Strength of Veneer Porcelain with Various Zirconia Thickness and Sintering

Objective: Evaluate the effect of various firing cycles and zirconia thickness on the flexural strength of two veneering porcelains.

Method: Vita YZ zirconia blocks (Vita Zahnfabrik, Germany) were sectioned and sintered to provide slabs of 0.5, 1.0, and 5.0 mm thickness. Vita VM9 and e.max ceram porcelain (Ivoclar, Liechtenstein) were mixed with deionized water, condensed in a mold 19mm diameter x 2 mm thickness, and sintered: (1)According to the manufacturer’s instructions; (2)Two cycles at peak temperature above the recommended value. A layer of carbon paint was applied to the zirconia to allow removal of the porcelain discs. Biaxial flexure strength was determined using an Instron, crosshead speed of 0.5mm/min.

Result: Strength of e.max Ceram and VM9 at various cycles and zirconia thickness N=10

e.max Ceram:

Peak Temp -Zirconia thickness	Flexural Strength MPa	Significant Difference
800°C - 0.5 Zr	120.4 ± 15.5	A
800°C – 5.0 Zr	114.6 ± 24.9	AB
800°C – 1.0 Zr	114.4 ± 14.5	AB
780°C - 1.0 Zr	107.6 ± 18.7	ABC
760°C - 1.0 Zr	100.8 ± 10.6	BCD
780°C – 0.5 Zr	99.0 ± 15.6	CD
780°C - 5.0 Zr	98.1 ± 15.6	CD
760°C – 0.5 Zr	94.4 ± 19.8	CD
760°C - 5.0 Zr	88.5 ± 12.3	D

VM9:

Peak Temp - Zirconia thickness	Flexural Strength MPa	Significant Difference
940°C – 1.0 Zr	122.6 ± 13.9	A
940°C – 0.5 Zr	121.2 ± 14.6	A
960°C – 5.0 Zr	120.4 ± 15.4	A
940°C - 5.0 Zr	118.7 ± 12.1	A
920°C - 1.0 Zr	116.2 ± 12.7	A
960°C – 5.0 Zr	114.6 ± 14.5	A
960°C -1.0 Zr	114.4 ± 14.5	A
920°C – 0.5 Zr	110.3 ± 15.4	A
920°C - 5.0 Zr	107.9 ± 21.7	A

ANOVA and Tukey analysis, p=0.05.

Conclusion: Firing cycle and zirconia thickness have a significant affect on the strength of e.max ceram.