Evaluation of the Effect of Planetary Micro Milling Time on the 3Y-TZP/TiO₂ Ceramic’s Microstructure for Dental Application - a Pilot Study.

Objectives: 3Y-TZP/TiO₂ composite aiming to improve dental implants can be produced by powder mixing using a ball milling machine for 10 to 12 hours. Planetary micro-milling could be an alternative to optimize the production of 3Y-TZP/TiO₂ powders. This work aimed to investigate the effect of planetary mixing time on the ceramic composite's microstructure.
Methods: 3Y-TZP and 11 mol% of TiO₂ powders were mixed using a planetary micro mill for one, two and three hours (500 rpm/min) in isopropyl alcohol. The ceramic powder was oven-dried, uniaxially pressed into discs (θ=1.9 mm) at room temperature and sintered at 1300°C for 10 hours. The specimens' shrinkage (N=6) was calculated. Qualitative phase analysis was performed by XRD, and the apparent densities were measured by the Archimedes principle.
Results: Density measurements for 1, 2 and 3 mixing hours were 5.64 g/cm³, 5.52 g/cm³, and 5.74 g/cm³, respectively. Three hours of mixing generated 97.75% densification compared to the theoretical density, followed by 1-hour mixing (96.05%) and 2-hours mixing (93.53%). A diameter shrinkage of 21.63% ±1.44% was observed for the 1-hour and 21.06% ±0.5% for the 2-hour mixing specimens, and a thickness shrinkage of 18.33% ±3.2% and 26.54% ±8.3% for 1 and 2 hours of mixing, respectively. Three hours of mixing presented a diameter and thickness shrinkage of 23%. Rietveld analysis indicated that 1-hour exhibited 89.52% tetragonal phase, 1.34% monoclinic phase and 9.12% cubic phase. Similar results were observed at the 2-hour (tetragonal 89.35%, monoclinic 2.63%, and cubic phase 8.01%) and 3-hour mixing specimens (tetragonal 87.29%, monoclinic 1.39% and cubic phase 11.31%).
Conclusions: The process developed in this study resulted in a reduction in the mixing time from 10 to 3 hours using planetary micro milling, producing a 3Y-TZP/11TiO₂ ceramic with high density. The 3Y-TZP/11TiO₂ mixed for three hours resulted in increased densification and good post-sintering shrinkage.