Assistant Professor, Department of Prosthodontics, Mustafa Kemal University Faculty of Dentistry, Hatay, Turkey.
Research Assistant, Department of Prosthodontics, Mustafa Kemal University Faculty of Dentistry, Hatay, Turkey.
J Prosthet Dent. 2020 May;123(5):731-737. doi: 10.1016/j.prosdent.2019.05.029. Epub 2019 Oct 23.
Information regarding the precision of monolithic zirconia crowns fabricated by using a standard computer-aided design and computer-aided manufacturing (CAD-CAM) workflow is available. However, information on the effect of a modified workflow using 3D laboratory scanning and/or cone beam computed tomography (CBCT) for monolithic zirconia crown fabrication is lacking.
The purpose of this in vitro study was to evaluate the effect of different scans on the marginal fit of CAD-CAM monolithic zirconia crowns fabricated by 3D laboratory scanning and CBCT.
An extracted maxillary left first molar was prepared and digitized by using a 3D laboratory scanner (D900; 3Shape A/S) (control group). The tooth was also scanned by CBCT (i-CAT; Imaging Sciences) to generate a second virtual 3D model (CBCTscan group). A tooth cast out of polyurethane (PU) (Zenotec Model; Wieland) was reproduced from the CBCT data by using a CAD software program (Dental System 2.6; 3Shape A/S) and milling machine (CORiTEC 550i; imes-icore) and further scanned by using the 3D laboratory scanner to generate a third virtual 3D model to represent a clinical scenario where a patient's cast is needed (PU3DLab group). A monolithic zirconia crown design (cement space: margin 40 μm, 1 mm above 70 μm) was used on the virtual models, and crowns were fabricated out of presintered zirconia blocks (ZenostarT4; Wieland) by using a 5-axis milling machine (CORiTEC 550i; imes-icore). The crowns were sintered (Sinterofen HT-S Speed; Mihm-Vogt), and the vertical marginal discrepancy (VMD) was measured by ×100-magnification microscopy. Measurements were made at 384 points in 3 groups of 16 specimens. The measurements for each specimen were averaged, and VMD mean values were calculated. The Kruskal-Wallis test was used for the statistical analysis (α=.05). The Mann-Whitney U test and Bonferroni adjustment were further used to compare the pairs (α=.017).
The mean VMD value was 41 μm (median: 38 μm) for the control group, 44 μm (median: 42 μm) for the CBCTscan, and 60 μm (median: 58 μm) for the PU3DLab. No significant difference was found between control and CBCTscan groups (P=.274). However, there was a significant difference between control and PU3DLab and CBCTscan and PU3DLab groups (P<.001).
Marginal fit of the crowns fabricated by using the 3D laboratory scanner and through the direct use of CBCT was better than that of the crowns fabricated by using the workflow that combined the use of CBCT, PU cast, and 3D laboratory scanner. All tested protocols enabled the fabrication of monolithic zirconia crowns with a marginal discrepancy smaller than 120 μm.
有关使用标准计算机辅助设计和计算机辅助制造 (CAD-CAM) 工作流程制造整体氧化锆冠精度的信息是可用的。然而，关于使用 3D 实验室扫描和/或锥形束计算机断层扫描 (CBCT) 制造整体氧化锆冠的修改工作流程的效果的信息是缺乏的。
本体外研究的目的是评估不同扫描对通过 3D 实验室扫描和 CBCT 制造的 CAD-CAM 整体氧化锆冠边缘适合性的影响。
使用 3D 实验室扫描仪 (D900; 3Shape A/S) (对照组) 对提取的上颌左侧第一磨牙进行数字化处理。牙齿也通过 CBCT (i-CAT; 成像科学) 进行扫描，以生成第二个虚拟 3D 模型 (CBCTscan 组)。通过 CAD 软件程序 (Dental System 2.6; 3Shape A/S) 和铣床 (Coritec 550i; imes-icore) 从 CBCT 数据中复制出由聚氨酯 (PU) (Zenotec Model; Wieland) 制成的牙铸件，并进一步使用 3D 实验室扫描仪进行扫描，以生成第三个虚拟 3D 模型，代表患者需要牙铸件的临床情况 (PU3DLab 组)。在虚拟模型上使用整体氧化锆冠设计(间隙空间:40μm，1mm 以上 70μm)，并使用预烧结氧化锆块(CoritestarT4; Wieland)通过 5 轴铣床 (Coritec 550i; imes-icore) 制造冠。将冠烧结(Sinterofen HT-S Speed; Mihm-Vogt)，通过 100 倍放大显微镜测量垂直边缘差异 (VMD)。在 3 组 16 个标本中测量 384 个点。对每个标本的测量值进行平均，并计算 VMD 平均值。使用 Kruskal-Wallis 检验进行统计分析(α=.05)。进一步使用曼-惠特尼 U 检验和 Bonferroni 调整来比较各对(α=.017)。
对照组的平均 VMD 值为 41μm(中位数:38μm)，CBCTscan 组为 44μm(中位数:42μm)，PU3DLab 组为 60μm(中位数:58μm)。对照组和 CBCTscan 组之间无显著差异(P=.274)。然而，对照组和 PU3DLab 组以及 CBCTscan 和 PU3DLab 组之间存在显著差异(P<.001)。
使用 3D 实验室扫描仪制造的牙冠和直接使用 CBCT 制造的牙冠的边缘适合性优于使用结合使用 CBCT、PU 铸型和 3D 实验室扫描仪的工作流程制造的牙冠。所有测试方案都能够制造出边缘差异小于 120μm 的整体氧化锆冠。
