After 15 years of observing the retention of Invisalign cases and a much longer time observing traditional orthodontic cases I would say that retention
depends more upon the specifics of any individual case and how compliant the patient has been with the plan for retention than upon whether the case was done with Invisalign or traditional orthodontics. However I have observed that cases in which teeth
have been extracted to created room generally are less stable particularly if the spaces that were created were slightly more than what was needed to resolve crowding. In Invisalign I personally almost never extract teeth to create room, but rather create space thru a combination of expansion
and polishing between the teeth.