Is it normal for teeth to become a little loose with braces?

Hi and thanks for your question!Mild tooth mobility is very common with orthodontic treatment, even with healthy bones and gums (i.e., periodontium). As the teeth move, the ligaments around the teeth (YES! teeth are connected to the underlying bone by ligaments) are stretched giving the sensation that the teeth are mobile. This mobility, however, is usually temporary and after treatment should stop. Now, if your bones and gums holding the teeth are weakened by disease you may notice significant mobility. A lower force on the teeth would be required, then, to produce healthy orthodontic tooth movement. If you are concerned or notice significant mobility changes in the teeth, please speak with your treating orthodontic specialist.Cheers!

If you have had gum disease and experienced bone loss, you could have loose teeth and the braces may be harmful.  I doubt this is the case.  Bone does get resorbed on the pressure side of a tooth being moved by braces.  This is normal for there to be some minor looseness.