This is the common problem with flippers. it happens because the extraction wound develops a bit of swelling as the healing process is going on. do warm saline rinses 2 to 3 times a day and gently try to put the flipper. if you can not insert it then either you have to wait for a day or go to the dentist and get it inserted. for more info on dentures you can visit the following link...... http://www.identalhub.com/articlecategory-dentures-50.aspx