Dentures that are loose is quite often a sign of bone tissue loss or an incorrect bite, or both.
New dentures tend to be loose for the first few days. They need this time to settle in, and for this reason, we always follow up with our patients after they have received their new dentures.
An exam, yearly, will allow us to keep the bite and fit in check to allow you to keep the best fit possible for your mouth.
Remember, that what you perceive as the fit, is made up of 2 things: the shape of the base of the denture, and the bite, where the upper teeth meet the lower teeth.