Statement of problem

A digital workflow in fixed prosthodontics may use a 3D printer to obtain a cast for porcelain application. Standards exist that define the accuracy of traditional casts, but the accuracy requirements of 3D-printed casts have not been defined.

Purpose

The purpose of this retrospective study was to investigate how the accuracy of 3D-printed casts affected prosthesis fit and whether they correctly reproduced interproximal contacts.

Material and methods

Copings with different die spacings were used to test different 3D-printed casts of the same dental arch. The accuracy of the 3D casts was assessed by imaging and comparing the resulting standard tessellation language (STL) files with the original through a matching software program. Accuracy scores were then correlated with a score measuring how well the copings fit the casts. The first data set was obtained from a patient receiving restoration of the 4 maxillary incisors. The teeth were prepared, the dental arch was imaged intraorally, and 10 resin casts were printed with four 3D printers. Two sets of 4 zirconia test copings were prepared, and 3 clinicians assessed their fit on each cast. A further set of casts was created from a second patient requiring prosthetic restoration for 5 adjacent teeth to assess whether undersizing affected the best fit of the copings on their dies.

Results

The clinical scores and accuracy scores did not correlate. The results suggested that printed dies showing a certain degree of undersizing might provide a better fit than those showing better correspondence to the actual anatomic structure. The oversized dies were the worst. Only 7 of 17 casts being assessed were deemed suitable for veneering of the copings. The undersized casts tested clinically better than casts printed by using the same printer under standard settings.

Conclusions

This retrospective study indicated that 3D-printed casts that do not allow copings to fit appropriately usually show mean excess oversizing. Axially undersizing the printed dies on casts might allow a better fit of copings to be veneered.

中文翻译：

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牙科模型 3D 打印的准确性：质量标准化的建议

问题陈述

固定修复术中的数字化工作流程可以使用 3D 打印机来获得用于瓷器应用的模型。存在定义传统铸件精度的标准，但尚未定义 3D 打印铸件的精度要求。

目的

这项回顾性研究的目的是调查 3D 打印模型的准确性如何影响修复体的贴合度，以及它们是否正确再现了邻面接触。

材料与方法

具有不同模具间距的内冠用于测试同一牙弓的不同 3D 打印模型。3D 模型的准确性通过成像来评估，并通过匹配的软件程序将生成的标准镶嵌语言 (STL) 文件与原始文件进行比较。然后将准确度分数与测量内冠与模型的匹配程度的分数相关联。第一个数据集来自接受 4 个上颌切牙修复的患者。准备好牙齿，口腔内对牙弓进行成像，并用四台 3D 打印机打印 10 个树脂模型。准备了两组 4 个氧化锆测试顶盖，并且 3 位临床医生评估了它们在每个模型上的适合度。

结果

临床评分和准确性评分不相关。结果表明，显示出某种程度的尺寸过小的印刷模具可能比那些显示出与实际解剖结构更好对应的模具更适合。过大的模具是最糟糕的。接受评估的 17 个石膏模型中只有 7 个被认为适合于顶盖饰面。在临床测试中，尺寸过小的模型比使用相同打印机在标准设置下打印的模型更好。

结论

这项回顾性研究表明，3D 打印的模型无法让内冠合适地贴合，通常会显示平均尺寸过大。轴向缩小铸件上印刷模具的尺寸可能会更好地贴合顶盖。