Postgraduate student, Department of Prosthodontics, Yonsei University College of Dentistry, Seoul, Republic of Korea.
Fellow, Department of Prosthodontics, Yonsei University College of Dentistry, Seoul, Republic of Korea.
J Prosthet Dent. 2018 Aug;120(2):225-231. doi: 10.1016/j.prosdent.2017.08.003. Epub 2018 Feb 7.
Intraoral scanners are effective for direct digital scans when dental restorations are fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM); however, if the abutment tooth cannot be dried completely or the prepared margin is placed subgingivally, accurate digital images cannot always be guaranteed.
The purpose of this in vitro study was to compare the internal and marginal discrepancies of zirconia copings fabricated directly using an intraoral scanner with those fabricated indirectly with impression scanning.
Forty-five resin dies fabricated with a 3-dimensional (3D) printer were divided into 3 groups: direct scanning (DS), impression scanning (IMP), and lost-wax casting (LW). For the DS group, a resin die was scanned with an intraoral scanner (Trios; 3Shape), whereas for the IMP group, impressions made with polyether were scanned with a cast scanner (D700; 3Shape). The zirconia copings were fabricated in the same way in the DS and IMP groups. For the LW group, impressions were made in the same way as in the IMP group, and Ni-Cr alloy copings were fabricated using LW. The marginal and internal discrepancies of the copings were measured by cementing them onto resin dies, embedding them in acrylic resin, and sectioning them in a buccolingual direction. The cement layer was measured, and the Kruskal-Wallis test was used to detect significant differences (α=.05). A nonparametric Friedman test was also performed to compare the measurements of each group by location (α=.05).
The mean marginal discrepancies in the DS, IMP, and LW groups were 18.1 ±9.8, 23.2 ±17.2, and 32.3 ±18.6 μm (mean ±standard deviation), respectively. The mean internal discrepancies of the DS, IMP, and LW groups in the axial area were 38.0 ±9.1, 47.0 ±16.3, and 36.5 ±15.8 μm, and those in the occlusal area were 36.7 ±16.9, 33.4 ±21.6, and 44.5 ±31.9 μm, respectively. No statistically significant differences were found in marginal or internal discrepancies among groups (P>.05).
Within the limitations of this study, the zirconia copings fabricated with CAD-CAM using different digitization methods and Ni-Cr copings fabricated using the lost-wax technique and casting produced clinically acceptable marginal and internal discrepancies. No significant differences were found among the DS, IMP, and LW groups.
当使用计算机辅助设计和计算机辅助制造（CAD-CAM）制作牙科修复体时，口内扫描仪可有效进行直接数字扫描；然而，如果基牙不能完全干燥或预备边缘置于龈下，那么则无法始终保证准确的数字图像。
本体外研究的目的是比较直接使用口内扫描仪制作的氧化锆全冠与间接使用印模扫描制作的氧化锆全冠的内部和边缘差异。
使用三维（3D）打印机制作 45 个树脂模型，分为 3 组：直接扫描（DS）组、印模扫描（IMP）组和失蜡铸造（LW）组。对于 DS 组，使用口内扫描仪（Trios；3Shape）扫描树脂模型，对于 IMP 组，使用聚醚制取印模并使用铸造扫描仪（D700；3Shape）扫描印模。DS 组和 IMP 组以相同的方式制作氧化锆全冠。对于 LW 组，以与 IMP 组相同的方式制取印模，并用失蜡铸造法制作镍铬合金全冠。将全冠粘接到树脂模型上，然后将其嵌入丙烯酸树脂中，并沿颊舌方向进行切割，以此测量全冠的边缘和内部差异。测量粘结层，使用 Kruskal-Wallis 检验检测显著性差异（α=.05）。还通过位置（α=.05）进行非参数 Friedman 检验比较每组的测量值。
DS、IMP 和 LW 组的平均边缘差异分别为 18.1 ±9.8、23.2 ±17.2 和 32.3 ±18.6μm（平均值±标准差）。DS、IMP 和 LW 组轴向区域的平均内部差异分别为 38.0 ±9.1、47.0 ±16.3 和 36.5 ±15.8μm，牙合面区域的平均内部差异分别为 36.7 ±16.9、33.4 ±21.6 和 44.5 ±31.9μm。组间边缘或内部差异无统计学意义（P＞.05）。
在本研究的限制范围内，使用不同数字化方法制作的 CAD-CAM 氧化锆全冠和使用失蜡技术及铸造制作的镍铬全冠产生了临床可接受的边缘和内部差异。DS、IMP 和 LW 组之间无显著差异。
