.0) for micro-SLA manufacturing.
No significant difference was found between the fit of the 2 techniques. The mean values of axial and occlusal median values were 10 and 5 to 6 times greater than machine's nominal values.
减法和加法计算机辅助设计和计算机辅助制造（CAD-CAM）蜡型加工是制作压瓷冠的 2 种方法。用减法铣削蜡型还是微立体光刻添加剂工艺制作的蜡型制作的锂硅二酸盐冠的边缘和内部拟合更好尚不清楚。
为一颗预备好的犬齿制作了 10 个硅橡胶印模。每个模具都收到 2 个锂硅二酸盐（IPS e.max）修复体，1 个来自铣削蜡块，1 个来自添加剂蜡。使用复制技术通过扫描电子显微镜在×80 放大倍数下测量拟合度。使用配对学生 t 检验分析边缘和内部拟合的收集数据。对于牙合面拟合，分数差异没有遵循正态分布，因此使用 Wilcoxon 符号秩检验（α=.05）。
当比较 2 种 CAD-CAM 制造工艺时，平均边缘、轴向和牙合面拟合没有显著差异（P>.05）。对于边缘拟合，铣削工艺的平均值（±SD）为 105.1μm±39.6，添加剂工艺为 126.2μm±25.2。铣削工艺的轴向拟合平均值为 98.1μm±26.1，添加剂工艺为 106.8μm±21.2。对于牙合面拟合，中位数（四分位距）值为减法制造的 199.0μm（141.5 至 269.9）和微 SLA 制造的 257.2μm（171.6 至 266.0）。
未发现两种技术的拟合之间存在显著差异。轴向和牙合面中位数的平均值是机器标称值的 10 倍到 6 倍。
