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, σi; Vickers hardness, VH; fracture toughness, KIc; fracture surface energy, γf; 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. σi was determined by piston-on-3-balls method in inert condition. VH was determined using 19.6 N load and KIc was determined by indentation strength method. γf was calculated from the Griffith–Irwin relation and B by the ratio of HV to KIc. IC and E2 showed higher values of σi, E, KIc and γf, and lower values of B compared to leucite-based glass-ceramic and porcelains. Positive correlations were observed for σi versus KIc, and KIc versus E1/2, 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.