Influence of heat‐treatment protocols on mechanical behavior of lithium silicate dental ceramics

Abstract In this work, three different commercial lithium silicate (LS) glass‐ceramics for computer aided design/computer aided machining systems, CeltraDuo‐Dentsply (LS‐C), E‐MaxCAD‐Ivoclar (LS‐E), and Suprinity‐Vita (LS‐S), were comparatively characterized. Following the protocols recommended by the manufacturers, the glass‐ceramics were heat‐treated under low vacuum and characterized by X‐ray diffraction, scanning electron microscopy, hardness, fracture toughness, Young's modulus, and flexural strength. Rietveld refinement indicated that the materials “as‐received” present mostly amorphous phase and Li ₂ SiO ₃ as secondary crystalline phase in LS‐E and LS‐S specimens, while LS‐C specimens also present Li ₂ Si ₂ O ₅ and Li ₃ PO ₄ as crystalline phases. All “as‐received” glass‐ceramics present hardness, fracture toughness, and Young's modulus of around 647‐678 HV, 1.15‐1.40 MPa.m ^1/2 , and 82‐92 GPa, respectively. After heat treatment, the LS‐C and LS‐S specimens presented decreasing of amorphous phase associated to Li ₂ SiO ₃ and Li ₂ Si ₂ O ₅ grains with low aspect ratio, while LS‐E indicates a reduction of amorphous phase and Li ₂ Si ₂ O ₅ elongated grains. Fracture toughness and Young's modulus increase about 10% due to the crystallization of residual amorphous phase for all materials. Moreover, crystallographic and microstructural characteristics are responsible for the higher flexural strength of LS‐E (327 MPa), regarding LS‐C and LS‐S. However, the glass‐ceramics LS‐E present lower Weibull modulus (m = 5.4) comparatively to LS‐C (m = 9) and LS‐S (m = 6).