Novel fabrication of pressure-less sintering of translucent powder injection molded (PIM) alumina blocks

A new method of fabricating translucent alumina brackets using powder injection molding (PIM) is reported. Alumina powder was mixed with MgO, La2O3, and Y2O3 to control grain size and porosity. The powders were mixed with a binder consisting of a mixture of paraffin wax and polyethylene in a 1:1 ratio to make feedstock for injection molding. The total amount of binder was limited to 14 wt% to minimize shrinkage and cracking after sintering. After injection molding, debinding was performed using the wicking method and samples were sintered in a vacuum at 1700 °C to achieve high density. Ultimately, translucent corundum was fabricated. The sintering additives resulted in a decrease in porosity and an improvement in translucency by promoting grain growth during pressure-less sintering. After sintering, Vickers hardness, bending strength, density, and transmittance of the fabricated parts were measured to show that those values were comparable to those of the commercially available dental brackets. Therefore, the translucent alumina block was successfully fabricated using PIM method to be potentially used as a dental bracket.