Effect of feldspar and silica variation on the properties of dental porcelain

Dental porcelain was produced by mixing feldspar, silica, kaolin and bone ash by varying the contents of feldspar and silica. The processing steps include milling, sieving, pressing/shaping, drying, and sintering while the characterisation techniques were Hardness, Compressive strength, X-ray diffraction, Scanning electron microscopy and Fourier Transform Infrared (FTIR). The mixture was subjected to temperatures of 1100 and 1200 oC in a sintering furnace. The chemical composition was determined using X-ray fluorescence and they confirm that SiO2 and Al2O3 are the two major constituents in feldspar and kaolin while CaO is the major constituent in bone ash. For samples sintered at 1200oC, the X-ray diffraction showed that some glass phase possibly consisting of hedenbergite, ilmenite and silica were formed while crystalline phases namely microcline and sanidine were obtained for samples sintered at 1100°C. The morphology of the grains revealed that samples sintered at 1200oC had some hexagonal silica crystals while flakes of different sizes were obtained for samples sintered at 1100oC. Hardness values between 262 and 536 BHN, compressive modulus values ranging from 219 MPa to 324 MPa and linear shrinkage values between 6.34 and 7.6% were obtained. The batches of different compositions with ranges: quartz (silica) (15-25%), feldspar (70-80%), kaolin (Edda/Bauchi) (4%) and bone ash (1%) were fired at 1100, 1200oC, and the developed properties were tested. The sample with 70 wt.% of feldspar, 25 wt.% silica, 4 wt.% of Bauchi clay, and 1 wt.% bone ash sintered at 1200oC gave the best properties and has the potential to be used in dental restoration.