Flexural strength and internal defects of some dental porcelains

The flexural strength, number (n), size, and form of pores in seven different dental porcelains were examined. The flexural strength was approximately 100 MPa for the core materials for metal bonding, 116 MPa for traditional alumina porcelains (NBK 1000, Vitadur N), 150 MPa for two new high-alumina porcelains (Vita Hi Ceram, Cerestore), and 240 MPa for a castable glass (Dicor). The mean pore diameter was approximately 10 microns in all porcelains except Dicor, but with a large and varying range. Dicor showed a mean pore size of 1 micron. The pore density varied from 36.5/mm2 in one of the porcelains for metal bonding to 4367/mm2 in Cerestore. The mean cross-sectional area occupied by pores was below 10% for most porcelains except Vitadur N and Cerestore, showing 17.5% and 32.5%, respectively. No correlation was found between flexural strength and frequency or cross-sectional area of pores of the various products.