Microstructural development during heat treatment of a commercially available dental-grade lithium disilicate glass-ceramic.

OBJECTIVE

To elucidate the microstructural evolution of a commercial dental-grade lithium disilicate glass-ceramic using a wide battery of in-situ and ex-situ characterization techniques.

METHODS

In-situ X-ray thermo-diffractometry experiments were conducted on a commercially available dental-grade lithium disilicate glass-ceramic under both non-isothermal and isothermal heat treatments in air. These analyses were complemented by experiments of ex-situ X-ray diffractometry, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, and field-emission scanning electron thermo-microscopy.

RESULTS

It was found that the non-fired blue block consists of ∼40 vol % crystals embedded in a glass matrix. The crystals are mainly lithium metasilicate (LiSiO) along with small amounts of lithium orthophosphate (LiPO) and lithium disilicate (LiSiO). Upon heating, the glassy matrix in the as-received block first crystallizes partially as SiO (i.e., cristobalite) at ∼660 °C. Then, the SiO crystals react with the original LiSiO crystals at ∼735 °C, forming the desired LiSiO crystals by a solid-state reaction in equimolar concentration (SiO + LiSiO → LiSiO). Precipitation of added colourant Ce ions in the form of CeO appears at ∼775 °C. These events result in a glass-ceramic material with the aesthetic quality and mechanical integrity required for dental restorations. It also has a microstructure consisting essentially of elongated LiSiO grains in a glassy matrix plus small cubic CeO grains at the outermost part of the surface.

SIGNIFICANCE

It was found that by judiciously controlling the heat treatment parameters, it is possible to tailor the microstructure of the resulting glass-ceramics and thus optimizing their performance and lifespan as dental restorations.