Postgraduate student, School of Health Sciences, Department of Dentistry, Section of Prosthodontics, Aristotle University of Thessaloniki, Thessaloniki, Greece.
Assistant Professor, School of Health Sciences, Department of Dentistry, Section of Prosthodontics, Aristotle University of Thessaloniki, Thessaloniki, Greece.
J Prosthet Dent. 2018 Mar;119(3):467-472. doi: 10.1016/j.prosdent.2017.04.015. Epub 2017 Jul 11.
The effect of thermal aging on the color stability of monolithic zirconia has not been thoroughly investigated.
The purpose of this in vitro study was to evaluate the color stability before and after thermocycling of monolithic zirconia specimens, which were either preshaded or characterized in the laboratory through the assessment of color parameters L*, a*, and b*.
A total of 80 specimens (10×10×15 mm) were prepared from zirconia disks (BruxZir) and divided into 2 groups. The first group consisted of preshaded specimens from disks 100, 200, 300, and 400, and the second group consisted of white specimens characterized before the sintering stage with coloring liquids in shades A2, B2, C2, and D2. Ten specimens of each shade were used. A double-beam ultraviolet-visible light recording spectrophotometer was used to assess the color parameters L*, a*, and b* before and after thermocycling. The color difference ΔE was calculated based on ΔΕ=[(ΔL*)+(Δa*)+(Δb*)]. The reliability of the examiner was investigated by MedCalc v12.5 software, and the tests of normality, homogeneity of variances, and 1-way ANOVA statistical analysis of variance were performed by IBM Statistics SPSS v20.0 software (α=.05).
No statistically significant ΔΕ (P>.05) was observed among the different groups after thermocycling. All ΔΕ values were below the limit of the 3.7 that an untrained observer can perceive. Only for the specimens in shades 200 and 400 was ΔΕ above 1, revealing a visible color difference, which, however, was still clinically acceptable. The L*, a*, and b* values for both liquid-shaded and preshaded zirconia specimens were not significantly affected by thermocycling. A higher color stability for laboratory-characterized compared with preshaded monolithic zirconia was observed irrespective of the color shade.
Within the limitations of this in vitro study, monolithic zirconia specimens of any shade, either preshaded or characterized in the laboratory, can be considered as color-stable materials after thermocycling.
热老化对整体氧化锆颜色稳定性的影响尚未得到彻底研究。
本体外研究的目的是评估预遮蔽或通过评估颜色参数 L*、a和 b在实验室中对氧化锆试件进行特征化处理后的试件在热循环前后的颜色稳定性。
从氧化锆圆盘（BruxZir）制备了 80 个（10×10×15mm）试件，并将其分为 2 组。第一组由圆盘 100、200、300 和 400 的预遮蔽试件组成，第二组由在烧结阶段之前用着色液 A2、B2、C2 和 D2 进行特征化的白色试件组成。每个色调使用 10 个试件。使用双光束紫外可见分光光度计在热循环前后评估颜色参数 L*、a和 b。根据 ΔΕ=[(ΔL*)+(Δa*)+(Δb*)]计算色差值 ΔE。使用 MedCalc v12.5 软件评估检查者的可靠性，并使用 IBM Statistics SPSS v20.0 软件进行正态性、方差同质性检验和 1 -way ANOVA 方差分析（α=.05）。
热循环后，不同组之间的 ΔΕ（P>.05）没有统计学显著差异。所有 ΔΕ 值均低于未经训练的观察者可感知的 3.7 的限值。只有在 200 和 400 色调的试件中，ΔE 值超过 1，显示出可见的颜色差异，但仍在临床可接受范围内。热循环对液体着色和预遮蔽氧化锆试件的 L*、a和 b值没有显著影响。与预遮蔽的整体氧化锆相比，实验室特征化的氧化锆具有更高的颜色稳定性，无论颜色色调如何。
在本体外研究的限制范围内，任何色调的整体氧化锆试件，无论是预遮蔽还是在实验室中进行特征化处理，在热循环后都可以被认为是颜色稳定的材料。
