Relationship between elastic and mechanical properties of dental ceramics and their index of brittleness

The purpose of the study was to verify the effects of a number of materials’ parameters (crystalline content; Young's modulus, E ; biaxial flexure strength, σ i ; Vickers hardness, VH; fracture toughness, K Ic ; fracture surface energy, γ f ; and index of brittleness, B ) on the brittleness of dental ceramics. Five commercial dental ceramics with different contents of glass phase and crystalline particles were studied: a vitreous porcelain (VM7/V), a porcelain with 16 vol% leucite particles (d.Sign/D), a glass-ceramic with 29 vol% leucite particles (Empress/E1), a glass-ceramic with 58 vol% lithium-disilicate needle-like particles (Empress 2/E2), and a glass-infiltrated alumina composite with 65 vol% crystals (In-Ceram Alumina/IC). Discs were constructed according to manufacturers’ instructions, ground and polished to final dimensions (12 mm × 1.1 mm). Elastic constants were determined by ultrasonic pulse-echo method. σ i was determined by piston-on-3-balls method in inert condition. VH was determined using 19.6 N load and K Ic was determined by indentation strength method. γ f was calculated from the Griffith–Irwin relation and B by the ratio of HV to K Ic . IC and E2 showed higher values of σ i , E , K Ic and γ f , and lower values of B compared to leucite-based glass-ceramic and porcelains. Positive correlations were observed for σ i versus K Ic , and K Ic versus E 1/2 , however, E did not show relationship with HV and B . The increase of crystalline phase content is beneficial to decrease the brittleness of dental ceramics by means of both an increase in fracture surface energy and a lowering in index of brittleness.