Department of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Fars, Iran.
Student Research Committee, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Fars, Iran.
PLoS One. 2023 Oct 24;18(10):e0275374. doi: 10.1371/journal.pone.0275374. eCollection 2023.
The durability of dental restorations is highly determined by an accurate marginal fit, which is in turn affected by the high temperature of porcelain firing. Information is inadequate about the marginal adaptation of metal-ceramic restorations fabricated by soft metal milling technologies after repeated firings. This study aimed to compare the effect of repeated ceramic firings on the marginal fit of copings fabricated from cobalt-chromium through soft metal milling and a conventional nickel-chromium casting alloy. A single standard brass die was designed, machined, and scanned, based on which, 20 frameworks were designed and fabricated through either soft metal milling or conventional casting (n = 10 per group) and porcelain veneered. The vertical marginal fit of the metal copings was measured after 3, 5, and 7 firing cycles by using a digital microscope on 16 points around the finish line of the metal die at ×80 magnification. The data were analyzed through repeated measures ANOVA and independent t-test (α = 0.05). The marginal fit of neither metal group was significantly affected by the number of firing cycles (P = 0.747). However, the marginal discrepancy was statistically lower in the soft metal milling group than that in the casting group (P<0.001). Repeated porcelain firings did not significantly affect the marginal fit of either alloy and remained within the clinically acceptable range after firings. However, the milled alloy had superior marginal fit regardless of the number of firing cycles.
牙科修复体的耐用性在很大程度上取决于精确的边缘适合度，而这反过来又受到瓷烧高温的影响。关于通过软金属铣削技术制造的金属陶瓷修复体在多次烧制后边缘适应性的信息不足。本研究旨在比较通过软金属铣削和传统镍铬铸造合金制造的钴铬基底冠在重复烧制后对边缘适合度的影响。根据单个标准黄铜模具的设计、加工和扫描结果，设计并制作了 20 个基底冠，通过软金属铣削或传统铸造（每组各 10 个）制作，并进行瓷贴面。使用数字显微镜在金属模具的完成线周围的 16 个点上，以 80 倍的放大倍数测量金属基底冠的垂直边缘适合度，在 3、5 和 7 次烧制循环后进行测量。通过重复测量方差分析和独立 t 检验（α=0.05）对数据进行分析。金属组的边缘拟合均不受烧制循环次数的影响（P=0.747）。然而，软金属铣削组的边缘差异在统计学上低于铸造组（P<0.001）。重复瓷烧制不会显著影响两种合金的边缘适合度，并且在烧制后仍保持在临床可接受的范围内。然而，无论烧制次数如何，铣削合金的边缘适配性都更好。
