Let's briefly discuss how your jawbone allows your teeth to shift into new positioning in the first place. Your bones have two kinds of cells that do all the work to remodel your skeleton as needed. Osteoclasts break down old bone and deliver it into your bloodstream (resorption), and osteoblasts build your bone where it needs to be reinforced (ossification). Bones are reinforced through osseointegration, where they are used the most.
For your jawbone, when you chew and bite, the force you exert through your teeth into your jaws sends signals to osteoblasts to keep that bone strong. After your teeth have been aligned with orthodontics, this process helps your teeth settle into place while a retainer holds them there.
Without a retainer, your teeth will relapse toward their original position before the bone has time to strengthen in the necessary areas to keep them in place.
Learn if retainers can realign your teeth.