Graduate student, Dental Materials Laboratory & Department of Prosthodontics, Peking University School of Stomatology, Beijing, PR of China.
Professor and Director, Dental Materials Laboratory & National Engineering laboratory for Digital and Material Technology of Stomatology, Peking University School of Stomatology, Beijing, PR of China.
J Prosthet Dent. 2018 Jun;119(6):1028.e1-1028.e6. doi: 10.1016/j.prosdent.2018.04.002.
Heat treatment has been used to reduce the residual stress of alloys fabricated by selective laser melting (SLM) to avoid deformation. Co-Cr metal-ceramic alloys are used to fabricate metal-ceramic restorations and removable partial dentures (RPDs) on the same substrate by SLM. A heat treatment that enables the fabrication of metal-ceramic restorations and RPDs with excellent mechanical properties should be evaluated.
The purpose of this in vitro study was to determine the effects of 2 heat treatments on the mechanical properties of SLM Co-Cr metal-ceramic alloys intended for the fabrication of thin RPDs.
Tensile bars were manufactured using cast metal-ceramics (C-MC group), RPD alloys (C-RPD group), and SLM Co-Cr metal-ceramic alloys. The SLM specimens were subjected to 2 different heat treatments, L1 at 880°C and L2 at 1100°C, and were further divided into subgroups (L1-MC, L1-RPD, L2-MC, and L2-RPD). Thirty-six tensile specimens were prepared in C-RPD, L1-RPD, and L2-RPD (simulated partial denture alloys for clinical use) and in C-MC, L1-MC, and L2-MC (simulated metal-ceramic alloys); 18 metal-ceramic bond strength specimens were prepared in C-MC, L1-MC, and L2-MC groups (n=6). The tensile test and 3-point bend test were conducted using a universal testing machine. The fracture surfaces of the L2-RPD tensile bar were examined using a scanning electron microscope. The Student t test (α=.05) was used for statistical analysis.
No significant differences were observed between the bond strengths of L1-MC and C-MC (P=.74) or between those of L2-MC and C-MC (P=.124). The 0.2% yield strength (σ) and elongation of all SLM specimens exceeded the minimum requirements required for the fabrication of thin RPDs as prescribed in ISO 22674:2016. The σ value of L1-MC and L2-MC was significantly higher than that of C-MC. Significant differences in σ values were found among the 3 RPD groups, L1-RPD>L2-RPD>C-RPD. For the elongation, significant differences were found among the 3 groups, L2-RPD>C-RPD>L1-RPD. The fracture surface of L2-RPD showed clear submicroscale dimples with fusion defects.
When Co-Cr metal copings and RPD frameworks were fabricated on the same substrate simultaneously using SLM, heat treatment at 1100°C was found more suitable than at 880°C to release residual stress, considering the toughness required for dental prostheses.
热处理已被用于降低选择性激光熔化（SLM）制造的合金的残余应力，以避免变形。Co-Cr 金属陶瓷合金用于通过 SLM 在同一基底上制造金属陶瓷修复体和可摘局部义齿（RPD）。应评估一种能够制造具有优异机械性能的金属陶瓷修复体和 RPD 的热处理方法。
本体外研究的目的是确定两种热处理对用于制造薄 RPD 的 SLM Co-Cr 金属陶瓷合金机械性能的影响。
使用铸造金属陶瓷（C-MC 组）、RPD 合金（C-RPD 组）和 SLM Co-Cr 金属陶瓷合金制造拉伸棒。SLM 试样分别进行两种不同的热处理，L1 在 880°C 和 L2 在 1100°C，然后进一步分为亚组（L1-MC、L1-RPD、L2-MC 和 L2-RPD）。在 C-RPD、L1-RPD 和 L2-RPD（用于临床使用的模拟局部义齿合金）以及 C-MC、L1-MC 和 L2-MC（模拟金属陶瓷合金）中制备了 36 个拉伸试样；在 C-MC、L1-MC 和 L2-MC 组中制备了 18 个金属陶瓷结合强度试样（n=6）。使用万能试验机进行拉伸试验和三点弯曲试验。使用扫描电子显微镜检查 L2-RPD 拉伸棒的断裂表面。使用 Student t 检验（α=.05）进行统计分析。
L1-MC 和 C-MC 之间的结合强度（P=.74）或 L2-MC 和 C-MC 之间的结合强度（P=.124）没有显著差异。所有 SLM 试样的 0.2%屈服强度（σ）和伸长率均超过 ISO 22674:2016 规定的用于制造薄 RPD 的最低要求。L1-MC 和 L2-MC 的 σ 值明显高于 C-MC。3 个 RPD 组之间的 σ 值存在显著差异，L1-RPD＞L2-RPD＞C-RPD。对于伸长率，3 组之间存在显著差异，L2-RPD＞C-RPD＞L1-RPD。L2-RPD 的断裂表面显示出清晰的亚微观压痕和融合缺陷。
当 Co-Cr 金属冠和 RPD 支架同时通过 SLM 制造在同一基底上时，考虑到牙种植体所需的韧性，1100°C 的热处理比 880°C 更适合释放残余应力。
