Rheological and extrusion behavior of dental porcelain slurries for rapid prototyping applications

This study investigates rheological and extrusion behavior of dental porcelain slurries for rapid prototyping applications. The pH value of the slurry greatly influences its viscosity and rheological behavior and therefore plays an important role in the shape of the cross-section of the extrudate. A pseudoplastic slurry is a basic requirement for obtaining extruded lines with rectangular cross-sections. In addition to the effects of the rheological behavior of the slurry and its wettability on the substrate, the cross-sectional geometry of the extrudate is also strongly affected by extrusion parameters including the extrusion nozzle height, nozzle moving speed, extrusion rate, and critical nozzle height. Proper combinations of these extrusion parameters are necessary in order to obtain single line extrudates with near rectangular cross-sections and 3D objects with dimensional accuracy, uniform wall thickness, good wall uprightness, and no wall slumping. Formulas and procedures for determining these extrusion parameters are proposed and demonstrated in experiments. The results obtained have been explained in terms of the interactions among the rheological properties of the slurry, the shear rate imposed on the slurry during extrusion, the wettability of the slurry on the substrate, and the forced flow of the slurry during extrusion.