New, tough and strong lithium metasilicate dental glass-ceramic

Abstract

Glass-ceramics have found widespread use in dentistry due to their favorable properties: biocompatibility, chemical inertness, high fracture strength and toughness, superior esthetics, color stability, and translucence. The objective of this work was to develop a new tough, strong and machinable glass-ceramic based on the lithium metasilicate (LS) crystal phase. We designed a glass composition aimed to yield LS crystals after proper treatment. We melted, casted, and crystallized the glass for a favorable microstructure. We then characterized its microstructure and relevant mechanical, optical and chemical properties with several experimental tools. We also measured the residual stresses. This newly developed glass-ceramic shows a house-of-cards microstructure composed of 50% vol. plate-like LS crystals of 5–25 μm, randomly dispersed in a glassy matrix. Lithium disilicate (12% vol.), two minor crystal phases, and 34% vol. residual glass are also present. The average fracture toughness measured by the double torsion technique is 3.5 ± 0.5 MPa m1/2. The average fracture strength, evaluated by the ball-on-three balls (B3B) technique, is 450 ± 40 MPa. The elastic modulus, determined by nanoindentation, is 124 ± 2 GPa, the linear thermal expansion coefficient is 13.6 × 10−6 °C-1, and the solubility in 4%vol. acetic acid is 215 ± 30 μg/cm2, which is below the limit established by the ISO 6872 standard for some applications, but improper for uncoated use. These properties could still be optimized. The improved toughness, strength, and reasonable machinability indicate that, after optimization, this glass-ceramic could be a very promising candidate for dental restorative applications.