Effect of veneering techniques on color and translucency of Y-TZP

This study compared the color parameters and total luminous transmittance of disc specimens by different veneering techniques in order to examine the effect of veneering technique on esthetics of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) all-ceramic restorations.

Thirty disc specimens (10-mm diameter, 0.50 +/- 0.01 mm thick) were fabricated of IPS e.max ZirCAD core material, and ZL1 IPS e.max ZirLiner (0.10-mm thick) was layered. The specimens were randomly divided into three groups (n = 10/group). Group ZP (fully anatomical technique) was veneered 0.60 mm by heat-pressing IPS e.max ZirPress fluorapatite glass-ceramic ingots; Group ZC (traditional layering technique) was veneered 0.60 mm by condensing and sintering IPS e.max Ceram low-fusing nano-fluorapatite veneering porcelain; Group ZPC (cutback technique) was veneered by partially pressed ingots and subsequently layered 0.30 mm with veneering porcelain. Color parameters (L*, a*, b*) and total luminous transmittance (tau) of zirconia core discs and core and veneer specimens were measured with ShadeEye NCC dental colorimeter and spectrophotometer, respectively. Color saturation (C*ab) and color difference (DeltaE) were calculated using color difference formula. One-way analysis of variance (ANOVA) combined with a Tukey multiple-range test were used to analyze the data (alpha= 0.05).

As to ZP, ZPC, and ZC groups, the value of a* increased (-1.35 +/- 0.07, -0.64 +/- 0.06, -0.36 +/- 0.05, respectively) (p < 0.05); b* decreased (27.01 +/- 0.07, 25.48 +/- 0.11, 23.28 +/- 0.25, respectively) (p < 0.05); and C*ab decreased (27.04 +/- 0.08, 25.49 +/- 0.11, 23.28 +/- 0.25, respectively) (p < 0.05). L* value and total luminous transmittance were highest in ZP group (87.53 +/- 0.48, 1.64 +/- 0.03, respectively), and lowest in ZPC group (82.14 +/- 0.18, 1.47 +/- 0.01, respectively) (p < 0.05).

Y-TZP all-ceramic restoration veneered by fully anatomical technique was the most transparent and lightest, while restorations veneered by cutback technique were the least translucent and the darkest.