Ultrafast-Laser-Processed Zirconia and its Adhesion to Dental Cement

Hard zirconia ceramic in its hot-isostatically pressed constitution can be machined precisely and reproducibly using ultrafast lasers. However, the pulse overlap turns out to be of significant influ- ence on the resulting surface quality. This can be traced back to particulate process emission from the workpiece surface that influences subsequent pulses in the case of large pulse overlapping and can even agglomerate to debris layers above the processed surface. Measurements of particle emission indicate that 90 % of the ablated particulate material consists of nanoparticles, raising the demands on safe machine housing and suction measures. To produce all-ceramic dental crowns directly from sintered blanks without thermal damage or tool wear, a processing station, including a femtosecond laser system, has been designed based on high necessary processing dynamics and considering safety aspects. Regarding its adhesion to dental cement, Y-TZP has deficits compared to dentin. The fixation between cement and Y-TZP surfaces can be improved by artificial microstructures, added to the inner surface of laser-processed dental crowns in a final step during ultrafast-laser-based manufacturing. Such microstructures have been evaluated by adhesion measurements between ceramic and cement that were based on shear and tensile strength tests, taking into consideration limit values from numeric simulations.