Donmez Mustafa Borga, Olcay Emin Orkun, Demirel Munir
Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Biruni University, İstanbul, Turkey.
Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Biruni University, İstanbul, Turkey.
J Prosthet Dent. 2021 Oct;126(4):589.e1-589.e6. doi: 10.1016/j.prosdent.2020.11.020. Epub 2021 Jan 8.
Zirconia is a widely used restorative material, yet its white color does not meet esthetic requirements and coloring is needed. However, the effects of different durations of coloring have not been thoroughly investigated.
The purpose of this in vitro study was to evaluate the effects of coloring liquid immersion of different durations on the flexural strength, Vickers hardness, and color of zirconia.
Fifty bar-shaped and 60 disk-shaped zirconia specimens were milled from nonshaded (Copran Zri) and preshaded (Copran Zri Precoloured Medium) disks by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system. Preshaded specimens were assigned to the group PS and received no further immersion. Nonshaded specimens were divided into 4 subgroups as per immersion time in coloring liquid (Copran Color A2 Shade): control (C; no immersion), G45 (45 seconds of immersion), G90 (90 seconds of immersion), and G135 (135 seconds of immersion). Bar-shaped specimens were subjected to a 3-point flexural strength test by using a universal testing machine (Lloyd LRX), following the International Organization for Standardization (ISO) 6872:2015 specification. Color coordinates of disk-shaped specimens were measured with a spectrophotometer (VITA Easyshade Advance 4.0) over a gray background. Color differences were calculated by using both CIE76 and CIEDE2000 formulas, followed by a comparison of obtained values with perceptibility (CIE76: 3.7, CIEDE2000: 0.8) and acceptability (CIE76: 6.8, CIEDE2000: 1.8) thresholds of each formula. Subsequently, Vickers hardness measurements were conducted. The data were statistically analyzed by using the Shapiro-Wilk test, 1-way ANOVA, and the Tukey HSD test (α=.05).
Immersing zirconia specimens in coloring liquid decreased the flexural strength and hardness values, as group C presented the highest values for both parameters. In addition, prolonged duration had a negative effect on mechanical properties. The flexural strength of groups PS and G45 (P=.993) and groups G90 and G135 (P=.999) was statistically similar. For Vickers hardness, group G135 presented the lowest values with the difference between groups G90 and G135 being statistically similar (P=.061). Color differences among groups varied from 2.49 to 27.33 for ΔE∗, whereas ΔE values ranged from 0.58 to 8.26. Compared with group C, ΔE∗ values of all shaded specimens exceeded the acceptability threshold of 6.8. The color difference between each group was higher than the acceptability threshold values of both ΔE∗ and ΔE except for groups G45 and PS.
Colored zirconia specimens had lower flexural strength and Vickers hardness values than nonshaded specimens, regardless of the immersion time or coloring technique.
氧化锆是一种广泛使用的修复材料，但其白色不符合美学要求，需要进行着色处理。然而，不同着色时间的效果尚未得到充分研究。
本体外研究的目的是评估不同持续时间的着色液浸泡对氧化锆的抗弯强度、维氏硬度和颜色的影响。
使用计算机辅助设计和计算机辅助制造（CAD-CAM）系统，从无阴影（Copran Zri）和预着色（Copran Zri Precoloured Medium）的圆盘上铣削出50个条形和60个盘形氧化锆试件。预着色试件被分配到PS组，不再进行浸泡。无阴影试件根据在着色液（Copran Color A2 Shade）中的浸泡时间分为4个亚组：对照组（C；不浸泡）、G45（浸泡45秒）、G90（浸泡90秒）和G135（浸泡135秒）。条形试件按照国际标准化组织（ISO）6872:2015规范，使用万能试验机（Lloyd LRX）进行三点抗弯强度测试。在灰色背景下，使用分光光度计（VITA Easyshade Advance 4.0）测量盘形试件的颜色坐标。使用CIE76和CIEDE2000公式计算颜色差异，然后将得到的值与每个公式的可察觉性（CIE76：3.7，CIEDE2000：0.8）和可接受性（CIE76：6.8，CIEDE2000：1.8）阈值进行比较。随后进行维氏硬度测量。数据采用Shapiro-Wilk检验、单因素方差分析和Tukey HSD检验进行统计分析（α = 0.05）。
将氧化锆试件浸泡在着色液中会降低抗弯强度和硬度值，因为C组在这两个参数上表现出最高值。此外，延长浸泡时间对机械性能有负面影响。PS组和G45组的抗弯强度（P = 0.993）以及G90组和G135组的抗弯强度（P = 0.999）在统计学上相似。对于维氏硬度，G135组的值最低，G90组和G135组之间的差异在统计学上相似（P = 0.061）。各组之间的颜色差异对于ΔE∗从2.49到27.33不等，而ΔE值范围为0.58到8.26。与C组相比，所有着色试件的ΔE∗值均超过了6.8的可接受阈值。除G45组和PS组外，每组之间的颜色差异均高于ΔE∗和ΔE的可接受阈值。
无论浸泡时间或着色技术如何，着色氧化锆试件的抗弯强度和维氏硬度值均低于未着色试件。
