Assistant Professor, Department of Dentistry Services, Vocational School of Health Services, Ondokuz Mayıs University, Samsun, Turkey.
Professor, Department of Prosthodontics, Faculty of Dentistry, Çukurova University, Adana, Turkey.
J Prosthet Dent. 2022 Apr;127(4):651-658. doi: 10.1016/j.prosdent.2020.10.006. Epub 2021 Feb 25.
Laser sintering devices have been increasingly used to fabricate the metal frameworks of metal-ceramic restorations. In the fabrication process, the sintering layer thickness is an important parameter; however, information on how it may affect the flexural strength of metal frameworks remains limited.
The purpose of this in vitro study was to evaluate the flexural strength of 3-unit and 4-unit cobalt-chromium (Co-Cr) metal frameworks laser sintered with 20-μm, 30-μm, and 40-μm layer thicknesses.
Three-unit and 4-unit master metal die models with premolar and molar abutments were prepared through direct metal laser sintering (DMLS). A total of 40 metal frameworks (n=10 for each metal die model) were fabricated by the lost-wax technique (group C, served as the control group) and through DMLS with 20-μm, 30-μm, and 40-μm layer thickness (experimental groups LS20, LS30, and LS40, respectively). Each metal framework was cemented to a master die with a polyvinyl siloxane impression material and then subjected to a 3-point bend test at a crosshead speed of 1 mm/min. The yield force of each metal framework was used to calculate the flexural strength. Data were statistically analyzed by using 1-way ANOVA followed by a Tukey honestly significant difference (HSD) test and an independent-samples t test (α=.05) The microstructure of the fracture surface was evaluated by scanning electron microscopy.
Group C reported the lowest mean flexural strength (P<.05), whereas group LS20 reported the highest mean flexural strength, although no significant difference (P>.05) in flexural strength was observed among the DMLS groups. The 3-unit metal frameworks exhibited a statistically significant higher mean flexural strength than the 4-unit metal frameworks (P<.05).
The sintering layer thickness did not significantly affect the flexural strength of the laser-sintered metal frameworks. However, the DMLS groups reported a higher mean flexural strength than the cast group.
激光烧结设备越来越多地用于制造金属陶瓷修复体的金属框架。在制造过程中，烧结层厚度是一个重要参数；然而，关于它如何影响金属框架的抗弯强度的信息仍然有限。
本体外研究的目的是评估激光烧结 3 单位和 4 单位钴铬（Co-Cr）金属框架的抗弯强度，其烧结层厚度分别为 20μm、30μm 和 40μm。
通过直接金属激光烧结（DMLS）制备三单位和四单位带前磨牙和磨牙基牙模型。通过失蜡技术（C 组，作为对照组）和 DMLS 分别用 20μm、30μm 和 40μm 层厚（实验组 LS20、LS30 和 LS40）制造总共 40 个金属框架（每组 10 个）。每个金属框架用聚硅氧烷印模材料粘接到主模具上，然后以 1mm/min 的十字头速度进行 3 点弯曲试验。每个金属框架的屈服力用于计算抗弯强度。使用单向方差分析（ANOVA），随后进行 Tukey 诚实显著差异（HSD）检验和独立样本 t 检验（α=.05）对数据进行统计分析。使用扫描电子显微镜评估断裂表面的微观结构。
C 组报告的抗弯强度最低（P<.05），而 LS20 组报告的抗弯强度最高，尽管 DMLS 组之间的抗弯强度没有显著差异（P>.05）。三单位金属框架的平均抗弯强度明显高于四单位金属框架（P<.05）。
烧结层厚度对激光烧结金属框架的抗弯强度没有显著影响。然而，DMLS 组报告的平均抗弯强度高于铸造组。
