BACKGROUND Desktop scanners are devices for digitization of conventional impressions or gypsum casts by indirect Computer-Aided Design/Computer-Assisted Manufacturing (CAD/CAM) in dentistry. The purpose of this in vitro study was: 1, to investigate whether virtual models produced by the extraoral scanner have the same trueness as sectioned casts; and 2, to assess if digitization with an extraoral scanner influences the surface information. METHODS A polimethyl-methacrilic acid (PMMA) cast and a reference scanner (TwoCam 3D, SCAN technology A/S, Ringsted, Denmark; field of view 200 mm, resolution 0.1 mm ± 0.025 mm) were used to create the reference data in standard tessellation format (STL). According to the extraoral CAD/CAM digitization steps, impressions, mastercasts, and sectioned casts were made, and STL files were generated with the reference scanner. The pivotal point of the study was to digitalize these sectioned casts with the extraoral scanner (Straumann CARES Scan CS2 Visual 8.0 software, InstitutStraumann AG, Basel, Switzerland) and STL files were exported. Virtual caliper measurements were performed. Absolute deviations were compared using multilevel mixed-effects linear regression. Relative distortions were calculated with mean absolute errors and reference values. RESULTS Differences were observed in measurements of tooth sizes. All four prepared teeth were affected. No relationship was observed in relative deviations. Absolute differences between all the indirect digitization steps considering arch distances were: impressions, - 0.004 mm; mastercasts, 0.136 mm; sectioned casts, - 0.028 mm; and extraoral scanner, - 0.089 mm. Prepared dies on the virtual casts (extraoral scanner) were closer to each other than those on the sectioned gypsum casts. Relative deviation calculations revealed no relationship with the position of the dies in the arch. CONCLUSION The trueness of the virtual models generated by the extraoral scanner system used in this study was different from the dimensions of the sectioned casts. The digitization of gypsum casts changes both the dimensions of dies and the distances between the dies. The virtual casts had smaller distances than any distances measured at previous steps. Either bigger dies or longer distances did not result in greater distortions. We cannot, however, generalize our results to all scanners available on the market, because they might give different results.

中文翻译：

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使用桌面扫描仪进行 CAD/CAM 数字化的真实性 - 一项体外研究。


背景技术台式扫描仪是用于通过牙科中的间接计算机辅助设计/计算机辅助制造（CAD/CAM）对传统印模或石膏铸件进行数字化的设备。本体外研究的目的是： 1、探讨口外扫描仪生成的虚拟模型是否具有与切片模型相同的真实度； 2，评估口外扫描仪的数字化是否影响表面信息。方法 使用聚甲基丙烯酸甲酯 (PMMA) 铸件和参考扫描仪（TwoCam 3D，SCAN technology A/S，Ringsted，丹麦；视场 200 mm，分辨率 0.1 mm ± 0.025 mm）创建标准中的参考数据曲面细分格式 (STL)。根据口外 CAD/CAM 数字化步骤，制作印模、母版和切片模型，并使用参考扫描仪生成 STL 文件。该研究的关键点是使用口外扫描仪（Straumann CARES Scan CS2 Visual 8.0 软件，InstitutStraumann AG，巴塞尔，瑞士）对这些切片模型进行数字化，并导出 STL 文件。进行虚拟卡尺测量。使用多级混合效应线性回归比较绝对偏差。使用平均绝对误差和参考值计算相对失真。结果 牙齿尺寸的测量结果存在差异。所有四颗准备好的牙齿都受到影响。在相对偏差中没有观察到任何关系。考虑牙弓距离的所有间接数字化步骤之间的绝对差异为： 印模 - 0.004 毫米；母版，0.136 毫米；分段铸件，- 0.028 毫米；和口外扫描仪，- 0.089 毫米。虚拟铸件（口外扫描仪）上准备好的模具比切片石膏铸件上的模具彼此更接近。 相对偏差计算显示与拱形中模具的位置没有关系。结论 本研究中使用的口外扫描系统生成的虚拟模型的真实度与切片模型的尺寸不同。石膏铸件的数字化改变了模具的尺寸和模具之间的距离。虚拟模型的距离比之前步骤中测量的任何距离都要小。更大的模具或更长的距离都不会导致更大的扭曲。然而，我们不能将我们的结果推广到市场上所有可用的扫描仪，因为它们可能会给出不同的结果。