Biaxial Flexural Strength of Three All-ceramics at Various Core:Veneer Ratios

Objective: To investigate the strength of three all-ceramic systems; IPS Empress 2, In-Ceram and Cercon, when combined with their veneer porcelains at various core:veneer ratios by means of biaxial flexural strength (BFS).

Methods: Thirty disc samples of each all-ceramic system, 15 mm. in diameter and 1.2 mm. in thickness, were fabricated following manufacturer's recommendations. The samples were divided into three groups (n=10 each) depending on different core:veneer ratio at 2:1, 1:1 and 1:2. All samples were subjected to BFS testing following ISO 6872(1995) on the universal testing machine with crosshead speed of 1.0 mm/min.

Results: The means ± SD of BFS at core:veneer ratio 2:1, 1:1 and 1:2 of IPS Empress 2 in group 1 - 3 were 246.3 ± 28.2, 266.7 ± 23.2 and 226.6 ± 26.4 MPa, respectively. For In-Ceram in group 4 - 6 were 338.9 ± 22.6, 294.4 ± 15.2 and 259.9 ±14.5 MPa, respectively. For Cercon in group 7 - 9 were 1009.5 ± 98.7, 895.7 ± 93.0 and 768.1 ± 73.2 MPa, respectively. ANOVA and Tamhane's test revealed that the BFS of Cercon was significantly higher than that of In-Ceram and IPS Empress 2. In IPS Empress 2 group, the BFS was not significant difference at any core:veneer ratio. In In-Ceram group, the BFS decreased significantly when the ratio of core:veneer decreased respectively, while in Cercon group was slightly significant (p=0.05).

Conclusions: BFS of veneered Cercon was significantly higher than those of In-Ceram and IPS Empress 2. The core:veneer ratios significantly affected the BFS of In-Ceram and slightly affects the BFS of Cercon, but these ratios did not affect the BFS of IPS Empress 2.