I’ve had aligners for 6 months and I’ve noticed that my teeth are becoming more mobile. Sometimes when I brush I can feel my lower front teeth moving. Has anyone experienced that? Is it normal?
Don’t freak out. This is totally normal. Aligners and braces are supposed to do that.
Braces and aligners’ goal is to move your teeth to its new position. To move the teeth, they need to be mobile so they can be pulled or pushed. So it’s normal to feel your teeth moving, especially the teeth that are misaligned.
My wife also noticed that just by wearing her first set of aligners. She got worried and she didn’t wear it for a couple of days because she thought that it would worsen the movement of her teeth. When she asked the provider, they said that is normal. So she wore her aligners again. Though she had a hard time adjusting to the movement of the teeth because she feels that her teeth will come off all of a sudden.
This is common. As your aligners gradually shift your teeth into their proper position, your gums are re-forming around each tooth as it moves.
Relax. Teeth are loosened for it to be moved into its new position.
I had the same experience. My dentist said it was okay and it is expected to move because that’s the goal of aligners or braces. She said to prevent playing the mobile teeth with my finger or tongue and keep monitoring the movement.
My wife can’t stop moving her mobile teeth with her tongue. 
I know how that feels. It’s kinda satisfying. I did it too the first time I felt my teeth moving. But my dentist said it’s better to leave it alone.
The jawbone is actually reforming around each tooth when you wear braces or aligners. It is said that your jawbone will dissolve on the part where there is pressure, then the tooth will move where the jawbone was dissolved. That’s how orthodontic appliance works.
So that’s why it hurts 
because braces dissolve our bone. Will the dissolved bone redevelop?
It will redevelop, though it will only take time. That’s why even though you don’t have braces or aligners anymore, your teeth will still move. It will take years for your bone to heal and your teeth to stabilize again.
How many months/years before bone will again redevelop?
So that’s the reason why retainers are important. To hold the teeth and make it stable too, right?