Color and Translucency of Translucent Zirconia Layered With High-translucent Zirconia

Objectives: Tetragonal zirconia polycrystals (TZPs) have been widely used in region of aesthetic dentistry. These TZPs are often layered with porcelain when used clinically because they are poor translucency, however, fracture and chipping of the veneering porcelain have also been reported. Recently, translucent and high-translucent TZP that enable color expression are commercially available, and there are high expectations for their clinical application. However, there has been no information regarding color and translucency of translucent TZP layered with high-translucent TZP. The purpose of this study was to investigate the effectiveness of translucent TZP layered with high-translucent TZP that have different thickness ratio adhered by resin luting cements with different shade.
Methods: Translucent TZP and high-translucent TZP (Tosoh, Tokyo, Japan), and resin luting cements (Kuraray Noritake Dental, Tokyo, Japan) were used in this study. Layered specimens of 13 mm diameter and 1.0 mm thickness with different thickness ratio were prepared, and adhered by resin luting cements. Monolithic specimens of each TZP with 1.0 mm thickness were also prepared as a control. Color evaluation was performed with the CIE L*a*b* color system against the black and white backgrounds, and translucency parameter (TP) values was calculated.
Results: In evaluation of color characteristics, the L* values of all layered specimens showed intermediate values between monolithic translucent and high-translucent TZP. The a* values and the b* values were changed depending on shades of cements, and showed significantly higher values than monolithic specimens. There was no significant difference in the TP values among different thickness ratio.
Conclusions: These results suggested that layering method of translucent TZP layered with high-translucent TZP adhered by different shade cements is clinically useful for esthetic dental treatment.