Porcelain chipping -off, supposed to be affected by the mechanical strength of porcelain material, residual stress and the interface bonding strength, is well documented as a reason for veneered zirconia crown failure. However, results from different tests were incomparable because the testing methods varied in respecting to specimen dimension, direction and frequency of loads, and simulation of intraoral environment. The standardized methods and evaluation index applied in testing the real strength and toughness of double-layer structure are the goals to be achieved in future, and the factors related to the strength and toughness should also be evaluated. In the current review, reported flaws leading to porcelain chipping-off were summarized.
