Effects of BN content on the mechanical properties of nanocrystalline 3Y-TZP/Al2O3/BN dental ceramics

3Y-TZP/3wt% Al2O3 powder was coated with varying amounts of BN using the urea and borate reaction sintering method, and then multiphase ceramics were prepared by hot pressing sintering. The micro-topography and the compositional analysis of synthesized ceramics were conducted through scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A mechanical tester was used to analyze the Vickers hardness, fracture toughness, and bending strength of the synthesized ceramics. The results showed that the ceramic with a BN content of 12wt% showed the best processability, but had diminished mechanical properties (such as fracture toughness and bending strength). The ceramic with a BN content of 9wt% showed better processability than those with 3wt% and 6wt% BN. However, the fracture toughness was affected by the addition of 9wt% BN, making this ceramic only usable as a base material for a three-unit fixed bridge. In contrast, the ceramics with a BN content of 3wt% or 6wt% fulfilled the criteria for use in multi-unit restoration, but their low processability made them unsuitable for milling after sintering.