Hi.. Welcome to HEALTHCARE MAGIC.. As per your query many a times teeth become slightly mobile or loose when orthodontic treatment is carried out to move the teeth in proper alignment and it is not abnormal.. But in case if tooth is depressible or move inside the socket also and is mobile significantly then it needs to be taken into consideration and immediate consultation with your treating dentist is needed to do the needful like reducing the intensity of force application over the teeth and also to check for gum infections that can occur due to improper cleaning while wearing the braces and after proper evaluation only proper treatment can be done.. The tooth will fall out or can be saved can be said only after a clinical assessment and investigation like x ray.. You can send me scans of x rays for further advise and appropriate guidence towards further treatment by clicking my profile on Healthcare Magic and click on Ask me a question.. Upload the recent x rays there.. Hope this helps.. Regards.