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The objective of this research is to focus improving the properties of machinable mica-based glass-ceramics in order for restorative dental materials. The glass-ceramics derived from the SiO2- Al2O3-MgO-MgF2-SrCO3-CaCO3-CaF2-P2O5 system were produced by a two-stage heat treatment. It was elucidated that the optimum nucleation and the crystallization temperatures were at 643°C and 892°C. The various heat treatment times in the first stage were applied as 3, 6, 12, 24, 48 and 72 h, respectively, on the optimum nucleation temperature to produce mica-based glass-ceramics. XRD results showed that specimens of variety of nucleation time had similar crystalline structures such as calcium-mica, fluorapatite, stishovite, anorthite, strontiumapatite and forsterite phases. The microstructures of glass-ceramics were observed by SEM basically as interlocked plate-like and needle-like microstructures of mica and fluorapatite, respectively, in all specimens. Furthermore, different heat treatment times influenced on the revealed crystal size of the glass-ceramics; the longer heat treatment, the smaller crystals. The resultant glass-ceramics gave the results of biaxial flexural strength (178-224 MPa) and Vickers hardness (295-393 HV) increasing with the formation of the interconnected mica phases which contributed to improve the machinability. The values of the properties were comparable to those of human enamel and suitable for some restorative dental applications.

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The research employed pigments, Fe2O3 and CeO2, into the glass frit for adjustable mechanical properties and coloration. Disc samples were prepared to determine microstructures and mechanical properties in terms of tribology and nano-indentation hardness as well as biaxial flexural strength. The glass system presented the crystalline phases, by XRD, of phlogopite Ca-mica, fluorapatite, stishovite, anorthite and strontium apatite. Furthermore, SEM micrographs revealed rod-like microstructures and parent glass phase in all specimens 1) GC, 2) GC + 1wt% CeO2, 3) GC + 0.1wt% Fe2O3 and 4) GC + 1wt% CeO2 + 0.1wt% Fe2O3. For the tribology test, specimens were tested by a pin-on-disc tribometer with 10 N load and 1,000 wear cycles. The obtained values of wear rate and friction coefficient of GCF were better than those of others. The nano- indentation hardness results showed that GC exhibited 3.2 GPa which lower than those of GCC, GCF and GCCF, respectively. The addition of pigments affected reddish yellow color. After crystallization, the contrast ratio is around 0.72 for GC and decreases to 58-75% for the mica glass-ceramics that contain the pigments. The values of biaxial flexural strength of all were acceptable (≥100 MPa) according to ISO 6872:2015.

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