Stress intensity factor threshold in dental porcelains

The stress intensity factor threshold (K-IO) is related to the stress level at which cracks start to grow stably, causing the weakening of porcelain prostheses during their use. The values of K-IO of seven dental porcelains (with and without reinforcing leucite crystal, KAlSi2O6) stored in air (22 degrees C, 60% relative humidity) and artificial saliva (37 degrees C) were determined by measuring the crack growth velocity of radial cracks generated at the corner of Vickers indentations. The results of K-IO were correlated with the leucite content, fracture toughness (K-Ic), and chemical composition of the porcelains. It was observed that K-IO increased with the increase of leucite content (only for the leucite-based porcelains) and with the increase of K-Ic. The increase in Al2O3 content or the decrease in the alkali oxide (K2O and Na2O) content of the material's glassy matrix tended to increase the K-IO values. Storage media (air and saliva) did not significantly affect the K-IO of porcelains tested, indicating that the control parameter of K-IO value was not the water content of the storage media.