The low temperature degradation, LTD or aging, is defined as spontaneous tetragonal-to-monoclinic transformation occurring over time at low temperatures.
The degradation represents thermodynamic stability, and lower transformation means less microcrack occurrence and decrease in strength.
While 21% of the tetragonal phase transformed to monoclinic for General Zirconia Disc after aging for 5 h at 132℃ and 0.2 MPa, ISO13356 standard, no degradation occurred on Perfit FS under identical conditions.