Cho Young-Eun, Lim Young-Jun, Han Jung-Suk, Yeo In-Sung Luke, Yoon Hyung-In
Department of Prosthodontics, Dankook University Dental Hospital, Cheonan 31116, Korea.
Department of Prosthodontics and Dental Research Institute, School of Dentistry, Seoul National University, Seoul 03080, Korea.
Materials (Basel). 2020 Oct 22;13(21):4726. doi: 10.3390/ma13214726.
Translucent zirconia, manufactured by increasing the yttria content, offers improved translucency, but may have a negative effect on esthetic outcomes under clinical conditions such as discolored abutment because of the reflection of the underlying color. The purpose of this in vitro study was to compare the translucency parameter and masking ability of 3 mol % yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP (Katana HT)), 4Y-ZP (Katana STML), and 5Y-ZP (Katana UTML) with those of lithium disilicate (Rosetta SM). Zirconia and lithium disilicate specimens of 10 mm diameters and 0.8 and 1.5 mm thicknesses were fabricated. Their CIE Lab* values (L*, brightness; a*, red-green value; b*, yellow-blue value) were measured at the center of the specimens against black and white backgrounds using a spectrophotometer, and translucency parameter (TP) values were determined. The microstructure of the specimens was observed using scanning electron microscopy. Four cylindrical backgrounds of different shades were prepared. The zirconia and lithium disilicate specimens were placed on the backgrounds without any intervening medium. CIE Lab* values were obtained, and the color difference value (ΔE) was calculated. Thresholds for acceptability and perceptibility were assumed as ΔE = 5.5 and ΔE = 2.6, respectively, to evaluate masking ability. Data were compared using one-way analysis of variance and post-hoc was performed using Scheffe's test (α = 0.05). In zirconia specimens, the TP value increased as the yttria content increased from 3 mol %, through 4 mol % to 5 mol %, and all zirconia specimens showed lower TP values than lithium disilicate specimens did. All zirconia specimens showed optimal masking ability against a normal dentin shade (ND3) and acceptable masking ability against titanium at a minimum thickness of 1.5 mm. However, no zirconia specimen could mask severely discolored dentin (ND9), regardless of thickness. The decrease in zirconia thickness from 1.5 to 0.8 mm significantly increased translucency. Monolithic Y-TZP ceramics could mask a normal dentin background but could not mask severely discolored dentin at either 0.8 or 1.5 mm thicknesses.
通过增加氧化钇含量制造的半透明氧化锆具有更好的半透明性，但在临床条件下，如由于底层颜色的反射导致基牙变色时，可能会对美学效果产生负面影响。本体外研究的目的是比较3摩尔%氧化钇稳定的四方氧化锆多晶体（3Y-TZP（Katana HT））、4Y-ZP（Katana STML）和5Y-ZP（Katana UTML）与二硅酸锂（Rosetta SM）的半透明参数和遮色能力。制作了直径为10毫米、厚度为0.8毫米和1.5毫米的氧化锆和二硅酸锂试样。使用分光光度计在试样中心对着黑色和白色背景测量其CIE Lab值（L，亮度；a*，红绿色值；b*，黄蓝色值），并确定半透明参数（TP）值。使用扫描电子显微镜观察试样的微观结构。制备了四种不同色调的圆柱形背景。将氧化锆和二硅酸锂试样放置在背景上，中间不使用任何介质。获得CIE Lab*值，并计算色差（ΔE）值。分别假设可接受性阈值和可感知性阈值为ΔE = 5.5和ΔE = 2.6来评估遮色能力。使用单因素方差分析比较数据，并使用谢费检验进行事后检验（α = 0.05）。在氧化锆试样中，随着氧化钇含量从3摩尔%增加到4摩尔%再到5摩尔%，TP值增加，并且所有氧化锆试样的TP值均低于二硅酸锂试样。所有氧化锆试样在最小厚度为1.5毫米时，对正常牙本质色调（ND3）显示出最佳遮色能力，对钛显示出可接受的遮色能力。然而，无论厚度如何，没有氧化锆试样能够遮盖严重变色的牙本质（ND9）。氧化锆厚度从1.5毫米减小到0.8毫米会显著增加半透明性。整体式Y-TZP陶瓷在厚度为0.8毫米或1.5毫米时，能够遮盖正常牙本质背景，但不能遮盖严重变色的牙本质。
