Marginal and internal fit of 3D printed resin graft substitutes mimicking alveolar ridge augmentation: An <i>in vitro</i> pilot study

Recent improvements in additive manufacturing technologies may facilitate the use of customized 3D printed grafts for horizontal and vertical augmentation of the atrophic alveolar ridge. The accurate fit of such grafts could reduce the clinical treatment time and contribute optimal bone regeneration. The aim of this in vitro study was to evaluate the marginal and internal fit of 3D printed resin grafts as they could be used for alveolar ridge augmentation. Alveolar ridge morphologic data were derived from the Cone Beam Computed Tomography (CBCT) scans of six patients with alveolar bone defects. These data were transferred to a segmentation program to produce virtual 3D reconstructions of the alveolar ridge models. Using a Computer Aided Design (CAD) program, the alveolar bone defects were defined and customized grafts were designed and both the defects as well as the grafts generated (CAM) as 3D projects. These projects were imported into a 3D printer and were manufactured in resin. Hereafter, the grafts were fitted to the defect sites of the corresponding models and new CBCT scans were performed. Based on these scans, measurements were made at the marginal and internal part of the fitted grafts to evaluate the marginal and internal fit, respectively. The statistical analysis revealed that the mean marginal fit was significantly better (P < 0.05) than the mean internal fit. The fit of the grafts was dependent on the shape and on the size of the grafts. Specifically, the total void surface between the fitted graft and the corresponding defect site was significantly larger in the large-defect grafts than the small-defect grafts (P < 0.05). Within the limitations of the study, it could be demonstrated that it is possible to fabricate 3D printed resin grafts with acceptable fit in customized shapes, when combining CBCT scans and computer aided design and 3D printing techniques.近年来，增材制造（Additive Manufacturing）技术的迭代升级推动了定制化3D打印移植物的临床应用，该类移植物可用于萎缩性牙槽嵴的水平向与垂直向骨增量修复。此类移植物的精准贴合，可有效缩短临床治疗周期，同时为最优骨再生提供支撑。 本体外（in vitro）研究旨在评估可应用于牙槽嵴骨增量术的3D打印树脂移植物的边缘贴合度与内部贴合度。研究通过6名牙槽骨缺损患者的锥形束计算机断层扫描（Cone Beam Computed Tomography，CBCT）影像获取牙槽嵴形态学数据，将上述数据导入图像分割软件以生成牙槽嵴模型的虚拟三维重建结果。借助计算机辅助设计（Computer Aided Design，CAD）软件，精准定义牙槽骨缺损区域，设计定制化移植物，并生成缺损区域与移植物的计算机辅助制造（Computer Aided Manufacturing，CAM）三维项目文件。将上述三维项目文件导入3D打印机，以树脂为材料完成移植物的打印制备。随后将打印完成的移植物贴合至对应牙槽嵴模型的缺损区域，并对贴合后的模型进行新一轮CBCT扫描。基于本次扫描影像，分别在贴合后移植物的边缘区域与内部区域开展测量，以分别评估其边缘贴合度与内部贴合度。 统计学分析结果显示，移植物的平均边缘贴合度显著优于平均内部贴合度（P < 0.05）。移植物的贴合效果与其自身形状及尺寸密切相关。具体而言，大缺损组移植物与对应缺损区域之间的总间隙表面积显著高于小缺损组（P < 0.05）。 鉴于本研究存在一定局限性，研究结果证实：联合CBCT扫描、计算机辅助设计与3D打印技术，可制备出贴合效果符合临床要求的定制化形状3D打印树脂移植物。